US2912951A

US2912951A - Method of and means for forming bellows

Info

Publication number: US2912951A
Application number: US595998A
Authority: US
Inventors: Melville F Peters
Original assignee: Individual
Current assignee: Individual
Priority date: 1950-12-13
Filing date: 1956-07-05
Publication date: 1959-11-17
Anticipated expiration: 1976-11-17

Description

Nov. 17, 1959 PETERS 2,912,951

; METHOD OF AND MEANS 0R FORMING BELLOWS Original Filed Deo 15, 1950 VE/VTOR. Melvlll .Pefers ATTORNEYS United States p t lVIETHOD OF AND MEANS FOR FORMING BELLOWS Melville F. Peters, Livingston, NJ.

Original .application December 13, 1950, Serial No. 200,561, now Patent No. 2,761,206, dated September 4, 1956. Divided and this application July 5, 1956, Serial No. 595,998

4 Claims. (Cl. 113116) This invention provides a method of forming curved surfaces for fluid seals and means to secure the curved surfaces together to form bellows.

This application is a division of an application, Serial No. 200,561, filed December 13, 1950, now Patent No. 2,761,206, issued September 4, 1956, by Melville F Peters, and entitled Method of and Means for Forming Bellows.

As hereinafter used, the term curvature of surfaces of minimum stress for bellows elements shall be understood to mean the surface formed when a flexible member or membrane is secured or supported by two cylindrical elements and a fluid pressure or its equivalent applied to one side of the membrane, so that the unsupported and unguided area will deform into a curved surface and if the pressure is great enough to exceed the elastic limit of the membrane in the unsupported area, the deformation will continue until the stresses in the membrane are reduced to the yield point.

If the curved surface of bellows elements are formed at a pressure nP and 11:1, the stresses in the elements in the rest position when subjected to a pressure P, is approximately equal to the yield strength of the material and if the bellows is oscillated through an amplitude of :X when subjected to the forming pressure, the stresses caused in the membrane by the oscillations must be algebraically added to the yield strength of the material. During the life of the bellows the curvature of the surfaces will change so as to accommodate itself to the greatest stress, but unless the bellows is subjected to conditions which will increase the curvature of the surface, the flexing life of the bellows will be short.

If the formed element is annealed and subjected to the forming pressure, there will be a small increase in curvatures because the yield point of the material is slightly lower in the annealed condition. This process of subjecting the membrane to the forming pressure and annealing may be repeated many times with a small increase in curvature, but at a decreasing rate of increasing curvature for each cycle. The same limiting curvature could have been obtained in one operation by making it slightly greater than 1.

If n is greater than 1 and, for the sake of illustration, is equal to 10, the stresses in the annealed membrane will be approximately ten percent of the yield strength, since the stress S in a membrane subjected to a pressure P, is S=KP, where K is a complicated function of the physical dimensions and properties of the membrane. If the membrane is oscillated through an amplitude '-X, the stresses developed in the membrane will be added algebraically to ten percent of the yield strength, so that Patented Nov. 17, 1959 by controlling the amplitude of oscillation the annealed membranes will operate within the elastic limit.

The surface formed by the pressure nP is not actually the surface of minimum stress for a pressure nP, because the deformation of the membrane stopped when the yield point of the material was reached, and therefore it difiers from the real curvature of a surface having minimum stress by an amount which is proportional to the modulus of elasticity of the membrane material, and approaches the true shape as the modulus of elasticity approaches zero. The true surface shape for each depth of curvature may be photographed or observed by applying fluid pressure to a soap or rubber film secured by its edges to appropriate forms. The surface shape or curvature may then be transferred to a die and flexible member stamped in the conventional manner.

It is an object of this invention to eliminate this procedure by providing a method for forming the curvature of membrane surfaces bounded by two other surfaces or areas, by applying a uniform pressure of n? over the confined surface, and after securing the membranes together by means of the bounding areas to form a bellows, to limit the working pressure of the bellows to a fluid pressure P. For all practical purposes the fiber stress in the curved surface of a membrane formed with n greater than one, will be the same as the fiber stress in a membrane with the curvature copied from the soap film, when both surfaces have the same depth of curvature and the working pressure does not exceed P. The curvature of the surface is controlled by the forming fluid pressure nP, so that by assigning a series of values to 111, a family of surfaces having minimum stress are obtained with the same fixture, and the forming fluid pressure required is determined by the working pressure P, the yield strength of the membrane material and the convexity or concavity of the surface subjected to the working pressure in the bellows.

Another object of the invention is to provide a method for forming the curvature of membrane surfaces by applying a fluid pressure of nP over an unsupported portion of the membrane until equilibrium is established between the forming pressure, the yield strength of the material and the thickness of the membrane, so that adjustment in curvature for non-uniformity of material thickness and composition is realized during the forming process, and two areas which serve as supports for the membrane during the forming process, are means for securing the membranes together to form a bellows.

It is a further object of the invention to provide a method of forming the curved surface with a fixture that changes the width of the curved surface throughout its perimeter, so that the amount of inertia of the formed surface is not constant throughout the perimeter, and thereby provide means for limiting the fiber stress in the regions of the surface where the ambient conditions lead to great shearing forces and large bending moments.

It is an object of the invention to provide a method of forming the curved surface with a fixture that permits changes in the width of one or both of the two bounding areas throughout the perimeter and thereby provide means for limiting the fiber stress in the regions of the surface where the ambient conditions lead to great shearing forces and large bending moments.

It is also an object of the invention to provide a method for forming diaphragms by supporting the outer area of a membrance and applying a fluid pressure to the central portion, thus causing the unsupported and unguided portion to deform until equilibrium is reached between the curvature of the deformed surface and the forming pressure.

It is an object of the invention to provide a method for forming surfaces of curvature of minimum stress by applying a greater pressure than the forming pressure nP and limiting the deformation to that of a membrane subjected to a forming pressure nP, by means of a limiting device.

Other objects and advantages of this invention relating to the arrangement and operation of the forming elements and economies of manufacture will be apparent to those skiiled in the art upon consideration of the description, drawings and appended claims.

The invention consists of the construction, combination and arrangements of parts, as herein illustrated, described and claimed.

In the accompanying drawings, forming a part hereof is illustrated one form of embodiment of the invention, and in which:

Figure 1 is a cross sectional view of the curvature of a surface having minimum stress and the arc of a circle shown in dashed lines superimposed on a portion thereof.

Figure 2 is a top plan view of a view of a blank from which the bellows element is formed in accordance with the present invention.

Figure 3 is a top plan view of the bellows element after its formation in accordance with the present invention.

Figure 4 is a cross sectional view taken on line 4-4 in Figure 2.

Figure 5 is a cross sectional view taken on line 55 in Figure 3.

Figure 6 is a fragmentary view in cross section showing the fixture by which the membrane discs are stressed with a portion of said disc therein, prior to the application of pressure.

Figure 7 is a view similar to Figure 6 showing the formed membrane within the fixture.

Figure 8 is a vertical section taken through a portion of a bellows assembly composed of a plurality of discs made in accordance with the present invention, Welded at their alternate edges to form a rigid fluid tight structure.

Referring to the drawings and particularly to Figures 1 and 2, 10 indicates a flat somewhat washer shaped blank stamped from some suitable metal such as copper, stainless steel or the like which blank has the generally cross sectional shape illustrated in Figure 4. The blank 10 is inserted within a fixture 11, best shown in Figures 6 and 7. The fixture 11 is shaped to conform substantially to the blank 1% and comprises an upper member 12 and a lower member 13. The upper member 12 is provided with downwardly extending jaw portions 14 which are adapted to bear upon the upper surface of the blank H1. The lower member 13 is formed with upwardly disposed jaw portions 15 adapted to bear upon the under side of the blank 10. The

jaw portion members

14, 15, grasp the blank 1t), therebetween at a point spaced from the inner and outer periphery of said blank. A suitable opening 16 is provided in the lower member 13 for the introduction therethrough of fluid under pressure. The upper member 12 may be formed with a vent 17 leading from the interior of the member 12 to the atmosphere. The

jaws

14, 15, may be provided with holding and sealing surfaces 18.

When it is desired to form a membrane in accordance with the present invention the membrane blank 10 is held and sea ed between the

jaws

14, 15 and the forming pressure applied until equilibrium is established between the curvature of the surface, the yield strength of the matrial, and the forming pressure nP. The process can be carried out by two or more steps by applying the pressure nP, annealing and then continuing the process by again applying the pressure nP, to form the blank with a curvature of surface of minimum stress. This curvature is illustrated in Figure 1, at '19.

An alternate procedure in applying the forming pressure is to apply a pressure greater than the forming pressure nP and have a conventional triggering device (not shown) release the pressure at the instant the forming of the surface is complete.

Referring to Figure 1, the curvature 19 is a cross sectional view of a surface having the defined surface curvature of minimum stress and is formed by subjecting an unsupported portion of the membrane 10 to a fluid pressure which stresses the membrane beyond the yield point of the material. A cross sectional view of an arc of a clrclehavin-g the same depth of curvature as 19, has been superimposed upon the showing of Figure 1, and appears as the dotted line 29. The margins or edges by which the blank 10 is supported during the forming operation are indicated at '21 and 22 in Figure l. These-

margins

21, 22, provide means for securing the curved members together to form a bellows as indicated in Figure 8.

In the formation of a bellows 23, shown in Figure 8, the curved surfaces 19, are prevented from touching during compression of the bellows 23 by forming the

adjacent margins

21, 22, on the assembled membranes of different sizes.

Referring again to Figures 6 and 7, the fixtures 11, with

chambers

24, 25, therein and

jaw members

14, 15, are shaped to form bellows elements or sections of bellows elements, which sections may be secured together to form elements. These formed elements consist of surfaces having the minimum stress bounded by areas or

edges

21, 22, and the separation of

jaw elements

14, 15, can be increased or decreased throughout their perimeter so as to increase or decrease the width of the curved surface 19 throughout the perimeter and thereby increase or decrease the moment of inertia along the perimeter to compensate for the unequal distribution of the shearing forces and bending moments induced in the elements, and thus meet the fiber stress in the element within the elasticity throughout. The width of the

margins

21, 22, can be increased or decreased by increasing or decreasing the width of the unformed membrane without placing limitations upon the separation of the

jaws

14, 15, so that the width of the two

areas

21, 22, can be changed throughout their perimeter to compensate for the unequal distribution of shearing forces and bending moments induced in the elements.

Having thus fully described the invention, what is claimed as new and desired to be secured by Letters Patent of the United States, is:

1. A device for forming bellows membranes from flat washer-shaped blanks comprising complementary upper and lower forming members, said upper member having downwardly extending spaced annular jaws and an intermediate connecting portion with a vent hole therein between said jaws defining a chamber for receiving the unconfined formed portion of the blank, said lower member having upwardly extending spaced annular jaws and an intermediate portion with a fluid introducing opening therein connecting said jaws and defining a chamber for applying fluid under pressure to the bottom side of the unsupported portion of said blank to form the same.

2. A device for forming bellows membranes according to claim 1 in which the upper and lower annular jaws are provided with fluid sealing surfaces to prevent the passage of fluid from the chambers between the jaws and the blank during the forming operation.

3. The method of forming bellows membranes comprising, the steps of stamping a substantially washershaped blank from a suitable metal, grasping and supporting the stamped blank on both sides but only in areas adjacent its peripheral edges, and thereafter subjecting one side of the unsupported portion of the blank to direct contact of fluid pressure of a magnitude to stress the said unsupported portion of the blank material beyond its elastic limit, by means of a pressure applying chamber surrounding said side of said unsupported portion of said blank.

4. The method of forming bellows membranes according to claim 3 in which the blank is subjected to successive fluid stresses upon the same unsupported side and annealed after each of said stress operations.

References Cited in the file of this patent UNITED STATES PATENTS Cutler et a1. Nov. 10, 1925 Seibt Apr. 26, 1927 Gulick June 10, 1930 FOREIGN PATENTS Germany Sept. 5, 1928 Great Britain Nov. 13, 1934