US2263029A - Heat treating apparatus - Google Patents

Description

NOV. 18, 1941: BUCKNER 2,263,029

HEAT TREATING APPARATUS Filed July 17, 1940 Hill!!! INVENTOR, PAUL BUCKNER.

A 7' TORNEYS tion will indicate whether or not the parts are- Patented Nov. 18, 1941 OFFICE- HEAT memo srrsnn'rus Paul Buckner, Inglewood, Cali! asslgnor to Northrup Aircraft, Inc

Hawthorne, 081". a corporation oi. California Application July 17, 1940, Serial No. 345,879

(01. ass-4) 9 Claims.

This invention relates to heat treating apparatus, and particularly to apparatus for heat treating the high tensile strength alloysof alum-v inum and magnesium. I Alloys of this class are extremelysensitive to heat treatment, their properties in respect their hardness, tensile strength, and especially their resistance to corrosion depending almost entirely upon the heat treatment which they have received. Specifically the alloy or group of alloys known as duralumin or dural, which are probably now the most widely used of the light, high tensile stren alloys, are particularly sensitive to such tr lneihty.

A typical alloy of s group for instance, containing aluminum, magnesium, manganese and copper, combines these elements in solid solution at temperatures somewhat, above 900 F., and the heat treatment tor this particular alloy requires that it be brought up to a temperature of 950 F. and maintainedat this temperature for one-half hour or more, depending on the thickness. The result or this treatment is that the solid solution above-referred to becomes substantially complete. If the temperature be reduced to slightly below the critical value, crystals or grains start to form within the body of the material, and the copper segregates out. oi. the

- influences, the copper is first attacked, resulting in what is known as inter-granular or intercrystalline corrosion, and a specimen in which such corrosion has occurred is worse than useless for structural purposes, for although its ap-' pearance may not indicate that anything has happened to it it may, in fact, be so lacking in strength as to fracture or even crumble under very slight stresses,

Ordinary tests of tensile strength or hardness on a newly fabricated part will not indicate when such segregation has occurred, and only corrosion tests followed by mierographicqexaminasuitable for use as structural members.

In aircraft structures many parts are fabricated of the materials under consideration and the reliability of, such parts is nearly in direct proportion to the speed with which .they have been cooled from the heat treating temperature. The parts have ordinarily relatively'large surface in comparison to their mass, and lose heat rapidly when, exposed to the air. Every efiort is made toremove them from the heat treating oven and introduce them into the quenching bath in as short a time as possible 'but with the best equipment presently available the period between removal from the oven 'and 'the quenching is ofthe order of from live to twenty sec-,

ends, and period of the latter length is dangerously long, while even live seconds is greater heat treating apparatus wherein the articles to be treated require no manual handling in thequenching process: to provide'heat treating apparatus wherein the entire equipment'may be handled by a single operator and wherein the time required for quenching is independent of thesize or the charge of material to be heat treated or the number of articles comprising the charge; and, specifically, to provide heat treating apparatus wherein the entire process of quenching may be accomplished in approximately two seconds, and in which, moreover, the oven.

need be open for a time no longer than this,

with a correspondingly small loss of heat.

Myinvention possesses numerous other obiects and features of advantage, some or which,

together with the foregoing, will be set forth in the following description of specific apparatus embodying and utilizing my novel method. .It is therefore to be understood that my method is applicable to other apparatus, and that'I do not limit myself, in any way, to the apparatus of the present application, as I may adopt various other apparatus embodiments, utilizing the method, within the scope of the appended claims.

Referring to the drawing:

- Fig. 1 is a view partly in elevation and partly in vertical section through heat treating equipment embodying my invention.

Fig. 2 is a plan view showing the means for mounting and operating the 'doors of the oven or heating portionoi the apparatus as shown in Fig. 1.

Fig. 3 isa front view on a scale larger than that of Fig. 1 showing the mounting oi the oven ,Fig. 4 isa horizontal view partly in elevation and partly in cross-section showing how the work-rack may be wheeled into the cage.

Considered broadly, the apparatus of my invention comprises an oven which is supported above the loading level from which it is to be operated at a distance which is sufiicient to clear the greatest vertical dimension of the objects to be heat treated. The oven itself is provided with charging doors on the lower surface thereof, these doors preferably opening to substantially the full available width of the oven, although space may be provided on the sides of the opening to permit the placement of heating elements. Positioned lmmediately beneath the oven, and below the level of the charging floor is a quenching tank which is also, of course,- of suflicient size to receive a complete charge of material to be treatof-hoist for protecting it from air currents during its travel between oven and quenching tank, and these baflles are also preferably provided with heat reflecting inner surfaces; in order to minimizeheat'loss by radiation as well as the loss by convection.

' The figures of the drawing show a preferred embodiment of my invention wherein the oven I is supported above the loading level 2 by struts 3 which carry a base frame 4. The actual construction of the oven itself is not material to the present invention; any accepted mode of construction will suffice, that illustrated in the l present case comprising sheet metal panels 5 packed with insulating material such as mineral wool, spun glass, kieselguhr or other refractory packings 1.

The oven is in the form of an open bottomed box, the full area of the bottom, with the exception of the space occupied by small flanges 9,

being open.. The flanges 9 are provided to form side recesses I0, wherein are located the heating elements H, which, in the present instance, are shown as electrical resistors, but it will be understood that any mode of-heating the oven may be used. In the present instance a 'motor l2, mounted on the top of the oven, drives'a blower I3 for circulating air within the oven and keeping the temperatures at all parts thereof uniform.

The bottom of the oven is closed by doors l4 s of similar construction to the oven proper, which slide horizontally so as to open, leavingthe entire bottom of the oven clear.

cated at each end of the oven. Track wedges l9 These doors are-- mounted on wheels I5 running on rails I! 10-,

are secured to the rails to wedge the doors tightly against the oven walls when they are in their closed position. Each door is operated by a pair of pneumatic cylinders 20, mounted parallel to the rails and having a stroke of sufficient length to accomplish the full movementof the doors.

It is thus possible to open the doors or to close them practically instantaneously. The valve mechanism for operating these cylinders is not illustrated, since 'itis conventional in form and the particulartype used is purely a matter of the choice of the designer, since it is merely a question of admitting air to one or the other cables or chains 22 of a hoist. In the present instance the cables arefixed to a cage 23 which engages guide bars within the oven; The

cables run over idler pulleys 25 and a drive pulley:

21, and are attachedat their other ends to counterweights 29. The drive pulley 21 connects to a longitudinal shaft 30 to which a drum 3| is aflixed, and a cable 32, wrapped around the drum is attached to the end of a plunger 33 working within a pneumatic cylinder 34, which forms the operating mechanism of the hoist. By reason of the different diameters of the drum 3| and the drive pulley 21, the hoist is operative through a range of something more than double the stroke of the pneumatic cylinder, and when the doors M are open the cage 23 can be lowered past the loading level 2 and into the quenching tank 35, which is sunk below the loading level immediately beneath'the oven.

On each side of the pathof the hoist cage are baflies 31, preferablyof bright sheet metal, which serves the double purpose of protecting the cage from air currents in its travel between the oven and the quenching tank, and of reflecting back to the cage heat radiated therefrom. The result of this that even when the cage has left the oven the material which it carries loses its heat relatively slowly, and since the whole apparatus is extremely quick acting, and the sliding doors may be opened, the hoist dropped into the quenching tank, and the doors closed again in approximately two seconds, the equipment is capable of turning out heat treated parts in which no segregation of materials is detectable. One of the baffles 31 may be opened as by end doors 3'! to load the cage 23.

In operation the cage 23 is held at the loading level between the oven doors and the liquid surface, with the oven doors closed. The work to be treated,.which has previously been-loaded on wheeled work racks I0, is rolled lengthwise from loading level 2 onto the cage; the open bafile is closed, the doors l4 are opened, and the cylinder 34 is operated to' draw the cage and work rack into the oven, after which the doors are closed and the material remains within the oven a sufficient length of time to stabilize its temperature at a point where complete solid solution can take place. The doors are then opened, the cage dropped to the water level, where it pauses while the doors close and the material is then quenched as has been described. After quenching the cage is raised again to the loading level while the work rack is wheeled off for unloading. It is preferable, but not necessary, that, the cage be then retracted within the oven and permitted to come back up to temperature while the rack is unloaded and either reloaded, or a previously loaded rackis substituted, whereafter thecycle is repeated.

I claim:

1. Heat treating apparatus comprising. an oven having a charging opening in the bottom thereof only, a cage fitting said oven and vertically movable in and out of said oven-through said charging opening, a tank of quenching fluid positioned beneath said oven and in line with the path ofthrough said oven for moving said cage from a position wholly within said oven to a position wholly within the liquid in said tank, means for closing said opening when said cageis wholly in and out of said oven, and means for supporting said oven with the bottom thereof a fixed distance above the surface of the liquid in said tank substantially corresponding to the vertical dimension of said cage whereby said cage may be loaded when positioned between said oven and said liquid.

2. Heat treating apparatus comprising an oven having a charging opening in the bottom thereof only, a cage fitting said oven and vertically movable in and out of said oven through said charging opening, a tank of quenchingfluid positioned beneath said oven and in line with the path of through said oven for moving said cage from a position wholly within said oven to a position wholly within the liquid in said tank, means for closing said opening when said cage is wholly in and out of said oven, and means for supporting said oven with the bottom thereof a fixed distance above the surface of the liquid in said tank not substantially greater than the vertical dimension of said cage whereby said cage may be loaded when positioned between said cage and said liquid.

3. Apparatus in accordance with claim 1 wherein vertical walls are provided enclosing the space through which said cage is moved between said oven and said liquid.

4. Heat treating apparatus in accordance with claim 1 including vertical baiile plates mounted on all sides of the path of said hoist between the bottom of said oven and the surface of the liquid in said tank and having heat reflecting inner surfaces treatedv to minimize radiation loss of heat in the passage between said oven and said tank.

5. Heat treating apparatus in accordance with claim 1 where said door is a pair of members meeting centrally to close the entire bottom of said oven and sliding horizontally to clear the same, and pneumatic means for sliding said doors. 1,

6. Heat treating apparatus in accordance with claim 1 where said door is a pair of members meeting centrally to close the entire bottom of said oven and sliding horizontally to clear the same, and pneumatic means for sliding said members, the abutting edges of said members being notched to form apertures, and hoisting cables attached to said hoist and operable through said oven and saidapertures when said members are abutting and said hoist is outside of said oven, permitting their closure irrespective of the position of said hoist.

'7. In heat treating apparatus wherein articles to be treated are moved from the interior of an oven into a tank of quenching liquid positioned a fixed distance beneath said oven, anarticle.

carrying rack movable from a position within said oven to a position beneath the surface of said liquid, and vertical bafiie plates mounted on all sides of the path of said rack between the bottom of said oven and. the surface of said liquid, said bailies having heat reflecting inner surfaces to minimize radiation loss of heat from said articles in the passage of said rack between said oven and said tank.-

8. Apparatus in accordance with claim 1 wherein the means for closing the charging opening includes a door horizontally movable on rollers over a track, said track being inclined upwardly as said door approaches a position closing the bottom of said oven, the inclination of said track being sufficient to force said door tightly against the open bottom of said oven to close said bottom.

9. In a heat treating apparatus wherein articles to be treated are moved from the interior of an oven into a tank of quenching liquid positioned a fixed distance beneath said oven, a door horizontally movable along a track to open and close the bottom of said oven, said track being inclined,

upwardly to force said door against the open bottom of said oven as said door reaches closing position.

PAUL BUCKNER.

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