KR840000602B1 - Production of metal casting sand moulds - Google Patents

Abstract

Lining pads which support the surface of a sand metalcasting mold produce a mold(2) cavity of a desired shape and dimension. They are formed of compsn. comprising; particulate refractory material, fibrous refractory material, finely divided Al, oxidizer for the Al, and a binder. The compsn. is free of fluoride and has a density of 0.3-1.1 g/cc. The pads (a) are provided at those parts of the mold where is desired a progressive directional solidification in the casting (1). The pads are used in casting shapes having heavy sections isolated from the metal feed, e.g. gear wheel blanks, valve bodies and bonnets.

Description

Manufacturing method of sand casting for metal casting

1 is a cross-sectional view of a mold by a known method for producing a steel casting.

2 is a cross-sectional view of a mold illustrating the metal padding used in a conventional steel casting factory.

3 is a cross-sectional view of a mold illustrating another conventional method using metal padding.

4 is a view showing an example using preformed and dried pad according to the present invention.

5 illustrates an example of the use of a pad made of a moldable mixture according to the present invention.

The present invention relates to a method for producing a metal casting sand mold, and more particularly to a method for manufacturing a steel casting sand mold.

To produce sound castings made of metal or alloy, the metal in the hot water spout must solidify at least simultaneously or after the last part of the casting solidify, and the passage of liquid metal from the hot water spout to all parts of the casting. It should be made to prepare for the shrinkage that occurs when the metal or alloy solution solidifies. Therefore, it is necessary to manufacture a sound casting so as to form a directional solidification gradually from the point farthest from the hot water supply hole toward the hot water supply hole by configuring the hot water inlet as the last part of the solidification casting. Unfortunately, the shape required by many castings is that directional solidification does not occur unless the design is changed. As a result, it is necessary to change the shape required for many steel castings and supply metal to each part of the casting which is far from the hot water. In general, this change causes the metal in each part of the casting to concentrate, resulting in premature solidification and shrinkage in the hot part. Changing the casting shape by adding extra metal is called metal padding.

Types of castings that are padded with metal to avoid internal shrinkage include cogwheel blanks, valve bodies and valve bonnets, H-arm wheels, idler wheels and pistons. , Rolls and turbine castings. There is a heavier weight apart from the metal source in the basic shape for these castings. Therefore, metal pads are placed to promote directional solidification throughout the casting.

In order to regain the original casting shape, the metal padding must be removed after the casting and the hot water spout has solidified. Removing the metal pad involves one or more of the following tasks: In other words, the work of spark cutting, sawing, polishing and machining is interposed. This work is time consuming, costly, and causes many difficulties in casting production. Therefore, removing the padding itself is uneconomical and the metal padding involves the additional melting of a larger amount of metal than is required for the metal casting itself.

Instead of metal pads, pads made of exothermic composition, which are placed in the mold space of the proper position and come into contact with molten metal to supply enough heat to ignite to prevent premature solidification of each part of the casting, thereby promoting the required directional solidification. To some degree of directional solidification. Aluminum-based exothermic compositions that have been used for this purpose are known and are described in British Patents 971,749 and 808,400, for example. These are generally one or more oxidizing agents for aluminum, such as nitrates or perchlorates of fine aluminum powders, alkali metals or alkaline earth metals, iron or manganese oxides, fluorides such as calcium fluoride or aluminum fluoride sodium, which can initiate and control exothermic reactions, sand, alumina One or more refractory filler powders such as grongs, chamottes or other refractory silicates and points such as starch, dextrins, alkali sulfites, gum arabic resins (e.g. phenol formaldehyde resins), sodium silicates, clays It consists of more than one payment. The amount of oxidant is usually such that the stoichiometric amount is insufficient to oxidize all the aluminum present.

If the pad made of such a pyrogenic composition is used correctly, even if gradual directional solidification is promoted, various problems are newly raised in use. Since the exothermic reaction releases the gas from the exothermic composition, the gas must be exhausted into the atmosphere to avoid defects due to porosity such as bubbles or pinholes in the casting. In some cases, it is difficult or impossible to find a path between the pad and the atmosphere through which the gas generated during the exothermic reaction can be released due to the positional relationship of the exothermic pad in the mold.

What is observed when using the exothermic pad material is that the surface of the metal casting in contact with the exothermic pad becomes rough or contaminated by unnecessary impurities such as aluminum or silicon resulting from the exothermic pad itself. Such surface unevenness and contamination are undesirable and may not necessarily be eliminated, although they can be reduced by adding additional inert coatings to the mold. As a result, even if the exothermic pad material is known, the above problems are raised, and thus are restricted in commercial applications.

In order to solve the problems associated with aluminum-based or other pyrogenic padding composition using an insulating pad made of a refractory fiber material, British Patent No. 1,240,301 uses such padding material in the manufacture of metal castings. have.

In general, these materials include refractory inorganic fibers, i.e. inorganic fibers such as aluminum silicate or calcium silicate, granular refractory fillers as described above, and binders such as colloidal oxidized hydrosols, starches or phenolformaldehyde resins. It is.

However, these padding materials do not contaminate metal castings with unnecessary impurities and do not cause defects caused by gas such as bubbles or pinhole porosity, but they are not thermally effective as exothermic padding materials in progressively promoting directional solidification. The surface treatment of each part of the casting that comes in contact with the surface is much worse than the other parts of the casting that come into contact with the rest of the mold. Therefore, the insulating pad is limited to use in commercial casting production.

Surprisingly, the present invention combines these two types of padding materials into a single padding composition to make it pyrogenic enough to overcome the thermal inefficiency of the pure insulation padding composition, as well as to prevent metal castings from being contaminated with unnecessary impurities such as aluminum. It was confirmed that it is possible not to contain any fluorine salt in the padding composition and to have a density within an appropriate range.

The method for manufacturing the death penalty according to the present invention is to arrange or support the metal contact surface of the death penalty by arranging the internal pads at one or more positions of the mold where the gradual solidification needs to be promoted during metal casting. Provide a space with shape and dimensions and make up the pad with a composition of granular refractory material, fine aluminum powder, oxidizing agent and caking agent for aluminum. -1.1g / c ³ .

The present invention is applied to each part of the model that requires the gradual solidification of the casting of the shape of the model and apply the foundry sand around the model and the composition to cure the composition to make a pad and to separate the mold and the pad manufactured from the model Can be.

The padding material of the present invention is composed of granular refractory material, fine aluminum powder, oxidizing agent and caking agent of aluminum in order to promote gradual solidification in metal castings. By or after forming a dry pad characterized by 1.1 / cm ³ It can be placed around the mold or the model, or the composition using the composition to form a flexible mat (mat) or located around the model It can be made in the form of a mixture which can be formed or can be typed in the space of the mold or around the model. Soluble mats or moldable mixtures may be heated to dryness or cured using chemical means. It is desirable to make a moldable mixture or flexible mat that can be chemically cured.

Among the suitable fibrous refractories are alumina fibers, aluminum silicate fibers and calcium silicate fibers such as steel wool, rock wool or mineral wool.

Examples of suitable granular refractory materials include alumina, mullite, silymanite, chamotte, glog, roasted refractory clay roasted flint clay, silica, expanded bee cumulite, expanded pearlite, roasted rice hull and coke ground. There should be no traces of fluorine in the granular refractory; otherwise, metal castings made using pads are susceptible to contamination with aluminum.

Among the suitable oxidants are alkali metal nitrates, alkali metal nitrates, alkali metals and chlorates, iron oxides and manganese oxides.

Examples of suitable binders include organic binders such as resins, dextrins, starches, alkali sulfites, gum arabic and inorganic binders such as alkali metal silicates, colloidal oxidized hydrosols and clays (e.g., kaolin or borclays). There is a payment.

The composition may contain small amounts of organic fibers (e.g. rayon fibers), especially when the composition is used in the form of a flexible mat. Suitable pad compositions are as follows.

To ensure good thermal insulation, the specific gravity of the pads should be as small as possible. In practice, it is satisfactory to use pads with a density of 0.3-1.0 g / cm ³ . Within this optimum density range, the optimum density for a particular material depends on the composition of the material because, in most compositions, the fire resistance also decreases as the density decreases.

As described above, the pad according to the present invention may be manufactured and used by using one of several methods. For example, in a suitable mixer, each additive component is mixed and water is added to have a consistency of the type possible. The mixture may be typed into a dead space, placed against a casting model, filled into a core box and then chemically cured or heated and dried in an oven-like device, or slowly with a gas flame. To dry.

Another method is to mix the additives and water to make a slurry, and then immerse a mesh forming machine of appropriate shape in the dew slurry to dehydrate it by applying a vacuum to make it into a desired shape. As detailed in 1,204,742. Dispersants such as aluminum sulphate may be added to ensure that the additives are well dispersed in the slurry. The green shape may be dried in an oven or chemically cured. The green shape may be dried or cured integrally like a mold or separately dried or cured. Drying the pads made in this way gives a density of 0.3-1.1 g / cm ³ , usually in the range of 0.45-0.95 g / cm ³ .

A suitable method for producing pads by chemical curing using a flexible mat or moldable mixture is to apply an alkaline substance to several points on the surface of the mat or molded mixture. As described in 380 and 808,400. Examples of suitable alkaline substances include hydroxides, carbonates and aluminates of alkali metals such as sodium, which are preferably applied to the pads in aqueous solution. The presence of water soluble nitrates, such as alkali metal nitrates, is essential for the chemical curing process to take place. Alkali metal nitrate may be dissolved in an aqueous solution of alkaline material or included at least as part of an oxidant in a composition of a flexible mat or moldable mixture.

To delay the onset of the chemical curing reaction, it is necessary to add small amounts of compounds such as boric acid, which passivates aluminum into the flexible mat or the composition forming the formable material, as described in British Patent No. 775,380.

The present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a view illustrating the manufacture of a steel casting having a dimension of 110 mm × 11 mm × 11 mm in the sand mold 2, using a plate 4 having a height of 4,220 mm, a width of 110 mm, and a thickness of 55 mm. (3) Separate the casting (1) from (diameter 3100mm-height 150mm). The cylindrical hot water inlet is equipped with a fire resistant heat insulating sleeve 5. If the metal padding or other type of padding material conventionally used is not used, the casting 1 will be unhealthy at the position of (6).

2 shows an example of metal padding used in a conventional steel casting plant, where the part of the plate 4 is the minimum additional metal part necessary for the soundness of the casting. The dotted line illustrates the amount of cutting and machining required to produce the required casting shape. Even if metal padding is used, the diameter of the hot water supply opening 7 should be increased from 100 mm to 125 mm.

Figure 3 illustrates another conventional method of using metal padding, where part 8 of plate 4 is the minimum metal part needed to make the casting 1 sound. Here too, it is necessary to increase the diameter of the feed port from 100 mm to 125 mm and to remove a significant amount of metal in order to produce castings with the required shape.

4 shows an example of using the preformed and dried pad according to the present invention, and the pad 9 preformed and dried is provided for the model at the position illustrated in manufacturing the mold 2. The composition of the pad is as follows.

The pad made in this way had a density of 0.47 g / cm ³ . The casting 1 produced using the pad 9 was sound and not contaminated with aluminum.

5 is a view illustrating an example of the use of a pad made of a mixture capable of molding according to the present invention.

The composition is made as follows.

90 parts by weight of water is added to 100 parts by weight of the composition to make a moldable mixture, and then into the space of the mold (2) at the position of (10). After the model is removed, a few drops of alkaline solution of the following composition are added to the exposed surface of the molded mixture.

Chemical reactions occur to cure the molded mixture to form pads. Tests using the same composition showed that the specific gravity of the pad was 0.90 g / cm ³ . Two hours after the addition of the alkaline solution, the steel casting (1) made by pouring molten steel into the mold (2) was sound and not contaminated with aluminum.

To illustrate the present invention, the following compositions were compared using a preformed pad and sand mold 4 as shown in FIG.

(1) A pyrogenic composition in which silimite was added as a refractory filler and 1 wt.% Of potassium cryolite and 1 wt.% Of sodium fluoride were added (British Patent No. 991749).

(2) An exothermic and heat insulating composition comprising 97.0 wt.% Of the preceding composition and 3.0 wt.% Of calcium fluoride.

(3) The preceding composition which does not contain a fluorine salt.

The specific gravity of each pad was recorded and the integrity of the aluminum impurity and casting in the casting in contact with the pad was measured. The results are as follows.

It can be seen from the table that the pad according to the present invention made in the composition 3 is sufficient to generate heat even if there is no fluoride and heat insulation is good enough to make a healthy casting and hardly incorporation of aluminum into the casting. In contrast, it can be seen that the exothermic composition 1 and the exothermic and heat insulating composition 2 both contain fluoride and aluminum is incorporated into the casting.

Claims (1)

In order to promote gradual solidification, the internal pads are arranged at one or more positions of the mold to form a metal contact surface of the sand mold, and a space having the required shape and dimensions is provided in the rest of the sand mold. And a method of producing a sand mold by constituting a pad with a composition made of a caking agent, wherein the composition is substantially free of fluoride salts, contains fibrous refractory, and has a density of 0.3-1.1 g / cm ³ for the metal casting. Production method of the death penalty.

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