Classifications

• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21C—PROCESSING OF PIG-IRON, e.g. REFINING, MANUFACTURE OF WROUGHT-IRON OR STEEL; TREATMENT IN MOLTEN STATE OF FERROUS ALLOYS
  • C21C7/00—Treating molten ferrous alloys, e.g. steel, not covered by groups C21C1/00 - C21C5/00
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B24—GRINDING; POLISHING
  • B24C—ABRASIVE OR RELATED BLASTING WITH PARTICULATE MATERIAL
  • B24C11/00—Selection of abrasive materials or additives for abrasive blasts

Definitions

• 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.
• 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.
• blasting agent 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.
• 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.
• 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.
• a granulated, surface-sintered slag is a suitable blasting agent.
• 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.
• the above-mentioned internal stresses render this material practically worthless as a blasting agent.
• 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.
• 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.
• a preferred form of the blasting agent, according to the invention, consists of a slag having substantially the following composition has proved excellently suitable:
• 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.
• 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.
• Example 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.
• 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.
• 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.
• 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.
• 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.
• a blasting agent comprising sintered slag particles.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Mechanical Engineering (AREA)
• Manufacture And Refinement Of Metals (AREA)
• Manufacture Of Iron (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=4525240

Family Applications (1)

Country Status (5)

Cited By (4)

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Citations (9)

• 1958
  • 1958-09-11 CH CH6382858A patent/CH379320A/de unknown
• 1959
  • 1959-07-22 BE BE580936A patent/BE580936A/fr unknown
  • 1959-09-04 GB GB30287/59A patent/GB914337A/en not_active Expired
  • 1959-09-09 US US838851A patent/US3155466A/en not_active Expired - Lifetime
• 1966
  • 1966-04-20 CY CY34466A patent/CY344A/xx unknown

Patent Citations (9)

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