US2148462A - Tubular heat treating furnace tray - Google Patents

Description

Feb 28, 1939; H, H. HARRIS TUBULAR HEAT TREATING FURNACE TRAY Filed se i. 16, 19s? lllllllllll lllllllllllll INVENTOR' Hel ar'g H. Harr'zs ATTORNEYS Patented Feb. 28, 1939 2,143,452.

UNITED STATES PATENT OFFICE 2,148,482 TUBULAR HEAT TREATING FURNACE TRAY I Henry H. Harris, Champaign', Ill.

Application September 16, 1937, Serial N0. 164,118

Claims. (01. 263-49) My invention relates to work supports, com- 'use of less metal and hence a lighter and cheaper monly called trays, for use in heat treating furproduct can be obtained. These openwork trays naces. are usually solid one-piece castings and neces- Conventionally, articles to be carburized are sarily represent a large number of intersections,

5 disposed within containers or boxes also having that is, points where the bars cross and there is 5 therein acarburizing compound, the container or a greater thickness of metal than through the I carburizing box being sealed and placed within ,bars themselves. Experience has shown that the a furnace or muiile and subjected to high heat, imperfections occur principally at these thicker and the carburizing effected under the influence points, and such imperfections subsequentlydeof the heat.

While the supports or trays'of the present inthermore in such conventional trays a very convention could be used for supporting .such carsiderable proportion of the exposed surfaces conburizing boxes, they are preferably made use of sists of relatively thin edges which tend to heat in furnaces and with heat treatments wherein up andto cool 011 more quickly than other parts articles to be heat treated are placed -or loaded of the trays and any defects even though original- 15 directly upon the supports or trays which are 1y slight in such edge portions are likely to detraveled, as by being pushed in tandem, through velop into larger cracks. The present invention the furnace, mufile or the like so as to be directly is directed to the solution of the problem of avoidexposed to the heat and furnace gases, prefering or reducing difficulties such as are referred to ably carbonaceous gas. This carbonaceous gas above. 20 is a saturated hydrocarbon, and when it comes I have found that by making the skeleton or into contact with the articles being treated, it is grid trays of hollow tubular construction, and apparently cracked and deposits acertain amount providing them with a minimum of metal interof soot on both the articles or work being treatsections and avoiding thin exposed edges, a subed and the support or tray upon which the work stantial decrease in the development of crack or 25 is carried. fissure formation results, making for longer use- Normally this soot is harmless, but if there are fu1 operative life and correspondingly increased ny perfections, such as cracks or shrinks, economical furnace operation. It is, therefore, either deep-seated or of superficial nature, in the the main object of my invention to provide a holalloymaterial, as nickel-chrome-iron alloy, of low tubular skeleton or openwork type of tray for 30 which the trays are usually made, the gas will use in heat-treating furnaces with aminimum of enter thereinto and deposit its carbon. At the. metal intersections and free or substantially free time of this deposit, the tray is being subjected from exposed edges and hence a minimum of to high heat and is largely expanded. Upon redanger spots.

moval from the furnace the trays come into con- These thicker danger points are not uniform 35 tact with a cooler atmosphere and a shrinkage in cross-section with the rest of the conventional takes place. This shrinkage contracts the metal tray, and in solid, i. e., non-hollow castings canaround the soot or deposited carbon, and what not be made uniform with the rest of the tray was nal y a a ly d s rn crack or fisto obtain a. uniform surface-to-mass ratio over 40 sure beco es l e a o e clearly defined. the entire structure. It is an object of my in- 40 pon r p tit n f this p ss and ns quent vention to provide a tray for-use in heat-treatsubjection of the tray to the action of heat, caring furnaces, which is of uniform thickness 11 p and cold, the Cracks u e y throughout with a correspondingly uniform surreach such proportions as to result in the virtual fao -to-mass ratio over the entire tray,

5 destruction oi'the trays as a usable article. In operation the trays or supports have loaded The conventional trays used in this type of furthereon the various articles to be heat-treated, nace operation have been of skeleton or openand the loaded trays areusually pushed through work formation, rather than continuous sheets the furnace in tandem, that is, a number of trays, or cast imperforate members. There are several similarly loaded, are placed within the furnace reasons for this, namely, that to obtain optimum and pressure applied against the rearmost there- 50 results in the heat treatment process it is necesof to push the trays through the furnace, each sary that every part or side of the article being tray communicating the pressure to the one in treated be exposed directly to furnace heat and front. The heated trays are thus subjected to this is possible only with use of an openwork supstresses in two transverse planes, namely, to load on port; also, the skeleton formation necessitates bearing stress and to compression stresses of the velop into destructive cracks "and fissures. Furl0 traveling pressure. During normal furnace operation, these stresses cause a great many tray failures since they tend to develop the cracks or shrinks, and cause buckling and bending. It is also an object of my invention, therefore, to provide a skeleton or open-work type of tray which will have a greater load bearing capacity in conjunction with ability to resist compression stresses.

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

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

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

Fig; 2 is a side view thereof, partly in section along the line 2-4 of Fig. 1;

Fig. 3 is an end view, partly in section, along the line 3-4 of Fig. 1; and

Fig. 4 is a transverse sectional view on the broken line H of Fig. l.

Reference numeral ll indicates the tray generally, which is either a one-piece alloy steel casting or is formed of two precast halves welded together. The tray, as a unit, comprises a number of generally.cylindrical hollow tubes l2, spaced apart in parallel relationship as at It, and secured in this relationship by a number of similarly generally cylindrical though somewhat flattened hollow tubes ll, extending cross-wise of tubes it, which tubes I are interconnected and communicate with tubes l2 as indicated at I. These tubes H which extend to the ends of the tray are provided with upstanding portions 2| cast as an integral part thereof to serve as an end retaining wall for work placed thereon.

Outer sides 22 of tubes 12a. and ill), at the front and back of tray it, are preferably formed fiat at those points thereon in line with cross tubes I, as at N, 24. Portions M, 24 are made flat to provide a bearing surface against which the pushing, tray-travelling pressure is exerted, when a plurality of trays I. are disposed in the furnace side by side, one pushing directly against the other until pushed out at the exit side of the furnace. The tubes ll extending endwise in the line of application of pushing pressure form transverse regions of great stiffness and strength to effectively take the pushing pressure without deformation thereby of the tray.

On the under side of tray it are formed a number of downwardly depending lugs 26 in line with the outer edge of cross-tubes H, which serve as guides to keep the trays aligned on the conventional skid rails 21 within the furnace, as indicated in Fig. 2. Holes 28 indicate openings cored in the top and bottom surfaces of the trays through which the sand of the cores may be removed from within the completed units. The holes also provide additional inlets for heat, but are not needed when the tray is cast in top and bottom halves and welded together along the medial line.

It will be seen that my tray, as a unit, is of substantially uniform cross-sectional thickness, made up of a number of hollow tubular mem bers l2, ll, arranged in criss-cross pattern. The completely hollow construction will not only give a greater load-bearing capacity than a similarly feature of my invention is that the tubes and cross-tubes are entirely hollow and slightly rounded in shape. The substantially uniform thickness at all points of the tray eliminates danger spots and sources of cracks and shrinks since the alloy material of which the tray is made will expand and contract under heat and cold at a substantially uniform rate over its entire area. There are no spots materially thicker and heavier than others, at which uneven expansion and contraction may take place, and hence the crack or fissure development-process outlined above as an inevitable consequence of the use of solid trays is avoided.

Another advantage secured by my tubular tray is that line or point contact is obtained between the load and the tray. The curved surfaces upon which the load rests aflords less surface contact and makes for freer heat circulation. Additionally, a cold load deposited upon a hot tray, because of this line or point contact has a minimum chilling effect, and there are fewer strains set up in initial heating.

The tube components of the tray have no exposed edges, except at their ends, and only their outer surface positions are directly exposed to heat, and the tube components will thus heat more uniformly, the circulation of heated air inside the tube facilitating the uniform heating throughout the tube, by the fiow or convection of such hot air.

By the use of component portions which are tubular and therefore much stronger and stiffer than if made up of bar or bar-like portions, as is usual, the criss-cross spacings in my improved tray can be spaced further apart and the number of crossings in a tray of given area are correspondingly reduced with no loss and usually with a gain in strength and stiffness.

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 plurality of hollow tubular members, and means to secure same in parallel spaced-apart relationship, said means comprising a second plurality of similarly hollow tubular members arranged transversely of and between the members of the first plurality.

2. A tray for use in heat treating furnaces comprising a plurality of hollow tubular members, and means to secure same in parallel spaced-apart relationship, said means comprising a second plurality of similarly hollow tubular members arranged transversely of, in the same plane with, and between the members of th first plurality, the interiors of both pluralities being in communication.

3. A tray for use in heat treating furnaces comprising a plurality of hollow tubular members extending from side to side of the tray, and means to secure same in parallel spaced apart relationship comprising a plurality of hollow tubular members extending from front to back of the tray the sides and edges of the first plurality of hollow tubular members defining the outer markings of the tray.

4. A tray for use in heat treating furnaces comprising a plurality of hollow tubular members, the tops and bottoms of which are flattened, and means to secure same in parallel spaced apart relationship comprising a second plurality of similarly hollow tubular members arranged transversely of the first plurality, the second plurality also having flattened tops and bottoms.

5. A tray adapted to be pushed through heat treating'tumaces comprising a. plurality of 1101- pushing stresses the outer sides of the outermost low tubular members extending from side to of the first plurality of hollow tubular members side of the tray, and means to secure same in being provided with a plurality of flattened porparaliei spaced apart relationship comprising a.

plurality of hollow tubular members extending out deformation.

from front to back of the tray in line with the HENRY H. HARRIS.

tions adapted to take the pushing pressure with--

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