US2003486A - Heat treatment of metals - Google Patents

Description

June 4, 1935. T, J, HANKINS, JR 2,003,486

HEAT TREATMENT OF METALS Filed Nov. 1, 1932 imam-g ("Hum INVENTOR' 7/105. 1 HANK/mm mutilate 4, less a c 2,003,486

UNlTED STATES PATENT OFFICE m'rraasnmmormsl-s Thomas J. llankins, .lr., Springfield, N. 1., asllgnor to Westinghouse LampOompany, a cornotation of Pennsylvania Application November 1, m2, Serial No. 040,021 2 Claims. .(Oi. 219-1!) This invention relates to the heat treatment of the clamps which prevents the ends of the m and in its more specific aspect is dibar from being heated tothe desired temperature the heat treatment of a refractory essential to complete the sintering.

I have found that after a bar has been osubmanufacture or preparation of refractory .ieoted to heat treatment, when clamps are em-' 6 as for example tungsten wires, it is cusployed, those portions of the bar, namely the to first prepare tungsten powder of the ends which are contiguous with the clamping sine and purity. This powder is then means are without the scope of the normal speciin a die of predetermined dimensions and ilcations. That is to say, the ends of the bar iected to a pressing operation in order to surrounded by the clamping means do not have 10 vert the same from .a powdered state into a the particles thereof completely sintered with reline so prepared bar hasnot much body wt to each other. The percentage of the bar but has suilicient strength so that it so clamped is about from live to twenty-five percent of the whole depending upon the length 'lhesecond stage generally comprises placing of the bar being treated. Since these ends are 15 Md tungsten bar in a hydrogen furnace without the normal specification, the bar must operated at a comparatively low temperature, as be out intermediate its ends in order to elimifor example 1250 degrees centigrade. The bar is nate those portions thereof that are not commaintained in said furnace for a sumcient length nletely ll-flared. The tungsten may. f e ur of time so that the particles of tungsten combe r rea d. This. however. rep n a high prising? barmaybeccme at least partially 1 operating loss and increases the cost of productes'ed any superficial oxidation of some of the. tion.

timgaten particles is obviated because of this re- One other method heretofore proposed for the osphere. I same general purpose and to avoid the use-o1 a The third stage, which is the stage with which clamping means involves simply butt-ending the this invention is specifically concerned, generally bar to betreated between a pair of plane con- W placing 12.1118 cintered bar between a tact terminals generally composed of tungsten or minals. an passing an electric current molybdenum; The bars that emerge from the through said bar in order to eflect a complete hydrogen furnace generally are not true-ended so m ofat least most ifnotall of the tungsten and the contact ,surfacesthereof that are to be P t cles compr sing said bar- The voltase placed between and contiguous with the contact M W m5 "1111111518 01 this bar to be terminals are not absolutely plane and oftentimes 1 M upon the size of the bar. are of a macroscopically non-planar contour.

. The magnitude of the current that Thesebarswhen placed between the contacts and I W the that the result! my in a butt-ended position do not form a firm large w a'z gz g :5: 2:1 surface contact between the contact terminals -Wtel7 unwed bar genemuy subjected to -1:13: v v iizfi the bar is energized by an g g in order to reduce the electric current in order to heat the same, there a? g m g g g gg g generally prevails an appreciable degree of arced the we $35335; maxi ize: M two step of this disclosure do not of the bar ends and also of the contact ter iinals form the essence of this invention. The crux of located adjacent thereto astheinventionreatdesinthethirdstepanditis In ddm inst ithat um especially concerned with the problem of cona m some 3 m t this heat treatment the bar under consideration, 'for one reason or another, becomes distorted.

, 32?; The result of this distortion is that the end of the and thereafter passv an electric current therewhich 18 with the 50 m m to mpletely mg a tact terminals, lifts therefrom at one edge to cle'sthereof. 'lhemalndisadvantageofthisproccause appreciable arcing w n that fa nd on is that the ends of the bar which are surthe contact terminal. :Whenthiscondition exists 'ramded by the clamp do not attain the desired the current density at that portion of the bar 42' temperature because of the thermal conduction which isdirectly contiguous with the contact ter- 5' EEEE? minal may be two or three times that at the center of the bar.

' This abnormally high energy input at the contacting area causes the metal immediately adjacent thereto to become fused so that it may flow and coat the contact at that point. This fusion may at times form a weld at the area of contact which may necessitate breaking the bar in order that it may be removed from the contact terminal. That portion which is firmly united with the contact terminal must be ground or subjected to some other operation in order that it may be removed therefrom. I

I have found that bars that are heat treated according to this method and even though they do not become welded to the contact terminals and may be removed therefrom. are not entirely satisfactory because of the metallic structure at these ends caused by the arcing between the contact terminals and the ends thereof. When a bar of this character is subjected to a rolling operation, the ends thereof may not be worked in the same manner as that portion of the bar intermediate said ends. This is generally evidenced by an apparent "fanning" of the ends thereof. Consequently it is apparent that the ends of the bar which become fan-shaped during the rolling operation must be severed therefrom.

In order to obviate the difficulties inherent in the clamping as well as in the beforementioned butt-ending means during the heat treatment at the third stage as heretofore set forth, I have developed the following invention.

The primary object of my invention is to provide means for the elimination of the end losses which are generally inherent in the past process as heretofore set forth.

Another object of my invention is to provide a simple and inexpensive means for emciently heattreating a refractory metal.

A still further object of my invention is to provide a simple and inexpensive means'for lowering the operating costs in the preparation of refractory metal bodies.

In order that my invention may be made readily apparent I shall describe the same with reference to the accompanying drawing wherein,

The single figure represents a somewhat diagrammatical representation with some of the parts in elevation and others in cross section of the means illustrating my invention.

. A device of the character generally employed in carrying out my invention may comprise a suitable yoke ll supported by legs ll resting on an appropriate foundation, not shown. United to said yoke is a base I2 having an insulating bushing it located therein. That side of the yoke oppositesaidbase llalsohasaninsulating bushing located-therein. Fixed to said bushing ll so that the same is stationary with respect to said yoke is a contact terminal II. The contact terminal l5 comprises a cylindrical portion ll extendingthroughan openinginsaidbushingami a flat plane faced disc l1 integral with the portion II.

The contact I, preferably composed of copper, may be provided with an insert l1 of tungsten, molybdenum or the like. The area of the face of the disc I1 is greater than the cross sectional area ofthebartobetreated. Asimilar contact II is located in an opening through the bushing II and is adapted to move vertically in said bushing. Said bushing if has a recess I! at one end thereof in which is located a compression spring 2| which surrounds the cylindrical portion 2l of said'contact and tends to force the relatively stationary the contacts ll and II with a suflcient quantity of loose tungsten powder 21 of the same general composition as that of the tungsten bar being located between the opposing faces of the contact terminalsandtheendsofthebar. Thispowder 21 preferably covers the entire surface of the ends of the bar 2 and may cover the entire surfaces of the contacts which I employ in this operation.

The depth of the tungsten powder 21, although variable, may generally be about to 1; of an inch. After the bar is positioned in the manner heretofore set forth with tungsten powder located 25 I between the ends thereof and contact terminals and, as illustrated in the drawing, an appropriate voltage is applied between the contacts II and II so that electric current may pass through the contacts, the powder and the tungsten bar. The magnitude of the current that through the bar and the time of so treating the bar are well known in the art and require no elucidation herein. It appears sufilcient to say that the time of treatment and energy input are so regulated that the bar may be sufflciently heated in order to completely sinter the particles thereof. This heating operation is preferably done in a reducing atmosphere of hydrogen.

In the course of this treatment, in the manner heretofore set forth, the bar 25 itself has the particles thereof completely sintered and the particles of added powder 21 between the ends of the bar and the contact becomes at least partially sintered. At the end of the heat treating operationthebarmaybereadilyremovedfromthe contact terminals by a mere hand puling operation. Generally, the bar so removed contains a partially sintered tungsten powder united thereto at the ends thereof. This layer of sintered powder at each end of the bar is somewhat fragile because the original tungsten powder at those places was comparatively loose. This sintered tungsten powder at each end of the bar may be readily removed therefrom by a mere rasping operation and when the bar so prepared is subjected to a rolling or mechanical operation generally followed in the preparation of tungsten wire, it is found very nearly one hundred percent of said barisutilizedinthepreparationofthewire and there are no appreciable end losses.

Moreover, 1 have found that when this invention is employed the contact terminals have a relatively long life because they are not subjected to heavy arcing and. therefore. are not generally pitted, which pitting requires repairs or re ments.

Although. I have described my invention with some particularity it is not to be limited thereby but is to be limited only by the prior art.

What is claimed is:

1. The method of treating a partially sintered bar which comprises locating said bar between a pair of contacts, placing a quantity of powdered tungsten between the outer ends of said bar and saidcontactswithsaidpowderbeingcontiguous with substantially only the faces of said contact and the i'aces oi said bar immediately adjacent each other, applying an electric potentialbetween said contacts to elevate the temperature of said- 5 bar to further sinter the particles 01. said bar,

maintaining said bar in position wholly by pressure exterted in the direction of the longitudinal axis or the bar.

2.- The method of sintering apartially sintered l0 tungsten bar whose, mechanical strength is low,

for greatlyincreasing the mechanical strength thereof.

' THOMAS J. HANKINS, JR,

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