Abstract:
A measuring device for detecting the state of wear of the bore walls of two interpenetrating housing bores, having mutually parallel bore axes, of at least two-shaft screw extruders has a carriage provided with rear drive wheels, front guide wheels and contactlessly operating distance sensors which can each be pivotally driven about a bore axis and can be positioned at a distance from the respective bore wall.

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
       [0001]    The invention relates to a measuring device for detecting the state of wear of the bore walls of two interpenetrating housing bores, having mutually parallel bore axes, of at least two-shaft screw extruders. 
         [0002]    Two-shaft and multi-shaft screw extruders have a broad range of overall sizes, namely from the smallest laboratory machines having bore diameters in the range of from 15 to 20 mm to large-scale machines having bore diameters of up to 400 mm. The screws rotating in the housing bores, in conjunction with the material processed or machined therein, cause wear to the bore walls. This gives rise to variations in the diameters of the housing bores and the screws. Whereas the screws are occasionally withdrawn, cleaned and if necessary calibrated, detecting wear of the bore walls is difficult. In practice, this requires the housings, which are generally constructed from individual housing sections, to be completely disassembled. 
         [0003]    With known mechanical measuring sensors, measuring the housing bores when the extruder housings are assembled is very difficult, as the sensors can remain suspended in the inlet and degassing openings. It is often impossible clearly to define the respective measuring planes and the respective measuring points on the circumference. In addition, material residues on the bore walls inevitably cause measurement errors. 
         [0004]    Also known are movable cylindrical bore measuring heads each having two capacitive distance measuring sensors having merely a narrowly delimited measuring range, so almost every size of extruder requires its own measuring head. In addition, only one housing bore can be measured at a time. Each time the measuring sensor passes through the housing bore, the measurement can be carried out merely in predetermined angular position relative to the bore axis. The measuring sensor therefore has to pass through each housing bore a relatively large number of times. 
       SUMMARY OF THE INVENTION 
       [0005]    The object of the invention is to provide a measuring device of the general type allowing the complete actual geometry of two bore walls to be detected in a single operation. 
         [0006]    According to the invention, this object is achieved by a measuring device for detecting the state of wear of the bore walls of two interpenetrating housing bores, having parallel bore axes, of at least two-shaft screw extruders, which device has a carriage, with rear drive wheels which are arranged on drive axles, the length of which is variable, with front guide wheels which are arranged on front axles, the length of which is variable, and with contactlessly operating distance sensors which each are pivotally drivable about a bore axis and are positionable at a distance from neighbored bore wall. The two distance sensors are located in a common measuring plane. On continuous advancement of the measuring device, the entire profile of the bore walls is detected approximately in the manner of a partial helical line, from gusset to gusset in each case. On the other hand, individual measuring planes can be approached and then measured exactly. The axles, the length of which may be varied, allow very simple adaptation to differing diameters of the bores in the extruder housing. 
         [0007]    The construction of the measuring device in which the carriage comprises modules and in which the carriage comprises a drive module with the drive wheels, a guide module with the guide wheels and a sensor module with the distance sensors allows a particularly simple construction of the measuring device. The developments in which the drive wheels and the guide wheels are exchangeable, in which the distance sensors are arranged on pivot arms which are pivotable about a bore axis and the length of which is variable, in which the pivot arms are each arranged on an angular gear connected to a common pivot drive via a shaft, the length of which is variable and in which the distance between the modules is variable allow particularly simple adaptation to differing diameters of the bores in the extruder housing or to differing distances between the axes of the bores. A measuring device in which the front guide wheels have an oblique camber or track provides simple centering of the gear wheels and therefore of the measuring device in the bores. 
         [0008]    A measuring device in which a distance measuring means is associated with the rear drive wheels and a measuring device associated with the distance sensors being a position transmitter detecting an angular position thereof show how the measured values are detected. 
         [0009]    Further features, advantages and details of the invention will emerge from the following description of an embodiment given with reference to the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  shows a schematic lateral longitudinal view of a measuring device according to the invention, 
           [0011]      FIG. 2  shows a plan view onto the measuring device, 
           [0012]      FIG. 3  shows a front view showing primarily the wheels of the measuring device, and 
           [0013]      FIG. 4  shows a cross-section, taken along the section line IV-IV in  FIG. 1  through the measuring device. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0014]    The basic construction of the measuring device shown in the drawings consists of three modules, namely a rear drive module  1 , a front guide module  2  and a central sensor module  3 . 
         [0015]    The drive module  1  has a central drive unit  4  having an electric motor as the drive motor  5  and a reduction and differential gear  6  downstream therefrom. Guided out of the gear  6  are rear drive axles  7 , attached to the outer ends of which are drive wheels  8 . The axles  7  can be inserted into the gear  6  or be extendable in a different manner, so the track width a of the drive wheels  8  can be varied by appropriately extending the axles  7 . In conjunction with the exchange or the extension of the axles  7 , the drive wheels  8  are also exchanged and replaced in each case by wheels of differing diameter b. The drive unit  4  also has a distance measuring means  9  which issues in a conventional manner a large number of signals, i.e. conventionally 512 signals, per revolution of each axle  7 , from which, in conjunction with the respective diameter b of the drive wheels  8 , the distance covered can be determined. 
         [0016]    The guide module  2  has a base frame  10  to which there are attached front axles  11  having at their free ends a respective guide wheel  12 . In order to allow their track width also to be varied, the front axles  11  are either insertably fastened to the base frame  10  or else extendable. 
         [0017]    As may be seen in  FIG. 3 , the width c of the guide wheels  12  is much greater than the width d of the drive wheels  8 . As may also be seen in  FIG. 3 , the drive wheels  8  are arranged parallel to each other. The guide wheels  12 , on the other hand, are inclined relative to the drive wheels  8  by a camber angle α, so their underside is located in each case between the drive wheels  8 . The camber angle α is identical for both guide wheels  12 . The running face  13  of the guide wheels  12  is curved. Instead of a camber angle α, the guide wheels can also have a track angle, i.e. they can approach each other toward the front. The wheels  8  and  12  preferably have rubber tyres. 
         [0018]    The sensor module  3  has a base plate  14  on which there are arranged an electric motor as the pivot drive  15  and a reduction and power take-off gear  16 . Insertably attached to the gear  16  are stay pipes  17  in which a respective shaft  18  is arranged. Attached to the outer ends of the stay pipes  17  is in each case an angular gear  19  into which the respective shaft  18  is guided. Attached to the output of each angular gear  19 , so as to rotate through 360°, is a pivot arm  20 ,  20 ′ which is driven by the motor  15  via the shaft  18  and the gear  19 . Attached to the respective outer end of each pivot arm  20 ,  20 ′ is a distance sensor  21 ,  21 ′. The stay pipes  17  with the shafts  18  are insertable and therefore exchangeable in each case. Similarly, the pivot arms  20 ,  20 ′ are also attachable and therefore exchangeable. 
         [0019]    The drive module  1  is connected to the sensor module  3  via a detachable and exchangeable connecting part  22 . The sensor module  3  is connected to the guide module  2  in a corresponding manner using an exchangeable connecting part  23 . 
         [0020]    Arranged on the base frame  10  of the guide module  2  is a power supply unit  24  via which the motors  5  and  15  are powered. The power supply unit therefore consists substantially of a battery. Obviously, it is also possible for the motors  5  and  15  to be supplied with electric current via guided electrical lines (not shown). Also provided on the base frame  10  of the guide module is a radio control unit  25  which both forwards the measurement data generated in the form of signals, to a central operating and control unit  26  and also provides the motors  5  and  15  with the requisite control data. 
         [0021]    The measuring device is used to measure the diameters e and f of the bores  27 ,  28  in an extruder housing  29 . The bores  27 ,  28  have mutually parallel axes  30 ,  31  and penetrate each other to form gussets  32 ,  33  so the distance g between the axes  30 ,  31  is smaller than e or f, e and f obviously being identical when the housing  29  is as it should be. The briefly described geometry of an extruder housing  29  is in practice generally conventional, so further discussion thereof can be dispensed with. Instead of two bores  27 ,  28 , three or more bores can also be arranged adjacently to one another, the axes  30 ,  31  each being arranged in a common horizontal plane. 
         [0022]    During advancement longitudinally through an extruder housing  29 , the measuring device is driven via the drive module  1 , the distance covered and therefore also the respective location of the measuring device being exactly detected—starting from the start of the bores  27 ,  28 —using the distance measuring means  9 . As may be seen from  FIG. 3 , the track width a of the drive wheels corresponds exactly to the axial distance g between the bores  27 ,  28 . 
         [0023]    The measuring device is guided and centred, so as to be arranged precisely mirror-symmetrically to a centre plane  34  passing through the gussets  32 ,  33 , via the guide wheels  12  which are inclined relative to the vertical and the running faces  13  of which are adjacent to the gussets  32 ,  33 , as may be seen from  FIG. 3 . The curvature of the running faces  13  corresponds to the curvature of the respective bore wall  35 ,  36 . As stated hereinbefore, the guiding and centering can be achieved not only through a corresponding camber angle α but also through a corresponding track angle of the guide wheels  12 . 
         [0024]    During advancement, the pivot arms  20 ,  20 ′ with the distance sensors  21 ,  21 ′ are pivoted in opposite directions, in the directions of the double-headed arrows in  FIG. 4  from gusset  32  to gusset  33  and, conversely, along the bore wall  35  or  36  respectively. In this case, the distance sensors  21 ,  21 ′ respectively detect the distance h or i from the bore wall  35  or  36 . As the pivot axes of the pivot arms  20 ,  20 ′ extend coaxially with the axes  30  and  31  of the bores  27 ,  28 , changes in the diameter e or f of the bore are thereby detected. As the sensor module  3  is also provided with a position transmitter  37 , which continuously issues a large number of signals during each pivoting movement of the pivot arms  20 ,  20 ′, the diameter e or f, respectively, of the bores  27 ,  28  can be measured exactly over the circumference of each bore wall  35  or  36  and, in conjunction with the distance measuring means  9 , over the length of the bores  27 ,  28 . The actual geometry of the bores  27 ,  28  can therefore be detected precisely. The measured values are forwarded to the central operating and control unit  26  via the radio control unit  25 . 
         [0025]    As will be apparent from the foregoing, the measuring device described can be used for bores  27 ,  28  in extruders having any desired diameters or distance between the axles. Only a few parts have to be exchanged. 
         [0026]    For any desired overall size of an extruder within specific overall size ranges, i.e. for any bore diameter e, f falling within this range and for any desired distance g between the axles, the following components are identical:
       drive module  1  except for the drive axles  7  and the drive wheels  8     guide module  2  except for the front axles  11  and the guide wheels  12     sensor module  3  except for the stay pipes  17 , the shafts  18  and the pivot arms  20 ,  21         
 
         [0030]    For any extruder overall size within the aforementioned overall size range and having an identical distance g between the axles but a differing bore diameter e, f (see  FIGS. 3 and 4 ), the following components are also identical:
       connecting parts  22 ,  23     stay pipes  17  and shafts  18         
 
         [0033]    In order for the pivot axes of the pivot arms to coincide in each case in an identical manner with the axes  30 ,  31  of the housing bores  27 ,  28 , the axles  7  and  11  have to have a uniform vertical distance j from a horizontal centre plane  38  spanned by the bore axes  30 ,  31 . The wheels  8 ,  12  are to be chosen accordingly in each case.