JPS6124099B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a mold manufacturing method in which a mold material mixture using an acid-curing resin as a binder and a salt made of a strong acid and a weak base substance as a hardening agent is rapidly hardened with a high-temperature gas such as air. Generally, molds using resin as a binder are made by adding resin and catalyst to molding sand made of refractory granules in advance, and then heating and hardening this mold material mixture through a mold, as in the shell mold method. Alternatively, methods such as the self-hardening mold method, in which a catalyst that reacts with the resin and hardens at room temperature is added to the molding sand, and a sufficient reaction time is given to harden the resin, have been adopted. However, the former method requires a mold that can withstand heat, resulting in high mold manufacturing costs and is difficult to apply to manufacturing non-mass-produced castings. If the pot life is short and the pot life is long, it will take a long time to harden, resulting in poor productivity. Therefore, there is a demand for the development of a method for rapidly curing by blowing gas. So far, two methods have been developed: a mold material using urethane resin as a binder and curing by blowing amine gas, and a mold material using acid-curing resin as a binder and adding peroxide such as methyl ethyl ketone peroxide. A method of curing by blowing sulfur dioxide gas has been devised. However, since aluminous gas and sulfur dioxide gas are harmful to the human body, when using them, it is necessary to prevent the gas from leaking into the workplace and to neutralize it before releasing it, which places a burden on equipment. big. The present invention uses a harmless gas such as air at a high temperature instead of a harmful gas.In addition to not requiring special equipment, a wooden mold can be used, and the mold material mixture has a sufficient pot life. , mold productivity is also good. The present invention will be explained in detail below. The binder used in the present invention is an acid-curing resin such as a furan resin or a phenolic resin, and the acid-curing resins currently used in self-hardening molds can be used as they are. The curing catalyst is a salt consisting of a strong acid and a weak base.
For example, when ammonium hydrogen sulfate or ammonium persulfate is used, it easily decomposes in hot gas, releases ammonium, which is a weak base, and leaves behind a strong acid.
Rapidly cures acid-curing resins. Furthermore, these salts do not easily decompose even when mixed with acid-curing resins, and have a sufficient pot life as a molding material mixture. Various methods have been tried in the past to harden the resin in the mold material mixture with high-temperature gas, but conventional methods involve applying a low concentration of acid to acid-curing resins, or applying weak acids to shorten the pot life. This method is either a method of curing by increasing the temperature and accelerating the reaction by increasing the temperature, or using a resin containing an organic solvent that is relatively easy to scatter, and curing by scattering the solvent. The curing properties were not sufficient. The present invention is based on a new method in which a salt consisting of a strong acid and a weak base substance is used as a catalyst, and after molding a mold material mixture, the mixture is converted into a strong acid by blowing high-temperature gas and hardened rapidly. The pot life of the mold material mixture is sufficiently long, and the curing properties with high-temperature gas far exceed those of conventional methods. In addition, with large molds, the penetration of high temperature gas may be insufficient, or the temperature may drop while passing through the mold, resulting in poor hardening in some areas. Vent holes are provided in the mold material to suck the air between the sand particles of the mold material, or a vibrator is attached to the model surface plate to apply slight vibrations, creating a fine gap between the model and the mold material mixture while creating a high temperature. Curing properties can be improved by blowing gas. The present invention will be specifically explained below using Examples. [Example 1] 100 g of ammonium hydrogen sulfate and 100 g of water were placed in a container and stirred to prepare a curing catalyst with a concentration of 50%. Next, add 50g of curing catalyst to 10kg of silica sand and make approximately
After mixing for 30 seconds, 100 g of furan resin was added and mixed for 1 minute to obtain a mold material mixture. Here, the mold material mixture is filled into a split mold having three cavities each having a diameter of 50 mm and a height of 50 mm at regular intervals, and air between the mold material mixture is sucked through a vent hole provided at the bottom of the mold. High-temperature air was sucked into the upper part using a hot air blower for about 2 minutes. The strength of the mold obtained here immediately after ventilation and the strength the next day are shown in relation to the elapsed time after preparing the mold material mixture as follows.

[Example 2]

After creating a mold material mixture in the same manner as in Example 1, the model surface plate and casting flask were placed on a vibrating table prepared in advance, and approximately 8 kg of the mold material mixture was poured into the flask and lightly tamped. Thereafter, while applying slight vibrations, the air between the particles of the mold material was sucked through a vent hole attached to the model surface, and the back surface of the mold was heated with a burner for about 2 minutes. Then immediately cut out the mold,
The hardness of the mold surface in contact with the model was measured using a hardness meter. The hardness was over 97, and the inside of the mold was also sufficiently hardened. From this result, it was confirmed that this foundry sand mixture had sufficient hardenability.

Claims (1)

[Claims] 1. A molding material mixture is prepared by adding an acid-curing resin such as a furan resin or a phenolic resin and a salt consisting of a strong acid and a weak basic substance to foundry sand, and after forming a mold,
A mold manufacturing method characterized by rapid hardening by aeration of high-temperature gas. 2. After forming a mold using the above mold material mixture, the air between the mold material particles is sucked through a vent hole attached to the model surface, and the hot gas supplied from the back of the mold is cured by improving ventilation. A method for manufacturing a mold according to scope 1. 3. The method of manufacturing a mold according to claim 1, wherein after molding a mold with the mold material mixture, a model surface plate is slightly vibrated and a high temperature gas is passed through to harden the mold.