Patent Application
20190329471
The disclosed subject matter is related to apparatus and methods for the extrusion of molten plastic material, and particularly to die pins for use in the same.
A variety of systems using molten thermoplastic extrusion are widely employed for the manufacture of plastic articles, including plastic containers and the like. Generally, plastic polymer pellets are melted within a heated extrusion apparatus under pressure and extruded through an outlet. In certain circumstances, the molten plastic or extrudate is extruded in the form of a tube or other hollow member, such as for blow molding techniques. For example, molten plastic is extruded from the extrusion apparatus in an annular space defined between an outlet and a tooling or die pin disposed within the outlet to shape the molten plastic into a hollow parison.
Die pins for extrusion of molten plastic for container blow molding are conventionally made of tool steel. However, steel die pins are susceptible to the accumulation of degraded molten plastic during repeated cycles of plastic extrusion. In rare instances, on the order of one in ten million, the accumulated degraded molten thermoplastic material may be ejected into a parison, resulting in a solid plastic contaminant. A representative contaminant associated with prior art die pins is shown in
To prevent container contamination associated with prior art die pins, it may be necessary to undertake laborious and expensive measures, including periodic phase resets to dislodge the contaminants and line shutdown to permit cleaning of the tooling. However, such efforts are time-consuming and costly, and further require line shutdown, resulting in reduced output. Line shutdown is also associated with increased energy consumption, as the molten plastic must be reheated upon restart.
There thus remains a continued need for an efficient and economic system for minimizing the undesirable accumulation of thermoplastic material in extrusion equipment. There further is a need for such systems with a die pin configured to contact an inner surface of a die ring to separate a hollow plastic parison being formed therebetween. The presently disclosed subject matter satisfies these and other needs.
The purpose and advantages of the disclosed subject matter will be set forth in and are apparent from the description that follows, as well as will be learned by practice of the disclosed subject matter. Additional advantages of the disclosed subject matter will be realized and attained by the apparatus particularly pointed out in the written description and claims hereof, as well as from the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the disclosed subject matter, as embodied and broadly described, the disclosed subject matter includes a die pin for forming a hollow plastic parison, the die pin comprising a base member having a proximal mounting portion, a body portion, and a distal frustoconical portion, wherein the base member comprises a first material; and a tip member mounted on the distal frustoconical portion, wherein the tip member comprises a second material, the second material being different than the first material.
For example, and as embodied herein, the distal frustoconical portion can include a mounting cavity. The tip member can include a rod extending into the mounting cavity of the distal frustoconical portion. The mounting cavity of the distal frustoconical portion can include interior threads configured to form a connection with exterior threads on the rod of the tip member. Thus, for illustration and not limitation, a threaded connection can be used between the distal frustoconical portion and the tip member. Additionally or alternatively, a bonding agent can be disposed between the tip member and the distal frustoconical portion.
As embodied herein, the base member can comprise metal and/or the tip member can comprise ceramic. The proximal mounting portion, body portion, and distal frustoconical portion of the base member can be integrally formed as a single piece. The proximal mounting portion of the base member can include threads configured to be coupled to a connection portion of an extrusion apparatus.
In accordance with another aspect of the disclosed subject matter, the disclosed subject matter includes an extrusion apparatus for forming a hollow plastic parison, the extrusion apparatus comprising a die ring having an inner surface defining an extrusion opening with a central axis. A die pin is disposed within the extrusion opening and aligned with the central axis. The die pin can comprise a base member having a proximal mounting portion, a body portion, and a distal frustoconical portion. The base member can comprise a first material. A tip member can be mounted on the distal frustoconical portion. The tip member can comprise a second material, the second material being different than the first material, and the tip member can comprise a base circumference that is less than a circumference of the extrusion opening. An annular space can be defined between an outer surface of the die pin and the inner surface of the die ring.
As embodied herein, the die pin can be moveable relative to the die ring to move axially toward and away from the extrusion opening.
As embodied herein, the outer surface of the base member can be configured to engage the inner surface of the die ring when the die pin is moved toward the extrusion opening. For example and not limitation, the outer surface of the distal frustoconical portion can be configured to engage the inner surface of the die ring when the die pin is moved toward the extrusion opening.
In accordance with another aspect of the disclosed subject matter, a method for forming a hollow plastic parison can comprise disposing a die pin within an extrusion opening defined by an inner surface of a die ring, the die pin being aligned with a central axis of the extrusion opening, wherein the die pin can comprise a base member having a proximal mounting portion, a body portion, and a distal frustoconical portion, and a tip member mounted on the distal frustoconical portion. The tip member can comprise a base circumference that is less than a circumference of the extrusion opening. The base member can comprise a first material and the tip member can comprise a second material, the second material being different than the first material. An annular space can be defined between an outer surface of the die pin and the inner surface of the die ring, and molten plastic can be directed through the annular space between the die ring and the die pin to form the hollow plastic parison without accumulation of the molten plastic on the die ring.
As embodied herein, the method can further include separating the hollow plastic parison by contacting an outer surface of the base member of the die pin with the inner surface of the die ring. For example, and not limitation, the method can include separating the hollow plastic parison by contacting an outer surface of the distal frustoconical portion of the die pin with the inner surface of the die ring.
It is to be understood that both the foregoing general description and the following detailed description and drawings are examples and are provided for purpose of illustration and not intended to limit the scope of the disclosed subject matter in any manner.
The accompanying drawings, which are incorporated in and constitute part of this specification, are included to illustrate and provide a further understanding of the apparatus of the disclosed subject matter. Together with the description, the drawings serve to explain the principles of the disclosed subject matter.
The subject matter of the application will be more readily understood from the following detailed description when read in conjunction with the accompanying drawings, in which:
Reference will now be made in detail to embodiments of the disclosed subject matter, an example of which is illustrated in the accompanying drawings. The disclosed subject matter will be described in conjunction with the detailed description of the system. The method of the disclosed subject matter will be described in conjunction with the detailed description of the figures and examples provided herein.
As disclosed herein, the apparatuses and methods presented herein can be used for minimizing the undesirable accumulation of thermoplastic material in extrusion equipment. In particular, the disclosed apparatuses and methods can be used to form a hollow plastic parison from molten thermoplastic material. Thermoplastic material can accumulate on the surfaces of the extrusion equipment during manufacturing and, in certain instances, can degrade and contaminate the plastic extruded through the equipment, e.g., by falling into a hollow plastic parison. The apparatuses and methods disclosed herein can use a die pin having a ceramic tip member to reduce or prevent such accumulation.
For illustration, such apparatuses and methods can be used in an extrusion apparatus in which a parison is separated from the extruded plastic material surrounding a die pin by contacting the die pin against a surrounding die ring, e.g. by relative movement of the die pin axially toward and away from the die ring. As such, the parison, extending through and beyond the extrusion opening, can be separated from the upstream extruded plastic material within the extrusion system as a result of the die pin contacting the surface of the die ring. In an extrusion apparatus that severs plastic parisons from the die pin by such contact, the die pin must be strong enough to withstand the force of repeated contact between the die pin and the die ring. Accordingly, specific configurations of die pins disclosed herein can be employed in such extrusion apparatuses, among others, to minimize the undesirable accumulation of thermoplastic material on the die pin while protecting the die pin from increased wear, and preserving or improving the overall durability of the die pin.
Unless otherwise defined, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art to which the disclosed subject matter belongs. Although methods and materials similar or equivalent to those described herein can be used in its practice, suitable methods and materials are described below.
It is to be noted that the term “a” entity or “an” entity refers to one or more of that entity. As such, the terms “a”, “an”, “one or more”, and “at least one” can be used interchangeably herein. The terms “comprising,” “including,” and “having” can also be used interchangeably. In addition, the terms “amount” and “level” are also interchangeable and can be used to describe a concentration or a specific quantity. Furthermore, the term “selected from the group consisting of” refers to one or more members of the group in the list that follows, including mixtures (i.e., combinations) of two or more members.
The term “about” or “approximately” means within an acceptable error range for the particular value as determined by one of ordinary skill in the art, based upon the technique used to measure the value, i.e., the limitations of the measurement system. For example, “about” can mean within 3 or more than 3 standard deviations, per the practice in the art. Alternatively, “about” can mean a range, for example, of up to +/−20%, or up to +/−10%, or up to +/−5%, or up to +/−1% of a given value.
In accordance with the disclosed subject matter, a die pin is provided for forming a hollow plastic parison. The die pin disclosed herein includes a base member having a proximal mounting portion, a body portion, a distal frustoconical portion, and a tip member mounted on the distal frustoconical portion. The base member comprises a first material and the tip member comprises a second material, the second material being different than the first material.
Solely for purpose of illustration, an exemplary embodiment of a die pin is shown schematically in
As illustrated, and with reference to
As embodied herein, the proximal mounting portion 210, body portion 220, and distal frustoconical portion 230 of the base member 205 can be integrally formed as a single piece. Alternatively, one or more of the proximal mounting portion 210, body portion 220, and distal frustoconical portion 230 can be separately formed and incorporated by any suitable means, including, without limitation, threading, welding, or the like. For example, the body portion 220 and distal frustoconical portion 230 can be integrally formed and the proximal mounting portion 210 can be separately formed and attached to the proximal end of the body portion 220.
For example, and not by way of limitation, the proximal mounting portion 210 can further include a feature to cooperate with and attach to a feature of the body portion 220 of the base member 205. For illustration only, the proximal mounting portion 210 can comprise a mounting cavity (not shown) to receive a rod (not shown) extended from the body portion 220 of the base member 205. This connection can be bonded or threadingly engaged to mount the body portion 220 onto the proximal mounting portion 210.
As illustrated in
As noted above and with reference to
As embodied herein, the tip member 240 and the base member 205 can be connected via any suitable means, as known in the art. For example, the distal frustoconical portion 230 of the base member 205 can comprise a mounting cavity 255 configured to receive the tip member 240. For example, as depicted in
Thus, and as illustrated in
As embodied herein, a connection can be formed between the mounting cavity 255 and the rod 260 using any suitable means. For example, as illustrated in
As embodied herein, the die pins disclosed herein can be suitable for incorporation into an extrusion apparatus for forming a hollow plastic parison. Such an extrusion apparatus can comprise a die ring having an inner surface defining an extrusion opening with a central axis. For illustration and not limitation, and with reference to
As illustrated in
As noted above, the materials of the apparatuses disclosed herein can be selected to simultaneously prevent the accumulation of thermoplastic material on the surface of the die pin and extrusion apparatus, while having the strength and durability to withstand the contact forces encountered during brushing of the die pin against the extrusion apparatus. Due to these two-fold requirements, the base member 205 and the tip member 240 can comprise two different materials.
For example, the material of the base member 205 can be selected to withstand the forces encountered during manufacturing, whereas the material of the tip member 240 can be selected to reduce or prevent accumulation of thermoplastic material on the die pin. As such, the base member 205 can be formed from a material that is more durable than the material used to form the tip member 240 (for example, ceramic as detailed below). As such and as shown in
Accordingly, the tip member 240 can be formed of a material that is selected for its material and surface properties suited to reducing buildup of thermoplastic material on the tip member 240 whereas the base member 205 can comprise a more durable material capable of withstanding repeated forces caused by brushing, the interaction between the die ring 245 and the inner surface of the die pin to sever the hollow plastic parison from the upstream portion of plastic being extruded between the die pin 200 and the die ring 245. Thus, as embodied herein, the base member 205 can comprise a first material and the tip member 240 can comprise a second material, with the second material being different than the first material. For example, and not limitation, the base member 205 can comprise a metal that is able to withstand the contacting or brushing forces encountered in the extrusion apparatus. For example, but not limitation, the base member 205 can comprise tool steel. In contrast, the tip member 240 can comprise a ceramic material.
As disclosed herein, it was determined that die pins comprising a tip member 240 formed of a ceramic material are not susceptible to the accumulation of molten thermoplastic material and therefore can minimize contamination of extruded plastic parisons. Without limitation to a particular theory, it appears that the higher specific heat capacity of ceramic prevents localized cooling of the tip member as it is subject to continuous flow of pressurized air during parison formation. The disclosed die pins are therefore less susceptible to condensation of the molten thermoplastic material on the die pin, and specifically, the tip member. Additionally, ceramic material is less susceptible to non-covalent (e.g., electrostatic, hydrogen-bonding, and Van der Waals) interactions with the molten thermoplastic material than conventional tool steel pins. The die pins with ceramic tip members disclosed herein can be used with existing molten thermoplastic extrusion apparatuses.
Thus, and in accordance with one aspect of the disclosed subject matter, at least the tip member 240 of a die pin for molten thermoplastic extrusion is composed of at least one ceramic material. As used herein, ceramics refer to inorganic, nonmetallic materials made by the action of heat at temperatures sufficient to cause sintering, solid-state reactions, bonding, or conversion partially or wholly to the glassy state, and include without limitation crystalline oxides, nitrides and carbide materials. Suitable ceramics for use with the disclosed subject matter include, without limitation, alumina-based ceramics, boron-based ceramics, zirconia-based ceramics, and silicon-based ceramics. Alumina-based ceramics suitable for use with the disclosed subject matter include, without limitation, alumina oxides having a composition of 90% or greater alumina oxide, including 96% alumina oxide, 99.5% alumina oxide, and 99.8% alumina oxide. Suitable boron-based ceramics include boron nitrides and boron carbides. Suitable silicon-based ceramics include silicon carbides and silicon nitrides. Suitable zirconia-based ceramics include zirconia oxides such as magnesia stabilized zirconia, yttria stabilized zirconia, and zirconia toughened alumina.
In accordance with the disclosed subject matter, the ceramic material can be provided with a relatively smooth surface finish. Depending on the extrusion application, surface finishes of less than about 25 μm (about 1000 μinch) average roughness (Ra) can be suitable for the tip member 240. For example, the ceramic material can have a surface finish of between about 0.1 μm Ra (i.e., approximately 4 RMS) to about 12.5 μm Ra (i.e., approximately 550 RMS). More particularly, the ceramic material can have a surface finish of between about 0.1 μm Ra and about 1.6 μm Ra (i.e., approximately 64 RMS). Furthermore, the ceramic material can have a surface finish of about 0.1 μm to 0.8 μm Ra (i.e., approximately 32 RMS).
As embodied herein, the die pin disclosed herein can be suitable for use in extrusion of molten thermoplastic polymers for plastic containers. The die pin can be suitable for extrusion of, without limitation, polyethylene, low density polyethylene, high density polyethylene, polyethylene terephthalate, polypropylene, polystyrene, and polyvinylchloride.
In accordance with another aspect of the disclosed subject matter, a method for forming a hollow plastic parison is disclosed. The method includes disposing a die pin within an extrusion opening defined by an inner surface of a die ring. The die pin can be aligned with a central axis of the extrusion opening. As described above, the die pin comprises a base member having a proximal mounting portion, a body portion, and a distal frustoconical portion, and a tip member mounted on the distal frustoconical portion. The base member comprises a first material and the tip member comprises a second material that is different than the first material.
As discussed above, the method can further include separating the hollow plastic parison by contacting an outer surface of the base member of the die pin with the inner surface of the die ring. Specifically, the method can include separating the hollow plastic parison by contacting an outer surface of the distal frustoconical portion of the base member with the inner surface of the die ring when the die pin is moved toward the inner surface of the die ring. Such an action can be achieved by forming the tip member with a base circumference that is less than the circumference of the inner surface of the die ring (i.e., the extrusion opening), through which the die pin is disposed.
While the disclosed subject matter is described herein in terms of certain preferred embodiments, those skilled in the art will recognize that various modifications and improvements can be made to the disclosed subject matter without departing from the scope thereof. Additional features known in the art likewise can be incorporated, such as disclosed in U.S. Patent Publication No. 2015/0061179 A1, which is incorporated in its entirety by reference herein. Moreover, although individual features of one embodiment of the disclosed subject matter can be discussed herein or shown in the drawings of the one embodiment and not in other embodiments, it should be apparent that individual features of one embodiment can be combined with one or more features of another embodiment or features from a plurality of embodiments.
In addition to the various embodiments depicted and claimed, the disclosed subject matter is also directed to other embodiments having any other possible combination of the features disclosed and claimed herein. As such, the particular features presented herein can be combined with each other in other manners within the scope of the disclosed subject matter such that the disclosed subject matter includes any suitable combination of the features disclosed herein. Thus, the foregoing description of specific embodiments of the disclosed subject matter has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosed subject matter to those embodiments disclosed.
It will be apparent to those skilled in the art that various modifications and variations can be made in the method, system, and apparatus of the disclosed subject matter without departing from the spirit or scope of the disclosed subject matter. Thus, it is intended that the disclosed subject matter include modifications and variations that are within the scope of the appended claims and their equivalents.
