PULPSTONE MOUNTING
United States Patent 3620462
A pulpstone mounting structure is adapted to center the pulpstone on a drive shaft and effect the transmittal or the driving force from a drive shaft to the pulpstone so as to maintain a relatively low preset axial compressive force on the pulpstone ends.
US Patent References:
Crusher roll
Battey - March 1922 - 1410546
Shell type pulpstone
Minarik - May 1959 - 2887276
Crushing rolls
McKenna - June 1964 - 3138338
Crusher roll
Battey - March 1922 - 1410546
Shell type pulpstone
Minarik - May 1959 - 2887276
Crushing rolls
McKenna - June 1964 - 3138338
Application Number:
05/045682
Publication Date:
11/16/1971
Filing Date:
06/12/1970
View Patent Images:
Export Citation:
Primary Class:
International Classes:
B24D5/16; D21B1/06; B24D5/00; D21B1/00; B02C4/30
Field of Search:
241/67,293,294
Primary Examiner:
Granville Jr., Custer Y.
Attorney, Agent or Firm:
Brownell K. W.
Claims:
1. A pulpstone-mounting structure comprising a pulpstone having a plurality of abrasive segments rigidly affixed to the periphery of an annular core, drive shaft, driving means for providing a driving engagement between said drive shaft and said pulpstone so as to substantially maintain a preset compressive force on the pulpstone ends, and independent means for centering said pulpstone being associated with and operatively connected to said pulpstone and said shaft.
2. A pulpstone-mounting structure in accordance with claim 1, wherein the driving means is slidably mounted on said shaft for movement in an axial direction.
3. A pulpstone-mounting structure in accordance with claim 2, wherein said annular core has a main bore, said drive shaft includes a pair of shoulders, each disposed within the main bore, and said centering means includes a pair of centering rings, each connected to a shoulder.
4. A pulpstone-mounting structure in accordance with claim 3, wherein the driving means includes a pair of flanges mounted on said drive shaft, each flange being slidable in an axial direction and being keyed for rotation.
5. A pulpstone-mounting structure in accordance with claim 4, further comprising bores passing axially through the annular core, boreholes in said flanges matching the bores in the annular core, tie rods passing through said bores and boreholes connecting said pulpstone and said flanges.
6. A pulpstone-mounting structure in accordance with claim 4, wherein said pulpstone further comprises a pair of hubs embedded in the annular core and projecting into the main bore, each hub abutting a centering ring.
7. A pulpstone-mounting structure in accordance with claim 6, wherein said centering ring has an outside surface tapered inwardly toward the center of the axis of rotation of said pulpstone, and said hub presents a flat face matching the taper of the centering ring.
8. A pulpstone-mounting structure in accordance with claim 7, wherein the enlarged portion of said drive shaft includes a plurality of axially aligned threaded bores, said centering ring includes a plurality of holes matching the threaded bores, and bolts attach said centering ring to the enlarged portion through the bores and threaded bores.
9. A pulpstone-mounting structure in accordance with claim 8, wherein said drive shaft includes key beds, said flanges have a bore with keyways located therein, and keys are located in said key beds and keyways.
10. A pulpstone-mounting structure in accordance with claim 9, including a sealing means being operatively associated with said drive shaft and said flanges.
2. A pulpstone-mounting structure in accordance with claim 1, wherein the driving means is slidably mounted on said shaft for movement in an axial direction.
3. A pulpstone-mounting structure in accordance with claim 2, wherein said annular core has a main bore, said drive shaft includes a pair of shoulders, each disposed within the main bore, and said centering means includes a pair of centering rings, each connected to a shoulder.
4. A pulpstone-mounting structure in accordance with claim 3, wherein the driving means includes a pair of flanges mounted on said drive shaft, each flange being slidable in an axial direction and being keyed for rotation.
5. A pulpstone-mounting structure in accordance with claim 4, further comprising bores passing axially through the annular core, boreholes in said flanges matching the bores in the annular core, tie rods passing through said bores and boreholes connecting said pulpstone and said flanges.
6. A pulpstone-mounting structure in accordance with claim 4, wherein said pulpstone further comprises a pair of hubs embedded in the annular core and projecting into the main bore, each hub abutting a centering ring.
7. A pulpstone-mounting structure in accordance with claim 6, wherein said centering ring has an outside surface tapered inwardly toward the center of the axis of rotation of said pulpstone, and said hub presents a flat face matching the taper of the centering ring.
8. A pulpstone-mounting structure in accordance with claim 7, wherein the enlarged portion of said drive shaft includes a plurality of axially aligned threaded bores, said centering ring includes a plurality of holes matching the threaded bores, and bolts attach said centering ring to the enlarged portion through the bores and threaded bores.
9. A pulpstone-mounting structure in accordance with claim 8, wherein said drive shaft includes key beds, said flanges have a bore with keyways located therein, and keys are located in said key beds and keyways.
10. A pulpstone-mounting structure in accordance with claim 9, including a sealing means being operatively associated with said drive shaft and said flanges.
Description:
Pulpstones used in the paper industry for grinding logs may be 80 inches in diameter, weigh as much as 15 tons and be driven with a 10,000 -horsepower motor or engine. They are typically mounted on driving shafts by spaced flanges which center the pulpstone and provide driving engagement between the shaft and the stone. Such flanges are normally mounted on threads integral with the shaft; right- and left-hand threads being provided so that the flanges may be tightened to center and drive the shaft. The stone is driven in a direction relative to the threads on the drive shaft such that the flanges are continuously tightened during use.
In another mounting method, the stone is set on the shaft and the shaft is expanded in length by means of a heated fluid introduced between the shaft and the stone. Collars which are placed in annular grooves in the shaft are in contact with the flanges. When the shaft cools to its normal temperature, a tensile load corresponding to its longitudinal contraction is transmitted to the pulpstone through the collars.
The high compressive force applied to the stone in these previously used mounting and driving methods together with the action of chemicals present in the wood and water, cause the parts compressively engaged to become bonded together. At the time of changing the wheel, the bonding action often has become so great that it is very difficult to remove the pulpstone from the shaft.
In conventional mountings, flanges mounted on the drive shaft can compress the pulpstone to such an extent that cracking thereof results.
Accordingly it is an object of the present invention to provide a new and improved mounting structure for pulpstones utilizing a relatively low preset compressive force on the pulpstone.
Other and further objects of the present invention will become apparent from the following description.
In accordance with the present invention, a pulpstone mounting structure is provided which comprises a pulpstone having a plurality of abrasive segments rigidly affixed to the periphery of an annular core, a drive shaft, driving means for providing a driving engagement between said drive shaft and said pulpstone so as to substantially maintain a preset compressive force on the pulpstone ends, and an independent means for centering said pulpstone on said shaft.
FIG. 1 is a fragmentary front elevation of the pulpstone mounting structure showing the top one-half of the pulpstone in section; and
FIG. 2 is a fragmentary, transverse section on line 2--2 of FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to the drawings, the pulpstone 11 is shown as having a concrete core 13 of annular shape. The core 13 may be reinforced with metal hoops and rods (not shown) to give it greater strength. A main bore 15 extends axially therethrough. The core ends 17 are flat radial surfaces, and its outer surface 19 is radially spaced from the axial center.
The terms outer and inner and the like as hereinafter used are applied only for convenience of description and should not be taken as limiting the scope of this invention.
A plurality of abrasive segments 21 in a peripheral layer 22 are rigidly mounted on the outer surface 19 of the concrete core with a plurality of fastening means 23. Each abrasive segment is of a vitrified bonded abrasive material, such as are well known in the art, see for example, U.S. Pat. No. 1,736,161.
The fastening means 23 generally are steel bolts with annular protrusions. One end of the fastening means 23 is anchored into a hole in the segments 21, the other end is either cemented into preformed holes in a hardened core or positioned in a wet concrete core 17. Hardening of the cement or concrete around the annular protrusions securely holds the segments to the core 17.
The core 17 is provided with a plurality of aligned longitudinal bores 25 intermediate its inner and outer peripheries. The bores 25 are equidistant from the longitudinal axis of the core 17 and equidistant from each other. Preferably each of the bores 25 is lined with a tube 27 which may be introduced by casting the core 17 around prearranged tubes.
Adjacent the ends of the core are a pair of annular hubs 29 which are embedded in the core 17 and which project into the main bore 15 toward the axis of rotation. Each hub 29 is coaxially aligned with core 17 so that the pulpstone 11 will be balanced around its center axis.
The drive shaft 33 has successively enlarged portions 35, 37. The latter enlarged portion 37 is disposed within the main bore 15 of the core 17 while the former portion 35 extends axially beyond the ends of the pulpstone 11. The enlarged portion 37 presents a pair of flat faces 39 or shoulders radially extending outwardly from the portion 35 of the shaft.
A centering means positions the pulpstone axially on the drive shaft. It includes a pair of centering rings 41, each of which presents an inner cylinder bore 43 to the main portion 35 of the drive shaft and an outer surface 45 gradually tapered inwardly toward the center of the axis of rotation of the pulpstone 11. As each centering ring 41 is moved toward the axial center, the outer surface 45 having an increasingly greater diameter acts to line up the axial centers of the pulpstone 11 and shaft 33. The outer surface 45 of the centering ring 41 contacts a hub 29 which presents a matching inner-tapered face 47 thereto.
Each centering ring 41 is positioned adjacent a shoulder 39. A plurality of bores 49 in the centering ring 41 are radially spaced and axially aligned. A plurality of bores 51 in each shoulder 39 for receiving bolts 53 or threaded screws match the bores 49 in the centering rings 41. Bolts 53 located in the bores when tightened draw the centering rings 41 toward the shoulder 39 thereby centering the pulpstone 11. The centering means is designed to center the wheel and prevent axial movement, not to drive the wheel by frictional means.
Since both centering rings are identical and are situated in a similar manner, it is believed that the aforementioned description of only one, as shown in FIG. 1, will suffice. The flanges and sealing means are hereinafter described in a similar manner.
The driving means includes a pair of flanges 55 slidably mounted on the drive shaft 35 for axial movement with respect thereto. Each flange 55 has a straight main bore 57 therethrough with an inside surface matching the cylindrical surface of the main portion 35 of the drive shaft. A keyway 59 which forms a channel is recessed in the main flange bore 57. A rectangular key bed 61 is located in the portion 35 of the shaft on either side of the pulpstone 11. A key 63 fits into the key bed 61 and the keyway 59. This mounting permits each flange 55 to freely move axially with respect to the drive shaft. The straight flange bore 57 slides over the drive shaft 35 and the flange keyway 59 slides over key 63. The aforementioned mounting results in little or no diaphragming or bending action on the flanges 55 and maintains a relatively constant compressive force on the ends 17 of the core 13.
A plurality of boreholes 65 which are radially spaced from the axial center of the flanges 55 match the bores 25 of the pulpstone 11. The boreholes 65 are set in a recessed well 67 which protects the mounting installation.
The flanges are securely attached to the pulpstone through the boreholes 65 so as to directly drive it. A plurality of tie rods 69 are positioned in the pulpstone bores 25 and boreholes 65. Preferably about eight to about 12 tie rods are used. They are tightened under a tensile stress so as to preload them to prevent loosening, but do not have to be tightened so as to drive the pulpstone by friction as the tie rods themselves act as drivers. In FIG. 2, although not shown, the tie rods will actually contact the inner surface of the tubes so as to directly drive the pulpstone.
Blotter pads 71 may be placed in between the flanges 55 and the ends of the pulpstone 11 to allow for irregularities in the concrete core ends 17 and permit an even application of compressive force thereto.
To prevent corrosive chemicals from effecting the mounting structure a sealing means is provided. It includes an annular collar 73 having a straight bore 75 axially contacting the drive shaft 35 around its periphery and an outwardly extending radial portion 77 abutting the exterior of the flange 55 and connected thereto with a plurality of bolts 79 or screws. Water cascading over the flanges does not contact the vital parts of the mounting structure.
In the installation of a pulp wheel utilizing the mounting structure of the present invention, no mounting or dismounting fixture is required. With the pulp wheel sitting on the floor in its shipping skid, it is possible for two men with a shaft lifting beam to mount the pulpstone. The shaft is located in the main bore 15 of the core 17 with the lifting beam so that the hubs 29 are in proximity to the shoulders 39 of the shaft. The pair of centering rings 41 are slid over opposite shaft ends and centering bolts 53 loosely put into place. A sheet metal template which fits the shaft and has a keyway to fit the key bed 61 in the drive shaft 35 and at least one hole corresponding in radius to the bores 25 in the pulpstone 11 is slid over one end of the driving shaft 35. The driving shaft is turned until a pulpstone bore 25 lines up with the hole in the template. The centering bolts 53 are then tightened to the enlarged center portion of the drive shaft sufficiently to center the pulpstone 11 and prevent axial movement. The template is removed and blotter pads 71 are positioned if not previously positioned. The flanges 55 are slid over the shaft ends, the boreholes 65 in the flanges 55 lining up with bores 25 in the cement core 17. The tie rods 69 are inserted through the bores 25 in the pulpstone 11 and respective boreholes 65 in the flanges 55 and tightened. In tightening, a 6 -foot wrench that one man can lift manually is all that is needed. The tie rods 69 are torqued to give a predetermined or preset compression to the blotters 71 so as to preload the tie rods to prevent loosening. The drive shaft with pulpstone 11 mounted thereon is then journaled to a drive means including a motor or engine.
To dismantle the pulpstone from the drive shaft the process is essentially reversed. The gradual taper of matching surfaces of the hub and centering ring, the light construction of the centering rings, and relatively low compression of the bolts 53 prevents the hub 29 and centering ring 41 from becoming unduly wedged together. A jackscrew may be employed by threading into the bore 49 in the centering ring and turning against the shoulder 39 to remove stubborn centering rings.
Pulpstones of various design and construction may be mounted with the mounting structure of the present invention. The pulpstone may incorporate various reinforcing means of a variety of materials in the core, such as metal drums, reinforcing wire, plates and tie rods. They may employ various means for fastening the abrasive segments to the annular core such as the method described in U.S. Pat. No. 2,516,693.
In one method of construction the pulpstone abrasive segments equipped with the fastening means are assembled in the form of an annulus. A fixture within which the free ends of the fastening means extend inwardly toward the center is used. Metal reinforcing hoops and rods are located in the core at this time. Concrete is poured between an inside cylindrical form inserted within the fixture and the inside annulus of segments so as to embed the fastening means, reinforcing rods, hubs and tubes in the concrete. After the core has set, the wheel is removed from the fixture.
In another method, the pulpstone may be constructed by first forming the concrete core with the base of the fastening means cemented therein and the remaining portion protruding outwardly. The abrasive segments may then be installed to the core by filling the machined holes in the abrasive segments with cement, aligning the fastening head and hole, then pressing the abrasive segment to the core. Upon setting of the cement, the segment will be tightly affixed to the core.
Although the flanges may be mounted to the pulpstone by the tie rods, bolts or other means securely and firmly connecting the ends of the pulpstone to the flanges may be used.
The centering rings are shown in FIG. 1 as abutting a hub, but they may also abut a properly formed inside conical surface of the cement core.
While preferred embodiments of this invention have been described and illustrated, it is to be recognized that modifications and variations thereof may be made without departing from the spirit and scope of this invention as described in the appended claims.
In another mounting method, the stone is set on the shaft and the shaft is expanded in length by means of a heated fluid introduced between the shaft and the stone. Collars which are placed in annular grooves in the shaft are in contact with the flanges. When the shaft cools to its normal temperature, a tensile load corresponding to its longitudinal contraction is transmitted to the pulpstone through the collars.
The high compressive force applied to the stone in these previously used mounting and driving methods together with the action of chemicals present in the wood and water, cause the parts compressively engaged to become bonded together. At the time of changing the wheel, the bonding action often has become so great that it is very difficult to remove the pulpstone from the shaft.
In conventional mountings, flanges mounted on the drive shaft can compress the pulpstone to such an extent that cracking thereof results.
Accordingly it is an object of the present invention to provide a new and improved mounting structure for pulpstones utilizing a relatively low preset compressive force on the pulpstone.
Other and further objects of the present invention will become apparent from the following description.
In accordance with the present invention, a pulpstone mounting structure is provided which comprises a pulpstone having a plurality of abrasive segments rigidly affixed to the periphery of an annular core, a drive shaft, driving means for providing a driving engagement between said drive shaft and said pulpstone so as to substantially maintain a preset compressive force on the pulpstone ends, and an independent means for centering said pulpstone on said shaft.
FIG. 1 is a fragmentary front elevation of the pulpstone mounting structure showing the top one-half of the pulpstone in section; and
FIG. 2 is a fragmentary, transverse section on line 2--2 of FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to the drawings, the pulpstone 11 is shown as having a concrete core 13 of annular shape. The core 13 may be reinforced with metal hoops and rods (not shown) to give it greater strength. A main bore 15 extends axially therethrough. The core ends 17 are flat radial surfaces, and its outer surface 19 is radially spaced from the axial center.
The terms outer and inner and the like as hereinafter used are applied only for convenience of description and should not be taken as limiting the scope of this invention.
A plurality of abrasive segments 21 in a peripheral layer 22 are rigidly mounted on the outer surface 19 of the concrete core with a plurality of fastening means 23. Each abrasive segment is of a vitrified bonded abrasive material, such as are well known in the art, see for example, U.S. Pat. No. 1,736,161.
The fastening means 23 generally are steel bolts with annular protrusions. One end of the fastening means 23 is anchored into a hole in the segments 21, the other end is either cemented into preformed holes in a hardened core or positioned in a wet concrete core 17. Hardening of the cement or concrete around the annular protrusions securely holds the segments to the core 17.
The core 17 is provided with a plurality of aligned longitudinal bores 25 intermediate its inner and outer peripheries. The bores 25 are equidistant from the longitudinal axis of the core 17 and equidistant from each other. Preferably each of the bores 25 is lined with a tube 27 which may be introduced by casting the core 17 around prearranged tubes.
Adjacent the ends of the core are a pair of annular hubs 29 which are embedded in the core 17 and which project into the main bore 15 toward the axis of rotation. Each hub 29 is coaxially aligned with core 17 so that the pulpstone 11 will be balanced around its center axis.
The drive shaft 33 has successively enlarged portions 35, 37. The latter enlarged portion 37 is disposed within the main bore 15 of the core 17 while the former portion 35 extends axially beyond the ends of the pulpstone 11. The enlarged portion 37 presents a pair of flat faces 39 or shoulders radially extending outwardly from the portion 35 of the shaft.
A centering means positions the pulpstone axially on the drive shaft. It includes a pair of centering rings 41, each of which presents an inner cylinder bore 43 to the main portion 35 of the drive shaft and an outer surface 45 gradually tapered inwardly toward the center of the axis of rotation of the pulpstone 11. As each centering ring 41 is moved toward the axial center, the outer surface 45 having an increasingly greater diameter acts to line up the axial centers of the pulpstone 11 and shaft 33. The outer surface 45 of the centering ring 41 contacts a hub 29 which presents a matching inner-tapered face 47 thereto.
Each centering ring 41 is positioned adjacent a shoulder 39. A plurality of bores 49 in the centering ring 41 are radially spaced and axially aligned. A plurality of bores 51 in each shoulder 39 for receiving bolts 53 or threaded screws match the bores 49 in the centering rings 41. Bolts 53 located in the bores when tightened draw the centering rings 41 toward the shoulder 39 thereby centering the pulpstone 11. The centering means is designed to center the wheel and prevent axial movement, not to drive the wheel by frictional means.
Since both centering rings are identical and are situated in a similar manner, it is believed that the aforementioned description of only one, as shown in FIG. 1, will suffice. The flanges and sealing means are hereinafter described in a similar manner.
The driving means includes a pair of flanges 55 slidably mounted on the drive shaft 35 for axial movement with respect thereto. Each flange 55 has a straight main bore 57 therethrough with an inside surface matching the cylindrical surface of the main portion 35 of the drive shaft. A keyway 59 which forms a channel is recessed in the main flange bore 57. A rectangular key bed 61 is located in the portion 35 of the shaft on either side of the pulpstone 11. A key 63 fits into the key bed 61 and the keyway 59. This mounting permits each flange 55 to freely move axially with respect to the drive shaft. The straight flange bore 57 slides over the drive shaft 35 and the flange keyway 59 slides over key 63. The aforementioned mounting results in little or no diaphragming or bending action on the flanges 55 and maintains a relatively constant compressive force on the ends 17 of the core 13.
A plurality of boreholes 65 which are radially spaced from the axial center of the flanges 55 match the bores 25 of the pulpstone 11. The boreholes 65 are set in a recessed well 67 which protects the mounting installation.
The flanges are securely attached to the pulpstone through the boreholes 65 so as to directly drive it. A plurality of tie rods 69 are positioned in the pulpstone bores 25 and boreholes 65. Preferably about eight to about 12 tie rods are used. They are tightened under a tensile stress so as to preload them to prevent loosening, but do not have to be tightened so as to drive the pulpstone by friction as the tie rods themselves act as drivers. In FIG. 2, although not shown, the tie rods will actually contact the inner surface of the tubes so as to directly drive the pulpstone.
Blotter pads 71 may be placed in between the flanges 55 and the ends of the pulpstone 11 to allow for irregularities in the concrete core ends 17 and permit an even application of compressive force thereto.
To prevent corrosive chemicals from effecting the mounting structure a sealing means is provided. It includes an annular collar 73 having a straight bore 75 axially contacting the drive shaft 35 around its periphery and an outwardly extending radial portion 77 abutting the exterior of the flange 55 and connected thereto with a plurality of bolts 79 or screws. Water cascading over the flanges does not contact the vital parts of the mounting structure.
In the installation of a pulp wheel utilizing the mounting structure of the present invention, no mounting or dismounting fixture is required. With the pulp wheel sitting on the floor in its shipping skid, it is possible for two men with a shaft lifting beam to mount the pulpstone. The shaft is located in the main bore 15 of the core 17 with the lifting beam so that the hubs 29 are in proximity to the shoulders 39 of the shaft. The pair of centering rings 41 are slid over opposite shaft ends and centering bolts 53 loosely put into place. A sheet metal template which fits the shaft and has a keyway to fit the key bed 61 in the drive shaft 35 and at least one hole corresponding in radius to the bores 25 in the pulpstone 11 is slid over one end of the driving shaft 35. The driving shaft is turned until a pulpstone bore 25 lines up with the hole in the template. The centering bolts 53 are then tightened to the enlarged center portion of the drive shaft sufficiently to center the pulpstone 11 and prevent axial movement. The template is removed and blotter pads 71 are positioned if not previously positioned. The flanges 55 are slid over the shaft ends, the boreholes 65 in the flanges 55 lining up with bores 25 in the cement core 17. The tie rods 69 are inserted through the bores 25 in the pulpstone 11 and respective boreholes 65 in the flanges 55 and tightened. In tightening, a 6 -foot wrench that one man can lift manually is all that is needed. The tie rods 69 are torqued to give a predetermined or preset compression to the blotters 71 so as to preload the tie rods to prevent loosening. The drive shaft with pulpstone 11 mounted thereon is then journaled to a drive means including a motor or engine.
To dismantle the pulpstone from the drive shaft the process is essentially reversed. The gradual taper of matching surfaces of the hub and centering ring, the light construction of the centering rings, and relatively low compression of the bolts 53 prevents the hub 29 and centering ring 41 from becoming unduly wedged together. A jackscrew may be employed by threading into the bore 49 in the centering ring and turning against the shoulder 39 to remove stubborn centering rings.
Pulpstones of various design and construction may be mounted with the mounting structure of the present invention. The pulpstone may incorporate various reinforcing means of a variety of materials in the core, such as metal drums, reinforcing wire, plates and tie rods. They may employ various means for fastening the abrasive segments to the annular core such as the method described in U.S. Pat. No. 2,516,693.
In one method of construction the pulpstone abrasive segments equipped with the fastening means are assembled in the form of an annulus. A fixture within which the free ends of the fastening means extend inwardly toward the center is used. Metal reinforcing hoops and rods are located in the core at this time. Concrete is poured between an inside cylindrical form inserted within the fixture and the inside annulus of segments so as to embed the fastening means, reinforcing rods, hubs and tubes in the concrete. After the core has set, the wheel is removed from the fixture.
In another method, the pulpstone may be constructed by first forming the concrete core with the base of the fastening means cemented therein and the remaining portion protruding outwardly. The abrasive segments may then be installed to the core by filling the machined holes in the abrasive segments with cement, aligning the fastening head and hole, then pressing the abrasive segment to the core. Upon setting of the cement, the segment will be tightly affixed to the core.
Although the flanges may be mounted to the pulpstone by the tie rods, bolts or other means securely and firmly connecting the ends of the pulpstone to the flanges may be used.
The centering rings are shown in FIG. 1 as abutting a hub, but they may also abut a properly formed inside conical surface of the cement core.
While preferred embodiments of this invention have been described and illustrated, it is to be recognized that modifications and variations thereof may be made without departing from the spirit and scope of this invention as described in the appended claims.