WO1994023863A1

WO1994023863A1 - Assembly of foundry shapes

Info

Publication number: WO1994023863A1
Application number: PCT/US1994/003936
Authority: WO
Inventors: William L. Tordoff; Jiang Fu
Original assignee: Ashland Oil, Inc.
Priority date: 1993-04-21
Filing date: 1994-04-11
Publication date: 1994-10-27
Also published as: JPH09501356A; AU6630794A; EP0695227A4; CA2161146A1; EP0695227A1

Abstract

This invention relates to an assembly of foundry shapes and a process for making such assemblies of foundry shapes by contacting the foundry shapes with a substrate having a pressure sensitive adhesive on both sides of the substrate. The temperature of such molten metal for non ferrous metals is typically from 600 °C to 1000 °C while the temperature of ferrous metals is from 1200 °C to 1600 °C. One of the advantages of this process is that excess adhesive is not squeezed from between the foundry shapes when they are brought into contact with each other. Excess adhesive results in casting defects such as porosity and burn-on.

Description

ASSEMBLY OF FOUNDRY SHAPES

TECHNICAL FIELD OF THE INVENTION

This invention relates to an assembly of foundry shapes and a process for making such assemblies by contacting the foundry shapes with a two-sided substrate having a pressure sensitive adhesive on both sides of the substrate. The foundry assemblies are used for casting molten metal. The temperature of such molten metal for non ferrous metals is typically from 600°C to 1000°C while the temperature of ferrous metals is from 1200^βC to 1600°C. One of the advantages of this process is that excess adhesive is not squeezed from between the foundry shapes when they are contacted with each other. Excess adhesive results in casting defects such as porosity and burn-on.

BACKGROUND OF THE INVENTION

Patterns, molds, cores, and other foundry shapes are used in casting metals. Patterns are foundry shapes which are lightweight, have generally smooth surface areas, and are the same shape as the casting to be made. Typically, patterns are made of polystyrene.

The pattern is coated, placed in a container, and surrounded by unbound sand. Then molten metal is gated into the pattern. The space occupied by the pattern is filled with molten metal and the pattern evaporates. The quality of the casting depends upon how well the coating on the pattern maintains it shape and allows gases and liquids, produced by the decomposed pattern, to pass through the coating to the surrounding unbonded sand when the coated pattern comes into contact with the molten metal. Patterns are typically held together in an assembly with hot-melt glue which is spread around the seams of the patterns to be joined together. A problem occurs if excess hot-melt glue is used. The excess glue (as well as the foam pattern) will generate gases when it comes into contact with the metal. This results in porosity in the casting. Additionally, the excess glue will result in an uneven surface on the pattern which is difficult to coat. Sand can enter the uneven surface on the pattern where the excess glue is present. When this happens and the glue burns, the molten metal covers the sand resulting in burn-on which is visible after the metal cools. These defects are frequently found in foundries and must be removed before the casting is used. Severe burn-on can cause the casting to be totally scrapped, particularly in the lost-foam process.

On the other hand, molds and cores are heavier, have rougher surface areas, and occupy space to keep metal from entering. They are the inverse shape of the casting to be made. Typically molds and cores are made from a foundry aggregate and reactive binder which holds the aggregate together as a foundry shape. After the molten metal to be cast is poured into and/or around the mold or core, the mold or core has to be removed from the casting.

Often it is necessary to use several molds and/or cores in an assembly and pour the molten metal through and/or around the assembly. The foundry molds and/or cores must be held together during the pouring of the molten metal. Typically the foundry shapes are held together in an assembly with a foundry adhesive paste. Examples of some highly effective adhesive pastes are disclosed in U.S. Patents 4,692,479 and 4,724,892.

Although adhesive pastes are quite effective in holding foundry shapes together in an assembly, they have drawbacks similar to the drawbacks associated with the hot-melt glues used in holding patterns together. It is difficult to meter out the correct amount of adhesive paste to hold the assembly of foundry shapes together. Too little paste will not be effective to hold the molds and cores together in an assembly and molten metal will penetrate into area which is not to be part of the casting.

Too much paste will cause seepage from between the foundry shapes. The excess paste will generate gases when it comes into contact with the molten metal which results in porous castings. Additionally, the excess paste will result in casting burn-on if sand enters the area where the adhesive burns.

Finally, these adhesive pastes are used only for making assemblies of cores and/or molds made from a foundry aggregate and reactive binder. They are not useful for making assemblies from patterns, particularly foam patterns.

SUMMARY OF THE INVENTION This invention relates to an assembly of foundry shapes and a process for making such assemblies. The process for making such assemblies comprises:

(a) contacting a first foundry shape and one side of a two-sided substrate, said substrate having a pressure sensitive adhesive on both sides;

(b) contacting a second foundry shape and the other side of said substrate.

The foundry assemblies are used for casting molten metal. The temperature of such molten metal for non ferrous metals is typically form 600°C to 1000°C while the temperature of ferrous metals is from 1200°C to 1600°C. In contrast to adhesives which are sensitive to temperature and difficult to apply uniformly in proper amounts, pressure sensitive adhesives are manufactured according to uniform specifications and can be cut to fit the shape of the foundry shape. Consequently, the subject process can be used without causing excess adhesive paste to be squeezed from the point of contact between the foundry shapes. This is significant because excess adhesive paste results in casting defects such as porosity and burn-on.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a representative polystyrene pattern 1.

Fig. 2 is coated polystyrene pattern 2 surrounded by unbonded sand 3 with fill container 4.

Fig. 3 shows a cup of molten metal 5 poured into and around the coated polystyrene pattern surrounded by the unbonded sand. Fig. 5 shows an assembly of polystyrene patterns 6 with excess glue 7.

Fig. 6 shows a casting 8 made from the polystyrene pattern showing burn-on 9 with amplification 10 and porosity 11 with amplification 12.

BEST MODE AND OTHER MODES OF THE INVENTION An assembly of foundry shapes is prepared by contacting a foundry shape and one side of a two-sided substrate having a pressure sensitive adhesive on both sides, and then contacting another foundry shape and the other side of the substrate. A pressure sensitive adhesive is an adhesive which will adhere to a surface and yet can be stripped from the surface without transferring significant quantities of adhesive to the surface. "Contacting" means to cause the surfaces of the foundry shapes to effectively touch the pressure sensitive adhesive in such a manner so that the resulting assembly can be effectively used for the making of metal castings.

For purposes of this disclosure, a foundry shape shall mean a pattern, mold, core or any other shape used in the casting of foundry parts from molten metal. Patterns are usually prepared from lightweight materials such as polystyrene. Molds and cores are typically made by binding a foundry aggregate together with a chemically reactive binder.

The patterns used in making mold assembly are usually coated with a refractory composition to provide reinforcement and a smoother surface finish for the casting. Refractory coatings for patterns are used in the foundry industry well known. Typically such coatings consist of a refractory material such as silica, aluminum silicate, mica, talc, zircon, or olivine; and a liquid carrier such as water or alcohol. The coating usually contains surfactants to promote wetting of the surface of the foundry shape, suspending agents to eliminate settlement of refractory flour particles in the liquid, viscosity modifiers, biocides to limit the growth of algae, fungi, bacteria, enzymes, binders which may be organic or inorganic, metal oxides, alkali silicates, etc.

Molds and cores are made by shaping a foundry mix made with a foundry aggregate and chemically reactive inorganic or organic foundry binder in amount such that the weight ratio of binder to aggregate is from 100:10 to 100:1. There are a wide range of aggregates and binders which can be used and they are well known. Examples are shown in U.S. Patents 3,409,579; 3,676,392; 4,127,157; 4,226,626; 4,526,219; and 4,780,489, all of which are incorporated into this disclosure by reference.

Generally any substrate having a pressure sensitive adhesive on both sides of the substrate can be used, depending upon the specific application. Examples of such substrates are paper (preferably moisture resistant) , rubber, plastic, film, and other substrates capable of holding the adhesive and holding up under the particular use conditions. The size of the substrate will depend upon the size and weight of the assemblies to be bonded together, their surface roughness or smoothness, and their relative degree of flexibility. The thickness of the substrate will also be dependent upon the conditions for use. For example, the thickness of polyester films typically range from 0.1 to 0.8 millimeter, and the thickness of foam substrates may have a thickness of 0.5 to 1.0 millimeter. Typically, the thickness of the substrate will range from 0.05 millimeter to 3.0 millimeters, preferably from 0.1 millimeter to 1.5 millimeters, most preferably from 0.1 millimeter to 1.0 millimeter.

The choice of the pressure sensitive adhesive will depend upon the surface of the foundry shapes to be held together, environmental conditions in the foundry, performance requirements, i.e. the tensile strength needed and shear forces to which the foundry assembly will be subjected. Typically used as the pressure sensitive adhesive are polymers based on acrylates, polyesters, vinyl chlorides, acrylonitriles, and polyurethane resins. Preferably used are rubber adhesives and most preferred are acrylic adhesives. Major manufactures of substrates with two-sided pressure sensitive adhesives are 3M and ADCHEM. Usually these products are labeled as "adhesive transfer tapes". Such products include Scotch™ brand Adhesive Transfer Tapes, ATG Adhesive Systems, Double Coated Tapes, Scotch-Mount Double Coated Foam Tapes, and Scotch Very High Bond Tapes sold by 3M. Foam tapes are preferably used for holding molds and cores together in an assembly while the very high bond tapes are preferably used for holding patterns together.

EXAMPLES 1-2

The examples which follow will illustrate specific embodiments of the invention. These examples along with the written description will enable one skilled in the art to practice the invention. It is contemplated that many other embodiments of the invention will be operable besides these specifically disclosed.

Example 1

Example 1 describes how to prepare an assembly of patterns and how it performs when used to make a metal casting. Four pieces of two-sided pressure sensitive adhesive tape are cut and used to connect five polystyrene patterns together by placing the tape between the block patterns. Each pattern is 1 1/8" x 1 1/8" x 1 1/2". The pressure sensitive adhesive tape is cut so that it fit the shape of the polystyrene patterns to be glued together.

The pressure sensitive adhesive is an acrylic pressure sensitive adhesive sold by ADCHEM under the tradename ADCHEM 256. The substrate of the pressure sensitive adhesive is a 0.5 millimeter polyester film. No creases or excess glue are observed.

The assembly, comprised of the five polystyrene patterns, which are joined together by the pressure sensitive adhesive, are coated with CERAMCOTE™ refractory coating and allowed to air dry. The assembly is then placed in a container and surrounded by compacted sand. Molten grey iron is then poured into the assembly. The pattern evaporates and the molten metal is allowed to cool. Another assembly is prepared as described, except hot- melt glue is used to hold the five patterns together in an assembly.

Example 2 This example illustrates the use of two-sided pressure sensitive adhesive tape to join two 7" sand cores into a core assembly. The cores are prepared by mixing Manley sand with 1.25 percent by weight of PEPSET® 1600/2600 no-bake foundry binder sold by Ashland Chemical, Inc. at a 55/45 weight ratio, and ramming the mixture into two core boxes until the foundry mix hardens. The PEP SET 1600 binder (Part I) contained 1.5 percent by weight of PEP SET 3500 catalyst.

The resulting cores are removed from the core boxes and then connected with an acrylic pressure sensitive adhesive tape having a 0.7 millimeter foam substrate sold by Coating Science, Inc. of Bloomfield, Connecticut. The adhesive tape is carefully trimmed to match the shape of the cores.

The procedure described was then repeated using a commercially available urethane forming adhesive paste known as ISOPASTE® 2000 PLUS adhesive paste sold by Ashland Chemical, Inc. Seepage was observed when the cores were connected with the adhesive film.

Claims

CLAIMS We claim:

1. An assembly of foundry shapes comprising at least two shapes bonded to each other by a two-sided substrate having a pressure sensitive adhesive on both sides of the substrate.

2. The assembly of claim 1 wherein the foundry shapes are foam patterns.

3. The assembly of claim 2 wherein the substrate is a polyester substrate having a thickness of 0.1 millimeters to 0.5 millimeters.

4. The assembly of claim 3 wherein the adhesive is a pressure sensitive acrylic adhesive.

5. The assembly of claim 1 wherein the foundry shapes are selected from the group consisting of molds, cores or mixtures thereof prepared by binding a foundry aggregate with a chemically reactive foundry binder.

6. The assembly of claim 5 wherein the substrate is a foam substrate having a thickness of 0.3 millimeters to 1.0 millimeters.

7. The assembly of claim 6 wherein the adhesive is a pressure sensitive acrylic adhesive.

8. A process for making an assembly of foundry shapes comprising:

(a) contacting a first foundry shape and one side of a two-sided substrate, said substrate having a pressure sensitive adhesive on both sides; (b) contacting a second foundry shape and the other side of said substrate.

9. The process of claim 8 wherein the shapes are coated foam patterns.

10. The process of claim 9 wherein the substrate is a polyester substrate having a thickness of 0.1 millimeters to 0.5 millimeters.

11. The process of claim 10 wherein the adhesive is a pressure sensitive acrylic adhesive.

12. The process of claim 8 wherein the foundry shapes are selected from the group consisting of molds, cores or mixtures thereof prepared by binding a foundry aggregate with a chemically reactive foundry binder.

13. The process of claim 12 wherein the substrate is a foam substrate having a thickness of 0.1 millimeters to 1.0 millimeters.

14. The process of claim 13 wherein the adhesive is a pressure sensitive acrylic adhesive.

15. A process of casting a metal comprising: A. fabricating an assembly of foundry shapes comprising:

(1) contacting a first foundry shape and one side of a two-sided substrate, said substrate having a pressure sensitive adhesive on both sides;

(2) contacting a second foundry shape and the other side of said substrate;

B. pouring metal while, in the liquid state, into and around said assembly; C. allowing said metal to cool and solidify so as to provide a formed metal article; and

D. separating said metal article from the sand.

16. The process of claim 15 wherein the shapes are coated foam patterns.

17. The process of claim 16 wherein the substrate is a polyester substrate having a thickness of 0.1 millimeters to 0.5 millimeters.

18. The process of claim 17 wherein the adhesive is a pressure sensitive acrylic adhesive.

19. The process of claim 18 wherein the foundry shapes are selected from the group consisting of molds, cores or mixtures thereof prepared by binding a foundry aggregate with a chemically reactive foundry binder.

20. The process of claim 19 wherein the substrate is a foam substrate having a thickness of 0.1 millimeters to 1.0 millimeters.

21. The process of claim 20 wherein the adhesive is a pressure sensitive acrylic adhesive.