Metal deforming – By use of roller or roller-like tool-element – Plural roller-couples
Reexamination Certificate
1999-11-16
2001-02-20
Butler, Rodney A. (Department: 3725)
Metal deforming
By use of roller or roller-like tool-element
Plural roller-couples
C072S043000, C072S041000
Reexamination Certificate
active
06189358
ABSTRACT:
FIELD OF APPLICATION
This invention concerns a tandem with two rolling stands employed in a rolling line to cold roll thin strips.
The tandem to which the invention refers consists of a pair of four-high rolling stands, of the reversible type, cooperating with at least one reel upstream and at least one reel downstream and suitable to produce up to 650÷750,000 tonnes per year of cold rolled thin strip.
In this invention, cold rolled thin strip or sheet should be taken to mean a strip of 0.18 mm or more in thickness, from 0.18 to 3 mm, advantageously from 0.18 to 1.2 mm; the invention has been conceived and designed to solve the considerable problems related to this type of extremely thin strip.
STATE OF THE ART
Tandems of four-high reversible rolling stands are employed at present to cold roll strip which normally has a minimum thickness of 1.2÷1.5 mm.
Below these values of minimum thickness the surface quality which can be obtained from the hot rolling mill which produces the strip is not such as to allow the rolling of lesser thicknesses.
The basic process normally includes a winding reel which first feeds the tandem with a hot rolled product of the appropriate thickness and the cold rolled product leaving the tandem is wound onto a first drawing reel.
From this first drawing reel the product is made to pass again, in the opposite direction, into the tandem and, following a further cold reduction, is wound onto a second drawing reel.
The two passes achieve a usual reduction of 50÷60%.
In order to obtain a further reduction there follows a possible final cold rolling pass.
With these passes it is not possible to go below certain values of thickness as the surface quality of the product which they are able to supply is poor and unsatisfactory.
This is because the working rolls which perform the final reduction pass no longer have the necessary surface quality in that the surface quality has deteriorated in the passes which precede the final pass.
One solution to this problem is proposed in DE-A-4310063, which describes a tandem with two four-high reversible rolling stands served by winding reels upstream and downstream.
This document provides that the last finishing pass is performed by specific finishing rolls, arranged in a stand-by position during the working cycle, which replace the working rolls used for the first reduction passes by means of a rapid change-over of the rolls performed by the apposite device.
This document makes no reference either to the thicknesses of the finished product obtained or to the lubrication systems or organs associated with the rolling stands.
JP-A-57156809 describes a reversible rolling mill with a single stand which includes a substantially unified lubrication system; the concentration of oil in the lubrication mixture is adjusted from time to time, according to the specific reduction pass which is to be carried out, by means of a complicated control system.
In any case, lubrication liquids with a high and low concentration are mixed together, so that the adjustment carried out by the control system, apart from being complex also risks being not very precise.
FR-A-2 533 467 describes a method for producing a strip in a single pass cold rolling mill with five stands, in which the last stand has special working rolls and a separate lubrication system.
JP-A-61052901 describes a method for producing a metallic strip in a rolling line comprising a first reversible stand having large-diameter work rolls and a second reversible stand having small-diameter rolls.
Each of these stands has an indipendent lubrication system.
These documents don't solve any one of the above cited problems regarding the reduction in the obtainable strip thickness and the increase in the resulting quality of the strip surface.
The purpose of this invention therefore is to obtain very thin strip using a rolling lubricant which is always coherent with the specific reduction passes.
To be more exact, a different lubricant is used between the initial reduction passes and the finishing passes, using an adjustment system which is extremely simplified and rapid in switching from one lubricant to the other coherent with the change in type of rolling.
The present applicant has designed, tested and embodied this invention to obtain this and other advantages compared to the state of the art.
DISCLOSURE OF THE INVENTION
The invention is set forth and characterised in the main claim, while the dependent claims describe variants of the idea of the main embodiment.
According to the invention, the reversible four-high rolling stands no longer receive motion directly in the working rolls, but in the respective back-up rolls.
This solution is already known per se from DE-A-4310063 where the back-up rolls are fed with motion in that the working rolls travel at the speed of the product being rolled, and do not cause any rubbing on the said product, given that their specific function is to ensure the highest surface quality to the product.
Feeding the back-up rolls instead of the working rolls also serves to assist and accelerate the change-over of the working rolls themselves; in this way, there can be two types of working roll, a first type for cold rolling to achieve an initial reduction, and a second type for cold rolling with a last pass, which achieves the surface finish.
According to the invention, the working rolls of the four-high reversible stands are equipped with sliders which cooperate with adjacent and substantially coaxial sliders which carry the replacement working rolls.
In this way, while the desired working rolls are introduced in a manner known to the state of the art, it is easy to expel the working rolls already present, and whose surface is already partly worn by the initial reduction passes, and vice versa.
According to the invention, the reversible stands are equipped with a double lubrication system; one system is associated with a first type of working roll, for example with a type of roll for cold rolling with substantial reductions in thickness, and the other system associated with the other type of working roll, for example the type used for cold rolling finishing.
Moreover, according to the invention, each of the two lubrication systems has its own containing reservoir tank connected to the collection tanks by means of its own switching valve means.
The containing reservoir tanks, in cooperation with their own specific pump means, serve to feed the respective feed conduits to send the lubricant to the strip being rolled.
In this way, the two lubrication systems are completely independent, there is no mixing of different types of liquid, and they can operate alternately, since the respective switching valve means are governed by a command and control unit which allows the functioning of the two systems to be inverted without any pause or downtimes whatsoever, and in a manner which is functionally correlated with the type of rolling pass being made.
The command and control unit is centralised and also manages, moment by moment, the adjustment of the concentration and the physical/chemical characteristics of the lubrication liquid, independently for the two systems, according to the rolling pass and also the technological and processing parameters such as the type of material, the final thickness required, any processes undergone by the material upstream or downstream and so on.
According to a variant, the valve means have an emptying position to empty the respective collection tanks; this position is assumed during cleaning and maintenance operations.
According to another variant of the invention, downstream and upstream of the tandem of four-high reversible stands there are drawing devices which serve to discharge the drawing tension from the reels.
There are also the usual heating systems, control systems, systems to maintain the temperature of the rolls and the oils, measurement systems, and so on.
REFERENCES:
patent: 4950415 (1990-08-01), Malito
patent: 5746081 (1998-05-01), Klamma et al.
patent: 57-156809 (1982-09-01), None
Fanchini Bernardo
Gualco Cesare
Antonelli Terry Stout & Kraus LLP
Butler Rodney A.
Danieli & C. Officine Meccaniche SpA
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