US2176073A - Heat-treating furnace tray - Google Patents

Description

Patented Oct. 17, 1939 UNITED STATES PATENT OFFICE 3 Claims.

My invention relates to work supports, commonly called trays, for use in heat-treating furnaces.

Conventionally, articles to be carburized are 5 disposed within containers or boxes also having therein a carburizing compound, the container or carburizing box being sealed and placed within a furnace or muie and subjected to high heat, and the carburizing effected under the influence of the heat. While the supports or trays of the present invention could be used for supporting such carburizing boxes, during travel through the furnace theyare preferably made use of in furnaces and with heat treatments wherein the articles to be treated are placed or loaded directly upon the supports or trays which are traveled, as by being pushed in tandem, through the furnace, mule 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 2,6 on both'the articles or work being treated and the support of 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 are usually made, the gas will enter thereinto and deposit its carbon. At the time of this deposit, the tray is being subjected to high heat and is therefore largely expanded. Upon removal from V the furnace, however, the trays come into contact with a cooler atmosphere and a shrinkage occurs. This shrinkage contracts the metal around the soot or deposited carbon, and what `:"W`as originally abarely discernible crack or fis- 40, sure and relatively insignificant becomes larger and more clearly defined. Upon repetition of this process and consequent subjection of the tray to the action of heat, carbon deposit, and cold, the cracks or lissures may reachv such proportions as to result in the virtual destruction of the trays as a usable article.

The conventional trays used in this type of furnace operation have been of skeleton or openwork formation, rather than continuous sheets or cast imperforate members. There are several reasons for this, namely, that to obtain optimum results in the heat-treatment process it is necessary that as much of the surface area of the article being treated as is possible be exposed 55 directly to the furnace heat and this can best be (o1. ass-47) effected with use of an openwork support; also, the skeleton formation necessitates the use of less metal and hence a lighter and cheaper product can be obtained.

These openwork trays are usually one-piece 5 castings and necessarily contain a large number of intersections, that is, points where the bars cross and there is a greater thickness of metal at and about the intersection than through the bars themselves. Experience has shown that the imperfections occur principally at these thicker points because of strains set up during the heating and cooling operations, which imperfections subsequently .develop into destructive cracks and fissures. The present invention is directed to the solution of the problem of avoiding or reducing diiculties such as are referred to above.

In operation, the trays or supports have loaded thereon the various articles to be heat-treated, and the loaded trays are usually pushed through the furnace in tandem, that is, a number of trays, similarly loaded, are placed within the furnace and pressure applied against the rearmost thereof to push the trays through the furnace, each 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 in the vertical plane and to compression stresses of the travelling pressure in the horizontal plane. During normal furnace operation, these stresses also cause a great many tray failures since they tend to develop the ultimately destructive cracks or shrinks, and cause buckling and bending. It is also an object of my invention, therefore, to provide a tray which will have a greater load-bearing capacity in conjunction with increased ability.. to resist compression stresses.

It is a lfurther object of my invention to provide a heat-treating furnace tray with means incorporated thereinto to directly take the compressive, travelling stresses.

It is a further object of my invention to provide a heat-treating furnace tray having a substantially flat top with openings to allow free passage of heat therethrough.

Other and related objects will in part be obvious and in part be pointed out specifically in connection with the following description of an illustrative embodiment thereof.

Figure 1 is a plan View of one form of device constructed according to and embodying my invention.

Figure 2 is a side view thereof, partly in section and partly in elevation, along the broken line 2-2 of Figure 1.

Figure 3 is an end view thereof, also partly in section and partly in elevation, along the broken line 3-3 of Fig. 1; and

Figure 4 is a section along the broken line 4-4 of Fig. 1.

Reference numeral II) indicates the tray generally, which is usually a one-piececasting of preferably nickel-chromium-iron alloy steel.

Tray l5 is preferably rectangular in shape, the front, back and side edges thereof being substantially straight. Tray I0 comprises at top portion I2 and substantially flat bottom portion I4. Portions I2 and I4 are the same length from front to back of the tray, but bottom I4 is narrower than top l2 from side to side thereof; see Fig. 2. Top I2 and bottom I4 are spaced apart and centrally connected by interior wall It, which defines a central well opening i1, also substantially rectangular in shape, through tray I0. This interior wall I6 at right angles to the plane of the tray top and bottom gives increased load-bearing strength to the tray. Top I2 and bottom I4 are also connected in the spaced-apart relationship by the inclined walls I8, I8 which extend from the edges of top I2 to the edges of bottom I4, at both sides of the tray. The space between top and bottom portions I2, I4 is left open at the front and back of the tray, as shown in Fig. 2 at the right. In this respect the tray generally resembles a attened tube having a transverse opening therethrough.

A plurality of openings 20 are provided in the upper tray portion I2, which are preferably in registry with a similar number of openings 22 in bottom portion I4. Openings 20, 22 are shown in registry, but they need not be, as for example, the openings might be in any desired staggered arrangement. Openings 20, 22 are provided to present as much of the surface of the work being treated as possible, and also to allow the heat to pass through the tray. These openings, together with central opening II and the spaced-apart relationship between the tray top and bottom, will allow the heat generated within the furnace to pass through the tray and reach and act upon work supported by the tray during passage through the furnace.

Upstanding walls 24, 26 are provided at the front and back of the tray, as are walls 28, 30 at the tray sides, to form retaining members to keep the articles placed on the tray from falling off therefrom during tray travel through the furnace. Walls 28, 35 are preferably formed by providing an upwardly rounded union between the inclined wall portions I8, I8 and the top member I2. Upstanding lugs SI are provided at separated points on the upper surface of member I2 to assist in retaining work in predetermined position on the tray.

The bottom I4, while generally domed or arched downward for strength, has widely separated at underside portions 32 along the sides thereof to provide wearing surfaces which bear on rails 34 on which the tray is travelled through the furnace. The junction of the inclined walls I8, I8 with the floor member I4 are so formed as to provide downwardly extending retaining flanges 36 at right angles to portions 32, which flanges 36 serve to keep tray I0 in line on tracks 34. If desired, rollers or tracks With rollers (not shown) may be used to cooperate with my form of tray for travel through the furnace.

Over the bearing portions 32, a pair of H-beams 5U, 50 equal in length to the length of tray IIJ from front to back, are inserted in the space between top I2 and bottom I4, substantially lling said space, and secured in this position within the tray by rivets 52. A plurality of lugs 54 are provided in the underside of top I2 and the upper surface of bottom I4 forming guide members to keep beams 5i), 50 in position. H- beams 50, 50 are incorporated into the tray at those points of the tray which overlie rails 34, because it is at these points that the tray travelling pressures are applied and the compression stresses are at their maximum. Beams 50, 50 not only take up and absorb the compression stresses, but also, since they substantially ll the space between the tray top and bottom, take up some of the load-bearing stresses, and in this regard the H-beams serve a double function. In the form shown, H-beams are utilized, but any other form of beam may be used, if desired, which will serve the same purposes.

My invention combines the strength of a solid tray with the lightness of a skeleton form tray, and by virtue of its particular construction is enabled to better resist the tray-travelling compression stresses and the load-bearing stresses and thus have a longer operative life.

Having now described my invention, what I claim and desire to secure by Letters Patent is:

1. A tray for use in heat treating furnaces comprising a top portion and a bottom portion, said portions being equal in length from front to back of the tray, and said bottom portion being shorter than said top portion from side to side of the tray, and means to secure said portions in spaced-apart relationship comprising a pair of inclined walls extending from the sides of the top portion to the sides of the bottom portion.

2. A tray for use in heat treating furnaces through which trays are travelled on rails in tandem comprising a top portion, a bottom portion on which the tray is travelled through the furnace spaced from the top portion, a pair of thrust transmitting and load supporting beams disposed therebetween, means formed integral with the top and bottom portions to keep the beams in place and means to secure the top portion and the bottom portion in said spaced relationship.

3. A tray for use in heat treating furnaces through which trays are travelled on rails in tandem comprising a top portion, a bottom portion on which the tray is travelled through the furnace, which bottom portion is spaced from the top portion, and a plurality of separate thrust transmitting and load supporting members disposed and secured within the tray extending from front to back thereof between the spaced-apart top and bottom portions.

HENRY H. HARRIS.

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