US3723198A - Method of straightening elongate inductively heated workpieces - Google Patents

Abstract

A METHOD AND APPARATUS FOR INDUCTIVELY HEATING AND STRAIGHTENING AN ELONGATE WORKPIECE WHEREIN STOP MEANS. SUCH AS ROLLERS, ARE ADVANCED INTO CONTACT WITH THE HEATED WORKPIECE NOT EARLIER THAN IMMEDIATELY PRIOR TO CESSATION OF INDUCTIVE HEATING SO THAT THE ROTATING WORKPIECE IS STRAIGHTENED AS IT COLLS. IN ONE APPARATUS THE WORKPIECE HOLDING ELEMENT IS PIVOTABLE FROM A POSITION ADJACENT THE INDUCTOR TO A POSITION ADJACENT A QUENCHING COIL SO THAT THE WORKPIECE CAN BE QUENCHED IMMEDIATELY AFTER HEATING.

Description

March 27, 1973 SEULEN ETAL 3,723,198

METHOD 0]" S'I'HALUH'IENLNG ELONGATE INDUCTlVlrJLY HEATED WORKPIECES v Filed NOV. 12, 1970 2 Sheets-Sheet 1 Fig.7

Fig.2 16 i Inventors March 27, 1973 SEULEN ETAL 3,723,198

METHOD OF STRAIGHTENING ELONGATE INDUCTIVELY HEATED WORKPIECES Filed Nov. 12, 1970 2 Sheets-Sheet 2 Inventor 42 /7426? ,fl uzfiv Ear/mm EVA/K ggm M United States Patent 3,723,198 METHOD OF STRAIGHTENING ELONGATE INDUCTEVELY HEATED WORKPIECES Gerhard Seulen and Friedhelm Reinke, Remscheid, Germany, assignors t0 AEG-Elotherm G.m.b.H., Remscheid-Hasten, Germany Filed Nov. 12, 1970, Ser. No. 88,548 Claims priority, application Germany, Nov. 25, 1969, P 19 58 994.7 Int. Cl. C2ld 1/78 U.S. Cl. 148131 Claims ABSTRACT OF THE DISCLOSURE A method and. apparatus for inductively heating and straightening an elongate workpiece wherein stop means, such as rollers, are advanced into contact with the heated workpiece not earlier than immediately prior to cessation of inductive heating so that the rotating workpiece is straightened as it cools. In one apparatus the workpiece holding element is pivotable from a position adjacent the inductor to a position adjacent a quenching coil so that the workpiece can be quenched immediately after heating.

This invention relates to a method and apparatus for straightening elongate workpieces which are held at each end and rotated while being inductively heated by a linear inductor of the type wherein straightening is accomplished by mechanical straightening means, such as straightening rollers, straightening beams or sliding blocks.

One method and apparatus for inductively heating elongate and similar workpieces as well as hardening their surfaces to major or minor depths is described in Seulen et al., application Ser. No. 676,753, filed Oct. 20, 1967, now Pat. No. 3,598,665, the disclosure of which is explicitly incorporated herein by reference. In this method the electromagnetic forces which are generated in the workpiece as it is inductively heated, urge the workpiece against the straightening means, usually idling or driven straightening rolls, to thereby mechanically straighten the work at the same time as it is inductively heated. The method of this previous application has been found to be particularly successful for heating and straightening workpieces in which the temperature is desired to be and is raised above the workpieces Curie point substantially throughout the cross-section. At this temperature all the stresses in the workpiece are relieved and the straightening effect of the magnetic field in co-operation with the straightening rolls takes full effect without leaving residual stresses in the straightened work. I

However, if only the surface of the workpiece, while being inductively heated and straightened by this method, is heated to a depth less than substantially the entire cross-section, for example, between 10 and of its diameter, for the purpose of subsequently hardening the surface by quenching, then considerable stresses remain in the core of the workpiece. The magnetic forces and the reactive effect of the straightening rolls generate residual stresses in the hardened parts which reduce the fatigue strength and/or the torsional strength of the part. Under many circumstances, this undesirable effect may even arise if the entire interior of the workpiece is heated to temperatures above the Curie point.

The present invention relates to a method and apparatus overcoming this difiiculty so as particularly to permit satisfactory straight workpieces to be obtained even when these are only locally heated for local surface hardening. According to the invention of this application this is accomplished by advancing the straightening devices into contact with the rotating workpiece, not while 3,723,198 Patented Mar. 27, 1973 the inductive heating is taking place, but at the earliest, immediately before the inductor is shut off. During the process of cooling, e.g. during the process of quenching, the workpieces are kept in contact with the straightening devices, which are preferably straightening rolls, while the workpiece continues to rotate.

The optimum time for applying the straightening devices in any particular instance can be readily found by a few simple trials. In any event contact by the straightening devices should not be made at least until immediately before the inductor is shut down, and may alternately be made at the same time or just after the inductor is shut down. Applying the straightening devices at this time ensures that the stresses in the workpiece can relieve themselves freely and that the rolls or other straightening devices are not applied until this has occurred.

A particular advantage afforded by the method of this invention is that it can be performed in equipment such as described in the above-mentioned Seulen et a1. application containing straightening rolls that can co-operate with the magnetic forces to straighten during heating. The application of straightening rolls is preferably automatically controlled by reference to a time program and the rolls or other devices are advanced at the desired point in time, be it immediately before, during or immediately after the shut-off of the inductor.

If it is intended to quench immediately after the cessation of heating, particularly when surface-hardening, then apparatus as hereinafter described may be used. The apparatus consists of a tilting workholder unit, equipped with workholding means for mounting the elongated workpieces and with straightening rolls, for conveying the workpiece from a heating station facing the stationary inductor to a quenching station facing a quenching spray in a simple tilting motion that can be rapidly performed.

Embodiments of the invention are hereinafter described and illustrated in the accompanying drawings, of which:

FIG. 1 shows a schematic representation of an apparatus for performing the method of the present invention,

FIG. 2 shows a side elevation view of the workholding unit,

FIG. 3 shows an alternative form of construction of the workholding unit, and

FIG. 4 shows a side view of a tilting unit according to the invention.

Referring to FIG. 1, a conventional current inducing apparatus having a linear inductor 2, and a return conductor 4 is provided adjacent workpiece 1 for inductively heating the workpiece. Inductor 2 is preferably fitted with laminated plates or a pressed soft iron magnetic core to provide a magnetic circuit generally indicated at 3. The transient direction of flow of the current through the inductor 2 and return conductor 4 and the current induced in the workpiece 1 which is preferably rotating in the direction of the arrow 8 are indicated by a cross and a dot in a circle, the cross designating a current into the plane of the drawing. It is, of course, understood that the current directions and direction of rotation can be reversed if desired.

If the workpiece 1 consists of a non-magnetic material or a material at a temperature above the Curie point, then the work will experience a thrust acting in the direction indicated by the arrow 7. As discussed in the above-mentioned Seulen et a1. application this thrust can be utilized for straightening the workpiece by providing stops, such as straightening rolls 5 and 6 against which the rotating workpiece is magnetically urged. However, according to the invention of this application, particularly if only the workpiece surface is to be heated for subsequent hardening, the rolls are not advanced during heating so that straightening takes place not during heating but rather the magnetic forces are allowed freely to take effect during inductive heating while the straightening rolls are in a retracted position. The straightening rolls and 6 which are movable as indicated at arrows 9 are not advanced into contact with the rotating workpiece in the direction of the arrow 10 until, at the earliest, immediately before inductor 2 is shut'otf.

In practice the best time for infeeding the rolls 10' in dependence upon the operation of the inductor is easily determinable by trial for a particular operation. As mentioned above, that time may be immediately before, during or immediately after the shut down of the inductor.

For performing the method according to the invention in the described arrangement in a continuous production line it is preferred to make use of apparatus which is also conventional, a side view of one of which is shown in FIG. 2. Immersed in a tank 11 filled with a quench 12 is an indexable workholder unit 13 which permits enlongated workpieces 14 to be horizontally mounted. Unit-13 is rotatable about its longitudinal axis, and distributed about its periphery there are provided at least three or more individual workholders. Each workholder supports the workpieces 14 on rolls 15 which participate in indexing motions of for example 12, 90, 60 or 45, depending upon the number of workholders distributed around the periphery.

An inductor 16, such as the one shown in FIG. 1, is provided adjacent unit 13 for heating workpieces preparatory to straightening and hardening as described above. At regular or irregular intervals determined, for instance, by an adjustable time delay relay, or functionally depending upon the surface temperature of the work, workholder unit 13 is indexed 90 in the direction indicated by arrow 17. The workpiece 14 including the straightening rolls 15 are thus immersed in quench 12 after inductive heating and straightened while being quenched. If desired an additional spray 18 may be provided for accelerating the quenching effect. The workpiece continues to be rotated in the direction of the arrow 19 while it is being quenched, but rotation in the opposite direction would be equally acceptable. The indexing intervals of the workholder unit are determined by the time needed for heating, since at least three times the heating time is available for quenching if the workholding unit is fitted with four separate workholders. However, if the workholder unit is provided with more workholding positions, then the quenching time may be further prolonged in relation to the heating-up time. It may be desirable to provide a supplementary quenching spray 18a in direct proximity with the inductor 16 to permit quenching to start with a minimum of delay after heating has been completed, and without having to wait for the workholding unit to complete its indexing motion. The rolls 15 are not advanced into contact with the workpiece during the performance of the process, as shown in the drawing, until the cooling and quenching process begins or just before.

It will be apparent that the same apparatus could also be used for hardening and straightening during heating as set forth in the above-mentioned Seulen et al. application. Accordingly, a single apparatus can be used for both methods.

Instead of horizontally mounting the workpieces as in FIG. 2, the workpieces may be vertically mounted, as shown in FIG. 3. In this embodiment the workpieces 14 are each heated in turn by an inductor 20 at a first station of the workholding unit. After heating each workpiece is first indexed to the quenching spray 22 while continuing to rotate in the arrowed direction, and then to position adjacent a second sprayer 23. When the workpieces are being treated according to the novel method of this application, the rolls 15 are not, of course, applied to the workpiece 14 until the inductor 20 has been shut off or just before or until cooling or quenching begins.

FIG. 4 is a side elevational view of apparatus which may be more particularly used when quenching is to begin as quickly as possible after heating has been completed, and principally when the workpiece is to be surfacehardened. The apparatus illustrated is a tilting workholding unit 24 which is tiltable in bearings 25. The shaft that works in these bearings 25 may be vertical or horizontal, the tilting unit either swivelling in the horizontal or tilting in the vertical. The tilting unit carries two workholders for the ends of a workpiece 26 that is to be treated. Straightening rolls 27 can be forced into contact with the workpiece in the direction indicated by the arrows 28. In the heating position the workpiece 26 is held facing inductor 29.. When the heating process is concluded the tilting unit is tilted in the direction of the arrow 30 and thus carries the workpiece 26 without delay into the quenching position facing the quenching sprayer 31. The straightening rolls 27 in this apparatus are likewise advanced in the direction of the arrows 28 into contact with the workpiece 26 at the instant the inductor 29 is shut off.

"Instead of tilting the workpiece substantially in the horizontal, the tilting unit may also be so disposed that the workpiece is lowered from an upper position downwards, substantially vertically. This latter arrangement may particularly be used when quenching of the workpiece is to take place in an agitated liquid quench and the surface of the quench is at a level high enough to permit the tilting unit to immerse the workpiece bodily in the quench.

For loading and unloading the tilting workholding unit it may be moved into a zero position 32 where a hardened and straightened workpiece can be removed and an untreated workpiece substituted. During this process the straightened rolls 27 are withdrawn.

Many changes and modifications of the above described embodiments of the invention can, of course, be made without departing from the scope of the invention and accordingly that scope is intended to be limited only by the scope of the appended claims.

What is claimed is:

1. A method of heating and straightening an elongated metal workpiece comprising the steps of:

inductively heating said workpiece,

rotating said workpiece, and

advancing stop means into contact with one side of said rotating workpiece not earlier than immediately before cessation of said heating and maintaining contact-during coding so that said workpiece is straightened while it cools.

2. A method as in claim 1 wherein said workpiece is rotated during said heating.

3. A method as in claim 1 further including the step of quenching said workpiece after said heating.

4. A method as in claim 3 wherein said workpiece is held in an indexing unit having a plurality of workholding means each adapted to hold a workpiece, at least a single inductive heating station and at least a single quenching station and further including the step of shifting said workpiece, after heating, from said heating to said quenching station.

5. A method as in claim 1 wherein said stop means are rollers and further including the step of rotating said rollers.

6. A method as in claim 1 wherein said stop means are advanced into contact with said workpiece immediately before cessation of said inductive heating.

7. A method as in claim 1 wherein said stop means are advanced into contact with said workpiece at roughly the same time as cessation of said inductive heating.

8. A method as in claim 1 wherein said stop means are advanced into contact with said workpiece immediately after the cessation of said inductive heating.

9. A method of straightening elongate workpieces held at each end while being rotated about their longitudinal axis and heated by a linear inductor, using a mechanical References Ci d straightening device; wherein the said straightening device UNITED STATES PATENTS is advanced into contact with one side of the rotating workpiece at a point in time, at the earliest, immediately 3,598,665 8/1971 Semen et before the inductor is shut off, and subsequently remains 5 3,562,030 2/1971 Seukn et 148-131 in contact with the rotating workpiece, and the work- 3,255,053 6/1966 Bard 148-131 516?; cooled while 1n contact with the said straightening RICHARD 0. DE Primary Examiner 10. A method according to claim 9 wherein the work- U S C1 X R piece is quenched while in contact with the said straight- 10 ening device. 148-143, 150, 154; 21910.41

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