JPH0240412B2 - KATAOYOBISHOMOGATANAKAGOYOHIFUKU - Google Patents

Description

Claim 1 (A) A base consisting of sand bound together by a binder; (B) (a) graphite, mica, fused silica, aluminum oxide, magnesium oxide,
about 30-80% by weight of an inorganic refractory material selected from the group consisting of carbon black and zircon powder; and (b) about 1-25% by weight of an inorganic binder selected from the group consisting of colloidal silica, clay and amine-treated bentonite. %; a first coating (C) of 250-5000μ thickness consisting of (a) a refractory material selected from the group consisting of fused silica, zircon powder, aluminum oxide; (b) consisting of colloidal silica, clay and bentonite; (c) an organic compound binder; and (c) an organic compound binder; A high-strength die-casting sand core having high pressure and high temperature resistance, good collapse resistance, surface penetration resistance and good demoldability for use in forming undercuts in castings.

2. The sand core according to claim 1, wherein the molten metal is made of aluminum.

3. The sand core according to claim 1, wherein the sand for the core is made of silica sand.

4. The sand core according to claim 1, wherein the core binder is made of an organic resin.

5. The sand core according to claim 1, wherein the organic resin is acid-curable.

6. The sand core according to claim 4, wherein the organic resin comprises furan.

7. The sand core of claim 1, wherein the first coating contains about 50-70% by weight inorganic refractory material.

8. A sand core according to claim 1, wherein the refractory material of the first coating consists of fused silica.

9. A sand core according to claim 1, wherein the binder of the first coating consists of clay.

10. The sand core according to claim 9, wherein the clay is kaolin clay.

11. The sand core according to claim 1, wherein the binder of the first coating comprises colloidal silica.

12. A sand core according to claim 1, wherein the refractory material of the second surface coating consists of zircon powder.

13 (A)(a) An inorganic refractory material selected from the group consisting of graphite, mica, fused silica, aluminum oxide, magnesium oxide, carbon black and zircon powder.
(b) about 1-25% by weight of an inorganic binder selected from the group consisting of colloidal silica, clay and amine-treated bentonite; and (c) an aqueous liquid vehicle. sand core
(B) drying said first coating and then (C) (a) refractory material selected from the group consisting of fused silica, zircon powder, aluminum oxide; (b) a suspending agent selected from the group consisting of colloidal silica, clay and bentonite; (c) an organic compound binder; and (d) an organic liquid vehicle.
Coating with a thickness of 100-2000μ; high pressure and high temperature resistance for use in forming undercuts on castings formed from molten metal in the die of high-pressure die-casting machines, each coating step consisting of , a method of coating sand cores consisting of sand bound together with a binder, which has good collapse resistance, surface penetration resistance and good demoldability.

14. The method of claim 13, wherein the molten metal comprises aluminum.

15. The method of claim 13, wherein the base sand consists of silica sand.

16. The method of claim 13, wherein the base binder comprises an organic resin.

17. The method of claim 16, wherein the organic resin is acid curable.

18. The method of claim 16, wherein the organic resin comprises furan.

19. The method of claim 13, wherein the first coating contains about 50-70% by weight inorganic refractory material.

20. The method of claim 13, wherein the refractory material of the first coating comprises fused silica.

21. The method of claim 13, wherein the suspending agent of the first coating comprises clay.

22. The method of claim 21, wherein the clay is kaolin clay.

23. The method of claim 13, wherein the binder of the first coating comprises colloidal silica.

24. The method of claim 13, wherein the refractory material of the second surface coating consists of zircon powder.

25. The method of claim 13, wherein the aqueous liquid vehicle is water.

26. The method of claim 13, wherein the organic liquid vehicle is isopropyl alcohol.

BACKGROUND OF THE INVENTION The present invention addresses a long-standing problem in die casting and die casting of metals such as aluminum, zinc, magnesium, copper, iron, and their alloys, namely, to produce castings with undercut regions. It is primarily concerned with solving the problem that no commercially viable die casting process exists. More particularly, this invention relates to coating compositions that are useful in expandable die casting cores, particularly in pressure die casting processes.

Surroundings of the Invention Traditional pressure die casting processes require a mold or die that can withstand high temperatures and pressures. Iron-based materials are commonly used in such molds. Molds or cores made of the above-mentioned materials cannot be used to manufacture die-castings having complex undercuts or reliefs because the cores for the undercuts and reliefs cannot be removed from the casting. To achieve such complex undercuts and reliefs, consumable and brittle sand cores are used under pressures below 30 psia, i.e., in gravity-fed casting methods.

Sand cores are used in high pressure die casting, and are composed of sand mixed with a binder. The mixture is shaped into the desired core shape and cured and bonded using heat or chemical reactions. The hardened core can be used in die casting methods.

A major problem with such consumable cores in high pressure die casting processes is that a single binder system cannot be used to satisfy the four core requirements. These four conditions are (a) good deformability (shake out), (b) good wash out resistance, (c) no surface permeability, and (d) Strength.

Good demoldability is necessary for easy removal of the core from the casting.

Collapse resistance is the ability of the core to withstand erosion due to high metal velocities that occur during injection of molten metal. The disintegrated sand adversely affects the acceptability of the finished part as the sand becomes embedded within the casting.

Surface permeability or hardness is caused by high temperatures and pressures that destroy the core surface and allow metal to penetrate between the sand particles creating a sand/metal mixture interface on the surface of the casting. This condition is unfavorable for subsequent machining and the life of the machine tool. Furthermore, the transported sand can separate from the surface of the casting and cause damage to related components, such as the lubrication system of an automobile engine, after assembly.

The strength of the core is determined primarily by the sand binder used. Therefore, a suitable coating and its composition must be compatible with the bonding agent having the desired strength.

PRIOR ART A number of core and mold coatings and coatings have been developed for general foundry manufacturing, i.e., gravity-fed molds, but are extremely poorly suited for the relatively harsh conditions associated with consumable, high-pressure die casting. Only a few coatings and paints have been proposed. Conventionally known coatings are as follows.

U.S. Patent No. 4,096,293 [issued June 20, 1978, title: “Mold and Core Coating”
Michael J. Skubon et al.] disclose a core wash consisting of a hydrocarbon solvent, fumaric acid resin, particulate calcium aluminate, and a suspending agent useful in pressure die casting processes. The composition consists of 5-90% by weight of solvent, 0.5-5% by weight of resin, 5-80% by weight of calcium aluminate, and 0.1-2% by weight of suspending agent. Fumaric acid resin. is described as being the reaction product of fumaric acid, gum rosin and pentaerythritol. Suspending agents are described as including high molecular weight polymers, polyacrylates, colloidal silica, clays, vegetable gums and amine-treated bentonites. Wetting agents are described in US Pat. No. 4,096,293 to include methyl alcohol, water and anionic, cationic, surfactants.

Further, U.S. Patent No. 4001468 (issued on January 4, 1977, title: “Method of Coating Sand Cores and Sand Molds,”
Skubon et al.) discloses another conventional technology,
This US patent discloses a wash coating useful for preventing core erosion. Included in the composition of the coating are an organic vehicle, a suspending agent, a refractory material, and an organic polymer or copolymer. The organic vehicle is described as having a Kauributanol value (ASTMD 1133) of 36 or higher. Suspending agents are described as including clays, vegetable gums, and amine-treated bentonites in a suspending agent:vehicle ratio of 1:80 to 1:250. The refractory powder includes graphite, coke, mica, silica, aluminum oxide, magnesium oxide, talc, and zircon fine powder, and the weight ratio of refractory material:vehicle is 1:2.5 to 1:
It is stated that it is included within the range of 3.5. Organic polymers or copolymers include vinyltoluene-butadiene polymers, styrene/butadiene copolymers, vinyltoluene/acrylate copolymers, styrene/acetylene copolymers, acrylate homopolymers, and styrene/butadiene copolymers, with a polymer/copolymer:vehicle weight ratio of 1 :50 to 1:200.

The disadvantage of Skubon's invention is that when heated, it releases gas and this gas creates cavities in the casting.
The use of organic binders loses strength. Furthermore, the Skubon coating is typically a powder;
It has low scratch resistance or hardness. Hardness is a measure of metal penetration or resistance of a metal to burning and erosion.

SUMMARY OF THE INVENTION One aspect of the invention is a first core and mold coating composition comprising: (a) a particulate refractory material; (b) an inorganic binder; and (c) a liquid vehicle; a second compositionally different surface coating (top
wash coating).

According to a second aspect, the invention is a method of treating a foundry core or mold by coating the surface of the sand core or mold with a coating of the composition described above.

According to a third aspect, the invention is a mold and a consumable core coated with the composition described above.

[Detailed description of the invention]

The first mold and core coating of the present invention (a core
and first mold wash composition) consists of a particulate refractory material, an inorganic binder and a liquid vehicle. This coating is suitable for use in sand cores and molds useful in die casting as well as gravity feed casting. The present invention satisfies the four core requirements by using a core system with a coating/binder system that enhances deformability, collapse resistance, and surface penetration resistance. The wash coatings of the present invention may also include accessory ingredients such as disinfectants, wetting agents, and antifoaming agents.

The coatings of the present invention are useful on cores made of uncoated sand and inorganic and organic binders which provide good demolding properties but lack adequate crumbling resistance, surface penetration resistance and strength. Preferably the core binder is a curable organic compound. More preferably the binder is an acid-curable organic resin and an oxidizing agent that cures upon exposure to sulfur dioxide.

Refractory materials suitable for this invention should not react with the binder and include graphite, mica, fused silica, aluminum oxide, magnesium oxide,
Including, but not limited to, carbon black and zircon powder. Preferred refractory materials are selected from the group consisting of fused silica, zircon powder and aluminum oxide. The most preferred refractory material is fused silica. The refractory material should preferably have a particle size in the range of about 1 to 100 microns. Most preferred are fused silicas having particle sizes within the range of about 1 to about 45 microns. The fused silica is preferably wet-pulverized.

Any commercially available inorganic binder can be used, such as colloidal silica, clay, amine-treated bentonite, or combinations thereof. Preferred suspending agents are selected from the group consisting of colloidal silica, clay and bentonite.
Most preferred is colloidal silica.

Liquid vehicles can be aqueous or organic. The choice of vehicle is usually based on the type of binder used to bind the foundry core and mold sand. If the core filler is aqueous, the coating vehicle should preferably be organic. If the core binder is organic, the coating vehicle is preferably aqueous.

The composition of the core coating of the present invention is preferably about 30 to
The range should be about 80% by weight refractory material, about 1 to about 25% by weight binder and about 20 to about 70% by weight liquid vehicle. A more preferable composition is about 50~
The range is 70% by weight refractory material, about 5 to about 12% by weight binder, and about 25 to about 40% by weight liquid vehicle. The most preferred composition is about 62% by weight refractory material, about 8% by weight binder and 30% by weight liquid vehicle.

The core coating of the present invention is preferably applied on the sand core to approximately
A coating should be formed having a thickness in the range of 250 to about 5000 microns. The preferred range of thickness is 1000
~about 3000 microns.

To prepare the consumable core of the present invention, sand and binder are mixed and blown or hand packed into a core box having the desired shape of the core. The core is hardened by heating the core box or by passing a suitable gas through the core box. The core is then removed from the core box as a solid mass.

The core can then be coated by conventional techniques such as dipping or spraying. The coating may be applied as a single coating or as a multilayer coating. The core and coating are then dried.

The coating of the present invention is optionally preferably coated with a top wash coating containing a refractory material, a binder, a suspending agent, and a liquid vehicle. This second coating improves protection of the core and facilitates removal of the core from the mold.

The refractory material of the surface coating can be selected from the group consisting of fused silica, zircon powder and aluminum oxide. A preferred material is zircon powder.

Surface coating suspending agents are selected from the group consisting of, but not limited to, high molecular weight polymers and copolymers, silica, vegetable gums, clays and mixtures thereof. Preferred suspending agents for surface coatings are selected from the group consisting of colloidal silica, clay and bentonite. The most preferred suspending agent is colloidal silica.

The surface coating binder may be organic or inorganic and may be selected from polymeric resins and suitable binders such as aluminum borate.

The surface coating liquid vehicle can be aqueous or organic. The choice of vehicle depends on the type, type and type of binder used to bind the foundry core sand.
It is common to do this based on the coating. If the binder is aqueous, the coating vehicle should preferably be an organic solvent. More preferably the surface coating consists of zirconium silicate, resin binder and isopropyl alcohol. The surface coating is preferably about 100 to about 2000 microns, preferably about
A cured coating should be formed on the sand core with a thickness in the range of 250-1000 microns.

The second coating should be applied as a single layer or as multiple layers.

Example 1 97.90% by weight foundry silica sand (AFS particle size No.
65), 1.47 wt% furan and 0.59 wt% methyl ethyl ketone peroxide and 0.04 wt%
A consumable sand core was made from silane. The core was treated with sulfur dioxide for 2 seconds at ambient temperature and pressure.

Core coating compositions containing various concentrations of fused silica, colloidal silica, and water were prepared. The fused silica particles had a particle size range of 1 to 45 microns. The above composition was ground by placing a magnetic ball in a container and rotating the container for 2 to 3 hours to break up large agglomerated particles. The ground composition was poured through a fabric paint strainer. The specific gravity of the composition was then checked and adjusted by adding a slurry of fused silica or colloidal silica until the Baume reading was in the range of 56-62. Approximately 10% methanol by volume was added. An additional amount of kaolin was added to the composition and then stirred for a minimum of 1 hour. The composition was then left for 24 hours.

The coated and hardened cores were used to produce complex aluminum alloy die castings with undercut areas. The core was then removed from the die casting using conventional mechanical demolding techniques. Cores and die-cast castings were tested for deformability, collapse resistance, and permeability, and their properties were evaluated.

Example 2 The cured coated core of Example 1 was immersed in the core coating composition for about 10 seconds, removed and drained.
The coating was allowed to dry. Dip the dried coated core into the core coating composition again for about 5 seconds, drain, and soak the core for about 5 seconds.
In an air circulation oven at 80℃175〓at least 3
Let dry for a minute. Creating a casting using the core,
Both were evaluated as in Example 1.

Example 3 Uncoated consumable cores were made as in Example 1, castings were prepared therefrom, and the cores and castings were evaluated as in Example 1.

Example 4 A consumable core was prepared as in Example 1. The core was cooled for at least 2 minutes and dipped for 2-3 seconds into a surface coating composition containing zirconium silicate, a resin binder, and isopropyl alcohol (Arcolite #412, Atlantic Reichhold Co.). The core was drained and dried for 30 minutes. A casting was made using the core.

The demoldability, collapse resistance, and permeability of the double-coated cores and castings were evaluated.

Example 5 Uncoated consumable cores prepared as in Example 3 were dipped into the zirconium silicate/resin binder coating composition of Example 4 and allowed to dry. Castings were made from the coated cores and evaluated.