Seal for a vacuum material lifter

Abstract

A seal for a vacuum lifter and method of manufacture wherein the seal has a continuous unbroken outer fluid resistant skin of elastomer which forms a boundary around a homogeneous cellular structure with no interior seams or joints.

Claims

1. A seal for a vacuum lifter vacuum pad sized to lift heavy objects, said seal comprising: a monolithic body comprising a core structure surrounded by an integral and continuous nonporous external skin, the monolithic body comprising a cured extruded natural rubber closed cell thermoset elastomer and the monolithic body having no open cells and not being laminated, the core structure and the external skin both being liquid and petrochemical resistant such that even if the external skin is ruptured the closed cell structure of the core structure provides resistance to saturation by a liquid, and the seal having a memory effect such that it is resistant to permanent compression set, and wherein the seal is formed by the process of curing an extruded natural rubber closed cell thermoset elastomer segment in a heated closed mold to form the external skin surrounding the core structure, and wherein the monolithic body, after the process of curing, is in the shape of a linear longitudinally extending segment that is cut to length and one end of the segment is bonded to an other opposite end of the segment to form the seal having a closed periphery which can then be received in a gland located about a periphery of the vacuum lifter vacuum pad.

2. The seal of claim 1, further comprising a cross section with rounded corners.

3. The seal of claim 1, further comprising an elliptically shaped cross section.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Preferred embodiments of the invention will now be described in further detail. Other features, aspects, and advantages of the present invention will become better understood with regard to the following detailed description, appended claims, and accompanying drawings (which are not to scale) where:

(2) FIG. 1 is a side view of a vacuum lifter with a pad and seal;

(3) FIG. 2 is a bottom view of a vacuum lifter pad with a seal;

(4) FIG. 3 is a cross-sectional view of the prior art seal for a vacuum lifter pad;

(5) FIG. 4 is a cross-sectional view of the improved seal of the present invention; and

(6) FIG. 5 is a flow chart of the process for manufacturing the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

(7) Turning now to the drawings wherein like reference characters indicate like or similar parts throughout, FIG. 1 illustrates a vacuum lifter 20 with its vacuum pad 22 attached to a boom 24 via a rotator 26. FIG. 2 shows the bottom surface 28 where a seal 30 is captured in a gland 32 which extends along the periphery 34 of the pad 22.

(8) FIG. 3 shows a cross section of the pad 22 with a prior art seal 36 located in the gland 32. The seal 36 has a first and second layer 38 and 40 polyisoprene rubber secured together by an adhesive lamination 42. The seal 36 is oriented in the gland 32 such that the skin 44 of these layers 38 and 40 extend downward from the gland 32 and bottom surface 34 of the pad 22. This leaves the top and bottom surfaces 46 and 48 of the prior art seal 36 with exposed open cell structure 50. As explained earlier, this leads to the deterioration of the prior art seal 36.

(9) FIG. 4 shows a cross section of the seal 52 of the present invention located in the gland 32 of the vacuum pad 22. It has a closed cell structure 54 surrounded by a continuous nonporous skin 56. As best seen in FIG. 4, the seal 52 of the present invention has a monolithic body 58 without any lamination. The continuous skin 56 is resistant to penetration by liquids. Thus, the skins seals the seal 52 from penetration by liquids. This prevents liquids such as hydraulic fluid from saturating the closed cell structure 54 and causing the seal 52 to prematurely deteriorate. If the skin 56 does rupture or a liquid otherwise penetrates the skin 56, the closed cell structure 54 provides resistance to saturation by a liquid.

(10) In the preferred embodiment, sharp corners are eliminated from the cross section of the seal 52. Thus, the seal 52 may have a square or rectangular cross section with rounded corners. Likewise, the seal may have a round or elliptical cross section.

(11) When installing the seal 52 into the gland 32 a single length of seal 52 may be used. Once installed, the two ends 62, 72 of the seal 52 will be adjacent to one another. Although not necessary for proper function, further protection to liquid penetration may be provided by adhering the two ends 62, 72 to one another.

(12) The seal 52 of the present invention is manufactured primarily as a molded article from any number of thermoset elastomers, such as natural rubber, polyisoprene, polychloroprene, EPDM, etc. that have a cellular closed cell cross-section 54 with a continuous unbroken outer skin 56. The manufacturing method disclosed herein describes the key process steps which are necessary to produce the preferred embodiment of the seal. To those skilled in the art, it will be recognized that each individual step in the disclosed manufacturing process is well known and understood; however, the novelty of this invention arises from the combination and sequence of these steps which results in the preferred embodiment of the seal.

(13) A mixed and uncured cellular rubber compound is first extruded through a die to produce a specific shape or pre-form. The shape and size of the pre-form is established based upon the desired molded density of the seal as well as the geometry of the pre-form that results in proper heat transfer into the pre-form in the subsequent molding process step to properly decompose the blowing agents within the rubber compound.

(14) After extrusion, the pre-form is placed into a closed mold cavity that provides the final cross-section size and shape desired. The mold cavity is heated using steam, electric heaters, hot oil or any other heating means. Heat is transferred to the uncured rubber pre-form by thermal conduction wherever the rubber comes into contact with the heated mold surfaces. When the blowing agents decompose, gas is released inside the rubber that expands the rubber to fill the mold cavity. The gas pressure causes the rubber to exert pressure between the outer skin of the rubber and the mold cavity. After the rubber is fully expanded, the rubber cures in the mold and assumes the shape of the mold cavity. Prior to installation in the gland 32 of a vacuum pad 22, it can be cut 67 to a length suitable to fit the pad. Various lengths of seal can be manufactured using this method, which produces a seal with a continuous unbroken outer skin, which forms a boundary around the cellular rubber structure on the interior of the seal. Several lengths of seal manufactured using this method can subsequently be vulcanization bonded or spliced together end-to-end.

(15) The fully cured exterior skin is much more resistant to penetration by liquids than the conventional exposed open cell seals previously used. This seal structure minimizes the rate and extent of penetration of liquids that can deteriorate the seal.

(16) In the preferred embodiment for a square or rectangular molded cross-section, the extruded rubber pre-form cross-section is generally circular or elliptical in shape, although, other shapes may be advantageously used to achieve the desired molded cross-section. This approach generally results in a molded seal cross-section without sharp corners on the seal that can catch on the edge of surfaces and tear, thus causing a premature failure.

(17) The foregoing description details certain preferred embodiments of the present invention and describes the best mode contemplated. It will be appreciated, however, that changes may be made in the details of construction and the configuration of components without departing from the spirit and scope of the disclosure. Therefore, the description provided herein is to be considered exemplary, rather than limiting, and the true scope of the invention is that defined by the following claims and the full range of equivalency to which each element thereof is entitled.