JPH0437436A - Method for adjusting curing time of inorganic self-curing molding sand - Google Patents

Abstract

PURPOSE:To enable adjustment of curing time in a mold and to easily and efficiently execute molding work in any season by specifying containing composition. CONSTITUTION:This composition is that containing refractory particles of silica sand, etc., sodium silicate as inorganic binder, propylene carbonate as curing agent and 1,2 butanediol, diacetate or ethylene carbonate as curing adjustor. As carbonic acid gas (H2CO3) generated in inner part of the mold is reacted with the sodium silicate at 100%, the firm mold is obtd. with little quantities of the propylene carbonate and the 1,2 butanediol diacetate or the ethylene carbonate and the adjustment of curing time can be freely executed even under surroundings having different temp. and fluidity of blending sand is good and packing density of the mold is high and casting product having high dimensional accuracy is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for adjusting the curing time of a foundry sand composition. More specifically, the present invention relates to a molding sand composition useful in the production of casting molds, and in particular to a method for controlling the hardening time of self-hardening molding sand for casting of cast steel, cast iron, and other non-ferrous metals.

[Prior Art] As a conventional hardening method for inorganic self-hardening molding sand, a hardening agent is appropriately added to silica sand, which is a product of the mold, and the molding sand is hardened by a chemical reaction caused by the hardening agent. Alternatively, there is a method of hardening inorganic self-hardening molding sand, such as a method of hardening molding sand using carbon dioxide instead of the hardening agent. Also, Tokuko No. 52-102825 or Tokuko No. 52-102825
There is a mold composition as shown in Japanese Patent No. 3-108826.

[Problems to be Solved by the Invention] However, in the curing method using the above-mentioned curing agent or carbon dioxide gas, or the curing method shown in the above-mentioned publications, the curing speed of the molding sand is dependent on the surface and internal parts of the mold. There is a difference in the curing speed between the molds, and especially in the case of large molds, the difference in the curing speed is large and there is a problem that it is difficult to judge the curing. In addition, the compositions described in the above publications may be difficult to prepare, the resulting compositions may have a short lifespan, or they may have a long lifespan. However, there was a problem in that it took a long time to obtain a mold with the required compressive strength.

Furthermore, although it is basic to harden the mold using the above-mentioned mold hardening means, it may be necessary to slow down the hardening speed depending on changes in temperature depending on the season, the size of the mold, or changes in productivity, etc. However, with conventional mold curing methods, it has been impossible to adjust the curing speed. In addition, the conventional carbon dioxide method, which hardens by passing CO□ gas through a sodium silicate mold, passes CO2 gas from the outside.
A sufficient cured state cannot be obtained unless the amount of C02 gas required for curing is equal to or more than twice the amount of sodium silicate blended. Therefore, there was a drawback that the casting cost was high.

[Means for Solving the Problems] The present invention has been made by focusing on the problems and drawbacks of the above-mentioned conventional examples, and consists of refractory particles such as silica sand, sodium silicate which is an inorganic binder, and a hardening agent. The composition containing propylene carbonate and the curing regulator 1.2 butanediol diacetate or ethylene carbonate makes it easy to control the curing time of the molding sand, and also allows the entire mold to be uniformly cured and hardened. The object of the present invention is to make it possible to manufacture a sound mold with good dimensional accuracy.

That is, unlike the conventional CO2 method, the present invention does not use CO2 gas or related equipment, and allows the curing time to be easily adjusted when producing a sodium silicate inorganic mold.

This adjustment is presumed to be due to the fact that 1,2-butanediol diacetate and ethylene carbonate change the rate of carbon dioxide gas generation. Because of this effect, a composition containing propylene carbonate and a hardening modifier, 1.2-butanediol diacetate or ethylene carbonate, works effectively for hardening self-hardening molding sand.

In other words, the basic curing reaction formula of the mold involved in the present invention is estimated to be as follows.

Propylene carbonate Na carbonate, O・n5i02+H2c03→Na2CO3+n
It is thought that a silicate gel is generated by the chemical reaction between SiO2+)120 sodium silicate and carbonic acid, and this gel firmly binds the sand particles.

Therefore, according to this invention, carbon dioxide gas generated inside the mold
()12cO3) reacts 100% with sodium silicate, so a strong mold can be obtained with a small amount of propylene carbonate and 1.2-butanediol diacetate or ethylene carbonate, and the curing time can be adjusted even in environments with different temperatures. It can be formed freely, the mixed sand has good fluidity, the mold has a high packing density, and a cast product with high dimensional accuracy can be obtained.

[Example] Examples of the present invention will be described below.

The test method was to change the molar ratio of sodium silicate and Baume to 100 silica sand (nearly 100 mesh), and to adjust the curing time to the blended amount, propylene carbonate, 1,2 butanediol diacetate, and ethylene carbonate were added. The added and adjusted mixed sand was kneaded for 2 minutes in a Simpson type mill to prepare a test material. The test material was collected at a specified time and was rammed for 50 m using a rammer for making standard test pieces of foundry sand.
mφx 50 mol! The mold properties such as compressive strength and air permeability were measured at specified times.

The formulations and test results of the experimental examples are shown in Tables 1 to 5.

That is, when mixing 4 wt% of propylene carbonate Q and 5 wt% of sodium silicate to 100 wt% of silica sand, the molar ratio of sodium silicate was varied from 2.0 to 27, and the Baume value was varied from 47 to 52. Changes in curing time and compressive strength as shown in 1 were obtained.

[-Food table wt% Silica sand (around 100 mesh) Propylene carbonate (pc) 0.4 The above example shows the molar ratio of sodium silicate and Baume to be blended into a mixture of 100 wt% silica sand and 0.4 wt% propylene carbonate. In this experiment, it was possible to adjust the curing time of the mold by changing it appropriately, but it is also possible to adjust the curing time of the mold by changing the amount of the propylene carbonate, which is the curing agent. . The results of this experiment are shown in Tables 2 and 3.

In other words, Table 2 shows that the molar ratio is 2.3 with respect to 100 wt% of silica sand.
The amount of propylene carbonate added to a mixture containing 5 wt% of sodium silicate with a Baume value of 50 is 0.
1-1. Table 3 shows the measurement of the curing time of the mold when the temperature was changed to 100 wt% of silica sand, and 5 wt% of sodium silicate having a molar ratio of 2.7 and a Baume value of 47 to 100 wt% of silica sand.
The amount of propylene carbonate mixed and added to the formulation is 0.1 to 1. This is a measurement of the curing time of the mold when changing the Owt%.

Sodium silicate (mole ratio 2.3, Baume 50) Propylene carbonate (PC) wt% 0.1-1.0 Table sludge - Edible silica sand Sodium silicate (mole ratio 2.7) , Baume 47) Propylene carbonate (pc) wt% C, 1 to 1.0 From the experiments shown in Tables 1 to 3 above, the molar ratio of sodium silicate and Baume may be changed, or propylene carbonate (p
The curing time can also be changed by changing the amount of c).

However, it was observed that the properties of the mold changed. An example will be described in which the curing time is adjusted by further adding a curing accelerator or curing retarder to the 0.2 carbonate formulation.

For example, during seasons with low temperatures such as winter, the hardening time of the mold is delayed, resulting in a decrease in productivity. In this case, therefore, ethylene carbonate is used as an additive to accelerate the curing time of the mold. In the experimental data shown in Table 4, the amount of ethylene carbonate blended was in the range of 0.05 to 0.2 wt% relative to 100 wt% of sodium silicate.

In practical terms, the curing accelerator composition is 0.02wt%.
As mentioned above, from an economic point of view, 002~0.12w
It is desirable that it is t%. Moreover, if it is less than 0.02 wt%, the effect of accelerating hardening is small and the strength of the mold is also reduced.

Next, during seasons with high temperatures such as summer, molding sand hardens quickly, making it difficult to mold the mold.In this case, additives are added to delay the hardening time of molding sand. According to the experimental data shown in Table 5 using 1.2 butanediol diacetate as the
The blending amount of butanediol diacetate was 100wt of silica sand.
% to 0.05 to 0.2 wt%.

Table 5: Weight% of weight Cure delay sound 1 (1,2-butanediol diayatate) 005-0.2 As a result, in practical terms, in relation to mold strength, the blend is 0.04wt% or more, but
Even if 0.2 wt% or more is added, there is no significant change, which is also a disadvantage from an economic standpoint.

Moreover, no significant effect is observed at 0.04 wt% or less. 0.005 to 0.1 wt% is practically sufficient.

[Effects of the Invention] As is clear from each of the above examples, the present invention provides a method of changing the molar ratio or Baume of sodium silicate added to a mixture containing silica sand as a main component for making a mold, or By selectively adding an appropriate amount of a curing retardant or curing accelerator to the silica sand-based formulation, the curing time of the mold can be adjusted, making it possible to easily and easily perform mold making operations, for example, throughout the year. The effect is that it can be done efficiently. Furthermore, since the mold obtained by the present invention has high air permeability, it absorbs less moisture during storage, and therefore the amount of gas generated during casting using this mold is small, so that the gas of the cast product is reduced. It has the advantage of being able to significantly reduce defects.

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Claims (1)

[Scope of Claims] 1. An inorganic material containing refractory particles such as silica sand, sodium silicate as an inorganic binder, propylene carbonate as a hardening agent, and 1,2-butanediol diacetate as a hardening regulator. How to adjust the hardening time of self-hardening molding sand. 2. A method for adjusting the hardening time of inorganic self-hardening molding sand containing refractory particles such as silica sand, sodium silicate as an inorganic binder, propylene carbonate as a hardening agent, and ethylene carbonate as a hardening regulator.