Disk screen or like shaft assemblies and method of making the same
Disk screens are desirable apparatus for screening or classifying discrete materials such as paper pulp, municipal wastes, and the like. Such screens comprise a screening bed having a series of corotating spaced parallel shafts each of which has a longitudinal series of concentric screen disks which interdigitate with the screen disks of the adjacent shafts. Spaces between the disks permit only material of acceptable size to pass downwardly through the rotating disks bed, and since the disks are all driven to rotate in a common direction from the infeed end of the screen bed to the outfeed or discharge end of the bed, the particles of material which are larger than the acceptable sizes of material will be advanced on the bed to the outfeed end of the bed and rejected. 
     Several prior expedients have been heretofore devised for mounting the disks on the shafts, but there has been a persistent need for improvements as will be apparent from the following discussion of certain prior arrangements. 
     For example, in U.S. Pat. No. 4,239,119 the disks are provided with central holes having spline projections that engage in perforated retaining plates arranged to be received about a shaft. The splines which extend through the perforations of the plates fit closely at their ends against the shaft and are wedged in the plates. In practice, though not so stated in the patent, it has been found necessary to weld the disks to the plates for stability. 
     In U.S. Pat. No. 4,037,723, the disks are in direct engagement at their inner edges with the square tubing shaft, and tubular spacers engage endwise with the disks. 
     In another arrangement, as disclosed in U.S. Pat. No. 4,301,930, the disks are welded to cylindrical module hubs and the modules are assembled end-to-end on shafts. 
     Difficulties with the described prior arrangements have been experienced. The modules are very difficult to remove after a short period of operation because of fretting and corrosion between the modules and the shaft. Fabrication and assembly are expensive and time consuming. Quality control is difficult, due to the number of operations and parts involved. In the welding and mechanical binding of the disks to the retainer plates or spacers or to the module hubs, there may be slight variations from true radial mounting so that there may be a certain amount of wobble or variations in interface spacings. It has been found that frequently the disks will loosen after several months of service. 
     In the copending application of Eduard Josef Thoma, Ser. No. 646,135, filed Aug. 31, 1984, now abandoned, tubular elastomeric spacers engage a square tubing shaft and the disks are supported on the spacers by means of shoulders on the disks, thereby maintaining inner edges of the disks spaced from the shaft. That arrangement does not lend itself to a modular organization of the disks. 
     It is to the overcoming of problems and deficiencies inherent in the prior constructions that the present invention is directed. 
     An important object of the present invention is to provide a disk screen apparatus in which the disks are assembled on the shafts in a new and improved manner which not only facilitates mounting of the disks onto shafts, but also facilitates disassembly when necessary. 
     Another object of the invention is to provide new and improved modular disk unit for disk screen shaft assemblies. 
     A further object of the invention is to provide a new and improved disk screen or like shaft assembly in which not only is there excellent control of disk wobble, but also an improved connection and support of the disks at their hubs. 
     Still another object of the invention is to provide a new and improved modular mounting for screen disks attaining positive shaft driving of the disks and preventing loosening of the disks, as well as attaining accurate modular length control and facilitating mounting or removal of the disks with respect to the shaft. 
     Yet another object of the invention is to provide a new and improved modular disk screen or like shaft assembly in which the disks are free from welding which permits use of any desired material for the disks, as well as attaining other advantages. 
     To the attainment of the foregoing and other objects of the invention, there is provided a disk screen or like rotatable shaft assembly, comprising an elongate metallic shaft member, a plurality of metallic screen disks mounted rotatably on the shaft member, and having central shaft-receiving openings complementary to the shaft member, but of slightly larger size so that edges defining the openings can be in spaced relation to the shaft member. Nonmetallic spacers are disposed between the disks and with surfaces of the spacers engaging the shaft member. There are means for connecting the disks and spacers together into a modular unit which can be slidably mounted on or removed from the shaft member, and the spacers support the disks on the spacers with the edges spaced from the shaft member, and the spacers separating the disks in predetermined spaced relation. 
     A plurality of the disk and spacer modules is adapted to be mounted end-to-end on each of the shafts in a disk screen. 
     A new and improved screen disk module and method of producing the same is provided. 
    
    
     Other objects, features and advantages of the invention will be readily apparent from the following description of a representative embodiment thereof, taken in conjunction with the accompanying drawings, although variations and modifications may be effected without departing from the spirit and scope of the novel concepts embodied in the disclosure, and in which: 
     FIG. 1 is a side elevational schematic illustration of a disk screen apparatus emboding the invention. 
     FIG. 2 is an enlarged fragmental top plan view of a portion of the screening bed of the apparatus. 
     FIG. 3 is a fragmentary vertical sectional detail view taken substantially along the line III--III in FIG. 2. 
     FIG. 4 is a fragmental, vertical sectional detail view demonstrating a step in the making of a disk module. 
     FIG. 5 is a similar view showing another, step in the making of the module. 
     FIG. 6 is a perspective view of one of the disk spacers; and 
     FIG. 7 is a fragmental longitudinal sectional detail view taken substantially along the line VII--VII in FIG. 3. 
    
    
     As represented in FIG. 1, a disk screen apparatus 10 comprises a frame 11 supporting a screening bed 12, having a series of corotating spaced parallel shaft assemblies 13 of cylindrical perimeter and similar length, and each of which has a longitudinal series of concentric metal screen disks 14. As best seen in FIG. 2, the disks 14 of each of the shaft assemblies 13 interdigitate with the disks of the adjacent shafts. Each of the shafts 13 is preferably hollow tubular with a stub shaft 15 at one end and a stub shaft 17 at the opposite end, and the stub shafts are suitably journaled on the frame 11. Unison driving of the shafts 13 in the same direction, clockwise as seem in FIG. 1, is adapted to be effected by suitable drive means 18. 
     Discrete material to be screened is delivered to the infeed end of the screening bed 8 by means of a chute 19. Acceptable size particles drop through screening slots defined by and between the interdigitated portions of the disks 14, and are received in a hopper 20. Particles which are too large to pass through the screening slots are advanced to and discharged, as indicated by directional arrows 21, from the rejects end of the screening bed, as by means of an outfeed chute means 22. The screening function of the disks 14, may be enhanced by a uniform generally sawtooth configuration of the outer perimeters of the disks 10 provided by teeth 23 (FIG. 3). The number of such teeth and their size may be dictated by the particular material to be processed. Although shown as relatively sharp, sawtooth shape, the teeth 23 may, depending upon use, be of different geometric forms, such as lobulate or the like. 
     Each of the disks 14 is spaced from each adjacent disk throughout the entire set of disks in each of the shaft assemblies 13, to provide the desired screening slot spaces between the annular interdigitated areas of the disks. 
     According to the present invention, the desired spacing between disks on each of the disk screen shaft assemblies 13, is attained and maintained by means of respective nonmetallic spacers 24 intervening between each adjacent pair of disks. In a practical arrangement, where the disks 14 are formed from metal of about 5/32 inch thickness and of a diameter from 15 inches to 19 inches, the spacers 24 may be about half the diameter of the disks. Each of the spacers 24 may be formed from a stiffly elastomeric synthetic plastic material, such as polyurethane of about 90 A durometer. Where a 6 mm spacing between the interdigitated disks is desired, and where the disk thickness is about 5/32 inch, the spacers 24 may comprise plates of about 5/8 inch thickness. 
     In a perferred construction, each of the disk screen shaft assemblies 13 comprises, as best seen in FIGS. 2, 3 and 7, a hollow tubular metal shaft 25 which is of a non-circular cross section, conveniently generally square, and of a length of about 10 feet to accommodate thereon up to 144 of the disks 14. Disk carrying shaft assemblies of this size are especially suitable for disk screens for screening materials such as wood pulp slurry in the paper making industry. 
     Each of the disks 14 has a central shaft receiving opening 27 complementary to the shaft cross section but of slightly larger size, as best seen in FIG. 7, so that the edges defining the openings can be in spaced relation to the shaft. Each of the circular spacers 24 has a central hole 28 therethrough which is complementary to the shaft cross section, and the hole is defined by edges dimensioned for engaging the shaft. 
     Means are provided for connecting the disks 14 and the spacers 24 so that the spacers support the disks with the inner edges, that is the edges defining the openings 27, spaced from the shaft. For convenience in assembling the disks 14 and spacers 24 on the shaft 25 in each instance, the disks and spacers are connected together in convenient size modules, such as twelve disks to each module. For this purpose, bolt means 29 are provided, such as four bolts extending through closely sized bolt holes 30 through the inner or hub margins of the disks 14 and matching bolt holes 31 in the spacers 24. Desirably the matching bolt holes 30 and 31 are located in equally spaced circumferential relation. 
     Each of the bolts 29 comprises a rod which may typically be about 0.750 inch in diameter and of a length which will extend sufficiently beyond each end of its module to accommodate, at each end, a snap ring retainer 32 received in an annular groove 33. Endwise projection of the bolts 29 at each end of the module is sufficiently less than the desired spacing between the disks of the modules, so that when the modules are placed end-to-end in assembly on the associated shaft 25 there will be no interference with proper spacing between the adjacent end disks 14 of the modules. Such spacing between the ends of contiguous modules in the series on the shaft is maintained by means of intermodule spacers 34 which are dimensioned generally similar to the spacers 24, but have clearance holes 35 therethrough large enough to accommodate the lockup snap ring carrying extermities of the bolts 29 of the contiguous disks module ends. 
     As demonstrated in FIGS. 4 and 5, assembly of the disk modules is easily effected by assembling a set of the disks 14 and intervening spacers 24 on a set of the rods 29 (FIG. 4) in a jig 37, which has an anvil 38 on which an endmost disk 14 of a module stack is placed. The connecting bolt ends carrying the snap rings 32 and associated with the anvil 38 are accommodated in a clearance recess 37. At this stage in the assembling process, the full set of disks 14 and intervening spacers 24 may be slightly longer than in the final assembly, occasioned by having the spacers 24 initially slightly thicker than desired in the final assembly. When the module assembly is placed under end-wise compression, the inner edges of the spacers defining the holes 28 will flow or extrude inwardly from a dimension which may be initially the same as the fixed dimension of the edges defining the openings 27 to the desired reduced dimensions of the spacer hole edges for engagement with the shaft when the module is assembled with the shaft. This inward flow displacement is show in FIG. 4 by comparison of the full line initial dimension of the edges 28 with the phantom line dimension. Such compression is desirably to assure a tight, firm, wobble free assembly of the disks 14 with the spacers 24. 
     Compression of the module assembly may be effected between the anvil 37 and compressing plunger means 40 as shown in FIG. 5, and the retainer snap rings 32 on the remaining ends of the bolts 29 (the top ends in FIG. 5) secured in place to maintain the module in its operative condition. It will be appreciated that when it is desired to replace any of the disks 14, such as disks that may have been damaged in service, it is a simple matter to reverse the assembly steps, effect any replacements necessary and then reassembly and compress the assembly and secure it as already described, utilizing the jig 37 or its equivalent. 
     After the disk modules have been individually assembled as just described, they are assembled in end-to-end relation on the selected shaft 25 and locked in place thereon. In one desirable arrangement, the shaft 25 carries at one end thereof a rigid clamping ring plate 41 through which the stub shaft 15 projects, and at the opposite end a rigid clamping ring plate 42 through which the stub shaft 17 projects. Means are provided for drawing up the plates 41 and 42 toward the associated ends of the series array of disk modules, in this instances comprising headed screw bolts 43 at one end of the shaft assembly and which are threadedly engaged in a rigid centering disk 44 secured as by means of welding intermediate the ends of the respective stub shaft 17 and welded within the associate end of the hollow shaft 25. A similar stabilizing disk 45 secures the inner end portion of the stub shaft 17 within the hollow shaft 25. A centering pin 47 extends from the disk 44 through the associated clamping plate 42. 
     At the opposite end of the shaft assembly, similar rigid centering and connecting disks 44 and 45 secure the stub shaft 15 to the shaft member 25. 
     For applying yieldable compression to the associated ends of the disk module array, takeup means are provided comprising a take-up spacer ring 48 which is thrust by the plate 41 toward the adjacent endmost disk 14, and a takeup spacer ring 49 is thrust by the takeup plate 42 toward the endmost disk 14 at that end of the shaft assembly. Desirably both of the spacer rings 48 and 49 may be formed from the same material as the spacers 24. Each of the spacer rings 48 and 49 may have holes 50 therethrough, similar to the holes 35 in the spacers 34, for accommodating the associated ends of the connecting bolts 29. 
     In order to standardize on the construction of the screen disk shaft assemblies 13, the arrangement may be such that by alternately turning, i.e. reversing, the several shaft assemblies end-for-end proper interdigitation of the disks will be attained. A desirable expedient for attaining this result is to have the spacer ring 48 of about the same width as the spacers 24, while the spacer ring 49 is of half the width of the spacer ring 48. The ends of the hollow shaft member 25 extend a sufficient distant beyond the opposite ends of the array of disk modules to support the spacer rings 48 and 49. 
     At the clamping plate 42 end of the hollow shaft member 25, it serves as a stop for this plate as drawn up by the bolts 43. 
     By constructing the screen disk modules according to accurate standards, assembly of the modules on the shaft member 45 by sliding the same into place, and then locking the modules on the shaft can be quickly and easily effected. Such accuracy is implemented by the fact that the spacers 24, 34, 48 and 49 can be accurately cast in material such as polyurethane, incorporating therein fairly accurately calculated width dimensions and durometer or stiffness characteristics so that when each module assembly is completed, and then the array of modules is locked in place on the hollow shaft member, predetermined compression will attain predetermined measured relative spacing results for the screen disks 14 both with respect to one another and with respect to the hollow shaft member 25 and then with respect to the associated shaft assemblies in the screening bed 12. For example, when completing each of the disk modules, as demonstrated in connection with FIG. 5, 8500 pounds compressing pressure may be applied where the material is polyurethane of 90 A durameter. Such compression may be calculated to provide for about 0.020 inch inward deflection and extension of the inner edges of the spacers 24 substantially uniformly about each of the spacer holes 28, thereby supporting the inner edges of the disks 14 in a uniform 0.020 inch spaced relation to the shaft member 25. 
     Although the bolts 43 draw up the plate 42 against the end of the shaft 25, means are provided at the opposite end of the shaft assembly for drawing up the plate 41 against the spacer 48 with a limited range of compression latitude for attaining reasonably accurate overall measurement for the shaft disk array. Therefore, the spacer extends a limited distance endwise from the associated end of the shaft 25, and a locknut 51 threaded on the stub shaft 15 is torqued against the pressure plate 41 with sufficient pressure to attain the desired locked up compression of the disk modules between the end spacers 48 and 49. To retain the locknut 51 against unintended backing off, a lock washer 52 may be provided having locking tabs 53 bent into interlock grooves in the outer surface of the nut after torquing. 
     Among the advantages of having the spacers 24 and 34 and the compression members 48 and 49 made from a nonmetallic material and maintaining the metal disks 14 and the metal shaft 25 separated, in that fretting and corrosion &#34;freezing&#34; of the disk modules is avoided, so that replacement of disks is facilated, should that become necessary. 
     It will be evident from FIGS. 5 and 7 that the spacers 24 in cooperation with the connecting means bolts 29 retain the inner edges of the disks 14 effectively spaced from the central holes 28 of the spacers and from the surface of the shaft on which the disk modules may be mounted and with which the inner edges defining the holes 28 engage. 
     It will be understood that variations and modificatins may be effected without departing from the spirit and scope of the novel concepts of the present invention.