JPS5842772B2 - Mold manufacturing method - Google Patents

Description

Detailed Description of the Invention The present invention uses a fire-resistant granular material such as silica sand mixed with a polyvinyl alcohol aqueous solution or a polyvinyl alcohol aqueous solution partially depolymerized with an oxidizing agent, and a gallic acid compound. , relates to a method for rapidly manufacturing a mold at room temperature using a basic gas.

Today, in the manufacture of molds, room temperature and heating methods are used, but curing molds at room temperature has great significance in reducing energy costs required for curing and improving the environment.

Molding methods that belong to room temperature curing can be roughly divided into those that rely on self-curing of a binder system and those that rely on dregs curing.

Among these, there are those that are based on self-hardening of binders, which use sodium silicate, cement, aluminum phosphate, and furan-based resin as binders, and are hardened at room temperature by adding a hardening agent. Also, the curing speed of the mold is slow,
Furthermore, since the mold material mixture undergoes a gradual curing reaction even at room temperature, its pot life is generally short, ranging from several minutes to several tens of minutes.

The CO2 process is a molding method that quickly hardens at room temperature.
There is an aeration method represented by the isocure method.

These molds can be quickly manufactured by filling a mold material mixture consisting of sand and a binder into a model and then passing a gas through which the binder hardens.

However, various problems also exist in such a ventilation molding method.

CO2 uses sodium silicate as a binder and hardens with CO2.
Although this process has many advantages, such as a cheap binder, rapid molding, and little contamination of the working environment, it has a major drawback in that it is difficult to remove sand after pouring.

On the other hand, the isocure method uses carbonic acid resin and isocyanate as a binder, and hardens the mold by passing a tertiary amine and air or nitrogen gas as a mixed gas or mist. The reaction limits the pot life of the sand mixture.

Furthermore, organic solvents used as binder solvents pose problems in terms of environmental pollution.

The present invention relates to a method for molding a mold material mixture that has a long pot life, hardens quickly at room temperature, has good disintegration properties after pouring, and causes less environmental pollution.

That is, the present invention basically relates to a method for quickly molding a mold by passing a basic gas through a molding material mixture using an aqueous polyvinyl alcohol solution as a binder and a halogen compound as a hardening accelerator.

The present invention will be explained in detail below.

The binder used in the present invention is basically obtained by dissolving polyvinyl alcohol in water.

As for the degree of polymerization of the polyvinyl alcohol used here, commercially available polyvinyl alcohols having a degree of polymerization of 300 to 2,400 can be used, but those having a degree of polymerization of about 300 to 700 are preferable.

When polyvinyl alcohol with a polymerization degree of 1,700 to 2,400 is used, the viscosity of the polyvinyl alcohol aqueous solution becomes high, making it difficult to uniformly coat the surface of the sand grains, resulting in a decrease in mold strength due to poor coating and poor starting.

If a large amount of water is added to lower the viscosity of a polyvinyl alcohol aqueous solution with a high degree of polymerization to make it have a viscosity of 200 to 300 cp at room temperature, uniform coating on the sand particle surface can be achieved, but the moisture in the mold material mixture increases. As a result, curing becomes slow and initial strength becomes weak.

If polyvinyl alcohol with a degree of polymerization of 300 or less is used, the concentration of the polyvinyl alcohol aqueous solution can be increased to 50% or more, making it possible to shorten the time required for curing, but the strength of the mold obtained in this case will be slightly lower. Not enough.

Regarding polyvinyl alcohol, it is also necessary to consider its degree of saponification.

Whether the degree of saponification of polyvinyl alcohol is high or low, its solubility in water becomes poor and the viscosity of the aqueous solution becomes high.

Therefore, in order to increase the solution concentration and harden the mold in a short time, it is desirable to use polyvinyl alcohol with a saponification degree of about 88 mol%.

In order to obtain a polyvinyl alcohol aqueous solution with high concentration, low viscosity, and good viscosity stability using commercially available polyvinyl alcohol, it is useful to partially depolymerize polyvinyl alcohol with an oxidizing agent, for example. .

Through this treatment, partial depolymerization occurs in the polyvinyl alcohol macromolecules, short circuits are formed, and aldehyde, carboxyl, ketone groups, etc. are generated within the polyvinyl alcohol molecules.

These are larger than hydroxyl groups and, due to their steric hindrance, prevent the formation of macromolecular aggregation points.

Therefore, even a highly concentrated aqueous solution of polyvinyl alcohol can maintain a low viscosity for a long time.

As the oxidizing agent used here, general oxidizing agents such as oxygen, ozone, hydrogen peroxide, potassium nitrate, sulfuric acid, potassium dichromate, potassium permanganate, potassium chlorate, and vegetable powder can be used, but peroxide An aqueous solution of hydrogen is convenient to handle.

As gelling agents for polyvinyl alcohol, boric acid compounds such as boric acid and silt are known.

Or, gelatinization can be achieved with a very small amount of sand compared to boric acid.

We have discovered that even when the amount of boric acid compound added is not enough to gel polyvinyl alcohol, adding a basic substance will quickly gel it, and in the present invention, we utilized this principle in molding the mold.

Although the amount of the boric acid compound to be added is not uniformly discussed, if it is limited to boric acid, the mold can be hardened by the method of the present invention if it is present in an amount of 1% based on polyvinyl alcohol.

However, it is preferably present at 5-20% for more rapid curing.

If 20% or more of fluoric acid is present, the fluidity of the mold material mixture deteriorates, and deterioration of mold strength due to poor compaction becomes unavoidable.

The basic substance used in the present invention needs to be easily vaporized, and from this point of view, ammonia, primary, secondary, and tertiary amines are preferable, and specifically ammonia, aqueous ammonia, ethylamine, diethylamine, and triethylamine. , tertiary-butylamine, isoprobylamine, etc. Among amines, tertiary amines are particularly desirable from the viewpoint of industrial hygiene.

Practically speaking, ammonia and triethylamine are most suitable.

These basic substances are applied as a gas mixture with air or nitrogen gas, or as a mist.

The mold produced by the method of the present invention shows an increase in strength by leaving it for a long time after being released from the mold.
High strength can be quickly obtained by drying by microwave heating or the like.

Furthermore, there is no problem in adding additives that are generally incorporated into mold material mixtures, such as coal powder and iron oxide, into the mold material mixture used in the method of the present invention.

The blending ratio of the binder and the refractory granules in the present invention may be the same as in the conventional Isocur method, with the binder being 0.5 to
A range of 5% by weight is practical.

If it is less than 0.5%, sufficient strength cannot be obtained, and if it exceeds 5%, the number of pores necessary for ventilation will decrease, which is unsuitable.

The present invention will be specifically explained below using Examples.

〔Example〕

Polyvinyl alcohol with a degree of polymerization of 300 to 700 and a degree of saponification of 88 mol% (trade name Kuraray Boval PVA205) 2
00g was placed in a Mitsuro flask equipped with a reflux device along with 800 yd of water, and stirring was continued at 95°C until the polyvinyl alcohol was completely dissolved.The viscosity at 20°C was 51.
A 5 cp polyvinyl alcohol aqueous solution was obtained.

Kawamura Silica Sand No. 6 10, in which 1000 g of the aqueous solution obtained here was preliminarily dispersed with Log fine powder boric acid,
kg, mixed for 1 minute with a laboratory speed maller,
The resulting mold material mixture was 11//8 inches in diameter and 2
It was molded into an inch cylindrical shape, and then various gases shown in the table below were bubbled through it for 20 seconds.

The strength of the mold obtained here immediately after ventilation was as follows.

From the above results, it is confirmed that curing occurs with basic gas.

Next, polyvinyl alcohol with a degree of polymerization of 300 to 7001 and a degree of saponification of 88 mol% (trade name: Kuraray Boval PVA20
5) 300 g of the solution was placed in a 35% aqueous hydrogen peroxide solution together with 6851 rL of water in a Mitsuro flask equipped with a reflux device, and the mixture was stirred at 95° C. for 6 hours to partially depolymerize the polyvinyl alcohol.

667 g of this aqueous solution was added to 10 kg of Kawamura Silica Sand No. 6, in which various finely powdered acrylic acid compounds had been dispersed in the scenery shown in the table below, and mixed for 1 minute with an experimental speed maller to form a mold material mixture. Obtained.

The resulting mold material mixture was molded into a cylindrical shape with a diameter of 8 inches and a height of 2 inches, and then a triethylamine-air mixture gas was passed through the mold for 20 seconds to obtain a mold.

The strength of the mold obtained here immediately after ventilation was as follows.

This result confirms the necessity of a boric acid compound for curing.

As described in detail above, it has been found that when a basic gas is passed through a binder made by adding a boric acid compound to polyvinyl alcohol, it exhibits a desirable curing as a mold material.

It is presumed that this is because polyvinyl alcohol and the boric acid compound form a Didiol-type bond due to the presence of a basic substance.

Next, using the samples of Examples 1 to 4, one day and night (24 hours)
The coercive pressures of those left standing and those heated and dried using microwaves were measured, and the results were as follows.

As is clear from this table, the mold made by the present invention has sufficient strength, and the disintegration properties after pouring are almost the same as those made by the conventional isocure method.
Moreover, unlike the isocure method, it is not necessary to use an organic solvent, which is a great practical effect.

Claims (1)

[Claims] 1. A mold is made using a molding material mixture containing fire-resistant granules, a polyvinyl alcohol aqueous solution or a partially depolymerized polyvinyl alcohol aqueous solution, and a oxalic acid compound, and a basic gas is bubbled through the mold. A mold manufacturing method characterized by hardening.