Abstract:
A tool for a street milling, coal-cutting mining machine or the like which includes a chisel with a chisel head and a chisel stem. The chisel stem is rotatably mounted in a receiver of a chisel holder. A perforated wearing protection element is mounted on the chisel head. The chisel head sits closely on the chisel holder while embracing the interposed wearing protection element. This invention achieves improved wearing protection behavior of such a tool. Thus, the inventive wearing protection element has one or more spring elements that elastically support the chisel head by way of the chisel holder.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a tool for a street milling, coal-cutting, mining machine or the like which has a chisel with a chisel head and a chisel shaft. The chisel shaft is rotatably mounted in a receiver of a chisel holder. A perforated wear protection element is mounted on the chisel head with the chisel head sitting closely on the chisel holder with the wear protection element interposed. 
     2. Description of Related Art 
     A tool is known from European Patent Reference EP 0 413 917 A1, where the wear protection element is formed as a circular steel sheet disk, from which an opening is punched in the center. The opening is extended in the direction of the chisel head. A chamfered part of the chisel head lies in this extension. The wear protection element lies flat on a contact surface of the chisel holder. During use of the tool, waste material can get past the chisel head and the wear protection element and reach the receiver. In this position, this material can block the free rotation of the chisel. 
     Another tool for mounting a chisel on a chisel holder is known from European Patent Reference EP 0 200 37 B1, where the chisel head is set directly on the chisel holder. The chisel holder is designed to be under spring tension on a base part that can be attached on its side to a milling roller. The chisel can also become fixed due to waste material penetrating into the receiver, and then the chisel can no longer rotate freely. 
     SUMMARY OF THE INVENTION 
     One object of this invention is to provide a tool of the above mentioned type, which has good wear behavior. 
     The wear protection element comprises one or more spring elements that elastically support the chisel head relative to the chisel holder. 
     Due to the spring-tensioned support of the chisel head, intermittent forces acting on the chisel are damped so that excessive material stresses are prevented. In addition, the spring force provides an axial play for the chisel, wherein the chisel head can then also move axially in the receiver of the chisel holder. With this axial play, there is a type of “pump effect” which can extract waste material that has reached the region of the receiver. Thus, the free rotation of the chisel can be maintained. 
     In order to keep the cost of parts and assembly to a minimum, according to a preferred embodiment of this invention, spring elements are formed integrally with the wear element. 
     In one possible embodiment of this invention, the wear protection element comprises a base part with at least one flat contact surface that contacts an opposing surface of the chisel head or the chisel holder. A circumferential section acting as a spring element is bent in the direction of the chisel holder or the chisel head from the base part. The spring element supports the chisel holder or the chisel head on the region of the spring element facing away from the base part. 
     However, it is also conceivable for several, preferably three, spring elements that are separated from each other to be bent from the base part. With these spring elements, a definite, statically determinate support situation is achieved. 
     In order to be able to achieve progressive or regressive spring characteristics, according to one embodiment of this invention, each spring element comprises two or more spring sections that exhibit different spring rigidity and/or the same or different spring deflections. 
     A tool according to this invention has an area around the opening in which the chisel shaft is inserted, with a circumferential centering attachment that projects in the direction of the chisel holder and that interacts with a centering extension of the receiver of the chisel holder. The centering extension of the chisel holder simplifies assembly of the chisel shaft in the receiver. During operation, the region of the contact surface on which the wear protection element is supported and which is arranged around the receiver gradually wears away. This is caused by rotation of the wear protection element on this contact surface. With a centering attachment at the wear protection element, the centering extension is worn away to the same degree as the contact surface. However, this causes the centering extension to remain in place. 
     A tool with a simple configuration and that is cost-effective to produce is obtained according to this invention when the wear element is produced as a stamped, bent part from a flat material blank, from which the opening for the chisel shaft is punched and whose edge or edges are bent for completely or partially forming the spring elements. 
     Here, one or more reinforcing ribs can be formed on the edges that form the spring elements. The reinforcing ribs increase the spring rigidity. Thus, a relatively low material strength can be used for the wear protection element yet still provide a high spring rate. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     This invention is explained in more detail in view of the drawings, wherein: 
     FIG. 1 is a chisel holder with an attached tool in a side view and partial cross section; 
     FIG. 2 a  is a wear protection element in a side view and partial cross section; 
     FIG. 2 b  is the wear protection element from FIG. 2 a  in a top view; 
     FIG. 3 a  is another embodiment of a wear protection element in a side view and a partial cross section; 
     FIG. 3 b  is the sear protection element from FIG. 3 a  in a top view; 
     FIG. 4 a  is a modification of the wear protection element shown in FIGS. 3 a  and  3   b  in a side view and partial cross section; and 
     FIG. 4 b  is the wear protection element of FIG. 4 a  in a top view. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 shows a chisel holder  20  with a base part  22 . The base part  22  carries a plug attachment  21  that can fix the chisel holder  20  to a holder part so that it can be removed. The holder part can then be attached to a milling roller or a coal-cutting machine or the like. For the sake of clarity, the holder part and the milling roller are not shown in FIG.  1 . The base part  22  has a receiver  23 . The receiver  23  is bored into the base part  22  starting from a level contact surface  24 . The receiver  23  expands outwards by means of a centering extension  25  at the contact surface  24 . A chisel  10  is fixed to the chisel holder  20 . The chisel  10  comprises a chisel head  11  and a chisel shaft  15 . The chisel head  11  has a receiver on its front side, in which a bit  12  is soldered. In an intermediate region, the chisel head  11  has a circumferential groove  13  that enables the disassembly of the chisel  10  from the chisel holder  20 , with a tool. In the transition region to the chisel shaft  15 , the chisel head  11  is sealed with a flange  14 . As shown in FIG. 1, an adapter sleeve  16  is mounted on the chisel shaft  15 . The adapter sleeve  16  holds the chisel  10  in the axial direction. Furthermore, the adapter sleeve  16  is braced due to radial expansion in the receiver  23  of the chisel holder  20 . In this way, the adapter sleeve  16  holds the chisel  10  in the chisel holder  20 , wherein the chisel  10  can freely rotate in the adapter sleeve  16 . Between the chisel head  11  and the chisel holder  20  there is a wear protection element  30 . The wear protection element  30  supports the chisel head  11  on the contact surface  24  of the chisel holder  20 . 
     The wear protection element  30  is produced as a stamped, bent part from a circular steel sheet blank and has a centering opening  35 , by which the wear protection element  30  is mounted on the chisel shaft  15 . In a region facing the chisel head  11 , the opening  35  tapers into an expanding, chamfered inlet  37 . The chamfered inlet  37  serves for easier assembly of the wear protection element  30 . The wear protection element  30  is initially loaded onto the end of the adapter sleeve  16  with its chamfered inlet  37  facing away from the chisel head  11 . Thus, the diameter ratio of the opening  35  of the wear protection element  30  relative to the tensioned diameter of the adapter sleeve  16  is selected so that the adapter sleeve can be inserted into the receiver  23  with minimum or no force. For final assembly of the chisel  10 , the wear protection element  30  is shifted by the application of force, for example, by means of hammer blows, along the adapter sleeve  16  until it goes beyond the end of the adapter sleeve  16  on the side of the chisel head. Then the adapter sleeve  16  is snapped in radially and is tensioned in the receiver  23 . In this assembled position, the chisel head  11  contacts the contact surface  36  of the wear protection element  30 . The contact surface  36  extends perpendicularly to the center longitudinal axis of the chisel  10  and connects to the chamfered inlet  37 . In the region of this contact surface  36 , the wear protection element  30  forms a base part, from which a spring element  32  is bent projecting outwards. The spring element  32  is formed from the outer edge of the wear protection element  30  which is placed at an angle to the contact surface  24  of the chisel holder  20 . The spring element  32  is supported at its end facing away from chisel head  11  by means of a support section  31  on the contact surface  24  of the chisel head  20 . As shown in FIG. 1, the wear element  30  has a circumferential centering attachment  33  designed with a geometry that makes a 45° angle with the chisel holder  20 , wherein this angle continues around the receiver  23  as the centering extension  25 . The centering extension  25  simplifies mounting of the chisel  10  in the receiver  23 . As shown in FIG. 1, the centering attachment  33  in its original state, not attached to the tool, is arranged at a distance to the centering extension  25 . This separation creates a spring deflection. If a tool, for example for a road surface, is attached to the tool of this invention, then the impact of the bit on the material to be removed is cushioned by the spring element  32  of the wear protection element. In this way, excessive material stresses on the bit  12  are prevented. During the removal process, the wear protection element  30  is flattened. After the tool is detached, the wear protection element  30  springs back into its output position, wherein the chisel shaft  15  is shifted along its axial direction in the receiver  23 . Due to this “pump effect,” waste material which gets past the chisel head  11  and the wear protection element  30  and reaches the receiver  23  can be extracted. Thus, the free rotation of the chisel  10  in the adapter sleeve  16  is maintained. 
     In the following, various embodiments of wear protection elements  30  are explained in view of FIGS. 2 a - 4   b.    
     The wear protection element shown in FIGS. 2 a  and  2   b  has a spring element  32  that is formed from the outer edge of the wear protection element  30 . The edge of the wear protection element  30  is bent so that it runs parallel to the longitudinal extension of the chisel  10 . This produces a flat, annular support section  31 , by which the wear protection element  30  is supported on the contact surface  24 . 
     A wear protection element  30  is shown in FIGS. 3 a  and  3   b , having an outer edge not bent 90° as shown in FIGS. 2 a  and  2   b , but rather at an angle less than 90°. 
     In FIGS. 4 a  and  4   b , the wear protection element  30  in FIG. 1 is shown in more detail. The outer edge that forms the spring element  32  has reinforcing ribs  34 . The spring rate of the spring element  32  can be increased by these reinforcing ribs  34 . 
     The production of the wear protection element  30  described above is simple. Here, a circular blank is first punched from a flat steel sheet blank. The opening  35  can be punched from the steel sheet blank. Then the region surrounding the opening  35  is stamped-so that the centering attachment  33  and the chamfered inlet  37  are obtained simultaneously. Then the spring element  32  is bent.