Patent Application
20140261040
The present disclosure relates to gas generant grain assemblies for inflatable restraint devices and more particularly to gas generant grain assemblies formed of multiple symmetric segment components.
This section provides background information related to the present disclosure which is not necessarily prior art.
Passive inflatable restraint systems are used in a variety of applications, such as motor vehicles. Certain types of passive inflatable restraint systems minimize occupant injuries by using a pyrotechnic gas generant to inflate an airbag cushion (e.g., gas initiators and/or inflators) or to actuate a seatbelt tensioner (e.g., micro gas generators), for example. Automotive airbag inflator performance and safety requirements are continually increasing to enhance passenger safety, while concurrently striving to reduce manufacturing costs.
Many conventional gas generant grains are pressed or extruded for use in airbag inflators. Grains with large or complicated geometry are often pressed to achieve the desired designs. Such pressed grains typically are relatively large and considered to be monolithic bodies, as they are a single unitary monolithic grain structure. Monolithic gas generant grain designs have many advantages, such as repeatable and well controlled combustion, by way of non-limiting example. However, they have several potential disadvantages. Large pressed grains require large press equipment (typically a hydraulic press) that is very expensive and often requires a slower cycle time, which in turn increases processing costs. These pressed grains also tend to be somewhat fragile. Broken grains can occur during processing, shipping, or during the life of the product after they are loaded into an airbag inflator. Broken grains during processing results in increased cost due to product scrap, while broken grains during life cycle can be more serious in that they have the potential to result in performance variation within the inflatable restraint device. Thus, it would be desirable to have robust pressed gas generant grains that have reduced breakage and reduced manufacturing costs, while exhibiting many of the performance advantages associated with conventional pressed monolithic grains.
This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.
In certain variations, the present disclosure provides a segmented gas generant grain assembly comprising a plurality of gas generant segments arranged together circumferentially to define a segmented body of the gas generant grain assembly. Each gas generant segment is pressed and has a shape that is symmetric with respect to at least one axis defined by the segment. Further, each gas generant segment comprises at least one void having a first dimension. In certain variations, each gas generant segment comprises two or more voids having the first dimension. The segmented body has a central aperture having a second diameter or dimension greater than the first dimension.
In other aspects, the present disclosure provides a segmented gas generant grain assembly comprising a plurality of gas generant segments arranged together circumferentially to define a substantially round and segmented body of the gas generant grain assembly. In certain variations, each gas generant segment in a final pressed form has an actual density of greater than or equal to about 95% of the maximum theoretical mass density. Further, each gas generant segment is substantially free of any binder and has a shape that is symmetric with respect to at least one axis defined by the segment. Moreover, each gas generant segment comprises at least one void having a first dimension. In certain variations, each gas generant segment comprises two or more voids having the first dimension. When the plurality of segments is assembled together, the substantially round and segmented body has a central aperture having a second diameter or dimension that is greater than the first dimension.
In yet other variations of the present disclosure, methods of making segmented gas generant grain assemblies are provided. For example, one such method comprises conveying a plurality of gas generant segments to a round receptacle capable of receiving the gas generant segments. Each gas generant segment has a shape that is symmetric with respect to at least one axis defined by the segment. The method includes sequentially introducing the respective gas generant segments into the round receptacle, where each symmetric segment self-orients to be arranged circumferentially within the round receptacle to form a segmented gas generant grain assembly having a substantially round body. In certain variations, the method also comprises removing the segmented gas generant grain assembly thus formed from the round receptacle.
Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.
Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.
Example embodiments will now be described more fully with reference to the accompanying drawings.
Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.
The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Although the terms first, second, third, etc. may be used herein to describe various components, elements, regions, layers and/or sections, these components, elements, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “primary,” “secondary,” “first,” “second,” or and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first or primary component, element, region, layer or section discussed below could be termed a secondary component, element, region, layer or section without departing from the teachings of the example embodiments.
Throughout this disclosure, the numerical values represent approximate measures or limits to ranges to encompass minor deviations from the given values and embodiments having about the value mentioned as well as those having exactly the value mentioned. Other than in the working examples provided at the end of the detailed description, all numerical values of parameters (e.g., of quantities or conditions) in this specification, including the appended claims, are to be understood as being modified in all instances by the term “about” whether or not “about” actually appears before the numerical value. “About” indicates that the stated numerical value allows some slight imprecision (with some approach to exactness in the value; approximately or reasonably close to the value; nearly). If the imprecision provided by “about” is not otherwise understood in the art with this ordinary meaning, then “about” as used herein indicates at least variations that may arise from ordinary methods of measuring and using such parameters.
As referred to herein, ranges are, unless specified otherwise, inclusive of endpoints and include disclosure of all distinct values and further divided ranges within the entire range. Thus, for example, a range of “from A to B” or “from about A to about B” is inclusive of A and of B. Disclosure of values and ranges of values for specific parameters (such as weight percentages, temperatures, molecular weights, etc.) are not exclusive of other values and ranges of values useful herein. It is envisioned that two or more specific exemplified values for a given parameter may define endpoints for a range of values that may be claimed for the parameter. For example, if Parameter X is exemplified herein to have value A and also exemplified to have value Z, it is envisioned that Parameter X may have a range of values from about A to about Z. Similarly, it is envisioned that disclosure of two or more ranges of values for a parameter (whether such ranges are nested, overlapping or distinct) subsume all possible combination of ranges for the value that might be claimed using endpoints of the disclosed ranges. For example, if Parameter X is exemplified herein to have values in the range of 1-10, or 2-9, or 3-8, it is also envisioned that Parameter X may have other ranges of values including 1-9, 1-8, 1-3, 1-2, 2-10, 2-8, 2-3, 3-10, and 3-9. Example embodiments will now be described more fully with reference to the accompanying drawings.
The present disclosure is drawn to gas generant grain assemblies and methods for making such gas generant grain assemblies suitable for use in inflatable restraint devices. By way of background, inflatable restraint devices have applicability for various types of airbag module assemblies for automotive vehicles, such as driver side, passenger side, side impact, curtain and carpet airbag assemblies, for example, as well as with other types of vehicles including, for example, boats, airplanes, and trains. Such pyrotechnic gas generants can also be used in other applications where rapid generation of gas is required, such as seat belt restraints, for example.
Gas generants, also known as ignition materials, propellants, gas-generating materials, and pyrotechnic materials are used in inflators of airbag modules, such as a simplified exemplary airbag module 30 comprising a passenger compartment inflator assembly 32 and a covered compartment 34 to store an airbag 36 of
The gas generant 50 can be in the form of a solid grain, a pellet, a tablet, or the like. The present disclosure pertains to gas generants 50 in the form of grains, meaning a solid compressed high density body formed of a gas generant composition having minimal or no binders, as will be discussed in greater detail below. Impurities and other materials present within the gas generant 50 facilitate the formation of various other compounds during the combustion reaction(s), including additional gases, aerosols, and particulates. Often, a slag or clinker is formed near the gas generant 50 during burning. The slag/clinker often serves to sequester various particulates and other compounds. However, a filter 52 is optionally provided between the gas generant 50 and airbag 36 to remove particulates entrained in the gas and to reduce gas temperature of the gases prior to entering the airbag 36. The quality and toxicity of the components of the gas produced by the gas generant 50, also referred to as effluent, are important because occupants of the vehicle are potentially exposed to these compounds. It is desirable to minimize the concentration of potentially harmful compounds in the effluent.
Various different gas generant compositions (e.g., 50) are used in vehicular occupant inflatable restraint systems. Gas generant material selection involves various factors, including meeting current industry performance specifications, guidelines and standards, generating safe gases or effluents, handling safety of the gas generant materials, durational stability of the materials, and cost-effectiveness in manufacture, among other considerations. It is preferred that the gas generant compositions are safe during handling, storage, and disposal, and preferably are azide-free.
In various aspects, the gas generant typically includes at least one fuel component and at least one oxidizer component, and may include other minor ingredients, that once ignited combust rapidly to form gaseous reaction products (e.g., CO2, H2O, and N2). One or more fuel compounds undergo rapid combustion to form heat and gaseous products; e.g., the gas generant burns to create heated inflation gas for an inflatable restraint device or to actuate a piston. The gas-generating composition also includes one or more oxidizing components, where the oxidizing component reacts with the fuel component in order to generate the gas product.
Improved gas generator performance in an inflatable restraint system may be achieved in a variety of ways, many of which ultimately depend on the gas generant formulation to provide the desired properties. Ideally, a gas generant provides sufficient gas mass flow in a desired time interval to achieve the required work impulse for an inflating device (e.g., airbag) within the inflatable restraint system. Although a temperature of gas generated by the gas generant influences the amount of work gases can do, high gas temperatures may be undesirable because burns and related thermal damage can result. Consequently, in certain aspects, it is desirable to provide a gas generant formulation for an inflatable restraint system that can achieve a high gas output at a high mass flow rate at relatively low flame temperatures.
Inflatable restraint devices generate gas in situ from a reaction of a pyrotechnic gas generant contained therein. In accordance with various aspects of the present disclosure, gas generant grain assemblies are formed that have desirable compositions and shapes that result in superior performance characteristics in an inflatable restraint device. In various aspects, the disclosure provides methods of making pressed gas generant grain assemblies that are robust and have lower breakage rates and manufacturing costs, while still having desirable properties associated with conventional monolithic gas generant grain assemblies having complex shapes, including high burn rates (i.e., rate of combustion reaction), high gas yields (moles/mass of generant), high achieved mass density, high theoretical density, and high loading density.
In various aspects, the present disclosure provides pressed gas generant grain assemblies, which are segmented, and thus comprise a plurality of symmetric gas generant pieces or segments. Each of the symmetric gas generant segments is pressed and comprises a gas generant material. The symmetric pieces or segments are arranged together circumferentially to define a segmented body of the pressed gas generant grain assembly. In certain aspects, the symmetric segments of the pressed segmented monolithic gas generant grain assemblies are substantially free of polymeric binder and have a high density, in contrast to conventional extruded gas generants that have polymeric binders and relatively low density. The term “substantially free” as referred to herein is intended to mean that the compound is absent to the extent that that undesirable and/or detrimental effects are avoided. In the present embodiment, a gas generant that is “substantially free” of binder comprises less than or equal to about 1% by weight binder, optionally less than or equal to about 0.5% by weight, and in certain embodiments comprises 0% by weight of the binder. Such symmetric segment pieces in accordance with the present technology may be formed into unique shapes that when assembled with other symmetric segments form segmented gas generant grain assemblies having an overall shape that optimizes the ballistic burning profiles of the materials contained therein. In segmenting a pressed grain assembly in accordance with various aspects of the present teachings, a more robust and less expensive gas generant having the desired performance properties is realized.
Various aspects of the disclosure provide forming a segmented gas generant having a grain assembly shape tailored to create rapid heated gas, like conventional monolithic unsegmented grains. Exemplary conventional monolithic gas generant grain shapes, formed as a single unitary unsegmented monolithic body, are described in commonly assigned U.S. Pat. Nos. 7,758,709 and 8,057,610 both to Mendenhall, et al. Suitable examples of gas generant compositions having desirable burn rates, density, and gas yield for inclusion in the gas generants manufactured in accordance with the present disclosure include those described in commonly assigned U.S. Pat. No. 6,958,101 to Mendenhall et al. However, any suitable fuels known or to be developed in the art that can provide gas generants having the desired burn rates, gas yields, and density described above are contemplated for use with the teachings of the present disclosure. The disclosures of U.S. Pat. Nos. 7,758,709, 8,057,610, and 6,958,101 are incorporated by reference as if fully set forth herein.
Such conventional monolithic pressed grains desirably exhibit a profile of the combustion pressure curve that is progressive to neutral, in accordance with desired ballistic behavior for gas generant grains. Progressive to neutral combustion pressure curves relate to improved protection for occupants, especially out-of-position occupants. The profile of this pressure curve relates to the amount of surface area of the gas generant which correlates to the mass of generant reacting, hence the mass gas generation rate (mg) and pressure of gas generated over time. This concept can also be expressed as a “rise rate” which is the rate at which the gas output from an inflator increases pressure (usually measured when the gas output is directed to a closed volume).
As background, it is commonly desirable that an inflatable restraint airbag cushion initially inflates in a relatively gradual manner to reduce injury to an occupant (particularly where the occupant is too close to the airbag or “out-of-position”) which is then followed by a period where the inflation gas passes into the airbag cushion at a relatively greater or increased pressure rate. A gas generant that creates such inflation is commonly referred to in the art as producing inflation gas in an “S” curve. Suitable gas generants approach a rise rate having an S curve, which is highly desirable, particularly for out-of-position occupants. Thus, desirable segmented pressed gas generant grain assembly designs prepared in accordance with the present disclosure provide a lower rise rate, while providing a higher average combustion pressure and superior control over the burning characteristics. Additionally, the absence of polymeric binder and/or perchlorate oxidizing agents in the segmented pressed gas generant grain assemblies prepared in accordance with the present disclosure, as compared to conventional extruded grains for example, improves burning characteristics and improves effluent quality.
This may be attributed to several aspects of the high density pressed grain assemblies, including that the gas generant composition is substantially free of polymeric binder and can be free of associated co-oxidizers, such as perchlorates, which raise the combustion flame temperature. Where combustion temperatures are higher, it has generally been observed that higher combustion temperatures result in greater levels or relative amounts of carbon monoxide (CO) and nitrogen oxides (NOx) combustion products, for example. In various aspects, a maximum combustion temperature (also expressed as flame temperature) for a segmented gas generant grain assembly prepared in accordance with the present disclosure is optionally less than about 2,300 K, for example, the flame temperature during combustion is about 1,400 K to about 2,300 K. In certain aspects, the flame temperature is optionally less than about 2,000 K.
Thus, in various aspects, the present disclosure provides a gas generant formed of a plurality of segments arranged together to form an overall grain assembly shape tailored to create rapid heated gas and provide other advantages associated with conventional monolithic gas generant grains. Such a segmented gas generant grain assembly provides various advantages over conventional monolithic unitary body gas generant grains, including lower breakage rates, greater robustness, and reduced manufacturing costs. Thus, in various aspects, the present teachings contemplate using multiple small, simple pressed grain segments or pieces to create a large gas generant grain body assembly. Furthermore, each pressed grain segment has a symmetric shape designed to have at least two distinct contact sides that are complementary to adjacent symmetric segments also having such contact sides. In this manner, each symmetric segment is capable of being placed in near proximity to and/or contact with another adjacent symmetric segment to nest tightly together to form a compact gas generant assembly shape. Such small grain segments have a symmetric shape that enables self-orientation of the respective segment pieces into larger round grain assembly shapes, especially when loaded onto a track during an assembly process. The ability to form a compact overall gas generant assembly by self-orientation of the symmetric segments eliminates the necessity for pins, fingers, or other components to retain the respective pieces together.
In one variation shown in
The gas generant segment 110 comprises a gas generant material and is pressed to form a small grain. Suitable gas generant materials are discussed in further detail below. The gas generant segment 110 comprises at least one void that has a first dimension (d1). As shown in
The overall shape defined by the perimeter of the gas generant segment 110 in
Thus, the plurality of symmetric gas generant segments 110A-110C can be assembled together in a circumferential pattern (see dotted central radial line in
The plurality of three symmetric gas generant segments 110A-110C are arranged together circumferentially to define a substantially round segmented body 130 of the pressed gas generant grain assembly. Each respective contact side face is adjacent to (in near proximity with) and in contact with another distinct contact side. Thus, a contact side 120A of gas generant segment 110A meets a contact side 120C of gas generant segment 110C, while another contact side 120A of gas generant segment 110A meets and interfaces with a contact side 120B of gas generant segment 110B on a second opposite side. Similarly, another contact side 120B of gas generant segment 110B meets the other contact side 120C of gas generant segment 110C. As arranged in contact with one another, circumferentially assembled gas generant segments 110A-110C form a ring or substantially round segmented body 130. The substantially round segmented body 130 thus has a centrally disposed aperture 132 that defines a second dimension or diameter “d2.” While not shown, the centrally disposed aperture 132 need not have the same diameter in every embodiment and need not have a substantially round shape, although in certain aspects it is preferred. Thus the second diameter (d2) may instead refer to a second dimension across the centrally disposed aperture having an alternative shape. In various aspects, the second diameter d2 of centrally disposed aperture 132 is larger than the first dimension or diameter d1 of the plurality of apertures 112 in the plurality of gas generant segments 110. The centrally disposed aperture 132 may be sized to receive a pin, squib, an auto-ignition material or other componentry within the inflator assembly, as are well known in the art.
The inventive gas generant designs provide particular advantages over the conventional monolithic unitary body pressed gas generants. While forming a gas generant grain assembly of multiple pieces might initially appear to add greater manufacturing complexity by having to form multiple pieces and the subsequent assemblage steps required, in various aspects, formation of small symmetric segments assembled into a larger segmented grain assembly has significant advantages. First, the assembly of a plurality of symmetric gas generant segments arranged together circumferentially to define a segmented body actually has the potential to provide a lower cost manufacturing process. This is because the segments can be pressed to appropriate densities on smaller high-speed rotary presses, as compared to the relatively large and pressed unitary body monolithic gas generant grains, which require much higher capacity, larger hydraulic presses which have much slower processing speeds. Thus, despite the additional complexity of forming multiple pieces that have to be arranged and assembled together, the ability to form the smaller grain segments on smaller presses actually realizes manufacturing cost reductions.
Further, the small grains are much more robust that larger grains. As discussed below, drop test results show significant improvement for a segmented gas generant grain assembly formed of a plurality of smaller symmetric gas generant segments. It is believed that the smaller grain segments introduce multiple slip planes within the assembly to allow them to absorb energy and move without breakage. Furthermore, the packaging required for less fragile, more robust gas generant assemblies prepared in accordance with the present teachings reduces costs of packaging and transport costs. Thus, despite the apparent advantages to forming a conventional unsegmented monolithic gas generant grain in a single pressing step, the potential fragility actually increases costs through high rates of breakage during manufacturing and more expensive packaging and transport. In certain variations, a segmented body of a pressed gas generant grain assembly prepared in accordance with the present disclosure has a rate of breakage significantly less than that of a comparative rate of breakage for a comparative monolithic unsegmented gas generant grain defining the same gas generant grain shape, as will be discussed further below. Further, enhanced robustness of a gas generant grain assembly reduces performance variability once the inflator assembly is in service within a vehicle. Additionally, small grain segments permit more flexibility in gas generant grain assembly design. For example, the inventive technology permits easier integration of an auto-ignition material, where one of the small grain segments can be replaced with a grain segment made from an auto-ignition material. Such flexibility in design significantly improves bonfire test performance, but does not significantly degrade inflator performance.
Thus, in certain aspects, the present teachings provide a pressed gas generant grain assembly comprising a plurality of symmetric gas generant segments arranged together circumferentially to define a segmented body of the pressed gas generant grain assembly. In certain aspects, the gas generant grain assembly comprises 3 to 6 symmetric gas generant segments that define the segmented body. Each symmetric gas generant segment is pressed and comprises at least one void having a first dimension. In certain variations, each symmetric gas generant segment comprises two or more voids having the first dimension. In certain preferred variations, each gas generant segment comprises at least two or more voids in the form of apertures having a first dimension or diameter. In certain variations, each symmetric gas generant segment comprises 3 to 7 apertures having the first dimension or diameter.
Further, each symmetric gas segment has a shape that is symmetric with respect to at least one axis of symmetry. In certain variations, the shape of each symmetric gas generant segment is symmetric with respect to two distinct axes of symmetry, such as an x-axis and a y-axis of the segment. Furthermore, in certain aspects, each symmetric gas generant segment has the shape defining 3 to 6 distinct sides. The shape may also comprise one or more concave or convex side regions. Each symmetric gas generant segment defines at least two distinct sides for being placed in proximity to or contact with adjacent complementary sides of two distinct adjacent symmetric gas generant segments. When the plurality of symmetric segments is assembled together, the segmented body thus formed has a central aperture having a second dimension or diameter. The second dimension or diameter is greater than the first dimension or diameter.
Another embodiment of a segmented gas generant grain assembly 200 according to certain aspects of the present disclosure is shown in
The gas generant segment 210 comprises at least one void having a first dimension, more specifically at least two or more apertures 212 having the first diameter (d1). In gas generant segment 110, four distinct apertures 212 are formed in a body region 216. The apertures 212 are disposed within body region 216 at equal distances from one another and notably, like the symmetric overall shape of the gas generant segment 210, are disposed symmetrically within the body region 216 of the gas generant segment 210. The apertures 212 are substantially round, thus forming cylindrical openings through body region 216. Like, the previous embodiment, while not shown, variations in dimensions, shape, and distribution with the body region 216 are contemplated. Furthermore, the gas generant segment 210 defines at least two distinct contact sides 220 having a complementary shape to adjacent gas generant segments.
Thus, the plurality of symmetric gas generant segments 210A-210D can be assembled together in a circumferential pattern to form a closed substantially round shape. A contact side 220A of gas generant segment 210A meets a contact side 220D of gas generant segment 210D, while another contact side 220A of gas generant segment 210A meets and interfaces with a contact side 220B of gas generant segment 210B on a second opposite side. Similarly, another contact side 220B of gas generant segment 210B meets the other contact side 220C of gas generant segment 210C. The opposite contact side 220C of gas generant segment 210C contacts contact side 220D of gas generant segment 210D.
As arranged in contact with one another, circumferentially assembled gas generant segments 210A-210D form a ring or substantially round segmented body 230. The substantially round segmented body 230 thus has a centrally disposed aperture 232 that defines a second diameter “d2.” Notably, the centrally disposed aperture 232 has a rectangular/square cross-sectional shape in
In yet another variation,
The gas generant segment 410 comprises at least one void having a first dimension and more specifically at least two or more apertures 412 having a first diameter (d1). In gas generant segment 410, three distinct apertures 412 are formed in a body region 416. The apertures 412 are disposed within body region 416 at equal distances from one another. The apertures 412 are substantially round. Furthermore, the gas generant segment 410 defines at least two contact sides 420 having a complementary shape to assemble to adjacent gas generant segments.
Thus, the plurality of symmetric segments 410A-410F can be assembled together in a circumferential pattern to form a closed substantially round shape. Contact side 420A of gas generant segment 410A meets contact side 420F of gas generant segment 410F, while another contact side 420A of gas generant segment 410A meets and interfaces with contact side 420B of gas generant segment 410B on a second opposite side. Thus, as shown, contact side 420E of gas generant segment 410E interacts with contact side 420F (of gas generant segment 410F) and contact side 420D (of gas generant segment 410D). Contact side 420D of gas generant segment 410D interacts with contact sides 420E (of gas generant segment 410E) and contact side 420C (of gas generant segment 410C). Similarly, contact side 420C of gas generant segment 410C interacts with contact side 420D (of gas generant segment 410D) and contact side 420B (of gas generant segment 410B). Contact side 420B of gas generant segment 410B interacts with contact side 420C (of gas generant segment 410C) and the other side of gas generant segment 410A at contact side 420A. As such, six gas generant segments 410A-410F are arranged together to define a ring or substantially round segmented body 430.
The substantially round segmented body 430 has a centrally disposed aperture 432 that defines a second diameter “d2.” Notably, the centrally disposed aperture 432 has a hexagonal star cross-sectional shape in
Such surface projections 460 on the upper surface 464 of the gas generant segments 450 define offsets or standoffs (when assembled into a stack of gas generant grain assemblies, like 500 in
Surface projections 460 are only formed on the upper surface 464 in
Suitable examples of gas generant compositions for forming the plurality of gas generant segments are selected to have adequate burn rates, density, and gas yield. For example, suitable gas generant compositions may include described in U.S. Pat. Nos. 6,958,101, 7,758,709, and 8,057,610, all to Mendenhall, et al., the disclosure of which is herein incorporated by reference in its entirety.
In various embodiments, the gas generant comprises at least one fuel. The fuel component may be a nitrogen-containing compound and preferably is an azide-free compound. In certain aspects, suitable fuels include tetrazoles and salts thereof (e.g., aminotetrazole, mineral salts of tetrazole), bitetrazoles, 1,2,4-triazole-5-one, guanidine nitrate, nitro guanidine, amino guanidine nitrate, and the like. These fuels are combined with one or more oxidizers in order to obtain an acceptable burning rate and production of desirable gaseous species. For example, in certain variations, the gas generant may comprise guanidine nitrate as a fuel. Examples of suitable acidic organic compounds include, but are not limited to, tetrazoles, imidazoles, imidazolidinone, triazoles, urazole, uracil, barbituric acid, orotic acid, creatinine, uric acid, hydantoin, pyrazoles, derivatives and mixtures thereof. Particularly suitable acidic organic compounds include tetrazoles, imidazoles, derivatives and mixtures thereof. Examples of such acidic organic compounds include 5-amino tetrazole, bitetrazole dihydrate, and nitroimidazole. According to certain aspects, a preferred acidic organic compound includes 5-amino tetrazole.
In other embodiments, a substituted basic metal nitrate can include a reaction product formed by reacting an acidic organic compound with a basic metal nitrate. Examples of suitable acidic organic compounds include, but are not limited to, tetrazoles, imidazoles, imidazolidinone, triazoles, urazole, uracil, barbituric acid, orotic acid, creatinine, uric acid, hydantoin, pyrazoles, derivatives and mixtures thereof. Examples of such acidic organic compounds include 5-amino tetrazole, bitetrazole dihydrate, and nitroimidazole. Generally, suitable basic metal nitrate compounds include basic metal nitrates, basic transition metal nitrate hydroxy double salts, basic transition metal nitrate layered double hydroxides, and mixtures thereof. Suitable examples of basic metal nitrates include, but are not limited to, basic copper nitrate, basic zinc nitrate, basic cobalt nitrate, basic iron nitrate, basic manganese nitrate and mixtures thereof. One particularly preferred gas generant composition includes about 5 to about 60 weight % of guanidine nitrate co-fuel and about 5 to about 95 weight % substituted basic metal nitrate. However, any suitable fuels known or to be developed in the art that can provide gas generants having the desired burn rates, gas yields, and density described below are contemplated for use in various embodiments of the present disclosure.
The desirability of use of various co-fuels, such as guanidine nitrate, in the gas generant compositions is generally based on a combination of factors, such as burn rate, cost, stability (e.g., thermal stability), availability and compatibility (e.g., compatibility with other standard or useful pyrotechnic composition components). Fuel components may be respectively present in an amount of less than or equal to about 75% by weight of the gas generant composition; optionally less than or equal to about 50% by weight; optionally less than or equal to about 40% by weight; optionally less than or equal to about 30% by weight; and in certain aspects, optionally less than or equal to about 25% by weight of the gas generant composition.
As appreciated by those of skill in the art, such fuel components may be combined with additional components in the gas generant, such as co-fuels or oxidizers. One or more co-fuel/oxidizers are selected along with the fuel component to form a gas generant that upon combustion achieves an effectively high burn rate and gas yield from the fuel. The gas generant may include combinations of oxidizers. Suitable oxidizers for the gas generant composition include, by non-limiting example, alkali (e.g., elements Group 1 of IUPAC Periodic Table, including Li, Na, K, Rb, and/or Cs), alkaline earth (e.g., elements of Group 2 of IUPAC Periodic Table, including Be, Mg, Ca, Sr, and/or Ba), and ammonium nitrates, nitrites, and perchlorates; metal oxides (including Cu, Mo, Fe, Bi, La, and the like); basic metal nitrates (e.g., elements of transition metals of Row 4 of IUPAC Periodic Table, including Mn, Fe, Co, Cu, and/or Zn); transition metal complexes of ammonium nitrate (e.g., elements selected from Groups 3-12 of the IUPAC Periodic Table); and combinations thereof.
In certain variations, an oxidizer for the gas generant material may comprise a basic metal nitrate. Generally, suitable compounds include basic metal nitrates, basic transition metal nitrate hydroxy double salts, basic transition metal nitrate layered double hydroxides, and mixtures thereof. Thus, suitable oxidizers for the gas generant compositions may include, by way of non-limiting example, basic metal nitrates (e.g., elements of transition metals of Row 4 of IUPAC Periodic Table, including Mn, Fe, Co, Cu, and/or Zn). Suitable examples of basic metal nitrates include, but are not limited to, basic copper nitrate, basic zinc nitrate, basic cobalt nitrate, basic iron nitrate, basic manganese nitrate and mixtures thereof. Ammonium dinitramide is another suitable oxidizing agent. Such oxidizing agents may be respectively present in an amount of less than or equal to about 95% by weight of the gas generant composition; optionally less than or equal to about 75% by weight; optionally less than or equal to about 50% by weight; optionally less than or equal to about 25% by weight; optionally less than or equal to about 20% by weight; and in certain aspects, less than or equal to about 15% by weight of the gas generant composition.
The gas generant composition may comprise an oxidizer comprising a perchlorate-containing compound, in other words a compound including a perchlorate group (ClO4−). As noted above, in certain variations, the gas generant compositions are substantially free of perchlorate-containing compounds. However, if such perchlorate-containing compounds are present, alkali, alkaline earth, and ammonium perchlorates are contemplated for use in gas generant compositions. Particularly suitable perchlorate oxidizers include alkali metal perchlorates and ammonium perchlorates, such as ammonium perchlorate (NH4ClO4), sodium perchlorate (NaClO4), potassium perchlorate (KClO4), lithium perchlorate (LiClO4), magnesium perchlorate (Mg(ClO4)2), and combinations thereof. If perchlorate oxidizers are present in the gas generant, it is preferably at less than about 20% by weight. By way of example, a perchlorate containing oxidizer is present in certain embodiments at about 0.5% to about 20% by weight; optionally about 0.5 to about 15% by weight; optionally about 1 to about 5% by weight of the gas generant.
If desired, a gas generant composition may optionally include additional components such as slag forming agents, coolants, flow aids, viscosity modifiers, pressing aids, dispersing aids, phlegmatizing agents, excipients, burn rate modifying agents, and mixtures thereof. Such additives typically function to improve the stability of the gas generant material during storage; modify the burn rate or burning profile of the gas generant composition; improve the handling or other material characteristics of the slag, which remains after combustion of the gas generant material; and improve ability to handle or process pyrotechnic raw materials.
For example, the gas generant compositions may optionally include a slag forming agent, such as a refractory compound, e.g., aluminum oxide and/or silicon dioxide. Generally, such slag forming agents may be included in the gas generant composition in an amount of 0 to about 10 weight % of the gas generant composition.
Coolants for lowering gas temperature, such as basic copper carbonate or other suitable carbonates, may be added to the gas generant composition at 0 to about 20% by weight. Similarly, press aids for use during compression processing, as will be described in greater detail below, include lubricants and/or release agents, such as graphite, and can be present in the gas generant at 0 to about 2%. While in certain aspects, the gas generant compositions can be substantially free of polymeric binders, in certain alternate aspects, the gas generant compositions optionally comprise low levels of certain acceptable binders or excipients to improve crush strength, while not significantly harming effluent and burning characteristics. Such excipients include microcrystalline cellulose, starch, carboxyalkyl cellulose, e.g., carboxymethyl cellulose (CMC), by way of example. When present, such excipients can be included in alternate gas generant compositions at less than 10% by weight, preferably less than about 5% by weight, and more preferably less than about 2.8%. Additionally, certain ingredients can be added to modify the burn profile of the pyrotechnic fuel material by modifying pressure sensitivity of the burning rate slope. One such example is copper bis-4-nitroimidazole. Agents having such an affect are referred to herein as pressure sensitivity modifying agents and they can be present in the gas generant at 0 to about 10% by weight. Such additives are described in more detail in U.S. Pat. No. 7,470,337 to Mendenhall et al. Other additives known or to be developed in the art for pyrotechnic gas generant compositions are likewise contemplated for use in various embodiments of the present disclosure.
In certain variations, a gas generant segment can be formed from a powder gas generant material. Powder preparation and processing may be conducted by creating a slurry distributing and thoroughly mixing several raw material components in water and/or a hydrophilic solvent, which may be followed by drying (e.g., spray drying). Such processes for forming powderized and/or granulated gas generants are merely exemplary and are well known to those of skill in the art. In certain aspects, the gas generant materials are in a dry powderized and/or pulverized form. The powderized materials can be placed in a die or mold, where an applied force compresses the gas generant materials to form a desired grain segment shape. The dry powders are optionally compressed with applied forces greater than about 50,000 psi (approximately 350 MPa), preferably greater than about 60,000 psi (approximately 400 MPa), more preferably greater than about 65,000 psi (approximately 450 MPa), and an in certain variations, greater than about 70,000 psi (approximately 483 MPa). In certain variations, a press force to apply to the dry powders in a die is greater than or equal to about 60,000 psi (approximately 400 MPa) to less than or equal to about 70,000 psi (approximately 483 MPa).
The formation of the smaller pressed grain segments improves robustness and also reduces high costs associated with manufacturing conventional unitary pressed monolithic gas generant grains. For example, lower cost manufacturing is realized in accordance with certain aspects of the present technology, because gas generant grain segments can be pressed on smaller, high-speed rotary presses. Conventional unsegmented monolithic grains have a large surface area and therefore require pressing on a hydraulic press to meet the press force requirements outlined above. Large hydraulic presses typically have processing speeds of about 4 to 6 strokes per minute. The gas generant segments prepared in accordance with the present disclosure have lower surface areas as compared to monolithic unsegmented gas generant grains and thus can be pressed on rotary tablet presses. Such rotary tablet presses have significantly greater processing speeds as compared to large hydraulic presses, for example, having processing speeds of up to 150 strokes per minute. Thus, even though a greater number of the smaller grain segments need to be pressed to form a larger grain assembly, the overall output on a rotary press is much higher (e.g., 4-12 times faster). Thus, manufacturing of smaller gas generant grain segments is significantly faster.
In various aspects, gas generant grain segments are compressed and in certain aspects, optionally have an actual density that is greater than or equal to about 90% of the maximum theoretical density. In certain aspects of the present disclosure, the actual density is greater than or equal to about 93%, optionally greater than about 95% of the maximum theoretical density, and optionally greater than about 97% of the maximum theoretical density. In certain aspects, the actual density of the gas generant grain segment exceeds about 98% of the maximum theoretical density of the gas generant material. Such high actual mass densities in gas generant materials are obtained in certain methods of forming gas generant grain assemblies in accordance with various aspects of the present disclosure, where compressive force is applied to gas generant raw materials that are substantially free of binder.
In certain aspects, it is preferred that a loading density of the gas generant segment is relatively high. A loading density is an actual volume of generant material divided by the total volume available for the shape (here of the segment). In accordance with various aspects of the present disclosure, it is preferred that a loading density for the gas generant segment is greater than or equal to about 50% and in certain variations is optionally greater than or equal to about 55%. In certain aspects, a gas generant segment has loading density of about 55 to about 63%.
Various aspects of the present disclosure provide a segmented gas generant having a shape (when the various gas generant segments are assembled together) that is tailored to create rapid heated gas. The overall grain assembly shape of the assembled gas generant segments has a desired surface area and shape to facilitate prolonged reaction and to create preferred gas production profiles at the desired pressures. The absence of the binder in certain embodiments from the gas generant segments further enables development of desirable burn and pressure profiles, as compared to conventional extruded gas generants. It is the combination of the selected gas generant material composition, initial surface area, shape, and density of the gas generant grain segments, when assembled together to form the overall segmented gas generant assembly shape, that maximizes desired combustion performance.
In certain aspects, the segmented gas generant has a shape that provides increasing surface area as the grain assembly burns. The desired shape of the segmented gas generant grain assembly formed of a plurality of symmetric pressed gas generant segments is linked to ballistic characteristics of the composition. The shape of the segmented gas generant grain assembly augments and controls the burn rate of the gas generant composition. In various aspects, a desirably high burning rate enables desirable pressure curves for inflation of an airbag. In this regard, an initial surface area of the segmented gas generant grain assembly is relatively low as compared to surface areas of traditional pellets and/or wafers; however, as the grain assembly shapes are burned, more surface area is progressively exposed, thus the amount of the composition combusting progressively becomes greater and generates a higher quantity of gas.
In accordance with certain aspects of the present disclosure, the segmented gas generant grain assembly has a linear burn rate of greater than or equal to about 1.0 inches per second (about 38.1 mm per second) at a pressure of about 3,000 pounds per square inch (about 20,865 kPa). In certain aspects, the segmented gas generant has a linear burn rate of greater than or equal to about 1.1 inches per second (about 28 mm/Sec); optionally greater than or equal to about 1.5 inches per second (about 38 mm/Sec); and optionally greater than or equal to about 1.9 inches per second (about 48 mm/Sec) at a pressure of about 3,000 pounds per square inch (psi) (about 20.7 MPa). In certain embodiments, the linear burn rate of the segmented gas generant is greater than or equal to about 2.0 inches per second (about 51 mm/Sec) at a pressure of about 3,000 psi (about 20.7 MPa). In certain embodiments, the burning rate of the segmented gas generant is less than or equal to about 2.1 inches per second (about 53 mm/Sec) at a pressure of 3,000 psi (about 20.7 MPa).
Additionally, in certain aspects, the gas generant segments that form the segmented gas generant grain assembly have a high mass density. For example, in certain embodiments, each gas generant segment has a theoretical mass density of greater than about 1.9 g/cm3, preferably greater than about 1.94 g/cm3, and even more preferably greater than or equal to about 2.12 g/cm3.
Further, in accordance with the present disclosure, the gas yield of the segmented gas generant assembly is relatively high. For example, in certain embodiments, the gas yield is greater than or equal to about 2.4 moles/100 grams of gas generant. In other embodiments, the gas yield is greater than or equal to about 2.5 moles/100 g of the gas generant assembly. In certain embodiments, the gas yield is greater than or equal to about 3 moles/100 g of the gas generant assembly; optionally greater than or equal to about 3.1 moles/100 g of the gas generant assembly; and optionally greater than or equal to about 3.2 moles/100 g of the gas generant assembly.
Expressed in another way, the amount of gas produced for a given mass of gas generant present at a specific volume is relatively high. In this regard, the product of gas yield and density is an important parameter for predicting performance of the gas generant assembly. A product of gas yield and density (of the gas generant assembly) may be greater than about 5.0 moles/100 cm3, and optionally greater than about 5.2 moles/100 cm3, in various embodiments.
In certain alternative variations of the present disclosure, one of the pressed segments may be formed of a pyrotechnic material having a distinct composition than the other gas generant segments. By “distinct” it is meant that the first composition differs from the second composition by at least one component and preferably exhibits a material difference in pyrotechnic characteristics. For example, in certain variations, one of the pressed gas generant segments may comprise an auto-ignition material.
An auto-ignition agent is a material that spontaneously combusts at a pre-selected temperature, preferably a temperature lower than that which would lead to catastrophic failure in a gas generant system, such as potential explosion, fragmentation, or rupture of the airbag inflator upon exposure to extreme heat in excess of normal operating condition temperatures. In current systems, these temperatures may range from about 135° C. to greater than about 200° C. The auto-ignition material ignites the booster/initiator composition and/or gas generant resulting in the safe functioning of the gas generant at elevated temperatures. Thus, the gas generant may be ignited by two separate pathways, which include the igniter and the auto-ignition material, enabling safe gas generant deployment during abnormal conditions. Such an auto-ignition material can also be employed to increase the burning of the gas generant during normal operating conditions, in effect, operating as a booster composition. Further, the auto-ignition material may improve coupling of certain pyrotechnic materials to one another.
An auto-ignition material may comprise a single auto-ignition agent or a mixture of agents formulated to auto-ignite at a desired pre-selected temperature. Some examples of suitable auto-ignition materials known in the art include silver nitrate and smokeless powders, such as those sold by E. I. DuPont De Nemours under the Trade Name IMR 4895™. Other examples of suitable auto-ignition materials include those disclosed in U.S. Patent Publication No. 2006/0102259 to Mendenhall et al., which is herein incorporated by reference in its entirety and describes an auto-ignition material comprising a mixture of azodicarbonamide (ADCA) fuel and basic copper nitrate (BCN) oxidizer.
Initiator or booster fuels may also be included in a pyrotechnic material of such an alternative embodiment. Such booster materials include ethyl cellulose, nitrocellulose, metal hydride pyrotechnic materials such as zirconium hydride potassium perchlorate (ZHPP) and titanium hydride potassium perchlorate (THPP), zirconium potassium perchlorate (ZPP), boron potassium nitrate (BKNO3), cis-bis-(5-nitrotetrazolato)tetramine cobalt(III)perchlorate (BNCP), and mixtures thereof. Some of these booster fuels, such as ethyl cellulose, may require the inclusion of an oxidizer. Such booster or initiator fuels can be present in an amount of less than or equal to about 50 weight % of the alternative pyrotechnic composition. Thus, the inventive technology permits more flexibility in gas generant grain assembly design. Such flexibility in design significantly improves bonfire test performance, but does not significantly degrade inflator performance.
For example, the inclusion of booster materials in a gas generant grain assembly can reduce or eliminate the need for an extensive igniter system. Similarly, inclusion of auto-ignition materials in a single pyrotechnic material grain assembly can streamline the architecture of the systems equipment by eliminating the need for separate containment of auto-ignition materials. Thus, the flexibility provided by the principles of the present disclosure provide the potential to reduce and/or eliminate complex hardware and staging systems, while further potentially avoiding safety and performance complications via the use of the improved pyrotechnic materials in a single unitary structure according to various embodiments of the present disclosure.
The distinct segmented gas generant grain assemblies 510 have a design like the previously described embodiment shown in
An exemplary gas generant assembly device 600 in accordance with certain aspects of the present technology is shown in
Before the first gas generant segment grains 530 are translated down the conveyor track 614 to the receiving end 610, plates 608 are closed together over the lower metal disc 522. Notably, plates 608 have hemispherical regions 624 at the mating edges that together form an opening for the central pin 526 of the strainer component 520 that protrudes during loading of the gas generant segments 530.
As shown in
The process can then be repeated as many times as necessary to form multiple gas generant grain assembly bodies 510 forming distinct layers, such as shown in
In certain preferred variations, the symmetric segments may not be physically connected or attached together, but rather just placed into near proximity and/or contact with other adjacent segments and retained in place by a strainer component or other holding receptacle or structure. This provides certain advantages, such as avoiding introducing additional materials to the gas generant grain assembly during combustion and improved burn profiles. However, in certain alternative embodiments, such as that shown in
In
In yet another embodiment, shown in
The gas generant segment 810 comprises at least one void having a first dimension, more specifically at least two or more apertures 812 having the first diameter (“d1”). In gas generant segment 810, three distinct apertures 812 are formed in a body region 816. The apertures 812 are disposed within body region 816 at equal distances from one another and notably, like the symmetric overall shape of the gas generant segment 810, are disposed symmetrically within the body region 816 of the gas generant segment 810. The apertures 812 are substantially round, thus forming cylindrical openings through body region 816. Like, the previous embodiments, while not shown, variations in dimensions, shape, and distribution of voids (e.g., apertures 812) with the body region 816 are contemplated. A plurality of symmetric gas generant segments 810 can be assembled together in a circumferential pattern to form a closed substantially round shape, in accordance with the assembly patterns shown in the previous embodiments.
Notably, an upper surface 820 of the gas generant segment 810 is contoured and thus defines a plurality of surface projections 822. The areas outside of the surface projections 822 thus define recessed regions 824 in the upper surface 820. Such surface projections 822 on the upper surface 820 of the gas generant segment 810 define offsets or standoffs creating spaces or gaps between stacked gas generant assemblies. Such spaces can thus serve as gas flow passages facilitating combustion of the gas generant, especially in an inflator device.
Notably, the surface projections 822 may be selectively placed in other locations on the upper surface 820 and may have different shapes from those shown in
Further, while surface projections 822 and recessed regions 824 are only formed on the upper surface 820 in
The following non-limiting examples further illustrate certain aspects of the inventive technology.
In one example, a 5-amino tetrazole substituted basic copper nitrate fuel is formed. 72.7 lb. of 5-amino tetrazole is charged to 42 gallons of hot water to form a 5-amino tetrazole solution. 272.9 lb. of basic copper nitrate is slowly added to the 5-amino tetrazole solution. 5-aminotetrazole and basic copper nitrate are allowed to react at 90° C. until the reaction is substantially complete. To the reaction mixture are added 139.95 lb. of guanidine nitrate and 14.45 lb. of silicon dioxide. The slurried mixture is then spray dried. 5.1 lb. of a release agent (inert carbon, i.e., graphite) and 20.83 lb. of basic copper carbonate (a coolant) are dry blended with the spray dried composition.
A blended powder as prepared in Example 1 is placed in a pre-formed die having the desired shape to from a pressed gas generant grain segment as shown in
For purposes of comparison, a blended powder as prepared in Example 1 is placed in a pre-formed die having the desired shape to from pressed unitary unsegmented monolithic gas generant grains as shown in
Thus, for purposes of comparison, a conventional unsegmented single gas generant monolithic grain 800 having a shape shown in
Similarly, for purposes of comparison, a conventional single gas generant monolithic grain 850 having a shape shown in
This example explores robustness of segmented gas generants formed in accordance with the present disclosure as compared to that of conventional unitary gas generant monolithic grains. A segmented gas generant grain prepared in accordance with certain aspects of the present disclosure, designated Example A, is compared to conventional single gas generant monolithic grains designated Comparative Example B (shown in
A drop test is conducted per U.S. Council for Automotive Research (USCAR) 5.2.4.8.6. More specifically, a horizontal drop test is used that includes disposing a stack of multiple layers of grains of the gas generant sample being tested under a tension within a simulated gas generator. Conical compression springs having a gap of 7 mm are used. The simulated gas generator holding the gas generant samples is then dropped on its side axis horizontally. Here, the horizontal drop test is conducted at a vertical height of 1.2 m (2 times on each axis) on a steel plate. The dropped samples are then removed from the simulated gas generator for assessment of any damage.
As can be seen in the photographs of the results of one horizontal drop test in
In multiple iterations of the horizontal drop tests, 16 of 19 of pressed unsegmented monolithic grains like those in Comparative Examples B and C failed the drop test by showing significant, extensive breakage and fracturing, thus having a rate of breakage of about 84%. However, in the same horizontal drop test, only 2 of 126 segmented gas generant grain assemblies like in Example A (having a 6-piece segmented gas generant grain assembly like in
The segmented gas generant grain assemblies according to various aspects of the present teachings share various advantages with monolithic gas generant grains, such as repeatable and well controlled combustion, while avoiding certain potential disadvantages. For example, conventional pressed monolithic grains, like those in Comparative Examples B and C tend to be somewhat fragile. Thus, broken grains can occur during processing, shipping, or during the life of the product (after the grain has been loaded into an airbag inflator). Broken grains occurring during manufacturing results in increased cost due to product scrap. Broken grains during life cycle can potentially be a more serious issue, because a broken grain could potentially experience variability in performance.
In certain variations, a segmented body of a pressed gas generant grain assembly prepared in accordance with the present disclosure has a rate of breakage that is significantly less than a rate of breakage for a comparative monolithic non-segmented gas generant grain defining the same gas generant grain shape. In certain variations, a pressed segmented gas generant grain prepared in accordance with the present disclosure has a rate of breakage of less than or equal to about 50% of all pressed segmented gas generant grains tested; optionally less than or equal to about 25%; optionally less than or equal to about 15%; optionally less than or equal to about 10%; optionally less than or equal to about 5%; and optionally less than or equal to about 4%; optionally less than or equal to about 3%. In certain variations, a pressed segmented gas generant grain prepared in accordance with the present disclosure has a rate of breakage of less than or equal to about 2% of all pressed segmented gas generant grains tested. Further, enhanced robustness of a gas generant grain assembly reduces performance variability once the inflator assembly is in service within a vehicle.
The inventive gas generant designs provide yet other advantages over the conventional monolithic unitary body pressed gas generants. While forming a gas generant grain assembly of multiple pressed pieces might initially appear to add greater manufacturing complexity by having to form multiple pieces and the subsequent assemblage steps required, in various aspects, formation of small symmetric segments assembled into a larger segmented grain assemblies has significant advantages. First, the assembly of a plurality of symmetric gas generant segments arranged together circumferentially to define a segmented body of the pressed gas generant grain assembly actually has the potential to provide a lower cost manufacturing process. Large pressed monolithic grains require large press equipment (typically a hydraulic press) that is very expensive and often requires a slower cycle time, which in turn increases process costs. However, the small gas generant segments can be pressed to appropriate densities on smaller high-speed high through-put rotary presses, as compared to the relatively large pressed unitary body monolithic gas generant grains. Thus, despite the additional complexity of forming multiple pieces that have to be arranged and assembled together, the ability to form the smaller grain segments on smaller presses results in faster manufacturing. Further, the pressed gas generant segments having a symmetric shape are capable of self-orienting during manufacturing and assembly into a gas generant grain assembly, which likewise speeds manufacturing and reduces overall cost. Due to enhanced robustness and reduced fragility, less packaging is required to transport the gas generant assembly components, thus reducing packaging and shipping costs.
Additionally, small grain segments permit more flexibility in gas generant grain assembly design. For example, the inventive technology permits easier integration of other pyrotechnic materials, such as an auto-ignition material. One of the small grain segments can be replaced with a grain segment having the same shape, but made from a distinct pyrotechnic material, such as an auto-ignition material.
In various aspects, the present disclosure provides pressed gas generant grain assemblies, which are segmented, and thus comprise a plurality of symmetric gas generant pieces or segments. Each of the symmetric gas generant segments is pressed and comprises a gas generant material. The symmetric pieces or segments are arranged together circumferentially to define a segmented body of the pressed gas generant grain assembly. In certain aspects, the symmetric segments of the pressed segmented monolithic gas generant grain assemblies are substantially free of polymeric binder and have a high density. Such symmetric segment pieces may be formed in unique shapes to form monolithic gas generant grain assemblies that optimize the ballistic burning profiles of the materials contained therein. In forming a segmented pressed grain assembly in accordance with various aspects of the present teachings, a more robust and less expensive gas generant grain assembly having the desired performance properties is realized.
In certain variations, the present disclosure provides a segmented gas generant grain assembly comprising a plurality of gas generant segments arranged together circumferentially to define a segmented body of the gas generant grain assembly. Each gas generant segment is pressed and has a shape that is symmetric with respect to at least one axis defined by the segment. Further, each gas generant segment comprises at least one void having a first dimension. In certain variations, each gas generant segment comprises two or more apertures having a first dimension. The segmented body formed when the plurality of symmetric gas generant segments are assembled together has a central aperture having a second diameter or dimension greater than the first dimension.
In certain variations, a shape of each gas generant segment has not only one axis of symmetry, but rather two axes of symmetry, which correspond to an x-axis and a y-axis of the segment. In certain embodiments, the segmented body comprises 3 to 6 of the gas generant segments. In certain variations, each symmetric gas generant segment comprises at least one void, which may be an aperture extending through the gas generant segment body. In certain embodiments, each gas generant segment comprises 3 to 7 apertures, which have the first diameter or dimension. In certain aspects, the shape of the gas generant segment may define 3 to 6 sides. In certain other aspects, each gas generant segment defines at least two distinct sides for contacting adjacent sides of two distinct adjacent gas generant segments.
In certain alternative variations, each gas generant segment may be physically attached to an adjacent gas generant segment. For example, in certain variations, each gas generant segment comprises an adhesive disposed between at least two complementary sides of adjacent gas generant segments. In other variations, an outer band may surround the plurality of gas generant segments to attach them together. For example, each gas generant segment may be coupled to adjacent gas generant segments by an outer circumferential band disposed about a perimeter of the segmented gas generant. In other aspects, each symmetric gas generant segment may have a contoured surface having one or more recessed regions that form offsets for fluid flow between adjacent symmetric gas generant segments.
In certain aspects, the segmented body of the pressed gas generant grain assembly has a rate of breakage less than or equal to about 50%; optionally less than or equal to about 25%, optionally less than or equal to about 10%, optionally less than or equal to about 5%, and in certain variations, less than or equal to about 2% of all pressed gas generant grain assemblies tested. In yet other variations, one of the plurality of gas generant segments forming the segmented gas generant grain assembly has a pyrotechnic composition that is distinct from the others of the plurality of gas generant segments. For example, the distinct pyrotechnic composition may comprise an auto-ignition material.
In other aspects, the present disclosure provides a segmented gas generant grain assembly comprising a plurality of gas generant segments arranged together circumferentially to define a substantially round and segmented body of the gas generant grain assembly. Each gas generant segment in a final pressed form has an actual density of greater than or equal to about 95% of the maximum theoretical mass density. Further, each gas generant segment is substantially free of any binder and has a shape that is symmetric with respect to at least one axis defined by the segment. Further, each gas generant segment comprises at least one void having a first dimension. In certain variations, each gas generant segment comprises two or more apertures having a first dimension. Thus, gas generant segment optionally comprises at least two or more apertures having a first dimension or diameter. When the plurality of segments is assembled together, the substantially round and segmented body has a central aperture having a second diameter or dimension that is greater than the first diameter or dimension.
In certain variations, a shape of each gas generant segment has not only one axis of symmetry, but rather two axes of symmetry, which correspond to an x-axis and a y-axis of the segment. In certain variations, each symmetric gas generant segment comprises at least one void, which may be an aperture extending through the gas generant segment body. In certain embodiments, each gas generant segment comprises 3 to 7 apertures, which have the first diameter or dimension. In certain aspects, the shape of the gas generant segment may define 3 to 6 sides. In certain other aspects, each gas generant segment defines at least two distinct sides for contacting adjacent sides of two distinct adjacent gas generant segments.
In certain alternative variations, each gas generant segment is attached to an adjacent gas generant segment. For example, in certain variations, each gas generant segment comprises an adhesive disposed between at least two complementary sides of adjacent gas generant segments. In other variations, an outer band may surround the plurality of gas generant segments to attach them together. For example, each gas generant segment may be coupled to adjacent gas generant segments by an outer circumferential band disposed about a perimeter of the segmented gas generant. In other aspects, each symmetric gas generant segment may have a contoured surface having one or more recessed regions that form offsets for fluid flow between adjacent symmetric gas generant segments.
In certain aspects, the segmented body of the pressed gas generant grain assembly has a rate of breakage less than or equal to about 50%; optionally less than or equal to about 25%, optionally less than or equal to about 10%, optionally less than or equal to about 5%, and in certain variations, less than or equal to about 2% of all pressed gas generant grain assemblies tested. In yet other variations, one of the plurality of gas generant segments forming the segmented gas generant grain assembly has a pyrotechnic composition that is distinct from the others of the plurality of gas generant segments. For example, the distinct pyrotechnic composition may comprise an auto-ignition material.
In yet other variations of the present disclosure, methods of making segmented gas generant grain assemblies are provided. For example, one such method comprises conveying a plurality of gas generant segments to a round receptacle capable of receiving the gas generant segments. Each gas generant segment has a shape that is symmetric with respect to at least one axis defined by the segment. The method includes sequentially introducing the respective gas generant segments into the round receptacle, where each symmetric segment self-orients to be arranged circumferentially within the round receptacle to form a segmented gas generant grain assembly having a substantially round body. In certain variations, the method also comprises removing the segmented gas generant grain assembly thus formed from the round receptacle.
In certain aspects, prior to sequentially introducing the gas generant segments, a strainer component having a central protruding pin and a lower metal disc is disposed in the round receptacle. During the sequential introducing, the gas generant segments can be seated onto the lower metal disc around the central protruding pin disposed within the round receptacle. Thus, during the sequential introducing of the gas generant segments, each symmetric segment self-orients to be arranged circumferentially around the central protruding pin. Thus, the removing step further comprises removing both the segmented gas generant grain assembly and the strainer component.
In other aspects, the method may include repeating the conveying and sequentially introducing steps one or more times, before the removing occurs. In certain variations, the conveying and sequentially introducing is conducted multiple times to form a stack of distinct segmented gas generant grain assemblies, which are removed from the round receptacle.
The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.
