Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C9/00—Moulds or cores; Moulding processes
  • B22C9/10—Cores; Manufacture or installation of cores
  • B22C9/103—Multipart cores
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C7/00—Patterns; Manufacture thereof so far as not provided for in other classes
  • B22C7/02—Lost patterns
  • B22C7/023—Patterns made from expanded plastic materials
  • B22C7/026—Patterns made from expanded plastic materials by assembling preformed parts
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22C—FOUNDRY MOULDING
  • B22C9/00—Moulds or cores; Moulding processes
  • B22C9/20—Stack moulds, i.e. arrangement of multiple moulds or flasks

Definitions

• 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 ⁇ 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 contacted with each other. Excess adhesive results in casting defects such as porosity and burn-on.
• 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.
• 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.
• 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.
• 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.
• 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.
• This invention relates to an assembly of foundry shapes and a process for making such assemblies.
• the process for making such assemblies comprises:
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• any substrate having a pressure sensitive adhesive on both sides of the substrate can be used, depending upon the specific application.
• 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.
• the thickness of polyester films typically range from 0.1 to 0.8 millimeter
• the thickness of foam substrates may have a thickness of 0.5 to 1.0 millimeter.
• 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.
• the pressure sensitive adhesive are polymers based on acrylates, polyesters, vinyl chlorides, acrylonitriles, and polyurethane resins.
• rubber adhesives 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".
• 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.
• 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 CERAMCOTETM 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.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Adhesives Or Adhesive Processes (AREA)
• Molds, Cores, And Manufacturing Methods Thereof (AREA)

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• 1994
  • 1994-04-11 AU AU66307/94A patent/AU6630794A/en not_active Abandoned
  • 1994-04-11 JP JP6523359A patent/JPH09501356A/ja active Pending
  • 1994-04-11 EP EP94914108A patent/EP0695227A4/de not_active Withdrawn
  • 1994-04-11 WO PCT/US1994/003936 patent/WO1994023863A1/en not_active Application Discontinuation
  • 1994-04-11 CA CA002161146A patent/CA2161146A1/en not_active Abandoned

Non-Patent Citations (2)

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