GB2199519A

GB2199519A - Finishing of hot-rolled tube

Info

Publication number: GB2199519A
Application number: GB08729257A
Authority: GB
Inventors: Karlhans Staat
Original assignee: Kocks Technik GmbH and Co KG
Current assignee: Kocks Technik GmbH and Co KG
Priority date: 1986-12-20
Filing date: 1987-12-15
Publication date: 1988-07-13
Also published as: JPS63168214A; GB8729257D0; FR2608472A1; IT1223275B; DE3643769A1; IT8722963A0

Abstract

Once a tube 2 has left the last stand of the last rolling line 3, the tube is first subdivided 4 into multiple lengths, followed by cooling 6, straightening 11, washing 16, testing 17 and final subdivision 24 into individual commerical lengths. Deburring 8, 15 takes place before and after straightening 11. Testing includes a test press 17 and non destructive testing 19. <IMAGE>

Description

DESCRIPTION FINISHING OF HOT-ROLLED TUBE The invention relates to a method of finishing hot-rolled tubes.

In a known method of finishing hot-rolled tubes, finish-rolled tube is subdivided beyond the last rolling stand of a rocking line into a large multiple of a commercial or prescribed stock length and these sections of finished tube sections are then delivered to a cooling bed. Following cooling on the cooling bed, the sections of finished tube are subdivided using a cold saw, and the pieces of tube are stored in an intermediate store. If higher quality tubes are to be supplied, that is, tubes which fulfil greater safety requirements, these pieces of tube are removed from the intermediate store and fed to a straightening machine.They are then tested by means of non-destructive testing apparatus and are subjected to a visual check, The pieces of tube are then cut into the desired commercial length and their stability and tightness are tested using a tube test press by subjecting them to high water pressure. Only then are the tubes ready for despatch.

As regards the economy and productive capacity of the plant as a whole, this known method is not optimum. For example, the extremely long finished tube is divided immediately before cooling into relatively short lengths by means of a hot saw, and immediately after cooling by means of a cold saw, which is disposed directly beyond the cooling bed.

Only when they have been cut into these short lengths are they fed to the straightening machine, and this impairs the throughput in weight per unit of time.

Furthermore, the proportion of inadequately straightened leading and trailing end portions of the entire tube length is greater for short pieces of tube. A particularly significant disadvantage of the known method is that the concluding testing of the tubes in a tube test press does not take place until after subdivision of the pieces of tube into the commerical lengths, that is, only after they have been cut to their shortest length. Each of these relatively short tubes has two untested end sections, because it is not possible to make a proper check of the tubes in the region of the sealing sleeves, or possibly the clamping sleeves, of the tube test presses.The number of untested end portions, at two per commercial length, is quite high, and it must be remembered that, given corresponding quality requirements, these untested end portions must be cut off and scrapped, which is uneconomical. This applies in particular to tube test presses which operate with self-holding testing heads which clamp onto the tube ends. The use of such testing heads results in particularly long untested end portions. However, it is also possible to use testing heads which are held on the ends of the tubes to be tested by the frame of the tube test press. Using such testing heads, the end portions which remain untested and are considerably shorter. However, there are still two untested end portions per commercial length.

Furthermore, testing using such testing heads does not correspond to the stress on the tube during operation because, when non-self-holding testing heads are used, tensile stress, which normally occurs during operation, does not occur. Furthermore, test presses of this type have collet chucks for holding the tubes and preventing them from buckling, in the region of which it is not possible to carry out optimum testing, because the tube wall is supported on the outside and cannot be observed.

It is an object of the invention to provide a method for finishing hot-rolled tubes which is more economical and which, in particular, enables a higher throughput rate to be achieved.

In accordance with the invention, a) following rolling, the finished tube is subdivided into sections of tube which are multiples of a prescribed commercial length; b) the sections of finished tube are then cooled on a cooling bed; c) after cooling, the sections of finished tube are straightened; d) following straightening, the sections of finished tube are fed transversely to their longitudinal direction to a washing station and their interiors are washed; e) the sections of finished tube are subsequently checked in a tube test press; and f) several sections of finished tube are collected together and are together subdivided into the desired commerical length.

This makes relatively long sections of finished tube available not only during cooling, but also during straightening. In this way, the total throughput of the straightening machine in weight per unit of time is increased, and furthermore, the proportion of inadequately straightened end portions in total production is reduced. Furthermore, additional cold sawing after cooling and prior to straightening, which is considerably expensive in comparison with hot sawing, can be dispensed with.

It is particularly advantageous that testing using a tube test press is carried out in the method according to the invention before subdivision into commercial lengths, and hence on a relatively long section of finish-rolled tube. As a result, there are two untested end portions per section of finished tube only, and not per commercial length. As the sections of finished tube are multiples of the commercial length, the proportion of untested end portions is clearly reduced, as is the amount scrapped of the untested end portions when they are cut off.

Furthermore, because of the small proportion of the untested end portions compared to the total tube length, it does not matter if these few end portions are somewhat longer. As a result, self-holding tube testing heads can be used in the method according to the invention when only an insignificantly larger proportion of the length is formed by the untested ends to be cut off. Using these testing heads, it is possible to subject the sections of finished tube, as in normal operation, to high tension in the longitudinal direction and, at the same time, to check their impermeability at a high testing pressure. At the same time, the entire length of the outside wall of the tube is visible, because there are no collets, which would prevent the finished tube sections from buckling, on the tube test press in such testing heads.The tube test press, which does not have to absorb any high longitudinal forces, can thus be of a simpler and lighter construction, and hence more cost-effective to produce. Furthermore, the throughput rate in weight per unit of time of a tube test press is considerably higher when the length of the tubes to be tested is greater, because the handling times are shorter. Shorter handling times are obtained for sections of finished tube which are a multiple of the commerical length, because several commercial lengths are tested simultaneously in one testing operation.

The most important advantage, however, it that all the resulting commercial lengths of tube are tested completely, including their end portions, with the exception of the first and last commercial lengths, each of which has, however, a maximum of one untested end. If tubes with bushings are to be manufactured, each end provided with a bushing must be checked once again following thread-cutting and screwing on of the bushings, in order to check the tightness of the bushing connection. If the end portions, which have not yet been tested, are then provided with bushings and subjected to the above-mentioned necessary test, all the ends of all the commercial lengths are satisfactorily tested without the end portions having to be cut off and scrapped.Even if no bushings are to be screwed onto the commercial lengths, there are so few untested end portions obtained in the method according to the invention, that most or all of them can be used as test pieces for carrying out a flattening test, expansion test or similar, and would therfore have been cut off in any case.

It is recommended, following cooling on a cooling bed and prior to straightening, to line up the sections of finished tube in the longitudinal direction and todeburr the leading end edges which are to enter the straightening machine first. This additional measure, which is employed between cooling and straightening, ensures that the burr produced by the hot sawing carried out at the beginning does not interfere with entry into the straightening machine, nor is it rolled into the outer surface of the tube during the straightening operation.

Furthermore, it is adviseable to line up the sections of funished tube following straightening and prior to washing, and to deburr the remaining end edges. In this way, it is ensured that the edges at both ends of the sections of finished tube are deburred prior to testing, so as to avoid damage to the testig heads, and in particular to their sealing elements. Deburring both end edges of the sections of finished tube prior to straightening should be avoided where possible, because too much time would otherwise be required for lining up the sections of finished tube. Prior to straightening, only those ends which are last to come out of the rolling line are in approximately the same position, whereas, following straightening, the other ends of the sections of finished tube are in approximately the same position.

When the ends are in approximately the same position, lining up takes less time, which has a favourable effect on the overall process.

Furthermore, it is advantageous to test the tube wall by means of non-destructive testing apparatus following testing in the tube test press and prior to subdivision into commercial lengths. This should also be carried out prior to subdivision of the sections of finished tube into commercial lengths. The non-destructive testing apparatus is not able to test the end portions satisfactorily. However, the measure in accordance with the invention produces only a few such untested ends.

The invention is further described, by way of example, with reference to the accompanying drawing which is a schematic representation of a plant which is suitable for carrying out the method according to the invention.

An induction furnace 1 is supplied by way of a roller table 2 with semi-finished tubes from a plant which is disposed upstream and which is not shown, the tubes being heated# in said furnace 1 to rolling temperature and fed to a stretch-reducing rolling line 3 connected downstream. The diameter of the tubes is reduced therein and their wall thickness is also usually changed such that they are given the finished cross section. Downstream of the stretch-reducing rolling line 3, there is a hot saw 4 which subdivides the finished tubes delivered from the stretch-reducing rolling line 3 into sections of finished tube which are whole multiples of a prescribed or desired commercial length.

The resulting sections of finished tube pass by way of a roller table 5 to a cooling bed 6, where they are cooled to a temperature which is slightly above room temperature. At the end of the cooling bed 6, there is a lining-up roller table 7, which moves the sections of finished tube against a stop (not shown), so that all the finished tube sections are in the same position at this point and the end edges of the end sections of the sections of finished tube, which have been lined up in this way, can be deburred by a deburring device 8. Following deburring, the sections of finished tube pass to a roller table 9, where they are conveyed to a straightening machine 11 with the aid of a drive apparatus 10.Beyond the straightening machine 11, a further roller table 12 conveys the sections of finished tube to a transverse conveyor 13, which in turn contains a lining up roller table 14, which moves the other end sections of the sections of finished tube into line, so that a seond deburring device 15 can debur the end edges at the other end of the sections of finished tube.

A washing station 16 is provided directly beyond the second deburring device 15. The interiors pf the finished tube sections are washed therein and thus cleansed of chips, scale and slag particles. The transverse conveyor 13 transports the sections of finished tube to a test press 17, in which the integrity and tightness of the tubes are tested. A roller table 18 transports the sections of finished tube in the longitudinal direction to a non-destructive materials testing device 19 in which hidden defects in the tube wall are detected.

Finally, a roller table 20 and a transverse conveyor 21 convey the sections of finished tube to a station 22 where a plurality of sections of finished tube (for example five or six) are put into a layer.

Such a layer of sections of finished tube passes by way of a correspondingly wide conveyor 23 to a cold saw 24, where the sections of finished tube are subdivided into the prescribed commercial lengths. A conveyor 25 transports the finished tubes, which have been subdivided into commercial lengths, to finishing devices, where these commercial lengths are made ready for despatch.

Claims

1. A method of finishing hot-rolled tubed, in which a) following rolling, the finished tube is subdivided into sections of tube which are multiples of a prescribed commercial length; b) the sections of finished tube are then cooled on a cooling bed; c) after cooling, the sections of finished tube are straightened; d) following straightening, the sections of finished tube are fed transversely to their longitudinal direction to a washing station and their interiors are washed; e) the sections of finished tube are subsequently checked in a tube test press; and f) several sections of finished tube are collected together and are together subdivided into the desired commerical length.

2. A method as claimed in claim 1, in which, following cooling on a cooling bed and prior to straightening, the sections of finished tube are lined up in the longitudinal direction and the leading end edges which are to enter the straightening machine first are deburred.

3. A method as claimed in claim 1 or 2, in which, following straightening and prior to washing, the sections of finished tube are lined up in the longitudinal direction and the remaining end edges are deburred.

4. A method as claimed in claim 1, 2 or 3, in which, following testing in the tube test press and prior to subdivision into commercial lengths, the tube wall is tested by means of non-destructive testing apparatus.

5. A method of finishing hot-rolled tubes, substantially as herein described with reference to the accompanying drawing.