Roll Assembly For Paper Machine

Abstract

A roll assembly for a paper making machine with a rotary shaft and a roll shell surrounding the shaft to rotate therewith, the shell being of a material such as granite and being under compression by being held by an annular compression head at one end of the shaft and another annular compression head at the other end of the shaft. The first head axially engages a radial surface on the shaft and the other head axially engages a split collar axially engaging a radial surface on the shaft. In one arrangement, the collar is positioned in the recess by relatively extending the length of the shaft preferably by heating it relative to the granite roll shell.

Description

BACKGROUND OF THE INVENTION

FIELD OF THE INVENTION

In a paper making machine after the paper web is formed on the fourdrinier section, it passes through subsequent machine sections including the press, the driers, and a calender. In the press section granite rolls are frequently employed wherein the roll construction employs an outer hardened ground granite surface. Different arrangements have been provided to obtain a granite roll and in one form of effective widely adopted construction, such a granite roll has a steel shaft extending through an outer granite roll shell. The steel shaft has ends equipped with bearings to rotatably support the roll and the outer granite roll shell is suitably supported on the shaft.

In a granite roll used in a press couple in a paper making machine the roll will be subjected to relatively high nip pressures as the web passes between it and a mating roll. Some deflection of the granite roll will occur, and in order to prevent cracking of the granite, and to give the roll assembly additional strength, the granite roll shell is placed under axial compression. Method and structures heretofore used employed nuts threaded onto the end of the roll shaft which have been discovered to have disadvantages which are obviated by the present invention. In a threaded shaft, as the roll rotates, continual stress reversals are encountered at the threads in the shaft resulting in fatigue of the metal and failure at the thread on the shaft. This condition is aggravated because of the high stress concentrations in the bottom of the thread. Such failure, of course, requires removal of the roll and reconstruction thereof with attendant loss in time of machine operation and cost of roll reconstruction. As is known to those skilled in the paper art, it is essential in paper making machine operation to attain as long continuous runs as possible since the cost of shut-down time in a machine is extreme, and a successful paper making machine cannot tolerate shut-downs for failure of many different areas of the machine, particularly since shut-downs are necessary in any event for certain replacements, such as, fourdrinier wire change.

It is, accordingly, an object of the present invention to provide a granite roll construction which employs a granite roll shell wherein the shell is held under compression and has a construction which will remain satisfactorily operative without failure for the normal operating life of the roll.

A further object of the invention is to provide a roll construction employing a roll shell with an internal shaft wherein an improved method and structure is employed for placing the roll shell under compression by forces applied by mechanical devices at each end of the shaft avoiding failure of the shaft due to such devices.

A still further object of the invention is to provide a granite roll construction wherein the granite roll shell is maintained under uniform compression without change for the life of the roll.

Other objects and advantages will become more apparent with the disclosure of the preferred embodiments of the invention in connection with the disclosure and description of the drawings, in which:

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical sectional view taken substantially through the axis of a roll assembly constructed in accordance with the present invention; and

FIG. 2 is a fragmentary vertical sectional view taken substantially along line II--II of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a granite roll assembly with a steel center shaft 10 and an annular granite roll shell 11 placed over and concentric with the shaft 10. While particular advantages are obtained with a non-metallic roll shell such as granite, the features of the invention may be utilized with shells of other materials. The shaft is of a size to fit within the opening of the roll shell, and the outer surface 12 of the granite roll shell is ground and polished. The granite roll of FIG. 1 is adapted to coact with a mating roll, not shown, to form a roll couple for receiving a paper web in a press section to extract water therefrom. The opposing roll will provide a force against the granite roll along a nip line indicated by the arrowed lines shown at the top of FIG. 1. This will cause a downward bending deflection of the roll assembly and to give strength to the assembly, because of the inherent lack of tensile strength of the granite material, and to prevent the cracking of the granite material, it is placed under an axial compression by end supports or annular compression heads 15 and 16. The granite material is of a natural or synthesized stone, having a tensile strength less than steel.

The end supports or compression heads 15 and 16, which are in the form of shaped annular rings engage the axially facing end surfaces 14 and 13 of the granite roll shell 11. The end surfaces are slightly tapered so that the granite roll shell 11 will tend to remain centered under load, and to aid in holding the roll shell centered during assembly and during operation, centering rings 11a and 11b are positioned at the ends of the roll shell between the shaft 10 and roll shell 11. The space 11c between the shaft 10 and roll shell 11 contains a filler such as a plastic foam.

The shaft is shaped with surfaces 17a and 17 for holding the annular compression heads 15 and 16 axially centered. The head 15 has a bearing support sleeve portion 18, and the end support 16 has a bearing support sleeve portion 19. On the sleeve portion 18 is mounted an annular bearing 20 which is supported in a bearing housing 22. On the sleeve 19 is mounted a bearing 21 which is supported in an annular housing 23. The sleeves 18 and 19 are tapered to receive the tapered inner surface of the bearings 20 and 21, and the bearings are pressed onto these tapered surfaces by locknuts 24 and 25 threaded onto the ends of the sleeves 18 and 19.

The housings 22 and 23 which support the bearings 20 and 21 for rotatably carrying the roll assembly are mounted in the frame of the machine to hold the roll assembly in the proper location for providing the press nip with the opposing roll.

The shaft is provided with an extension 26 at one end for receiving a drive couple or other means for driving the roll assembly.

For axially holding the end support 15 on the shaft, the shaft has a flange 27 formed at one end with an axially inwardly facing shoulder 28 which receives the annular end 29 of the end support 15.

At the other end of the roll shell, the end support 16 is axially held by a split collar 32, 33. An annular groove 30 is formed in the end of the shaft 10 to provide an inwardly axially facing shoulder 31. The annular end 36 of the end support 16 abuts the sections 32, 33 of the collar to hold the roll shell 11 in compression. To hold the sections 32, 33 of the collar in place, a ring 37 surrounds the collar sections and may be shrunkfit into position. Other devices such as a horseshoe shaped key may be used in place of the split collar 32, 33.

The compression force placed on the granite roll shell 11 is a function of the size of the roll shell, the size of the shaft 10, and the distance between the shoulders 28 and 31 on the shaft. The size of the roll shell, and the size of the shaft are dictated by the operating environment of the roll. When this is determined, with application of the known factors of stress versus strain of the roll shell and shaft, the distance between the surfaces 28 and 31 is readily computed to provide the desired compressive stress in the granite roll shell 11. The shaft is constructed accordingly, and for assembly, the shaft is elongated relative to the roll shell in amount sufficient to provide clearance for dropping the sections 32, 33 of the split collar in place. In a preferred arrangement, the shaft is heated to a temperature sufficient to cause its elongation relative to the roll shell to permit placing the collar sections 32, 33 in place. This is preferably done by raising the temperature of the shaft with the end support 15 in place and then slipping the shaft within the roll shell, placing the end support 16 over the shaft and placing the split collar sections 32, 33 in place and holding them with the ring 37 and permitting the shaft to cool. Preferably this is done by heating the shaft externally of the assembly, but it will be seen that internal heating means such as electrical resistance wires could be inserted into the shaft during its manufacture, or the shaft could be hollowed to accommodate such heating means. Also, mechanical relative compression of the roll shell and elongation of the shaft could be performed, but these alternative procedures offer disadvantages that are avoided by externally heating the shaft before inserting it within the roll shell.

When the shaft has cooled to room temperature, the granite roll shell will be drawn into compression. The compressive force on the roll shell is preferably sufficient to maintain a compression therein of at least 200 pounds per square inch when the roll shell is subjected to the maximum nip pressure.

In prior art devices the collar 27 and ring 32, 33 are in the form of nuts threaded on the shaft 10. With the shaft 10 under high tensile stress severe stress concentrations will occur in the bottom of the threads causing the shaft to break at the thread area. With the structure of the present invention it will be observed that the threads have been eliminated. Generous radii may now be employed at critical stress areas such as at 41, 42, 43 and 44 on one end of the shaft 10 and at 51, 52, 53 and 54 at the other end thus eliminating the high stress concentration areas of the prior art.

Thus, it will be seen that I have provided a roll assembly which meets the objectives and advantages above set forth and which has a unique structure and which employs a new method of construction and assembly.

Claims

I claim as my invention:

1. A roll assembly comprising,

a shaft under tensile stress,

first and second annular compression heads axially slidably mounted on each end of the shaft,

an annular roll shell mounted on said shaft between said heads,

a first shoulder means on one end of said shaft extending at right angles to the shaft axis in axial abutting relationship with the outer surface of the first one of said heads,

a second shoulder means on the other end of said shaft extending at right angles to the shaft axis in spaced relation to the outer surface of the second one of said heads, thereby providing for an axial space between said second shoulder and said second head, and rigid means filling said space between said second shoulder and said second head whereby the tensile stress in said shaft causes said heads with said shell therebetween to be urged toward each other so that the shell is subjected to compressive forces.

2. A roll assembly constructed in accordance with claim 1 wherein said roll shell is formed of granite.

3. A roll assembly constructed in accordance with claim 2 wherein the shaft is under a tension so that the granite roll shell is held under a compression of at least 200 pounds per square inch at maximum nip load on the roll assembly.

4. A roll assembly constructed in accordance with claim 1 wherein said shaft has an annular recess and said space filling means includes a split collar with a retaining sleeve surrounding the collar holding it in said annular recess in the shaft.

5. A roll assembly constructed in accordance with claim 1 wherein said first shoulder is formed by an annular ridge on the shaft of a diameter larger than the shaft.

6. A roll assembly comprising in combination,

a roll shaft having means at the ends for rotary support,

a roll shell for engaging a radial load at one side positioned over the shaft to rotate therewith and being of a hard surfaced non-metallic material with a tensile stress less than metal,

first end support means at one end of the shell axially fixed relative to the shaft end and axially supporting the end of the roll shell, and second end support means axially supporting the other end of the roll shell being fixedly mounted on the shaft and holding the shell in compression,

said second end support means having an axially outwardly facing shoulder at right angles to the shaft axis,

said shaft having an integral axially inwardly facing shoulder with a substantial area at right angles to the shaft axis axially supporting said shoulder of said second end support means and fixing its axial position and holding said roll shell in compression.

7. A roll assembly constructed in accordance with claim 6 wherein the shaft has an integral continuous circumferential radial surface engaging the axial outer end of the first support, and an integral continuous circumferential radial surface engaging a collar means between it and said second support.