JPH04319042A - Precision casting mold, its manufacturing method, and precision casting method using the mold - Google Patents

Abstract

PURPOSE:To make rough shake out work of mold, to which much labor and time are necessary and working surroundings are made to worse in the conventional precision casting with lost wax method, unnecessary or at least drastically easy. CONSTITUTION:At the time of manufacturing the mold for precision casting with the lost wax method by dipping a tree of wax into water slurry of colloidal silica, repeating sanding of stucco material and drying and executing dewaxing and burning, granular CaCO3 is beforehand added into slurry and changed into CaO with a series of burning work. After casting, by acting water to the mold, desirably during hot-state of the mold, CaO is hydrated, and by vol. expansion and powering due to generation of Ca(OH)2, the mold is easily collapsed.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to precision casting technology using the lost wax method, and provides an easily collapsible mold, a method for manufacturing the mold, and a precision casting method using the mold.

0002

[Prior Art] The mold used in the lost wax method, which is a typical precision casting method, is a tree in which multiple wax models are assembled around a sprue, and is usually made by dispersing colloidal silica in an aqueous medium. A green mold is prepared by repeating the process of dipping it in slurry, sprinkling refractory particles called stucco on top of it, sanding it to make it adhere, drying it, and dipping it in the slurry again several times. It is manufactured by heating a mold to remove wax and then firing it to form a fired mold.

[0003] Casting consists of pouring molten metal into the mold obtained in this way and removing the mold after solidifying, and the product is obtained by separating individual castings from the tree-shaped cast body. There is.

One of the points to be improved in precision casting is the rough disassembly of the mold after casting. Rough dismantling of molds is usually done manually using a hammer or using a shake-act machine, but either method requires a lot of labor, generates noise and dust, creates a poor working environment, and is time-consuming. Moreover, the product may be damaged by mistake.

[0005] As one measure to solve these problems, the inventors proposed using CaCO3 as a part of the refractory material, that is, the stucco material constituting the mold, and firing it to make the mold ( Patent application No. 3-3342).
Since this mold collapses when brought into contact with water after casting, rough disassembly is easy. The mechanism is that CaCO3 added to the stucco material turns into CaO by firing.
When CaO comes into contact with water, it hydrates and becomes Ca.
(OH)2, and the accompanying powdering and expansion lead to collapse. The rapid heat generation due to hydration generates water vapor and causes an explosion state, thereby promoting the collapse of the mold.

As a result of further research, the inventors discovered that C.
We have found that by using granular aCO3, directly mixing it with colloidal silica, and attaching it to a wax model to form a mold, effects equivalent to or better than those described above can be obtained.

[0007]

[Problems to be Solved by the Invention] An object of the present invention is to provide an easily collapsible precision casting mold that facilitates rough dismantling of the mold after casting in precision casting, by utilizing the above new knowledge. , and a method for manufacturing such a mold. It is also an object of the present invention to provide a precision casting method using the mold.

[0008]

Means for Solving the Problems The precision casting mold of the present invention has a layer in which granular CaCO3 is solidified using colloidal silica slurry as a binder and converted to CaO by firing.

[0009] Granular CaCO3 has a particle size of 0.2 to 12
．． 0 mm, preferably 0.3 to 0.7 mm.

[0010] This mold manufacturing method involves adhering a slurry of colloidal silica in which granular CaCO3 is dispersed to the outside of a wax model, drying it at least once to prepare a green mold, and heating the green mold. After removing the wax model, it is fired to make a firing mold, and the CaCO3 is
It consists of changing to O.

[0011] Granular C is added to the silica binder in the firing mold.
Depending on the size and shape of the mold, a single layer in which aO is retained may be sufficient. This is because the slurry in which granular CaCO3 is dispersed can be formed into a much thicker layer than the slurry alone. However, in general, it will be necessary to repeat the conventional sanding process, i.e., applying the stucco material and then reapplying the slurry after drying, to create a thick mold. As the stucco material, granular refractories such as mullite, silica, chamotte, zircon sand, etc. can be used as in the conventional method, or CaCO3 can also be used according to the technique proposed earlier. Of course, it is also possible to use a mixture of granular refractories and CaCO3, or to layer them separately.

The precision casting method of the present invention uses the above mold, that is, a precision casting mold having a layer in which granular CaCO3 is solidified using colloidal silica slurry as a binder and converted to CaO by firing. The process consists of pouring molten metal into a mold and solidifying it, then applying water to the mold to collapse the mold and removing the casting.

[0013] The contact with water may be carried out by spraying or flowing water onto the mold, or by placing the mold in water, and any method may be used. After casting, water may be applied after cooling to room temperature, but if the mold is at a high temperature (for example, 40
If the disintegration is carried out while the temperature is between 0 and 800°C, the disintegration will proceed more effectively and the product can be taken out quickly, which is advantageous.

[0014]

Operation: Application of the slurry to the wax tree, sanding of the stucco material, drying and firing of the resulting green mold can be carried out according to known techniques. Firing is typically carried out at a temperature of around 1000° C., thereby removing the wax model and providing the mold with the required strength. CaCO3 is changed into CaO by firing as described above.

[0015] When molten metal is poured into this mold and solidified, water is applied to hydrate CaO and form Ca(OH)2.
As in the invention described above, expansion of volume and pulverization cause collapse. In the present invention, the presence of CaO in the silica binder layer results in a mold that is more easily disintegrated than a mold in which CaO is present only in the stucco material or a portion thereof. Therefore, in many cases, it is possible to omit the conventional rough demolition work and move on to the next step, for example, a sand removal step by shot blasting or sandblasting.

[0016]

[Example] A wax model of automobile steering parts was assembled into a tree. A slurry in which crushed CaCO3 particles with a particle size of 0.3 to 0.7 mm were added to an aqueous slurry of colloidal silica at a ratio of 10% by volume was used, and three molds of each of the following five types and a bending test piece were used. was produced. As the stucco material, chamotte grains with approximately the same grain size were used, except for three CaCO grains (same as those added to the slurry). Slurry application by dipping and dry sanding were repeated to form a green mold with 8 layers of coating, which was heated to dewax and then baked at 1000° C. for 2 hours.

Mold A: CaC in the 4th layer (counting from the inside)
Using slurry with O3 and CaCO3 stucco Mold B: Using slurry with CaCO3 in the 4th layer, omitting sanding of this layer Mold C: Slurry with CaCO3 in the 4th and 5th layers and CaCO3 stucco. Mold D: Use slurry with CaCO3 added to the 4th and 5th layers, and omit sanding of these layers. Mold E.
: Conventional mold that does not contain CaCO3 Cast steel is cast into three molds each, one when the mold surface temperature reaches 800℃, another when the mold surface temperature drops to 400℃, and the last one when the mold surface temperature drops to 400℃. The pieces were left for one day to cool to room temperature, and then immersed in water to examine disintegration and the quality of the cast products.

[0018] On the other hand, the bending test pieces were those in a green state;
After firing at 1000° C. for 2 hours, the bending strength was measured at room temperature.

The results are as follows. The quality of all cast products was good.

[0020] Mold strength (kg/cm2)
Disintegration when immersed in water
Raw mold Baking mold 800℃
Leave at 400℃ for 1 day A
37 39 Completely collapsed Large crack appeared
B 38 35
Large cracks occur Small cracks occur
C 32 36
Completely collapsed and a large crack appeared
D 42 35
Large cracks occur Small cracks occur
E 40 43
No cracks No cracks

002
1]

[Effects of the Invention] According to the present invention, a mold can be obtained that has the same strength as a conventional precision casting mold in either the green or fired state, and can be practically handled in the same way as a conventional precision casting mold. In addition, the mold can be easily collapsed by applying water after casting, so rough dismantling work can be omitted or at least easily performed. After casting, if water is applied while the temperature of the mold is still high,
Collapse is easier. The quality of the product obtained by the casting method of the present invention is as good as before, and there is no fear of scratches during rough disassembly of the mold.

Claims (6)

[Claims] Claim 1: Granular CaCO3 is solidified using a slurry of colloidal silica as a binder, and by firing it
A precision casting mold with a layer changed to aO. [Claim 2] Granular refractory or granular CaCO3
2. The mold of claim 1, comprising a stucco layer of. [Claim 3] Granular CaC on the outside of the wax model.
A slurry of colloidal silica in which O3 is dispersed is attached and dried at least once to prepare a green mold.The green mold is heated to remove the wax model and then fired to form a fired mold, converting CaCO3 into CaO. A method for manufacturing a precision casting mold, which comprises changing to a mold for precision casting. 4. The method of claim 3, further comprising the step of depositing granular refractory material or CaCO3 stucco material subsequent to depositing the slurry. [Claim 5] Granular CaCO3 is solidified using colloidal silica slurry as a binder, and the carbon is removed by firing.
Precision casting consists of using a precision casting mold with a layer changed to aO, pouring molten metal into the mold and solidifying it, and then applying water to the mold to collapse the mold and take out the casting. Method. 6. The precision casting method according to claim 5, wherein the molten metal is brought into contact with water while the temperature of the mold is high after solidification.