JPH0557058B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a mold used in casting a casting and a method for making the same.

[Prior art] There are many types of molds, including green sand molds using clay as a caking agent (hereinafter referred to as synthetic sand molds), and various inorganic and organic molds including water glass and carbon dioxide molds. The main type is a special mold using a caking material (hereinafter referred to as a self-hardening sand mold).

The above synthetic sand mold uses clay as a caking material, so its strength is 0.5 to 2.
The mold hardness is approximately 60 to 95 on a mold ^hardness tester. On the other hand, the mainstream of self-hardening sand molds is currently organic self-hardening sand molds, and their strength is largely determined by the amount of organic matter as a caking agent and the curing time depending on the amount of hardening agent. It has a strength of 7 to 40 kg/cm ² , more than 10 times that of synthetic sand molds. In general, self-hardening sand molds have a strength at a demolding time of at least 7 kg/cm ² with a coercive pressure. For this reason, the mold hardness of self-hardening sand molds is so high that it cannot be measured with a normal mold hardness meter.

[Problems to be Solved by the Invention] However, in casting, buoyancy that lifts the upper mold of the mold acts due to the pressure of the molten metal during pouring.
This leads to a decrease in the dimensional accuracy of the mold due to the tension, and also to a leakage phenomenon in which molten metal leaks from the mold mating surface between the upper mold and the lower mold.To prevent this, a weight or a clamp is used. In this case, if the buoyancy that lifts the upper mold is F according to the hydrostatic pressure equation when pouring the metal, then F = ΥSH (where, Υ: specific gravity of the molten metal, S: area occupied by the molten metal on the mold mating surface, H: molten metal head). ), and this buoyant force F is considered to be applied as the static pressure of the molten metal, and the holding weight corresponding to this, for example, the buoyant force F
A pressing weight approximately three times that of the weight is applied as the weight of the weight or clamping force.

At this time, since the counter pressure of the synthetic sand mold is often 2 kg/cm ² or less, the surface of the casting mold space is about to be crushed by the weight of the presser foot (however,
If the mold is crushed, it cannot maintain its function as a mold, so the upper and lower molds are in close contact around the entire circumference of the mold mating surface, maintaining the cushion), and in this state, molten metal leakage from the mold mating surface is prevented. Although this has been prevented, there is still a problem in that it is difficult to achieve dimensional accuracy of the mold.

On the other hand, self-hardening sand molds have higher strength than synthetic sand molds, so even if you apply weight like synthetic sand molds, if the precision of the mold mating surface is not achieved,
The mold mating surfaces do not come into close contact and a slight gap occurs. For this reason, as shown in FIG.
The mating surfaces 24 of the molds 2 and 23 are sealed to prevent melt leakage, and in addition to requiring time and effort to apply the seal material 21, the molds 22 and 23 may have problems with dimensional accuracy due to the seal material 21. If there are many mold spaces 25 for casting on the mold 22 side, there is still a large possibility of molten metal leaking, resulting in a problem of poor casting workability. In addition, in the figure, 26 is self-hardening sand, and 27 and 28 are upper and lower frames.

Therefore, the present invention skillfully utilizes synthetic sand and self-hardening sand to provide strength and excellent dimensional accuracy, as well as cushioning properties to prevent water leakage without using a sealing material. This is an attempt to solve the problems of the prior art described above.

[Means for Solving the Problem] That is, the first invention molds the surrounding part of the casting mold space in the frame with self-hardening sand, and the remaining part in the frame, including the mold mating surface, is made of synthetic sand. The gist is a mold that is characterized by being molded with.

In the second invention, self-hardening sand is poured onto the model leaving the inner peripheral part of the frame, and then the inside of the frame is molded with synthetic sand while promoting the hardening of the self-hardening sand, and the self-hardening sand is hardened. The gist of this invention is a method for making a mold, which is characterized by removing the model after completion.

[Function] When casting this mold, if the upper and lower frames are placed together and the weight is applied with a weight or clamp, the molten metal will leak from the mold mating surfaces due to the cushioning action of the synthetic sand. The use of self-hardening sand, which has excellent strength and dimensional accuracy, allows castings with high precision to be obtained.

Further, as a molding method, when molding the inside of the frame with synthetic sand, self-hardening sand is also molded by the molding pressure of the synthetic sand.

[Example] Next, an example of the present invention will be described with reference to FIGS. 1 to 4.

In this example, first, as shown in FIG.
Self-hardening sand 3 is poured onto the model 2 placed above. In this case, an appropriate distance 6 is left between the inner peripheral portion of the frame 5 and the self-hardening sand 3 on the mold mating surface 4.

Next, as shown in FIG. 2, the inside of the frame 5 is shaped with synthetic sand 7 while a hardening accelerating gas is blown into the self-hardening sand 3 to promote hardening of the self-hardening sand 3. As a result, the self-hardening sand 3 is also shaped by the shaping pressure of the synthetic sand 7.

Next, as shown in FIG. 3, after the hardening of the self-hardening sand 3 is completed, the model 2 is demolded. As a result, a mold 9 is obtained in which the surrounding part of the casting mold space 8 in the frame 5 is molded with the self-hardening sand 3, and the remaining part in the frame 5 is molded with the synthetic sand 7.

When casting the mold 9, as shown in FIG. 4, the mold 9 is fitted with a mating mold 10 of a mating mold formed in the same manner as the mold 9 without using glue or a mold seal. Apply pressure with a clamp and pour the molten metal.

At this time, self-hardening sand 3, 3 is placed on the mold mating surface 4.
Even if these parts do not come into close contact with each other, the synthetic sands 7, 7 in the peripheral parts of the molds 9, 10 come into close contact with each other on the mold mating surfaces 4 due to the cushioning action of the synthetic sands 7, 7 in the peripheral parts of the molds 9, 10, thereby preventing leakage of the molten metal.

After cooling the molten metal, the molds 9 and 10 are dismantled.
At this time, since the peripheral parts of the molds 9 and 10 are made of synthetic sand 7 and 7, they are relatively easily collapsed and separated. The obtained casting has good precision due to the self-hardening sands 3, 3 having good precision.

[Effects of the Invention] As described above, in the present invention, since the self-hardening sand has strength and excellent dimensional accuracy, castings with high precision can be obtained by using castings, and the cushioning effect of the synthetic sand makes it possible to easily form molds during casting. It is possible to prevent molten metal from leaking from the mating surfaces, eliminating the need for sealing materials, and the synthetic sand improves the collapsibility of the mold after casting.

Furthermore, as a molding method, by molding the inside of the frame with synthetic sand while promoting the hardening of the self-hardening sand, the self-hardening sand is also molded by the molding pressure of the synthetic sand, speeding up the molding work.

[Brief explanation of the drawing]

1, 2, and 3 are longitudinal cross-sectional views for explaining the process of an embodiment of the present invention, FIG. 4 is a vertical cross-sectional view of the frame-aligned state, and FIG. 5 is a longitudinal cross-sectional view of the conventional frame-aligned state. FIG. 3... Self-hardening sand, 5... Frame, 7... Synthetic sand, 8
...Mold space for casting, 9...Mold, 10...Mold.

Claims (1)

[Scope of Claims] 1. A mold characterized in that the surrounding portion of the mold space for casting within the frame is molded with self-hardening sand, and the remaining portion within the frame, including the mold mating surface, is molded with synthetic sand. 2. Put self-hardening sand on top of the model, leaving the inner circumference of the frame, then mold the inside of the frame with synthetic sand while promoting the hardening of the self-hardening sand, and after the hardening of the self-hardening sand is completed, remove the model. A mold making method characterized by molding.