Tire Retreading Bladder

This invention relates to a novel method of retreading tires either manually, semi-automatically or fully automatically by inserting an annular bladder within the interior of a tire and positioning the tire within a mold, and creating an annular low pressure area between marginal portions of the bladder and a pair of axially opposed bead aligner wheels.

The foregoing object creates an annular partial vacuum between marginal edge portions of each bladder and the associated bead aligner wheels to assure that upon further inflation of the bladder, the tire is urged into intimate conformity with the mold and, just as importantly, that there is no misalignment between the assembled components during the retreading operation.

An object of this invention is to provide a novel tire retreading bladder of a generally U-shaped cross-sectional configuration defined by a bight portion and a pair of legs each terminating in a generally circular axially outwardly directed annular sealing bead and having inboard thereof a plurality of circumferentially spaced valleys to which pressurized air may be introduced into and exhausted from the bladder, each leg having interior and exterior surfaces, means disposed along each of the exterior surfaces for venting air from between such exterior surfaces and an interior surface of an associated tire adapted to receive therewithin the bladder, and each exterior surface defining between radially inboard portions of each venting means and the associated sealing bead a generally smooth uninterrupted annular sealing surface adapted to form a hermetic line of sealing with an associated bead aligner wheel outboard of the associated terminal edge.

Still another object of this invention is to provide a novel tire retreading bladder of the type aforesaid wherein the valleys open in an axial direction and are in axially opposing relationship to each other.

Still another object of this invention is to provide a novel tire retreading bladder of the type aforesaid wherein the bladder has a cross-sectional thickness greatest at the beads and the thickness of the legs diminish in a direction toward the bight portion, and the venting means include ribs projecting above the exterior surfaces and being disposed generally radially.

Yet another object of this invention is to provide a novel tire retreading bladder which includes a generally annular member of a U-shaped cross-section defined by a bight portion and a pair of legs having respective terminal edges and interior and exterior surfaces with means disposed along each of the exterior surfaces for venting air from between such exterior surfaces and an interior surface of an associated tire adapted to receive therewithin the bladder, each of the venting means on each of the exterior surfaces having a radially inboard portion terminating radially short of the associated terminal edge, each exterior surface defining between the radially inboard portions of each venting means and the associated terminal edge a generally smooth uninterrupted annular sealing surface, and the venting means being in the form of a plurality of pairs of closely adjacent ribs with each pair of ribs setting off a venting groove therebetween.

Still another object of this invention is to provide a novel retreading bladder of the type immediately aforesaid wherein each pair of ribs and associated venting grooves on the exterior surfaces merge with each other across the bight portion, and the ribs including venting slots along the length thereof with the slots in the ribs of each pair of ribs being in generally radially offset relationship to each other.

With the above and other objects in view that will hereinafter appear, the nature of the invention will be more clearly understood by reference to the following detailed description, the appended claims and the several views illustrated in the accompanying drawings.

FIG. 1 is a perspective front view of a novel automatic retreading machine constructed in accordance with this invention, and illustrates a pair of platens in the open position thereof carrying segmented matrices with a tire located upon a lower bead aligner wheel.

FIG. 2 is a front elevational view of the machine of FIG. 1 partially in cross-section, and illustrates the matrices closed and a bladder under pressure maintaining a tire to be retreaded in conformity with the interior of the matrices.

FIG. 3 is a cross-sectional view taken generally along line 3--3 of FIG. 2, and particularly illustrates means for imparting motion to the bead aligner wheels and the drive for relatively moving the platens carrying the matrices relative to each other.

FIG. 4 is a fragmentary enlarged sectional view of a tire positioned within the closed matrices.

FIG. 5 is a fragmentary enlarged sectional view of a tire positioned within the opened matrices, and particularly illustrates the manner in which a partial vacuum retains the tire beads against the bead aligner wheels.

FIG. 6 is a fragmentary top plan view of the bladder associated with the machine of FIGS. 1 through 3, and illustrates raised ribs upon an exterior surface defining therebetween vent means or passages terminating short of enlarged beads at inner edges of the bladder.

FIG. 7 is a sectional view taken generally along line 7--7 of FIG. 6, and more fully illustrates the raised beads above the exterior surface of the bladder and notches in opposing surfaces of the beads defining means for permitting the introduction of fluid into and the removal of fluid from the bladder interior.

FIG. 8 is a fragmentary enlarged cross-sectional view taken along line 8--8 of FIG. 6, and more fully illustrates the manner in which the notches of the bladder beads are in axial alignment.

FIG. 9 is a view looking axially at one of the pair of bead aligner wheels of this invention, and illustrates a circular continuous uninterrupted sealing rib and a plurality of venting grooves adapted to be placed in fluid communication with atmosphere through bores in a flange of the bead aligner wheels.

FIG. 10 is an axial sectional view taken through a pair of bead aligner wheels of the invention, and illustrates the manner in which fluid is introduced into the bladder as well as the manner in which air is vented to atmosphere from between the exterior surface of the bladder and an interior surface of a tire undergoing a recapping operation.

FIG. 11 is a fragmentary elevational view partially in section of a modification of the machine of FIGS. 1-3, and illustrates the manner in which the diameter of a tire is foreshortened by being mechanically clamped to the bead aligner wheels in lieu of a vacuum clamping to be described hereinafter with respect to the machine of FIGS. 1-3.

FIG. 12 is a sectional view identical to FIG. 11 but illustrating the matrices in their closed position.

FIG. 13 is a fragmentary top plan view of another bladder constructed in accordance with this invention for use in the machine of FIGS. 1-3, and illustrates pairs of raised ribs upon an exterior surface defining therebetween venting means in the form of a groove associated with and between each pair of raised ribs.

FIG. 14 is a sectional view taken generally along line 14--14 of FIG. 13, and illustrates a plurality of slots in the raised ribs which augment the venting of air from between the exterior surface of the bladder and an associated interior surface of a tire to be retreaded.

FIG. 15 is a sectional view taken generally along line 15--15 of FIG. 13, and illustrates beads at inboardmost peripheries of the bladder having aligned notches for pressurizing and depressurizing purposes.

FIG. 16 is a sectional view taken generally along line 16--16 of FIG. 13, and illustrates details of one of the pair of ribs, the groove and the associated slots.

FIG. 17 is an axial sectional view similar to FIG. 10, but illustrates the bladder of FIGS. 13 through 16 during a recapping operation.

FIG. 18 is a sectional view similar to FIG. 16, except the thickness of the bladder is not reduced in the area between the venting ribs.

Reference is first specifically made to a machine 10 of FIGS. 1 through 3 which includes a conventional base 11 which has secured thereto in a conventional manner a pair of upstanding cylindrical supports 12, 13. An upper platen 14 is fixedly secured to an upper end portion (unnumbered) of the supports 12, 13 by nuts (unnumbered) in the manner readily apparent from the upper right hand portion of FIG. 2. The upper end portions (unnumbered) of the supports 12, 13 are, of course, threaded to receive the nuts and the latter may be adjusted or threaded to achieve alignment between the upper fixed platen 14 and a lower movable platen 15.

The movable platen 15 is provided with conventional bushings (unnumbered) which surround the supports 12, 13 and, thus, the platen 15 may be readily moved between the open position (FIG. 1) thereof and the closed position illustrated in FIG. 2.

Means for imparting relative movement between the platens 14, 15 is generally designated by the reference numeral 20 and includes an electric motor 21 connected to a suitable electrical source (not shown) which drives a sprocket 22 keyed to an output shaft 23 of a gear reducer 24. A drive chain 25 is entrained about the sprocket 22 and about a sprocket 26 (FIG. 2) suitably secured to a tubular stub shaft 27 which in turn is welded or otherwise secured to an internally threaded nut 28. A reciprocal member 30 in the form of a screw is threaded within the nut 28 in the manner readily aparent from FIGS. 2 and 3. A lower end portion 31 of the screw 30 is capable of descending into a suitable lubricant, such as oil O, maintained within a generally cylindrical reservoir or sump 32. Accordingly, upon the ascent of the screw 30, the oil deposited upon the end portion 31 will maintain the threads (unnumbered) of the nut 28 continuously lubricated during the reciprocal motion imparted to the platen 15.

An upper end portion 33 of the screw 30 is provided with means, generally designated by the reference numeral 35, for achieving self-centering between the platen 15 and the platen 14. The means 35 is simply a convex surface on the end portion 33 of the screw 30 which bears against a planar (unnumbered) surface of the platen 15. Thus, if there is any misalignment of a minor nature between the platens 14, 15 and the matrices associated therewith, to be described more fully hereinafter, the platen 15 will tilt or cock as need be to an extent permitted by the bushings (unnumbered) associated with the supports 12, 13, thus, assuring alignment between the matrices and the tire therein. Furthermore, the platen 15, though of a relatively rigid construction, can still flex somewhat under the force applied thereto by the screw 30 and this in turn achieves a self-adjusting or self-centering between the platens 14, 15 and the matrices carried thereby.

An upper bead aligner wheel 40 and a lower bead aligner wheel 41 (FIGS. 2, 3 and 10) are reciprocally carried by the respective platens 14, 15 and are mounted thereon for relative reciprocals movement toward and away from each other in a conventional manner. More specifically, a pair of fluid motors 42, 43 carried by the upper platen 14 include identical pistons 44 (only one of which is illustrated in FIG. 3) which are secured to the upper bead aligner wheel 40 for imparting motion thereto in a conventional manner. Likewise, fluid motors 45, 46 carried by the lower platen 15 include piston rods 47 (only one of which is illustrated) for reciprocating the bead aligner wheel 41 in the manner readily apparent from FIG. 3.

During the reciprocal motion imparted to the bead aligner wheels 40, 41 guidance is provided by guide rods 50, 51 secured to the bead aligner wheel 40 and by the guide rods 52, 53 (FIG. 2) secured to the bead aligner wheel 41. The rods 50, 51 and 52, 53 are slidably received in tubular guides 54, 55, respectively, (only one of each being shown in FIG. 2) carried by the respective platens 14, 15.

Conventional segmented matrices 56, 57 are carried by the platens 14, 15 and are operative in the manner described in commonly assigned abandoned U.S. Ser. No. 287,826 in the name of Kenneth T. MacMillan in favor of which was filed a Rule 60 Continuation Application under Ser. No. 514,486 filed Oct. 15, 1974 which was in turn abandoned in favor of another Rule 60 Continuation Application filed Apr. 16, 1975 under Ser. No. 568,734, and now abandoned. Through specifically utilizing segmented matrices 56, 57, the machine may be modified in the manner to be described hereinafter in order that the same can utilize "full" or nonsegmented circular matrices.

Reference is now made specifically to FIG. 10 which illustrates the bead aligner wheels 40, 41 in more specific detail. Since the bead aligner wheels 40, 41 are essentially of an identical construction, like reference numerals have been applied thereto. The bead aligner wheels 40, 41 each include opposing sealing surfaces 60, 60 which are essentially normal to the axis of the bead aligner wheels 40, 41 and to the axis of the screw 30. Radially outboard of each of the sealing surfaces 60, 60 is a raised continuous uninterrupted circular rib 61, 62 (FIGS. 9 and 10) each of which is cooperative with a bladder 65 in a manner to be described more fully hereinafter. Radially outboard of each rib 61, 61 is a generally curved shoulder or surface (unnumbered) which has formed therein a plurality of bleed notches or grooves 62,62 each of which terminates at a bore 63 formed in a flange 64 of each bead aligner wheel 40, 41. The notches 62 and bores 63 cooperate with the bladder 65 in a manner to be described more fully hereinafter to bleed entrapped air from between an exterior surface of the bladder 65 and an interior surface of a tire T between the matrices 56, 57 to atmosphere during the pressurization of the interior of the bladder 65.

It is mandatory to preclude the bladder 65 from being pinched during the closing of the matrices 56, 57 as well as during the closing of the bead aligner wheels 40, 41 and, accordingly, one or both of the bead aligner wheels 40, 41 are provided with a plurality of axially projecting bosses 66 (FIG. 9). In the embodiment of the invention illustrated, the bead aligner wheel 41 has four such bosses 66 and during the closing of the bead aligner wheels 40, 41, the bosses 66 contact the sealing surface 60 of the bead aligner wheel 40 and assure that the bladder disposed therebetween will not be pinched. The bosses 66 are also preferably disposed with their axis on a common circle such that they also serve as means for locating the bladder upon the bead aligner wheels 40, 41, as will be described more fully hereinafter.

Inasmuch as it is necessary in keeping with the invention to inflate the bladder 65, a pressurized fluid, which is preferably heated air, is introduced into the space between the sealing surfaces 60, 60 of the bead aligner wheels 40, 41 through a port 67 which is in turn connected by a pipe 68 (FIG. 1) and a flexible conduit 70 to a suitable source (not shown) of a pressurized fluid as, for example, hot air or a heated, nonexploxive, noncompressible liquid or a source of steam or the like. Suitable conventional control means within a control panel 71 (FIG. 1) are provided for maintaining pressure internally of the bladder 65 at a desired level and suitable means may be provided for circulating the fluid media within the bladder 65. As an alternative, the fluid media need not be heated nor circulated within the bladder 65 and instead may be utilized simply to inflate the bladder 65 to a desired pressure with the heat required for the curing operation being achieved by conventionally heating the matrices 56, 57 electrically or by the circulation of a heating fluid therethrough.

Reference is now made specifically to FIGS. 6-8 of the drawings which more specifically illustrate the bladder 65 as a generally annular member of a U-shaped cross-section (FIG. 7) defined by a bight portion 72 and a pair of arms or legs 73, 74 terminating in inboardmost terminal edges of beads 75, 76, respectively. The cross-sectional thickness of the legs 73-74 is thickest adjacent the beads 75, 76 and tapers progressively radially outwardly to a thinner though generally uniform cross-sectional thickness in the area of the bight portion 72. This tapering permits the bight portion 72 to conform to the interior configuration of the tire prior to outward progressive conformation of the leg 73, 74 against the inner surface of the tire sidewalls, as will be described more fully hereinafter. An exterior surface 77 of the bladder 65 includes a plurality of radially directed raised ribs 78 between which are defined valleys 80 which serve as bleed or venting passages for air entrapped between the inner surface of the tire sidewall and the exterior surface 77 of the bladder 65 in conjunction with the bleed grooves 62 and the notches 63 of the bead aligner wheels 40, 41. In other words, as the bladder 65 is being inflated (FIG. 10), the bight portion 72 thereof begins to progressively conform to the inner surface of the crown (unnumbered) of the tire T and in doing so, air between is forced toward the tire beads (unnumbered). Air which would otherwise be thus entrapped is expelled through the vents 80, at least some or all of which are aligned with the notches 62 of the bead aligner wheels 41, 42 resulting in the passage of this air to atmosphere through the bleed bores 63 of both bead aligner wheels 40, 41.

In order to assure that the bladder 65 is pressurized, the beads 75, 76 of the bladder 65 have respective aligned notches, valleys or grooves 80, 81 (FIGS. 7 and 8). Therefore, upon the introduction of fluid into the bladder 65 in the manner indicated by the unnumbered headed arrows in FIG. 10, the aligned notches 80, 81 define port means for the introduction of such fluid into the bladder 65, as well as the exhausting therefrom.

A highly important feature of this invention is the manner in which the annular chambers A (FIG. 10) are formed between the sealing surfaces 60, 60, the ribs 61, 61, and the inboardmost portions of the arms 73, 74 of the bladder 65. Each annular chamber A is defined between two radially spaced annular sealing lines (unnumbered), a first of which is defined by the annular sealing contact between each of beads 61 and the annular portion of the bladder in contact therewith and a second of which is defined by the annular sealing contact between each of the surfaces 60 and the associated beads 75, 76. The significance of this feature is more specifically applicable to full circle matrices, as opposed to segmented matrices. In the former, the normal diameter of the tire T must be foreshortened in order that the full circle matrices may be closed without closing upon the tire T and/or assuring that the tire will be subsequently expanded from its foreshortened condition to seat properly within the full circle matrices. In order to fully appreciate this, reference is now made to FIGS. 4 and 5 of the drawings.

In FIG. 4, the matrices 56, 57 are shown closed and the inner surfaces thereof are in perfect conformity with the exterior of the tire T. The bladder 65 is, of course, pressurized at this point and due to the pressurization thereof, which is greater than atmosphere, the annular channels A are actually under a partial vacuum and, therefore, the beads 75, 76 are in hermetic sealing relationship with the surfaces 60, 60 of the bead aligner wheels 40, 41 and a tight hermetic seal is achieved between the ribs 61, 62 and the portions of the legs 73, 74 of the bladder 65 against which they contact. Therefore, upon the opening of the matrices, which in this case are full circle matrices, the partial vacuum within the annular chambers A holds the portions of the bladder legs 73, 74 inboard of the ribs 61, 61 tightly against the bead aligner wheels 40, 41. Accordingly, as the bead aligner wheels 40,41 move away from each other, the diameter of the tire T is foreshortened (FIG. 5) thereby permitting the matrices 56,57 to be fully closed prior to the movement of the bead aligner wheels 40, 41 toward each other to achieve the positive seating between the tire T and the matrices, as shown in FIG. 4. Thus, the built-up tire may be positioned in the manner shown in FIG. 5 and when the bladder is prrssurized, it will assume the position shown in this same figure. Thereafter, and with the bead aligner wheels 40, 41 spread apart, the full circle matrices are closed and, thereafter, the bead aligner wheels may be moved to the closed position of FIG. 4 incident to the performance of the curing operation.

Another machine 10' constructed in accordance with this invention is illustrated in FIGS. 11, 12 and components thereof corresponding to those of the machine 10 of FIGS. 1 thorugh 3 bear like reference numerals, though the same have been primed. In keeping with the construction of the machine 10', the matrices 56', 57' are full circle matrices, not segmented. As compared to the machine 10, the machine 10' utilizes the concept of foreshortening a tire T' prior to the closing of the matrices, but the beads thereof are mechanically gripped in the manner illustrated in FIG. 11. The mechanism includes a plurality of rods 90 passing through suitable guide bores (unnumbered) and terminating in angular ends 91. The opposite ends of the rods 90 are rotated and reciprocated by conventional apparatus.

The tire T' is inserted between the matrices 56', 57' when the latter and the platens 14', 15' are in their fully opened positions after which the bead aligner wheels 40', 41' are moved toward each other and the beads (unnumbered) of the tire T' are automatically located. Thereafter, the rods 90 are rotated from an out of the way position to the position shown in FIG. 11, and the bead aligner wheels 40', 41' are retraced to the illustrated position of FIG. 11. The bladder 65' is then inserted in the manner illustrated in FIG. 11 after which the full circle matrices 56', 57' are closed. Once the latter are closed, the bead aligner wheels 40', 41' then move toward each other to their final position (FIG. 12) and fluid is introduced into the bladder 65' to pressurize the interior sufficiently depending, of course, upon the cure time, temperature, tire compound, etc. involved.

The machines 10 and 10' are provided with suitable control means including, of course, the control cabinet 71 and the components thereof which, for the most part, are conventional. However, in keeping with this invention, the circuitry for the motor 21 includes a switch (not shown) carried by either of the platens 14, 15 such that upon the closing of the latter, the switch will be activated to de-energize the motor 21. Preferably, the switch actuates through a trip relay of a conventional construction on which the amperage may be adjusted to automatically shut off the drive motor 21 when the matrices 56, 57, or 56', 57' come together with sufficient force. When the motor 21 shuts off, a conventional break automatically locks, although the latter is not an absolute requirement of the system. However, due to this adjustable nature of the relay, it is unnecessary to adjust the distance between the platens at any time even if the matrices are changed or when spacers are inserted in a conventional manner, and this also makes the machines 10, 10' self-adjusting.

Reference is now made to FIGS. 13 through 17 of the drawings which illustrate another bladder 105 which is generally of a U-shaped cross-section (FIG. 14) and includes a bight portion 106 and a pair of legs 107, 108 terminating in inboardmost terminal edges or beads 110, 111. The bight portion 106 and the legs 107, 108 of the bladder 105 include an exterior or outer surface 112 and an interior surface 113, the latter of which defines a chamber 114 which is adapted to be inflated with pressurized air during a retreading operation (FIG. 17) in a manner to be described more fully hereafter, and, of course, the same chamber 114 is deflated or unpressurized after a retreading operation.

The thickness of the legs 107, 108 between the associated surfaces 112, 113 is generally uniform, as is that of the bight portion 106. However, positioned along the exterior surface 112 of the legs 107, 108 and the bight portion 106 are a plurality of pairs of means in the form of raised ribs 115 with each pair 115 being formed by individual ribs 116, 117 and between each adjacent ribs 116, 117 there is a valley 118 (FIG. 16) which is of a generally concave outwardly opening configuration having a lowermost surface (unnumbered) which is beneath the exterior surface of the legs 107, 108 and the associated bight portion 106. The individual ribs 116, 117 also include a plurality of grooves or slots 120, 121, respectively, which are on two inch centers and are each approximately one-eighth inch long. These slots, grooves or the like 120, 121 are also in staggered relationship to each other, as is most readily apparent in FIG. 13.

The means 115 and more specifically the ribs 116, 117 and each valley 118 therebetween all terminate short of the terminal edges 110, 111 and in so doing define a smooth uninterrupted annular area or zone on the exterior surface 112 of each of the legs 107, 108 against which the beads 61, 61 of the bead aligner wheels of FIG. 17 can seat and define therewith a circular line of hermetic sealing, agains as will be described more fully hereinafter.

The terminal edges 110, 111 of the respective legs 107, 108 terminate in axially opposite directed annular beads 125, 126 having generally right-cylindrical concentric inner and outer surfaces 127, 128 and 129, 130 (FIG. 14). Axially inboard portions (unnumbered) of the beads 125, 126 include frusto-conical surfaces 131, 132 which merge with the inner surface 113 of the legs 107, 108. The surfaces 131, 132 form a smooth transition area which prevents the edges 110, 111 from interlocking with each other during any phase of the retreading operation utilizing the bladder 105. The bladder 105 may, of course, also be provided with axially opposing and axially opening notches 133, 134, just as in the manner of the notches or slots 80, 81 associated with the bladder 65 (FIGS. 6 and 7).

The ribs 116, 117 (FIG. 16) may also have embedded therein a suitable coil, cord, string or fabric (not shown to stiffen these ribs and ensure that the life thereof will be extended. Moreover, even when in use should the mold become relatively hot and, of course, the bladder 105 become similarly hot, the material of the latter will not become so soft as to render the venting effected by the means 115 to become ineffective because of the reinforcing nature of the cords 135 which will assure that air can bleed from between an associated tire T' (FIG. 17) and the exterior surface 112 of the bladder 105 to atmosphere through the gaps or slots 120, 121 and the associated valleys 118. States another way, the cord or fabric 135 in the ribs will prevent the ribs from flattening to such an extent that the apices (unnumbered) thereof are flattened to lie in the plane of the exterior surface 112. Thus, fluid communication will at all times be maintained over the entire exterior surface 112 of the bladder 105 and the associated inner surface (unnumbered) of the tire T' (FIG. 17) during a retreading operation. Thus, as is best illustrated in FIG. 17, air may be introduced into the interior 114 of the bladder 105 through the conduit 67' and the notches or slots 133, 134 with, of course, the bead aligner wheels 40, 41 in their closed (illustrated) position. During the inflation of the bladder 105, any air between the exterior surface 112 thereof and the interior surface of the tire T is forced through the venting means 15, including the slots 120, 121 and the valleys 118 of all of the venting means 115 toward and into the annular area or zone 125 from which the air can be exhausted to atmosphere through the grooves or slots 62' of the associated bead aligner wheels 40', 41' and the ports 63' in the flanges 64' of the bead aligner wheels. At the same time, the annular beads 61' of the bead aligner wheels 40', 41' form the hermetic seal in the same manner described relative to the operation of the bladder of FIGS. 6 through 8 in the associated bead aligner wheels of FIGS. 9 and 10. Thus, each of the beads 125, 126 effect a hermetic inboard circular sealing line, while the line of contact between each of the bead aligner wheel beads 61' and the associated smooth zone 125 of each of the legs 107, 108 defines another hermetic circular line of sealing with the associated chambers A' which during the pressurization of the bladder 105 become partially evacuated in the manner heretofore described relative to FIG. 4.

Reference is now made to FIG. 18 which shows another bladder 105' which is identical to the bladder 105 of FIGS. 13-16 and thus the reference numerals associated therewith have been primed to indicate identical structure. As in the case of the bladder 105, the bladder 105' includes a valley 118' between ribs 116' and 117' which project beyond an exterior surface 112' of the bladder 105'. However, in the case of the bladder 105' the lowermost surface of the valley 118' lies generally in a plane through the exterior surface 112' or slightly exteriorly outwardly of the latter-noted plane whereas a plane through the lowermost surface of the valley 118 (FIG. 16) lies in a plane below the exterior surface 112 of the bladder 105. Thus, the cross-sectional thickness of the legs, 107, 108 of the bladder 105 in the area of the valleys 118 is less than the overall thickness of the legs 107, 108 resulting in an obvious weakening in these areas. However, in the case of the bladder 105' the cross-sectional thickness in the area of the valleys 118' is equal to or greater than the overall thickness of the legs 107, 108 and thus there is no weakening and no cause for malfunctioning of the bladder through rupture as might, of course, occur in areas which are thinned, again as in the case of the bladder 105 in the area of the thinner cross-sectioned valleys 118.

While preferred forms and arrangements of parts have been shown in illustrating the invention, it is to be clearly understood that various changes in details and arrangement of parts may be made without departing from the scope and spirit of this disclosure.