US 3804967 A
A diffusion furnace has a processing member with a rectangular cross section having an arcuate-like top wall and a heating element of a substantially elliptical-like cross section surrounding the processing member.
Description (OCR text may contain errors)
United States Patent 1191 Johnson 219/390 Wer ch A r. 16 1974 RECTANGULAR TUBE DIFFUSION 1,144,981 6/1915 Lightfoot... 219/390 x FURNACE 1,500,609 7/1924 Dixon 219/390 X 2,274,190 2/1942 Cramer 219/390 Inventor: Ewald y Elm Grove. 3,299,196 1/1967 Lasch,Jr. et a1. 13/24 3,311,694 31967 L 11,]. 13 24  Assgnee Bas'c f 3,406,242 10/1968 13/22 Mllwaukee 3,409,727 11/1968 Hampton 13/20 22 Filed: Oct. 13 1972 3,541,293 11/1970 MacDonald et al. 219/390 21 APPL 297,205 FOREIGN PATENTS OR APPLICATIONS 693,878 7/1953 Great Britain 219/388 ' US. Cl 13/22, 13/25, 2l9/388,
219/390, 219/406 Primary ExaminerVolodymyr V. Mayewsky s 1 Int. Cl. H0511 3/66 Attorney, 8 m and Moore  Field of Search 219/388, 390, 406, 411,
219/553; 13/20, 22, 24, 25 57 ABSTRACT  References Cited A diffusion furnace has a processing member with a rectangular cross section having an arcuate-like top UNITED STATES PATENTS wall and a heating element of a substantially elliptical- 714,373 11/1902 Hewett et a1. 219/390 like cross section surrounding the processing member. 904,529 l1/1908 Hammond et a]... 1,035,596 8/1912 1 Claim, 4 Drawing Figures 1 RECTANGULAR TUBE DIFFUSION FURNACE The present invention relates to diffusion furnaces and particularly to the heating element and processing or tube member through which work to be processed is passed or held.
A conventional diffusion furnace essentially comprises a hollow processing member or tube constructed of a suitable material, such as quartz, and surrounded by a heating element in the form of a helical coil. It has been generally considered to be desirable to have the heating element positioned as close as possible to the processing member. Accordingly, the cross-sectional configuration of the heating element was made similar to that of the cross-sectional configuration of the processing member, and in many cases, the heating element fitted very closely around the processing member. Thus, where diffusion furnaces for different operations were provided with processing members of various cross sections, such as circular, square, or rectangular, the heating elements for these furnaces had the corresponding cross-sectional shapes. This introduced certain difficulties in the manufacture of diffusion furnaces since it was necessary to manufacture and stock heating elements having the same shapes as the processing members. Further, difficulties were frequently encountered in mounting such heating elements upon the processing members.
One of the objects of the present invention is to provide an improved diffusion furnace.
Another of the objects of the invention is to provide an improved construction of the heating element with respect to the processing member.
According to one aspect of the present invention, a diffusion furnacemay comprise a substantially hollow processing member or tube having a processing zone therein. The processing member has a rectangular cross section with the upper wall or roof having an arcuate-like section. A heating element surrounds the processing member and supplies heat to the processing zone. The heating element has a substantially elliptical cross section and comprises a helical coil. Portions of the heating element opposite respective faces of the rectangular processing member are slightly flattened.
These and other objects, advantages and features of the invention will become apparent from the following description and drawings which are merelyexemplary.
In the drawings:
FIG. 1 is an overall perspective view of a diffusion furnace incorporating the present invention with portions of the furnace being cut away;
FIG. 2 is a sectional view taken along the line 2-2 of FIG. 1;
FIG. 3 is a sectional view taken along the line 3-3 of FIG. 1; and
FIG. 4 is a side elevational view ofthe heating element incorporated in the diffusion furnace of this invention.
Proceeding next to the drawings wherein like reference symbols indicate the same parts throughout the various views, a specific embodiment of the present invention will be described in detail.
As may be seen in FIG. I, a diffusion furnace incorporating the present invention is indicated generally at 10 and comprises a tubular processing member 11 formed of a suitable material, such as quartz, and having a rectangular cross section with an arcuate upper wall or roof such as shown in FIG. 2. The processing member 11 is surrounded by a heating element 13, comprising a helical coil and having the cross-sectional shape as shown in FIG. 2.
As mentioned, the roof or upper portion is arcuately shaped.
The processing member 11 can be supported on strips or blocks 12 carried on ceramic structure 15.
The heating element 13 is substantially elliptical-like in shape but has portions thereof flattened which are opposite the several faces of the processing tube. The result is a substantially elliptical-like shape having opposed portions thereof flattened as shown in FIG. 2.
The heating element is supported within the furnace in a suitable manner, and a plurality of ceramic separators 14 can be provided to maintain separation between turns of the heating element. The separators are cemented to a tubular ceramic structure 15 which can be enclosed in an outer casing 16 having substantially the same cross-sectional shape as the heating element 13.
Flanges 17 and 18 of a suitable material, such as refractory or ceramic, are mounted within the casing 16 on opposite ends of the heating element 13, and each is provided with an opening 19 and 20 which is substantially of the same size as the inner opening of the tubular processing member 11. I
In the form shown in FIG. 4, the furnace is provided with three zones as defined by the turns of the heating coil. The turns of the several zones are connected by alloy strips 21 and 22 to suitable sources of electrical energy.
It should be apparent that variations can be made in details of construction without departing from the spirit of the invention except as defined in the appended claims.
What is claimed is:
1. In a diffusion furnace including a ceramic outer tubular structure, the combination of a tubular processing ceramic member of generally rectangular cross section in said outer structure and having an arcuately shaped roof and a processing zone therein, said processing member being supported by extruded quartz block means, an electrical helical coil heating element surrounding said processing member and mounted in said ceramic outer structure by ceramic separating means attached to said outer structure, and metal conductive strips extending through said outer structure and connected to said coil heating element and a source of electrical energy to supply current to said coil heating element and thereby to heat said processing zone, said heating element having a substantially elliptical-like cross section and wherein the major axis thereof is parallel to the longer sides of the rectangular processing member and opposed sides are generally flattened with reference to the straight side walls of said processing member.