US3096738A - Method of shaping sheet metal wheel covers - Google Patents

Description

July 1963 M. J. CELOVSKY METHOD OF SHAPING SHEET METAL WHEEL COVERS 5 Sheets-Sheet 1 Original Filed Sept. 25, 1957 IIIIIIIIIIII INVENTOR. Mtk eel I flelor BY A 'I I'ORNEYS July 9, 1963 M. J. CELOVSKY 3,096,738

METHOD OF SHAPING SHEET METAL WHEEL COVERS Original Filed Sept. 23, 1957 5 Sheets-Sheet 2 IN V EN TOR. Mzk a 6*! J (e/onsfiy WAMW. wig/$449M A TTORNISYS July 9, 1963 M. J. CELOVSKY METHOD OF SHAPING SHEET METAL WHEEL COVERS Original Filed Sept. 25. 1957 5 Sheets-Sheet 3 INVENTOR. Mztae/ (elm L 4 BY Wm W M W ATTORNEYS METHOD OF SHAPING SHEET METAL WHEEL COVERS Original Filed Sept. 25. 1957 5 Sheets-Sheet 4 INVENTOR. Mz'oeel IQ/orgy BY WW W ATTORNEYS United States Patent 3,096,738 METHOD OF SHAPING SHEET METAL WHEEL COVERS Michael J. Celovsky, Detroit, Mich, assignor to Lyon Indorporated, Detroit, Mich, a corporation of Delaware Original application Sept. 23, 1957, Ser. No. 685,493, now

Patent No. 3,016,853, dated Jan. 16, 1962. Divided and this application Nov. 25, 1960, Ser. No. 71,670

3 Claims. (Cl. 113-116) The present invention relates to improvements in shaping of sheet metal wheel covers and more particularly concerns the final shaping of the marginal structure of drawn circular sheet metal covers which are adapted to be applied to the outer sides of vehicle wheels.

The present application is a division of my copending application Serial No. 685,493 filed September 23, 1957, now Patent No. 3,016,853 granted January 16, 1962.

A highly desirable method of making wheel covers is disclosed in the patent of George Albert Lyon, No. 2,7 07,- 449, issued May 3, 1955'. A salient feature of that method resides in the turning radially outwardly an axially projecting rib at juncture of an axial flange having retaining means thereon and the body portion of the cover, so as to increase the overall diameter of the cover and also to provide a concealing, overhanging margin for the retain ing means. However, under certain circumstances and particularly where a generally open high ridge contour is to be provided on the margin of the cover and including the out-turned portion, a substantial problem is encountered in a tendency for the underturned flange portion of the turned marginal structure intermediate the retaining fingers provided as the cover retaining means to buckle or twist as the shaping pressure is applied to the cover margin. This tendency toward buckling is especially pronounced where an extremely narrow axially turned extremity of the underturned flange is located between the retaining fingers.

It is accordingly an important object of the present invention to provide an improved method for effectively providing an out-turned high ridge contour marginal formation on a wheel cover without danger of warping the material in the underturned flange of the cover margin between retaining finger extensions on the underturned flange.

Another object of the invention is to provide an improved method of marginally shaping sheet metal wheel covers in a manner enabling substantial economy in the use of material.

A further object of the invention is to provide an improved method of shaping marginal portions of wheel covers as the margin is being finally shaped, whereby to maintain a proper symmetry throughout the marginal formation.

Other objects, features and advantages of the present invention will be readily apparent from the following description of a preferred embodiment thereof taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is an outer side elevational view of a wheel structure having a cover made according to the present invention;

FIGURE 2 is an enlarged fragmentary radial section-a1 detail view taken substantially on the line 11-11 of FIG- URE 1;

FIGURE 3 is a fragmentary sectional detail view taken substantially on the line III-III of FIGURE 1;

FIGURE 4 is a fragmental radial sectional View through a sheet metal cover blank in a partial stage of shaping thereof;

FIGURE 5 shows the partially formed blank in a further stage of shaping;

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FIGURE 6 shows the same blank in still a further stage of shaping;

FIGURE 7 is a vertical fragmentary radial sectional detail view through die apparatus for practicing the method of the present invention;

FIGURE 8 is a fragmentary vertical radial sectional detail view through the same die apparatus but taken in a different plane; and

FIGURE 9 is a sectional detail View similar to FIG- URE 8 but showing the die apparatus as the parts thereof appear at the conclusion or" a cover margin shaping stroke.

Referring to FIGURES l, 2 and 3, a wheel cover '15 is dimensioned for substantially overlying the outer side of a Vehicle wheel including a wheel body or spider 17 supporting a multi-flange drop center tire rim 18 having a generally axially extending and radially inwardly facing annular intermediate flange 19 merging into a terminal flange 20 and adapted to support a pneumatic tire 21.

The cover 15 is adapted to be made by die pressing or drawing from suitable sheet material such as stainless steel, brass or the like. Centrally the cover comprises a crown portion 22 for substantially overlying the wheel body 17 and merging with a generally inwardly dished annular intermediate portion 23 from which extends generally radially and axially outwardly an annular tire rim overlying portion 24. On a generally axially outwardly projecting reinforcing annular rib or ridge juncture 25 at the radially and axially outwardlymost side of the cover portion 24 is an annular generally radially outwardly and axially inwardly sloping marginal portion 27 provided with an underturned extremity bead-like open rib reinforcing and finishing edge 28 for bottoming against the terminal flange 20 adjacent juncture thereof with the intermediate flange 19. Extending radially inwardly from the turned edge 28 is a short annular underturned flange portion 29 which, inwardly beyond the inside diameter of the intermediate flange 19 is provided with cover retaining means, herein in the form of a plurality of integral generally axially inwardly extending retaining finger extensions 30 which are constructed and arranged to telescope into the intermediate flange 19 and retainingly engage the rim flange through the medium of turned generally radially and axially outwardly oblique short and stiff retaining finger terminals 31 which effect a firm gripping biting-like self-retaining engagement with the surface of the rim flange under resilient tension of the retaining fingers 30 which are placed under radially inward resilient deflection from a slightly greater diametar at the tips of the terminals 31 incident to mounting of the cover on the wheel. In applying the cover to the outer side of the wheel, of course, a valve stem opening 32 in the cover portion 24 is registered with a valve stem 33.

In a preferred construction, there are four of the fingers 30 derived from the material at four corners of a square blank, and with each of the fingers of substantial width, comprising in a typical structure about /s of the perimeter of the circle described about the fingers, and with each of the resilient fingers sub-divided into a plurality of individual finger extremities 34 by shallow sub-dividing notches 35 (FIG. 6).

Intermediate the finger extensions 30, the undertu-rned flange 29 is provided with only a short turned extremity 35, if anything at all, serving as a reinforcement between adjacent ones of the finger extensions 30. This construction, it will be evident, provides a highly resilient cover marginal structure enhancing the resilient characteristics of the retaining fingers 30.

Drawing of the cover 15 may proceed generally in accordance with the method as taught in Patent 2,707,449 until the final shaping of the marginal structure of the 1 cover. To this end, in the initial phases of the drawing of the sheet metal blank, the crown portion 22, the intermediate portion 23 and the radially outer portion 24 of the cover are drawn to shape, with the portion 24 extended radially and axially outwardly into an annular axially inwardly opening hollow axially outwardly projecting rib R having a radially inner side wall joining the body of the cover through the intermediate portion 23. From the radially outer side or wall of the rib projects a flat margin M comprising primarily material from the four corners of a square blank. Thereafter, the fiat marginal material M is worked into axially inward direction to afford a generally cylindrical radially outer side wall for the rib R, and with the cover retaining means on its free portion, comprising the retaining fingers 30 trimmed to afford the sub-divisions 34 thereof, and the finger terminals 31 are formed. Then, the rib R is partially collapsed and the walls thereof are turned generally radially outwardly into concealing relation to the cover retaining mean-s, that is, the retaining fingers 30, while maintaining the axial disposition of the retaining fingers 30 axially inwardly beyond a transverse or circumferential shoulder bend line 37, with the outwardly tilted rib R remaining open at the inner side thereof. The cover as formed up to this point as generally depicted in FIGS. 4, and 6, and with the inner wall of the turned rib facing generally axially outwardly and the outer wall of the rib facing generally axially inwardly, is now ready for final shaping of the rib R into the reinforced, ridged marginal structure of the finished cover.

Bending and shaping of the turned out rib R to provide from the radially inner side wall portion thereof the principal area of the marginal portion 27, and from the spaced radially outer side wall or flange thereof the underturned flange 29 and the radially outer extremity of the cover portion 27, is effected by forming pressure applied to the radially inner portion of the rib R while the remaining portions of the cover, and more particularly the immediately adjacent portion 24 of the cover, are held to shape. This accomplished advantageously in the die apparatus of FIGURES 79.

In a preferred form, the die apparatus includes a lower die assembly having a preferably stationary die bed plate or block 38 carrying attached thereto a base ring 39 supporting an upstanding forming die ring structure 40. On its upper face, the die ring 40, as best seen in FIGURE 7, is provided with a transverse contour complementary and conformably receptive of the inner side of the annular dished cover portion 23 in a circular groove-like inner upper marginal hollow or recess 41 from which slopes generally radially outwardly and axially upwardly an oblique face surface 42 conform-able to the sloping radially outer surface 24 of the cover. At its upper end, the forming face or surface 42 terminates in a generally axially upwardly facing annular rib or ridge 43 which is shaped to conform to the desired axial-1y inner surface of the marginal rib or ridge into which juncture of the cover portions 24 and 27 is to be ultimately shaped. At its radially outer side, the forming ridge 43 is provided with a downwardly and radially outwardly generally oblique forming surface 44 against which the ridge end portion of the annular cover margin 27 is to be shaped. A cylindrical radially outer circumferential wall surface 45 on the ring die member 40 is of a diameter to receive telescopically thereabout the cover retaining finger extensions in freely slidable but close relationship.

Centrally slidably guided by the inner periphery of the die ring member 40 is a die member pad 47 having a crown contour receptive conformably of the inner surface of the cover crown 22 in complementary relation. Normally the cover supporting central pad member 47 is supported by a suitable number of upward biasing springs 48, with the crown of the supporting pad member elevated substantially above the forming surfaces of the ring member 40 to support the cover clear of the forming ring member 40.

Cooperatively related in reciprocal forming stroke relation above the lower die assembly is an upper forming die assembly which includes a circular hold-down pressure die member 49 having a lower face contoured to fit complementally into the dished cover pontion 23 and conformable with the adjacent portions of respectively the crown supporting die member 47 and the radially outer cover portion 24, with the outer perimeter of the die member 49 of a diameter coincident with the tip of the forming ridge 43 of the lower die ring member 40. Reciprocable support for the die member 49 is provided by a supporting plate member 50 which may be removably secured to the underside of a press ram or block member 51. Suitable annular series of bolts 52 connect the die member 49 to the supporting plate 50 and are reciprocably mounted in the plate member 50 to enable support of the die member 49 a limited spaced distance below the supporting plate 50, into which spaced relation the die member 49 is normally urged by yieldable compression springs 53. Thereby, as the upper die assembly is projected toward the lower die assembly in a concentric forming stroke, the die member 49 moves as the initial contacting portion of the upper die assembly into hold-down thrusting engagement against the cover supported in elevated relation upon the lower yieldable supporting die member 47. By having the lower die member supporting springs 48 slightly more yieldable than the upper compression springs 53, continued downward thrusting movement of the upper die assembly causes the lower supporting die member 47 to yield downwardly in opposition to the springs 48 under the thrust of the hold-down and pressure die member 49 until the cover marginal formation is brought into engagement with the forming ring die member 40.

When the cover portions '23 and 24 bottom against the ring die complementary surfaces 41 and 42, respectively, as thrust by the upper ring die member 49, yielding of the springs 53 under the continued thrust of the press ram carries a forming die ring member 54 fixedly supported by the supporting plate 50 into marginal shaping engagement with the turned cover marginal rib R. On its inner diameter, the die ring 54 provides a cylindrical guide surface for the corresponding slidably complementary outer diameter cylindrical surface of the upper hold-down die member 49.

The construction and relationship of the die ring member 54 with respect to the upper die assembly and more particularly the hold-down die member 49' is such that normally the die member 49 is projected downwardly sufficiently beyond the lower face of the forming die ring 54 to make initial engagement with the upper opposing surfaces of the partially formed cover in advance of the die ring 54 in the initial phases of the forming stroke of the upper die assembly. Thereby, the partially formed cover is driven into firm seating relation with the lower upwardly facing forming die ring 40 before the upper die ring member 54 acts formingly upon the partially turned out cover rib R.

When the partially formed cover has been clamped between the opposing surfaces of the lower die ring 40 and of the upper hold-down die member 49, continued downward thrusting movement of the upper die assembly carries the lower forming face of the die ring member 54 into forming engagement with the freely radially outwardly projecting cover marginal rib R. As a result, a lower forming face forming surface 55 on the inner margin of the forming face of the die ring member 54, opposing and complementary to the forming surface 44 of the lower die ring member 40, and contoured to the ultimately desired shape for the marginal cover portion 27, formingly presses down against the now upwardly facing cover marginal rib R. In this instance the forming surfaces 44 and 55 are complementally respectively concavely and convexly shaped on a substantial radius.

Progressively as the forming thrust pressure of the forming surface 55 acts upon the cover rib R, the radially inner wall portion of the rib R is bent down about the fulcrum provided by the forming ridge 43- of the lower die ring 40 uniformly entirely about the circumference of the cover, and the radially inner wall of the rib R is converted into the cover marginal portion 27 between the forming surfaces 44 and 55. At the same time, the radially outer wall of the cover marginal rib R is bent down to a substantially horizontal plane to provide the underturned flange 29 of the cover, with some of the material of the radially outer rib wall working over into the radially outermost extremity portion of the cover marginal portion 27, at the axially outer side of the juncture extremity 23 or edge of the cover. This results in a substantial stiffening cold working of the marginal extremity of the cover for enhancing the self-sustaining highly resilient character of the margin of the completed cover.

While the cover margin is being completed by the interaction of the lower and upper die members 40* and 54, the axially extending retaining fingers 30 engage slidably in firmly backed up relation against the lower die ring outer peripheral face 45, thus maintaining their shape and generally cylindrical disposition to a predetermined circumference or diameter. At completion of the forming operation, as indicated in dash outline in FIG. 7, the retaining fingers 30 are, of course, concealed behind the cover margin, with the now completely radially turned out rib R of the cover providing a substantially larger diameter for the cover than described about the retaining fingers 30.

Although the retaining fingers 30 due to their substantial width and axial extent axially inwardly beyond the bend line shoulder 37 afford ample area for resisting twisting or buckling of the finger extensions or the aligned portions of the underturned flange 29 incident to the bending forces and stresses during the final marginal formation of the cover, due to the thorough backing of the substantial area of the retaining fingers 30' against the lower die ring back-up surface 45, a substantial problem is encountered isofar as the marginal areas between the fingers 30 is concerned. Since the slightly turned extremity of the underturned flange portion 29 affords no significant back-up engagement possibility against the back-up surface 45 of the lower die r-ing member, there is a tendency for the radially outer wall portion of the cover rib R to buckle and twist and deform during the final marginal formation of the cover between the lower die ring member 40 and the upper die ring member 54. To take care of this situation, the lower die ring member 40 is provided at suitable circumferentially spaced intervals, in the present instance at four intervals corresponding to the four between-finger areas of the cover margin, with respective supplemental retaining die members 57 (FIGS. 8-9). Operation of the holding or retaining members 57 is coordinated with forming strokes of the upper reciprocable die assembly.

The function of the die member 57 in each instance is to provide a positive anti-buckling back-up for the between finger areas of the radially outer wall portion of the cover rib R during marginal formation of the cover but to remain positively clear of the cover margin during any reciprocal or up and down movements of the cover margin relative to the lower die assembly before or after the restrike marginal formation completing actions of the die apparatus. To this end, the respective dies members 57 are movably mounted for actuation into and out of operative position during the forming stroke cyclical operation of the die apparatus. Herein, this is accomplished by providing the die member 57 with a body block 58 which may be of generally rectangular outline in plan and radially reciprocably slidably mounted on the lower supporting ring member 39 within a respective cut-out 59 in the lower forming die ring 40. This cut-out 59 is formed below the forming ridge 43 which thus remains continuous 6 and unbroken throughout the complete annulus of the forming ring member 40. However, the uppermost limit of the cut-out S9 is close enough to the divergent surfaces of the ridge 43 and more particularly the forming sur-' face 44 so that a radially outwardly projecting horizontally disposed holding rib nose 60 on the upper marginal extremity of the radially outer face of the die member body 58 is at the proper elevation to conformably engage above the lower and radially inner extremity portion of the radially outer flange wall portion of the cover rib R during the forming stroke of the die apparatus. Moreover, the upper or crown surface of the die member body 58 adjacent to the retaining rib nose 60 closely slidably engages as a supporting bearing with a downwardly facing flat bearing surface 61 on the underside of the portion of the forming ridge 43 that bridges across the gap provided by the clearance cut-out 59. Thereby, forming pressure against the bridging portion of the ridge 43 in each instance is eifectively prevented from damagingly deflecting the bridging portions of the ridge by virtue of the solid support aiforded by the movable die member. body 58 which rests solidly on the supporting die ring 39.

Normally the die member 57 is urged by a pair of compression springs 62 (FIG. 8) toward retracted position wherein the retaining nose rib '60 underlies the forming ridge 43 and Within the perimeter of the vertical radially outer surface 45 of the forming ring 40. Locating sockets 63 for the respective springs 62 are provided in a retaining block 64 mounted on the bed plate 38 within a respective locating notch in the outer periphery of the supporting die ring member 39. In the retracted position of the die member 57, .a clearance cut-back or recess 67 in the upper portion thereof radially inwardly from the nose rib 60 and generally conforming to the contour of the lower forming die ring surface 42 is provided to clear the cover portion 24 as the cover is driven downwardly by the upper hold-down die ring member 49 during a forming stroke of the upper die assembly.

Means are provided for effecting protraction of the holding rib nose 60 in coordination with the forming stroke of the upper die assembly. Herein this is effected by means of a cam die member 68 carried by the upper ram portion 51 in backed up relation against the outer periphery of the head plate 50 and the forming ring member 54 (FIGS. 8 and 9). On its lower end portion which projects suitably below the lower face of the forming die member 54, the cam die member 68 has an oblique cam surface 69 which faces generally outwardly and is engageable in proper coordination with the forming die ring 54 to engage a complementary cam surface 70 provided at the outer side of a clearance opening 71 in an integral outwardly projecting actuating tongue 72 on the retaining die body 58 and slidably supported upon the retaining block 64 which is provided with a clearance recess 73 in the upper face thereof into which the driving cam end of the cam die can project in operative relation as seen in FIG. 9. A pair of removable gibs 74 cooperate with lateral longitudinal side flanges 75 on the actuating tongue 72 to serve as reciprocation guides for the tongue.

The relationship of the cam die member 68 to the actuating tongue '72 is such that after the partially formed cover has been pressed by the hold-down ring die member 49 against the forming die member 40, and before the forming die member 54 exerets any appreciable forming pressure on the cover rib R, the driving cam 69 engages the cam surface 70 and begins to move the die member 57 outwardly into position over the underlying extremity of the between-finger extent or area of the radially outer flange wall of the cover rib R. Hence, as the cover margin is formed by the forming surface 55, the retaining nose 60 is projected progressively radially outwardly into the radially inwardly opening groove defined between the formed cover marginal portions 27 and 29 and more particularly is driven toward the underturned flange turned extremity 35 which engages firmly against a complementally formed undersurface 77 provided in undercut relation on the lower side of the rib nose 60, as best seen in FIG. 9. Since the rib nose 60 and the undercut forming and retaining surface 77 thereof are circumferentially curved complementary to and conformable to the curvature of the cover margin, a thorough back-up support for the underturned between-finger flange portion of the cover margin is provided which prevents buckling or undesirable distortion but maintains substantially symmetry with respect to the portions of the underturned flange aligned with the retaining fingers 30.

After the forging operation or stroke, the upper die assembly is backed off by the actuating means of the press and as an incident thereto, the cam die member 68 releases the die member 57 in each instance. Hence, the biasing springs 62 retracts the die member 57 to withdraw the retaining and forming nose rib '60 from over the cover flange 29 and out of the interior of the radially inwardly opening groove or chamber now defined within the turned-over cover rib R in the finished cover margin. Then, the spring biased supporting pad 47 of the lower die assembly can act as a stripper to elevate the now fully formed cover clear of the lower die forming ring 40 for removal from the die assembly and replacement by a succeeding partially formed cover to be subjected to the action of the die assembly on a repetition of the forming stroke cycle.

It will be understood that modifications and variations may be effected without departing from the scope of the novel concepts of the present invention.

' I claim as my invention: l 1. In a method of making a sheet metal wheel cover, drawing a sheet metal blank to provide a circular cover body and an annular outer marginal narrow rib projecting in one axial direction with a radially inner wall joining said body and a radially outer wall extending in the opposite axial direction and having cover retaining means on the free portion thereof, bending said rib and thus said walls generally radially outwardly into concealing relation to said cover retaining means and thereby turning said inner wall to face generally in said one axial direction and said outer Wall to face in said opposite axial direction, then bending said turned inner wall to provide a marginal portion which slopes angularly in generally said opposite axial direction and radially outwardly from an annular reinforcing ridge juncture with the cover body, and at the same time moving said turned outer wall and said retaining means in said opposite axial direction and into substantially spaced relation to said turned and bent inner wall marginal portion and said reinforcing rib juncture and relative to said cover body.

2. In a method of forming sheet metal 'wheel covers, (a) initially shaping and forming a sheet metal blank into a cover member including a circular body having a marginal rib projecting in one axial direction and having (1) radially inner and outer spaced wall port-ions (2) with the radially outer wall portion provided with retaining finger extensions projecting axially in the opposite direction from the rib,

(b) bending the rib generally radially outwardly to a larger diameter than the diameter of the finger extensions for concealingly overlying the finger extensions and which includes bending said outer wall portion along a juncture line with said finger extensions to maintain the finger extensions in substantially fixed circumferential diametrical relation,

(0) bending said radially inner Wall portion on a circular line juncture with the circular body and swinging said radially outer wall portion to slope in generally said opposite axial direction,

(d) and while thus swinging the radially inner wall portion, moving said previously bent radially outer wall portion and the finger extensions in said axially opposite direction and relative to said circular body with the finger extensions slidably moving along an axially extending back-up surface so as to maintain the finger extensions in substantially fixed circumfercntial diametrical relation.

3. In a method of forming a sheet metal wheel cover,

(a) initially shaping and forming a sheet metal blank into a cover member including a circular body having -(1) a marginal rib projecting in one axial direction and having radially inner and outer spaced wall portions (2) with the radially outer wall portion having retaining finger extensions projecting axially in the opposite direction from the rib (3) and separated by substantial edge areas of the outer wall portion generally aligned circumferentially with the baseportions of the fingers at juncture thereof with the outer wall portion,

(b) bending the rib generally radially outwardly to a larger diameter than the diameter of the finger extensions for concealinglyoverlying the finger extensions and including turning over the outer wall portion by bending along said junctures,

(c) then bending said radially inner wall portion on a circular line joining it to the circular body to swing into a sloping position generally in said opposite axial direction (d) and at the same time moving said bent outer wall portion and said finger extensions in said opposite axial direction relative to the cover body while slidably supporting the finger extensions against an axially extending back-up surface so as to maintain the finger extensions in substantially fixed circumferential diamctrical relation, t

(e) and during such swinging of the inner wall portion supporting said edge areas against buckling distortion whereby to maintain such areas in general circumferential alignment with the portions of the outer wall portion aligned with the finger extensions.

References Cited in the file of this patent UNITED STATES PATENTS 2,101,888 Ambrosius Dec. 14, 1937 2,878,769 Lyon Mar. 24, 1959 2,921,548 Lyon Jan. 19, 1960 2,942,569 Lyon June 28,: 1960

Claims (1)

1. IN A METHOD OF MAKING A SHEET METAL WHEEL COVER, DRAWING A SHEET METAL BLANK TO PROVIDE A CIRCULAR COVER BODY AND AN ANNULAR OUTER MARGINAL NARROW RIB PROJECTING IN ONE AXIAL DIRECTION WITH A RADIALLY INNER WALL JOINING SAID BODY AND A RADIALLY OUTER WALL EXTENDING IN THE OPPOSITE AXIAL DIRECTION AND HAVING COVER RETAINING MEANS ON FREE PORTION THEREOF, BENDING SAID RIB AND THUS SAID WALLS GENERALLY RADIALLY OUTWARDLY INTO CONCEALING RELATION TO SAID COVER RETAINING MEANS AND THEREBY TURNING SAID INNER WALL TO FACE GENERALLY IN SAID ONE AXIAL DIRECTION AND SAID OUTER WALL TO FACE IN SAID OPPOSITE AXIAL DIRECTION, THEN BENDING SAID TURNED INNER WALL TO PROVIDE A MARGINAL PORTION WHICH SLOPES ANGULARLY IN GENERALLY SAID OPPOSITE AXIAL DIRECTION AND RADIALLY OUTWARDLY FROM AN ANNULAR REINFORCE RIGID JUNCTURE WITH THE COVER BODY, AND AT THE SAME TIME MOVING SAID TURNED OUTER WALL SAID RETAINING MEANS IN SAID OPPOSITE AXIAL DIRECTION AND INTO SUBSTANTIALLY SPACED RELATION TO SAID TURNED AND BENT INNER WALL MARGINAL PORTION AND SAID REINFORCING RIB JUNCTURE AND RELATIVE TO SAID COVER BODY.

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