GB2061787A

GB2061787A - Pilger roll design

Info

Publication number: GB2061787A
Application number: GB8034215A
Authority: GB
Original assignee: Mannesmann AG
Current assignee: Vodafone GmbH
Priority date: 1979-10-23
Filing date: 1980-10-23
Publication date: 1981-05-20
Also published as: DE2943240C2; BE885809A; FR2467643B1; GB2061787B; HU184808B; DE2943240A1; CS237303B2; FR2467643A1; RO84962A; IT1133911B; IT8025352A0; RO84962B

Abstract

Known designs of pilger roll have a typical working angle of 180 DEG to 210 DEG which is divided into three regions; the jaw, the finishing groove, and the delivery zone. The present invention seeks to optimize the profiles of the respective zones so that a single curve can define both the jaw and the delivery zone and provide an increased working angle. According to the invention the jaw comprises a linear rear portion over about 25 DEG of rotation preceded by a portion defined by the curve: y = d (a + b . e<cx>)<n> where d, a, b, and c are constants dependant upon the diameter of the roll body. The jaw and the delivery zone are symmetrically arranged on either side of the finishing groove, and the zones are in the ratio 36%, 28%, and 36%. <IMAGE>

Description

SPECIFICATION Pilger roll design The invention relates to a pilger roll design for optimising the use of the roll.

As is known, the circumference of a pilger roll is divided into the working zone and the inoperative groove. The working zone of the roll consists of: reducing cone (jaw) finishing groove exit cone (delivery point), which are defined by groove depths with the associated angles or distances.

The pilger roll designs known at present have a total working angle of 1 80 to 210 degrees, with proportions of 48-54% for the jaw, 30-36% for the finishing groove and 12-18% for the delivery. The corresponding angles of the roll circumference depend on the total angle taken up by the working length of the rolls.

Depending on the travel time, the greatest wear on the pilger rolls occurs in the jaw-at the point of application between the hollow blank and the rolls. This point determines the dimensions required in the mechanicai refinishing and hence the number of possible times of use of the rolls.

To obviate the need for refinishing to great depths, it has been proposed to displace the point of application towards the working groove, since re-dressing can then be carried out with less reduction in diameter. However, this measure means that the zone of delivery is displaced a long way towards the inoperative groove and at this point, owing to the large aperture of the inoperative groove, there is insufficient roll material to provide the desired curve function for the exit cone. An excessively steep and hence short exit cone results in rapid detachment of the rolls from the tube. The full roll pressure still prevailing acts on too small a compressed surface area.

Consequently, excessively high pressure per unit of area will result in damage to the tube, going beyond the permissible tolerance limits and leading to high failure rates.

Another proposal is that the exit cone be constructed as a reducing roll cone as set forth in German Patent No: 545,843. The advantage of this construction is supposed to be that, after the first contact cone has become worn, the rolls can simply be turned, without any re-dressing, to make them ready for use again. In practice, this proposed construction has the following disadvantages: -The curves for the reduced cone and the exit cone have clearly different paths, owing to their different tasks.

-When the exit cone is converted into a reducing cone, the steeper path of the jaw curve means that the rolls are released from the tube too quickly and the abovementioned damage occurs to the tube.

-During the machine re-finishing treatment required, the working zone of the rolls is displaced towards the inoperative groove. However, in this region, there is not enough roll material to provide the desired groove form.

It is generally known that larger tension cracks (also known as heat cracks or water cracks) are formed on the roll body in the region of the jaw. If the exit is converted into a second jaw, these flaws are thus moved through about 180 again. This further weakens the cross-section of the core of the roll. The notch effect increases this weakness still further. As a further complication, the maximum rolling force is exerted in the region of this weakening of the crosssection.

This weakening of the cross-section of the roll results in a number of fractures and thus has economic disadvantages.

The aim of the invention is to provide a roll design with which it is possible to obtain a significantly better degree of use of the pilger rolls without any detrimental effects to the quality of the tubes. To this end, the invention provides a pilger roll having a roll design consisting of a reducing cone, a finishing groove and an exit cone wherein: (a) the reducing cone extends in substantially linear manner at an angle of substantially 25 in its rear portion nearest the finishing groove and the adjoining portion between 25 and 50 accords with the function y=d . (a+b . ec ), (b) the working zone 0-Ill of the roll comprises 210 to 235 degrees of rotation; and (c) the subdivision of the working zone into working cone/delivery point-finishing groove working cone/delivery point is in the ratio of substantially 36%, 28% and 36%.

The roll design according to the invention sets out to optimise the curves for the reducing cone and the exit cone so that one curve path can take over both functions. For this purpose, the reducing cone, which is formed by a curve of higher function (hyperbolic, parabolic e function), is converted, in its rear portion nearest the finishing groove, into a curve of substantially linear course. The portion designed in this way should preferably enclose an angle of about 25 and not exceed the following limiting values: Diameter of roll body Groove depth over base circle of groove 1200-850 mm 1.5-1.8mm/10 degrees 840-400 mm 0.8-1.2mm/10 degrees 390-250 mm 0.4-0.6mm/10 degrees.

In the adjoining zone between about 25 and 50 , the curve accords with the function n y = d . (a + b .

The following limiting values apply, depending on the diameter of the roll body: Diameter of roll bodv Function

1,200-850 mm y=d. 9.424 5310-2 9 0.6] 50, 0.6 d = 14.25 to 20.0 840-400 mm y=d. x l y = d. 1 .94049. 1 0 -' + 1 .326 33 1 0 - e64096' Os I d=7.3to 14.3 390-250 mm y""'d. x 1.g404g.10-l+1.32633.10-3.e6A096. ops y=d. 1.Q$04990-191 .3283318-3.es.409e 50 J d = 4.0 to 7.2 According to the invention, the working zone of the roll is enlarged from 180-210 degrees to 210-235 degrees. The subdivision of the working zone into working cone/delivery-finishing groovorking cone/delivery is in proportions Gf about 36%, 28% and 36%.

During the machining re4inishing treatment, the angles of the individual working zones for all diameters of roll bodies are kept constant with a fluctuation of plus or minus 3 degrees.

The roll designing according to the invention provides a method of roll design and a sequence of groove diameters adapted to the diameter of the roll bodies, in order to minimise the amount of re-dressing required and avoid fractures in the rolls. In the upper region of the diameter of the roll (30 to 40% of the working portion), a roll design according to the invention with two reducing cones is used.

For the remaining 60%, approximately, of the working portion, the roll is designed in the conventional manner with only one reducing cone. In this way, the tension cracks in the region of the second jaw and the detrimental effects connected with them are eliminated.

After the roll has been used six times, a groove diameter which is larger by at least the amount of re-dressing effected is cut in the upper region of the roll diameter. This larger groove diameter is then retained for a further 4 to 6 applications with two reducing cones. Then the roll is re-grooved to the conventional groove form. The groove diameter selected must again be larger by at least the amount of re-dressing effected.

The accompanying drawings schematically illustrate a known pilger roll design and a roll design according to the invention.

Figure 1 shows a known roll design; and Figure 2 shows a roll design according to the invention.

Fig. 1 shows a roll design of the kind described above in which the point of application of the hollow blank to the roll is indicated at "A". The total working angle of 180"-210" is shown between 0 and ill, the jaw region being shown between 0 and I, the finishing groove between I and 11, and the delivery zone between II and lli. The respective percentages of the total working angle are also indicated.

Fig. 2 shows the working zone of the roll from 0 to Ill; i.e., from 210 to 235 degrees. The working zone-is subdivided into working cone/delivery-finishing glroove--working cone/delivery in proportions of about 36%, 28% and 36%, these angles being kept constant during redressing of the individual working zones for all diameters of roll bodies with a fluctuation of plus or minus 3 degrees.

Claims

1. . A pilger roll having a rdll design consisting of a reducing cone, a finishing groove and an exit cone wherein: (a) the reducing cone extends in substantially linear manner at an angle of substantially 25 in its rear portion nearest the finishing groove and the adjoining portion between 25' and 50" accords with the function n y = d . (a + b . eco ), (b) the working zone 0-Ill of the roll comprises 210 to 235 degrees of rotation; and (c) the subdivision of the working zone into working cone/delivery point-finishing groove working cone/delivery point is in the ratio of substantially 36%, 28% and 36%.

2. A pilger roll substantially as described herein with reference to Fig. 2 of the accompanying drawings.

3. A method of using a pilger roll according to Claim 1 or Claim 2 wherein, after being used several times, the groove is refinished by machining, the angles of the individual working zones being kept constant for all diameters of the roll bodies within a tolerance of plus or minus 3 degrees, and wherein the exit cone is conventionally grooved for the last time or times of use.

4. A method of using a pilger roller substantially as herein described.