Quartz jackets for rollers of dynamo steel-annealing furnaces

Abstract

Rollers with jackets of quartz ceramic are used for movement of steel sheet in dynamo steel-annealing furnaces. The furnace consists of positions in which i00 rollers are installed. The metal sheet is annealed in a medium of hydrogen at 850-I050~ and the maximum temperature is created in three positions; 73, 74, and 75.According to the data of Creusot-Laire Enterprises, Paris, jackets of Masrock quartz material with 99.8 wt. % of Si02, an open porosity of 12-15%, an apparent density of 1.8-2.0 g/cm 3, a compressive strength of 50-80 MPa, and a coefficient of linear thermal expansion in the 0-i000 ~ range of 0.54"I0-6~ -i has found wide use in world practice for such furnaces.The quartz jackets are made with a weight of about 70 kg (Fig. i). The Jackets must have a smooth outer surface and only small deviations of the dimensions of the fastening holes in the ends. The guaranteed life of imported jackets is not less than 6 months. The actual life of jackets installed for the first time is close to this figure.For the purpose of testing domestic refractories produced according to the method for quartz nozzles [i] in a dynamo steel-annealing furnace, a lot of jackets was prepared.* A portion of the jackets was cast in a gypsum mold placed vertically. In this case, long assembly of the pieces (18-20 h) was necessary and there was a significant (up to 10%) difference in density of the jackets over the height after firing.To eliminate these disadvantages, a method of casting the jackets in a horizontal mold was tested, and the best results were obtained in oscillation of the mold during pouring from 0 to 90 ~ in an axial plane. In pouring in a horizontal mold the time of assembly of the pieces was reduced to 5-6 h and the difference in density of the parts after firing was reduced to 1-2%. The fired pieces were machined by trimming the ends on a cut-off machine, grinding the outer surface on cylindrical grinder, and drilling the end holes on a radial drilling machine.The characteristics of the jackets were 98.3-98.5 wt. % SiO 2, apparent density 1.78-1.80 g/cm 3, open porosity 20-22%, and compressive strength 20-30 MPa.In parallel with the production of this lot, the State Institute for Quartz Glass produced cast jackets of quartz glass. A blank of tubular form was melted from quartz sand concentrate in a rotary furnace. Melting of the sand occurred with simultaneous rotation of the molten glass mass around a graphite electrode, which made it possible to obtain a tubular blank. The ends were cut on the cooled blank and the surface was ground to the necessary dimensions. The SiO 2 content in the jackets depended upon the purity of the original quartz material, the open porosity did not exceed 1%, and the apparent density was 2.0-2.1 g/cm 3. Jackets produced by slip casting in a gypsum mold and produced from molten material were tested in a dynamo steel-annealing furnace in different positions. After 3 months, the jackets were removed from the furnace as the result of build-up on their surface.In the foreign literature th...

Highly concentrated ceramic bonding suspensions: Dispersion composition and porosity of casting

“…ic, d), the casting made from suspension 2 have the higher porosity (13.5%). During forming by this method [12], the solid phase of the suspension with the original grain size composition, corresponding to curve i, under the influence of the centrifugal forces, is deposited on the surface of the metal molds. The relative grain-size composition of these suspensions is very different from curves i and 2.…”

Development, introduction into production, and service of unfired quartz refractories

“…In addition, quartz refractories have started to be widely used as constructional elements for a number of metallurgical furnaces such as furnaces for annealing of dynamo steel in the form of large shells of rollers [3]. At present in the USSR tens of furnaces of such a type, for which domestic refractories in place of imported ones are necessary, have been placed in operation or are in the construction stage.…”

“…The centrifugal forming method is quite widely used in methods for normal concretes [i0, ii] and is also starting to be used in the production of refractories [3,12]. The essence of centrifugal forming and compacting is that in rapid rotation of a mold witha suspension uniformly distributed in it a pressing centrifugal pressure, under the influence of which the liquid with the highly dispersed fractions suspended in it is squeezed from the system being formed, occurs.…”