RU2229488C2 - Cold-hardening blend - Google Patents

Abstract

FIELD: molding equipment. SUBSTANCE: cold-hardening blend for manufacturing mold cores and molds contains 100 wt parts of quartz sand, 1.5-2.5 wt parts of alkaline polyphenol resin, and ester-type hardener in proportion of 25-30% on the weight of resin, said hardener being, in particular, composed of ethylene glycol acetates or their mixtures with γbutyrolactone or propylene carbonate. EFFECT: enabled controlling viability and hardening rate of cold-hardening blends within a wide range. 14 tbl

Description

The invention relates to foundry, in particular to rod and molding cold-hardening mixtures (CTS) for the manufacture of foundry cores and molds.

Cold-hardening mixtures with synthetic resins of urea-furan (for example, BS-40), phenolic (for example, SF-3042) or phenolofuran (for example, FF-1F) class, cured by acid catalysts are known. Resins of these classes are highly toxic. The content of free formaldehyde in the resin BS-40 reaches 1.7% (with MPC = 0.5 mg / m ³ ), the content of furyl alcohol - 40% or more, nitrogen - 12%. In phenolic resins, the content of free phenol reaches 15% (with MPC = 03 mg / m ³ ). Resins of the listed classes have low heat resistance, and the mixtures themselves on these resins often cause the formation of a metallized burn, sieve porosity and gas shells in castings.

The ability to control the survivability and hardening rate of such mixtures is extremely limited. It can be carried out only by changing the concentration of the catalyst or its content in the mixture.

In foundry, phenol-formaldehyde resins are often used as binders for the preparation of CTS, which are divided into novolac and resol, depending on the conditions of their preparation. Novolac resins are obtained in an acidic environment, and resol resins in an alkaline environment.

XTS based on phenol-formaldehyde resole resin RSF-3010 was taken as the prototype closest to the present invention. The resin is a product of resole polycondensation of phenol and formaldehyde in the presence of a synthesis catalyst - magnesium oxide (Reference "Molding materials and mold technology" p.91, table 46). The content of free phenol in the resin RSF-3010 is not more than 15%, free formaldehyde is not more than 2%.

The composition of the XTS on the resin RSF-3010, parts by weight:

Quartz sand 100

Resin RSF-3010 2

Water solution of benzenesulfonic acid

(BSK), density 1.265 g / cm ³ 1.2

The survivability of the mixture is 5-15 minutes; compressive strength (MPa) after 1 h = 0.8; 3 h = 1.5; 24 hours = 2.5 (tab. 46, p. 91. Reference "Molding materials and mold technology"). The disadvantages of HTS on RSF-3010 resin (according to the prototype) are high toxicity due to the high content of free phenol and formaldehyde, limited ability to control survivability and hardening speed, and a frisky decrease in strength and hardening speed at low air temperatures. In addition, phenol-formaldehyde resins similar to RSF-3010 and CTS based on them lead to the formation of a metallized burn and other defects on castings.

According to the present invention, the known resol phenol-formaldehyde alkaline water-soluble resin, which is a phenol-formaldehyde oligomer converted due to alkali (caustic potassium or caustic soda) to the form of polyphenolate, is used as a binder in the composition of a cold-hardening mixture. A binder and self-hardening system based on it were developed by the British concern Borden Chemical UK. This system is called the α-set process. In the early 90s of the 20th century, the α-set process began to be widely used in Europe, the USA, and Japan. Currently, it is beginning to be used at enterprises of the Russian Federation. The essence of the process is described, in particular, in the article CJ.Nybergh (company OYLUX AB, Espoo, Finland) "Alphaset process and its use in Russia" (Magazine "Foundryman of Russia" No. 3, 2002, pp. 35-40 ) Resin production for the α-set process has been mastered at Uralchimplast OJSC. She was awarded the FSM-1 trademark.

According to TU 6-00-5751766-4-88 "Furan and Phenolic Silanized Resins" developed by Uralchimplast OJSC FSM-1 is a reaction product of diphenylpropane, phenol and formaldehyde modified with furyl alcohol, ethylene glycol and organosilicon monomers. Resole alkaline phenolic resins have a pH of 12.5-14; the content of free formaldehyde in them is not more than 0.3%, and free phenol - not more than 0.2%. Mass fraction of water in the resin - up to 40%. Synthetic resins (phenol-formaldehyde, urea-and phenolofuran) currently used for the preparation of CTS have a pH of about 6.5-8.4. All of them are practically water insoluble.

The fundamental difference between alkaline resins and other classes of synthetic resins used for the preparation of CTS is that the former are cured with ester reagents, and the latter with acid catalysts (H ₃ PO ₄ , benzenesulfonic acid - BSA, n-toluenesulfonic acid).

Due to the lack of the α-set hardener required for alkaline resins on the Russian market, the α-set process has found extremely limited use in our country, with a focus on imported hardeners only. Table 1 shows the test results of six brands of ester hardeners produced by two foreign companies under different trademarks for the α-set process and providing mixtures with different survivability values. The composition of foreign hardeners is unknown. Hardeners were tested in mixtures on an alkaline resin of OJSC “Uralchimplast” of the FSM-1 brand with the following content of components, parts by weight:

Quartz sand 100

Resin FSM-1 2.5

Hardener 0.75

The mode of preparation of the mixture on a laboratory paddle mixer: mixing the hardener with a filler for 1.5-2 minutes, after which the resin was introduced and the mixture was mixed for 45-50 s. The strength of the mixtures was tested for compression after 20 minutes, 1 hour, 3 hours and 24 hours of hardening. The survivability of the mixtures was determined on the device design TsNIITMASH.

The table shows that different brands of foreign hardeners have different activity, which allows to obtain, depending on the production need, the corresponding survivability and hardening speed of the mixtures.

An object of the present invention is a cold hardening mixture comprising 100 parts by weight quartz sand, 1.5-2.5 parts by weight alkaline polyphenolic resin (or alkaline polyphenolate) and 25-30% by weight of an ester hardener resin - ethylene glycol acetates, or mixtures thereof with γ-butyrlactone in a weight ratio of 1: 9 to 9: 1, or mixtures thereof with propylene carbonate in their mass in a ratio from 1: 1 to 25: 1, which allows to control a wide range of survivability and hardening speed of cold-hardening mixtures.

Instead of silica sand, other highly refractory materials, such as granular disten-sillimanite, chromite, zircon, corundum, and others, can be used as filler for the preparation of CTS. Since highly refractory fillers have a higher density than silica sand, the content of binder and hardened in the mixture should be adjusted in the direction of their decrease.

Alkaline polyphenol resins (alkaline polyphenolates) used for the α-set process under various trademarks are used as a binder in mixtures, including resins manufactured by Uralchimplast under the FSM trademarks, for example, FSM-1 resin, with which we conducted main tests.

The ester hardeners can be stand alone ethylene glycol acetates (ACEG) or two-component hardeners consisting of ethylene glycol acetates and one of two cyclic ethers: γ-butyrlactone or propylene carbonate, which regulate the survivability and hardening rate of mixtures depending on the particular production air or temperature .

Γ-butyrlactone is proposed as one of the cyclic ethers when the ratio of ACEG to γ-butyrlactone varies from 1: 9 to 9: 1 by weight. In this case, the survivability of the mixture is regulated in the range from 6 to 30 minutes, and the hardening time is from 9 to 48 minutes with a simultaneous increase in strength.

Another cyclic ester of the present invention is propylene carbonate. It is more active than γ-butyrlactone. With a change in the ratio between ACEG and propylene carbonate ranging from 1: 1 to 25: 1, the survivability of the mixture increases from 2 to 20 minutes, and the hardening time from 4 to 32 minutes.

When using ATSEG in its own form, the survivability of the mixture can be increased up to 40-60 min with a significant decrease in strength at the initial stages of hardening.

The invention is illustrated by the following examples. One of the main components of our ester hardeners is ethylene glycol acetates. This is a mixture of ethylene glycol di- and monoacetates. The preparation of ethylene glycol acetates consists in the synthesis of a product from acetic acid and ethylene glycol. Structural formulas of ethylene glycol diacetate and monoacetate:

The technology for producing ethylene glycol acetates was developed with our participation. Currently, the industry produces 5 grades of ATSEG for the cured liquid glass XTS. They differ in fractional composition - the ratio between ethylene glycol di- and monoacetate, which leads to their different curing ability, which allows changing the survivability of liquid-glass CTS from 5-6 minutes to 1.5-2.0 hours. The designations of hardener grades we adopted for liquid glass XTS and their composition are given in Table 2.

Table 3 shows the properties of XTC on the FSM-1 resin with 6 grades of ATSEG. The composition of the test mixture, parts by weight:

Quartz sand 100

Resin FSM-1 2.5

Hardener ATsEG 0.75

It follows from Tables 2 and 3 that with an increase in the grade of hardener and a decrease in the content of ethylene glycol monoacetate in it, the survivability of the mixtures noticeably increases, and the strength properties at the initial stages of hardening slightly decrease, while the daily strengths are leveled. In industrial conditions, sometimes it becomes necessary to use mixtures with a pot life of 60 minutes or more. In this case, an ACEG consisting of pure ethylene glycol diacetate and practically free of ethylene glycol monoacetate (conventionally marked with 5OOM) can be used. The properties of such a mixture are also given in table.3.

The properties of the mixtures shown in table 3, obtained at temperatures of 18-20 ° C. It is not possible to obtain survivability of less than 25 minutes and to accelerate the hardening of the mixture with the help of only ATSEG. Nevertheless, ethylene glycol acetates can be used independently for curing alkaline phenolic resins with moderate requirements for the survivability of the mixture (25-60 minutes) and hardening rate at medium and elevated ambient temperatures. In relation to these conditions, they correspond to foreign hardeners AN-61 and N-30 (table 1).

However, at temperatures of + 10-15 ° C and below, the survivability of the mixtures increases sharply, the hardening rate decreases and strength decreases. In winter, for example, opening of core boxes and broaching of models when using ATSEG as hardeners can be carried out no earlier than after 1.5-3 hours, which in most cases is unacceptable for production practice.

To reduce the survivability, as well as to regulate broadly the survivability and hardening rate of CTS with alkaline phenolic resins, we proposed the use of cyclic esters, which, in theory, should more actively cure CTS on alkaline resins compared to ACEG. According to our data, the most effective representative of a large group of cyclic esters for curing alkaline resins is γ-butyrlactone. Get it by dehydrogenation of 1,4-butanediol, followed by distillation. The release of γ-butyrlactone is carried out according to TU 64-9-07-87, according to which the mass fraction of γ-butyrlactone in the product is not less than 99.0%, density 1.1266-1.1286 g / cm ³ .

The structural formula of γ-butyrlactone

The empirical formula is C ₄ H ₆ O ₂ . The molecular weight is 86.09.

Another cyclic ether - propylene carbonate - is a complete, cyclic ether of propylene glycol and carbonic acid. Structural formula of propylene carbonate

The content of the main substance in the product is not less than 98%. Density 1,198-1,200 g / cm ³ (TU 2435-378-05742746-2001).

A test under equal conditions with the same mixture composition (parts by weight: quartz sand - 100, resin FSM-1 - 2.5, hardener - 0.75) of the best foreign fast hardener AN-51 and γ-butyrlactone, BSM (fast hardening for resin) designated by us, showed that BSM hardener significantly surpasses the best foreign analogue in strength characteristics (at the same survivability) (see table 4).

It is technically possible to use γ-butyrlactone as an independent hardener, but it may prove economically disadvantageous due to the relatively high cost of γ-butyrlactone.

A two-component hardener, consisting of ATSEG and γ-butyrlactone (BSM) at various ratios, allows controlling the survivability and curing rate of CTC in a wide time interval while increasing strength. The curing time is about 50% more than the survivability of the mixture. The effect of the composition of a two-component hardener at various ratios between the AC CMEG of grade 3 CM and γ-butyrlactone (BSM) on the survivability, hardening time, and strength of the mixtures are presented in Table 5.

The composition of the mixture for testing was selected as follows, parts by weight:

Quartz sand 100

FSM-1 2.0 alkaline phenolic resin

Variable hardener 0.6

The tests were carried out at temperatures of 18-20 ° C. In the composition of the hardener, the ratio between the ACEG and BSM varied from 9: 1 to 1: 9 (in parts by weight). Numbers 1 and 9 show the properties of the mixture at 100% ACEG (mixture 1) and 100% BSM (mixture 9). In mixture 2, for example, with the ratio of ACEG: BSM = 9: 1, the hardener consisted of 90% ACEG and 10% BSM; in mixture 5 at a ratio of ACEG: BSM = 1: 1, the hardener consisted of 50% ACEG and 50% BSM, etc.

In Table 5 and the following Tables 6–13, ACEEG grade 3 CM, which is a mixture of ethylene glycol mono- and diacetate, was used in the compositions of ester hardeners. The content of monoacetate in this hardener is in the range of 22-26% by weight.

From table 5 it is seen that as the ratio between the ACEG and BSM (γ-butyrlactone) decreases or the content of the BSM hardener increases in the composition of the hardener, the survivability of the mixture and the hardening time gradually decrease, while a significant increase in strength at all stages of hardening. The lower limit of the ratio between the ADC and BSM, equal to 9: 1, must be selected taking into account the strength after 1 h and a moderate value of survivability (not more than 30 minutes), and the upper limit of the ratio between the ADC and BSM should be limited to 1: 9, taking into account the higher cost γ-butyrlactone (about 2 times) compared with ACEG, and also because the survivability and strength of the mixtures change slightly from 1: 9 to one γ-butyrlactone. In everyday production practice, it is preferable to use a two-component hardener with the limits of the ratio of the AEG and BSM from 4: 1 to 1: 4.

The survivability, hardening time and initial strength of the mixture are significantly affected by the temperature of the ambient air and the starting ingredients.

Tables 6 and 7 show data on the effect of temperature on the properties of a mixture with different hardener compositions.

Table 6 presents the properties of mixtures at a temperature of 8-10 ° C with two types of hardeners: two-component at a ratio of AECEG: BSM = 1: 1 and a single-component at one AECEG.

Table 7 shows the effect of temperature on the survivability and initial strength of the mixture (after one-hour hardening) with a ratio of 1: 1 in the ACEG and BSM hardener.

With decreasing temperature, the survivability of the mixture increases sharply, and the initial strengths decrease. There is no hourly strength for a mixture with one ACEG hardener at 10 ° C, and with a further decrease in temperature the mixture hardens very slowly and its use becomes impossible. In relation to these conditions, the use of a two-component hardener is a prerequisite.

Another representative of cyclic esters capable of controlling the survivability and hardening rate of XTC with alkaline resins is propylene carbonate (PCT), an ester of propylene glycol and carbonic acid. Table 8 shows the properties of ChTS on an alkaline polyphenolic resin with two-component hardeners at various ratios of ACEG: PCT, varying from 1: 1 to 25: 1 (mixture 1-8). The same table shows the properties on one hardener ACEG (mixture 9).

The data in Table 8 show that as the ratio of ACEG: PCT increases, the survivability of the mixtures increases from 2 min (at a ratio of 1: 1) to 20 min (at a ratio of 25: 1).

A comparison of the data in tables 5 and 8 shows that propylene carbonate, in comparison with γ-butyrlactone, more actively affects the survivability and curing time of the mixture with a lower content in the hardener. In this case, the strength properties, in contrast to mixtures with γ-butyrlactone, vary slightly. Table 8 shows the properties of the mixtures at a temperature of 20 ° C. At different temperatures, with the same ratios between the ACEG and the PCT, the survivability values and hardening time will be different.

The lower limit of the ratio of ACEG: PCT, it is advisable to limit 1: 1, which ensures the survivability of the mixture, equal to 2 minutes With a lower ratio, the mixture becomes non-technological. The upper limit of the ACEG: PCT ratio is limited by us to 25: 1, at which the survivability of the mixture is quite acceptable for production purposes, and the strength properties of the mixture are quite high. If necessary, increase survivability, you can use the hardener ATSEG in its own form (mixture 9, table 8). In addition, with a ratio of more than 25: 1, difficulties may arise in the preparation of a two-component hardener due to the small amounts of propylene carbonate.

Tables 9 and 10 show the compositions and properties of mixtures at the boundary and average ratios between the AECEG and γ-butyrlactone (BSM), and in Tables 11 and 12, the compositions and properties of the mixtures at the boundary and average ratios between the AECEG and propylene carbonate.

Table 13 shows three specific compositions of CTS with an FSM-1 alkaline resol resin: with a minimum binder content of 1.5 parts by weight. (mixture 1), with an average content of 2.0 wt.h. (mixture 2) and with a maximum resin content of 2.5 parts by weight (mixture 3), with various hardeners, as well as XTC prototype (mixture 5). Mixture 4 contains an ester hardener with a varying ratio between ACEG and BSM ranging from 1: 9 to 9: 1.

Table 14 shows the properties of these mixtures.

From a consideration of Tables 13 and 14, it follows that at the lower limit for the binder content (1.5 parts by weight), it is possible to prepare CTS with satisfactory strength and technological properties using high-quality enriched quartz sand. On ordinary quartz sand with a clay content of up to 2% of a mixture with 1.5 wt.h. binder have a relatively low strength and increased crumbling. With a further decrease in the binder content, even when using enriched quartz sand, the mixtures become non-technological. The upper limit on the content of alkaline phenolic resin should be limited to 2.5 parts by weight, since the strength properties of XTS with 2 and 2.5 parts by weight differ little, and increasing the binder content increases the cost of the mixture and increases its gas content.

The optimal content of alkaline phenolic resin in the mixture should be considered 1.8-2.2 wt.h.

A comparison of the properties of mixtures 2 and 4 on the FSM-1 resin with the mixture of the prototype (5) shows that the properties of the first two mixtures compares favorably with the properties of the mixtures of the prototype, both in terms of strength properties and the possibility of controlling survivability and hardening rate.

The method of preparing the two-component ester hardener of the present invention consists in mixing two esters - ethylene glycol acetates with one of the cyclic esters: γ-butyrlactone (BSM) or propylene carbonate in the ratios indicated in the invention (in parts by weight) under mechanical stirring and at ordinary temperatures .

Using esters - ethylene glycol acetates and two representatives of cyclic esters: γ-butyrlactone and propylene carbonate, for the first time in the Russian Federation a gamma of domestic one- and two-component hardeners for CTC on alkaline polyphenolic resins has been proposed, which makes it possible to control survivability over a wide time interval (from 5-6 min up to 60 min) and the speed of hardening of mixtures.

The proposed hardeners are not inferior, and in a number of indicators superior to the best foreign analogues.

CTS on alkaline resins with hardeners developed according to the present invention have undergone extensive production tests and have been implemented at a number of plants, including the Cherepovets Foundry and Mechanical Plant OJSC, the Kolomna MetalLitmash LLC and other enterprises.

Technical appraisal and economic advantages of the invention in comparison with the known CGS on synthetic resins are as follows:

- improves the quality and surface finish of castings from cast iron and steel, including castings from manganese steels;

- virtually eliminated the formation of metallized burn and "notches";

- the number of defects and rejects of castings is reduced several times, including gas shells and sieve porosity;

- due to a sharp decrease in the composition of the resin of free phenol and formaldehyde (by ten times), the sanitary and hygienic working conditions of workers and the environmental situation in foundries are significantly improved.

Claims (1)

Cold hardening mixture, including 100 wt.h. quartz sand, 1.5-2.5 parts by weight an alkaline polyphenolic resin and 25-30% by weight of an ester hardener resin - ethylene glycol acetates or a mixture thereof with γ-butyrolactone in a weight ratio of 1: 9 to 9: 1, or a mixture thereof with propylene carbonate in a weight ratio of 1: 1 to 25: 1.