US2779579A - Conveyor for high temperature furnaces - Google Patents

Description

Jan. 29, 1957 R. STElNlTZ 2,779,579

CONVEYOR FOR HIGH TEMPERATURE FURNACES Filed July 6, 1954 2 Sheets-Sheet 1 Jan. 29, 1957 Filed July 26, 1954 R. STEINITZ CONVEYOR FOR HIGH TEMPERATURE FURNACES 2 Sheets-Sheet 2 CONVEYOR FOR HIGH TEMPERATURE. FURNACES Application July 26, 1954, Serial No. 445,788

2 Claims. (Cl. 263-8) The invention relates to high temperature furnaces and processes for making the same.

In high temperature furnaces, for use in treating metals at high temperatures, or for firing porcelain and similar applications, it is of great importance to provide an inner furnace lining of high heat conductivity so as to assure that all parts of the interior heated furnace space are maintained at a substantially uniform temperature. In the past, it has been found that to achieve such uniform high furnace temperature, it is best to use as the interior furnace lining, or at least for the furnace hearth, bricks of silicon carbide because of its high heat conductivity. However, bricks of silicon carbide have serious limitations and disadvantages. They burn in oxidizing atmospheres at 1350 C. and sublime at 1600 C. even in a neutral atmosphere or in vacuum. In addition, they produce in the furnace a carburizing atmosphere which is in many applications, harmful to the object that is being heated.

Among the objects of the invention is a high temperature furnace having an interior furnace lining, or at least a part of the interior furnace lining formed of furnace brick of high heat conductivity capable of assuring a uniform distribution of heat, which brick at the same time does not burn in oxidizing atmospheres or form a reducing or carburizing atmosphere at the high internal furnace temperature.

Among other objects of the invention is a high temperature furnace having as interior furnace lining a high temperature brick of high heat conductivity, which brick is stable in oxidizing atmospheres up to 1700 C. and which brick does not melt below 2000 C. and does not decompose or sublime below its melting temperature.

Among other objects of the invention is to provide an improved conveyor belt for high temperature furnaces.

This invention is based on the discovery that high temperature furnaces can be heated to much higher temperatures than possible in the past and maintained at uniform temperatures by making the interior furnace lining at least in part of bricks consisting of molybdenum disilicide.

The foregoing and other objects of the invention will be best understood from the following description of exemplifications thereof, reference being had to the accompanying drawing in which:

Figure 1 is a partially diagrammatic cross-sectional view of constructional features of a high temperature furnace exemplifying the invention.

Fig. 2 is a cross-sectional view of a mufile furnace made according to the invention.

Fig. 3 is a longitudinal cross-sectional view of the furnace of Fig. 2.

Fig. 4 is a longitudinal cross-sectional view of a continuous furnace provided with a conveyor belt made according to the invention.

Fig. 5 is an enlarged cross-sectional view of one of the units of the conveyor belt of Fig. 4.

re States Patent Fig. 6 is a top plan view of the conveyor belt.

As explained above, in constructing high temperature furnaces, it has been found in the past necessary to use bricks of silicon carbide either for the entire inner lining layer of the furnace or at least for the hearth of the furnace in order to assure that all parts of the heated interior furnace space are maintained at and are brought quickly to a substantially uniform temperature. It was also long known that the use of silicon carbide bricks as interior furnace lining of high temperature furnaces has certain disadvantages compared to furnaces having an interior lining of common firebricks. Among the disadvantages of silicon carbide bricks is the fact that silicon carbide burns in an oxidizing atmosphere at about 1350 C. and thus limits the maximum temperature to which such furnace may be heated. In addition, silicon carbide sublimes even in a neutral atmosphere or in vacuum and accordingly, a furnace having such brick lining could not be heated to 1600 C. even if vacuum or a neutral atmosphere is maintained in the interior furnace space. Furthermore, the presence of silicon carbide bricks in the interior of the heated furnace results in. the production of carburizing or reducing furnace atmospheres which in many cases impair the characteristics of the objects heated or treated in the furnace. By way of example, in heating ceramic ware in a high temperature furnace having an interior of silicon carbide bricks, specks of graphite are deposited on the ceramic Ware thereby impairing its quality. For this reason, high temperature furnaces have an interior lining with only the hearth plate formed of silicon carbide bricks with the major area of the inner furnace lining consisting of the conventional firebricks.

According to the invention, the difiiculties encountered with the use of silicon carbide bricks as the inner lining for high temperature furnaces are eliminated by making such high temperature furnaces with an inner lining of bricks consisting predominantly or in their entirety essentially of molybdenum disilicide MoSiz or chromium disilicide CrSiz.

Such bricks of the invention are very effective because of their high heat conductivity, resistance to oxidation, resistance to temperatures of up to 2000 C., and high heat shock resistance. Furnaces made of such bricks may be heated for long periods of time to temperatures as high as 1800 C.

In particular, the heat conductivity of a molybdenum disilicide MoSiz brick is about .075 cal./cm./C. /sec. If desired, this high heat conductivity of such bricks can be reduced by making them porous or hollow without decreasing the heat or oxidation resistance of the brick.

There Will now be described by Way of exemplification in connection with the figures of the drawing, several forms of structural features of high temperature furnaces exemplifying the principles of the invention. The furnace 10 of Fig. 1 has a floor comprising an inner layer of bricks 12 and an outer layer of bricks 13, two opposite side walls comprising similarly an inner layer of bricks 16 and an outer layer of bricks 17 and a top Wall comprised similarly of an inner layer of bricks 21 and an outer lay of bricks 22. The additional outer bricks 31, 32, 33 of the furnace which surround its two inner brick layers 12, 13, 16, 17, 21, 22 are formed of conventional firebricks consisting essentially of clay or the like. The bricks 12, 16 and 21 which form the inner layer of the furnace are all of molybdenum disilicide MoSiz or chromium disilicide CrSiz or a 50/50 combination of MoSiz and CrSiz.

Good results are obtained by making the inner lining of the high temperature furnace out of a layer of dense molybdenum disilicide bricks and making the next outer layer of the furnace of molybdenum disilicide bricks Patented Jan. 29, 1957.

3 having high porosity so as to reduce their heat conductivity and reduce the loss of heat from the furnace while contributing to the high heat conductivity of the inner layer formation of the furnace. Instead of making-the outer layer of the furnace lining of porous MoSiz bricks, it may be made out of hollow MoSiz bricks.

Instead of using as inner furnace lining, bricks consisting entirely of MoSiz, it is of advantage to make these bricks of a combination of MoSiz and CrSiz in 50/50% proportions (by weight). By making the bricks of MoSiz and CrSiz in 50/50% proportions, there are obtained bricks of the superior oxidation resistance because in such proportions, the two disilicides go into solid solution. I

In assembling a top wall of the furnace with a double layer 21, 22. of bricks, it might be desirable to assemble each pair of the two similarly shaped bricks which are to form the inner and outer layers of the top wall before cementing the bricks into the wall. If desired, only the floor portion of the furnace may be lined with the disilicide bricks. Aluminum oxide bricks, for example, are low cost, highly effective refractory bricks with low conductivity and are well adapted to be employed with the bricks of the invention.

The heating structures of the furnace are not shown since they are not a part of the present invention. Since the furnace is resistance to high temperatures and oxidizing conditions it does not make any difference what means is employed to heat the furnace. For example, it may be heated electrically by resistance heater or by fuel gas.

Figs. 2 and 3 show a muflie type furnace which is adapted to be heated by gas. in this furnace 40, the muffie parts 41 are made of the MOSiz, CrSiz or mixtures thereof. The mufiie is supported on a plurality of firebricks 42 in a spaced position from walls 43 so as to form a chamber 44 between muffie 41 and walls 43. Walls 43 are supported on the outside by brick walls 45. Metal braces 46 surround the outside wall 45. Openings 47 are provided for firing the furnace.

A very satisfactory way of making the muifie parts 41, etc., is by extrusion. A finely powdered mixture of 50% molybdenum disilicide and 50% chromium disilicide are mixed with water and a binder such as carboxymethyl cellulose or water soluble methyl cellulose to form a coherent paste, which is then extruded to the form desired. From /2 to 4% of the binder is satisfactory. After extrusion theparts are sintered at 1600 C. to 1900 C. to burn off the binder and cement the particles together.

Figs. 4, and 6 show a continuous type furnace equipped with a conveyor belt made up of units of the molybdenum disilicide or chromium disilicide. According to this modification the said disilicides are formed into units 50 such as shown in Fig. 5 having end portions 51, 52 containing loopholes 53 through which connecting rods 54 are adapted to be passed. The end portions 51, 52 as ShOWIl'il'l Fig. 6 are narrower than central portion 55 thus enabling the units to be interfitted and united by connecting rods 54. The belt is pulled through the muffle tube 61 of furnace '60 by means of spurred roller containing the spurs 71 adapted to fit under the ends 51 or 52 of units 50. Roller 72 at the entrance end of the furnace need not contain such spurs 71.

A very satisfactory way of making the links or units 50 is to press such links in the form of plates, as solid pieces without the holes 53 therein, presinter the pressed plates at about l0001200C., drill the holes 53 in the presintered plates and finally sinteringat a temperature of about 1500 C. to 1700 'C.

It is also possible, of course, to press the links 50 initially with the holes 53 therein. The rod 54 may be made of molybdenum disilicide also and this rod may be formed by extruding a molybdenum silicide powder mixed with a temporary binder, and then sintering.

The features and principles underlying the invention described above in connection with specific exemplifications will suggest to those skilled in the art many other modifications thereof. It is accordingly desired that the appended claims shall not be limited to any specific features or details shown and described in connection with the exemplifications thereof.

I claim:

1. In a high temperature furnace having an interior furnace space, a belt-like endless conveyor structure having a plurality of linkmembers with each link member movably joined to a preceding and succeeding link memher and consisting essentially of a solid solution of molybdenum disilicide and chromium disilicide, said link members being arranged to be moved along a predetermined path'facing the interior of said furnace space for carrying objects to be heated in said furnace space.

2. A conveyor structure for a high temperature furnace as claimed in claim 1 wherein said link members consist essentially of a solid solution of molybdenum disilicide and chromium disilicide with each of said two disilicides constituting about 50% of the total disilicide content.

References Cited in the file of this patent UNITED STATES PATENTS 1,696,822 Tytus Dec. 25, 1928 1,895,072 Fenton et al. Jan. 24, 1933 2,116,399 Marth May 3, 1938 2,116,400 Marth May 3, 1938 2,612,443 Goetzel et al. Sept. 30, 1952 2,615,701 Ipsen Oct. 28, 1952 2,665,474 Beidler et al. Jan. 1 2, 1954 OTHER REFERENCES Metal Powder Report, Volume 6, Number 11, July, 1952, published in London, England, by Powder Metallurgy, Ltd., page 176.

Machinist, Volume 97, Number 23, Published in England, by McGraw-Hill (United States agent), pages 927- 930, inclusive.

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