US3155466A - Balsting agent and process for the production thereof - Google Patents

Description

United States Patent 3,155,466 BLASTING AGENT AND PRGfiESS FOR THE PRGDUCTIUN THEREUF Kurt Griitter, Choindez, and Heinrich Starnptii, Courrendlin, Switzerland, assignors to Gesellschaft der Ludw. von Rolischen Eisenwerke Aktiengeseilschat't,

Gerlatingen, Switzerland, a Swiss company No Drawing. Filed Sept. 9, 1959, Ser. No. 838,851 -Clahns priority, application Switzerland, Sept. 11, 1958,

63,828 3 Claims. (Cl. 51-307) This invention relates to blasting agents. More particularly, it relates to a new blasting agent which consists of slag; and to a method of producing said new blasting agent.

In industry, so-called blasting agents are usually employed to clean metallic surfaces, more especially to prepare them to receive a colour or metal coating, the blasting agents being projected on to the surfaces at high speeds and thus treating them in the desired manner.

Generally speaking, it is required of a blasting agent that it may be used for as long as possible, that is to say, that it can be used a number of times without losing its properties, and, in addition, the blasting agent must be inexpensive. Blasting agents presently employed are: steel grit, moulding sand, corundum and various types of quartz sand, such as pure quartz sand or river sand and the like. All present blasting agents are usually attended by certain disadvantages. Blasting agents consisting of cast iron or steel hammer the surface in such manner that the surface becomes too rough, which increases the danger of under-rusting in the case of spray metallization and painting. Very good properties are possessed by quartz sand, which, on the one hand is of low cost and on the other is a relatively wear-resistant material which permits several applications, that is to say, it can be used several times for blasting surfaces. However, this blasting agent, which is at present generally employed, has an outstanding disadvantage of another kind, which causes more and more opposition to its use. It has been found that the presence of quartz leads to silicosis, so that practically all of the workmen engaged in blasting installation are exposed to the danger of silicosis. Both the insurance companies and factory inspection authorities are endeavouring to ban this dangerous substance from production processes and, thus, to eliminate such danger to the workers.

Accordingly, it is an object of the present invention to provide for a blasting agent which is inexpensive, as are the commonly used blasting agents, such as quartz sand, and which is also free from the danger of causing silicosis in the lungs of the workmen.

An extremely valuable agent having optimum proper ties is granulated corundurn. its cost of production, however, is so high that, here again, general use is found to be impracticable.

It is another object of the invention to provide for a blasting agent having properties similar to those of corundum.

It is in itself obvious that, in the search for a suitable blasting agent, the materials first considered were waste products, such as slag and the like, since they were obtainable at a low cost. Furnace slags exist which contain no free silica (quartz) and, therefore, give no rise to danger of silicosis. When such slags are granulated,

3,155,466 Patented Nov. 3, 1964 for example by quenching with water, a substance is formed which at first sight appears to be readily usable as a blasting agent. This slag has a hardness of about 7, but is subject to internal stresses. Consequently, the individual grain, when projected on to the metal surface, rapidly disintegrates into extremely fine constituents and, thus, cannot be used.

It is another object of the invention to provide for a blasting agent using furnace slags.

We have now found that a granulated, surface-sintered slag is a suitable blasting agent. By the term surfacesintered, we understand the following phenomena: if ordinary hot slag is cooled at a relatively rapid rate, a plurality of granules result, having fissures which are caused by this sudden cooling. These granules would, under the impact of mechanical stress, disintegrate along these fissures into smaller particles. In addition, the above-mentioned internal stresses render this material practically worthless as a blasting agent. We have now found that, by a suitable treatment of the slag, we are able to eliminate both fissures and internal stress. This treatment consists in subjecting the particles to the iniluence of heat, such that, by softening or sintering the surface of the particles, with no merging of the surfaces of different particles, the surface fissures are closed. In this process, whereby the fissures are closed and the internal stresses are resolved, the granules acquire very surprising properties, substantially similar to those of corundurn, in regard to wear and resistance, as well as efiectiveness as a blasting agent. The sintering temperature and the sintering period, which must be such as to cause closure of the fissures, must, naturally, be adapted to the chemical composition of the slag and the size of the grains. These two conditions, sintering temperature and period, are dependent upon whether the heat treatment is eifected by radiant heating or by heat transfer.

A preferred form of the blasting agent, according to the invention, consists of a slag having substantially the following composition has proved excellently suitable:

Percent SiO 25-45 CaO-l-MgO 35-60 A1 0 8-25 And the ratio value P=CaO/SiO -=0.8-2.

SiO 33-35 CaO-l-MgO 43-48 A1 0 15-20 With a ratio of CaOzSiO ranging from about 1.2-1.4.

In order that the invention may be better understood, the following examples are given:

I. A typical slag from a blast furnace for the processing of iron ore was granulated by pouring the slag in an essentially liquid state, having a temperature of about 1400 C., in water of a temperature of about 15 C.

:3 =3 The granular slag, with a grain size of up to about 3 mm., and a weight per unit volume of 1.4 kilograms per dm. and a hardness number, in terms of Mohs scale, of about 7 resulted.

The chemical composition of the slag, before and after granulation, was:

Percent CnO 43.6

SiO 33.8 A1 16.5 MgO 3.1 FeO 0.9

And traces of manganese, chrome, phosphor, etc.

A portion of the granulated material was heated by radiation in a furnace of the vaulted type (Borell furnace) for a period of about one hour. The temperature of the furnace ranged from 920940 C. The resulting granulated material was cooled for a period of ten minutes, and showed a marked change in appearance as compared with the granulated slag before heating. The starting material had a light grey to greenish color and a glassy appearance. After heating, the material was dark grey to black and had a dull appearance.

II. The procedure of Example I was repeated, with the exception that the heating for obtaining the surface-sintering of the slag was carried out in a rotary kiln at a temperature ranging from 950970 C. for a period of about five minutes. The resulting surfacesintered granulated slag was, in appearance and elfectiveness, as a blasting agent, equivalent to the product of Example I. The latter attribute shall be discussed in the following example.

III. The slag resulting from Example H was tested as to its effectiveness as a blasting agent. The granulated material was sieved and the fraction with the average size ranging from 1.0-1.5 mm. was used in a blasting apparatus, having a nozzle with an inner diameter of six millimeters and a working pressure of 4 atmospheres. The blasting material was blasted with this apparatus upon sheet-iron, with a distance of 5 cm. between nozzle and sheet-iron. In the following table the stability of the blasting agent was tested by running a given sample a number of times (3, 6, 9, 12) through the blasting process. The numbers in columns 2-5 give the percentage of the granulated material retaining its original grain size.

The comparison of the values in columns 3 and 5 demonstrates that the properties of the surface-sintered slag compare with the properties of corundum. The values of the slag, according to Examples I, gave the same values as the slag resulting from Example II, with the margin of error of the measurement of the grain size.

It is to be noted that the values given in Examples I and II are not meant to limit the invention. Any slag, with the above composition, and an appropriate degree of hardness, will give, after appropriate sintering of the surface, a suitable blasting material. Neither the temperature values nor the period of heating are critical. The optimal degree of heating for a given slag with a given size of the granules, is the one which provides for complete closing of the fissures without merging of the granules with each other. The optimal period of heating is the shortest period of heating which, at a given temperature, is necessary for attaining the closure of the fissures or surface-sintering.

Adaptation of the conditions of treatment for a given slag will be evident to anyone experienced in the arts and using the above-specified teaching.

Various changes and modifications may be made without departing from the spirit and scope of the present invention, and it is intended that such obvious changes and modifications be embraced by the annexed claims.

Having thus described the invention, what is claimed as new and desired to be secured by Letters Patent, is:

l. A method of preparing a blasting agent from slag granules having surface fissures, which comprises reheating solidified fissured slag granules to a temperature and for a period of time sufiicient to cause sintering of a relatively thin surface layer of the slag granules thereby to fuse and close said fissures but insutficient to cause sintering of the interior of the slag granules and substantial agglomeration of adjacent granules and thereafter slowly cooling said granules to avoid internal stress.

2. A blasting agent comprising sintered slag particles.

3. A method as claimed in claim 1, wherein said cooling is effected within about ten minutes.

discrete surface- References Cited in the file of this patent UNITED STATES PATENTS 1,763,937 Stievater June 17, 1930 1,980,432 Power Nov. 13, 1934 2,038,251 Vogt Apr. 21, 1936 2,461,011 Taylor et al. Feb. 8, 1949 2,532,548 Heide Dec. 5, 1950 2,533,633 Schott Dec. 12, 1950 2,610,922 Beck Sept. 16, 1952 3,054,139 Bartholomew et al. Sept. 18, 1962 FOREIGN PATENTS 667,016 Great Britain Feb. 20, 1952 OTHER REFERENCES The Canadian Mining and Metallurgical Bulletin for March 1954, Montreal, pages -169.

Claims (2)

1. A METHOD OF PREPARING A BLASTING AGENT FROM SLAG GRANULES HAVING SURFACE FISSURES, WHICH COMPRISES REHEATING SOLIDIFIED FISSURED SLAG GRANULES TO A TEMPERATURE AND FOR A PERIOD OF TIME SUFFICENT TO CAUSE SINTERING OF A RELATIVELY THIN SURFACE LAYER OF THE SLAG GRANULES THEREBY TO FUSE AND CLOSE SAID FISSURES BUT INSUFFICIENT TO CAUSE SINTERING OF THE INTERIOR OF THE SLAG GRANULES AND SUBSTANTIAL AGGLOMERATION OF ADJACENT GRANULES AND THEREAFTER SLOWLY COOLING SAID GRANULES TO AVOID INTERNAL STRESS.

2. A BLASTING AGENT COMPRISING DISCRETE SURFACESINTERED SLAG PARTICLES.