Patent Application
20080029240
thermal load bearing capacity of the molding parts Two mixtures were prepared in a blade mixer within 3 minutes and subsequently shot on a core shooting machine to form 4 cores each. It was decided to use a suspension of amorphous SiO2 previously prepared with part of a binding agent in order to obtain, in an accelerated way, a homogenous mixture of the components. The suspension has a pH value of 9.2 and was mixed together with the other components in the mixer, as described above. The shooting pressure amounted to 5 bar, the shooting time was 1 second and the vacuum applied amounted to 0.9 bar. The cores were pre-hardened in the core box for 30 seconds at 180° C. in the machine, removed in the form of green compacts, subsequently dried in a microwave oven for 3 minutes at 1000 watts and finally weighed. They were cores for casting a longitudinally extending bendable bolt of 185.4 mm by 22.7 mm by 22.7 mm. For casting purposes, use was made of a grey iron melt at a mean temperature of 1275° C.±25° C. in the casting ladle. The cast bolt was removed from the cores after a cooling time of 3 days. Subsequently, 4 bolts each were tested for their bending characteristics.
The bending characteristics of a casting result from the thermal load on the core during the casting operation, combined with the buoyancy force generated by the in-flowing metal. It is a measure for the temperature resistance and dimensional accuracy of a core material. The bending factor was determined on the finished bolts aligned transversely to the measuring device in the bolt center as the average deviation of the outer edges from the horizontal line. The molding material mixtures and the measured values are listed in the table below.
The cores produced in accordance with embodiments of the invention confirm, on average, a low bending inclination of the cores during the casting operation.
A lower bending rate indicates that the molding part comprises an improved structure which is able to accommodate the deformation stresses occurring under thermal loads. The deformation stresses result from de-watering and sinter processes which are caused in the molding parts by the high temperature of the inflowing metal. The inventors assume that the uniformly distributed SiO2 spheres, via their surface swelling phase, during the drying process, form a plurality of binding agent bridges with adjoining sand articles. As a result of the large number of small binding agent bridges, which connect particles, it is possible for deformation stresses to be distributed as a result of the homogeneous interlocking of the molding material particles via a plurality of binding agent bridges to larger volumes of molding parts and to be elastically compensated for.
The homogeneous fine type of interlocking is believed to explain the increased thermal load bearing capacity of a molding part produced in accordance with embodiments of the invention.
As described in example 1, two mixtures were cast to form a core. Four identical, bar-shaped cores of identical volumes were produced of each mixture. The mixtures and weights are listed in the table below.
On average, the inventive cores comprise a higher weight. In members of identical volumes, a higher weight corresponds to a higher density. It is believed that the only slight deviation of the individual core weight from the mean value can be explained by the improved flowing and densification behavior relative to the molding material mixture with silicone oil.
In spite of the added flowing agent, the reference mixture comprises a lower mean mass of the cores. Furthermore, the weights of the individual cores clearly feature greater deviations from the mean value.
The densities achieved comprise a more uniform, improved flowing ability of the molding material mixture while being shot into the mold. It is believed that the SiO2 spheres with their swelling phase on their surface allow the molding material particles to slide past one another more easily. It is believed that the swelling phase permits the molding sand particles to slide more easily over the small-surface contact points on the SiO2 spheres. This can explain why in the molding material mixture, during the flowing process, blocking inter-engaging quartz sand particles apparently occur to a lesser extent. It is believed that the individual sand particle comprises an improved mobility relative to the adjoining molding material particles and even at high shear forces such as they occur when the shooting operation takes place at an increased pressure, the molding material mixture comprises a more uniform and improved flowing ability.
As will be explained below, it is believed that the green strength and the end strength of the cores reflects the results of the weight determination. In the inventive embodiment cores, the green strength and the end strength determined under point load up to deformation fluctuate clearly to a lesser extent.
It is believed that the mixture in accordance with the embodiments of the invention made it possible, with a reduced binding agent content, to achieve more constant and higher densities in the cores produced.
To examine the influence of the added SiO2 on the end strength of the cores, there was prepared a suspension of amorphous, spherical SiO2 in a larger quantity of binding agent. Subsequently, a total of 4 batches with the further components were processed under the same conditions as described in example 1 into 4 cores in each case. Subsequently, there was prepared a reference mixture as described in example 2 and also processed into 4 cores.
The cores with the added SiO2 all exhibited the increased density as known from example 1. The finish-dried cores were placed into a 3-point bending device and the force leading to the fracture of the core was determined. In the following table, said force is referred to as “breaking force”. The cores with the added SiO2 featured a bending strength which increased from core batch to core batch. This phenomenon was correlated with the pH value of the sequentially added SiO2 binding agent suspension. A maximum bending strength was achieved at a constant pH value of the prepared suspension. The following table shows the pH value which was determined at the time when the suspension was added, the approximate holding time of the suspension and the average bending strength for each 4 cores.
The table of example 3 shows that by adding partially dissolved, spherical, amorphous SiO2 to a molding material mixture, the bending strength of a core produced therefrom is improved.
Furthermore, the influence of the pH value of the SiO2 suspension becomes clear. First the pH value of the alkali suspension decreases, which it is believed can be explained by the use of OH− ions during the formation of the swelling phase. After 4 minutes the pH value is reduced by 0.6 pH; thereafter, this value changes only slightly. After approximately 4 minutes—according to the explanatory model of the inventors—the surface of the amorphous SiO2 can be regarded as being fully partially dissolved and being surrounded by a swelling phase. The alkali, amorphous SiO2 is accompanied by a clearly improved bending strength of the core as produced.
Further tests regarding the pH value stability in an alkali suspension of amorphous, spherical SiO2 were carried out as described below.
An amorphous, spherical SiO2 with a degree of purity and grain size characteristics as described above was suspended in an alkali silicate suspension and/or in a sodium hydroxide solution with a pH value of 9 to 14. The content of SiO2 in the suspension ranged between 10 and 80 percent by weight, alternatively 20 to 79 percent by weight. The pH value of the alkali suspension was subsequently determined at intervals of 30 seconds. At the start of the test, the suspensions exhibited the above-described rapid decrease in the pH value. After no more than 4 minutes, the pH value, with a maximum change of approx. 0.1 pH per minute, was stable. After a maximum holding time of 10 minutes, the suspension of the alkali amorphous SiO2 showed no further change in the pH value for several hours.
Apart from the improved flow behaviour as mentioned in example 2, the alkali SiO2 suspensions with a stable pH value feature the improved end strength of the cores produced therefrom, as shown in table 3 of example 3.
With an alkali concentration which was clearly greater than the concentration of a batch for a pH value of 14, a slowly and surely decreasing core diameter of the SiO2 particles was identified. It is believed that this can be explained by a slow dissolution of the SiO2 particles as a result of the frequently over-stoichiometric concentration of alkali. Molding material mixtures produced in this way feature neither an improved flowing ability nor a better end strength of the molds produced, which can be explained by the deviating morphology of the dissolving SiO2 surface.
It is believed that with a set pH value of less than 9, all suspensions did not achieve the formation of a swelling phase with an expansion of 1 to 2% within the first 4 minutes. If the expansion was less than 1%, the suspensions featured fluctuating improvements in the flowing ability apparently without achieving the flow ability values achieved previously with a stable swelling phase. Swelling phases which were characterized by an expansion of the mean grain diameter of 1 to 2% exhibited the above-described improved flowing ability. In the subsequent tests, the suspensions were set to a pH value of at least 9 in order, reliably, to achieve within the first 4 minutes a stable pH value and a swelling phase with an expansion of the mean grain diameter of the original, dry SiO2 of 1 to 2%.
Advantageously improved molding parts were found in further tests with mixtures wherein the mean grain size of the sand particles and the mean grain size of the amorphous SiO2 were identical. For example, there were prepared molding material mixtures which contained a classified and sorted quartz sand fraction with a grain size in the range of 0.01 mm, which corresponds to 10 micrometers, and 1 to 10% amorphous, spherical SiO2 with a mean grain diameter between 10 and 45 micrometers. At the same stirring speed, such molding material mixtures provided a homogeneous mixture in a shorter time and during the production of the molding part, even at a lower shooting pressure, achieved molding parts with an improved density and uniformity and greater profile accuracy.
The results of example 2 support the theory that a continuous, stable alkaline swelling phase on the amorphous SiO2 whose surface has been activated, contributes to the formation of binding agent bridges through additional binding centres. It can be assumed that the surface of such an alkali SiO2 is characterized by negatively charged oxygen groups.
More particularly in plants in which the individual components of a molding material mixture are stored for several days in large containers, the alkali SiO2 suspension can be advantageously produced by mixing dry, amorphous, spherical SiO2 with an alkaline binding agent. By producing the suspension directly prior to being used, the amorphous SiO2 is set to be alkaline in a fresh condition and in a uniform quality. With a percentage of 1 to 10 percent by weight of SiO2 freshly set to be alkaline, with reference to the quantity of sand, it was possible, in the tests, to provide a molding material mixture with an improved flowing ability and an increased end strength of the molding parts produced therefrom.
Molding material mixtures with further additives which consisted of phosphoric and/or boric acid were found to be disadvantageous. Such additives which are known to be used for improving inorganic binding agents decrease the pH value in the molding material mixtures and adversely affect the flowing ability of the mixture. It was found that binding agents based on alkali silicate with acid additives react by forming salts. With a binding agent purely based on alkali silicate without any additives of the above-mentioned type with a binding agent content of 1 to 10% of the total mixture, the effects in accordance with the invention were reliably identified.
Furthermore, slightly basic accompanying substances such as metal oxides which can be bound into silicate structures were found to reduce the drying time. As compared to a pure alkali silicate binding agent, a binding agent based on alkali silicate with a content of iron, aluminum and/or cadmium of 0.01 to 0.50% was found to reduce the drying time by 5% when producing molding parts.
The inventive embodiment mixture achieves a higher end strength of the cores.
In order to test the inclination of an inventive molding material to form adhesion bridges during casting, there were prepared two mixtures as described in example 2 and processed to form 4 cores each. The cores were designed for casting bolts whose cross-section has an H-profile. During the casting process, there is thus offered an increased surface for the formation of possible adhesion bridges. As above, use was made of a grey iron melt with a mean temperature of 1275° C.±25° C. in the casting ladle, and the cast bolt was removed from the cores after a cooling time of 3 days. First the bolts were vibrated by a hammer and subsequently, if necessary, freed of the adhering core parts by a mandrel, cleaned and finally tested for stubborn adhesions and metal penetration.
Molding material mixtures and assessment of adhesions are listed in the table below.
After having been cast, the inventive embodiment cores can be easily removed by several hammer blows. The bolts exposed in this way still contain sand adhesions which were removed in an ultrasound bath.
The reference cores were only partially removed from the bolts by hammer blows. After the bolts were exposed by a mandrel, the bolts were cleaned in an ultrasound bath and subsequently tested. On the one hand, there were found stubborn sand adhesions which were removed by a mandrel. On the other hand, there was found metal penetration in the case of which the adhering sand could only be partially removed by the application of high forces as a result of which the bolt surface was damaged.
The comparison showed that the inventive molding material mixture was removed much more easily and more quickly after the casting operation. Cores produced from the inventive embodiment molding material resulted in the production of castings with easily removable, slight sand adhesions. Metal penetration such as it occurred in the reference castings was not found.
To test the disintegration properties of molding parts of the inventive embodiment molding material mixture, there were prepared two mixtures as described in example 2 and processed to form 4 cores each. After the casting operation, the cores were tested for their disintegration properties. As already described, use was made of a grey iron melt in the casting ladle, and the molding parts with the cast bolts were tested after a cooling time of 3 days. The molding parts were tested after the castings connected to a vibration generating device were aligned in an overhead position. The vibration generating device subjected the casting to a 30 Hertz vibration with a pulse peak of up to 1.4 kW power. In the process, the time was measured within which 90% as well as 99% of the molding part had fallen off the casting.
The molding material mixtures and the assessment of the disintegration properties are listed in the following table.
After the casting operation, the molding parts of the inventive embodiment mixture clearly exhibit shorter times for removing the molding part from the casting. The molding parts of the inventive embodiment mixture featured a rapidly spreading, small-cell crack pattern which, shortly afterwards, lead to a uniform peeling of the molding part into small-part segments. Any remaining adhering sand on the casting surface was removed in an ultrasound bath or even manually with a simple cloth.
The disintegration behavior of the reference mixture clearly exhibited longer peeling times and irregular crack formations in the molding part as well as irregular peeling into different sized segments. Furthermore, after 99 percent by weight of the molding part had been peeled off, the surface is still covered with strongly adhering sand grains which, in contrast to the inventive embodiment mixture, could not be completely removed, neither manually nor in the ultrasound bath.
The inventors attribute the superior disintegration behavior to uniformly formed, interlocking binding agent bridges between the sand particles and the amorphous SiO2. The large number of uniformly distributed binding agent bridges, on the one hand, increases the strength and elasticity of the molding part, but on the other hand, locally and with reference to the individual binding agent bridge, under the influence of an abrupt pulse, they can be broken by a much reduced force. The interlocking of the bridges is thus more uniform, but also much less pronounced than is the case with the reference mixture. The increased number of binding agent bridges combined with a reduced load bearing capacity of the individual bridges thus results in an advantageous combination of improved strength and a more advantageous disintegration behavior.
After the removal of the core after the casting operation, the inventive embodiment molding parts feature a more rapid and more uniform disintegration behavior.
The inventive embodiment molding material mixture permits the production of molding parts which, during the subsequent casting operation, have a more uniform compensating effect under thermal loads. The castings now accessible are characterized by an improved accuracy of shape, which is believed can be explained by the uniform interlocking of the molding material particles via the binding agent bridges formed by the amorphous, partially dissolved SiO2.
The densification behavior of the molding material mixture prepared in accordance with embodiments of the invention was particularly advantageous. It was possible to achieve an excellent flow ability and a very uniform packing density.
Table 3 shows a slight fluctuation in the strength values, which explains the high degree of uniformity of the molding parts produced in accordance with the embodiments of invention.
As far as the disintegration behavior is concerned, the molding parts, after the casting operation, are characterized by a uniform, improved crack formation and, quite clearly, quicker core removal times.
The swelling phase formed on the SiO2 particles, in connection with the uniform packing density, results in a high bending strength of the bolt portions produced by the cores. The swelling layer exhibits a very small degree of interlocking as compared to a SiO2-containing molding material mixture strengthened via pure binding agent bridges. The low degree of interlocking leads to small, locally delimited adhesion islands (module block adhesion) which, following the use of cores, accelerate disintegration (micro-fractures). The disintegration behavior of the inventive molding materials and molding parts therefore had to be regarded as surprisingly advantageous. There was no need for any additional aids of any kind.
One feature or aspect of an embodiment is believed at the time of the filing of this patent application to possibly reside broadly in a molding material or molding part for foundry purposes, comprising 1-10% of binding agent based on alkali silicate, an aggregate containing 1-10 percent by weight of amorphous silicon dioxide, remainder quartz sand with a grain size range of 0.01 to 5 mm, wherein the amorphous silicon dioxide is present in a spherical shape, wherein the percentage of particles with a diameter of 45 or more μm amounts to a maximum of 1.5 percent by weight; that on the surface of the amorphous silicon dioxide, there is formed a swelling phase comprising a thickness of 0.5 to 1% with reference to the mean grain diameter.
The components disclosed in the various publications, disclosed or incorporated by reference herein, may possibly be used in possible embodiments of the present invention, as well as equivalents thereof.
Another feature or aspect of an embodiment is believed at the time of the filing of this patent application to possibly reside broadly in the molding material or molding part, wherein the mean grain diameter of the amorphous silicon dioxide ranges between 10 and 45 μm.
All of the references and documents, cited in any of the documents cited herein, are hereby incorporated by reference as if set forth in their entirety herein. All of the documents cited herein, referred to in the immediately preceding sentence, include all of the patents, patent applications and publications cited anywhere in the present application.
Yet another feature or aspect of an embodiment is believed at the time of the filing of this patent application to possibly reside broadly in the molding material or molding part, wherein the amorphous silicon dioxide comprises a degree of purity in excess of 85%.
The abstract of the disclosure is submitted herewith as required by 37 C.F.R. §1.72(b). As stated in 37 C.F.R. §1.72(b):
A brief abstract of the technical disclosure in the specification must commence on a separate sheet, preferably following the claims, under the heading “Abstract of the Disclosure.” The purpose of the abstract is to enable the Patent and Trademark Office and the public generally to determine quickly from a cursory inspection the nature and gist of the technical disclosure. The abstract shall not be used for interpreting the scope of the claims. Therefore, any statements made relating to the abstract are not intended to limit the claims in any manner and should not be interpreted as limiting the claims in any manner.
It will be understood that the examples of patents, published patent applications, and other documents which are included in this application and which are referred to in paragraphs which state “Some examples of . . . which may possibly be used in at least one possible embodiment of the present application . . . ” may possibly not be used or useable in any one or more embodiments of the application.
Still another feature or aspect of an embodiment is believed at the time of the filing of this patent application to possibly reside broadly in the molding material or molding part wherein, on its surface, the silicon dioxide set to be alkali comprises negatively charged oxygen groups.
The summary is believed, at the time of the filing of this patent application, to adequately summarize this patent application. However, portions or all of the information contained in the summary may not be completely applicable to the claims as originally filed in this patent application, as amended during prosecution of this patent application, and as ultimately allowed in any patent issuing from this patent application. Therefore, any statements made relating to the summary are not intended to limit the claims in any manner and should not be interpreted as limiting the claims in any manner.
A further feature or aspect of an embodiment is believed at the time of the filing of this patent application to possibly reside broadly in the molding material or molding part, wherein between the silicon dioxide set to be alkali and the quartz sand, there are formed binding agent bridges via additional binding centers.
The background information is believed, at the time of the filing of this patent application, to adequately provide background information for this patent application. However, the background information may not be completely applicable to the claims as originally filed in this patent application, as amended during prosecution of this patent application, and as ultimately allowed in any patent issuing from this patent application. Therefore, any statements made relating to the background information are not intended to limit the claims in any manner and should not be interpreted as limiting the claims in any manner.
Another feature or aspect of an embodiment is believed at the time of the filing of this patent application to possibly reside broadly in the molding material or molding part, wherein the binding agent comprises a content of iron, aluminum and/or cadmium of 0.01 to 0.50%.
All, or substantially all, of the components and methods of the various embodiments may be used with at least one embodiment or all of the embodiments, if more than one embodiment is described herein.
The purpose of the title of this patent application is generally to enable the Patent and Trademark Office and the public to determine quickly, from a cursory inspection, the nature of this patent application. The title is believed, at the time of the filing of this patent application, to adequately reflect the general nature of this patent application. However, the title may not be completely applicable to the technical field, the object or objects, the summary, the description of the embodiment or embodiments, and the claims as originally filed in this patent application, as amended during prosecution of this patent application, and as ultimately allowed in any patent issuing from this patent application. Therefore, the title is not intended to limit the claims in any manner and should not be interpreted as limiting the claims in any manner.
The description of the embodiment or embodiments is believed, at the time of the filing of this patent application, to adequately describe the embodiment or embodiments of this patent application. However, portions of the description of the embodiment or embodiments may not be completely applicable to the claims as originally filed in this patent application, as amended during prosecution of this patent application, and as ultimately allowed in any patent issuing from this patent application. Therefore, any statements made relating to the embodiment or embodiments are not intended to limit the claims in any manner and should not be interpreted as limiting the claims in any manner.
Yet another feature or aspect of an embodiment is believed at the time of the filing of this patent application to possibly reside broadly in a process of producing a molding material or molding part for foundry purposes, wherein as the aggregate, an amorphous, partially dissolved, spherical SiO2 with a percentage of particles with a grain size in excess of 45 μm is transferred into a suspension with a solid matter content of 20 to 70% silicon dioxide, with a pH-value of 9-14 being set, that the amorphous silicon dioxide is held during the alkaline treatment for at least 4 minutes until the swelling phase has formed on the silicon dioxide surface, that the silicon dioxide is homogeneously mixed with molding sand and binding agent, wherein the mixing ratio of binding agent/SiO2 to molding sand is held at a ratio of 1 to 10 to 90, that the silicon dioxide, together with the molding sand and the binding agent is shot under pressure into a molding box and dried to form a finished core.
All of the patents, patent applications and publications recited herein, and in the Declaration attached hereto, are hereby incorporated by reference as if set forth in their entirety herein.
The purpose of the statements about the technical field is generally to enable the Patent and Trademark Office and the public to determine quickly, from a cursory inspection, the nature of this patent application. The description of the technical field is believed, at the time of the filing of this patent application, to adequately describe the technical field of this patent application. However, the description of the technical field may not be completely applicable to the claims as originally filed in this patent application, as amended during prosecution of this patent application, and as ultimately allowed in any patent issuing from this patent application. Therefore, any statements made relating to the technical field are not intended to limit the claims in any manner and should not be interpreted as limiting the claims in any manner.
Still another feature or aspect of an embodiment is believed at the time of the filing of this patent application to possibly reside broadly in the process, wherein the surface of the amorphous silicon dioxide is partially dissolved, wherein the mean grain diameter of the silicon dioxide is widened by 2% and a swelling phase is formed.
The corresponding foreign and international patent publication applications, namely, Federal Republic of Germany Patent Application No. 10 2006 036 381.7, filed on Aug. 2, 2006, having inventor Ralf-Joachim GERLACH, and DE-OS 10 2006 036 381.7 and DE-PS 10 2006 036 381.7, are hereby incorporated by reference as if set forth in their entirety herein for the purpose of correcting and explaining any possible misinterpretations of the English translation thereof. In addition, the published equivalents of the above corresponding foreign and international patent publication applications, and other equivalents or corresponding applications, if any, in corresponding cases in the Federal Republic of Germany and elsewhere, and the references and documents cited in any of the documents cited herein, such as the patents, patent applications and publications, are hereby incorporated by reference as if set forth in their entirety herein.
The details in the patents, patent applications and publications may be considered to be incorporable, at applicant's option, into the claims during prosecution as further limitations in the claims to patentably distinguish any amended claims from any applied prior art.
A further feature or aspect of an embodiment is believed at the time of the filing of this patent application to possibly reside broadly in the process, wherein the treatment for forming a swelling phase, starting with a set pH-value ranging between 9 and 14, is ended after a maximum of 10 minutes.
The purpose of the statements about the object or objects is generally to enable the Patent and Trademark Office and the public to determine quickly, from a cursory inspection, the nature of this patent application. The description of the object or objects is believed, at the time of the filing of this patent application, to adequately describe the object or objects of this patent application. However, the description of the object or objects may not be completely applicable to the claims as originally filed in this patent application, as amended during prosecution of this patent application, and as ultimately allowed in any patent issuing from this patent application. Therefore, any statements made relating to the object or objects are not intended to limit the claims in any manner and should not be interpreted as limiting the claims in any manner.
Another feature or aspect of an embodiment is believed at the time of the filing of this patent application to possibly reside broadly in the process, wherein the set pH-value ranging between 9 and 14 percent is lowered with a maximum modification of 0.1 pH per minute.
The sentence immediately above relates to patents, published patent applications and other documents either incorporated by reference or not incorporated by reference.
The embodiments of the invention described herein above in the context of the preferred embodiments are not to be taken as limiting the embodiments of the invention to all of the provided details thereof, since modifications and variations thereof may be made without departing from the spirit and scope of the embodiments of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2006 036 381.7 | Aug 2006 | DE | national |
