GB2072224A - Apparatus and method for annealing non-ferrous strip material in a continuous drawing or rolling process - Google Patents

Abstract

In a method for annealing non- ferrous strip material in a continuous drawing or rolling process wherein the strip material, subsequent to drawing or rolling is continuously fed around a pair of spaced pulleys, an induction coil is placed in the run between the pulleys and powered by a variable supply of suitable frequency. One of the pulleys has a double grooved electrically conducting rim which electrically short circuits the incoming to the outgoing strip material thus creating a single turn short circuit around the pulleys thereby forming a movable, short circuited secondary winding of the induction coil serving to heat the strip. The required annealing temperature is controlled by controlling the power to the induction coil. A combined quenching and annealing apparatus is also disclosed for quenching the annealed strip material after annealing. The quenching apparatus employs means for maintaining the level of the quenching fluid constant. <IMAGE>

Description

SPECIFICATION Apparatus and method for annealing nonferrous strip material in a continuous drawing or rolling process Field of the Invention The present invention relates to a method and apparatus for annealing non-ferrous strip material such as copper and aluminium, in a process known as drawing or rolling of the material.

Background of the Invention The process of drawing or rolling material of the above-mentioned type consists of a system whereby copper or similar rod is drawn through a die to shape the material in the form of the die which may be square or rectangular in an infinite number of sizes and combinations.

The shape of the final material is dependent on the particular application in which the material is to be employed, such applications being generally winding of power transformers, electrical motors and the manufacture of buzz bars, power stations as well as the wiring of light and heavy power control equipment.

Another method of manufacturing copper or similar strip material involves rolling the material into the shape of a rectangle or square, once again of a cross section dependent on the final application and of the current carrying capability of the application requirement.

When the material has been drawn or rolled into shape it becomes work-hardened making it difficult to wind in the final application, as well as brittle which renders it unusable due to breakage during the winding process. In order to overcome these problems the material has to be annealed, that is it has to be softened by heat treatment whereby once raised to a certain temperature the stress built into the material after rolling or drawing is relieved and the material emerges soft and suitable for winding on drums.

Previous well-known methods of annealing strip material involved winding the strip after drawing on to large drums and then inserting the drums into an oven or furnace after vacuum heating the furnaces to a predetermined temperature and for a predetermined period of time.

This process is known as batch annealing and although still used it has disadvantages in being an expensive process as regards power consumption, the labour and handling involved, and it also produces "stickiness" between successive turns of the material strip wound on the drums.

Summary of the Invention The method and apparatus of electrical annealing which will be described in details hereinafter, eliminates many of the earlier problems and produces a commercially acceptable strip material at an economical price.

According to the invention there is provided apparatus for annealing non-ferrous strip material in a continuous drawing or rolling process for forming the metal strip and comprising a pair of spaced pulleys one of which has a double grooved rim which is electrically conductive, one of the grooves being provided to lead in the strip material after drawing or rolling for winding around the pulleys, the other groove to lead the strip material off the pulleys after annealing for subsequent quenching, and an induction coil between the pulleys to provide an attendant magnetic flux through which the strip material passes during movement on the pulleys, whereby to effect heating of the strip material to anneal temperatures.

This system obviates the disadvantages of the prior art in that the strip material can be annealed as a continuous process during the rolling or drawing operation and prior to subsequent quenching of the strip material.

Other features and advantages of the present invention will become apparent from the description which follows.

Brief Description of the Drawings An embodiment of the present invention will now be described by way of example with reference to the accompanying drawings wherein: Figure 1 is a diagrammatic view of apparatus for continuously annealing non-ferrous strip material according to an embodiment of the invention together with a detail of one of the winding pulleys; Figure 2 is a diagrammatic view of apparatus for continuously annealing strip material according to an embodiment of the invention together with electrical means for controlling the annealing process; and Figure 3 is a diagrammatic view of a combined annealing and quenching apparatus in a continuous drawing or rolling process incorporating the annealing apparatus of Figures 1 and 2.

Best Modes of Carrying Out the Invention The annealing apparatus shown in Figure 1 comprises two spaced pulleys 1 and 2 for winding strip material 3. An induction coil 4 is positioned in the run of the strip material between the pulleys 1 and 2, the induction coil 4 being coupled to an alternating source of electrical current 5.

The upper pulley 1 is formed of an insulating material, while the lower pulley 2 is provided with an electrically conducting rim 6 having parallel peripheral grooves 7 and 8.

The incoming strip material from the drawing or rolling apparatus for forming the strip material (not shown) is continuously fed at 9 to the pulley 8 and thereafter passes through the induction coil 4 and around the pulley 1. The outgoing strip material 10 emerges from the pulley 2 in the groove 7, as annealed strip, whereafter it is subsequently quenched in apparatus to be hereinafter described. It will be appreciated that the process of annealing using the apparatus of Figure 1 is continuous with drawing or rolling of the material into strip form and quenching of the strip material subsequent to annealing.

The strip material on the pulleys effectively forms a single loop, with the double-grooved conducting rim comprising grooves 7 and 8, electrically short-circuiting the incoming strip material to the outgoing strip material thus creating a single turn short circuited secondary winding of the induction coil.

Due to the existence of a magnetic flux in the coil 4 a short circuit current flows in the loop which raises the temperature of the strip within the loop because of the inherent resistance of material.

The loop of strip material on the pulleys, and the pulleys 1 and 2 themselves are enclosed in an inert atmosphere of steam, nitrogen, argon and the like to prevent surface oxidation.

The apparatus of Figure 1 is shown in Figure 2 coupled to electrical circuit means for controlling the annealing process.

The circuit means includes a variable power controller 11 connected to an alternating supply 12 for feeding power to the primary winding 13 of the induction coil 4 shown diagrammatically in Figure 2.

The controller 11 is operably responsive to a signal A from a computing device 14 to maintain the annealed temperature at the desired value.

A Tacho generator 15 monitors the rotational speed of the pulley 2 to give a signal B representative of the line speed of the strip material, which signal B is fed into the computing device 14.

A further signal C representative of the voltage induced in the loop strip material on the pulleys 1 and 2, is also fed to the computing device 14, as is a signal D representative of the ambient temperature from a thermometric device 16.

From the signals B, C and D the device 14 computes a temperature at which the strip material on the pulleys is being annealed and compares this with a pre-selected desired temperature set by a potentiometric device 1 7 and stored in the device 14.

Any resulting signal A indicating a difference in the comparison is used to operate the controller 11 to adjust the power fed to the primary winding 13 of the induction coil, thereby to maintain the required anneal temperature.

The degree of anneal requirement may vary in different applications and while in some instances a fully soft material is required, in some other applications a half hard or 3/4 soft strip could be utilised.

The combined annealing and quenching apparatus shown in Figure 3 comprises a quenching tank 1 8 for housing the apparatus of Figure 1, the tank 18 being provided with quenching fluid 1 9 which is retained at a constant level 20. The quenching fluid may be water, oil or other suitable substance.

The quenching tank 18 has an upper and a lower part 1 8A and 1 SB respectively. The quenching fluid 1 9 is contained in the lower part 18B.

Aithough not shown the pulley 1 of the apparatus of Figure 1 is mounted in the upper part 18A and the lower pulley 2 in the lower part 1 SB, to be partially or wholly immersed in the cooling fluid 19.

The incoming strip material from the drawing or rolling process enters the lower part 18B through the inlet passage 18C and to the groove 7 of pulley 2.

The strip then passes to the upper pulley 1 through the passage 18D, in which the induction coil 4 is housed, and back to the groove 8 of the lower pulley 2, through passage 18E at which stage it is quenched in the cooling fluid 1 9 to be led out of the lower part 18B through outlet passage 18F.

The cooling fluid 19 is supplied to the tank 18 from a makeup tank 21 through a conduit 23. A solenoid operated valve 22 is positioned to control passage of fluid through the conduit 23 to maintain the fluid in the quenching tank 18 at the same level as that in the makeup tank 21, namely level 20. The tanks 18 and 21 are provided with safety valves 18A and 21 A respectively.

Steam is introduced into the cooling fluid 1 9 in the tank 18 through conduit 24 from a steam supply 25. The steam from the supply passes through a solenoid valve 26 and steam pressure regulator 27.

The steam is introduced from the external steam supply 25 into the annealing system as a means of inert atmosphere to prevent surface oxidation of the cooling fluid. The steam raises the temperature of the cooling water 19 to boiling point which is an important requirement in this process as it exhausts all oxygen from the cooling water.

The makeup tank 21 is installed and fitted with a heater 28 to ensure that the makeup of water in the cooling tank 18 is at the correct temperature of near boiling point and is also oxygen free.

The water fed into the makeup tank 21 is supplied from either a soft water supply 29 or a deoxiding plant (not shown), through branch conduits 30 and 31 fitted with a makeup stopcock 32 and fast flow solenoid valve 33, respectively, and a main inlet conduit 34 provided with a solenoid valve 35. The soft water ensures that no salt deposits are formed on any part of the contact pulleys of the annealing apparatus mounted in the tank 18.

The atmosphere above the fluid level 20 in the quench tank 19 and the makeup tank 21 must be kept inert. This is achieved by steam fed to the tanks 18 and 21 through conduits 37 and 38, at a pre-selected pressure by means of control device 36. The inert atmosphere could alternatively be nitrogen or argon or any similar gaseous means.

The normal operating level of the cooling water 19 is at the level of the water in the makeup tank 21 namely level 20. A switch 39 in the makeup tank 21 monitors the normal operating level namely level 20, and a further control switch 40 is positioned in the makeup tank 21 at a level which would constitute an emergency alarm level. The switch 39 is operable to control selective entry of makeup water into the tank 21 from the supply 29 and to control solenoid valve 22 so that the level 20 is maintained constant corresponding to the desired normal operating level of the quenching fluid.

Claims (10)

1. Apparatus for annealing non-ferrous strip material in a continuous drawing or rolling process for forming the metal strip and comprising a pair of spaced pulleys one of which has a double grooved rim which is electrically conductive, one of the grooves being provided to lead in the strip material after drawing or rolling for winding around the pulleys, the other groove to lead the strip material off the pulleys after annealing for subsequent quenching, and an induction coil between the pulleys to provide an attendant magnetic flux through which the strip material passes during movement on the pulleys, whereby to effect heating of the strip material to anneal temperatures.

2. Apparatus as claimed in Claim 1 wherein the other spaced pulley is an electrically insulating pulley at least in respect of its rim around which the strip material passes.

3. Apparatus as claimed in Claim 1 or 2 wherein the primary winding of said induction coil is connected to a variable power supply of either 50 to 60 cycles main frequency or an elevated frequency up to 1000 cycles.

4. Apparatus as claimed in any preceding claim including circuit means for controlling the anneal temperature of said strip material, said circuit means comprising means for determining the temperature of the strip material being annealed, means for comparing the actual anneal temperature with a pre-selected temperature necessary to attain a required anneal condition of the strip material, and control means for adjusting the heating power of said induction coil to maintain the heat generated in the strip material at said pre-selected temperature.

5. Apparatus as claimed in any preceding claim mounted in a quenching tank to quench the annealed strip, the quenching tank having an upper and lower part, the lower part housing said double grooved pulley wholly or partially immersed in quenching fluid to quench the outgoing strip material, the upper part containing the other pulley, and entrance and exit passages of the tank for incoming and outgoing strip material to and from the pulleys respectively.

6. Apparatus as claimed in Claim 5 including variable steam pressure supply means for providing an inert atmosphere above the levels of fluid in the quenching and makeup tanks at an equal pressure.

7. Apparatus as claimed in Claim 6 wherein the quenching fluid and makeup fluid is water, said quenching water in the quenching tank being in communication with a source of steam to prevent surface oxidation of the quenching fluid.

8. Apparatus as claimed in Claim 7 wherein heating means are provided within the makeup tanks to maintain the makeup water at a temperature of substantially boiling point and oxygen free.

9. Apparatus for annealing non-ferrous metal strip material in a continuous drawing or rolling process for forming the strip, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

10. Apparatus for annealing and quenching non-ferrous metal strip material in a continuous drawing or rolling process for forming the strip, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.