Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Inorganic compound
Patent
1996-09-25
1997-10-14
Howard, Jacqueline V.
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Inorganic compound
427424, C10M17300
Patent
active
056772688
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a lubricant for use in hot rolling of stainless steel, especially stainless steel having a high chromium content, to prevent roll scoring.
BACKGROUND OF THE INVENTION
Since stainless steel strip and steel sheet (as used herein "steel sheet" refers to both steel sheet and steel strip) need to have a beautiful surface, during the production of stainless steel the formation of surface defects should be prevented as far as possible. However, when stainless steel is hot rolled by means of a tandem mill, defects may be caused in the surface of the steel sheet by part of the stainless steel being rolled being picked up by rolls and transferred to the material.
Roll scoring is considered to arise from contact between the surfaces of the hot rolling rolls and the hot rolled material (metal to metal touch). In particular, the higher the chromium content of the surface, the more difficult it is for scale to form on the surface. Also, since when scale does form it forms at a very slow rate, in the hot rolling of high chromium stainless steel there is increased opportunity for metal to metal contact to occur, and therefore a tendency toward a higher incidence of roll scoring. Such roll scoring degrades the shape of roll surfaces, and this degradation is transferred to the surface of the rolled material, degrading the shape of the rolled material. The surface defects of the cold rolled product, even if they are of a slight extent, not only limit application of the product, for example, make the product unsuitable for use in mirror finished applications, but also require to be remedied by polishing for use in other applications. Extensive surface defects can mean a financial loss, since the product can only be used as scrap.
Various approaches have been made in efforts to resolve such problems. These approaches include reduction of the rolling load, selection of rolling conditions, selection of roll material, and selection of lubricants.
Various animal and vegetable fats and oils, and various mineral and synthetic lubricants, have been proposed as lubricants to be applied to rolls to prevent roll scoring. Methods have also been studied comprising spraying rolls with rolling lubricating oil in which are dispersed particles having a lubricating function. However, these methods do not completely prevent roll scoring, especially in hot rolling of high chromium stainless steel. JP-A-64-83309 describes an aqueous lubricant for use in hot rolling of stainless steel to prevent roll scoring, which comprises a viscous aqueous solution having dispersed therein from 1 to 30% by weight of iron oxide powder. As described therein, the invention of this disclosure is based on the idea that if slow formation of surface oxide scale is what causes roll scoring during hot rolling of stainless steel, the problem can be resolved by actively supplying iron oxide powder from the exterior to supplement the scale that is lacking. The disclosure mentioned Fe.sub.2 O.sub.3 and Fe.sub.3 O.sub.4 as iron oxide powders that could be used in a particle size not exceeding 10 .mu.m dispersed in an aqueous solution thickened to an appropriate viscosity by a water soluble high molecular weight compound. As examples of the water soluble high molecular weight compound that could be used to thicken the solution, the disclosure mentioned polyacrylic acid and carboxyvinyl polymer.
JP-A-63-254195 discloses a lubricating oil composition for use in suppressing roll scoring during hot rolling of stainless steel comprising a suspension of iron oxide powder in lubricating oil, or a composition comprising a lubricating oil to which are added iron oxide powder and a polymer substance that is not water-soluble but does dissolve in the oil.
While the above disclosures are directed at supplying iron oxide from an external source to between the rolls and the material being rolled, there have been other approaches in which the object is to oxidize the roll surface. In one example of such an approach, JP-B-54-35985 describes
REFERENCES:
patent: 5468402 (1995-11-01), Hachiya et al.
Hiramatsu Akifumi
Omosako Kouji
Yamada Toshiro
Howard Jacqueline V.
Nisshin Steel Co. Ltd.
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