Boot Arrangement for Piston-Cylinder Assembly

This invention relates to fluid springs of the type employed between metal-forming dies, and, more particularly, to a piston rod boot arrangement for preventing the ingress of dirt, liquids and other contaminants to the working parts of the cylinder, piston and piston rod.

Where metal is shaped, cut or otherwise formed between a pair of dies it is not uncommon to employ a plurality of fluid cylinders between the opposed die members for biasing them apart, that is, to the open or separated position, when the work stroke has been completed. Frequently one side of each cylinder is connected to a source of inert gas (nitrogen) at high pressure which applies a constant high pressure against one side of the piston in the cylinder, the piston rod on the other side of the cylinder bearing against the movable die member. The life of such piston-cylinder assemblies is often relatively short because of the dirt and other contaminants which accumulate or are deposited on the working surfaces of the cylinder, piston and piston rod.

The primary object of this invention is to prolong the life of such piston-cylinder assemblies by preventing the ingress of dirt and other common contaminants to the working parts of such assemblies.

More particularly, it is an object of this invention to provide a boot sealed around the piston rod and adapted to elongate and contract in response to reciprocation of the piston. The boot is sealed to the cylinder at one end and to the rod at its other end. Passageways are provided in the rod end of the cylinder which establish free communication between the boot and the adjacent end of the cylinder. A check valve is also provided for relieving the pressure in the boot when it exceeds a predetermined value. Thus, the atmosphere surrounding the working parts of the piston, piston rod and cylinder is comprised exclusively of the high pressure gas to which the head end of the cylinder is connected.

Other features, objects and advantages of the present invention will become apparent from the following description and accompanying drawing, in which:

FIG. 1 is a vertical sectional view of a piston-cylinder assembly arranged between a pair of dies and embodying the boot arrangement of the present invention;

FIG. 2 is a sectional view along the line 2--2 in FIG. 1;

FIG. 3 is a sectional view along the line 3--3 in FIG. 1; and

FIGS. 4 and 5 are fragmentary sectional views of modified forms of the invention.

In FIG. 1 there is illustrated an upper movable die member 10 and a lower fixed die member 12. Between these die members there is arranged a piston-cylinder assembly generally designated 14. Assembly 14 comprises a cylinder 16 supported within a bore 18 by means of a sleeve 20. Sleeve 20 is threaded into bore 18 as at 22 with an O-ring 24 forming a sealed connection therebetween. Cylinder 16 is resiliently mounted in sleeve 20 by means of a circumferential annular flange 26 disposed between rubber washers 28 within the sleeve 20 and held in place by means of a ring 30 threaded into the upper end of sleeve 20. The lower end of cylinder 16 is open and communicates directly with bore 18. A passageway 32 in die member 12 establishes free communication between bore 18 and a reservoir 34 which is filled with an inert gas, such as nitrogen, under a relatively high pressure.

Within cylinder 16 there is arranged a piston 36 having a piston rod 38 connected thereto. Piston rod 38 extends through a bushing 40 in the wall 42 at the rod end of the cylinder. Bushing 40 is preferably formed of plastic. The upper end of piston rod 38 engages the upper die member 10 as at 44. The above described arrangement with cylinder 16 resiliently supported for tilting movement is generally similar to that shown in my U.S. Pat. No. 3,947,005, dated Mar. 30, 1976. However, with respect to the present invention, the piston-cylinder assembly may be of any conventional type.

On the upper end of cylinder 16 there is secured, as by screws 46, a cap 48. Cap 48 is in sealed relation with the upper end of the cylinder. A bushing 50 is secured to piston rod 38 adjacent its upper end by means of a pair of snap rings 52. Bushing 50 is sealed to piston rod 38 by means of an O-ring 54. An expandable boot 56, preferably in the form of a bellows, is connected to cap 48 in sealed relation thereto by means of a clamp 58. A similar clamp 60 connects the upper end of boot 56 with bushing 50. Boot 56 is preferably formed of a waterproof, rubber-coated fabric and is capable of withstanding a predetermined pressure, for example, about 25 pounds per square inch. The interior of boot 56 freely communicates with the upper end of cylinder 16 by means of passageways 62 which extend through the top wall 42 of cylinder 16 and cap 48. Within bushing 50 there is formed a passageway 64 in which a check valve assembly 66 is arranged. Valve 66 is urged into closed relation with its seat 68 by means of a spring 70. Spring 70 is dimensioned and constructed to maintain valve 66 closed until the pressure within boot 56 reaches a predetermined maximum, say, one to five pounds per square inch, at which time the pressure within the boot is relieved to atmosphere through passageway 64.

Any suitable means for lubricating the piston-cylinder assembly may be employed. In the arrangement illustrated the lubricating means comprises a wick 71 extending axially through piston rod 38 and communicating with a plurality of radially extending wicks 72 in piston 36. Wicks 72 in turn connect with a wick 74 extending circumferentially around piston 36 and contacting the inner cylindrical wall of cylinder 16. The wick assembly described can be saturated with oil through an opening in the upper end of piston rod 38 which is sealed by a threaded plug 76. An additional oil-saturated wick or fibrous pad 77 is secured to the lower face of bushing 50.

With the above-described arrangement it will be appreciated that gas under a relatively high pressure from reservoir 34 is always in communication with the open lower end of cylinder 16. This gas pressure urges piston 36 and piston rod 38 upwardly and, thus, biases die member 10 in an upward direction. During the working stroke of the press on which the die is located die member 10 is driven downwardly to force at least a portion of the gas below piston 36 back into reservoir 34. As the piston moves downwardly in cylinder 16 the working chamber 78 thereof decreases in size while the idle chamber 80 between piston 36 and top wall 42 progressively increases. Thus the gaseous fluid in boot 56, which collapses or contracts when piston 36 moves downwardly, is forced into idle chamber 80. Consequently, when piston 36 moves upwardly the gaseous fluid in idle chamber 80 is forced through passageway 62 into boot 56 and then is forced back into the idle chamber 80 when boot 56 collapses by reason of the downward movement of the piston. As the piston 36 reciprocates in cylinder 16 it is likely that at least a small amount of pressurized gas will seep by the piston from time to time from a chamber 78 into idle chamber 80 and boot 56. When the pressure of the gas in boot 56 exceeds the setting of check valve 66 the valve will open and relieve the pressure in the boot. Thereafter the assembly will operate in the manner described until the pressure within the boot again exceeds the setting of valve 66. Thus, at no time is air from the surrounding atmosphere permitted to enter into the boot. Likewise, the boot itself prevents dirt particles, contaminated lubricant, liquids, etc. from reaching the working parts of the piston-cylinder assembly. Accordingly, the arrangement described prevents any contaminated air, dirt, liquid, etc. from entering boot 56 and cylinder 16. In this way the life of the piston-cylinder assembly is prolonged substantially. In the arrangement shown in FIG. 4 the cylinder 82 is of the generally conventional type, the head end of which has a threaded extension 84 for connecting the cylinder to a lower fixed die member, such as shown at 12 in FIG. 1. The rod end of cylinder 82 comprises a wall 86 on which the lower end of a boot 88 is clamped in sealed engagement by means of a ring 90 secured in place by screws 92. The upper end of boot 88 is secured to the upper end of piston rod 94 by means of a clamp 96 and held in place by a pair of snap rings 98. The interior of boot 88 communicates with the idle chamber 100 of the cylinder between top wall 86 and the upper end of piston 101 by means of one or more passageways 102 in end wall 86. Idle chamber 100 communicates with the surrounding exterior atmosphere through a check valve 104 and passageway 106. This arrangement operates substantially in the same manner as that previously described with the exception, however, that the pressure relief connects directly with idle chamber 100 rather than with the interior of boot 88.

The arrangement shown in FIG. 5, insofar as the piston and cylinder are concerned, can be substantially the same as shown in FIG. 1 or 4. The primary difference between this arrangement and those previously described resides in the construction of the bushing 108 at the upper end of the piston rod 110. Bushing 108 comprises a lower section 112 and an upper section 114 which are secured together by screws 116. The bushing is retained at the upper end of piston 110 by snap rings 118. Lower section 112 of the bushing has a crowned upper surface 120 which conforms generally with the concave lower surface 122 of upper section 114. The upper end of boot 124 has a radially inwardly extending flange 126 which is sealingly clamped between these surfaces.

Lower section 112 has a central upwardly extending portion 128 formed with a plurality of radially extending passageways 130. The inner ends of passageways 130 communicate with the clearance space 132 between the bore in section 112 and the outer periphery of piston rod 110. The outer ends of passageways 130 communicate with a circumferential groove 134 around the outer periphery of extension 128. A rubber O-ring 136 is seated in groove 134. An oil wick 138 is seated within a pocket in lower section 112 which surrounds the piston rod.

The upper section 114 of bushing 108 is formed on its underside with a central recess 140, the peripheral wall of which is spaced radially outwardly from the outer periphery of extension 128 to provide an annular passageway between the two sections of the bushing. One or more radial passageways 142 are formed in upper section 114 which communicate with the annular passageway between the sections and with the surrounding atmosphere. Upper section 114 is sealed to piston rod 110 by means of an O-ring 144.

The arrangement shown in FIG. 5 differs only slightly from that shown in FIG. 1. In this arrangement a very close control of the pressure at which the boot will be relieved can be obtained by the design of O-ring 136. This is true because the O-ring presents substantially greater area on the pressurized side thereof than a spring-biased check valve such as shown in FIGS. 1 and 4. While oil wick 138 is not exposed directly to the interior of boot 124, nevertheless, as the boot contracts and expands, the slight amount of compression and decompression of the gas therein will cause the gas to flow through wick 138. Thus, the gaseous fluid within boot 124 becomes saturated with oil to lubricate the piston rod. This lubrication will be adequate when it is considered that the press on which the fluid cylinder is mounted may be operating at as high as 100 strokes per minute.

In each of the embodiments illustrated in the drawings the cross sectional area within the boot is shown slightly larger than the cross sectional area of the idle chamber of the cylinder. In actual practice the construction is such that these cross sectional areas are not substantially different. As long as the cross sectional areas are not substantially different, the flexibility of the boot wall and the setting of the check valve will eliminate any problems of an unduly high pressure or vacuum in the boot.