The invention pertains to a hoisting cushion or pad with two reinforced walls that are manufactured of rubber or of a rubber-like material. The walls of the cushion (a) are linked around the full extent of the edges and define an hermetically sealed inner space that is accessible via a nipple, and (b) reveal on their external surface fairing which is sited outside of the reinforcing.
In hoisting cushions of the type, to which reference is made in the introductory remarks and to which German Patent 75 38 274 or respectively the parallel U.S. Pat. No. 4,067,544 refer, no fairing of the external surface of both walls is evident. In contrast, however, the cushions that are constructed in accord with the principles of these publications do reveal fairings on the external surfaces of their walls. Hoisting cushions are also disclosed in U.S. Pat. Nos. 4,036,472; 4,143,854 and 4,104,425. Hoisting cushions in the form of compressed or compact cushions are familiar for example from U.S. Pat. No. 4,880,035. Here, too, the hoisting cushions that are in practical use and available on the market reveal some fairing on one outside surface of at least one wall, in general on that wall which faces away from the leak.
A fairing in the form of rubber ribs is familiar. This fairing derives from ribs that are 20 mm along their edge, 2 mm wide and 2 mm high and that extend regularly over the outer surface of the walls. This fairing-contouring prevents the cushion from slipping especially on surfaces that are smooth, soiled or slippery. The fairing creates also a surface that has an aesthetically pleasing and technically effective exterior surface structure.
A disadvantage of the fairing that is already familiar is, however, that dirt can collect in the inner corners between the points where the rubber ribs intersect. Generally speaking, this dirt cannot easily be removed, and it is in the way when the hoisting cushion is subsequently used.
A further disadvantage of the fairing that is already familiar is the fact that the ribs do not allow any cross drainage. When working on wet or oil-coated surfaces on which the cushion must be placed, this can lead to problems.
The invention addresses this point. It is the purpose of this invention to avoid the disadvantages of the hoisting cushions of the kind to which reference is made in the introductory remarks and to develop the fairing in such a way that the surface of the cushion can be more easily cleaned while tending to provide opportunity for dirt to collect. The fairing should also be aesthetically satisfying and suitable for practical use.
Proceeding from the type of hoisting cushion to which reference is made in the introductory remarks this problem is solved by having the fairing formed from circular disc-shaped protrusions that are arranged regularly over the surface. These protrusions project outwardly from the outer surface of the walls, this surface being otherwise flat. They have a diameter of 10 to 30 mm, and they project 0.2 to 0.5 mm beyond the outer surface of the wall. They are so arranged that the distance to the nearest adjacent protrusion is smaller than the diameter of the protrusions.
A fairing configuration of this type has no ideal spot, especially no inner corners, in which dirt can collect. The protrusions form, in contrast to the familiar fairing pattern, a relatively large surface area of their own, and this ensures that the cushion sits snugly on objects on which it is set. The fairing configuration that is in accord with the invention effectively prevents the cushion from slipping. Practical tests were able to demonstrate this. In practice, the fairing configuration can be effectively achieved by incorporating in the mold for the cushions of the type noted in the introductory remarks, the protrusions as depressions. The protrusions are then formed during the process of vulcanization, and additional steps in the production process that are intended to manufacture the protrusions are not required.
The protrusions should have a diameter of at least 10 mm in order to provide a surface of their own that is sufficiently large. Smaller protrusions have, in practical tests, proven to be unsatisfactory. However, even protrusions with a diameter in excess of 30 mm have resulted in poor test values with respect to the grip of the cushion on some surfaces, for example oily as well as soiled surfaces. The stated dimension defining the height of the protrusions has also proven effective in practical use. Protrusions which are smaller than 0.2 mm result in practical terms in no positive grip whatsoever, and protrusions which exceed 5 mm in height tend in practice to be damaged.
This description of the protrusions as circular disc-shaped is to be understood here as indicating that they have their own plane and a surface that runs parallel to the outside surface of the wall. It is to be further understood as indicating that they are limited by an outer jacket with a surface that is circular and that has essentially the shape of a cylinder or a blunt cone. The transition between the surface of the protrusion and the outer surface of the jacket can be rounded as can the transition between the jacket surface and the surface of the wall. When formed as a blunt cone, the angle of the cone is below 40.degree., and the cone narrows proceeding from the surface of the wall as it moves towards the surface of the protrusion. Ideally, the curvatures are so constructed that their radius does not exceed 3 mm.
In the preferred type of the invention, the protrusions are linked integrally with the material of the wall. They are formed in the process of vulcanization under heat that manufactures the walls. In a further preferred development of the invention, the actual surface area of the protrusions totals at least 40%, and preferably 50%, of the total surface area of the outer side of the cushion. In contrast to cushions manufactured according to the present state of the art, cushions manufactured in accordance with this invention have a considerably greater surface area that is covered by these protrusions. For in cushions presently available, approximately 20% only of the total surface is taken up by the rib-shaped fairing. The new development therefore leads to lower tensions/pressures and to less deformation in the walls of the cushions when the inflated cushion is subjected to load.
Finally, it has proven advantageous to arrange the center points of the circular, disc-shaped protrusions on straight lines that run parallel to one another, the distance between the center points of adjacent protrusions on the same straight line being less than four times the radius of the protrusions and the protrusions on adjacent straight lines being arranged in a juxtaposed manner so that they face towards vacant spaces. The advantages of such an arrangement are especially evident when the cushion is employed on a line-shaped support, for example, along an edge, for when employed in such a situation, you can be sure that some of the protrusions will be resting along the edge. It will never happen that the edge will be resting between protrusions.
Further advantages and characteristics of the invention are evident from the remaining claims filed and from the following description of types of the invention, it being understood that the types that are described do not limit in any way the claims that are sought. These types are described in greater detail with reference to the drawings.