JPS5910442A - Material of casting mold - Google Patents

Abstract

PURPOSE:To provide a material of casting mold having considerably improved moisture resistance and shelf life by using magnesium oxide and phosphate as essential binder components and adding a water-soluble polymer thereto. CONSTITUTION:A small amt. of a water-soluble polymer is added and compounded with a material of casting mold consisting of phosphate and magnesium oxide as essential binder components. The water-soluble polymer is carboxymethylcellulose, methyl cellulose, polyethylene glycol, sodium polyacrylate or the like, dissolves at about >=0.2g in each 100g of water at 25 deg.C and has preferably about 1,000-1,000,000 average mol. wt. The water soluble polymer is generally added at 0.05-10pts.wt. based on 100pts.wt. magnesium oxide. The moisture resistance and shelf life of the molding material are thus improved considerably and the deterioration in properties such as expansion in curing and expansion in heating is virtually obviated.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a molding material having magnesium oxide and phosphate as the main binders, and more particularly to said molding material having improved moisture resistance.

Mold materials whose main binders are magnesium oxide and phosphate are used in the lost wax method, which is one of the precision casting methods, and are collectively called phosphate mold materials.

Phosphate mold materials have excellent heat resistance and strength, and cure expansion can be controlled over a wide range by adjusting the concentration of colloidal silica in the slurry.
It is mostly used for precision casting of high melting point non-noble metals such as o-0r.

However, with regard to phosphate molding materials, (1) the quality of the product varies due to moisture in the atmosphere and in the raw material powder during manufacturing; ■
It has the disadvantage of poor storage stability. That is, the presence of moisture subtly affects curing time and dimensional stability. Therefore, when manufacturing phosphate molding materials, the utmost care must be taken to control the moisture content in the raw material powder and the humidity within the manufacturing facility during the rainy season and high temperature periods.

In addition, once the user uses it, the physical properties of the mold material such as curing time and curing expansion change over time, making it impossible to cast with good dimensional accuracy, so storage should be done in the presence of moisture. It had to be stored in a cool, dry place, and it had to be used up as quickly as possible.

As mentioned above, the variation in quality and poor storage stability of phosphate molding materials are caused by the moisture contained in or in contact with the product, and the mechanism for this is shown in equation (2). This is thought to be due to the formation of porium/acid magnesium ammonium hexahydrate due to the reaction of magnesium oxide and phosphate, which are binders, with moisture.

Mg O+ NH4H2P 04 + 5 Tl* O
-+ NHa MgP 04' 6 Ht O---
---Magnesium ammonium phosphate hexahydrate produced by the ■■ formula acts as a seed crystal during curing of the mold material, speeding up curing and reducing curing expansion.

Furthermore, if the water supply is sufficient, most of the binder will be consumed by the reaction of type (2) before use, resulting in extremely slow curing or, in some cases, no curing at all. For example, if a commercially available molding material is opened and exposed to a hot and humid atmosphere, the curing expansion will drop to below the original b within 1 to 2 days. Furthermore, even if the raw material contains moisture during production, the curing time will be shortened and the curing expansion will also be reduced.

In order to overcome these drawbacks of phosphate molding materials, it is necessary to prevent the reaction of type (2) from proceeding during storage. Therefore, during production, (1) $1 raw materials, especially pulverized raw materials that easily absorb moisture, should be stored in a sealed container, and raw materials with a high moisture content should be stored in a sealed container after sufficient drying.

Q) If the humidity inside the manufacturing facility during manufacturing is high, it is necessary to take measures such as dehumidifying or discontinuing manufacturing.

Furthermore, when using the product, once opened, measures must be taken such as storing it in a desiccator containing a desiccant such as silica gel.

However, during production, it requires a large amount of equipment and space to hermetically store, dry, and remove raw materials, which is not economical.

Also, the lateral pressure used is inconvenient, even if it is stored in a desiccator containing a desiccant. Furthermore, it is necessary to take it out of the desiccator each time it is used, and at that time it is exposed to moisture in the atmosphere, and ammonium dihydrogen phosphate, which has strong hygroscopicity, absorbs moisture in the atmosphere and causes the reaction of formula (2). 413 profile gradually deteriorates. To make matters worse, general users rarely actually store the mold material in a desiccator containing a desiccant. At most,
The reality is that it is stored in a well-sealed container with a tightly capped container. Because of this, each time the container is opened, it is exposed to fresh air containing moisture, causing the mold material to deteriorate even more quickly.

The present inventors have conducted intensive research to economically and easily solve the above-mentioned instability of phosphate molding materials during manufacture and use, and have succeeded in obtaining a molding material that is not easily affected by atmospheric humidity. Ta. That is, in the present invention, magnesium oxide, which is a binding material for phosphate template material, is surface-treated with a specific chemical, and
This is a treatment method that prevents deterioration of the mold material due to the reaction of the formula and has good performance as a mold material.

It is generally known that as a means to prevent hygroscopicity of powder, the surface thereof is coated with a hydrophobic substance. Also, as surface treatment methods, methods such as surface functional group reaction and surfactant treatment are known. Surface treatment methods using surface functional group reactions require special equipment and processes. On the other hand, surfactant treatment does not require any special equipment or process and is a method that can be easily carried out using ordinary mixing equipment.

However, when imparting moisture resistance to phosphate molding material through surface treatment, regardless of which method is used, when using a general hydrophobic surface treatment agent, the molding material is slurried with water or an aqueous colloidal silica solution. The surface coating must be removed when Otherwise, the mold material may not cure, may cure significantly more slowly, or exhibit significantly less cure expansion. Further, a situation may occur in which the slurry cannot be mixed uniformly due to an increase in the viscosity of the slurry or the floating of loose materials.

The inventors of the present invention were able to obtain, in particular, the above-mentioned mold material by an extremely simple method, which prevents the mold material from deteriorating due to moisture in the atmosphere. In other words, by adding a small amount of water-soluble polymer to a molding material whose main binder components are phosphate and magnesium oxide, the moisture resistance and storage stability of the molding material are significantly improved, and it is possible to prevent curing expansion, heating expansion, etc. They discovered that the physical properties were hardly impaired.

In other words, by coating magnesium oxide with a water-soluble polymer, the contact reaction between magnesium oxide and phosphate does not occur in the amount of moisture supplied from the air, which causes a decrease in cure expansion. It was discovered that reaction products with acid salts are not produced, and when kneaded with an aqueous colloidal silica solution as a template material, it is easily dissolved and does not inhibit the reaction like hydrophobic polymers do, leading to the completion of the present invention. Ta.

The water-soluble polymer used in the present invention is not particularly limited as long as it is a polymer that dissolves in water, but preferably
A polymer that dissolves 0.2 II or more per polymer is used.

Typical water-soluble polymers that are preferably used include:
Polymers such as cellulose types such as carboxyl methyl cellulose, methyl cellulose, hydroxypropyl cellulose, and hydroxyethyl cellulose, polyVfin glycol types such as polyethylene glycol, polyacrylic types such as polyvinyl alcohol types, polysodium acrylate, and polyvinyl pyrrolidone types. be.

The average molecular weight range of these water-soluble polymers is not particularly limited as long as it has sufficient physical properties to be used as a template material, but is generally preferably from 1,000 to 1,000,000. If the molecular weight is too low, the coating effect will be poor; if the molecular weight is too high, it will be difficult to uniformly coat the powder surface.

A feature of the present invention is that moisture resistance is primarily imparted to phosphate-based molding materials by adding a small amount of water-soluble polymer. That is, the weight of the water-soluble polymer to be added varies depending on the amount of magnecrum oxide and the type of water-soluble polymer, but generally 0.05 to 10 parts by weight, particularly 0.1 to 21 parts by weight, per 100 parts by weight of magnesium oxide is sufficient. It has a great effect. If the amount of water-soluble polymer added is too small, it will not be possible to impart sufficient moisture resistance to the mold material, and if it is too large, it will be economically disadvantageous and at the same time, the strength of the mold material before firing will decrease. This is not desirable because it causes problems.

In the present invention, the water-soluble polymer is added according to various known methods related to powder surface treatment techniques.

For example, a method in which a water-soluble polymer is dissolved in an appropriate solvent such as water or methanol in advance, magnesium oxide is added and mixed therein, and the solvent is then removed; a water-soluble polymer and magnesium oxide are simultaneously ground and oxidized. A method of coating the surface of magnesium with fine polymer powder can be suitably employed.

The present invention provides a molding material with good moisture resistance and storage stability in a simple manner and at low cost by simply adding and blending a small amount of water-soluble polymer to a conventional phosphate molding material.

The present invention will be described in more detail with reference to Examples below, but the present invention is not limited thereto.

In the examples, "before aeration" means immediately after the mold material is manufactured, and "after aeration" means that the mold material 200I was heated to 30cIIL×20
It means after being spread on a vat of α and left in an atmosphere of 20° C. and relative humidity of 85° C. for 13 hours. The curing expansion was measured in the following manner. The molding material is kneaded with 20 g of colloidal silica liquid, and the kneaded material is poured into the mold shown in J Engineering's T66o4 (method for measuring curing expansion of calcined gypsum). Immediately after curing, the restraint was removed, and the amount of expansion after 2 hours was measured using a dial gauge.

For curing, use a Vicat needle (load xooI! Needle cross-sectional area 1W2)
) was determined as the point at which one part of the mixture entered the kneaded product.

Comparative example 1 A mold material was prepared using the following ingredients.

0 When the above mold material is kneaded with colloidal silica liquid, the curing expansion coefficient before aeration and the curing time are 1.20 cm and 1.0 cm, respectively.
3 minutes, the curing expansion coefficient after aeration and the curing time were o, respectively.
o8%, 8 minutes.

Examples 1 to 3 Magnesium oxide was added to a methanol solution of hydroxypropylcellulose, and the solvent was evaporated while stirring to obtain magnesium oxide coated with hydroxypropylcellulose.

Various molding materials were prepared with the same composition as in Comparative Example 1 using magnesium oxide coated with 0.1, 0.5, 1.0 parts by weight and 1' parts of magnesium oxide on hydroxypropyl cellulose.

The results of these changes in curing expansion are shown in Table 101 Table 1 Examples 4 to 8 In place of the hydroxypropyl cellulose in the previous example, the following water-soluble polymer was used at a ratio of 0.5 to magnesium oxide. The curing expansion was measured using the same composition as Comparative Example 1 by adding parts by weight. The results are shown in Table 2.

2 6 Example 9 Polyethylene glycol (MY
2000) was added thereto, and the mixture was pulverized and mixed using a pulverizer for 2 hours. Using the magnesium oxide surface-treated with the composition of Comparative Example 1, changes in curing expansion over time were investigated. The curing expansion rates before and after aeration were 1.2 inches and 0.5%, respectively, and the curing times were 15 minutes and 15 minutes 60 seconds, respectively.

Comparative Example 2.3 Polystyrene solution in benzene Magnesium dioxide was added and benzene was evaporated to obtain magnesium oxide coated with polystyrene. Measurements were made using the same composition as in Comparative Example 1.

A similar operation was also carried out for polymethyl methacrylate.

The results obtained are shown in Table 6.

4

Claims (2)

[Claims] (1) A molding material whose main binder components are magnesium oxide and phosphate, and a water-soluble polymer added thereto. (2) The water-soluble polymer is a type of polymer selected from the group consisting of 7 types (cellulose, polyacrylic, polyvinyl alcohol, polyolefin glycol, polyvinyl pylori). 1)
The amount of water-soluble polymer added in the mold material described in Section (5) is
0.05 to 10 per 100 parts by weight of magnesium oxide
The mold material according to claim (1), which is in parts by weight.