JPH069726B2 - Resin coated sand - Google Patents

Description

TECHNICAL FIELD The present invention relates to a resin coated sand used for a shell mold having both low expansion property and easy disintegration property.

[Prior Art] As one of the methods for making a precision mold in the foundry industry, for example, resin coated sand coated with synthetic resin such as novolac resin added with hexamethylenetetramine (Regin Coated Sand, hereinafter abbreviated as RCS) A method is generally used in which a shell mold is formed on a model by filling and contacting it with a preheated model and heating the shell mold or core. In this case, the most common casting sand that is an aggregate covered with resin is high-purity silica sand with a silica (SiO ₂ ) content of 90% or more. This high-purity silica sand has excellent heat resistance. It is widely used for various castings because it has high strength and high strength and has good wettability with a binder.

[Problems to be Solved by the Invention] However, since a mold (especially a core) using this high-purity silica sand as an aggregate expands considerably by pouring, it is sufficiently compatible with improvement in dimensional accuracy of castings. could not.

The present inventors have previously found that foundry sand consisting of granular nickel slag is excellent in low expansion characteristics in characteristics such as basic slag containing MgO and SiO _2, and high purity silica sand with scarce resources. As a very suitable casting sand superior to the above, a casting sand made of the above slag was proposed (Japanese Patent Application Nos. 60-288237, 60-288238, 60).
-282444). RCS using aggregate of low expansion molding sand (hereinafter referred to as NE sand) obtained from nickel slag containing MgO / SiO ₂ as a main component is a product that requires high dimensional accuracy due to its excellent low expansion characteristics ( For example, automobile parts)
It has been used very suitably in obtaining

However, RCS using NE sand as an aggregate has low expansion when used as core sand, for example, and the movement of sand due to thermal expansion during pouring is small, resulting in vibration or vibration. There is a case where there is a problem in terms of disintegration under the field work condition of type with low knock pressure and there is still a lot of room for improvement.

For example, in the case of cores used for casting products with complicated internal structures such as engine cylinder heads,
At the time of pouring, the strength must be sufficient to withstand the pressure of the hot water, and the disintegration after casting must be particularly good. Therefore, for example, a phenol resin composition (hereinafter abbreviated as easily disintegratable resin) to which a halogen compound such as an organic bromine compound or an inorganic bromine compound is added at the time of resin production for the purpose of decomposing the phenol resin at a low temperature range. It is carried out by adding it to NE sand, or by adding, for example, phenol, formaldehyde, and a bisphenol A purification residue (residue produced when bisphenol A is synthesized by condensation of phenol and dimethyl ketone and purified) to prepare an acidic catalyst. The resin obtained by reacting in the presence of bisphenol A, the by-product containing bisphenol A obtained when bisphenol A is produced, is treated at a high temperature in the presence of an alkaline catalyst to remove the high boiling point product out of the system. Cleavage residue having molecular weight phenolic hydroxyl group or the cleavage residue and pheno A novolac-type phenol resin obtained by condensing compounds with formaldehyde in the presence of an acidic catalyst, and an aromatic carboxylic acid and / or an anhydride thereof (hereinafter abbreviated as low expansion resin). The present situation is that methods such as adding to high-purity silica sand are used.

However, the composition of RCS is usually about 97 foundry sand.
The amount of resin added is about 3 parts by weight with respect to parts by weight, and it is difficult to improve the properties of the foundry sand and to obtain RCS that is substantially free of problems with only such a small amount of resin, which is a fundamental solution. Has not arrived.

In view of such circumstances, the present invention solves the above problems by using a mixture of low-expansion casting sand and casting silica sand obtained from the nickel slag as an aggregate, and has both low expansion and easy disintegration. The purpose is to provide RCS.

[Means for Solving Problems] The RCS according to the present invention is a low-expansion casting sand having a grain shape factor of 1.4 or less obtained from a slag containing MgO.SiO ₂ as a main component, particularly a nickel slag, and a casting silica. It is characterized in that an aggregate made of a mixture with sand is coated with a coating resin made of a low expansion resin and / or an easily disintegrating resin. That is, the present invention, various studies to improve the insufficient disintegration due to the excellent characteristics of the extremely low expansive cast ore sand obtained from nickel slag containing MgO.SiO ₂ as the main component. As a result of the above, the present invention was completed by finding that the use of silica sand for foundry together with the low expansion foundry sand can improve the disintegration without impairing the low expandability in practical use.

Nickel slag is, for example, nickel ore mixed with anthracite and limestone, smelted in a rotary kiln, crushed and subjected to beneficiation (specific gravity beneficiation, magnetic beneficiation, etc.), and about 50 t to obtain nickel 1t. It is said that slag will occur. This nickel slag is MgO ・ Si
It is a basic granular material having a mineral composition of O ₂ , which has been conventionally used in a small amount as an aggregate for concrete and asphalt.

In such nickel slag, impurities segregated due to the difference in specific gravity remain on the surface, and since the grain shape is deteriorated by the crushing process, strength and heat resistance when used directly as foundry sand as aggregate. Since the above problem may occur, it is more preferable to subject the nickel slag to a grinding treatment and use it as a granular material having a grain shape factor of 1.4 or less.

As this type of grinding treatment, a dry grinding treatment using a pneumatic reclaimer or an impact scriber is usually adopted. It is not impossible to reduce the above nickel slag to a preferable grain shape factor of 1.4 or less by such a dry treatment method, but since this method generally has a low treatment capacity, it is necessary to use a large-scale facility in an actual production line. The equipment cost becomes expensive. Therefore, it is more preferable to perform the grinding treatment using a wet scrubbing grinder. There are several types of wet grinding treatments. Among them, a trough-type grinding machine is used to obtain a pulp concentration, that is, the ratio of nickel slag to water is nickel slag: water = 1: 0.
It is preferably carried out under the condition of 1 to 0.25. If the amount of water is larger than this, the fluidity is improved and the co-rubbing effect is reduced. Conversely, if the amount of water is less than this, it becomes difficult to feed the nickel slag. In some cases, a trough-type grinding machine may be used to perform dry grinding treatment without using water.

As described above, the slag grinding is preferably performed until the final grain shape factor becomes 1.4 or less, more preferably 1.3 or less. The grain shape factor indicates that a perfect spherical shape is 1, and the closer it is, the closer the shape is to a sphere. By setting the grain shape coefficient to 1.4 or less, improvement in mold strength and the like is brought about. It is considered that this is because the cleaning of the surface of the aggregate particles and the reduction of the specific surface area promote the increase of the caking layer (coating layer) and the increase of the packing density to improve the thermal conductivity.

The silica sand for foundry used in the present invention may be silica sand conventionally used as foundry sand, and is not particularly limited, but the most common one is silica (SiO ₂ ) content 90.
% Or more of high-purity silica sand, and such silica sand is more preferably used.

There is one aspect that the degree of the effect of the present invention varies depending on the mixing ratio of the NE sand used as the aggregate and the silica sand for casting, and in order to enjoy the effect of the present invention more reliably and effectively,
The mixing ratio of NE sand and silica sand for casting is NE sand 10
It is more preferable to use 25 to 90 parts by weight of silica sand for casting with respect to 75 parts by weight.

As the coating resin used in the present invention, a novolac resin, a resole resin, an ammonia resol resin, a phenolic resin such as a benzyl ether resin, a composition of the resin and a bromine-containing organic compound or a bromine-containing inorganic compound, and the above There are low expansion resins and easily disintegrating resins. Particularly, the low expansion resin and the easily disintegrating resin described above are more preferable. The addition amount of the coating resin is appropriately selected depending on the required performance of the RCS from the shape of the cast product and the like, but is 0.5 to 10 parts by weight, more preferably 1.0 to 4 parts by weight per 100 parts by weight of the aggregate. RC with better low expansion and easy disintegration when 0 parts by weight of coating resin was added
Can be S. In this case, the low-expansion resin or the easily disintegrating resin is preferably used alone or in combination so that 10 to 100% by weight of the amount of the coating resin added is occupied by any one of the resins.

When the low-expansion molding sand, the casting silica sand, and the coating resin are out of the more preferable ranges, the expansion coefficient of RCS slightly increases or remains as compared with the case of being in more preferable conditions. When the RCS of the present invention is applied to a core used when casting a product having a complicated internal structure such as an engine cylinder head, for example, the RCS of the present invention may be deteriorated to some extent as strength increases. As described above, when easy disintegration is required, it is more preferable to use the RCS in which each constituent element is in the suitable region.

[Operation and Effect of the Invention] As described above, in the RCS according to the present invention, the silica sand for foundry mixed and added to the NE sand enhances the disintegration property without impairing the low expansion function of the NE sand. As a result, it has both excellent low expansion and easy disintegration.
When low-expansion foundry sand (NE sand) is added to ordinary foundry silica sand, the thermal expansion tends to decrease and the disintegration tends to deteriorate. However, addition of the easily disintegrating resin may cover the deterioration of disintegration. it can. In this case, the larger the amount of the resin, the less the thermal expansion, but the worse the disintegration property, but the addition of the low-expansion molding sand suppresses the thermal expansion, so the amount of the resin can be small and economical. It also has good disintegration.
In this respect, the same applies to the case of the low expansion resin, and the addition of the low expansion molding sand can save the amount of the resin used, improve the economical efficiency, and improve the disintegration property. That is, according to the present invention, the combination of the low-expansion molding sand with the ordinary molding sand and the selection of the resin can provide a unique effect which has not been obtained in the past. Therefore, when the RCS according to the present invention is molded, it is possible to satisfy the conditions required as a mold sufficiently, and at the same time, to provide the properties essential for producing a product with high dimensional accuracy represented by automobile parts, that is, low expansion and easy disintegration. It became possible to obtain a good mold equipped with it.

[Examples] The present invention is described in detail below with reference to examples, but the present invention is not limited to these examples.

The method for measuring the characteristics of RCS used in the examples is as follows.

(1) Shell thermal expansion coefficient a) Testing machine Thermomechanical analyzer (Thermoflex TMA standard type) (manufactured by Rigaku Denki Co., Ltd.) b) Test piece firing 200 ℃ x 120sec c) Test bead size 7 ¢ x 20mm d) Temperature rising rate 20 ℃ / min e) Test atmosphere Reducing atmosphere (N ₂ gas conduction, about 300ml / min) f) Measurement temperature range Room temperature to 1000 ℃ 2) Normal temperature coercive pressure, hot coercive pressure, residual strength (coercive pressure) ) A) Testing machine High temperature tester for casting sand (manufactured by Tokyo Hoki Co., Ltd.) b) Steady piece firing 250 ℃ × 90sec c) Test piece size 30 ¢ × 50mm d) Test peat heat exposure 600 ℃ × 23min e) Heat exposure Atmosphere Non-oxidizing atmosphere (test piece wrapped in aluminum foil) f) Test timing Normal temperature coercive pressure: Test piece is left in desiccator after firing, measured after 24 hours Hot coercive pressure: Test piece is fired in desiccator Measured by leaving it for 24 hours and then exposing it to heat. Residual strength: After baking the test piece Left in a water tank, heat after 24 hours and left in a desiccator, and after 24 hours.Measure granular nickel ore that has passed through a crusher, filter, etc. with a rotary kiln, water granulate it, then crush it with a crusher to obtain a specific gravity. The slag after the nickel was sorted by the beneficiator and the magnetic beneficiator was used as a raw material. The slag obtained by such a rotary kiln method does not completely vitrify in a semi-molten state, unlike the one using an electric furnace, a blast furnace, etc., and therefore sand-like slag having a particle size distribution corresponding to foundry sand by water granulation. can do.

This slag is treated in the steps (A to I) shown in FIG.
I got E Sand. The particle size distribution and chemical composition of the obtained NE sand are shown in Tables 1 and 2. Table 1 shows the particle size distribution of the silica sand for castings used in the examples.

Using this NE sand and foundry silica sand as an aggregate, RCS was manufactured with the composition (weight basis) shown in Tables 3 and 4, and the expandability and strength were measured. The results are shown in Table 5 and FIGS. 2 and 3. The resin A shown in Table 4 is a general RCS resin and a novolac resin. Resin B
Is a resin A to which zinc bromide is added. Resin C is a resin obtained by blending phenol formaldehyde and bisphenol A purified residue and reacting them in the presence of an acidic catalyst.

Using the RCS obtained in the formulations shown in Tables 1 to 4, 250 ° C.9
Cylindrical type (50φ x 50) as shown in Fig. 4 fired in 0 seconds
The shell core mold 1 is set in the main mold 2 and the feeder mold 3 made with the following composition, and about 14 molten metal of ordinary cast iron (FC25 equivalent) is set.
The molten metal was poured at 30 ° C., and the amount of sand removed was measured at each knockout time with an air hammer (air pressure 1.0 kg / cm ² ) using a core knock machine 4 shown in FIG.

(Main mold composition) Husen No. 5 sand (AFS index around 40) ... 100 parts by weight Furan resin ... 1.2 parts by weight / sand Curing agent (organic sulfonic acid) 50 parts by weight / resin The results of this disintegration test (sand removal rate) are shown in Table 6.

As is clear from these Examples and Comparative Examples, it is clear that the RCS of the present invention has excellent disintegration performance, that is, excellent disintegration properties without impairing the low expansion property of NC sand.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a flow chart showing a manufacturing process of low expansion molding sand containing MgO.SiO ₂ as a main component, and FIGS. 2 and 3 are heats of RCS of Examples and Comparative Examples. The measurement result of expansion coefficient is shown. FIGS. 4 (a) and 4 (b) are schematic views of the mold used for confirming the disintegration property, and are perspective views of the core knock machine used for the disintegration measurement shown in FIG.

Claims (2)

[Claims] 1. An aggregate comprising a mixture of low-expansion casting sand having a grain shape factor of 1.4 or less and a silica sand for casting obtained from a nickel slag containing MgO.SiO ₂ as a main component and / or other slag. Is coated with a coating resin composed of a low expansion resin and / or an easily disintegrating resin. 2. The resin coated sand according to claim 1, wherein the amount of the coating resin added is 0.5 to 10 parts by weight per 100 parts by weight of the aggregate.