JPH01148436A - Resin coated sand - Google Patents

Abstract

PURPOSE:To obtain low expanding ability together with easy-collapsibility by using mixing material of molding sand having low expansion obtd. from the specific Ni ore slag and silica sand for casting as aggregate. CONSTITUTION:The molding sand having extremely excellent low expanding ability obtd. from nickel ore slag containing MgO, SiO2 as main components is used together with the silica sand for casting. By this method, the collapsibility is improved without any bad influence to the low expanding ability. The nickel ore slag is the one which anthracite and lime stone are blended to the Ni ore and discharged after smelting with a rotary kiln and crushing and dressing, and is basic granular material having ore composition of MgO and SiO2. Grinding treatment is executed to this and spheroidized. By this method, cleaning of aggregate grain surface composing of the mixing material of the molding sand and the casting silica sand, increase of coating layer caused by decrease of specific surface area and improvement of heat conductivity caused by increase of packing density, etc., are promoted. Therefore, by coating the aggregate of the mixing material with resin for coating, the resin coated sand providing low expanding ability together with easy-collapsibility is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a resin coated sand used for shell molds that has both low expansion properties and easy disintegration properties.

[Prior Art] One method of making precision molds in the foundry industry is to use resin coated sand coated with a synthetic resin such as novolac resin to which hexamethylenetetramine is added.

A commonly used method is to make a shell mold or a core by filling and contacting a preheated model (hereinafter abbreviated as RC5) to form a shell mold on the model and heating it. In this case, the most common foundry sand that is the aggregate coated with resin is high-purity silica sand with a silica (SiO□) content of 90% or more, and this high-purity silica sand has excellent heat resistance. It is widely used for various castings because it has high strength and properties, and has good wettability with binders.

[Problems to be solved by the invention] However, molds (particularly cores) using this high-purity silica sand as aggregate expand considerably when poured, so they cannot sufficiently respond to improvements in the dimensional accuracy of castings. could not.

The present inventors have previously discovered that foundry sand made of basic granular nickel slag containing MgO and Sin□ has superior low expansion properties, and has found that it is extremely superior to high-purity silica sand, which is a scarce resource. As a suitable foundry sand, foundry sand made from the slag was proposed (Japanese Patent Application No. 60-288237, No. 60-2).
88238, 6O-282444). MgO・Si
RCS, which uses low-expansion foundry sand (hereinafter abbreviated as NE sand) obtained from nickel slag containing O2 as its main component, is used as an aggregate for products that require a high degree of particle size (for example, automobile parts) due to its excellent low-expansion properties. etc.) has been used very suitably.

However, when RCS with NE sand as aggregate is used as core sand, for example, it has low expansion, so there is little movement of sand due to thermal expansion during pouring, resulting in vibration and vibration. Under on-site working conditions for type baluns with low knock pressure, problems may arise in terms of disintegration, and there is still much room for improvement.

For example, in the case of cores used for casting products with complex internal structures such as engine cylinder heads,
It must maintain sufficient strength to withstand the pressure of hot water during pouring, and must have particularly good disintegration properties after pouring. For this purpose, for example, phenol resin compositions, etc., in which halogen compounds such as organic bromine compounds and inorganic bromine compounds are added during resin production for the purpose of decomposing the phenol resin at low temperatures (hereinafter abbreviated as easily disintegrating resin), etc. or by blending, for example, phenol, formaldehyde and bisphenol A purification residue (residue produced when bisphenol A is synthesized by condensation of phenol and dimethyl ketone and purified). , a resin obtained by reacting in the presence of an acidic catalyst, a by-product containing bisphenol A obtained when producing bisphenol A, was treated at high temperature in the presence of an alkaline catalyst, and the low-boiling point acid was removed from the system. A novolac type phenolic resin obtained by condensing the cleavage residue having a high molecular weight phenolic hydroxyl group or the cleavage residue and phenol with formaldehyde under an acidic catalyst, and an aromatic carboxylic acid and/or its anhydride. At present, a method is employed in which a resin composition containing the following (hereinafter abbreviated as low expansion resin) is added to the high-purity silica sand.

However, the composition of RCS is usually foundry sand, which is an aggregate of about 9
The amount of resin added is about 3 parts by weight compared to 7 parts by weight, and it is difficult to improve the properties of foundry sand and obtain RCS with virtually no problems with just a) small amount of resin, and it is difficult to obtain RCS with virtually no problems. No solution has been reached.

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

[Means for Solving the Problems] The RCS according to the present invention uses an aggregate made of a mixture of low expansion foundry sand and foundry silica sand obtained from nickel slag containing MgO-5iO□ as a main component for coating. It is characterized by being coated with resin. That is, the present invention provides MgO・
As a result of conducting various researches in order to improve the insufficient collapsibility that occurs due to the favorable characteristics of foundry sand, which has excellent extremely low expansion properties obtained from nickel slag containing SiO2 as the main component, we have developed silica sand for foundry use. The inventors have discovered that by using the above-mentioned low expansion foundry sand in combination with the above-mentioned low expansion foundry sand, it is possible to improve the collapsibility without practically impairing the low expansion property.

Nickel slag is produced by mixing anthracite coal and limestone with nickel ore, smelting it in a rotary kiln, and then crushing and beneficiation (gravitational beneficiation, magnetic beneficiation, etc.). Approximately 50 tons are required to obtain nickel IF. It is said that slag is generated. This nickel slag is Mg
It is a basic granular material with a mineral composition of O.SiO2, and has traditionally been used in small amounts 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 the particle shape has deteriorated due to the crushing process, so if it is used as foundry sand as aggregate, it will have poor strength and heat resistance. Since the above problem may occur, it is more preferable to subject the nickel slag to a polishing treatment and use it as a granule having a grain size coefficient of 1.4 or less.

As this type of polishing treatment, dry polishing treatment using a pneumatic reclaimer, an impact scriber, or the like is usually employed. It is not impossible to reduce the above-mentioned nickel slag to a preferable particle size coefficient of 1.4 or less by such a dry processing method, but this method generally has a low processing capacity, so in an actual production line, large-scale equipment is required. This results in high equipment costs. Therefore, it is more preferable to perform the polishing treatment using a wet scrubbing polisher. There are several types of wet polishing, but among them, a trough-type polishing machine is used to adjust the valve concentration, that is, the ratio of nickel slag to water in a weight ratio of nickel slag:water = 1:0.
It is preferable to carry out under the conditions of 1 to 0.25. If the amount of water is greater than this, the co-rubbing effect will decrease because the fluidity will improve. On the other hand, if the amount of water is less than this, it becomes difficult to feed the nickel slag. In some cases, dry grinding may be performed using a trough-type grinding machine without using water.

The final grain shape coefficient of slag grinding ore! As mentioned above, it is preferable to carry out the process until the value becomes 4 or less, and it is more preferable to carry out the process until the value becomes 1.3 or less. The grain shape coefficient is defined as 1 for a perfect spherical shape, and the closer it is to 1, the closer the shape is to a sphere.The fact that setting the grain shape coefficient to 1.4 or less improves mold strength, etc. This is thought to be due to the improvement of thermal conductivity due to the increase in the caking layer (coating layer) due to cleaning of the surface of the aggregate particles and the decrease in the specific surface area, and the increase in the packing density.

The foundry silica sand used in the present invention may be any silica sand conventionally used as foundry sand, and is not particularly limited, but the most common one is high purity with a silica (SiO□) content of 90% or more. It is silica sand, and such silica sand is more preferably used.

The extent of the effects of the present invention varies depending on the mixing ratio of NE sand and foundry silica sand used as aggregates, and in order to enjoy the effects of the present invention more reliably and more effectively,
The mixing ratio of NE sand and foundry silica sand is NE Sand I.
It is more preferable to use 25 to 90 parts by weight of foundry silica sand to 0 to 75 parts by weight.

The coating resin used in the present invention includes phenolic resins such as novolak resin, resol resin, ammonia resol resin, and benzyl ether resin, compositions of the resin and bromine-containing organic compounds or bromine-containing inorganic compounds, and the above-mentioned compositions. There are low expansion resins, easily disintegrating resins, etc. In particular, the above-mentioned low expansion resins and easily disintegrating resins are more preferred. The amount of coating resin added is selected as appropriate depending on the performance required for RCS from the shape of the cast product, etc.
When 0.5 to 10 parts by weight, more preferably 1.0 to 4.0 parts by weight, of the coating resin is added per 100 parts by weight of aggregate, RC with better low expansion and easy disintegration properties can be obtained.
It can be S. In this case, the low expansion resin or easily disintegrating resin is added in an amount of 10 to 10 times the amount of the coating resin added.
It is preferable to use one of the above resins alone or in combination so that 0% by weight is occupied by one of the resins.

Note that if the low expansion foundry sand, foundry silica sand, and coating resin are outside the more preferred ranges, the expansion rate of RCS may increase slightly or residual When the RCS of the present invention is applied to a core used for casting a product with a complex internal structure, such as an engine cylinder head, for example, the RCS of the present invention may cause a slight deterioration of collapsibility as the strength increases. In particular, when easy disintegration is required, it is more preferable to use an RCS in which each component falls within the above-mentioned preferred range.

[Operations and Effects of the Invention] As explained above, in the RCS according to the present invention, the foundry silica sand mixed and added to the NE sand has the effect of improving the originability without impairing the low expansion function of the NE sand. However, it has both excellent low expansion properties and 5-disintegrability.

Therefore, when molding RC3 according to the present invention, it fully satisfies the requirements for a mold, and at the same time has the characteristics essential for manufacturing products with high dimensional accuracy, such as automobile parts, such as low expansion and crystallization/decomposition properties. It became possible to obtain an excellent mold with

[Examples] The present invention will be 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 RC5 used in the Examples is as follows.

(+) Shell thermal expansion coefficient a) Testing machine thermomechanical analyzer (Thermoflex TMA standard type) (manufactured by Rigaku Denki ■) b) Test piece firing 200°C x 120 sec
C) Test piece dimensions 7@X20mmd) Heating rate 20℃/l! l1nC) Test atmosphere Reducing atmosphere (N2 gas conduction, approx. 300m1/m1n) [) Measurement temperature range Room temperature to 1000℃2) Room temperature resistance pressure, hot resistance pressure, residual strength (resistance pressure) a) Testing machine Foundry sand high temperature Testing machine (Tokyo Hoshiki manufacturing rupture) b) Test piece firing 250℃X 90secC
) Test piece dimensions 30t x 50 city d) Test piece heat exposure 600℃ x 231! l1ne) Heating atmosphere Non-oxidizing atmosphere (test piece wrapped in aluminum foil) f) Test timing After baking the room temperature anti-pressure crab test piece, leave it in a desiccator, measure after 24 hours Baking the hot anti-pressure crab test piece After leaving it in a desiccator, after 24 hours, exposing it to heat, and measuring residual strength: After baking, leaving the test piece in a desiccator, after 24 hours, exposing it to heat, and leaving it in a desiccator, 24 hours.
Measurement after time Granular nickel ore passed through a crusher, filter, etc. is heated in a rotary kiln, crushed into water, crushed in a crusher, and the nickel is sorted using a gravity separator and magnetic separator.The raw material is slag. used as. Unlike slag obtained using an electric furnace, blast furnace, etc., the slag obtained by this rotary kiln method is in a semi-molten state and does not completely vitrify. It can be made into slag.

This slag is treated in the step (A-1) shown in Figure 1 and N
I got an E sandwich. The particle size distribution and chemical composition of the obtained NE sand are shown in Tables 1 and 2. Further, the particle size distribution of the foundry sand used in the examples is shown in Table 1.

This NE sand and foundry silica sand were combined with aggregate to produce RC5 with the formulations (based on weight) 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. Note that resin A shown in Table 4 is a general RC3 resin and is a novolac resin. Resin B
is resin A to which zinc bromide was added. Resin C is a resin obtained by blending phenol formaldehyde and bisphenol A purification residue and reacting the mixture in the presence of an acidic catalyst.

250℃ using RC3 obtained with the formulations shown in Tables 1 to 4.
・Cylindrical shape (50φ) as shown in Figure 4, fired for 90 seconds
×50) Main mold 2 made by molding shell core mold 1 with the following composition
The molten metal of ordinary cast iron (equivalent to FC25) was poured into the feeder mold 3 at a temperature of about 1430°C, and the core knock machine 4 shown in Fig. 5 was used with an air hammer (air pressure 1.0 kg/cm
In 2), the amount of sand falling was measured at each knockout time.

(Main mold composition) Fusen No. 5 sand (AFS index around 40) - 100 parts by weight Furan resin - 1.2 parts by weight / sand Table 1 Particle size distribution of aggregate Table 2 Chemical components Table 3 RCS compounding conditions (weight Table 6 Disintegration (Sand removal rate, %) Curing agent (organic sulfonic acid) - 50 parts by weight/resin The results of this disintegration test (Sand removal rate) are as 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 properties, that is, excellent disintegration properties without impairing the low expansion properties of NC sand.

[Brief explanation of the drawing]

Figure 1 is a flowchart showing the manufacturing process of low expansion molding sand whose main components are MgO/SiO2, Figures 2 and 3.
The figure shows the measurement results of the coefficient of thermal expansion of RCS of Examples and Comparative Examples. FIGS. 4(a) and 4(b) are schematic views of the molds used to confirm the disintegration properties, and FIG. 5 is a perspective view of the core knock machine used to measure the disintegration properties.

Claims (4)

[Claims] (1) A resin-coated sand characterized in that an aggregate made of a mixture of low-expansion foundry sand obtained from nickel slag containing MgO.SiO_2 as a main component and foundry silica sand is coated with a coating resin. (2) The resin-coated sand according to claim 1, wherein the aggregate is a mixture consisting of 10 to 75 parts by weight of the low expansion foundry sand and 25 to 90 parts by weight of foundry silica sand. (3) The coating resin is 0.5 to 1 per 100 parts by weight of aggregate.
The resin-coated sand according to claim 1 or 2, which contains 0 parts by weight. (4) The resin-coated sand according to any one of claims 1 to 3, wherein the coating resin is a low expansion resin and/or an easily disintegrating resin.