GB2041273A

GB2041273A - Producing extrusion profiles

Info

Publication number: GB2041273A
Application number: GB7904072A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1979-02-06
Filing date: 1979-02-06
Publication date: 1980-09-10
Also published as: GB2041273B

Abstract

A billet 11 of preselected billet length l is processed in a press 2 and the extruded length is measured during the extrusion process. Upon reaching the desired extruded length Lx either the process is stopped and the billet length l varied so as to obtain the optimum butt thickness, or the extrusion process is stopped upon reaching the minimum permissible butt thickness and the billet length l is enlarged sufficiently as to obtain the desired extrusion length Lx in the next cycle. A billet hot shearing unit 1 has an adjustable longitudinal feed stop 9, 10 and cuts the billets 11 to length for supply to the press 2. A first length recorder 21 measures the butt thickness p and a second length recorder 34, 38, 39 measures the extrusion length L. The measured actual values of the butt thickness p and the extrusion length L are supplied to a controller 40 which compares them alternately with corresponding reference input values of the butt thickness Px or the extrusion length Lx respectively and actuates a positioning element 13 which adjusts said longitudinal feed stop 9, 10. <IMAGE>

Description

SPECIFICATION A method of and an apparatus for producing extrusion profiles The invention relates to a method of and an apparatus for producing extrusion profiles having a desired extrusion length, in particular from cast metal billets.

In the extrusion of rods, tubes, profiles, and the like of metal, for example aluminium, normally an extruded profile is produced from a billet having a certain length. The length of the extruded profile depends on the length of the billet being extruded and on the press ratio, i.e. the ratio between the pressure pad cross section and the extrusion cross section. The length of the extruded portion of the billet then corresponds to the original billet length minus the length of a residue or butt to be discarded, the so-called butt thickness.

The butt retains impurities contained in, on or at the billet and protects the die from overload.

The butt thickness is of the order of from 3% to 5% of the billet length and forms part of the waste produced in extrusion processes.

It is an object of the invention to produce extruded profiles of desired extrusion lengths, at a given, approximately known press ratio, from billets having such a length that the butt'thickness is as small as possible and is maintained at the rated optimum thickness value which still provides some reserves as compared to the minimum permissible butt thickness with regard to the quality of the extruded profile and the permissible loading of the die.

According to the present invention, in a method of producing extrusion profiles of a desired length from billets of adjustable severence length, (a) a billet of preselected billet length ("/") is subjected to extrusion, (b) the extrusion length (L) is measured during the extrusion process, and either (c) the extrusion process is stopped when the profile being extruded has reached the desired extrusion length (Lx) and the billet severence length (' r') is then varied so as to obtain a butt thickness closer to the optimum butt thickness ipx) in the next extrusion cycle, or (d) the extrusion process is stopped when the billet being extruded has reached the minimum permissible butt thickness (pro) before the desired extrusion length (Lx) has been reached and the billet severence length ( 'r ) is then increased so as to obtain an extrusion length (L) closer to the desired extrusion length (Lx) in the next extrusion cycle.

An apparatus for carrying out this method is characterised by (a) a billet hot shearing unit having an adjustable longitudinal feed stop for altering the billet severence length, (b) a press to which the billets severed length by the billet hot shearing unit are supplied, (c) a first length recorder for measuring the butt thickness, associated with the press, (d) an extrusion withdrawing unit for withdrawing the extruded profile from the press, (e) a second length recorder for measuring the extrusion length, associated with the extrusion withdrawing unit.

(f) a controller, whose inputs are reference input values and the measured actual values of the butt thickness and the extrusion length, respectively, and which effects a reference valueactual value comparison alternatively with respect to the butt thickness or the extrusion length in accordance with whether the measured actual value of the extrusion length or that of the minimum permissible butt thickness first reaches the respective reference value during the extruding process, and which generates actuating signals which represent the differences between said reference and actual values, and (g) a positioning element which adjusts the longitudinal feed stop of the billet hot shearing unit upon receipt of the actuating signals so as to reduce the said differences in the next extrusion cycle.

The method and apparatus according to the invention, on the one hand, permit a correct preselection of the extrusion length, thus avoiding the extrusion of unnecessary lengths of material.

On the other hand, a minimum of billet length or original billet weight is required to obtain the desired extruded profile length. Together these two aspects afford the possibility of extruding with a very high utilization of the material, with a very small degree of waste. Thus the method and apparatus according to the invention permit more economic operation than heretofore possible.

Conveniently the individual steps mentioned are repeated in successive cycles, always using the most recently adjusted billet length instead of the original preselected billet length, until finally the actuating signal which represents a difference from the rated value or reference input value of the butt thickness becomes zero. This procedure is typical of a feedback control system. In the present case either the butt thickness or the profile length represents the controlled variable, depending on whether the desired extrusion length is reached or failed to be reached during the first pressing, in other words whether the reaching of the minimum permissible butt thickness is signalled previously.In the latter event the deficiency in billet length, i.e. the enlargement of the billet length required to obtain the desired extrusion length, is determined on the basis of the press ratio which is defined by the ratio between the pressure pad cross section and the extrusion cross section.

The feedback control may be effected in consideration of a correction ratio between the butt cross-section (which corresponds to the pressure pad cross-section) and the billet crosssection of the hot billet.

The controller includes a computer in which the actual data detected by the length recorders are compared with the reference input values at the end of an extrusion cycle and are processed to form the positioning or actuating signals. A third length recorder is provided to detect the billet length. The output signal of this recorder is also applied to the controller.

Conveniently each length recorder comprises a rotary pulse emitter with a counter. Here the longitudinal displacement, which has been converted into rotation in a manner known per se, is sensed in a digital manner and transmitted to the computer in the controller as the actual value.

The positioning element conveniently comprises a positioning motor which adjusts the longitudinal feed stop by way of a screw spindle upon receipt of a positioning signal.

The invention may be carried into practice in various ways, but one specific embodiment thereof will now be described by way of example, with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a diagram of the various component parts of a billet extrusion installation embodying the invention, showing how the various elements combine to cooperate in accordance with the method of the invention.

Figure 2 is a block diagram of a feedback control loop provided in the installation of Figure 1; Figure 3 is 3 flow chart illustrating the course of the extrusion process performed in the installation of Figure 1 in an easily understandable sequence of the individual steps taken.

In Figure 1 the three principal component parts of the apparatus, namely a billet hot shearing unit 1, a press 2, and an extrusion withdrawing unit 3 are shown only diagrammatically since they are known per se. The billet hot shear may be of the design described in detail in German patent specification No. DE-OS 26 04 418, laid open.

From a preheating furnace 4 a billet 5 is fed to the billet hot shearing unit 1 by a roller guide means comprising rollers 6, and is then passed through a stationary shear ring 7 and a movable shear ring 8 up to an adjustable longitudinal feed stop 9, including an abutment roller 10. The vertically movable shear ring 8 serves to sever the material supplied into billets 11 of severence length "I", determined by the position of the feed stop 9.

As the longitudinal feed stop 9 is adapted to be displaced in the longitudinal direction on a spindle 12 by means of a positioning motor 13, the severence length r of the billet is variable. An electronic rotary pulse emitter 1 4 is coupled to the positioning motor 1 3. In combination with a counter (not shown) it serves for digitally sensing a change in position of the longitudinal feed stop 9 and thus a variation in severence length r of the billet, which length "/" is measured from the shear edge designated 0 and located in the vertical plane between shear rings 7 and 8 to the abutment roller 10. A first severence billet length r can be preselected by means of a selector 1 5.

The sheared-off billet 11 having a length "/" is supplied to the container 1 6 of the press 2 where it is processed (extruded) by means of a ram 17, constituted by the extrusion stem and the pressure pad ahead of the same (not shown), extruding the billet through a die 18 which has an orifice 1 9 corresponding to the desired cross sectional shape of the extruded profile 20. It is not the entire length r of the billet which will be extruded, but instead a length reduced by the thickness p of the butt which is determined by the press stroke h.

The butt thickness must not be less than the minimum permissible butt thickness p,. The optimum rated value Px of the butt thickness p which still warrants satisfactory quality of the extruded profile 20 and, moreover guarantees that the die 1 8 is not subjected to undue stress, is somewhat greater than the smallest permissible butt thickness pO.

A stroke length measuring instrument 21, including a screw spindle 22 which is rotated by advancing the ram 1 7, a rotary pulse emitter 24, including a counter (not shown), a linear scale 25, and an indicator 23 moved along with the ram 17, are all associated with the ram 1 7. Thus the actual value p of the butt thickness which is derived from the press stroke h, can be determined as illustrated by block 26 in Figure 1.

The extrusion withdrawing unit 3 comprises a carriage 32 which is supported on rollers 31 for movement along a pair of rails 30 arranged in parallel with the extruded profile 20. The carriage is driven by a motor 34 acting through a chain 33.

The extruded profile 20 is grasped by the carriage by means of a fixed jaw 35 and a parabolic jaw 37 adapted to swing about a pivot 36, the jaws taking along the extruded profile 20 until the desired extrusion length Lx has been reached or the press stroke h has terminated upon reaching the minimum permissible butt thickness p,. The actual length L of the extruded profile is detected by a rotary pulse emitter 38 associated with the motor 34 and forming the actual value L (block 39 in Figure 1). The actual values of the butt thickness p (from block 26 in Figure 1) and of the extrusion length L (from block 39 in Figure 1) are applied to a controller 40 incorporating a computer.The controller and computer 40 also receive the output signal of the rotary pulse emitter 14, which signal is representative of the respective billet severence length r Furthermore, reference input values Px and Lx representing the optimum butt thickness and desired extrusion length, respectively, are applied to the controller 40, these values being adjustable, for instance by potentiometers, at reference input adjusters 41, 42. Additional inputs into the controller and computer 40 are the fixed values of, the minimum permissible butt thickness pOr the press ratio as defined previously, and the billet section correction ratio likewise defined previously, the input of these values being effected through corresponding input means 50, 51, 52.

Based on these values the controller and computer 40 form a quantitative output signal which is applied from an output 43 to the positioning motor 1 3 of the longitudinal feed stop 9 to effect a corresponding change of the billet severence length "S' in a follow-up open loop control. The change made is reported back to the controller and computer through a "feedback /" signal so as to terminate the adjustment of the longitudinal feed stop 9 as soon as the calculated value of "t' has been attained.

The functioning and mode-of operation of the method and apparatus shown in Figure 1 will be understood by reference to Figures 2 and 3. The block diagram of the feedback control loop according to Figure 2 shows the individual blocks of the feedback control loop with the same designations as used in Figure 1. The controlled variable is the actual butt thickness p or, in case of insufficient billet severence length r, the extrusion length L. The controlled system is formed by the press 2 and the withdrawing unit 3.

The actual values of the buttthicknessp are determined by the length measuring instrument 21 and given in block 26, while the actual values of the extrusion length L are formed by means of the rotary pulse emitter 38 and given in block 39.

These values are applied to the controller and computer 40 to which the reference input values Px and Lx of the butt thickness and extrusion length, respectively, are also applied from the reference input adjusters 41, 42. Further inputs into the controller and computer are the additional data mentioned, namely the minimum permissible butt thickness p,, the press ratio, and the correction ratio. The customary comparison between rated or reference values and actual values is made in the controller and computer and, based on such comparison, an actuating signal generated at the output 43 is applied to the positioning motor 1 3 to adjust the longitudinal feed stop 9 of the billet hot shearing unit 1 and thus vary the billet severence length "r' in the sense tending to eliminate the actuating signal.

The reference input values Px and Lx are used alternatively. If the desired extrusion length Lx is reached without the press having reached the minimum permissible butt thickness pO, the reference input valve p, of the butt thickness is compared in the controller with the actual value of the butt thickness. The billet severence length t then is increased or decreased in dependence on the actuating signal, i.e. in response to a positive or negative difference between the reference input values and the actual values.

If, on the other hand, the minimum permissible butt thickness p0 is reached before the desired extrusion length Lx is obtained, the extrusion length Lx is taken as the reference input value and compared with the actual value of the extrusion length L. In this case the controller and computer determine the lacking billet length on the basis of the difference between the actual extrusion length and the rated extrusion length, utilizing the press ratio, and generate a corresponding actuating signal to be applied to the positioning motor 1 3 for an increase of the billet severence length "/".

In detail the course of the individual method steps in operating the apparatus according to Figure 1 may be taken directly from Figure 3.

Claims

1. A method of producing extrusion profiles of a desired length from billets of adjustable severence length, in which method: (a) a billet of preselected length is subjected to extrusion, (b) the extrusion length and the butt thickness are measured during the extrusion process, and either (c) the extrusion process is stopped when the profile being extruded has reached the desired extrusion length, and the billet severence length is then varied so as to obtain a butt thickness closer to the optimum butt thickness in the next cycle, or (d) the extrusion process is stopped when the billet being extruded has reached the minimum permissible butt thickness before the desired extrusion length (Lx) has been reached, and the billet severence length is then increased so as to obtain an extrusion length closer to the desired extrusion length in the next extrusion cycle.

2. A method as claimed in Claim 1, in which upon reaching of the minimum permissible butt thickness the deficiency in billet length, i.e. the enlargement of the billet severence length required to obtain the desired extrusion length, is determined on the basis of the press ratio (ram pressure pad cross-section/extrusion crosssection).

3. A method as claimed in Claim 1 or Claim 2, in which using the respective most recently adjusted billet severence length instead of the original preselected billet length, the method steps defined are repeated in a number of successive cycles until the actuating signal representing the difference between the actual measured butt thickness and the reference input value of the butt thickness becomes zero.

4. A method as claimed in any one of Claims 1 to 3, in which the ratio between the butt crosssection and the billet cross-section of the hot billet is taken into account as a correction ratio in adjusting the billet severence length.

5. An apparatus for carrying out the method claimed in any one of Claims 1 to 4, which comprises: (a) a billet hot shearing unit having an adjustable longitudinal feed stop, (b) a press to which billets severed to length by the billet hot shearing unit are successively supplied, (c) a first length recorder associated with the press for measuring the butt thickness, (d) an extrusion withdrawing unit for withdrawing the extruded profile from the press, (e) a second length recorder for measuring the extrusion length, associated with the extrusion withdrawing unit, (f) a controller whose inputs are reference input values and the measured actual values of the butt thickness and the extrusion length, respectively, and which effects a reference value - actual value comparison alternatively with respect to the butt thickness or the extrusion length in accordance with whether the measured actual value of the extrusion length or that of the minimum permissible butt thickness first reaches the respective reference value during the extruding process, and which generates actuating signals which represent the differences between said reference and actual values, and (g) a positioning element which adjusts the longitudinal feed stop of the billet hot shearing unit upon receipt of the actuating signals so as to reduce the said differences in the next extrusion cycle.

6. Apparatus as claimed in Claim 5, in which a third length recorder is provided for detecting the billet severence length, the output signal of this recorder being likewise applied to the controller.

7. Apparatus as claimed in Claim 5 or Claim 6, in which the controller incorporates a computer in which the actual data detected by the length billet severence and extrusion length recorders are compared at the end of each extruding process with the respective reference input values, and any differences are processed to form the actuating signals.

8. Apparatus as claimed in Claim 6 or Claim 7, in which each length recorder comprises a rotary pulse emitter with a counter which detects the respective longitudinal displacement converted in per se known manner into rotation, and transmits a signal representing that displacement as an actual value to the controller.

9. Apparatus as claimed in any one of Claims 5 to 8, in which the positioning element comprises a positioning motor which adjusts the longitudinal feed stop by means of a screw spindle in response to an actuating signal.

10. Apparatus as claimed in any one of Claims 5 to 9, which includes a reference input adjuster for the reference input values of the butt thickness and extrusion length as well as a selector for adjustment of the initial billet severance length.

11. Apparatus as claimed in any one of Claims 5 to 10, which includes input means for feeding inputs representing the press ratio and a correction ratio (butt cross section/billet cross section of the hot billet) into the controller.

12. A method of producing extrusion profiles of a desired length from billets of adjustable severance length, substantially as specifically described herein with reference to the accompanying drawings.

1 3. Apparatus for providing extrusion profiles of a desired length from billets of adjustable severance length, substantially as specifically described herein with reference to the accompanying drawings.