JPS5844944A - Casting sand - Google Patents

Abstract

PURPOSE:To decrease residual compressive strength and burning by coating water glass on the surfaces of refractory aggregate or adding an org. binder to old sand of water glass base and mixing both materials. CONSTITUTION:Molding sand prepd. by coating water glass on the surfaces of refractory aggregate (silica sand, zircon sand, chromite sand) or using old sand of water glass base as aggregate, adding an org. binder (phenolic resin, alkyd resin) which cures even with alkalinity to said sand and mixing both materials. Such molding sand has low residual compressive strength and causes less burning, thus preventing casting defects such as high temp. cracking of castings.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides foundry sand using conventional water glass as a caking agent, and 7
Advantages of foundry sand using organic binder such as orchid resin
This relates to foundry sand that remains as it is and eliminates its respective drawbacks.

Cast steel and large cast iron molds use silica sand as aggregate (refractory material).
Zircon sand, chromite sand, etc. are used, and water glass is often used as a caking agent, but recently 7-run resin has been increasingly used.

Molds using these binders have the following drawbacks.

(1) Foundry sand using water glass as a caking agent has poor fluidity (high viscosity) and takes a long time to overflow during casting.

(2) Molds made with foundry sand that uses water glass as a caking agent are sintered by the water glass and aggregate due to the heat during casting, resulting in poor mold disintegration and reducing the number of sand removal steps required for P castings. To increase.

(3) Ancient material recovered from molds using water glass as a binding agent? (Water glass old sand) Fi, because it is difficult to recycle,
When used again, the fire resistance decreases due to the water glass remaining on the surface of the aggregate and the newly added water glass, making it impossible to use it as core or skin sand.

(4) Foundry sand that uses 7-run resin as a caking agent has a large thermal expansion, and its compressibility (cushioning properties) in the high temperature range is tk%A.
As a result, casting defects such as paning, adhesion, and hot cracking of the casting occur.

On the other hand, the above casting? (Cast 11) has the following advantages.

(1) Foundry sand that uses water glass as a caking agent is compressible (flexible) in a high temperature range and has few casting defects such as veining and hot cracking.

(2) Foundry sand using furan resin as a caking agent has good fluidity and requires less molding time.

(3) Molds using 7-run resin as a binder have good collapsibility and require less man-hours for removing sand from castings. It is easy to process and the foundry sand can be used repeatedly.

As described above, the binder for molds for cast steel and large cast iron is gradually shifting from water glass to furan resin due to the moldability of foundry sand and the ease of reusing old sand. However, molding sand using 7-run resin as a binder is not compressible at high temperatures, and the expansion of the aggregate acts directly on the casting. In the case of i, casting defects such as hot cracking caused by the solidification shrinkage of the casting being restricted by the expansion of the mold occur more frequently than in those using water glass as the caking agent.

Many attempts have been made to solve these problems, such as: (1) reducing the high-temperature strength of the mold by minimizing the amount of binder added; (2) wood flour. A method of adding medium polystyrene-based polymer powder and making it disappear in the heat during casting to give the mold flexibility. There are methods such as using aggregate to soften and melt the aggregate to make it compressible.

However, even with this method, in the case of (1), there is a limit of R for reducing the addition amount in terms of room temperature strength.
In the case of (2), the amount of caking agent added is t% due to the increase in powder.
In the case of (3), there is a problem in that low-grade sand accumulates due to repeated use through recycling, reducing the overall fire resistance.

Therefore, currently, chromite sand with low expansion and zircon sand are used as a measure to prevent molding, paning, and adhesion.However, the cost of sand is high, and recycled sand is The problem is that the effects of accumulation are unknown.

In view of the above points, the present invention has been developed to improve the shrinkability and properties of water glass 6 at high temperatures while maintaining the fluidity of foundry sand, the collapsibility of molds, and the ease of recycling that are unique to organic binders. Take advantage of
The present invention provides a foundry sand that eliminates the panning, phosphorus layer, and hot cracking of castings found in the above-mentioned Fran sand.

In other words, the present invention provides coating sand by adhering water glass to the surface of refractory aggregate such as silica sand, chromite sand, and Jirune sand to impart shrinkability, and coating sand or water glass-based old sand. The present invention relates to foundry sand made by adding and kneading an organic binder that hardens even in alkali as an aggregate.

The foundry sand of the present invention is made by first adding and mixing water glass to the above-mentioned ordinary fire-resistant aggregate to form a coating sand. In this case, the amount of water glass added is less than 1% by weight. The desired mold shrinkability of the present invention cannot be obtained, and if the weight exceeds 10 weight it, the fire resistance of the mold decreases and mold defects such as a phosphorus layer occur, so it is recommended to set the amount to 1 to 10 weight %. preferable.

In addition, in the present invention, water glass-based old sand can be used as a substitute for the above-mentioned coating sand.

In the next step, the above-mentioned O-coating sand or old water glass sand (hereinafter referred to as ;-ting sand) can be used as the organic binder to be mixed with K, such as ordinary phenolic resin, alkyd resin, etc. Water glass that can be hardened even in alkali can be used, and the amount of O added depends on the properties of the sand (particle size distribution,
Particle shape % P1'% (temperature, specific gravity) and temperature change, but if there is too little, the required strength of the casting will not be obtained, and if there is too much, it will result in excessive strength and various types of Because glass defects occur, it is usually O,S~2.0wt.
It is preferable that

In addition, the foundry sand of the present invention may be mixed with ordinary hardening agents and accelerators in dry amounts.

Hereinafter, the functions and effects of the foundry sand of the present invention will be specifically explained using Example t.

Example 1 Among the above formulations, first, after kneading silica sand and water glass, 1
The sand was dried at 05.+-.5.degree. C. to obtain water glass sand, a phenol resin composition was kneaded into the sand, and a mixture of a polyisocyanate composition and a pyridine derivative composition was added and mixed. The obtained foundry sand is referred to as foundry sand 1.

Example 2 The cross-wire method for the above formulation was the same as in Example 1. The obtained casting is referred to as casting Tip 2.

In addition to the above foundry sands 1 and 2, for comparison, foundry sand with silica sand (new sand) T-aggregate and water glass as caking agent (comparison #
! 1) and foundry sand (comparatively designated 2) using silica sand (new sand) as an aggregate and a 7-run resin caking agent. Using these foundry sand 1.2 and comparative sand 1,2 and pipe 11×
A 2-inch I11 test piece (cast m>) and a second test piece (cast m)' of a 50φ plate 5ON- were prepared, and the expansion characteristics and collapsibility were examined.

(1) Expansion characteristics: The above lit test piece was inserted into a furnace at 1150° C. (inner atmosphere), and the sound of rapid thermal expansion over time was measured. The result is the first
It was the same as shown in the figure.

In the mosquito diagram, 1 indicates the measurement results of comparative sand 1, 2 indicates the measurement results of comparative sand 2, and 5 indicates the measurement results of casting #1 according to the present invention.

It should be noted that almost the same results as foundry sand 1 were obtained with foundry sand 2 according to the present invention.

As is clear from FIG. 1, in the case of comparative sand 1 using water glass as a caking agent, the mold expands due to the expansion of the aggregate at the initial stage of heating, but when the water glass softens, the mold contracts. Therefore, when casting using a mold made of Comparative Sand 1, the shrinkage of the mold during the softening of water glass absorbs the partial expansion of the mold and the solidification shrinkage of the casting, thereby preventing casting defects such as peninda and hot cracking. It is to prevent it.

On the other hand, in the case of Hishoku Sand 2, which uses 7-run resin as a binder, as is clear from Figure 811, it expands in the same way as Comparative Sand 1 at the initial stage of heating, but continues to expand after that, albeit slowly. . Therefore, when casting is performed using the casting m made of Comparative Sand 2, hot cracking occurs due to cracking of the mold → vening, penetration of molten metal, or restraint of solidification shrinkage of the casting.

On the other hand, in the case of the foundry sand 1 according to the present invention, as is clear from Fig. 1, it exhibits the same tendency of expansion and contraction as the comparative sand 1.

As shown schematically in Figure 45 (6) (state at room temperature) @ (state after heating), the water glass 12 coated on the surface of the aggregate 150 is softened by heating, and the aggregate 1s is This is by absorbing expansion. Therefore, in the case of casting with a mold using the foundry sand according to the present invention, no casting defects due to high temperature cracking occur, similar to Comparative Sand 1 using water glass as a caking agent. Note that 11 in Figure 3 (4) is an organic binder! 11' in 51E103) represents the carbide.

(2) Collapsibility 2 The above second test piece was wrapped in aluminum foil and inserted into a furnace kept at a predetermined temperature, heated for 1 hour, then cooled in the furnace and the residual compressive strength was measured. The results were as shown in Figure 2. In FIG. 2, 1 indicates the results for comparative sand 1, 2#'i for comparative sand 2, and 5 for foundry sand 2 according to the present invention. Note that the same results as foundry sand 2 were obtained with foundry sand 1 according to the present invention.

The lower the residual compressive strength, the better the disintegration property.

As is clear from Figure 2, in the case of comparative sand 1, 800~
When heated to 1000°C, the water glass softens and sinters the aggregate, increasing the residual compressive strength, which causes poor collapsibility, whereas Comparative Sand 2 was heated to over 800°C. If this happens, the resin will carbonize and lose its strength, which will cause the disintegration to be good.

On the other hand, in the case of the foundry sand 2 according to the present invention, as is clear from FIG.
It has low residual compressive strength at temperatures above 00°C and has good disintegration properties. This can be explained using the schematic diagram in FIG. 5 (4), 03). Even if the water glass 12 on the surface of the aggregate 1s is softened and melted at high temperature, the residual carbide 11 of the surrounding KN mechanical caking material 11 remains.
It is presumed that this is because sintering of the aggregate 1s is hindered because of the presence of .

As explained above, according to the foundry sand of the present invention, (1)
Using an organic binder, the mold is made of water glass (
By imparting cushioning properties], casting defects such as hot cracking of parts and castings caused by panning and vaning can be prevented without impairing collapsibility. Similar effects can be obtained by using water-class old sand as a substitute for the contacting aggregate, and old sand can also be used as a core, whereas until now only the back sand could be used. .

The effect of 1m can be achieved.

[Brief explanation of drawings]

$1111 is a chart showing the actual measured value of the change in rapid thermal expansion of the mold with each molding sand over time, Wl, Figure 2 is the actual measured value of the residual compressive strength when the mold with each molding sand is heated at each temperature and then cooled in the furnace. Table 3 shows the structure of the foundry sand of the present invention, and (6) shows the state at room temperature and (6) shows the state after heating. 11. Rijin Ryo Hagiwara - Spear 1 Illustration Kagou Tokimuki (Sword

Claims (1)

[Claims] Coated sand with water glass coated on the surface of refractory aggregate, or foundry sand made by mixing old water glass sand with an organic caking agent added.゛