Abstract:
The invention relates to a charging arm for conveying, treating and discharging different starting materials in order to produce glass fiber armored plastic pipes.

Description:
FIELD OF INVENTION 
     The invention relates to a feeding arm for conveying, preparing and supplying various starting materials for the production of glass-fiber-reinforced plastic pipes. 
     BACKGROUND OF THE INVENTION 
     A feeding arm usually comprises a kind of a filling station at one end to which the various starting materials such as glass fibers, sand, resin, catalyst as well as further optional filler materials and additives are supplied. The conveyance of said starting materials is performed through pipes of different diameter along the feeding arm to the so-called head of the feeding arm at the other end. There, the continuously conveyed glass fibers (strands of glass fibers, glass fiber yarns) are cut to the respectively desired length with the help of a cutting device, are mixed with the further starting materials and discharged radially (spun off) from where they are centrifuged in a drum-like rotating matrix (mould). The feeding arm moves in an alternating reciprocating manner back and forth in the axial direction of the mould. In this way a pipe with the desired diameter and the desired wall thickness is gradually built up. 
     Thereafter, the feeding arm is pulled out of the mould and introduced into a new free mould, whereas the previously produced pipe such as a sewage pipe for example is cured in the mould and is thereafter removed from the mould. 
     Such a method is known as the HOBAS method for the production of centrifuged glass fiber reinforced plastic pipes. 
     The cutting device consists of three rollers which are arranged in a mutually axially parallel way. A first and second roller are used as conveying rollers. They are both provided with a smooth surface, rotate in opposite directions and their surfaces roll off on one another, whereby they simultaneously convey the strands of glass fibers which are guided along the roller surfaces. 
     A third roller, a so-called cutter block, is arranged behind the first and second roller. This roller is provided on its surface with a plurality of knives which are arranged spaced from one another in the axial direction of the roller. The cutter block rotates against the direction of the second roller, with the knives rolling off on the surface of the second roller (meaning that they touch the same). 
     The strands of glass fibers which are conveyed with the help of the first and second roller (conveying rollers) are thereafter guided between the second and third roller and cut to a corresponding length according to the distance between the knives on the cutter block. 
     The cut glass fibers are thereafter mixed with the further starting materials and discharged from the feeding arm in the manner as described above. 
     A feeding arm with the aforementioned cutting device has principally proven its worth in practical operations. It has been noticed, however, that the cutter block in particular can heat up to temperatures between 50 and 60° C., particularly during continuous operation. This heating leads to an increased wear of the knives. It was further observed that chemicals will deposit on the surface of the conveying rollers with which the glass fibers are coated for the purpose of better adherence in the matrix material of the pipe to be produced. This, in turn, can lead to increased wear by friction of the surfaces of the conveying rollers and consequently to an adverse grip of the fibers. 
     The invention is based on the object of providing a feeding arm of the kind mentioned above in which the described increase of temperature in the zone of the cutting device is at least reduced in order to avoid the aforementioned disadvantages. 
     One possibility would be the exchange of the predominantly metallic rollers against such made of plastic or hardwood which comprise a particularly lower heat conductivity. These rollers, however, comprise a considerably reduced mechanical strength and would therefore have to be exchanged more frequently. This would lead to undesirable standstill periods of the production plant. 
     Another possibility would be the cooling of the rollers by means of cooling air. This also entails a number of disadvantages: Cooling air would have to be supplied separately. In this respect, an additional cooling air conduit along the feeding arm would be necessary. As a result of the large number of conveying lines in the feeding arm for the numerous starting materials the provision of a further conveying line would lead to a space problem. Moreover, the cooling air would have to be distributed over the entire area of the roller surfaces. This would also lead to considerable space problems. Finally, the cooling air would have to be blown with a respective flow speed onto the rollers, thus making the guidance of the strands of glass fibers and the cut glass fibers uncontrollable in the zone of the cutting device. 
     BRIEF SUMMARY OF THE INVENTION 
     In the course of extensive preliminary tests various constructional modifications were tested. As a result, a completely different approach proved to be advantageous: 
     The desired object can be achieved in such a way that the aforementioned first roller (i.e. the roller that is not in contact with the cutting roller) is provided with a profiled surface. 
     By profiling the surface of the first roller a smaller surface contact is obtained between the first and second conveying roller. In this way, air can be additionally entrained during the conveyance of the strands of glass fibers between the rollers, which air has a cooling effect, particularly also in the direction towards the downstream third roller. This effect is supported by the rotational movement of the first roller which thus acts in the manner of a fan. 
     Accordingly, the invention relates in its most general embodiment to a feeding arm for the conveyance, preparation and supply of various starting materials for the production of glass fiber reinforced plastic pipes with the following features:
         A cutting device arranged on the output end for cutting glass fiber yarns to a predetermined length;   the cutting device is provided with at least three rollers which are arranged in an axially parallel manner;   the first roller is arranged with a profiled surface and is arranged such that it rolls off with its surface on a second roller which rotates in a direction opposite to that of the first roller;   a third roller is provided on its surface with a plurality of knives which extend spaced from one another in the axial direction of the roller and are arranged such that they roll off with their surface on the second roller which revolves in a direction opposite to that of the third roller.       

     In accordance with an embodiment, the second roller of the cutting device is to be provided with a reversibly deformable surface. In this way the “pressing pressure” of the first roller against the second roller can be increased with the advantage of a purposeful leadthrough of the strands of glass fibers. “Reversibly deformable surface” shall mean that the profiled surface of the first roller can press slightly into the surface of the second roller and that the surface will thereafter deform back again once the respective profiled element of the roller no longer has any contact with the surface of the second roller. 
     The second roller can consist superficially or in full of a respective material on the basis of plastic or caoutchouc for example. 
     The profiling of the first roller comprises in accordance with a further embodiment some ribs which extend in the axial direction of the roller. In this way the roller is provided with a “wave profile” on its surface. Particularly this embodiment shows a strong expression of the aforementioned “fan effect” which can be achieved with the roller. 
     It is sufficient to arrange the ribs with a relatively low height such as 1 to 5 mm for example. The distance of the ribs from one another can be as well within this range. 
     The first roller can have a smaller diameter than the second and third roller. This leads to a higher rotational speed as compared with the second roller. The higher rotational speed leads to an intensifying of the aforementioned cooling effect, with the air being conducted in the conveying direction of the strands of glass fibers in the direction towards the third roller. 
     The described cooling effect further leads to the consequence that the described deposits of additives (coating agents) of the strands of glass fibers are reduced considerably or avoided totally. The reduced surface contact between the first and second roller which is caused by the profiling of the first roller also contributes to this phenomenon. 
     Although the described cooling also allows considerably reducing the wear of the knives of the third roller, they are naturally still subject to a certain amount of wear. 
     It is therefore provided for in an embodiment to exchangeably fasten the knives of the third roller in the roller&#39;s body. 
     Finally, the invention provides to resiliently carry the first roller and/or the second roller, thus allowing the pressing pressure against the adjacent roller to be set to a desired amount either permanently and/or according to the respective application. 
     Further features of the invention are obtained from the features of the subclaims and the other application documents. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is now explained in closer detail by reference to an embodiment. Schematic illustrations thereof show as follows: 
         FIG. 1  a perspective view of a cutting device. 
         FIG. 2  a cross section through a feeding arm in the zone of the cutting device. 
     
    
    
     Components with a same or similarly function are shown with the same reference numerals in the figures. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The cutting device comprises a first roller  10  which is provided in the zone of its surface  10 . 1  with an axial ribbing  12 . As a result, ribs  12 . 1  which extend in the axial direction of the roller  10  and valleys  12 . 2  which extend parallel thereto between the ribs  12 . 1  are formed. Roller  10  is thus provided with a structural shape in the manner of a fan. During the rotation of the roller  10  in the direction of arrow D 10  air (cooling air) is accordingly conveyed in the direction towards a third roller (the cutting roller  30 ) which is arranged behind the same. 
     A second roller  20  is arranged coaxially to roller  10  adjacent to the latter, with the surface  20 . 1  of said second roller being provided with a coating made of rubber. Roller  10  rolls with its ribbing  12  on the surface  20 . 1  of roller  20  which rotates accordingly in the direction of arrow D 20 . 
     The cutting roller  30  is arranged coaxially to the second roller  20  behind the roller  10  and rotates in the direction of arrow D 30 . The cutting roller  30  also comprises a profiled surface  30 . 1 , similar to the first roller  10 . Trapezoid recesses  32  can be recognized in the surface zone of the cutting roller  30 , which recesses extend in the axial direction of the third roller  30 . Corresponding roller elements  34  rest in said recesses  32  whose surface extends the ribbing of the adjacent sections of the cutting roller  30 . The roller elements  34  rest in a stationary manner in the recesses  32  and simultaneously fix the knives  36  which extend in the axial direction of the cutting roller  30  and are fixed between the corresponding flanks of the roller elements  34  and the recesses  32  and project over the ribs  38  of the third roller  30 . 
     The cutting roller  30  is arranged in such a way that its knives  36  (here: 14 knives) touch the surface  20 . 1  of the second roller  20  or roll off from the same. 
     In this way the strands of glass fibers which at first are guided between the rollers  10 ,  20  are cut on their way between the rollers  20 ,  30  into corresponding sections according to the distance between the knives  36 . 
       FIG. 2  schematically shows the path of the strands of glass fibers (indicated there with reference numeral  40 ) with arrow G. 
       FIG. 2  also shows that the glass fiber strands  40  supplied in the axial direction of the rollers  10 ,  20 ,  30  via various pipes  50  are deflected before their path through the cutting device along a curved path  52  of the pipes  50 . 
       FIG. 2  also shows, in a schematic form, a resilient bearing (spring  14 ) of the first roller  10  or the second roller  20  (cylinder  16 ). 
     The profiling of the first roller  10  in particular leads to a dramatically increased supply of cooling air to the cutting device in total as compared with the known cutting devices and in particular to the contact zone of the first roller  10  with the second roller  20  or the second roller  20  with the third roller  30 . Respective tests have shown that as a result of the described arrangement it is possible to limit the increase of temperature of the rollers to 3 to 5 degrees.