US2669209A

US2669209A - Die assembly for utilizing hydrostatic pressure in a deep body of water for forming sheets

Info

Publication number: US2669209A
Application number: US128836A
Authority: US
Inventors: Frederick C Hoffman
Original assignee: Lockheed Aircraft Corp
Current assignee: Lockheed Corp
Priority date: 1949-11-22
Filing date: 1949-11-22
Publication date: 1954-02-16
Anticipated expiration: 1971-02-16

Description

Feb. 16, 1954 F. c. HOFFMAN DIE ASSEMBLY FOR UTILIZING HYDROSTATIC PRESSURE IN A DEEP BODY OF WATER FOR FORMING SHEETS Filed Nov. 22, 1949 4 Sheets-Sheet 1 ID INVENTOR FREDERICK C.HOFFMAN F. C. HOFFMAN Feb. 16, 1954 DIE ASSEMBLY FOR UTILIZING HYDROSTATIC PRESSURE IN A DEEP BODY OF WATER FOR FORMING SHEETS Filed Nov. 22, 1949 4 Sheets=Sheet 2 INVENTOR. FREDERICK C, HOFFMAN Agent F. C. HOFFMAN DIE ASSEMBLY FOR UTILIZING HYDROST Feb. 16, 1954 ATIC PRESSURE IN A DEEP BODY OF WATER FOR FORMING SHEETS Filed NOV. 22 1949' 4 Sheets-Sheet 3 INVENTORI FREDERICK C.HOFFMAN Alt gent Feb. 16, 1954 c, H F A 2,669,209

. DIE ASSEMBLY FOR UTILIZ ROSTATIC PRESSURE IN A DEEP BODY OF WATER FORMING SHEETS Filed Nov. 22, 1949 4 Sheets-Sheet 4 INVENTOR.

FREDERICK C.HOFFMAN Patented Feb. 16, 1954 DIE AssEMELY FOR UTILIZING HYDRO- STATIC PRESSURE IN'A' DEEP'BODY OF WATER FOR o MING SHEETS Frederick O .Hofl'man, North Hollywood, Calif asslgnor to Lockheed se saw!- APPHcationNovemlier to actluponthesheet and'force' it ihtdthe'. die

cavity to form the same. When largefpanelsand sheetsare to be formedlit is'necess'ary to pro- ,;.vide: heavy, expensive J torming, equipment and ,where hydraulic fluid is utilized as the forming medium powerful pumps must be operated to .develop sufiicient pressure to shape or form. the

sheets. Furthermore, in such cases, the dies must .have'strong, heavy walls to withstand the'pressures to which they are subjected. For example, whenworkp'ieces of, say, forty feet long and fifteen fee wide are to ,be formed, thewalls ofthe die H prop and. of the fouteroil retainer would, of necessity, be of tremendous size and thickness .towithstand the internalihydraulic pressuresfor an excessively large' press or clamping mechanism would be necessaryto. contain the internal pres- ,sures. 'Owing to. these and other factors the provision of theequipmentnecessary to form wlargepanels, andthe like, involvesa great initial expenditure of money and the operation and maintenance of the large costly equipment is a source of substantial expense. 3 It is a general object 0t this invention to pro- :vme an inexpensive dependable apparatus for -forming, $haping and embossing sheets, panels,

Aircraft Corporation,

22, I949, scram. 128,836 eams (01. 113-44 5 Another object of the invention is toprovide apparatus of the class referred to that may be mployed in the forming and shaping of sheets, plates, and assembled panels of practically any size. Because the hydrostatic pressures in'the sea, deep lakes, shafts, etc. are very great at substantial depths and are substantially uniform throughout any given depth strata, it is possible to form extremely large'panels, and the like 1 and to'shap'e plates of considerable thickness. 'Ihe utilization of thesehigh hydrostatic 'pre res does not, of course, necessitate the provi's'io or operation of pressure developing pumps a nd may be accomplished by'means of relativelysiniple hoisting means, draw works, 'or the like Another object of the invention 'isgto provide apparatus of the character describecljf'fwlierein th dies and ,associatedparts need not beprovided with heavy walls or'reinforcement's to withstand the sheetforming pressures. f 1n accordance with the invention,the dieandassociated parts are submerged inithe liquid to be subjected ,throughout their exposed surfaces to like or identical h drostatic" ressures so that fit utinecessary to construct them with heavy pressure rsi'stant walls. Q V u H [A further object of the'invention islto'pro 'de apparatusof'this"class in which two :or moi: die assemblies are associated with "thef i iwpring or hoisting lines in'sucha way 'a'sto counterbalance "one another, thereby reducing"thepower refquird to raise the diesfromth'e ocean, lakefor shaft; one form of "th'e'invention "one 'or'more fdi' e'as'semblies are securedto each endofa line cable so that theweight ofthe dieor' dies-at one end of the cable:counterbalances'the weight y' die or dies at the other] end of "the able -p1ates,-,and the like, which does not require the installation and operation of largecostly form- 'ing equipment or the'provision ando'peration of pumps for. developing highfluid pressures.

Another object. or thelinvention is to provide apparatus of the l'ilr aracter' mentioned which 1 utilizes. the hydrostatic pressures existing in -the sea, lakes, deep" wells, abandoned ,water' -fille'd mine shafts, etc. as the force for' shaping and :forming the panels,fplates;- or sheets-"Inho- 1 cordance with the invention the hydrostatic pres- 1' sures existing at selecteddepths'in the sea, deep Qjlakes, etc. "may act directly upon the'sheet's or panels to form and'shape them intoconforman'ce through the waterto form its contsm aisiieettr panel, thereby markedly reducing the time. 13%- quired for the successive forming'operations.

another embodiment .of' the invention, a se" pr dies is {being lowered through the,wet

another series or j diesfis; being successively} se d .to the surface, providing; a substantia tinuous multiple forming sequence or ope on. A still further object of the invention, is topro- 'vide a. practical, eflective submersible hydro- 7 static. die assembly wherein the workpiece s secureIy-anchored at its: marginsxand, iSadequately protected and wherein means is'ryrlflfidt the process of being lowered into the sea or lake;

Figure 1A is a fragmentary plan view of. a 7

portion of the apparatus illustrated in Figure 1 showing the hoisting drum and associated parts;

Figure 2 is a fragmentary side elevation similar to Figure 1 illustrating another embodiment of the invention wherein one die assembly serves to counterbalance another die assembly;

Figure 3 is a view similar to Figure 2 illustrating still another form of the apparatus of the invention; i

Figure 4 is an enlarged fragmentary perspective view illustrating one of the connections between the line and die of the equipment shown in Figure 3;

Figure 5 is an enlarged transverse detailed sectional view of a die assembly of the character illustrated in Figure 1 showing the sheet or workpiece in full lines in the unformed condition; I v Figure 6 is an enlarged fragmentary transverse detailed sectional view of another form of die assembly of the invention showing the workpiece or plate in the stretched and formed condition'; and

Figure 7 is an enlarged longitudinal sectional view of the air pressure relief valve incorporated in the die assembly shown in Figure 6.

The method of the invention broadly considered, may be said to comprise generally the provision of a die having a die cavity, the securing of a sheet, plate, panel, or other workpiece in the form of an assembly or one piece part on the die to extend across the mouth or the die cavity, the lowering of the assembly to a selected depth in a body of "water, such as the ocean, a lake, or deep shaft, to subject the workpiece to the hydrostatic ressure at said depth to form the workpiece to the cavity and then raising the assembly to permit removal of the formed workpiece from the die. In the following detailed description I will describe several forms of the -'am'aaratu's of the invention and will describe the method as practiced in utilizing the apparatus, it being understood that various forms 'of equipment or apparatus may be employed. in performing the method.

The apparatus of the invention as illustrated in Figures 1, 1A and 5-, may be said to comprise generally a support at the surface of the body of water, which support may take the form of a float or vessel [0, a die assembly 11, having a 'die cavity i2 across which a workpiece I3 is se- 4 platform, or the like, mounted on the earths surface at the mouth of the shaft. In other instances, where a deep relatively still body of water is to be utilized as the source of hydrostatic pressure, the support may be in the nature of a platform, or the like, mounted on the earths surface at the mouth of the shaft. In other instances, where a. deep relatively still body of water is to be utilized as the source of hydrostatic pressure, the support may be in the form of a barge, float, pontoon, or the like. Such a barge, raft,--float or pontoon may, of course, be

employed as the support where the operations are to be carried on at sea. Accordingly, the

to be utilized as the source of hydrostatic pr es.

invention is not to be construed as limited to the use of a shipor vessel It), as illustrated.

'The vessel 10 is employed to support and carry the hoisting means M, the derrick means I6 employed to handle the die assemblies and other equipment, and forms a carrier for the necessary powerplants, auxiliary equipment, etc. as well as serving as a convenient work platform for the workmen. The vessel 10 may or may not be selfpropelled. I have shown a self-propelled vessel l0 having a propeller l1 and rudder 18 so that the vessel maybe sailed to and from the shore or dock and the desired area of deep water. With the vessel at the selected deep water region it may be anchored in position and I have shown an anchor chain l9 extending from the bow.

The vessel 10 may be constructed to facilitate the lowering and raising of the die assembly II and the handling of the die equipment when the worksheets or pieces l3 are installed for forming and are to be removed after being formed. The particular vessel I0 illustrated, has a vertical shaft or well 20 located substantially amidships through which the die assembly i l and line i5 may be raised and lowered, it being apparent that outrigged or outboard supports may be supplied for this purpose, if desired. A platform 2! is provided on the ship deck, adjacent the shaft 20, upon which the die assemblies H may be placed prior to and after forming operations. The derrick means 16, mentioned above, is located adjac'entthe platform 2! and has a line 22 carrying a hoisting hook 2 3 and operating over a pivoted boom 24. The derrick means I6 includes an appropriate power source or engine 25 for operating the line 22 and boom 24.

The die assemblies Il may, of course, take dif-- ferent forms and may be varied considerably in construction without departing from the invention. It is a feature of the present invention that the dies may be large to handle large sheets, panels, and plates that would require the provision of exceedingly large, heavy, costly forming presses, or the like, of the conventional type. In Figure l, I have shown a die assembly ll of the form shown in detail in Figure 5, it being understood that the die assembly of Figure 6 or other forms of die assemblies may be used with the apparatus of Figure 1.

The die assembly ll includes a die body 215 which may be a generally rectangular block-like part and which is provided at one side with the above mentioned die cavity 52. The die cavity l2 may, of course, be of practically any configuration. The panel, sheet, plate, or other workpiece l3, to be drawn or formed, is arranged against the face of the die body 28 to extend across the mouth of the cavity l2. A continuous groove 2-! is formed in the face of the die body 26 to contain a sealing ring '28 for sealingwith the underface of the workpiece l3 around the treason :cavity I2to prevent the entrance at the water into the die cavity. The sealing ring 28 may be the outer face of the workpiece I3 to entirely cover the same.

The sealing sheet 29 is not essential in all applications of the invention but serves to protect the workpiece I3 against contact by the sea or lake water.

A draw or clamp plate 30 is engaged against :the outer side of the sheet 28 or when the sheet 29 is omitted the clamp plate 30' is arranged against the outer side of the workpiece I3. The

clamp plate 30 is tightly clamped toward the die body 26 to secure the marginal portions of "the workpiece I3 in the die assembly. In the simple case illustrated, aligned lugs 3I are provided on the die body and plate and bolts 32 are arranged through openings in the lugs 1 to clamp the plate30 toward the body and thus secure the margins of the workpiece I3 in the die, The draw plate, or clamp plate 30, may be in the form of a ring to leave the major area of theworkpiece I3 and/or its sealing sheet 29, exposed. However, I have shown the plate 30 provided with an apron or skirt 34 extending inwardly to a central opening 33. The under side of the skirt 34 is relieved or concave to leave a pressure chamber 35. This chamber 35 is at least as large in area as the die cavity I2 and its margins follow the marginal contour of the die cavity I2 so that the pressure in the chamber may act on thefull area of the workpiece I3 that is to be pressed into the die cavity. The

opening 33, which is of substantial capacity, admits thewater to the chamber 35 and permits the hydrostatic pressure to act fully upon the workpiece I3 to form the same. The perforate skirt 34 protects the workpiece I3 against injury when the die assembly is being lowered into the sea, raised to'the vessel I0, etc.

A ring 36, or the equivalent, is provided on an end of the die body 26 and the above mentioned line I5, which is preferably in the form of a cable, .is secured'to the ring to carry the die assembly II. In the embodiment. of the invention being described, provision is made to maintain the interior of the die cavity I2 at atmospheric pressure so that air is not trapped and compressed in the cavity during the forming of the workpiece I3. IA port 31 is provided in the die body 26 to communicate with the inner portion of the die cavity I2 and a hose 38 is secured to the body 25 to have one end communicate with the port. The air hose 38 has its other end in communication with the atmosphere to allow the free displacement of air from the cavity I2 during the I forming of the workpiece.

As shown in Figure 1 of the drawings, the hose 38 and the line I5 pass through the well or shaft 20 to the hoisting mechanism I4. The hose 38 may be formed of rubber, or synthetic rubber, and is preferably v, shielded with wire braid, or the-like.

, accordance with the broader aspects of the invention any appropriate or available'means may be utilized to raise and lower the die assembly II. In Figures 1 andlA, I have illustrated in a r'n'oreor fess diagrammatic m'annen'a drawworks or hoisting mechanism I4 including an engine or power plant 40 driving a sprocket H which, in turn, drives a chain 42. The chain 42 operates over a sprocket 43 secured on the shaft 'of a winding drum 44. The drum 44 is appropriately mounted on the deck of the vessel *III a'ndhas an intermediate flange 45 dividing its active spool into two parts 45 and 41. The cable I5 is wound on the drum-part 46 while the air hose 38 is wound on the part 41. A direction changing pulley 48 is mounted on the vessel I0 -at the mouth of the well or shaft 20 and the line I5 and hose 38 extend from the drum 44 to pass over the pulley 48 into the shaft 20 so that upon operation of the drum the die assembly II may be raised or lowered through the shaft.

In employing the apparatus of Figures 1, 1A and 5, 'in carrying out the method of the invention, the vessel I0 is anchored or otherwise secured at a point where the ocean or lakeis'of suflicient depth to provide adequate hydrostatic pressures for the shaping or forming of the given or particular workpieces I3. The material of which the workpiece I3 is formed, the thickness of the workpiece, the size and shape of the die cavity I2 to which the workpiece is to be formed, and other factors, determine the hydrostatic pressure that will be required to shape or form the work. For example, at a depth of 3000 ft. the hydrostatic pressure is approximately 1,290- p. s. i., the hydrostatic pressure in pounds per square inch being substantially equal to the depth in feet multiplied by .43. The workpiece I3 is se cured in the die assembly I I, as illustrated in is operated or controlled to reel off the cable I5 and hose 38, the heavy die assembly II sinking by gravity. As the die assembly descends the hydrostatic pressure admitted to the outer-face of the workpiece I3 by the opening 33 and chamber 35 increases, tending to force the workpiece into the die cavity I2. The hose 38 maintains the interior of the cavity I2 at atmospheric pressure so that a pressure difierential exists across the workpiece I 3, this differential increasing with the depth of the die assembly I I. The gradually increasing hydrostatic pressure acting inwardly on the workpiece I3 forces or presses the workpiece inwardly to stretch and form it to the configuration of the cavity I2, the marginal portions of the workpiece being confined between the die body 26 and the draw or clamp plate 30. The broken lines in Figure 5 illustrate the position and shape assumed by the formed workpiece I3. When the workpiece I3 has been been shaped or formed in this manner at the calculated or previously determined depth in the water, the hoist mechanism I4 is operated to reel in the cable I5 and hose 38 to raise the die assembly II to the surface. When the die assembly II has been raised through the well or shaft 20 the boom 24 and line 22 may be utilized to hoist it on to the platform 2i where the plate 30 and protective sheet 29 are removed to allow withdrawal of the shaped workpiece I3 from the die body 26. Another workpiece I3 may then be assembled or attached to the line margin.

flange 69 fitting a channel in thedie body and From the foregoing it will be seen that the method of the invention as practiced with the apparatus of Figures 1 and 1A, comprises the steps or operations of arranging a workpiece across the mouth of the die cavity of a die, lowering the die into a body of water to a substantial depth to expose the workpiece to the hydrostatic pressure therein which forms the workpiece into configuration with the die cavity, the withdrawal of the die from the body of water and the detachment of the formed workpiece from the die.

Figure 2 illustrates another form of the invention where two die assemblies are operated on a line or cable 5| in such a manner that one die assembly is lowered as the other is raised, thereby reducing the hoisting or lifting power required and markedly increasing the overall speed and efficiency of the forming operations. In this embodiment of the invention the barge, float, or vessel 52 has two spaced vertical wells or shafts 53 and a drum 54 is rotatably mounted on the vessel between the two shafts. A chain and sprocket drive 55 extends between an engine 56 on the vessel and the drum54 to drive the drum. The line or cable 5|, which has one or more turns-on the drum 54, has itsopposite other assembly 50 is at the deck of the vessel.

It will be seen that by properly operating the drum 54 one die assembly 56 is lowered and the other is raised, the weight of the first assembly partially counterbalancing the weight of the second assembly to reduce the power required to operate the drum 54.

The derrick means I6 is preferably located on the vessel l0 soas to handle the die assemblies 59 when they are to be raisedfand lowered through the two shafts 53.

Die assemblies I I, of the type illustrated inFigure. 5 of the drawings, may be operated on the .line or cable 5| in which case the air hoses'38 associated with the die assembliesare handled by the drum 54 as the assemblies are lowered and raised. However, I have shown die assemblies 50, r

of the character illustrated in. Figures 6 and. 7,

Each of these. assemblies 50 includes a die body 60 provided at its activeside with a die cavity 6| of the required con- ."figuration. The workpiece 62 is arranged across the mouth of the die cavity Bl' to have its marginal portions bear on the face of the die body 60. A seal ring 63, similar to the ring 25 described, above, is arranged in a groove 64 in the body 60' to seal with the inner side of the worktherewith, having a tapered lip58 for cooperating with the undercut surface 68. This engagement positively anchors the workpiece 52 at its The clamp ring 51 has a peripheral Ins and bolt connections H removably secure-the ring to the die body 69, It will be seen that the clamp ring 61 is positively anchored or' held against movement toward the center of the die assembly by the engagement of-the flange. 59

the ch n el 0 a d. t l p o er ti wi the surface 66 positively anchors the margin of the workpiece 62.

If desired, or found necessary, a protective and sealing sheet ll of rubber, or synthetic rubber, may be arranged across the outer face of the workpiece 62 and the clamp ring 61 to prevent the waterfrom contacting the workpiec e. Further, a protective plate 1;, of steel or the v l ike,n' a y be arranged across the face of the die assembly.

Cap screws 13, or the-like, secure'the sheet! [and plate 12 to the clamp-ring 61,- The plate l2 is bowed or curved outwardly from adjacent the clamp ring 5? to leave a chamber 14 at the outer face of the workpiece 62 and sheet i! and a rather large central opening l5 is provided in thef'plate 12 to admit the hydrostatic pressure to the chamher to act upon the workpiece.

The die assemblies 5i may be provided with ports 37 and air hoses 38, such as above described, to permit the free displacement of air from the die cavities BI during the forming of the workpieces 52. Howeve gin Figure 6, I have shown the die body 55 provided with an internal cavity 16 V communicating with the die cavity 5! to receive the air as it is displaced from the chamber 62. The chamber 15 maybe cored in the body 50' and it is desirable to have the capacity of the chamber "E5 equal to or greater than the capacity of the die cavity 5 E, so thatupon shaping or forming of theworkpiece 52 the volume of the air in the die is decreased one-half or less. This prevents the development of any appreciable air pressure hehind or under the workpiece 52 as it is being shaped or formed by the external hydrostatic pressure. It is preferred to provide perforated reinforcing webs I! in the chamber 16 to strengthen the chambered die body 60. A central port 18.joins the inner wall of the die cavity'fil and connects with lateral ports 19 in the die body 56 to maintain communication between the die cavity and the chamber 55.

Valve means is provided on the die assemblies 59 to allow the escape of air under pressurefrom the chambers '55 as the'dieassemblies are elevated to. the surface of the water. As shown in Figures 6 and 7,, the body '6!)- of each die assembly 59 has a port leadingv fro'm the chamber #5 and unseats the ball 83' and air is allowed to escape from the die assembly 58. The ball 83. cooperating with the seat 82 of course serves to prevent the entrance of the water'under pressure into the chamber l5.-

It is believed that the manner of performing the method of. the invention with the apparatus of Figures 2, 6-and 7 will be readily apparent from the foregoing detailed description of the apparatus. Assun'iingv that a workpiece 52 is secured in the dieassembly 59,.illustrated at a depth in the sea at the right side of Figure 2, and that a formed workpiece 62 is to be'removed from the die assembly 58 at the left side of the figure, the drum 5 1- is operated toraise the latter assembly as high as'possible to permit it to be engaged by the derrick; means i 5. The drum 54 is l ock 'ed and the line is secured whereupon the assembly 50, at the left, is raised onto the platform 2| so that its workpiece 62 may be removed. A new workpiece 62 is then installed in the die assembly 59 and the assembly is lowered through the left shaft 53 into the sea. The drum 54 is operated to lower the left die assembly 59 and to raise the right assembly 50. As the left die assembly 50 is lowered the hydrostatic pressure increases and acts upon the workpiece 62 through the opening 15 and chamber 14 to press and form the workpiece to the wall of the die cavity 6|. Air from the cavity BI is displaced into the chamber 16 as described above. When the left die assembly 59 reaches the maximum depth the right die assembly reaches the right shaft 53 where it is accessible for engagement by the derrick means It. The drum 54 and line 5| are locked and the right assembly 50 is opened to remove its formed workpiece 92. It will be observed that the die assemblies 50 counterbalance one another during the raising and lowering operation so that a minimum of power is required. The foregoing operations may be repeated to successively or alternately raise and lower the two die assemblies 50 to form or shape the workpieces 62 by the hydrostatic pressures existing in the sea or deep lake.

Figures 3 and 4 illustrate still another form of hydrostatic pressure forming apparatus wherein a plurality of die assemblies 59 is secured to a continuous line or cable system 86. In this type of apparatus the vessel 52 may be substantially the same as in the form of the invention shown in Figure 2, being provided with the two spaced vertical shafts 53. A large diametered drum 8! is mounted between the two shafts 53 and a suitable engine 88 drives the drum through a speed reduction gearing and drive system 89. The cable system 86, which operates over the drum 8?, includes two spaced parallel cables provided with sets 01' pairs of horizontally aligned clamps 90. Figure 4 of the drawings illustrates one of the clamps 90 in detail. Trunnions 9! project from the opposite sides of the die bodies 60 and are rotatably received in bosses 92 on the adjacent clamps 90. Removable nuts 93 are threaded on the trunnions 9| to prevent disengagement of the trunnions from the clamp bosses 92. Spacers 94 are arranged on the trunnions 9| to hold the clamps 90 spaced away from the die assemblies 50. There may be any desired or required number of spaced pairs of clamps 90 provided on the cables 9'6 to carry the die assemblies 50. The die assemblies 50 are supported by the trunnions 9| and clamps 90 to hang between the two cables 86.

In operating the apparatus of Figures 3 and 4 to form the workpieces 62 by the method of the invention, the shaped or formed workpieces are removed from the die assemblies 50 as the assemblies successively reach the vessel 52 and the new or unformed workpieces 62 are assembled or secured in the die structures positioned to enter the ocean. By intermittently rotating the drum 81 in one direction the die assemblies 50 are successively brought to the vessel 52 for the removal of the formed workpieces 62 and for the insertion 10 of the new workpieces. The intermittent advancement of the drum 8'! also successively lowers the die assemblies 50 to the maximum depth for the full shaping or forming of the workpieces 62 to the configuration of the die cavities 6! by the hydrostatic pressures of the ocean or lake. With the apparatus of Figures 3 and 4, it is possible to maintain a production line operation wherein a number of parts of the same shape, size, etc. or of different shapes and sizes, are drawn or formed. Thus a minimum of equipment is required in the economical forming of a large number of parts. As illustrated in Figure 3, the derrick means It may be utilized to facilitate the handling of the die assemblies 50 at the vessel Having described only typical forms of the invention I do not wish to be limited to the specific details herein set forth, but wish to reserve to myself any variations or modifications that may appear to those skilled in the art or fall within the scope of the following claim.

I claim:

A die assembly for utilizing the hydrostatic pressures in a deep body of water for forming sheets, plates, and like workpieces, comprising, a die body having a die face, an external die cavity formed in said face shaped to conform to the shape desired to be produced on a workpiece, means for securing the marginal portions of the workpiece to the die face with theworkpiece extending across the mouth of the external die cavity and closing the same, said die face having a sealing groove, a sealing ring arranged in said groove to seal the inner side of said workpiece, said die body having an internal cavity communicating with said external die cavity to receive air as it is displaced from said external die cavity, said die body having a port communicating with said internal cavity, a tubular insert mounted in said port having an internal valve seat, and a ball valve yieldably urged against said valve seat in the direction of said internal cavity so as to permit air under predetermined pressure to exhaust from said internal cavity without allowing the water to enter therein.

FREDERICK C. HOFFMAN.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Ganots Physics, Pub. by Wm. Wood and Co., New York, 1919, pp. 97, 98, 99, and 101, Copy in Div. 14.