Metal deforming – By use of roller or roller-like tool-element – Comprising tool movable relative to stationary work-portion...
Patent
1985-07-15
1987-04-28
Spruill, Robert L.
Metal deforming
By use of roller or roller-like tool-element
Comprising tool movable relative to stationary work-portion...
72237, 72238, 72243, 72244, B21B 2100, B21B 3104, B21B 3114, B21B 3126
Patent
active
046604006
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to the manufacture of tubes and has specific reference to pilger mill stands which are essential parts of a mill.
BACKGROUND OF THE INVENTION
The rolling of thin-walled tubes from metals and alloys that are reluctant to yield to deformation poses now the problem of increasing the robustness of stands, increasing the accuracy of roll setting, and preloading the rolls in the radial direction.
DESCRIPTION OF THE PRIOR ART
There is known a cold pilger mill stand (cf. Federal Republic of Germany Pat. No. 1,287,541; B21B 31/04; 1967) incorporating a housing with carriers which are located pairwise on either side of the rolling axis oppositely to each other. A cap is attached to the carriers, and bearing chocks are fitted into vertical guides of the carriers to give support to the work rolls located one above the other.
The stand is provided with a means of preloading the work rolls, which consists of coupling screws designed to link the bearing chokes vertically pairwise. This arrangement provides for an accurate dimensioning of the tubes during rolling. At the same time, all the rolling pressure is sustained by the bearing chocks of work rolls only, for the stand is not provided with backup rolls. Therefore, the strength of the chocks limits the amount of deformation of the tube blank in operation. Apart from that, the mill must be stopped for preloading the rolls so that the operating availability of the mill is consequently reduced.
The known stand lacks a means of monitoring the preloading. This feature invites difficulties in maintaining dimensional stability of the tubes rolled.
Also known is a pilger mill stand (cf. Polulchin, U.S. Pat. No. 4,237,714) which is adopted as the prototype of the invention. This stand incorporates a housing with carriers which are located pairwise on either side of the rolling axis oppositely to each other. A cap and a means of preloading the stand are pivotally attached to the carriers.
The stand is provided with an upper backup roll and a lower one supported by chocks. Work rolls, one overlaying the other, are arranged between the backup rolls and supported by relevant chocks which fit into vertical guides of the carriers. For preloading the stand, the backup rolls can be moved vertically integrally with their bearing chocks towards the work rolls.
The prototype mill stand is simple and reliable. It can turn out accurately dimensioned tubes from any material, even one which deforms reluctantly. Robustness of the stand and of the means of preloading the rolls is a factor providing for good performance. By pressing the work rolls against each other with the aid of the backup rolls, the work rolls/backup rolls/housing system is prestressed rapidly and uniformly. The amount of prestressing can be varied over a wide range without stopping the mill. Pressure transducers permit a constant monitoring of the prestressed state.
However, since the work rolls are preloaded by means of the backup rolls directly, high compressive stresses are set up in the work rolls at the place of their contact with the backup rolls at the instant when the work rolls begin to deform the tube blank. These stresses coming into play in the areas of contact between the work rolls and the backup rolls bring about rapid local wear of the rolls. Flaking and local crumbling-out of rolls are also likely to occur when the stresses become critically high. Particularly prone to damage are the work rolls, for the maximum load they sustain is invariably confined to the same localities on the rolls.
Since the total load due to the rolling pressure and the prestressing action is carried by the bearing chocks of backup rolls only, these chocks wear down rapidly. This not only shortens the service life of the bearing chocks of backup rolls but also impairs the reliability of the stand.
SUMMARY OF THE INVENTION
The main object of the invention is to provide a pilger mill stand wherein the means of prestressing the stand and the work rolls are designed so as to
REFERENCES:
patent: 3307386 (1967-03-01), Ward et al.
patent: 3431762 (1969-03-01), O'Brien
patent: 4237714 (1980-12-01), Polukhin et al.
Gremyakov Ivan P.
Potapov Ivan N.
Sheikh-Ali Alexei D.
Styrkin German D.
Katz Steve
Moskovsky Institut Stali i Splavov
Spruill Robert L.
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