Abstract:
A drive wheel for off-center drive of an annular saw blade in a cutting machine, consists of at least two components, which are separable but held together during operation, namely a holding disc and a drive ring, the latter having an encircling drive groove for the inner edge of the saw blade, the drive ring being arranged radially outside a central portion of the holder disc.

Description:
TECHNICAL FIELD 
     The invention relates to a drive wheel for off-centre drive of an annular saw blade in a cutting machine. 
     BACKGROUND OF THE INVENTION 
     U.S. Pat. No. 4,472,880 describes a cutting machine with annular saw blade, which has an inner edge which is bevelled in a wedge-shaped manner, co-operating with a drive wheel inside the inner edge of the blade. The drive wheel consisted according to this patent of two halves which were pressed against each other in axial direction by a strong string. At the same time, the two halves of the drive wheel pressed the inner edge of the cutting blade between themselves, which gave a good grip but which also resulted in a hard wear. This design therefor was abandoned for an undivided drive wheel with a design disclosed in U.S. Pat. No. 4,793,065, FIG. 3. The grip between the inner edge of the saw blade and the drive wheel with its groove in this design is provided by the blade being pressed in a radial direction into a groove in the drive wheel. The wear thereby is reduced in comparison with the wear in the first embodiment according to U.S. Pat. No. 4,472,880 but is nevertheless substantial. Both the drive wheel and the saw blade are therefor to be considered as replacement parts which must be replaced when they have been worn out. The drive wheel in general certainly has a longer lifetime than the saw blade, but the costs for the exchange are nevertheless considerable. Nor is it beneficial from all parts of view that the saw blade and the drive wheel are replacement parts with substantially different lifetime, since this may increase the number of necessary replacement operations. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The object of the invention is to address the above problem complex. This is accomplished by the drive wheel consisting of at least two annular components which are separable but held together during the operation, namely a holder disc and a drive ring, the latter having an encircling drive groove for the inner edge of the saw blade, and that the drive ring is arranged radially outside of a central portion of the holder disc. By this design, the drive ring can be made as a very simple machine element with a small mass, which in its turn opens up for possibilities to manufacture the drive ring of a comparatively plane construction material, preferably a plane structural steel, which suitably wears down at the same rate as the saw blade and is replaced at the same time as the saw blade, while the holder part—the holder disc—is made of a more high-grade constructional material. As an alternative, the drive ring is made of a still more high-grade constructional material than the holder disc, e.g. a high-grade high speed steel or cemented carbide material with very long lifetime and is in this case not to be considered as a replacement part in the normal sense of the word. 
     Additional characteristics and aspects of the invention appear from the claims and from the following detailed description of a preferred embodiment. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the detailed description, reference is made to the accompanying drawings, of which 
     FIG. 1 is a side view of a cutting machine, where the drive wheel according to the invention can be used, 
     FIG. 2 shows a view II—II in FIG. 1, 
     FIG. 3 shows a drive wheel in cross section, mounted on a drive shaft, and 
     FIG. 4 shows a variant of how a sealing between the drive wheel and a drive motor can be performed. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference first to FIGS. 1 and 2, a cutting machine is denoted  1  and an annular saw blade, driven by a hydraulic motor  2 , is denoted  3 . The main parts of the cutting machine  1  consist of a chassis  4  on which the hydraulic motor  2  is mounted and which contains not shown guide rollers for the saw blade  3 , a support roller cover  5 , which contains not shown support rollers for the saw blade, and a manoeuvring arm  6  with controls for the hydraulic motor  2 . The hydraulic motor  2  is mounted on the chassis  4  and is of the type described in U.S. Pat. No. 5,381,723. A pair of conduits for hydraulic oil has been denoted  12 ,  13  and a conduit for cooling water has been denoted  14 . 
     Between the chassis  4  and the support roller cover  5 , there is a drive wheel  21  which is rotated by the hydraulic motor  2  via a drive shaft, generally denoted  20 , FIG.  3 . 
     The drive wheel  21  consists of a drive ring  18 , a holder disc  19  and an attachment plate  24 . In addition, there is included in the mounted unit a washer  25  and a screw  26 , which co-operates with a threaded, central hole  27  in a shaft journal  28 . On the shaft  20  there is also a flange  29  inside the shaft journal  28 . A bearing housing on the hydraulic motor  2  has been denoted  30 . For the bearing of the shaft  20  in the bearing housing, there is a ball bearing,  31 . Between the bearing  31  and the drive wheel  21  there are inner sealing means  32  and outer sealing means, which in some different embodiments have been denoted  33   a ,  33   b  and  33   c , respectively. It should be understood that two different embodiments have been illustrated in FIG. 3 in order to reduce the number of drawings. 
     The holder disc  19  consists of a central portion  36  and a peripheral portion  37 . The central portion  36  has a centre hole  38 , which matches the outer shape of the shaft journal  28 . The latter is bevelled to approximately oval shape in a known manner and the hole  38  has a corresponding shape, which prevents the holder disc  19  from rotating on the shaft journal  28 . The central portion  36  of the holder disc  19  further has a peripheral, circular-cylindrical surface  39 . The peripheral portion  37  of the holder disc is axially displaced from that section of the central portion  36  on which the circularcylindrical surface  39  is provided. The outer diameter of the holder disc  19  is somewhat smaller than the outer diameter of the drive ring  18 . The peripheral portion  37 , finally, has an annular flange  41 , facing the drive ring  18 . 
     The drive ring  18  has a inner circular-cylindrical surface  42  and is thread upon the central portion  36  of the holder disc  19  with good fitting between the two cylindrical surfaces  39 ,  42 . Both sides  43 ,  44  of the drive ring  18  are flat. In the drive ring  18  there is a groove  23 , here called a drive groove, and which may have a shape known per se in order to accommodate the wedge shaped inner edge  22  of the saw blade  3 . The groove  23  thus in cross section has a wedge-shaped mouth, a rounded bottom and parallel walls between the mouth and the bottom. The invention is however not limited to the shown geometries of the inner edge of the saw blade and the drive groove. To the extent that other geometries exist, or can be suggested, the principle of the invention can be used for those as well. 
     In the mounted drive wheel  21 , the drive ring  18  is pressed upon the central portion  36  of the holder disc  19  with the two cylindrical surfaces  39  and  42  in contact with each other. The screw  26  presses the washer  25  against the attachment plate  24 , the outer edge portion of which is pressed against the outside of the drive ring  18 , so that the drive ring is clamped between the outer flange  41  of the holder disc and the edge portion of the attachment plate  24 . Moreover, the holder disc  19  and thus the entire drive wheel  21  is pressed against the flange  29  of the drive shaft  20 . The sealing rings  33   a ,  33   b  or  33   c  accomplishes a sealing between either the shaft  20  and the bearing housing  30 , more precisely between the shaft flange  29  and the bearing housing  30 , according to the two alternatives shown in FIG. 3, that is with the sealing ring in embodiment  33   a  or  33   b , or between the drive ring  21  and the bearing housing  30 , as with the sealing ring  33   c , FIG.  4 . In embodiment  33   a , the sealing ring consists of an inner steel washer, which is clamped on the flange  29  and a rubber ring with lips, one of the lips contacting the bearing housing  30 . In embodiment  33   b , the sealing consists of a labyrinth sealing, comprising a ring which is clamped on the flange  29 . 
     The embodiment  33   c , FIG. 4, is a combined glide sealing and labyrinth sealing, comprising a rubber ring  50  with a tongue  51  in slidingly contact with the holder disc  19 ′, and a bent steel ring  52 . The rubber ring  50  is pressed into the steel ring  52 . The steel ring itself is pressed in on the inside of the bearing housing  30  and is provided with a tongue  53  which extends into an annular groove  54  in the upside of the holder disc  19 ′, which gives labyrinth effect. 
     The drive ring  18  may be made of a very high-grade material, such as a high-grade high speed steel or cemented carbide, whereby it gets a long lifetime but on the other hand becomes relatively costly. As an alternative, the drive ring  18  may instead consist of a relatively plain constructional steel with comparatively low hardness. This has the potential benefit that the grip between the groove  23  and the wedge shaped edge  22  of the saw blade  3  may be very efficient as compared with what can be achieved when the drive ring  18 —or the entire drive wheel, according to known technique—has a greater hardness. Another beneficial and desired effect is that the drive ring  18  may be worn out at essentially the same rate as the saw blade, or be durable for the lifetime of a few saw blades, and therefor suitably may be replaced at the same time as the saw blade is replaced. When the saw blade  3  and the drive ring  18  are to be replaced, the support roller cover  5 , FIG. 2, is loosened whereby at the same time the support rollers are removed and the screw  26  is exposed. The saw blade  3  is thereafter completely loosened by loosening of the guide rollers in the chassis  4  by means of the handle  47 , FIG. 1, whereafter the saw blade is removed. Thereafter, the screw  26  is loosened, whereafter the entire drive wheel  21  can be loosened from the shaft journal  28 . Finally, the drive ring  18  is pulled loose from the holder disc  19  and is replaced by a new one, whereafter the continued mounting takes place in a way that not ought to demand any further explanation. In order to facilitate the pulling to loosen the drive ring, it is bevelled in its upper, inner edge, so that the length of contact between drive ring and holder disc becomes short. Additionally the drive disc  19  is provided with recesses  19   a , FIG. 4, for a key or other grip means. It should be mentioned in this connection that the sealing ring, no matter which of the embodiments  33   a ,  33   b  or  33   c  is used, is all the time stuck either to the shaft flange  29  or in the bearing housing  30  and normally does not need to be replaced.