US2466435A - Manufacture of molded articles from coal - Google Patents

Description

Patented Apr. 5, 1949 2,466,435 RIANUFACTURE 9F MQLDED ARTICLES FlttDlVi CAL No Drawing.

Application July 30, 1945, Serial No. 667,910. in Great Britain August 17, 1944 3 Claims.

In United States Patent application Serial No. 492,968, now U. S. Patent No. 2,404,208, is described the manufacture of moulded articles from coal by subjecting an intimate mixture of certain finely comminuted bituminous coals and a softening agent in a mould to a pressure of at least about 256 atmospheres at a temperature which is at least 256 C. and, under the pressure used, lies between the temperature at which the mixture as a whole begins to soften and that at which it undergoes intumescence. Certain filling materials may, if desired, be incorporated with the coal-softening agent mixture to be moulded. Articles moulded from the coal-softening agent mixture alone appear to the eye to have a homogeneous and non-porous structure, and they have a conchoidal fracture, and do not produce a black streak when rubbed on paper.

Owing to the incorporation of the softening agent with the coal, it is possible to use coals which, when heated alone, only begin to soften at or near the temperature of the onset of intumescence. This is due to the fact that the coal-softening agent mixture softens at a lower temperature than does the coal when heated alone, and that the intumescence temperature of the mixture, as compared with that of the coal alone, either is not lowered or is lowered to a much less extent than the softening temperature is lowered.

We have now found that it is possible with mixtures of certain finely divided coals and modifiers as hereinafter defined to obtain moulded articles which are especially stable to organic solvents, and to reduce the temperature and time of moulding, if the mixture is subjected to a preliminary briquetting and heat treatment as hereinafter described.

According to this invention a process for making moulded articles comprises preparing an intimate mixture of finely divided coal having an agglutinating value greater than zero and as a modifier a, finely divided coal tar pitch having a melting point of at least 110 C. in a proportion such that the coal-modifier mixture softens at a temperature lower than does the coal when heated alone and not exceeding about 25 per cent. of the combined weight of the coal and modifier, briquetting the resulting mixture, heating the briquettes at a non-carbonizing temperature ranging from 250 C. to 400 C. for at least one hour until their content of constituents extractable by toluene is at most about 22 per cent. based on the weight of the modifier, disintegrating the heat-treated briquettes, subjecting the disintegrated material in a mould to a pressure of at least about 250 atmospheres at a temperature at which under the pressure used the mixture softens as a whole without undergoing intumescence, and then slowly cooling the moulded article.

The expression agglutinating value greater than zero has reference to the agglutinating value as determined by the method described in British standards specification No. 705, 1936, and. the expression content of constituents extractable by toluene refers to the extraction test hereinafter described for determining the fixation of toluene-soluble constituents; and it is in these senses that the foregoing expressions are to be interpreted in the appended claims.

The disintegrated heat-treated briquettes may be subjected in the mould to a pressure of 250- 260 atmospheres. The cooling of the moulded article should be sufficiently slow to avoid the formation of cracks in the article.

The relative proportions of the coal and modifier may be varied, provided that the proportion of the modifier does not exceed about 25 per cent. of the combined weight of the coal and modifier, and is not below the proportion at which it is capable of acting as a modifier, that is to say, not below the proportion required to yield a moulding composition which will soften without undergoing intumescence under the pressure used for moulding; and it is in this sense that the words as a modifier are used herein and in the appended claims. Generally speaking a suitable proportion of modifier is from about 18 to 25 per cent. calculated on the basis above mentioned.

The articles moulded from the disintegrated heat-treated briquettes alone are free from bubble structure, give a conchoidal fracture, are of very low electrical conductivity, and have a good resistance to acids and alkalies.

The fixation of toluene-soiuble constituents in the heat-treated briquette or moulded articles as measured by the content of constituents extractable by toluene is determined by the following extraction test:

A heat-treated briquette or moulded article is crushed and sieved through a 120 mesh B. S. S. sieve. 1 gram of the crushed sample is placed in a small dry Soxhle't thimble, which is then closed with a plug of cotton wool, and the whole is weighed. The sample in the plugged thimble is extracted with toluene in a Soxhlet extraction apparatus until colour is no longer imparted to the toluene. The thimble is then removed and dried at C. until its weight becomes constant. The percentage of material extracted based on the Weight of the modifier in the pretreated mixture is calculated by the method described in B. S. S. No. 771, 1938, appendix B.

In the moulded articles made by the invention the degree of fixation of the toluene-soluble constituents is somewhat higher than that of the 3 heat-treated briquettes from which the moulded articles are made.

It is important that the coal and modifier to be subjected to the pretreatment should be in a suificiently intimate state of contact to ensure that substantially all the coal particles including the finest sizes are in contact with the modifier or are coated with a film of the latter. Under these circumstances the assimilation of the modifier into the coal substance during the heat treatment proceeds evenly throughout the mixture. In general a satisfactory state of sub-division of the coal is obtained by grinding it sufficiently to pass a 240 mesh B. S. S. sieve.

The coal tar pitch should have a melting point below the temperature of the heat treatment. There may be used, for example, coal tar pitches whose melting points are within the range of 110 C. to 210 C. We have found that the higher the melting point of the pitch, for example, pitches having melting points of approximately 180 C., the better is the fixation of the toluenesoluble constituents under the same conditions of heat treatment, for example, at 330 C. for 5 hours. In order to keep the temperature low in the moulding operation it is desirable that the content of free carbon of the pitch should not exceed about 50 per cent.

Improved mechanical properties in the moulded articles may be obtained by incorporating with the coal-modifier mixture prior to the heat treatment or with the disintegrated heat-treated briquettes filling materials, for example, those described in United States patent application Serial No. 492,968. There may also be used fillers which impart a desired colour or lustre to the moulded article, for example aluminium powder or copper bronze powder. Surface finishes may also be obtained in known manner by the use of powder, sheets or gauzes applied to the mould.

In order to assist the flow of the composition during moulding, there may be incorporated with the coal-modifier mixture prior to the heat treatment, or with the disintegrated heat-treated briquettes polymerised methyl methacrylate, which does not decompose at the pretreatment temperature or, if incorporated subsequently to the pretreatment, at the moulding temperature.

The moulded articles made in accordance with the invention may be subjected to a subsequent heat treatment in a non-oxidising atmosphere, for example, at temperatures up to 800 C., in order to increase their density and impart electrical conductivity thereto, which properties may be desirable for certain uses of the articles.

The following example illustrates the invention, the parts being by weight:

40 parts of a South Wales coking coal (having an agglutinating value of 30, a volatile matter content of 25 per cent, and swelling number of 9 as determined by B. S. S. 1016) ground to pass a 240 mesh B. S. S. sieve, 10 parts of coal tar pitch of melting point 120 C. from a horizontal coke oven, and 50 parts of a mixture of equal parts of stone dust and asbestos powder (which mixture has been Well dried by heating it to at least the moulding temperature) are thoroughly mixed together in a ball mill for /2 hour. The mixture is then briquetted at 100- 120 C. under a pressure of /2 ton per square inch. The briquettes are then heated in an oven to a temperature of 330 0., preferably in a nonoxidising atmosphere, and maintained at that temperature for one hour. The briquettes are then ground in a ball mill to pass a mesh B. S. S. sieve, and during the grinding 4 per cent of polymerised methyl methacrylate calculated on the weight of the final mixture is added. The latter substance may be added in a very finely powdered form or in the form of a solution in benzene.

The ground material is then introduced into a mould which is heated to 250 C. It is subjected in the mould to a pressure of 450 atmospheres at 250 C. for 5 minutes. The moulded article is ejected from the mould and allowed to cool slowly at a rate of not more than 3 degrees centigrade per minute until its temperature is C. The further cooling may be rapid, if desired. The moulded article has a tensile strength of not less than ton per square inch. The percentage of toluene-soluble constituents capable of extraction from a crushed sample of the moulded article by the test hereinbefore described is 10.9 based on the weight of the pitch used.

We claim:

1. A process for making moulded articles, which comprises preparing an intimate mixture of finely divided coal having an agglutinating value greater than zero and as a modifier a finely divided coal tar pitch having a melting point of at least 110 C. in a proportion such that the coal modifier mixture softens at a temperature lower than does the :coal when heated alone and not exceeding about 25 per cent. of the combined weight of the coal and pitch, briquetting the resulting mixture, heating the briquettes at a non-carbonising temperature ranging from 250 C. to 400 C. for at least one hour until their content of constituents extractable by toluene is at most about 22 per cent. based on the Weight of the modifier, disintegrating the heat-treated briquettes, subjecting the disintegrated material in a mould to a pressure of at least about 250 atmospheres at a temperature at which under the pressure used the mixture softens as a whole without undergoing intumescence, and then slowly cooling the moulded article.

2. A process as claimed in claim 1, wherein a filling material is incorporated in the mixture of coal and modifier prior to the heat treatment.

3. A process as claimed in claim 1, wherein a filling material is incorporated in the mixture after the heat treatment and prior to the moulding operation.

WALTER IDRIS JONES. DAVID CLARENCE RHYS JONES.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,623,588 Germain Apr. 5, 1927 1,891,893 Spengler et a1 Dec. 20, 1932 2,088,422 Kemmer July 2'7, 1937 2,404,208 Bangham et a1 July 16, 1946