US2761187A - Expendable wave guide pattern and method of manufacture - Google Patents

Description

Sept. 4, 1956 COURTER 2,761,187

EXPENDABLE WAVE GUIDE PATTERN AND METHOD OF MANUFACTURE File d March 27, 1952 IN VEN TOR. DONOM/V R COUR TE R A T TORNE Y Unite States EXPENDABLE WAVE GUIDE PATTERN AND METHOD OF MANUFACTURE This invention relates to improvements in techniques and facilities for manufacturing wave guides and particularly to the manufacture of wave guides including one or more integrally formed chokes.

A wave guide is a tubular member of. either rectangular or circular section and of precise dimensions and, as the name implies, is used for guiding or directing ultra high frequency (UHF) energy or so-called microwaves. A wave guide for use in combining systems is generally provided with a so-called choke at one or more of its open ends to reduce power leakage at the joints between connected guides. In addition to providing a flange to which a second flanged guide may be aifixed, such a choke includes a so-called energy ring or wave trap in the nature of an annular channel surrounding the central guide bore. The trap forms a short circuit which blocks wave propagation in the joint.

The tubular portion of wave guides are presently either fabricated, electro-formed or cast, the choke or chokes being formed or afiixed thereon subsequent thereto. Chokes are presently machined either independently of the guide and thereafter afiixed to the guide or from a blank cast on an end of the guide. Reject rat-e on a fabricated guide normally runs from 20 to 40%, and although the reject rate on a cast guide with an integral choke blank is somewhat better, the cost of this procedure is almost prohibitive. I have now developed a method and apparatus for casting a wave guide as a unit including a choke in its finished form, the method involving adaptations of the principles of lost wax casting and the utilization of an expendable pattern of particular configuration and design.

In lost wax casting an expendable pattern is produced from a permanent mold, the pattern is sprued on an acceptable support and casting plaster is poured around the pattern. After the plaster has hardened it is usually heated to liquify or vaporize the expendable pattern material, whereby it is removed from the mold, leaving a plaster mold in which the end product is cast. The mold is, of course, destroyed in removing the end product and the procedure is repeated for each item. I have now developed an expendable pattern for a wave guide choke which is so designed as to form an integral part of an expendable wave guide pattern which, upon use in the above described procedure, will result in a wave guide including an integrally formed and finished choke. The invention permits of close tolerances and etfectuates major economies in elimination of complex machinery operations.

In one aspect, therefore, the invention contemplates an expendable pattern for Wave guide chokes comprising a plate having obverse and inverse faces, a central port traversing the plate and comprising stepped sections enlarging away from the obverse face, an annular integrally formed lip projecting from the inverse face and defining an annular channel opening at the obverse face and deeper than the plate, an annular groove in the obverse atet face concentric with the lip, the plate forming a projecting flange outwardly of the groove.

In using the above described apparatus an expendable pattern for the tubular portion of the wave guide is extended into the port and bottomed therein upon a shoulder formed between stepped sections, so that when the entire pattern is sprued and enclosed in plaster in the manner above described a plaster mold of a complete wave guide results.

In a preferred embodiment of the invention the central port in the expandable pattern includes an integral tubular extension projecting from the inverse face of the guide and defining in part the stepped sections of the port. The walls of the tubular extension are tapered outwardly from the central axis of the port throughout that portion of the extension which defines the larger of the port sections. The taper is such that the inside dimensions increase toward the outer end of the extension while the outside dimensions remain constant. This preferred embodiment has the advantage of permitting the casting of the expendable tube pattern in association with the expendable choke pattern, thereby eliminating the need of manual assembly between the tube and choke patterns.

In addition to the expendable pattern itself the invention contemplates the method of casting a wave guide comprising forming an expendable choke pattern having a port enlarged in part to a size larger than the internal cross section of the desired guide, forming a tubular pattern of expendable material corresponding to the dimensions of the desired guide with the latter extending into and bottomed in the enlarged part of the port, forming a plaster mold around the expendable pattern, eliminating the expendable pattern from the plaster mold and casting the desired wave guide in the resultant plaster mold.

Again, preferred practice constitutes casting the tubular expendable pattern in a cavity mold and in conjunction with the choke pattern so that no manual pattern assembly is required.

The invention will be more clearly understood by reference to the following detailed description taken in conjunction with the accompanying drawing in which:

Fig. 1 is a front elevation of an expendable choke pattern in accordance with the invention;

Fig. 2 is a rear elevation of a preferred form of an expendable pattern in accordance with the invention;

Fig. 3 is a sectional elevation through a pattern mold showing the pattern of Fig. 2 in sectional elevation and the means of using the choke pattern in forming an expendable guide pattern;

Fig. 4 is a revolved elevation of in the mold of Fig. 3;

Fig. 5 is a rear elevation of another form of pattern in accordance with the invention;

Fig. 6 is a sectional elevation taken on the line 6-6 of Fig. 5; and

Fig. 7 is a sectional elevation through another embodiment in accordance with the invention.

Referring to Figs. 1, 2 and 3 of the drawing, the expendable pattern there shown comprises a plate 10 having an obverse face 10A and an inverse face 103 shown in Figs. 1 and 2 respectively. The plate has a central port 12 defining the cross sectional opening of the desired wave guide, the port forming stepped sections 12A, 12B and including a tubular extension 14 (see Fig. 3) projecting from the inverse face of the plate. The sides of the tubular extension taper outwardly away from an extension of the center line of the port 12 for reasons hereinafter made apparent. The stepped sections 12A, 12B of the port form a shoulder 12C which serves a function hereinafter made apparent.

An annular lip 16 projects from the inverse side 10B of the plate defining an annular groove 16A opening at the pattern developed the obverse face A of the plate, the groove 16A forming the short circuiting wave trap heretofore mentioned. An annular groove 18 is formed in the plate exteriorly and concentrically with the grooveil6A, thegroove 18 forming a housing for an O ring or other sealing gasket (not shown).

'In. using the pattern 10 to produce an expendable wave guide, pattern, a pattern mold 20 is provided with a cavity 21 defined by membersZtlA, 20B. The member2tlB has a bore 22 defining the exterior dimensions of the desired wave guide and opening on the central axis of the cavity 21. The mold section 20A has a bore 24 to receive a core 26 mounted through the bore 24 and extending into the bore 22. The core 26 defines the interior dimensions of the wave guide forming an annulus within the bore 22 corresponding with the wall thickness of the wave guide.

.Pattern 10 is mounted in the cavity 241! shown, the integral tubular projection 14v extending into the bore 22 and engaging against the walls thereof. The core 26 passes through port 12 of the pattern, section 12A of which is dimensioned to correspond to the inside of the wave guide and hence the core dimensions. As illustrated, the core 26 is spaced from the walls of bore 22 in mold section ZtlB thereby defining an annular passageway in the mold sections. When wax or other expendable pattern material is poured into the mold it flows into this passageway as illustrated in Fig. 3 to form a tubular pattern 28. The injected wax is excluded from the cavity 20 by the seal formed between the tubular extension 14 and the walls of the mold bore 22 and forms a comparatively rugged connection with the expendable choke pattern 10 through a union bottomed on the annular shoulder 12C and extending along the inner surface of the larger section 12B of the port as defined in part by the tapered walls of the integral tubular extension 14.

The wax injected in the annular passageway formed between the core 26 and wall of bore 22 in mold section 20B thus forms an annular tube which extends into the stepped sections in the pattern member 11 and forms an integral part with the member 10 of the wave guide pattern. The composite pattern may then be withdrawn fromthe mold and employed in accordance with conventional lost wax casting techniques to form a wave guide. This is accomplished by spruing this expendable pattern on a support and coating it with a refractory material such as casting plaster. The casting plaster is allowed to'set around the pattern which is then disposed of byburning it or melting it out of the plaster mold. Molten metal may then be poured into the refractory mold to form the wave guide.

Fig. 4 is an elevation view of the revolved pattern as developed in the mold of Fig. 3.

A somewhat simpler form of the invention is shown in rear elevation in Fig. 5 and sectional elevation in Fig. 6. Pattern 30 shown in these figures is similar to pattern 12 heretofore described, differing therefrom. only in the absence of the integral tubular extension 14. In the pattern 30 a port 32 is undercut from the inverse side 30B to form stepped sections 32A, 32B defining a .circumscribing shoulder 32C. An integrally formed lip 34 corresponding to the-lip 16 of the above described embodiment projects from the inverse side 30B of the plate and defines a channel opening in the obverse face of the plate. In this particular embodiment the lip 34 is undercut or broached at 34A to define a continuation of the larger section 32B of .the port' 32, so that a tubular wax pattern of exterior dimensions conforming to this section of the port can be inserted and bottomed on the shoulder 32C. The broached portion of the lip34 helps support such a tube, which may be additionally supported'by moistening the edges of the port section 323 with suitable solvent .to temporarily soften at that point the expendable material from which the choke patternis made.

" The" embodiment shown in sectionalel'evationin' Fig. 7

is a pattern for a wide band choke which is characterized by a somewhat shallower but thicker (radial dimension) wave trap. This pattern comprises a plate 40 having obverse and inverse faces 40A, 4013 respectively, a central port 42 including an integral tubular extension 44 defining stepped port sections 42A, 42B. As in the embodiment of Fig. 3, the walls of the tubular extension forming the larger of the two port sections are tapered and for the same purpose. In this respect this pattern differs from that of Fig. 3 in that the circumscribing step or shoulder 42C formed by the stepped sections is displaced on the axis of the port so that a tubular wax pattern associated therewith does not extend as far into the port. The configuration of the port defining tubular extension 44 of this figure may be employed as an alternative arrangement of the pattern of Fig. 3.

The plate 45) is provided with an annular lip 46 projecting from the inverse face and defining a channel 47 opening at the obverse face, the lip and channel differing from the corresponding elements of the foregoing embodiments in being shallower and of larger radial dimensions. A concentric annular channel 48 in the obverse face 40A of the plate is adapted to receive a sealing ring as above described.

The choke pattern of the invention may be made from any expendable plastic, styrene being the presently preferred form of plastic. Dimensional stability and a certain amount of rigidity are of course essential. The pattern of the invention can be turned out in large quantities and sold for use anywhere in the country; it is extremely economical and experience shows that there are practically no rejects of the finished molds.

I claim:

1. An expendable pattern for wave guides comprising a plate having obverse and inverse faces, a central port traversing the plate and comprising stepped sections enlarging away from the obverse face, an annular integrally formed lip projecting from the inverse face radially of the center port and defining an annular channel opening at the obverse face and deeper than the plate, an annular groove in the obverse face concentric with and radially of the channel, the plate forming a projecting flange outwardly of the groove.

2. An expendable pattern for wave guides comprising a plate having obverse and inverse faces, a central port traversing the plate and comprising two stepped sections enlarging away from the obverse face and forming a circumscribing rearwardly facing shoulder at their juncture, an annular integrally formed lip projecting from the inverse face radially of the center port and defining an annular channel opening at the obverse face and deeper than the plate, an annular groove in the obverse face concentric with and radially of the channel, the plate forming a projecting flange outwardly of .the groove.

3. An expendable pattern for wave guides comprising a plate having obverse and inverse faces, an annular integrally formed lip projecting from the inverse face and defining an annularchannel opening at the obverse face and deeper than the plate, a central port the central axis of which'coincides with the axis of the annular lip and comprising two stepped sections, the smaller section opening at the obverse face, an annular groove in the obverse face outwardly of and concentric with the lip, the plate forming a projecting flange outwardly of the groove.

4. An expendable pattern for wave guides comprising a plate having obverse and inverse faces, a central port extending through the plate and comprising two stepped sections, an integral tubularextension projecting from the inverse face of the plate and defining the port, an annular integrally formed lip projecting from the inverse face radially of the center port and defining an annular channel opening at the obverse face and deeper than the plate, an annular groove in theobverse face concentric with and radially of the channel, the plate forming a projecting flange outwardly of the groove.

5. An expendable pattern for wave guides comprising a plate having obverse and inverse faces and a centrally disposed integral tubular extension projecting from the inverse face, a central port in the plate defined by a hole in the plate and said tubular extension, the port consisting of two stepped sections, the smaller of which opens at the obverse face, an annular integrally formed lip projecting from the inverse face radially of the center port and defining an annular channel opening at the obverse face and deeper than the plate, an annular groove in the obverse face concentric with and radially of the channel, the plate forming a projecting flange outwardly of the groove.

6. An expendable pattern according to claim wherein the portion of the walls of the tubular extension defining the larger of the port sections taper outwardly in inside dimensions so that the wall thickness of the tubular extension at its outer end is less than that adjacent the inner end of the larger port section.

7. A method of forming an expendable wave guide pattern for casting wave guides which comprises forming an expendable choke pattern including a tubular extension defining a central port having stepped sections, mounting the pattern in a guide mold with the outer edge of the tubular extension sealing against the mold and with a mold core passing concentrically through the central port and being spaced therefrom to form an annular passageway, injecting a normally solid expendable pattern material in fluid form into this passageway to form a continuous tube extending into the stepped sections of the choke pattern and becoming an integral part with the choke pattern of a composite wave guide pattern.

8. A method of forming an expendable wave guide pattern which comprises preforming an expendable choke pattern including a plate having a central port in two stepped sections, mounting the choke pattern in a mold with a mold core passing concentrically through the port and fitting snugly in the small port section and forming a concentric passageway extending from the choke pattern, and injecting a normally solid expendable pattern material in fluid form into this annular passageway to form a tubular expendable pattern around the core and extending into and sealed in the larger port section whereby the tubular pattern and the choke pattern form an integral composite wave guide pattern.

9. A method of forming an expendable wave guide pattern which comprises preforming an expendable choke pattern including a plate having a central port and an integral tubular extension defining a continuation of the central port, the port constituting two stepped sections with the portion of the walls of the tubular extension defining the larger of the stepped sections flaring outwardly in inside dimensions, mounting the choke pattern in a mold with the outer edge of the tubular extension sealing against the mold and with a mold core passing concentrically through the port and fitting snugly in the smaller of the port sections and passing concentrically through a bore in the mold and being spaced from the walls of the bore to form an annular passageway therein, injecting a normally solid expendable pattern material in fluid state into the mold annular passageway to form a tubular pattern around the core extending into the larger port section of the choke pattern and sealing against the flared wall portion of the tubular extension to become an integral part with the choke pattern of a composite wave guide pattern.

10. A pattern for wave guides comprising a plate having obverse and inverse faces, a central port traversing the plate and comprising two stepped sections enlarging away from the obverse face and forming a circumscribing rearwardly facing shoulder at their juncture, an annular integrally formed lip projecting from the inverse face radially of the center port and defining an annular channel opening at the obverse face and deeper than the plate, an annular groove in the obverse face concentric with and radially of the channel, the plate forming a projecting flange outwardly of the groove.

11. A pattern for wave guides comprising a plate having obverse and inverse faces, a central port extending through the plate and comprising two stepped sections, an integral tubular extension projecting from the inverse face of the plate and defining the port, an annular integrally formed lip projecting from the inverse face radially of the center port and defining an annular channel opening at the obverse face and deeper than the plate, an annular groove in the obverse face concentric with and radially of the channel, the plate forming a projecting flange outwardly of the groove.

12. A pattern for wave guides comprising a plate having obverse and inverse faces and a centrally disposed integral tubular extension projecting from the inverse face, a central port in the plate defined by a hole in the plate and said tubular extension, the port consisting of two stepped sections, the smaller of which opens at the obverse face, an annular integrally formed lip projecting from the inverse face radially of the center port and defining an annular channel opening at the obverse face and deeper than the plate, an annular groove in the obverse face concentric with and radially of the channel, the plate forming a projecting flange outwardly of the groove.

13. An expendable pattern for wave guides comprising a plate having obverse and inverse faces, a rectangular port opening through the center of the plate and comprising two stepped sections, the larger section opening at the inverse face of the plate, an annular integrally formed lip projecting from the inverse face radially of the port and defining an annular channel opening at the obverse face and deeper than the plate, the lip having an inside diameter just less than the dimension of the major axis of the rectangular port and being undercut adjacent opposite ends of the port to form extensions of the end surfaces of the larger port section.

14. A method of forming an expendable wave guide pattern for casting wave guides which comprises forming an expendable choke pattern defining a central port having stepped sections, mounting the pattern in a guide mold with a mold core passing concentrically through the central port and being sealed against the smaller of the stepped sections and spaced from the larger section and from the mold to form an annular passageway, injecting a normally solid expendable pattern material in fluid form into this passageway to form a continuous tube extending into the stepped sections of the choke pattern and becoming an integral part with the choke pattern of a composite wave guide pattern, removing the composite expendable pattern from the mold, coating the exterior of the pattern with a refractory material, allowing the refractory material to set, removing the expendable pattern from the set refractory material and casting the wave guide in the resultant mold whereby the guide tube and choke are integrally formed.

References Cited in the file of this patent UNITED STATES PATENTS 1,675,732 Schweitzer July 3, 1928 2,456,424 Neiman Dec. 14, 1948 2,462,370 Drake Feb. 22, 1949 2,466,272 Porter et a1. Apr. 5, 1949 2,495,402 Bentsen Ian. 24, 1950 2,508,546 Skinner May 23, 1950 2,635,294 Rolaston Apr. 21, 1953 OTHER REFERENCES Palmer: Foundry Practice, 3rd ad, page 385 relied on; by John Wiley & Sons.

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