Crane

Abstract

A crane has at least one telescopic crane arm with at least two sliding arms that are moveable against each other. At least one gliding element, which is housed loosely in a frame, is arranged between the sliding arms. The gliding element has a separate spring element projecting over the gliding surface of the gliding element.

Description

The present invention relates to a crane with at least one telescopic crane arm with at least two sliding arms movable against each other, wherein at least one gliding element, which is housed loosely in a frame, is arranged between the sliding arms, and also the gliding element itself.

Gliding elements arranged between two sliding arms are to keep the friction resistance low when the sliding arms are moved against each other upon retraction and extension. It is essential that the gliding elements are housed immovable at predefined points in order to be effective in each relative position of the sliding arms. It has therefore already been proposed to glue or screw the gliding elements to one of the sliding arms. However, as the gliding elements wear over time and must be replaced, this manner of attachment is unfavourable for swift and problem-free replaceability.

As an alternative to this, it has been attempted to hold the gliding elements in a metal frame, the metal frame having to be developed much smaller than the thickness of the gliding elements in order not to come into contact with the opposite surface upon the relative movement of the sliding arms. As a result, in the past, worn gliding elements were sometimes pushed over the small metal frame out of the bearing.

The object of the present invention is to further develop the known gliding elements of a crane such that both a stable housing and a swift replaceability are ensured.

This is achieved according to the invention in that the gliding element has a separate spring element projecting over the gliding surface of the gliding element.

Through the spring element projecting over the gliding surface of the gliding element, the gliding element is always pressed onto the bearing surface with the side facing away from the gliding surface, as a result of which it cannot escape even from very small holding frames.

In a particularly simple and stable version, the spring element is developed as a leaf spring.

In order to keep the contact surface of the spring element with the opposite surface as small as possible, it is favourable for the spring element to be housed in a recess in the gliding element. Operational reliability can be increased by securing the spring element against falling out, in particular by lateral projections from the wall of the recess.

The gliding element is preferably produced from plastic. In this connection it is possible to provide co-extruded spring elements made of plastic instead of the leaf spring.

Further advantages and details of the present invention are illustrated by the following description of the figures. There are shown in:

FIG. 1 a slide frame of a telescopic crane arm in which two gliding elements according to the invention are housed,

FIG. 2 a a longitudinal section through two sliding arms having a rectangular cross-section during load “lifting”,

FIG. 2 b a longitudinal section through these sliding arms during load “pressing” and

FIG. 3 a perspective detail view of a gliding element according to the invention housed in a frame.

In FIGS. 1, 2a and 2b, two sliding arms of a telescopic crane arm are shown in simplified form. The sliding arm 1a shown in FIG. 1 has a hexagonal cross-section with the result that each of the gliding elements 2 according to the invention are arranged in pairs in the two bottom and top surfaces. FIGS. 2a and 2b on the other hand assume a rectangular cross-section of the sliding arms 1a and 1b with the result that each bearing is formed by a single gliding element 2.

The sliding arms 1a and 1b are movable in longitudinal direction against each other. In the case of the load operation shown in FIG. 2a in which a load applies a force in the direction of the arrow 10, the inner sliding arm 1b is pressed against the bearings at the top left and at the bottom right. In the opposite, somewhat rarer case, which is shown in FIG. 2b, the force acts in the direction of the arrow 11. In this case, the load stress is on the auxiliary gliding elements 9 which, on account of the rarity of this load operation, are normally designed much simpler than the gliding elements 2 according to the invention. The auxiliary gliding elements 9 also hardly need replacing.

As FIG. 3 shows in detail, the gliding element 2 according to the invention is composed of a flat plastic block. Cavities 7 in the shape of longitudinal grooves which can house lubricant are worked into the gliding surface 3. When new and after each maintenance, the cavities 7 are filled with lubricant to further reduce the coefficient of friction.

The gliding element 2 has a central recess 5 into which a spring element 4 in the shape of a pretensioned leaf spring is inserted. This spring shape has proved particularly successful. Spiral springs and any other spring systems that have a comparable effect are also conceivable. The leaf spring is secured at its ends against falling out by the projections 6 and, in the middle section, stands well above the gliding surface 3 of the gliding element 2. Even if the opposite surface takes off from the gliding surface 2 of the gliding element 2, the spring element 4 ensures that pressure continues to be applied to the gliding element 2 and it is pressed onto the foundation as a result. The metal frame 8 provided around the gliding element 2 can therefore be developed very low in order to ensure that it does not come into contact in any way with the opposite surface.

The leaf spring can be easily replaced if it is defective, as can the gliding element 2 which merely rests loosely in the frame 8 but is not screwed or glued to the base.

Claims

1. Crane with at least one telescopic crane arm with at least two sliding arms movable against each other, wherein at least one gliding element, which is housed loosely in a frame, is arranged between the sliding arms, characterized in that the gliding element has a separate spring element projecting over the gliding surface of the gliding element.

2. Crane according to claim 1, characterized in that the spring element is developed as a leaf spring.

3. Crane according to claim 1, characterized in that the spring element is housed in the gliding element.

4. Crane according to claim 1, characterized in that the spring element is housed in a recess in the gliding element.

5. Crane according to claim 1, characterized by means for securing the spring element against falling out.

6. Crane according to claim 1, characterized by lateral projections from the wall of the recess for securing the spring element against falling out.

7. Crane according to claim 1, characterized in that cavities for lubricant are provided in the gliding surface.

8. Crane according to claim 1, characterized in that the gliding element is made of plastic.

9. Gliding element with a spring element projecting over the gliding surface of the gliding element, characterized in that the spring element is developed as a leaf spring.

10. (Canceled)

11. Gliding element according to claim 9, characterized in that the spring element is housed in the gliding element.

12. Gliding element according to claim 9, characterized in that the spring element is housed in a recess in the gliding element.

13. Gliding element according to claim 9, characterized by means for securing the spring element against falling out.

14. Gliding element according to claim 9, characterized by lateral projections from the wall of the recess for securing the spring element against falling out.

15. Gliding element according to claim 9, characterized in that cavities for lubricant are provided in the gliding surface.