JPH0248344B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a consumable sand core for use in a dacast mold for casting dacast castings having an undercut area.

There are problems with die casting of metals such as aluminum, zinc, magnesium, copper and their alloys which have undercuts. Pressure die casting processes are known to require molds or dies that can withstand the high temperatures and pressures encountered. Therefore, iron-based materials are generally used for die casting molds. These die materials are not easily disassembled, and therefore complex die casting shapes, such as castings with undercuts, cannot be easily removed from this type of die casting mold.

Semi-permanent die casting molds have been used with consumable cores at pressures on the order of about 30 psi. For these low pressure applications, the core is constructed from foundry sand mixed with a binder or resin.
Using either heat, catalysts or chemical reactions, the sand grains are bonded into their respective shapes and used in the casting process. The heat released during solidification and cooling of the actual cast part displaces water vapor or chemically decomposes the binder within the core. This facilitates removal of the core from the casting.

Cores using glass and soluble salts have also been used in the past and are described in GB 1179241. This type of core has disadvantages in terms of lack of process control, economy, handling and corrosive effects of salts.

In die casting at pressures of several thousand psi (high pressure die casting), the main problem has been the inability to provide three important properties in a single core/binder system. These have excellent shakeout and washout resistance.
resistance) and surface penetration resistance.

In the present invention, the sand release property (or mold release property) refers to the ability to withstand the molten metal press-injected under high pressure until it solidifies in the die, and then reduce the bonding force of the binder due to the heat of the molten metal, and also to the rocking mechanism. Therefore, the sand grains easily collapse and fall from the casting, and collapse resistance refers to the core's resistance to the high-speed molten metal that is press-fitted. Excellent collapse resistance is the property of ensuring the dimensional stability of the finished casting and the stability of the casting. Prevents sand from getting into the core.

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. It is not possible to obtain castings with This condition has a very negative impact on subsequent machining and tool life. Furthermore, if the sand in the casting were to separate from the casting after component installation, it would cause damage to associated components, such as the lubrication system of an automobile engine. Consumable cores developed in the past for high-pressure injection have either good sand release properties but a high degree of disintegration and surface permeability, or good disintegration resistance and surface permeability but very poor resistance. It shows excellent sand release properties. The problems mentioned above are solved by the use of the core according to the invention.

More specifically, according to the present invention, there is provided a consumable core for use in a die casting mold for forming a die casting casting having an undercut region, the technical configuration of the present invention being: A (a) Casting and (b) boron in an amount of 3 mol % to 40 mol % based on the number of moles of aluminum, and the molar ratio of the total number of moles of phosphorus to aluminum and boron is 2:1 to 4:1. , 0.3~ of foundry sand
a boronated aluminum phosphate binder in an amount of 3.5% by weight; (c) 10-20% by weight of a curing agent which reacts with the aluminum phosphate to harden said binder to the extent that the core can be handled without damage; d) From 15 to the total weight of boronated aluminum phosphate and water
B. a suspension agent in which the core has a coating of a predetermined viscosity to substantially seal the surface pores of the core, and the coating has a content of 4 to 30% by weight; and 60-95% by weight of particulate refractory material and 1
~10% binder, interacting with said suspending agent and said binder to obtain said predetermined viscosity.
% by weight of an organic liquid solvent.

Objects and advantages of the invention will become apparent from the following description, which refers to the accompanying drawings. This drawing is useful in explaining a casting operation in which the three problems mentioned above occur. Plunger 11 is used to inject molten metal 12 into a die casting mold formed by steel members 13 and 14 and sand core 15. It should be noted that the final die casting shape includes an undercut area.
FIG. 1 shows an example of the area affected by the molten metal 12 during casting into the sand core 15 of the present invention. In the case of the sand core shown, reference numeral 16
The area indicated by is the area where molten metal is likely to penetrate into the surface of the sand core, and the area with reference numeral 17 is an undercut area near the injection part of high-pressure molten metal, so it is difficult for the coating to collapse (washout). This is an easy area.

The consumable core of the present invention is designed to be suitable for high temperatures and pressures for use in high pressure die casting processes to economically produce castings with undercut areas.

The consumable core of the present invention can be used to produce die castings having undercut regions and for this purpose includes a binder, which binder ranges from about 3 mole percent to about
It comprises boronated aluminum phosphate in an amount of 40 mole percent, with a molar ratio of phosphorus to total moles of aluminum and boron of about 2:1 to about 4:1. This binder is mixed with suitable foundry sand and a suitable hardener to form the core. The core is also coated to improve surface penetration and collapse resistance.

The boronated aluminum phosphate binders described above are described in detail in US Pat. No. 3,930,872, the disclosure of which is incorporated herein by reference. especially,
This U.S. patent contains boron in an amount of about 3 mole percent to about 40 mole percent relative to the moles of aluminum, and the molar ratio of phosphorus to the total moles of aluminum and boron is about 2:1 to about It states that the binder is comprised of a 4:1 ratio of boronated aluminum phosphate, an alkaline earth metal material containing an alkaline earth metal and oxide, and water. This time, it was confirmed that this binder, when present in an amount of about 0.3 to 3.5% by weight based on foundry sand, imparts sand release properties useful for die casting. When using typical silica foundry sand with AFS No. 65 fineness, it is preferred to use a binder in the range of about 1.0 to 3.5% by weight. The lower limit is required to provide sufficient core strength to withstand subsequent handling, while the upper limit is caused by (a) non-uniform density associated with changes in sand fluidity during core manufacture; This upper limit should not be exceeded in order to avoid problems with blow molding and (b) significantly reduce sand removal efficiency. If a heavier foundry sand is used, such as zircon, less binder is required, ie on the order of about 0.3-1.5% by weight. The upper and lower limits, respectively, are chosen for the same reasons as for silica sand. Of course, the use of other commonly used foundry sands having densities different from those described above is also within the scope of the invention. These other types of sand will require the use of an amount of binder appropriate to their density.

The curing agent should be present in an amount sufficient to cure the binder and thereby provide the core with the strength necessary to handle and install it in a die casting machine without damaging the core. Said U.S. Patent No.
When a hardening agent is used in the sand core, for example, an alkaline earth metal material containing an alkaline earth metal and an oxide, as described in No. 3930872, about 10 to 20% by weight. A binder in the range of . As the amount of curing agent described in US Pat. No. 3,930,872 is reduced, the bench life increases. However, this advantage is offset by a loss in sand release properties and core strength. Other known curing agents, such as ammonia gas, are also contemplated and would be suitable for use with the sand cores of the present invention.

Approximately 1% iron oxide as Fe ₂ O ₃ as required to further improve hardening and sand release properties.
It can be present in the sand core in an amount of ~4%. Amounts of Fe ₂ O ₃ greater than about 4% result in undesirable loss of core strength.

Further, as taught in U.S. Pat. No. 3,930,872, water is included in the sand core composition for this taught purpose in an amount of 15% based on the total weight of boronated aluminum phosphate and water. ~50% by weight.

To produce the consumable core of the present invention, the binder, solid hardener, and optionally Fe ₂ O ₃ should be mixed into the foundry sand. If a gaseous hardener is used rather than a solid, the binder and Fe ₂ O ₃ are mixed with the sand and then the gaseous hardener is passed through the mixture to initiate hardening of the binder.

After manufacture, the core is coated to further improve its performance in terms of collapse resistance and surface penetration resistance. Generally, the core coating consists of a suspending agent, a refractory material, a binder, and a solvent.

Suspending agents are usually clays or clay derivatives. These materials should be present in sufficient amounts to function to maintain the refractory material in suspension. The suspending agent should be about 4 to 30% by weight, based on total solids weight.
Present in an amount in the range of % by weight.

Typical particulate refractories useful in coating compositions include, but are not limited to, graphite, silica, aluminum oxide, magnesium oxide, zircon, and mica. These materials are generally present in amounts ranging from about 60 to 95 percent by weight, based on total solids weight.

The materials of the coated particles are bound together by the use of a binder, such as a thermoplastic resin. This type of binder comprises about 1 to 10% by weight, based on the total solids weight of the coating composition. The binder and suspending agent should be compatible with the particular solvent, which may be an organic liquid. Solvents should be used in amounts effective to provide the necessary viscosity to control coating thickness and uniformity.

Core coatings for die casting should satisfy the desired properties more fully than core coatings suitable for other casting methods. The core coating should have the ability to substantially seal the pores on the core surface. Because die casting involves forcing molten metal under pressure, any pores on the surface of the core are penetrated by the molten metal, resulting in sand being trapped on the surface of the cast part. Proper core coating on the core prevents penetration of molten metal into the sand core.

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

Other core coatings found suitable for use in conjunction with the bonding system of the present invention are disclosed in U.S. Pat.
No. 4096293, the disclosure of which is incorporated herein by reference. In particular, the coating material should have a thickness and uniformity of coating sufficient to substantially seal the surface pores of the core and provide good collapse resistance and surface penetration resistance during die casting. and about 5 to 90% by weight of the organic liquid solvent, about 0.1 to 2% by weight of the suspension, and about 5 to 90% by weight of the suspension.
~80% by weight of calcium aluminate particles with an average particle size of 20 to 25 μ and no particles larger than about 70 μ, and a hard resin, the hard resin being a reaction product of fumaric acid, gum rosin, and pentaerythritol. and optionally a wetting agent present in a weight ratio of about 0.5 to 5 parts by weight per 100 parts of the composition.
It can also be added in amounts in the range of 2% by weight.

Once the core is formed in the mold and removed, it is strong enough to be handled. The core coating is then applied by brushing, dipping, spraying or equivalent method. Once the coating is dry, the core is placed into a die on the casting machine. The steel portion of the die forms the surface profile of the metal part that is not formed by the core. The core is placed within the die and positioned by pins, indentations or other means known to those skilled in the art, the core is placed in a fixed position and the die is closed, after which molten metal is injected into the die.

Heat is released from the casting while it solidifies in the die. A portion of this heat transfers into the core and increases the temperature of the core. This transfer of heat decomposes the binder in the core and releases the resulting moisture. After the molten metal solidifies within the die, the die casting mold is opened and the resulting casting and consumable core are removed. After cooling to room temperature, sand is mechanically removed from the core.

The present invention will be explained below with reference to Examples.

Example 1 Zircon foundry sand (AFS fineness No. 120) containing an aluminum boron phosphate binder in an amount of about 1.25% by weight of the foundry sand and the alkaline earth hardener in an amount of about 20% by weight of the binder. An aluminum alloy was die cast into the shape shown in FIG. 1 using the core. The core contains 15% by weight amine-treated bentonite suspension agent, 5% by weight thermoplastic binder and 80% by weight thermoplastic binder.
With a core coating consisting of 2% by weight of silica refractory material
Coated twice. After cooling to room temperature, good sand removal properties were observed when the core was mechanically separated from the casting. This casting exhibits good surface penetration resistance and also good collapse resistance.

Example 2 Core containing silica foundry sand (AFS fineness No. 65) and about 2.5% by weight of the foundry sand of an aluminum boron phosphate binder and 20% by weight of the binder of the alkaline earth hardener. was used to die cast an aluminum alloy into a pump component with an S-shaped core. The core was coated twice with a core coating of the composition described in Example 1. Good sand removal properties were observed when the core was mechanically separated from the casting after cooling to room temperature. This casting exhibits good surface penetration resistance and also good collapse resistance.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a mold portion of a die-casting machine. 11... Plunger, 12... Molten metal, 13,1
4...Steel die, 15...Sand core, 16...Surface penetration part, 17...Collapse occurrence area.

Claims (1)

[Claims] 1. An undercut region having excellent sand release properties, excellent collapse resistance, surface penetration resistance, excellent shelf life, and high core strength capable of withstanding pressures exceeding several thousand psi. A consumable sand core that is applied to die-casting castings having the following composition: A (a) foundry sand; and (b) 3 mol% to 40% of the mole of aluminum. mol % of boron, and the molar ratio of the total number of moles of phosphorus to aluminum and boron is from 2:1 to 4:1, and the foundry sand contains boron in an amount of 0.3 to 4:1.
(c) 10-20% by weight of a curing agent which reacts with the aluminum phosphate to harden said binder to the extent that the core can be handled without damage; d) 15 for the total weight of boronated aluminum phosphate and water
B. The core has a coating of a predetermined viscosity to substantially seal the surface pores of the core, and the coating has a suspension of 4 to 30% by weight. agent and 60 to 95% by weight particulate refractory material and 1
~10% binder, interacting with said suspending agent and said binder to obtain said predetermined viscosity.
% by weight of an organic liquid solvent. 2 The foundry sand is made of silica sand, and the binder is 1.0~
Sand core according to claim 1, characterized in that it is present in an amount of 3.5% by weight. 3. The sand core according to claim 1 or 2, wherein the foundry sand is made of zircon sand, and the binder is present in an amount of 0.3 to 1.5% by weight of the foundry sand. . 4. Sand core hardener is 10 to 20% by weight of the binder.
A sand core according to any one of claims 1 to 3, characterized in that the sand core is made of an alkaline earth material containing an alkaline earth metal and an oxide in an amount of . 5. A sand core according to any one of claims 1 to 4, characterized in that Fe ₂ O ₃ is present in the core in an amount of 1 to 4% by weight of the foundry sand. 6 an organic liquid solvent containing 5 to 90% by weight of the coating material;
0.1 to 2% by weight of a suspending agent, 5 to 80% by weight of calcium aluminate particles having an average particle size of 20 to 25μ and containing no particles larger than about 70μ, and a hard resin; The sand core according to claim 1, wherein is a reaction product of fumaric acid, gum rosin, and pentaerythritol, and is contained in an amount of 0.5 to 5 parts by weight per 100 parts by weight of the coating composition.