GB2039285A

GB2039285A - Binders for cold-curable moulding sand mixtures, their preparation and use

Info

Publication number: GB2039285A
Application number: GB7901313A
Authority: GB
Original assignee: NAUCH PROIZV OBIEDINE TEKHNOL
Current assignee: NAUCH PROIZV OBIEDINE TEKHNOL
Priority date: 1979-01-12
Filing date: 1979-01-12
Publication date: 1980-08-06
Also published as: SE7900146L; DE2903071C2; FR2448399A1; ATA22179A; GB2039285B; SE415451B; DE2903071A1; FR2448399B1; AT385512B

Abstract

The binder comprises a urea- formaldehyde resin and, as a modifier therefor, an oil-in-water emulsion comprising a heavy fraction of a shale resin having a specific gravity of at least 1.01 g/cm<3>, an organic solvent, an emulsifying agent and water.

Description

SPECIFICATION Binders for cold-curable moulding sand mixtures, their preparation and use The present invention is concerned with binders for cold-curable moulding sand mixtures as used in foundries for making casting moulds, with a method of making such binders, and with moulding sand mixtures containing such binders.

Binders for cold curable moulding sand mixtures which are based on urea-formaldehyde resins are known and it is known to incorporate modifying agents in such binding agents in order to control the binding power of the resins. A known and widely used modifying agent for this purpose is furyl alcohol which is used in amounts up to 20%, based on the weight of the resin. However, furyl alcohol has certain disadvantages.

We have now found that oil-in-water emulsions of the heavy fraction of shale resins constitute effective modifying agents for urea-formaldehyde resin in such binders and enable better heat resistance and mechanical strength to be obtained than when urea-formaldehyde resins are used alone, without any substantial increase in cost. Urea-formaldehyde-based binders comprising such emulsions as the modifying agent are also more plastic at high temperatures than known binders of this kind.

According to the present invention, therefore, there is provided a binder for a cold-curable moulding sand mixture, which comprises a urea-formaldehyde resin and, as a modifying agent for said resin which controls its binding power, an emulsion containing a heavy fraction of a shale resin with a specific gravity of at least 1.01 glcm3, an organic solvent capable of dissolving carbonaceous components of said shale resin fraction, an emulsifying agent and water, the components of the emulsion being present in such proportions that the emulsion is of the oil-in-water type.

Preferred binders according to the invention have the following compositions, in parts by weight: urea-formaldehyde resin 65 to 90 heavy fraction of shale resin with a specific gravity of at least 1.23 g/cm3 3 to 15 organic solvent 1 to 8 emulsifying agent 0.2 to 1.5 water 5 to 20.

The shale resin heavy fraction is preferably a product resulting from the processing of shale in a gas-generator fu rnace at a temperature of about 500"C.

A suitable heavy fraction of a shale resin is, for example, a product resulting from the processing of Estonian shales containing phenolic compounds and about 86-90% of carbon. The coke value of the product is 45-55%. This product has the following physico-chemical properties: 1. Specific gravity, g/cm3 1.01 - 1.28 2. Engler viscosity at 50"C 10 - 20 3. Brenken flash point, "C at most 90 4. Water content, % at most 3.5 5. Mechanical impurities, % at most 2.5 6. Sulphur content, % at most 1.5 7. Total acid number 1.6-5.6 8.Content of inorganic acids calculated for KOH, % 0.01 - 0.35 This heavy fraction has the following composition, percent by weight: asphaltenes 15.74 resins 20.00 oils 42.26 phenols 22.00 Suitable organic solvents for use in the binder according to the invention are, for example, white spirit, kerosene and diesel fuel; the amount of organic solvent in the binder is preferably from 1 to 8% by weight.

Suitable emulsifying agents for use in the binder according to the present invention include anionic, cationic and non-ionic surfactants, for example alkylarylsulphates, alkylarylsulphonates, hydroxyethylated phenols, mercaptans, and long-chain aliphatic amines. Preferred surfactants are the sodium salts of alkylarylsulphonic acids having from 8 to 12 carbon atoms in the alkyl radical and of alkylsulphonic acids having from 12 to 18 carbon atoms in the alkyl radical, and mixtures of such salts. The surfactant is preferably present in an amount of from 0.2 to 1.5% by weight; incorporation of larger or smaller amounts of surfactant usually results in the final cured moulding sand mixture having a reduced mechanical strength.

Another kind of emulsifying agent which may be used in the binder according to the invention is a finely divided hydrophilic inorganic compound, for example refractory clay, bentonite, CaC03, A1203, and BaS04; such emulsifying agents are preferably used in an amount of from 0.2 to 1.5% by weight. The use of such powdered materials in an amount below 0.2% by weight impairs distribution of the binder over the grains of the refractory filler in the moulding sand mixture, whereas amounts above 1.5% by weight of these materials substantially reduce the binder viscosity and its reactivity.

Moulding sand mixtures comprising a binder according to the invention are preferably of the following composition, in parts by weight: filler 100 binder 2-5 curing agent 0.3-1.0 water 0.5- 1.0 According to a further aspect of the invention, there is provided a method of preparing the binder according to the invention, which comprises (1) mixing the shale resin fraction, the organic solvent and the emulsifying agent, and then (2) adding the urea-formaldehyde resin with stirring to form a uniform product, water being present in the first and/or the second stages so that an oil-in-water emulsion is obtained.The first stage of this process is, for example, carried out by mixing the shale resin heavy fraction, the solvent and the emulsifying agent using a rotating agitator operating at a speed of 400 to 600 r.p.m. at a temperature of from 40 to 70"C for a period of from 40 to 50 minutes. The urea-formaldehyde resin and water are then added to the resulting mixture and agitation is continued under the same conditions for 40-50 minutes. The amount of water used should be such that (i) an oil-in-water emulsion is obtained and (ii) the final binder has the required specific gravity. It is preferred that the binder should have a specific gravity of 1.15 to 1.20 g!cm3.

Instead of the foregoing procedure, the water may be added in the first stage, the other conditions of the process being otherwise the same.

It may be desirable to carry out at least the first stage of the process under a reduced pressure of, for example, 0.3 to 0.5 atm. The use of a reduced pressure is preferred when water is not added in the first stage, but only in the second.

In order that the invention may be more fully understood, the following examples of binders and their prepartion, in which all proportions are by weight, are given by way of illustration.

Example 1 A binder was prepared from the following components: urea-formaldehyde resin 65% heavy fraction of shale resin 15% white spirit 8% surfactant (alkylarylsulphonate) 1.5% water 10.5% The shale resin fraction, solvent and surfactant were mixed in a reactor using an agitator rotating at a speed of 500 r.p.m. at a temperature of 50"C and under a pressure of 0.5 atm for 45 minutes. A mixture of the urea-formaldehyde resin and the water was added to the resulting mixture. The composition was further agitated under the same conditions for a period of 40 to 50 minutes.

The binder obtained had a specific gravity of 1.18 g/cm3 and a viscosity (4 mm funnel) of 70 sec.

Example2 A binder was prepared from the following components: urea-formaldehyde resin 90% heavy fraction of shale resin 3% white spirit 1% alkylarylsulphonate 0.2% water 5.8% The procedure used was as described in Example 1. The specific gravity of the binder obtained was 1.20-1.23 9 cam3 and its viscosity (4 mm funnel) was 90 sec.

AdlllHlC 3 A binder was prepared from the following components: urea-formaldehyde resin 70% heavy fraction of shale resin 10% kerosene 5.0% sulphonate 0.6% water 14.4% The binder was prepared in a closed vessel by mixing the water, solvent, heavy fraction of shale resin, and emulsifying agent with an agitator rotating at a speed of 600 r.p.m. for 40 minutes at a temperature of 60"C.

The urea-formaldehyde resin was then added to the resulting mixture and agitation was continued for a further 50 minutes.

The resulting binder had a specific gravity of 1.18 g/cm3 and a viscosity (4 mm funnel) of 70-75 sec.

Example 4 A binder was prepared from the following components: urea-formaldehyde resin 70% heavy fraction of shale resin 4% kerosene 5% powdered hydrophilic inorganic compound 1% water 20% The binder was prepared following the procedure described in Example 3, with the exception that after the addition of water, agitation was carried out for 45 minutes.

The resulting binder has a specific gravity of 1.14 g/cm3 and a viscosity (4 mm funnel) of 60-70 sec.

In the foregoing Examples optimum compositions have been presented for the preparation of the binder; however, it will be understood that different proportions of the components can also be used provided that a uniform oil-in-water emulsion is obtained.

To prepare a cold-curable moulding sand mixture, a binder according to the invention is mixed with the filler in an amount of from 2.0 to 5.0% by weight of the filler. Use of less than 2.0% by weight of binder does not provide the desired mechanical strength in the cured mould because there is insufficient binder to treat the filler surface. The use of more than 5% of binder is also inexpedient since no substantial increase in mechanical strength is obtained, while gas liberation from the mixture is increased and the curing cycle required becomes longer.

For the preparation of the moulding sand mixture, any suitable refractory filler may be used such as is generally employed for foundry moulding sand mixtures. Suitable fillers are, for example, quartz sand, olivine, chromomagnesite, and disthensilimanite, of which the first is generally preferred.

Suitable curing agents for the preparation of cold-curable moulding sand mixtures including binders according to the present invention are, for example, acidic materials such as acids, either organic or inorganic, for example phosphoric acid, sulphuric acid, hydrochloric acid, sulphonic acids, such as p-toluenesulphonic acid, or axalic acid, and acidic salts, such as ammonium chloride, ferric chloride and compounded curing agents, such as a mixture of hydrochloric acid and ferric chloride or ferrous chloride.

In order that the invention may be more fully understood, the following examples of moulding sand mixtures and their preparation, in which all parts and proportions are by weight, are given by way of illustration.

In each of the following examples, the mixture was prepared by adding phosphoric acid to quartz sand and agitating for 1-2 minutes, then adding the binder and water and continuing agitation for a further 1-2 minutes. From the mixture thus obtained, moulds and cores were made by conventional procedures.

Example 5 A moulding sand was prepared from the following components: quartzsand 100 binder of Example 1 2.0 phosphoric acid (60% concentration) 0.3 water 1.0.

The mixture set in 10-15 minutes.

The curing time of samples (50 mm diameter, 500 mm height) was 15.17 min. The compression strength ol the samples was as follows, kg/cm2: after curing 1 hour 3-3.5 after curing 3 hours 5-6 after curing 24 hours 14-17.

The heat resistance of the cured samples was shown by the residual strength of samples after heating to a temperature of 800 - 9002C which was 1.8 kg/cm2.

Example 6 A moulding sand mixture was prepared from the following components: quartz sand 100 binder of Example 2 5.0 phosphoric acid (60% concentration) 1.0 water 0.5.

The mixture set in 10-12 minutes; the curing time of samples made therefrom was 15-17 minutes.

The compression strength of samples made from this mixture was as follows, kg/cm2: after curing 1 hour 12-15 after curing 3 hours 18 - 25 after curing 24 hours 50 - 60 and after heating to 800-9002C, was 4.0 kgicm2.

Example 7 A moulding sand mixture was made from the following components: quartz sand 100 binder of Example 1 3.5 curing agent (ferric chloride and ferrous chloride and a solution of hydrochloric acid of the composition: Fecal3.6 H20 - 1000 9 {litre; FeCI2 - 30-50 gilitre; HCI - 20-30 g!litre; specific gravity 1.17 - 1.18 gilitre) 0.5 water 0.5.

The mixture set in 8-10 minutes and its curing time was 15-17 minutes. The compression strength of samples made from the mixture was as follows, kg/cm2: after 1 hour 12-15 after 3 hours 22 - 24 after 24 hours 56 - 58, and after heating to 800-900"C, was 4.0 kglcm2.

Example8 A moulding sand mixture was prepared from the following components: quartz sand 100 binder of Example 3 4.5 curing agent (60% orthophosphoric acid) 0.7 water 0.3.

The mixture set in 12-15 minutes and its curing time was 17-20 minutes. The compression strength of samples made therefrom was as follows, kg/cm2: after 1 hour 13-14 after 3 hours 20 - 22 after 24 hours 47 - 52 and after heating to 800-900"C, was 3.5 kg/cm2.

Example 9 A moulding sand mixture was prepared from the following components: quartz sand 100 binder of Example 4 5 curing agent 1.0 water 0.3.

The mixture set in 12 to 15 minutes and its curing time was 18 to 20 minutes. The compression strength of samples made therefrom was as follows, kg/cm2: after I hour 13-17 after 3 hours 22 - 24 after 24 hours 53 - 55, and after heating to 800-900"C, was 4.3 kg/cm2.

In order to illustrate the advantages of the binders of the present invention over binders comprising urea-formaldehyde resin alone, a comparison of the properties of the binders is given below.

The comparison is based on the testing of binders for thermal stability by the procedure of coke value determination.

A portion of the binder(10 was placed in a porcelain crucible which was then put into a steel crucible which was closed with a cover. A burner was placed under the bottom of the crucible and the test sample was calcined at 800"C to a constant weight of coke residue. The coke value is calculated as a ratio of the coke residue weight to the weight of the portion of the test binder (in per cent by weight).

The thermal strength of the cold-curable moulding sand mixture is given by the residual strength of samples made from the test mixture after heating to 800 C. The test results are shown in the following Table.

Type of the binder Coke value, Residual strength of employed % moulding sand mixtureX of Example 5 at 800"C Urea-formaldehyde resin 14 0.8 Binder of the present invention 25 1.8 x/The test mixture had the following composition, parts by weight: quartz sand 100 binder 2.0 phosphoric acid (60% concentration) 0.3 water 1.0.

As will be seen from the above Table, the thermal strength of the moulding sand mixture incorporating a binder according to the invention is about twice as great as that of a mixture having urea-formaldehyde resin alone as the binder.

Claims

1. A binder for a cold-curable moulding sand mixture, which comprises a urea-formaldehyde resin and, as a modifying agent for said resin which controls its binding power, an emulsion containing a heavy fraction of a shale resin with a specific gravity of at least 1.01 g/cm3, and organic solvent capable of dissolving carbonaceous components of said shale resin fraction, an emulsifying agent and water, the components of the emulsion being present in such proportions that the emulsion is of the oil-in-watertype.

2. A binder according to claim 1, which comprises, in parts by weight: urea-formaldehyde resin 65 to 90 heavy fraction of shale resin 3 to 15 organic solvent 1 to 8 emulsifying agent 0.2 to 1.5 water 5 to 20.

3. A binder according to claim 1 or 2, in which the shale resin fraction is a product resulting from the processing of shale in a gas-generator furnace.

4. A binder according to any of claims 1 to 3, in which the emulsifying agent is a surfactant.

5. A binder according to claim 4, in which the surfactant is an alkylarylsulphonate.

6. A binder according to any of claims 1 to 3, in which the emulsifying agent is a finely divided hydrophilic inorganic compound.

7. A method of preparing a binder according to any of claims 1 to 6, which comprises (1) mixing the shale resin fraction, the organic solvent and the emulsifying agent, and then (2) adding the urea-formaldehyde resin with stirring to form a uniform product, water being present in the first and/or the second stages so that an oil-in-water emulsion is obtained.

8. A method according to claim 7, which is carried out at a temperature of from 40 to 70"C.

9. A method according to claim 7 or 8, in which at least the first stage is carried out at a reduced pressure of from 0.3 to 0.5 atm.

10. A moulding sand mixture comprising a filler, a binder, a curing agent and water, in which the binder is a binder according to any of claims 1 to 6 and the components are present in the following proportions, in parts by weight: filler 100 binder 2 to 5 curing agent 0.3to 1.0 water 0.5 to 1.0.

11. A cinder for a cold-curable moulding sand mixture substantially as herein described in any of Examples 1 to 4.

12. A cold-curable moulding sand mixture substantially as herein described in any of Examples 5 to 9.

13. A method for preparing a binder for a cold-curable moulding sand mixture substantially as herein described in any of Examples 1 to 4.