US2176072A - Heat-treating furnace tray - Google Patents

Description

HEAT-TREATING FURNACE TRAY Filed Oct. 12, 1957 ic i.

INVENTOR Henry H. Harris BY ,O M SU ATTORNEY$ Patented Oct. 17, 1939 UNITED STATES PATENT orrl'cs 6 Claims.

Th pr s n inv n ion r l t to W k p r hence a lighter and cheaper product can beobcommonly called trays, for use in heat-treating furnaces.

conventionally, articles to be carburized, or otherwise heat treated, are disposed within boxes or containers having therein a carburizing compound. The container or carburizing box is then sealed and placed within a furnace or muffle and subjected to high heat and the carburizing efiected under the influence of this heat. While the supports or trays of my invention could be used for carrying such boxes or containers, I preferably use same in furnaces and with heat treatments wherein articles to be treated are placed or loaded directly upon the supports or trays which are then moved, as by being pushed in tandem, through the furnace, mufiie or the like so as to be directly exposed to the heat and furnace gases, preferably carbonaceous gas.

This carbonaceous gas is a saturated hydrocarbon, and when it comes into contact with the articles being treated it is apparently cracked and deposits a certain amount of soot on both the articles or work being treated and the support or tray upon which the work is carried. Normally, this soot is harmless, but if there are any imperfections such as cracks or shrinks, either deep: seated or of superficial nature, in the alloy material of which the trays or supports are made, gas will enter thereinto and depositits carbon. At the time of this deposit, the tray is being subjected to high heat and is largely expanded. Upon removal from the furnace, however, the tray comes into contact with a cooler atmosphere and a shrinkage takes place. This shrinkage contracts the metal around the soot or deposited carbon, and what might originally have been .a barely discernible crack or fissure becomes larger and more clearly defined. Repetition of this process and consequent subjection of the tray to the action of heat, carbon deposit, and cold, causes the cracks or fissures to reach such proportions as to result in the virtual destruction of the tray as a usable article.v j

The conventional trays used in this type of furnace operation have necessarily been of skeleton or open-work formation, rather than continuous sheets or cast imp-erforate members. There are several reasons for this, namely, in order to obtain optimum results in the heat treat ment process it is necessary that every part or side of the article being treated be exposed directly to furnace heat and this is possible only with use of an open-work support; also, the skeleton formation necessitates use of less metal and tained. These open-work trays or grids are usually solid one-piece castings and necessarily represent a large number of intersections, that is, points where the bars forming the tray cross or intersect and there is a greater thickness of metal than through the bars themselves. Experience has shown that the imperfections'occurprincipally at these thicker points, subsequently to develop into, destructive cracks or fissures.

I have found that by making the tray of uniform thickness and avoiding angular intersections, sharp corners and thick heavy places, a substantial decrease in the development of crack or fissure formation results, making for a longer useful operative life and correspondingly increased economical furnace operation. It is, therefore, an object of my invention to provide a tray for use in heat-treating furnaceswhich is of uniform thicknessthroughout, with no. angular intersections or sharp corners, and hence a minimum of danger spots.

In operation the trays or supports have loaded thereon the various articles to be heat-treated, and the loaded the furnace in tandem, that is, a number of trays, similarly loaded, are placed within thefurnace' and pressure applied against the rearmost theretrays are usually pushed through of to push the trays through the furnace, each 7 tray communicating the pressure to the one in front. The heated trays ,are thus subjected to stresses in two transverse planes; namely, to load-bearing stresses and to compression stresses of the travelling pressure. During normal fur: nace operation, these stresses also cause a great many tray failures since they tend to develop cracks or shrinks, and cause spreading, buckling and bending.

A further object of my invention is the provision of atray which will be able to expand and contract during' furnace operation without destructive after-effects. I accomplish these objects by the particular construction whichwill' be explained below in connection'with the following description of an illustrative embodiment. Other objects of my invention will in partbe ob- Vious, and in part pointed out specifically.

In the drawing annexed hereto and made a, part hereof,

Figure 1 is a, plan view of one form of device constructed according to and embodying my invention;

Fig. 2 is a front elevational view thereof;

Fig. 3 is a section on the broken line 3 3 of Fig.

Fig. 4 is a section similar to Fig. 3 of a modified form of tray also constructed according to and embodying my invention;

Fig. 5 is a partial front elevational view of the form of tray illustrated in Fig. 4; and

Fig. 6 is a partial plan view of another form of tray, also constructed according to and embodying my invention.

Reference numeral l0 indicates the tray generally, which is formed of a heat and corrosion resisting alloy, preferably of nickel, chromium and iron composition. Tray It] may be formed of individually cast bars or pieces welded together into the desired form, or of a single rolled or forged bar of substantial thickness, bent into the desired shape, but I preferably cast the entire tray as a unitary, one-piece proposition. The tray In shown is formed of a continuous bar of substantial thickness extending sinuously back and forth upon itself at regular intervals to provide a plurality of straight bar portions l4 evenly spaced apart in parallel relationship, connected at alternate ends by curved portions 16. The preferably cast bar of which the tray as a unit is formed is substantially rectangular in crosssection and of uniform thickness throughout its entire length and will contract and expand at a substantially uniform rate throughout. I have shown the tray of Figs. 1 to 3, used in connection with a furnace equipped with ordinary flattopped skid rails or tracks, as 20, 20, with the flat undersides of bars I4 making sliding contact with the said rails, 20, 20, but it will be readily understood that my tray l0 may be adapted on suitable modification for travel through furnaces equipped with roller rails as will be explained below in connection with the modification illustrated in Figs. 4. and 5.

A pair of downwardly depending lugs l8, [8 are formed on the bottom of each of bar portions l4, one near each side thereof; the lugs on each side of the tray being formed equidistantly in from the edges of bars l4 so as to form two rows of lugs l8 in longitudinal alignment. These two rows extend below the tops of tracks 20, 20 and on the outer sides thereof, as shown in Fig. 2, and serve to guide tray II] and keep it in line on the tracks during travel of the tray through the furnace.

As pointed out hereinabove, trays Ill are usu ally travelled through the furnace in tandem; that is, a line of end-to-end abutting trays is formed extending longitudinally through the furnace, and pressure applied to the rearmost of the trays in the line to advance those in front. This pressure is transmitted transversely of the trays from the rearmost tray to the one imme diately next to it, and so on until the tray at the far end of the line is pushed out of the furnace at the exit side. It is obvious that the trays must be sufficiently strong to withstand these compressive stresses, and among the objects of the present invention is the provision of a light, strong and flexible tray so constructed as to be able to transmit while itself resisting the ordinarily destructive effects of the pushing tray travelling pressures.

On the same or corresponding side of each of bar portions M but one, I provide a plurality of studs 22, which are of uniform size and thickness, and extend horizontally outward from each of bar portions l4 into substantially abutting relationship with the next bar portion M. The tray Ill as shown has six bar portions I4, and studs 22 are formed on but five thereof. In the form shown, three studs are formed on each of the bar portions but one, the last bar [4 having no studs projecting outwardly therefrom to break up the tray outlines. The studs 22 are formed in longitudinal alignment, one behind the other, forming three rows of aligned studs, one row extending centrally of the tray and the lines of studs on each side thereof being formed at that part of the tray which overlies tracks 20, 2|]. The number of studs on each bar may be varied, but I have found that the tray operates more efficiently when at least three lines of studs are formed. The studs project from one bar into substantially abutting relationship with the bar in front. Studs 22 are preferably cast as an integral part of bars I4 and when formed as shown serve a three-fold purpose: One, to keep bars M from buckling or bending out of parallel alignment when the transverse, tray-travelling pressures are applied; another, to better transmit the travelling pressure to the tray in front; and third, to define the limit of contraction when the heated tray comes into contact with a cooler atmosphere. During travel through hot furnaces, the tray inevitably expands, and there is danger of contraction out of usable shape when the tray is removed from the furnace. This danger is removed by the provision of studs 22.

Tray I0 is shown in Figs. 1 to 3 in use on fiattopped skid rails 20, 20. In Figs. 4 and 5 I have shown tray l0 fitted for use in a furnace equipped with roller rails, for example. In this form I provide a pair of fiat shoes 30 each of which has formed therein, at the ends thereof, a pair of up standing lugs 32, 32. Shoes 30 are the same length as tray l0, and when the tray is mounted on the shoes, bars M of the tray are at right angles to said shoes 30, 3E]. Holes 34 are provided through the front and rearmost bars Ma and Nb, and countersunk bolts 35 screwed thereto to fasten the shoes 30, 30 to the tray and provide it with a flat bearing surface which can be used for travel over roller rails, if desired. The provision of shoes 3|] also serves another purpose, for it provides a means for limiting expansion of tray I0. Anchoring the front and rearmost bars Ma and Mb to shoes 30, and the intermediately disposed studs 22, will reduce to a minimum the extent to which the tray will expand. A loose connection may be made at 34, if desired to better take care of expansion and contraction.

Shoes 30 are provided with downward flanges 40, which operate, as do lugs l8, to keep tray ID in line of rails 20, 20, during furnace travel.

In Fig. 6, I have illustrated a modified form of stud arrangement. In this form, I provide a plurality of split studs 50, 52. Instead of forming a single stud which projects from one bar to the one in front, I provide shorter studs on each side of each of bars I4, the studs 50, 52 meeting preferably in the middle of the inter-bar space, and abutting against one another. Bars 54, 56 are formed on each of studs 52, 50 respectively, and each pair of studs is loosely tied together by means of wires 58. With this stud arrangement, the bars will not only be prevented from expanding unduly but will also be prevented from contracting beyond the parallel relationship of the bars as originally formed.

Various other modifications may be resorted to without departing from the spirit of my inven tion, which is not to be limited by the various modifications shown, but only to the scope of the claims appended hereto.

I claim:

1. An open work tray for use in heat treating furnaces consisting of a bar of uniform thickness extending back and forth upon itself to form a plurality of straight members spaced apart in parallel relationship, the parallel relationship being subject to change during use, and means to keep the parallel relationship constant during use.

2. An openwork tray for use in heat treating furnaces consisting of a bar of uniform thickness extending back and forth upon itself to form a plurality of straight members spaced apart in parallel relationship, the parallel relationship being subject to change during use, and means on and a part of the straight members to keep the parallel relationship constant during use.

3. An openwork tray for use in heat treating furnaces consisting of a bar of uniform thickness extending back and forth upon itself to form a plurality of straight members spaced apart in parallel relationship, the parallel relationship being subject to change during use, and means to keep the parallel relationship constant during use comprising a plurality of shoes on which the tray is supported and to which the tray is secured.

4. An openwork tray for use in heat treating furnaces consisting of a bar of uniform thickness extending back and forth upon itself to form a plurality of straight members spaced apart in parallel relationship, the parallel relationship being subject to change during use, and means on and a part of the straight members to keep the parallel relationship constant during use, comprising a plurality of studs extending from one side of each of the straight members up to the next adjacent member.

5. A tray for use in heat treating furnaces comprising a bar of uniform thickness extending back and forth upon itself to form a plurality of straight members spaced apart in parallel relationship, the parallel relationship being subject to change during use, and means on and a part of the straight members to keep the parallel relationship constant during use comprising a plurality of opposed studs extending outwardly from the sides of each of the straight members and abutting midway between the members.

6. A tray for use in heat treating furnaces comprising a bar of uniform thickness extending back and forth upon itself to form a plurality of straight members spaced apart in parallel relationship, the parallel relationship being subject to change during use, and means on and a part of the straight members to keep the parallel relationship constant during use comprising a plurality of opposed studs extending outwardly from the sides of each of the straight members and abutting midway therebetween, said studs having ears formed integral therewith and extending outwardly therefrom, and means engaging the ears of the opposed studs to secure said studs together.

HENRY H. HARRIS.

.Patent No. 2,176, 7

CER TIFICATE OF' CORRECTION.

October 17, 1959.

HENRY H. HARRIS.

It is hereby certified that error appears in the printed specification ofthe above numbered patent requiring correction as follows: Page 5, sec- 0nd column, lines 6 and Y and 17 and 18, claims 5 and 6 respectively, for the words "A tray for use in heat treating furnaces comprising" read An openwork tray for use inheat treating furnaces consisting of; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this lhth day of November, A. D. 1959.

Henry Van Arsdale,

(Seal) Acting Commissioner of Patents.

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