JPS649898B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a consumable sand core for high-pressure die casting molds.

More particularly, the present invention relates to consumable sand cores for die casting of metals such as aluminum, zinc, magnesium, copper and alloys thereof.

BACKGROUND OF THE INVENTION Conventional conventional casting techniques use consumable or disposable cores to produce castings with undercut areas. This was possible because the pressure requirements for this type of application are 30 psia, compared to at least about 1000 psia (70.31 Kg/cm ² ) required for high pressure die casting.
(2.11Kg/cm ² ) or less.

(Problems to be Solved by the Invention) A problem in die-casting the various metals mentioned above is that there is no die-casting technique that can be used industrially to produce castings having undercut regions. The pressure die casting technology used requires a die casting mold that can withstand the high temperatures and pressures to which the mold is exposed. For example, iron-based materials are generally used in die-casting molds. Because these die materials cannot easily collapse, molds with complex undercut areas and undulations cannot be used. This is because if these are present, the casting cannot be removed from the mold.

A typical sand core is composed of foundry sand mixed with a binder or resin. By using heat, catalysts, or chemical reactions, the sand grains can be bonded into their respective shapes, which can then be used in the casting process. The heat generated during solidification and cooling of the actual cast part evaporates the moisture contained in the core or chemically disrupts the binder. This achieves relatively easy removal of the core from the casting.

The present invention uses a consumable sand core as part of a high pressure casting mold to provide undercut areas in die castings made using high pressure techniques.

In developing a consumable sand core suitable for use in producing high-pressure die castings, the inventors have identified four main core properties that are a function of the core/binder: I couldn't satisfy you. The four characteristics are excellent shakeout properties and woshout resistance.
resistance), surface permeation resistance, and core strength.

In the present invention, sand releasability (or mold release property) refers to the ability to withstand the molten metal press-fitted at high pressure until it solidifies in the die, and then reduce the bonding force of the binder by the heat of the molten metal, ), sand grains easily collapse and fall from the casting, and collapse resistance refers to the resistance of the coating on the core to the high-speed molten metal that is press-ined. Provides dimensional stability and prevents sand from getting into the casting.

Furthermore, surface penetration resistance is a property that prevents molten metal from penetrating between the sand grains on the surface of the core. If molten metal penetrates into the surface of the core, it will destroy the surface of the core and create protrusions on the surface of the casting, resulting in a smooth surface. making it difficult to obtain castings with This condition is extremely detrimental to subsequent machining and tooling. Furthermore, if the sand is separated from the surface after part loading,
Damage to associated parts, such as automobile parts, may result. High strength on the core is desirable. This is because the core is more resistant to fracture during handling and more resistant to fracture during severe casting. The present invention generally solves the above problems by providing a core/binder system that can impart the four properties described above to the core.

(Means for Solving the Problems) More specifically, according to the present invention, there is provided a consumable sand core for high-pressure die casting molds, which contains about 1.0% of the casting sand and the weight of the casting sand. ~2% of an acid-curing resin binder, and is characterized by improved sand release properties, improved collapse resistance, surface permeation resistance, and core strength during die-casting operations.

Examples Objects and advantages of the invention will become apparent from the following description, which refers to the accompanying drawings. This drawing is useful in illustrating problematic casting methods.

The plunger 11 transfers the molten metal 12 to a steel mold 13.
and 14 and a sand core 15 for injection casting into a die casting mold. It should be noted that the final die cast shape has undercut areas 18,19. Surface penetration of the metal 12 into the sand core 15 occurs along the shaded area designated as 16 in the drawing. Deformation of the sand core usually occurs in the area indicated by reference numeral 17, for example. Sand releasability is determined by the ability to take out the sand core 15 during solidification of the die-casting, the removal of the sand core 15 from the die-casting die,
Involves subsequent cooling to room temperature.

In the present invention, a consumable sand core is used under high pressure as part of a high pressure die casting mold to produce a die casting having an undercut area. For this purpose, a binder consisting of about 1 to 2% by weight of acid-hardening resins, based on the weight of the foundry sand, is used. If less than 1% binder is used, 1000psia (70.31Kg/
cm ² ), the sand core collapses and the undercut area of the casting is thus destroyed. On the other hand, if more than 2% binder is used, 1000psia (70.31Kg/
cm ² ) or more, the sand core becomes too hard and the casting cannot be mechanically sanded, and there is a possibility that the cast product may be damaged when separated from the sand core. The amount of particular binder selected depends on the sand core shape, sand core thickness, method of securing the sand core in the casting mold, and casting conditions. Sand cores are made from foundry sand and a binder mixed with a suitable amount of oxidizing agent. If desired, the finished sand core may be coated to provide a coating that provides improved resistance to molten metal penetration and disintegration.

Acid-curable resin binders that can be used for the purposes of the present invention may be those described in US Pat. No. 3,879,339, which is incorporated herein by reference in its entirety for the same purpose. This binder has been found to be beneficial for sand release properties in high pressure die casting applications when present in an amount of about 1.0-2.0% by weight of foundry sand. The lower limit amount is required to give the sand core sufficient strength to withstand handling, while the upper limit amount is required to avoid problems caused by blowing during sand core manufacturing and the problem of the sand core becoming too hard than necessary. The problems caused by this blowing are associated with fluctuations in sand flow and an undesirable reduction in sand shedding effectiveness. The molding sand used is AFS No.
It should have a fineness of 65 and the amount of binder used should be about 1.0-2.0%. If heavier foundry sands are used, such as zircon, less binder is required, ie on the order of about 0.5-1.0%. Respectively preferred upper and lower limits are selected for the same reasons as for the general ranges. Of course, the use of other commonly used foundry sands with different densities than the sands mentioned above is also within the scope of the invention. These other sands preferably require the use of a density-matched amount of binder.

Acid curable resin bonding systems suitable for use in the present invention include urea/formaldehyde, phenol/formaldehyde, furan and copolymer resins. Preference is given to using furan. This is because this system is more resistant to deformation immediately after sand core production than other systems. Furthermore, copolymers of these resins and epoxidized compounds or unsaturated compounds can also be used.

The resins of the present invention can optionally be silanized, for example, by adding about 1 to 10% by weight of a silane, such as gamma-amino-propyl-triethoxysilane, to the resin. Such addition acts to strengthen the sand core.

When making consumable sand cores, an oxidizing agent such as methyl ethyl ketone peroxide should be present in an amount ranging from about 20 to 70 percent by weight based on the weight of the resin. To ensure complete curing, 30~
An amount of 50% is preferred. The oxidizing agent acts to react with the gaseous sulfur dioxide to produce sulfuric acid, which then cures the resin. Other suitable oxidizing agents include peroxides, hydroperoxides, hydroxyhydroperoxides, chlorates, perchlorates, chlorites, hydrochlorides, perbenzoates, metal oxides, permanganates, monoperiphthalic acid, and hydrogen peroxide. but not limited to. Oxidizing agents of this type are typically added to the resin as a liquid to facilitate mixing, although the use of solid or gaseous oxidizing agents is not outside the scope of this invention.

To make the consumable sand cores of the present invention, the sand and acid curable resin are mixed, then optionally silane can be added to the mixture, and then an oxidizing agent is added to the mixture. This mixture can then be air blown or hand packed into a core box having a core of the desired shape. A curable gas, such as sulfur dioxide, is passed through the core box to cure the resin. The core is removed from the core box as a solid mass and used in the die casting process.

The core can be coated after its manufacture to further improve its anti-collapse and anti-surface permeation performance. The core coating is composed of a general suspending agent, a refractory material, a binder, and a solvent.

Core coatings for die casting are more important than core coatings suitable for other casting methods. The core coating should be capable of substantially sealing the pores on the core surface. Since die casting involves forcing molten metal under pressure, any porosity on the core surface allows the molten metal to penetrate and trap sand on the surface of the cast part. By applying a suitable core coating to the core, a finish that prevents molten metal from penetrating into the sand core can be obtained. The suspending agent in the core coating is usually a clay or clay-derived material. These materials should be present in sufficient amounts to function to maintain the refractory material in suspension. Suspending agents of this type may be present in amounts ranging from about 4 to 30% by weight, based on total solids weight.

Typical particulate refractories that may be used in coating compositions include graphite, coke, silica, aluminum oxide,
Consisting of, but not limited to, magnesium oxide, zircon, mica, talc and calcium aluminate. These materials are generally present in amounts ranging from about 60 to 95 percent by weight, based on total solids weight.

The particulate materials in the core coating are bonded together by the use of a binder, such as a thermoplastic resin. Binders useful in the practice of this invention generally comprise from about 1 to 10 percent by weight, based on the total solids weight of the coating composition. Binders and suspending agents should be compatible with the particular solvent, which may be an organic liquid. The solvent should be present in an effective amount to provide the necessary viscosity to control coating thickness and uniformity to ensure good collapse and surface penetration resistance during die casting.

A typical core coating is 4% by weight of total solids.
~30 wt% amine-treated bentonite suspending agent and 1-10 wt% thermoplastic binder;
It consists of 95% by weight of a refractory material such as silica. The above components are mixed in powder form with a sufficient amount of organic liquid vehicle to provide the necessary viscosity upon drying to provide the desired coating thickness and to act to seal the pores on the core surface. obtain.

Other suitable core coating compositions may also be used, including organic liquid solvents having a Kauributanol number (test value for solvent quality evaluation) of at least 36, such as liquid 1,1,1-trichloroethane. with a suspending agent; with a powdered refractory material such as graphite, coke, mica, silica, aluminum oxide, magnesium oxide, talc or zircon powder; with an organic polymer such as vinyltoluene/butadiene copolymer, styrene/butadiene copolymer. Polymer, vinyltoluene/acrylate copolymer, styrene/acetylene copolymer or acrylate homopolymer. The weight ratio of organic polymer to organic liquid solvent is maintained from about 1:50 to about 1:200, and the weight ratio of powdered refractory material to organic liquid solvent is maintained from about 1:2.5 to 1:3.5. These and other coating compositions that may be used are disclosed in US Pat. No. 4,001,468.

Other core coatings that have been found satisfactory for use in combination with the binder system of the present invention are described in U.S. Pat. No. 4,096,293, the disclosure of which is incorporated herein in its entirety for this purpose. Described for reference. The coating material has a viscosity sufficient to substantially seal the surface porosity of the core, and a coating thickness and uniformity that provides good collapse and surface penetration resistance during die casting. suitable for getting. The coating is about 5 to 90% organic liquid solvent, about 0.1 to 2% suspending agent, and about 5 to 80% calcium aluminate with an average particle size of 20 to 25 microns and no particles larger than about 70 microns. It consists of particles and a hard resin, which is a reaction product of fumaric acid, gum rosin and pentaerythritol,
The resin is present in a weight ratio of about 0.5 to 5 parts per 100 parts of the composition, where all percentages are expressed as % by weight of the composition. If desired, wetting agents can be added in amounts ranging from about 0.01% to 2%.

After manufacturing the core in the core box and removing it, the core is strong enough to be handled.
The core coating is then applied by brushing, dipping, spraying or equivalent methods. Once the coating is dry, the core is placed in a mold mounted on the casting machine. The steel portion of the mold forms the surface profile of the cast part that is not formed by the core. Put the core into this mold,
Fixation is performed using pins, indentations, or other methods commonly known to those skilled in the art. The mold is then closed to maintain the core in a fixed position, and molten metal is then injected into the mold.

During the solidification process in the mold, heat is released from the casting. Some of the heat flows into the core, increasing its temperature. This flow destroys the binder and releases moisture and gaseous substances. Once the molten metal has solidified in the mold, the apparatus is opened and the resulting casting and consumable sand core are removed. Once cooled to ambient temperature, the sand core can be mechanically defrosted.

(Example) Specific examples of the present invention will be explained using the following examples.

An aluminum alloy was die cast into the shape shown in the drawings using a consumable sand core containing silica foundry sand (AFS fineness No. 65). Using furan as a binder in an amount of 1.5% based on the weight of foundry sand,
40% oxidizing agent, methyl ethyl ketone peroxide, based on the weight of the resin, and 3% silane, based on the weight of the resin, were used. The sand core thus produced was coated with the sand core coating described above before die casting. The sand core strength was good. After cooling to ambient temperature, good sand release properties were observed when mechanically separating the sand core from the casting. The foundry sand exhibited good surface penetration resistance and good collapse resistance.

(Effects of the Invention) According to the improved die-casting mold of the present invention and the die-casting method using the same, a metal product having an undercut area of 1000 psia (70.31 Kg/cm ² )
Die-casting is possible under high pressures.

[Brief explanation of the drawing]

The drawing is a sectional view of a mold portion of a die-casting device. 11... Plunger, 12... Molten metal, 1
3, 14...Steel mold, 15...Sand core, 16...
...Surface penetration part, 17... Collapse area, 18, 19...
...undercut area.

Claims (1)

[Claims] 1. A consumable sand medium having excellent sand release properties, excellent collapse resistance, surface permeation resistance, excellent shelf life, and high core strength that can withstand pressures exceeding several thousand psi. in which said sand core is applied to define an undercut area of a die casting: A) the sand core comprises: a) sand; and b) a binder comprising 1 to 2% by weight of said sand;
The binder mainly consists of an acid-curable resin and an oxidizing agent, the oxidizing agent being a silane consisting of 20 to 70% by weight of the resin, and the sand core being hardened with sulfur dioxide.B) In the hardened sand The child coating mainly consists of: a) 4-30% by weight suspending agent consisting of clay, b) particles of graphite, coke, silica, aluminum oxide, magnesium oxide, zircon, mica, talc and calcium aluminate. 60-95% by weight of a granular refractory material selected from the group consisting of; and c) 1-10% by weight of a binder consisting of an organic compound. 2. The consumable sand core for die-casting molds according to claim 1, wherein the binder for sand cores comprises 1 to 10% by weight of silane. 3. The consumable sand core for a die-casting mold according to claim 1, wherein the silane is γ-amino-propyltriethquine silane. 4. The consumable sand core for a die-casting mold according to claim 1, wherein the acid-curable resin is comprised of furan. 5. The consumable sand core for die casting molds according to claim 1, wherein the oxidizing agent is selected from the group consisting of methyl ethyl ketone peroxide, hydroperoxide, hydroxy hydroperoxide, and hydrogen peroxide. 6. The consumable sand core for a die-casting mold according to claim 5, wherein the oxidizing agent comprises methyl ethyl ketone peroxide.