DE3217650A1 - WITH RESIN-COATED SHAPED SAND AND METHOD FOR THE PRODUCTION THEREOF - Google Patents

Description

Resin-coated molding sand and its method

Manufacturing

Description;

The invention relates to a resin-coated molding sand or foundry sand for forming molds and cores or foundry cores for use in the sand casting process, and a method of manufacturing of the resin-coated sand. In this resin-coated sand becomes a crystalline unsaturated one Polyester used.

In conventional shell-mold sand-casting processes, phenolic resin was usually used as the binder used to make a resin-coated sand. It actually has one with phenolic resin Coated sand has great fluidity and is therefore convenient for handling and yielding In addition, sand molds and cores that have a sufficiently high strength after the heat treatment (after baking). In practice, however, sand molding processes using a phenolic resin have posed problems, such as those of US Pat Use of the phenolic resin are attributable. First

the resin releases gases that have an unpleasant odor and are unfavorable for environmental hygiene, if during the manufacture of the resin coated Sand is heated during the heat treatment of the molded molds and cores and / or during the casting of the

³ ^ melted sand into the sand molds. Second,

stick to the casting process of aluminum alloys, which are compared by very low casting temperatures with gray cast iron or gray iron casting process charak terized, the molds and cores are in a very firm and tough state, even at the shaking stage after solidification of the poured molten metal, due to partial carbonization of the phenolic resin, so that the shaking process or the final emptying process lead to difficulties leads. In particular, the disintegration of the sand cores must be preceded by a firing process the mold assemblies containing aluminum alloy castings and sand cores to high temperatures are heated to thereby decompose the carbonized phenolic resin.

Because of such problems inherent in phenolic resin coated sand, the U.S. Patent recommends 4,246,165 a resin-coated sand in which a crystalline unsaturated polyester instead a phenolic resin is used. The recommended one, coated with resin; Sand does not give off an irritating odor, even when heated, and as a more essential advantage, not only shapes, but also cores, molded from this resin-coated sand and used in an aluminum alloy casting process are easily disintegrated and the shakes - or final emptying stage can be used without the

° standing combustion processes are carried out.

However, unsaturated polyester resins inherently have inferior physical strength than Phenolic resins. Therefore, molds or cores made from a resin-coated sand sometimes lead

17650

produced using an unsaturated polyester, an insufficient one physical strength on and especially in those cases where the cores are relatively thin-walled Have proportions, the increase in the number of defective cores poses a serious problem in the commercial Seen from the point of view. While it is possible to increase the strength of the molds and cores by increasing the size of the To increase the proportion of unsaturated polyester resin to the sand to be coated, however, this is quite inconvenient due to an inevitable increase in production cost and increased Probability of casting defects, such as blowholes, due to considerable amounts of gas being increased from the Resin are released.

In preparing a resin-coated sand using a crystalline unsaturated polyester resin, it is necessary to add an organic peroxide, which acts as a radical polymerization catalyst, to the unsaturated polyester resin in order to harden the resin in the heat treatment step during the formation of the molds and cores enable. In view of this, the first publication of JA patent application 55 (1980) -165250 recommends the joint use of at least two types of radical polymerization catalysts on condition that the half-life

time of each catalyst is at a temperature below 130 ⁰ C to 10 and is different from the temperature of the defined in the same manner .anderen - catalyst or those defined in the same way temperatures of the other catalysts. According to

of this JA patent application can be a resin coated Sand that was made using a

crystalline unsaturated polyester and a combination of special catalysts / uniform hardened, even in cases where molds and cores with both relatively thick wall parts; as well as relatively thin wall parts are formed.

When examining the resin-coated sand according to the aforementioned JA patent application, it was found however, it has been shown that the strength of cores formed from this resin-coated sand it is still insufficient if the cores have a very complicated shape and uneven wall thicknesses have, such as the core for casting for a water jacket in the cylinder head one Motor vehicle engine, so that the number of defective cores is much larger than when using a phenolic resin-coated sand for the same

2Q chen purpose .. The reason for this is that the high temperature strength, this resin-coated sand maximum at a particular heat treatment or bake temperature, such as 25O ⁰ C and is reduced either at lower heat treatment temperatures or at higher heat treatment temperatures, while the temperature distribution in the core during the heat treatment becomes very uneven if the core has a very complicated shape and

has uneven wall thickness. 30th

An object of the invention is to provide an improved sand-coated resin for formation of molds and cores for use in sand mold casting processes or sand mold mask casting processes, 35

including casting processes using

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Aluminum alloys, the coated sand being a crystalline unsaturated polyester as shown in U.S. Patent 4,246,165, but improved Values for high temperature strength over a wide range of heat treatment or baking temperatures having.

Another object of the invention is to provide a method of making one according to the invention resin-coated sand.

The invention provides a resin coated sand which includes a binder in the form of a coating. the surfaces of the individual particles of a foundry sand. The binder comprises a crystalline unsaturated polyester which is a barely tacky solid at room temperature. is- ,, as a main component, and at least one organic peroxide which serves as a radical polymerization catalyst for curing the unsaturated polyester. The improvement achieved by the invention is primarily that the above-mentioned, at least one organic peroxide is a combination of a first organic peroxide, the half-life of which is 10 hours at a temperature of not below 130 ^° C. and of a second organic peroxide, its half-life 10 hours at a temperature below 130 ⁰ C, but not below

"Q is 100 ^° C. The total amount of the combination of the first and second peroxides is in the range of 0.1 to 5 parts by weight per 100 parts by weight of the unsaturated polyester in the binder, and the amount of the first peroxide is Range from 90 to 10 wt%

the total amount of the first and second peroxides.

^: ·· ^: · ^: · 3Ζ17650

The term "crystalline unsaturated polyester" as used herein means a polyester which is at least partially crystalline, to such an extent that the crystalline areas are clearly visible can be identified by X-ray diffraction analysis, and the crystalline unsaturated Polyesters described in U.S. Patent 4,246,165; are useful according to the invention.

A typical example of the first organic peroxide as defined above is cumene hydroperoxide whose half-life becomes 10 hours at 158 ° C, and a typical example of the second organic peroxide as defined above is dicumyl peroxide whose half-life becomes 10 hours at 117 ° C . The first and second organic peroxides are preferably chosen such that the difference between the temperature at which the half-life of the first peroxide becomes 10 hours and the temperature at which the half-life of the second peroxide becomes 10 hours is at least 10 ^° C.

Optionally, the binder can be a monomer or Prepolymer which is copolymerizable with the unsaturated polyester as a crosslinking agent in in an amount not greater than 50 parts by weight per 100 parts by weight of the unsaturated polyester. It is also possible to choose a small amount

° to add silane coupling agents to the binder.

As an effect of using together the above-defined first peroxide which is a High temperature radical polymerization catalyst, and the second peroxide which it is is a medium-temperature radical polymerization catalyst, shows the inventive, resin coated sand improved considerably

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Values with regard to its temperature resistance over a very wide range of heat treatment and Baking temperature, which extends to a very high temperature such as about 350 ⁰ C. Therefore, by using the resin-coated sand, it is possible to form molds and cores with a sufficiently high strength even if the molds and cores have a very complicated shape and / or uneven wall thicknesses. This resin-coated sand retains the benefits attributed to the use of a crystalline unsaturated polyester. This means that the cores formed from this resin-coated sand can be easily disintegrated in the dumping step even in an aluminum alloy casting process despite the increase in the original strength of the cores. Moreover, the preparation of the resin-coated sand, the formation of molds and cores using the resin-coated sand, and the pouring of molten metal into the molded molds can be carried out; without the disadvantage of harmful or irritating gases occurring.

A method according to the invention for making resin-coated sand comprises the steps of mixing a major amount of the heated foundry sand with a lesser amount of ^OW of binder, which is a crystalline unsaturated polyester, which is a barely tacky solid at room temperature than contains a main component, so that the unsaturated polyester is liquefied and attached to the particles of the foundry

sandes adheres to the addition of a combination of a

first organic peroxide as defined above and a second organic peroxide as defined above organic peroxide to the mixture of the foundry sand and the binder, while the temperature of the The mixture is such that the binder remains in a liquid state on the sand particles, however, stirring the resultant does not readily cure even in the presence of the first and second peroxides Mixture, whereby the first and second peroxides are dispersed in the mixture, and the Lowering the temperature of the resulting mixture with continued stirring until the solidification of the Binder that adheres to the sand particles. Both the total amount of the first and 'second organic apparent peroxide based on the amount of unsaturated ester and the amount of the first peroxide in total of first and second peroxides are defined above.

Preferably, the first and second peroxides become the one coated with the liquefied binder Sand in the form of a mixed solution in an organic solvent with a relatively low Boiling point, for example ethyl alcohol, added.

The following are preferred embodiments of the Invention described. A crystalline unsaturated polyester useful in the present invention becomes obtained by esterification reaction between at least one unsaturated dibasic acid with steric Symmetry, such as fumaric acid and / or mesaconic acid, and at least one glycol that is sterically symmetric is like ethylene glycol, 1,3-propanediol, diethylene glycol, 1,4-butanediol, dipropylene glycol, neo-

pentyl glycol, hydrogenated bisphenol A, 2,2-bis- / 4- (hydroxy ethoxy) -phenyr / -propane and / or 2,2-bis- £ 4- (hydroxypropoxy) -pheny17-propane.
5

If the crystalline structure of the product is retained, some of the unsaturated may be symmetrical dibasic acid can be replaced by at least one unsaturated dibasic acid with asymmetrical molecular structure, such as maleic anhydride, Citraconic acid and / or itaconic acid and / or at least one saturated dibasic acid, such as Phthalic acid, isophthalic acid, tetrahydrophthalic anhydride and / or 3,6-endomethylene-A -tetrahydrophthalic anhydride, or one or more addition or substitution derivatives thereof. It is also possible, to replace part of the glycol with the sterically symmetrical structure by at least one Glyko'l, which has an asymmetrical molecular structure, such as propylene glycol and / or 1,3-butanediol and / or at least one polyhydric alcohol such as glycerol and / or trimethylolpropane or one or more Derivatives thereof.

By suitable choice of the reaction components and control of the reaction conditions for the esterification According to a known or customary method, it is possible to use a crystalline unsaturated polyester to achieve .der a suitable molecular weight

from about 1000-2000 and is a non-sticky solid or hardly sticky at room temperature, and through a sieve with openings of 4.76 mm (4 mesh) too small particles can be divided. In the synthesis of such a crystalline unsaturated Polyesters can optionally be 100 to 1000 ppm one

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i. ^:: .- ^{': ..:. "Ie: .."} -321765Q

known polymerization inhibitor such as a quinone or a phenol m add ReaktionskOittponenten. Typical examples of compounds suitable for this purpose are p-benzoquinone, hydroquinone and catechol or catechol. According to the invention it is preferred to use an unsaturated polyester which has a viscosity value below about 500 dPa. s (P), and particularly preferably up to 15O ⁰ C under about 250 dPa.s (P) at a temperature in the range of about one hundredth

According to the invention it is possible, optionally, a. Resin composition to use, which is made by mixing a crystalline unsaturated Polyesters in a heated and liquefied state, with at least one monomer or prepolymer *, that is copolymerizable with the unsaturated polyester and serves as a crosslinking agent. Examples of useful monomers and prepolymers are Styrene, divinylbenzene, vinyltoluene, ^ -Methylstyrene, diallyl phthalate, diallyl phthalate prepolymer, diallyl isophthalate, Diallyl isophthalate prepolymer, Ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, Neopentyl glycol dimethacrylate, trimethylolpropane trimethacrylate, Triallyl cyanurate, triallyl isocyanurate, triallyl trimellitate, diacetone acrylamide and N-methylol acrylamide. The total amount of to Crosslinking agent to be added to 100 parts by weight of unsaturated polyester should not be 50 parts by weight exceed, since the addition of a larger amount of crosslinking agent leads to a resin with coated sand made using the resin composition becomes sticky and therefore has a low flowability and bulk density,

when it is charged into a cavity mold, so that the molds and cores formed from the resin-coated sand have insufficient physical strength. The amount of the crosslinking agent per 100 parts by weight of unsaturated polyester is preferably limited to the range from 10 to 30 parts by weight. It is also preferred that the resin composition has a viscosity value below about 500 dPa.s (P) and most preferably below about 250 dPa.s (P) at a temperature in the range of about 100 to about 150 ⁰ C.

To further increase the physical strength of the molds and cores resulting from the sand-coated Resin have been formed, a silane coupling agent can be added to the resin composition described above be joined. For this purpose it is suitable to use a connection that is shown is given by the general formula

R ₁ R-,
Si '

^R 2 ^R 4

wherein R- is an organic functional group with at least one alkenyl group, alkenylphenylalkyl group, acryloxyalkyl group, methacryloxyalkyl group , glycidoxyalkyl group, epoxycyclohexylalkyl group and halogenated alkyl group, and each of the radicals R " ₂ , R ₃ and R. represents a hydrolyzable group selected from alkoxy groups, alkoxyethoxy groups, Acetoxy groups and halogens, examples of silanes, are represented by this general formula,

are γ- chloropropyltrimethoxysilane / vinyltrichlorosilane, vinyl-tris- (ß-methoxyethoxy) -öilati, 'y'-methacryloxypropyltrimethyloxysilane, ß- (3,4-epoxycyclohexyl) -äthyltrimethoxysilan, rimethoxysilropyltrimethoxysilane , N- (ß-aminoethyl) -y-aminopropyltrimethoxysilane, and ^ -uridopropyltriethoxysilane * If desired, two or more of these silanes can be used together.

In the case of the use of one or more silane coupling agents. the total amount of the silane coupling agent or agents should be 0/1 to 10 parts by weight per 100 parts by weight of the crystalline unsaturated polyester in the resin composition. The addition less than 0.1 part by weight of silane coupling agent is hardly effective in increasing the strength of sand molds and cores. However, it increases Effect of the silane coupling agent (s) on the strength of the sand molds and cores is not significant, even if more than 10 parts by weight of the silane coupling agent (s) are added, and the use such a large amount of the silane coupling agent is unfavorable from the economical point of view.

As mentioned above, a first feature of the invention provides the common use of a radical ^{polymerization catalyst, the half-life of which at a temperature of not below 130 0} C is 10 hours (hereinafter, the catalyst of this class is referred to as catalyst A) and another radical polymerization catalyst, the half-life of which at a temperature below 13O ⁰ C, but not below 100 ⁰ C 10 hours (in the following the catalyst of this class is called

Catalyst B).

It is useful to check the half-life of each peroxide useful as a radical polymerization catalyst, at a predetermined temperature by dissolving of the peroxide in a solvent that is relatively inactive to the decomposition of the peroxide Free radicals are to be measured, obtaining a solution with a peroxide concentration of 0.1-0.2 mol / l and thermal decomposition of the peroxide in the solution at the predetermined temperature in a gas-tight sealed glass tube, after replacing the air in the tube with nitrogen gas.

Examples of catalysts A are p-menthane hydroperoxide, 2,5-dimethyl-2,5-di- (t-butylperoxy) -hexyl-3, 1,1,3,3-tetramethylbutyl hydroperoxide, cumene hydroperoxide and 2,5-dimethylhexyl-2,5-dihydroperoxide.

Examples of catalysts B are methyl ethyl ketone peroxide, t-butyl hydroperoxide, t-butyl cumyl peroxide, Di-t-butyl peroxide, dicumyl peroxide, 2,5-dimethyl-2,5-di- (t-butylperoxy) -hexane, 2,5-dimethyl-2,5-di- (benzoylperoxy) -hexane, t-butyl peroxyacetate, 2,2-bis (t-butylperoxy) butane and t-butyl peroxybenzoate.

These catalysts A and B can be combined in various ways, but according to the invention it is special preferred to cumene hydroperoxide as catalyst A ■ and dicumyl peroxide as catalyst B together use. It is often sufficient if the mixed catalyst which is present according to the invention is sufficient a catalyst A and a catalyst B, but the mixed catalyst may if desired

two or more types of the catalysts A and / or two or more kinds of the catalysts B contain.

In each case is the total amount of catalysts A and Β, which are used according to the invention the range from 0/1 to 5 parts by weight per 100 parts by weight the crystalline unsaturated polyester used to make the resin-coated sand used is limited. When the total amount of the mixed catalyst is less than 0.1 part by weight it is difficult to obtain a satisfactorily high strength of the molds and cores that are produced from the resulting resin-coated sand to be formed. However, the effect of the mixed Catalyst does not significantly increase the strength of the sand molds and cores, even if the total amount of the catalysts mixed is increased beyond 5 parts by weight, and the use such a large amount of the catalyst is unfavorable from an economical point of view. Preferably the total amount of the catalysts A and B falls in the range of 1 to 3 parts by weight per 100 parts by weight of unsaturated polyester.

To obtain a resin-coated sand with satisfactorily high temperature resistance values over a wide range of heat treatment and Baking temperatures achieved in the formation of the sand molds and cores should use catalysts A and B be used in such a proportion that the catalyst A 10 to 90 wt. · - * and preferably 20

up to 80% by weight of the total amount of the mixed catalyst amounts to.

Catalysts A and B are preferably selected from those listed above as examples Connections such that the difference

between the temperature at which the half-life of the selected catalyst A, that is, the radical polymerization catalyst of the high temperature type, becomes 10 hours, and the temperature at which the half-life of the selected catalyst B, that is the radical polymerization catalyst of the medium temperature type, becomes 10 hours, at least 10 ⁰ C is. The reason for this is as follows. During the heat treatment or baking of a mold or a core formed from a resin-coated sand according to the invention, it is inevitable that the outer surface of the mold or the core in contact with a metal mold is heated more intensely than the inner area of the Shape or core, so that the temperature in the inner area remains considerably lower than the temperature on the outer surface. In order to achieve a sufficiently high strength of the sand mold or the core, it is necessary to fully cure the unsaturated polyester used as the binding material not only on the outer surface but also in the inner area of the mold or the core, despite the low temperature in the inner area. Therefore, it is favorable if the above-mentioned temperature difference between the catalyst A (high temperature type catalyst) and the catalyst B (medium temperature type catalyst) in the mixed catalyst is as large as possible and at least 10 ^° C. When the temperature difference is less than 10 ^° C., the effect of using the catalysts A and B together on the degree of hardening in the inner region of the sand mold or the core is not much different from the effect of using the catalyst A alone or the catalyst B alone ,

³ ^ so that it is sometimes difficult to find a sufficient

To achieve strength of the sand mold or the core.

Resin-coated sand according to the invention is made by a known or customary hot melt procedure manufactured / but taking into account the common use described above the catalysts A and B. According to a preferred embodiment, the hot melt process carried out in the following way.

First, a silicon dioxide sand, which is suitable as a molding sand, is heated to a temperature above the softening temperature of the unsaturated polyester selected for this process, for example 150 to 200 ^° C., and fed into a conventional sand mixer whose stirrer is in operation. Soon after, the unsaturated polyester or a resin composition containing the unsaturated polyester and a crosslinking agent is charged into the mixer in the form of small solid particles and stirring is continued, causing the unsaturated polyester to be melted by the heat of the sand and that the sand particles are coated with the liquefied polyester. Is stirred when the temperature of the coated sand to an adequate degree, as 120-100 ⁰ C, lowered to a selected combination of catalysts A and B is added to the coated sand ι while continuing to achieve a

³ ^ uniform dispersion of the catalysts. In this method, it is favorable to use a catalyst solution prepared by dissolving both catalysts A and B in an organic solvent having a relatively low boiling point such as a low alcohol. It goes without saying that

the addition of the catalysts A and B takes place in a stage in which the sand temperature is still high enough is to make the unsaturated polyester coated on the sand particles in liquid or to get softened state, but is not so high that a rapid hardening of the polyester by Action of the added catalysts takes place. Stirring of the resulting mixture is continued, until the sand temperature is far below the softening temperature of the unsaturated polyester, what causes the sand particles coated with polyester to separate from one another. Possibly can add a small amount of wax or a higher fatty acid or its salt * to the sand-polyester mixture after the addition of the catalysts are added, with the purpose of increasing the flowability of the resin-coated Raise sand. It is also possible, if appropriate, to use one or more auxiliary additives, such as Disintegrability-improving agents, crystallization agents and / or the viscosity To add agents to the unsaturated polyester or the above resin composition. A suitable one Range of weight ratio of unsaturated. Polyester to the molding sand to be coated, ranges from 1: 100 to 7: 100.

Using a resin-coated sand of the present invention, molds and cores for sand mold casting can be manufactured in a conventional manner. For example, the coated sand 'is injected into a preheated metal mold assembly and then 0.5 subjected to 5 minutes at 200 to 350 ⁰ C to a heat treatment or baked.

The following examples and comparative experiments serve to further illustrate the invention.

example 1

In a 2 liter four-necked flask were 1137.5 g of fumaric acid, 33.2 g of isophthalic acid and 651.7 g of ethylene glycol of an esterification reaction according to a customary procedure subjected to the formation of about 1,400 grams of an unsaturated polyester having an acid number from 25.

After cooling of the unsaturated polyester to 140 ⁰ C 20 parts by weight diallyl phthalate were 2 parts by weight (200 Japan Aerosil Inc. AEROSIL) was added f-methacryloxypropyltrimethoxysilane and 0.8 parts by weight of ultra fine particles of silicic anhydride and carefully mixed with 100 parts by weight of the unsaturated polyester. The resulting mixture was allowed to cool to room temperature and was allowed to stand for a while. A resin composition obtained by this method was a non-sticky solid containing a crystalline unsaturated polyester. The resin composition was pulverized into fine grains which passed through a sieve with openings of 2.00 mm (10 mesh).

For making resin-coated sand by a hot melt method using

the resin composition described above was added 4 kg of a commercial Siliciumdioxidsandes for foundry purposes to 170 ⁰ C preheated and fed to a speed mixer. While stirring the sand, 122.8 g of the powdered resin composition was added to the sand, resulting in the resin composition

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was melted by the heat of the sand, and that the sand particles were coated with the liquefied bath composition. While the temperature of the sand treated in this way was kept in the range from 120 to 100 ^° C. with further stirring, a catalyst solution was prepared by dissolving 1.5 g of cumene hydroperoxide (catalyst A) and 1.5 g of dicumyl peroxide (catalyst B) in. 20 g of ethyl alcohol was poured into the mixer and the equipment was further stirred for uniform dispersion of the catalysts in the resin coating of the individual sand particles. When the sand temperature was reduced to about 70 ⁰ C, 5 g of calcium stearate was added to the resin coated sand in the mixer and stirring was continued until the already agglomerated sand so loose and was flowable, that the individual sand particles separated from each other. Then the resin-coated sand was removed from the mixer.

The resin coated sand of this example was subjected to a high temperature strength test along with resin-coated sands of the following reference examples in a later-described comparative attempted.

Reference example 1

Using 4 kg of the silica sand mentioned in Example 1, a resin-coated one was made Sand, generally produced according to Example 1, but using the following catalysts instead of the combination of catalysts A and B in Example 1. In the reference example. 1 became a Used catalyst solution which was prepared by dissolving 1.0 g of dicumyl peroxide (catalyst B),

1.0 g of t-butyl peroxybenzoate, its half-life is .10 hours at 104 ⁰ C (Catalyst S), and 1> Ö g t-butyl peroxy-2-äthylhexanat (whose half-life at 72 ° C for 10 hours) in 20 g of ethyl alcohol.

Reference example 2

Resin-coated sand was generally prepared according to Reference Example 1, but was

a combination of 1.5 g of dicumyl peroxide (Catalyst B) and 1.5 g of t-butyl peroxybenzoate (Catalyst B) was used in place of the combination of the three kinds of peroxides in Reference Example 1.
15th

Comparison attempt 1

In this experiment, samples of each of the three resin-coated sands of Example 1 and Example 1, respectively, were made Comparative Experiments 1 and 2 were taken and subjected to a high temperature strength test which was carried out using a high temperature tensile strength tester for molding sand of the molding mask type. Each test piece for this test was made, in one set formed from upper and lower metal molds provided with heating devices by filling the cavity in the form set (the cavity had a horizontal cut surface, like a dumb-ball) and a shallow depth in relation to their horizontal

Cross-sectional area on) with a resin-coated sand to be examined and heat-treating or baking the sand in the mold cavity for 70 seconds. The heat treatment temperature (measured on the metal mold surface) was ^{varied in the range from 230 to 330 °} C. as shown in Table I below. Each test piece passed the test immediately

subjected to the completion of the heating treatment. For each resin-coated sand, the test was performed on five 5 test pieces at each heat treatment temperature to show the high temperature resistance and the average value of the five measurements. The results of the comparative experiment are shown in Table 1.

Table 1

High temperature strength (unit: kg / cm ² )

Heat treatment temperature

overdone ■
sand 1 230 3, ⁰ C 250 4, ⁰ C 270 4, ⁰ C 290 5, • c 310 4, 9 330 ⁰ C example 1 2 1 3, 8th 1 3, 2 1 3, 7th 1 2, 2 1 1/ 1 13, 7th Reference example 1 3, 0 1 3, 3 1 3, 1 1 2, 0 1 1, 0 9, 5 Reference example .1 4th 1 7th 1 5 1 8th 1 9, 3

From the data in Table 1, it can be seen that the resin-coated sand of Example 1, manufactured in By using the catalysts A and B together, a significantly better high-temperature strength was achieved than the resin-coated sands of Reference Examples 1 and 2 made were using catalysts B, however

_or . without using any catalyst A, which is true for a wide range of heat treatment temperatures used in this experiment. In addition, the experimental results show that the combination of the catalysts A used in Example 1

og and B a very effective increase in high temperature strength of the resin-coated sand when

resulted in considerably high heat treatment temperatures.

Example 2

Resin-coated sand was prepared using the silica sand mentioned in Example 1 and the unsaturated polyester resin composition prepared by the method described in Example 1 using the same materials. , 4 kg of preheated to 170 ⁰ C Siliciumdioxidsandes were stirred and 122.8 g of the pulverized resin composition was added to the sand in the mixer, with the result that the sand with the resin composition melted by the heat of the sand, were coated. The temperature of the sand was maintained with continued stirring in the range of 120 to 100 ^0C and a catalyst solution prepared by dissolving 1.5 g of p-menthane hydroperoxide, whose half-life at 133 ° C for 10 hours (catalyst A) and 1.5 g of dicumyl peroxide (Catalyst B) in 20 g of ethyl alcohol was poured into the mixer and the mixture was further stirred to disperse the catalysts evenly. When the sand temperature was dropped to 80-70 ⁰ C, 5 g of calcium stearate was added to the resin coated sand. The resin coated sand was removed from the mixer when the individual sand particles separated from each other.

. A comparative experiment based on this example, another example and a reference is given below described.

Example 3
35

Resin-coated sand was generally prepared according to Example 2, except that 1.5 g of 2,5-dimethyl

hexy1-2,5-dihydroperoxide, whose half-life at 154 ⁰ C for 10 hours (catalyst A) instead of 1.5 g of p-menthane hydroperoxide (catalyst A) of Example 2 were used.

Reference example 3

Resin-coated sand was made generally according to Example 2, but in this example Trap 3.0 g of p-menthane hydroperoxide (catalyst A) instead of the combination of catalysts A and B. of example 2 is used.

Comparative experiment 2

Samples of each of the three types of resin-coated sand prepared in Examples 2 were made and 3 or from Reference Example 3 and taken from the high-temperature tensile strength test described in Comparative Experiment 1 subjected. The results are shown in Table 2.

Table 2
25th

High temperature strength (unit: kg / cm ² )

overdone
sand 230 3, Heat treatment temperature 250 3, ⁰ C 270 ⁰ C 290 4, ⁰ C 31 0 ° C 330 2, ⁰ C 30th Example 2 1 3, ⁰ C 1 3, 8th 14, 0 1 4, 1 13th , 7th 1 3, 9 Example 3 1 7, 2 1 9, 9 14, 4th 1 3, 8th 14th 1 1 1, 0 Reference example 3 6th 8th 12, 5 1 3 12th 6th 1 0 3 35

-yt-

The experimental data in Table 2 show that when compared with the use of only the catalyst A the joint use of the catalysts A and B is very effective in increasing the high temperature strength values of the resin-coated sand and to widen the heat treatment temperature range, in which the sand-coated resin has satisfactorily high high temperature strength values results.

Example 4

In a 2 liter four-necked flask were 1102.6 g of fumaric acid, 83.1 g of terephthalic acid ,. 614.5 grams of ethylene glycol and 147.6 g of nebpentyl glycol from an esterification reaction subjected to a conventional procedure, with the formation of an unsaturated polyester with an acid number of 30.

After cooling of the unsaturated polyester to 135 ⁰ C 10 parts by weight diallyl phthalate were ,, 3 parts by weight • p-Glycidoxypropyltrimethyloxysilan and added 0.8 wt, parts by ultra fine particles of silicic anhydride (Aerosil 200) and carefully with 90 weight . Parts of the unsaturated polyester mixed. The resulting mixture was allowed to cool to room temperature and was allowed to stand for a while. A resin composition obtained by this method was a non-sticky solid containing a crystalline unsaturated polyester. The resin- SQ composition was pulverized into fine grains and then passed through a sieve with openings of 2.0 mm (10 mesh).

Using 4 kg of the material used in Example 1

The silica sand and 125 g of the resin composition prepared in Example 4 became the preparation

of the resin-coated sand in the same way as in Example 1. While the temperature of the coated with the molten resin composition sand in the range of 120 to 100 ^0C was was added a catalyst solution prepared by dissolving 0.3 g of cumene hydroperoxide (catalyst A) and 2.7 g of dicumyl peroxide (catalyst B) in 20 g ethyl alcohol Poured into the mixer and the mixture was further stirred to disperse the catalysts evenly. When the temperature of the sand ^{had decreased to about 70 °} C., 5 g of calcium stearate were added to the resin-coated sand, and when the individual sand particles separated from one another, the resin-coated sand was removed from the mixer.

A comparative experiment relating to this example, other examples and reference examples will be described later.
20th

Example 5

Resin-coated sand was prepared generally as in Example 4 except that 0.6 g of cumene hydroperoxide and 2.4 g of ⁵ ^ Dicumylpearoxid used in this case. This means that the mixed radical polymerization catalyst in this example consisted of 20% catalyst A and 80% catalyst B, based on weight, whereas the mixed one

Catalyst in Example 4 from 10% catalyst _ * and 90% catalyst B passed.

Example 6

Resin coated sand was prepared generally according to Example 4 except that 2.4 grams of cumene hydroperoxide were used and 0.6 g of dicumyl peroxide were used what

Sb

means that the mixed catalyst consists of 80%
Catalyst A and 20 % catalyst S consisted.

Example 7

Resin-coated sand was generally prepared according to Example 4 except that 2.7 g cumene hydroperoxide and 0.3 g dicumyl peroxide were used.
meaning that the mixed catalyst consisted of 90% catalyst A and 10% catalyst B.

Reference example 4

Resin-coated sand was prepared generally according to Example 4, except that 0.15 g cumene hydroperoxide and 2.85 g dicumyl peroxide were used, meaning that the mixed catalyst was 5%
Catalyst A and 95% Catalyst B consisted.

Reference example 5

Resin coated sand was generally prepared according to Example 4 except that 2.85 g cumene hydroperoxide and 0.15 g dicumyl peroxide were used.
which means that the mixed catalyst consisted of 95% Catalyst A and 5% Catalyst B.

Comparative experiment 3
30th

Samples of each of the six resin-coated sands prepared in Examples 4 were made
to 7 and Reference Examples 4 and 5, respectively, and subjected to the high-temperature tensile strength test described in Comparative Experiment 1. The results are shown in Table 3.

Table 3

High temperature strength (unit: kg / cm ² )

coated heat treatment temperature sand

230 ⁰ C 250 ⁰ C 270 ⁰ C 290 ⁰ C 310 ⁰ C 330 ⁰ C

■ ■

Example 4

(Catalyst A 10%) 13.0 13.2 13.7 14.3 14.0 13.1

Example 5

(Catalyst A 20%) 13.1 13.7 14.2 14.7 14.4 13.2

Example 6

(Catalyst A 80%) 12.2 12.8 13.5 14.3 13.6 12.9

Example 7

(Catalyst A 90%) 11.7 12.3 13.0 13.8 13.1 11.6

Reference example 4

(Catalyst A 5%) 13.3 13.6 13.2 12.5 10.9 9.8

Reference example 5

(Catalyst A 95%) 9.7 10.2 12.8 13.4 12.5 11.0

From Table 3 it can be seen that the joint use of Catalysts A and B in Examples 4 to 7 while limiting the amount of Catalyst A ² ^ in the mixed radical polymerization catalyst to the range of 10 to 90 wt the high temperature strength of the resin coated sand resulted in a wide range of heat treatment temperatures. The results

the investigation on the samples of Reference Examples 4 and Figure 5 shows that the effect of using Catalysts A and B together, particularly on latitude the range of heat treatment temperature in which the resin coated sand has very high strength values shows can hardly be obtained when the amount of either the catalyst A or the catalyst B in the mixed catalyst exceeds 95% by weight.

Claims (33)

Claims 1. Resin coated sand to form molds and cores for use in sand molding casting processes, wherein the resin coated sand has a binder in the form of a coating on the contains individual particles of a foundry sand, the binder a crystalline unsaturated Polyester, which at room temperature is hardly sticky "riger solid is, as a main component and contains at least one organic peroxide that acts as a radical polymerization catalyst acts to harden the unsaturated polyester, characterized in that at least ' at least one organic peroxide, which is a combination of a first organic peroxide, its half-life at a temperature of not TELEPHONE (OBS) 233ββ2 TELEX OS-M3βΟ TELEGRAMMS: MQNAPAT * mm O -. below 130 ⁰ C is 10 hours, and a second organic peroxide, the half-life of which at a temperature of below 130 ⁰ C, but not below 100 ⁰ C is 10 hours, acts in a total amount of the combination of first and second peroxide in the range of 0.1 to 5 parts by weight per 100 parts by weight of the unsaturated polyester, and the amount of the first peroxide is in the range of 90 to 10% by weight of the total amount of the first and second peroxides. 2. Resin-coated sand according to claim 1, wherein the difference between the temperature at which the half-life of the first organic peroxide is 10ahr. and the temperature at which the half-life of the second organic peroxide becomes 10 hours is at least 10 ^° C. 3. Resin-coated sand according to claim 2, in which the total of the first and second peroxides ranges from 1 to 3 parts by weight per 100 parts by weight of the unsaturated polyester. 4. Resin-coated sand according to claim 2 or 3, in which the amount of the first peroxide is in the range from 80 to 20% by weight of the total amount of the first and second peroxides. 5. Resin coated sand according to claim 1, 2, 3 or 4 in which the first organic peroxide is selected is from the group of p-menthane hydroperoxide. Cumene hydroperoxide, 2,5-dimethyl-2,5-di- (t-butylperoxy) -hexyl-3, 1,1,3,3-tetramethylbutyl hydroperoxide and 2,5-dimethylhexyl-2,5-dihydroperoxide, and the second organic peroxide is selected is from the group of methyl ethyl ketone peroxide, t-buty! hydroperoxide, di-t-butyl peroxide, dicumyl peroxide, t-butylcumyl peroxide, 2,5-dimethyl-2,5-di- (t-butylperoxy) -hexane, 2,5-dimethyl-2,5-di- (benzoylperoxy) -hexane, t-butylperoxyacetate, 2,5-bis- (t-butylperoxy) -butane and t-butyl peroxybenzoate. • 6. Resin-coated sand according to claim 1, 2, 3, 4 or 5, in which the first organic peroxide is cumene hydroperoxide and the second organic peroxide Is dicumyl peroxide. 7. Resin-coated sand according to claim 1 or claim one of claims 2 to 6, in which the binder also has at least one crosslinking agent Contains agent which is a monomer and prepolymer that is copolymerizable with the unsaturated polyester, the total amount of the at least one crosslinking Means is not greater than 50 parts by weight per 100 parts by weight of the unsaturated polyester. 8. Resin coated. Sand according to claim 7, in which the total amount of the at least one crosslinking Means in the range of 10 to 30 parts by weight per 100 parts by weight of the unsaturated polyester lies. 9. Resin coated sand according to claim. 8, in which the at least one crosslinking agent contains diallyl phthalate. 10. Resin-coated sand according to claim 7 in ° "which the binder also contains at least one silane coupling agent, the total amount the at least one silane coupling agent ranges from 0.1 to 10 parts by weight per 100 parts by weight of the unsaturated polyester. 11. The resin coated sand of claim 10, wherein the total amount of the at least one silane coupling agent in the range of 0.5 to 5 parts by weight per 100 parts by weight of the unsaturated polyester lies· 12. The resin coated sand of claim 10, wherein each of the at least one silane coupling agent is a compound represented by the general formula V / ³ Si
/ \ ^R 2 ^R 4 where R _{1 is} an organic functional group with at least one alkenyl group, alkenylphenylalkyl group, acryloxyalkyl group, methacryloxy alkyl group, glycidoxyalkyl group, epoxycyclo-25 hexylalkyl group and halogenated alkyl group, and each of the groups R_, R ₃ and R _{4 represents} a hydrolyzable group selected from alkoxyl group, alkoxyethoxy group, acetoxy group and halogens. 13. Resin-coated sand according to claim 1, or one of claims 2 to 12, in which the unsaturated polyester has a viscosity value of less than about 500 dPa.s (or P) at a temperature in the range from 100 to 150 _oc ⁰ C. -δ-Ι 14. The resin-coated sand according to claim 13, in which the unsaturated polyester has a viscosity value of less than about 250 dPa.s (or P) at a temperature in the range of 100 to 150 ⁰ C. 15. Resin-coated sand according to claim 1 or any one of claims 2 to 14 in which the weight ratio of the unsaturated polyester to the molding sand is in the range from 1: 100 to 7: 100. 16. A method of making a resin-coated sand for forming molds and cores for use in sand mold casting processes, characterized in that one a main amount of heated foundry sand with a smaller amount of a binder, that is a crystalline unsaturated polyester that is a barely tacky solid acts at room temperature, contains as the main component, mixed so that the unsaturated Polyester is liquefied and attached to the particles of the foundry sand adheres; the combination of a first organic peroxide, which serves as a radical polymerization catalyst for curing the unsaturated polyester, * Q and whose half-life is 10 hours at a temperature of not below 130 ⁰ C, and a second organic peroxide, which serves as a radical polymerization catalyst Hardening of the unsaturated polyester * acts, and its semi-. value time at a temperature below 130 ⁰ C, but not below 100 ⁰ C, 10 hours is added to the mixture of sand and the binder, while rend the temperature of the mixture is maintained such that the binder is in the liquid state Remains, but does not harden easily, even in the presence of the first and second peroxides, wherein the total amount of the first and second peroxides in the range of 0.1 to 5 parts by weight per 100 parts by weight of the unsaturated polyester, and the amount of the first peroxide in the range of 90 to 10% by weight. the total of the first and second peroxide lies; agitating the resulting mixture to disperse the first and second peroxides in the mixture; and lower the temperature of the resulting mixture with continued stirring until solidification of the binder enters, which adheres to the particles of the sand. 17. The method according to claim 16, characterized in that the first and second organic peroxides are selected such that the difference between the temperature at which the half-life of the first peroxide is 10 hours and the temperature at which the half-life of the second peroxide is 10 hours, at least 10 ⁰ C. 18. The method according to claim 17, characterized in that the total amount of ■ first and second peroxides ranging from 1 to 3 parts by weight per 100 parts by weight of the unsaturated Polyester chooses. 19. The method according to claim 17 or 18, characterized in that the amount of first peroxide in the range of 80 to 20% by weight of the total amount of the first and second peroxides chooses. 20. The method according to claim 16, 17, 18 or 19, characterized characterized in that the first organic peroxide selected from the group of p-menthane hydroperoxide, cumene hydroperoxide, 2,5-dimethyl-2,5-di- (t-butylperoxy) -hexyl-3, 1,1,3,3-tetramethylbutyl hydroperoxide and 2,5-dimethylhexyl-2,5-dihydroperoxide, and the second organic peroxide selects from the group of methyl ethyl ketone peroxide, t-buty! hydroperoxide, di-t-butyl peroxide, Dicumyl peroxide, t-butylcumyl peroxide, 2,5-dimethyl-2,5-di- (t-butylperoxy) -hexane, 2,5-dimethyl-2,5-di- (benzoylperoxy) -hexane, t-butyl peroxyacetate, 2,5-bis (t-butylperoxy) butane, and t-butyl peroxybenzoate. 21. The method according to claim 20 or one of claims 16 to 19, characterized in that that the combination of the first and second peroxides to the mixture of the sand and the binder as a solution in an organic solvent. 22. The method according to claim 21, characterized in that geke η η is al:
low alcohol used. draws that one as a solvent 23. .Verfahren according to claim 22, characterized in that the solvent used is ethyl alcohol used. - "ft · - 24. The method according to any one of claims 16 or 21, or one of claims 17 to 19/22 and 23, characterized in that the first organic peroxide is cumene hydroperoxide and the second organic peroxide used is dicumyl peroxide. 25 : Process according to claim 16 or one of claims 17 to 24, characterized in that a binder is used which also contains at least one crosslinking agent which is a monomer or prepolymer which is copolymerizable with the unsaturated polyester wherein the total amount of the at least one crosslinking agent is not greater than 50 parts by weight per 100 parts by weight of the unsaturated polyester. 26. The method according to claim 25, characterized in that a total amount of the at least one crosslinking agent in the range of 10 to 30 parts by weight per 100 parts by weight of the unsaturated polyester is used. 25th 27. The method according to claim 25 or 26, characterized in that as at least a crosslinking agent diallyl phthalate is used. 28. The method according to claim 25, 26 or 27, characterized in that there is a binder used, which also contains at least one silane coupling agent, the total amount of the at least one silane coupling agent in the range of 0.1 to 10 parts by weight per 100 parts by weight of the unsaturated polyester. 29. The method according to claim 28, characterized draws a total of the at least one silane coupling agent in the range of 0.5 to 5 parts by weight per 100 parts by weight of the unsaturated polyester is used. 30. The method according to claim 28 or 29, characterized in that as each of the at least one silane coupling agent uses a compound represented by the general formula / Si ^R 3 \ / ^R 2 ^R 4 where R _{1 is} an organic functional group with at least one alkenyl group, alkenylphenyl alkyl group, acryloxyalkyl group, methacryloxyalkyl group, glycidoxyalkyl group, epoxycyclohexylalkyl group and halogenated alkyl group, and each of R ₂ , R and R is a hydrolyzable group Represents a group selected from alkoxy group, 25th Alkoxyethoxy group, acetoxy group and halogens. 31. The method of claim 16 or any one of claims 17 to 30, characterized in that there is used an unsaturated polyester having a viscosity value below about 500 dPa.s (or P) at a temperature in the range of 100 to 150 ⁰ C. . 32. The method according to claim 31, characterized in that one is an unsaturated Polyester used, which has a viscosity value -ΙΟΙ has less than about 250 dPa.s (or P) at a temperature in the range of 100 to 15O ⁰ C. 5 33. The method according to claim 16 or one of claims 17 to 32 / characterized in that there is a weight ratio of the unsaturated polyester to the foundry sand in the range of 1: 100 to 7: 100. 10