US 2984473 A
Description (OCR text may contain errors)
May 16, 1961 M. N. ORNITZ ETAL 2,934,473
FURNACE CONVEYOR ROLLS AND THE LIKE Filed July 14, 1958 1, I, lljlz c) o @v'" Fig.2. 20 I8 2| INVENTORS Martin N. Orniiz B Roy H. English United States Patent O "FURNACE CONVEYOR ROLLS AND THE LIKE Martin N. Ornitz, Wilkinsburg, and Ray H. English,
McCandless Township, Allegheny County, Pa., as-
signors to Blaw-Knox Company, Pittsburgh, Pa., a corporation of Delaware Filed July 14, 1958, Ser. No. 748,320
8 Claims. (Cl. 263-6) This invention relates to furnace conveyor rolls and the like and particularly to furnace conveyor rolls over which metallic strip is passed and advanced through a heating furnace.
The invention will be particularly illustrated and described as embodied in a furnace conveyor roll for passing steel strip through an annealing furnace. It is well known in the metal treating arts that difficulties are encountered by reasons of the collection of accretions of material from metal strip on the metallic conveyor in the heating furnace, e.g., metallic conveyor elements used in annealing strip with the strip passing over or around the rolls. The problem has been, particularly, acute in the treatment of high silicon steels and other steels which require high treatment or annealing temperatures. This problem appears to be influenced by a variety of factors including the tension of the strip, the composition of the strip, the temperature of the furnace atmosphere, as well as the characteristic of the roll surface. Various attempts to solve this problem have been heretofore proposed, such as, coating the surface with various materials resistant to the formation of accretions, however, these coatings heretofore proposed have been subject to the diificulty of spalling when the temperature changed materially in the furnace and, particularly, where the furnace was cooled down between runs. This spalling problem has, in some instances, been almost as bad as the original problem of the formation of the accretions.
We have invented a conveyor roll and the like which overcomes both the problems of accretions forming on the surface, as well as the problem of spalling. The conveyor roll of the present invention has a structural metal body with a stabilized zirconia work engaging surface. Preferably, the body of the roll is of metal; a high temperature alloy of known composition desirably being employed. We have found that the zirconia used for the work engaging surface must be stabilized with calcium oxide or an equivalent stabilizing agent. Unstabilized zirconia has proven unsatisfactory and is subject to the spalling problem, previously mentioned. Preferably, the metal roll is provided with a coating or film of Nichrome prior to the addition of the stabilized zirconia coating. We have found that the interposition of the Nichrome film on the roll improves the life of the stabilized zirconia surface over that of zirconia alone on ferrous base rolls. The metal roll body may be a hollow body such as that commonly used in conveyor rolls or it may be of any other roll design.
In the foregoing general description we have attempted to set out certain of the problems of the furnace conveyor roll art together with certain objects, purposes, and advantages of our invention. Other details, purposes, objects and advantages will be apparent from the following description of a present preferred embodiment of the invention and the accompanying drawings in which:
Figure 1 is a diagrammatic view of a heat treating chamber showing that a high strip can be supported on the furnace conveyor rolls of this invention;
2,984,473 Patented May 16, 1961 face sprayed with stabilized zirconia; and
Figure 4 is a diagrammatic fragmentary cross section to enlarged scale of apart of the roll body of Figure '2.
Referring to the drawings, we have illustrated a furnace chamber 10 through which strip 11 is adapted to be drawn, the strip passing over a series of rolls 12 at the top of the furnace and then passing over rolls 12 at the bottom of the furnace. It is desirable that the rolls be of uniform construction. The rolls 12 may be driven or turned idly as the strip passes through the chamber 10. The chamber 10 is heated internally by suitable heating methods not illustrated herein.
Referring more particularly to Figures 2 and 3, the furnace conveyor roll 12 includes a metal body 13 made up of a barrel 14, two shaft ends 15, andtwo closure plates 16. The shaft ends 15 are filled with heat insulating material 17. The barrel 14 and shaft ends 15, and the closure plates 16 may be of any suitable alloy such as is used in the manufacture of furnace conveyor elements. Preferably we use a heat resistant alloy. The barrel 14 has a thin film of Nichrome 18 applied to its outer surface. This film may be applied by any conventional means, as for example, spraying. The outer Work engaging surface coating .20 of stabilized zirconia is then applied to the Nichrome. Here again the coating may be applied by any known method which will provide a fused surface. For example, the stabilized zirconia may be applied by high temperature spraying and to this end a metallizing gun 19 is provided tomelt and spray the stabilized zirconia.
The shaft ends 15 have cylindrical portions 21 fitting within the ends of barrel 14,'tapered portions 22, cylindrical end portions 23 and trunnions 24 which may be mounted for rotation in a conventional manner.
The ends of the barrel 14 are welded to the ends of the shaft ends 15 by weldments 25. The closure plates 17 are welded to the shaft ends 15 by weldments 26.
The stabilized zirconia surface 20 constitutes the working engaging surface of the roll and is the only portion of the roll which comes in contact with the strip being carried over the roll.
The advantages of the present roll are perhaps best illustrated by the following test.
A ferrous roll body containing 25% chromium and 12% nickel was spray coated over /2 of its length with a film of -20 Nichrome (80% nickel and 20% chromium). A coating of stabilized zirconia (zirconia stabilized for example with CaO) was applied to /3 of the Nichrome coated length. A coating of alumina was applied to another third of the Nichrome coated length and a coating of zirconium silicate was applied to the remaining 6 of the Nichrome coated length. Identical coatings of stabilized zirconia alumina and zirconium silicate were applied to the portions of the roll which did not have the Nichrome coating. The roll was then subjected to cycles of temperature change such as would be encountered in heating and cooling a strip treating furnace. After the first cycle the alumina had spalled on both Nichrome coated and uncoated areas to an extent that it would be unsatisfactory for further use. The zirconium silicate showed signs of spalling in both cases but could still he used. After the second cycle only the stabilized zirconia on the Nichnome film remained intact. After five cycles all of the coatings had spalled 01f except the stabilized zirconia which still remained unimpaired.
Another roll of nickel base alloy containing 48 /2 Ni, 28% Cr, 15 /z% Fe and 5% W was coated directly 2,9s4,4.7s H r with stabilized zirconia on /2 of its length and with Y alumina over the other V2 of its length. The roll was then subject to heating and cooling cycles. Again, the alumina spelled off to anextent that it would be unsatisfactory for'furtheru'se" after the first cycle whereas-the stabilizedzirconia remained unimpaired after five cycles.
,It is apparent from the foregoing examples'that stabilizedzirconia work surfaces on conveyor rolls will overcome the difficulties of spelling heretofore experienced. The stabilized-zirconia coating must be applied to a roll jbodyfof proper composition and physical properties for the temperature in the particular'furnace involved. The zirconia coat maybe used in certain cases without an undercoat, however, where any difliculty with spalling is encountered a Nichrome film applied to the roll surface priorto the application of the stabilized zirconia will eliminate the spalling problem. I
While We have illustrated and described a present preferred embodiment of our invention it will be understood that the invention may be otherwise embodied within the scope of the following claims.
We claim: e
1. A furnace conveyor roll and the like comprising a work supporting metal body and a coating of stabilized zirconia covering the work engaging portion of said body and being fixed thereto.
2. A furnace conveyor element and the like comprising a work supporting metal body and a stabilized zirconia coating on the work engaging surface of said body, said stabilized zirconia covering the entire work engaging portion of the body and being fused thereto.
bonded thereto and an outer coating of stabilized zirconia fixed to the nickel chromium alloy film over the entire work engaging surface of the body.
5. A furnace conveyor roll and the like comprising a work supported metal body and a coating of zirconia stabilized with calcium oxide-covering the work engaging portion of said body and fused thereto.
6. A furnace conveyor element and the like comprising a work supporting ferrous body and a zirconia coating stabilized with calcium oxide on the work engaging surface of said body, said stabilized zirconia covering the entire work engaging portion of the body and being fused thereto.
7. A furnace conveyor element and the like comprising a ferrous body, a nickel chromium alloy film on the work engaging portion of said body and bonded thereto and an outer coating of zirconia stabilized with calcium oxide fused to the nickel chromium alloy film over the entire work engaging surface of the body.
8. A furnace conveyor element and the like comprising ;a ferrous body, a nickel chromium alloy film consisting essentially ofbetween about %80% nickel and between 40%-20% chromium onthe work engaging portion of said body and bonded thereto and an outer coating of stabilized zirconia fixed to the nickel chromium alloy film over the entire work engaging surface of the body.
References Cited in the file of this patent UNITED STATES PATENTS Rechter et a1 Aug. 19, 1958 OTHER REFERENCES Pages 109 and 110 of Bulletin 186 by the Department of the Interior (Bureau of Mines) in 1921 titled, Investigations of Zirconium With Especial Reference to Printing Office, Washington, DC.