US2724222A - Pulpstone - Google Patents

Description

Nov. 22, 1955 G. N. JEPPSON PULPSTONE 2 Sheets-Sheet l Filid Aug. 4, 1953 IN V EN TOR.

gEDR'GE N. JEPPSUN A True/v5 Y Nov. 22, 1955 G. N. JEPPSON 2,724,222

PULPSTONE Filed Aug. 4, 1953 2 Sheets-Sheet 2 INVENTOR. EEURGE N. JEFF'SUN A TTOENEY United States Patent PULPSTONE George N. Jeppson, Brookfield, Mass., assignor to Norton slpmpany, Worcester, Mass., a corporation of Massausetts Application August 4, 1953, Serial No. 372,352

6 Claims. 01. 51-206.4)

The invention relates to segmental pulpstones, and more particularly to improved means for anchoring abrasive segments to a central support.

One object of the invention is to provide a simple and thoroughly practical pulpstone. Another object is to provide an improved anchoring means for abrasive segments. Another object is to increase substantially the breaking strength of the union between the abrasive segments and the central support. Another object is to eliminate or reduce cracking or spalling of the abrasive segment due to diiferential expansion of the segments and the central support.

Another object is to provide an anchoring clamp for abrasive segments whereby the clamp may be pre-stressed to the segment. Another object is to provide a clamp with a tie bar whereby the clamp may be adjustably prestressed to the abrasive segment.

Another object is to provide each segment with a V- shaped bottom surface to increase the contact area between the segment and the concrete core. Another object is to provide each segment with a V-shaped bottom which serves in combination with the pie-stressed clamp to give greater resistance to the pulling out of the clamp, particularly as the result of centrifugal force in normal operation.

Another object is to provide a thin rubber gasket between the clamp and the abrasive segment to take up unevennesses of both, and in combination with the prestressed clamp to avoid any movement between the clamp and segment as the result of vibration in normal operation.

Other objects will be in part obvious or in part pointed out hereinafter.

In the accompanying drawings in which is shown one of various possible embodiments of the mechanical features of the invention,

Fig. 1 is an end elevation of a pulpstone constructed in accordance with this invention, having parts broken away and shown in section to show details of construction;

Fig. 2 is an end elevation, on an enlarged scale, of one of the segments showing the clamp for attaching the segment to the central portion of the pulpstone;

Fig. 3 is a cross sectional View, taken approximately on the line 33 of Fig. 2, through the segment and the clamping bracket;

Fig. 4 is a fragmentary elevation of a small portion of the pulpstone, showing the segment shapes and the joint material therebetween; and

Fig. 5 is a modification showing a fragmentary elevation of a pulpstone, showing the arrangement of the equilateral hexagon shaped segments.

A pulpstone has been illustrated in Fig. 1 comprising a plurality of bonded abrasive segments and a central reinforced concrete core 11. The segments are arranged in circular rows to form a hollow body of abrasive segments with an outer surface of revolution.

The abrasive segments 10 may be made of any suitable abrasive, such as silicon carbide or aluminum oxide, bonded by any suitable bond, vitrified bond being preferable. Other bonds such as phenol-formaldehyde resin, rubber, shellac, magnesium oxy-chloride or metal bond may be used. The abrasive segment is molded to shape by the conventional well known molding procedure, after which the segment is fired to mature the bond. As illustrated in the drawings, the peripheral portion of the segment is hexagonal in shape and each segment is provided with a V-shaped bottom surface 12 to increase the contact area between the segment and the concrete core.

While the segment is in a green state, that is before firing, grooves 15 and 16 are cut into the radial side faces 17 and 18. The upper ends of the grooves 15 and 16 are provided with pockets 19 and 20 respectively to facilitate clamping.

A clamping unit 25 is formed of steel strips which are rectangular in cross section. The clamp 25 comprises two opposed clamping brackets 26 and 27 having their upper ends bent inwardly at right angles to the brackets 26 and 27 respectively to form hooks 28 and 29 which engage the pockets 19 and 20 respectively in the segments 10. The lower ends of the brackets 26 and 27 are provided with inwardly projecting portions 30 and 31 the inner ends of which butt against each other. A tie bar 3-2 extends between the brackets 26 and 27 and is fastened thereto by a pair of screws 33 and 34. The screws 33 and 34 pass through clearance holes in the brackets 26 and 27 and are screw threaded into the upwardly extending portions of the tie bar 32.

As illustrated, the clamps 25 are preferably formed in two halves to facilitate assembly. If desired, however, the clamp may be formed as a single U-shaped member having inwardly projecting ends or hooks at the upper ends of the U which may be sprung into place after which a tie bar may be used to pre-stress the clamp to the segment. The clamps 25 are formed of relatively heavy steel flat stock which is rectangular in cross section, for example 1%" x "in assembling the clamp 25 on each of the segments 10, a piece of resilient rubber 35 and 36 is placed between the brackets 26 and 27 and the grooves 15 and 16. The piece of resilient rubber preferably extends into the pockets 19 and 20. The tie bar 32 is then placed in position and the clamping screws 33 and 34 are tightened to pro-stress the clamp to the abrasive segment 10. The clamping screws 33 and 34 are preferably tightened by means of a torque wrench to between 20 to 30 foot pounds on a three-eighths inch 16 pitch screw. By use of the thin sheet of resilient rubber gasket between the clamps and the segment, unevenness in the clamp and the segment is taken up so that the pre-stressed clamp and segment are prevented from moving relative to each other as the result of vibration due to normal operation of the pulpstone.

After the required number of segments have been thus provided with clamps 25, they are assembled into an annulus with sheets of joint material 13 therebetween. This joint material is preferably that described in the U. S. Patent No. 2,446,513 to Y. H. Nordstrom, dated August 3, 1948, to which reference may be had for details of disclosure not contained herein.

A reinforcing cage comprising a plurality of concentric reinforcing rings 40, 41 and 42 is placed in position. These rings are made of heavy steel rod and are preferably wired together to hold them in position during assembly. The cage consists of a plurality of concentric rings arranged in different planes to reinforce the stone. Each of these sets of rings is spaced from each other and wired to form an integral cage structure which may be placed on the mold plate at the time the assembly of the pulpstone segments is started. As shown in Fig. 1, the clamping bracket 25 projects inwardly between the rows of reinforcing rings 40.

After one row of abrasive segments has been assembled with sheets of joint material inserted therebetween, layers of joint material are placed upon the upper faces of the first row of segments after which a second row of segments is assembled in a similar manner. After the successive rows of abrasive segments have been completely assembled, they are securely clamped together by circumland cement with sand and a suitable amount of trap rock is poured into place between the mold center and the annulus of abrasive segments 10. The concrete mixture fills the entire area between the mold center and the abra- 'sive segments to form a solid central support integral with the abrasive annulus which is reinforced by the metal rings of the reinforcing cage. The concrete fills the area between each of the clamps 25 and the tie bars 32, and also between the tie bars 32 and the V-shaped bottom surfaces of the segments securely to anchor each segment to the concrete center 11.

In the grinding of wood pulp, the wood logs are forced against the periphery of the pulpstone under a considerable pressure and normally the surface of the stone is cooled by a coolant fluid. Occasionally the coolant is cut off for various reasons, mostly accidental, which permits the stone (revolving at 240 R. P. M. or 5,000 S. F. P. M. or more) to heat up due to friction of grinding to a sufficient extent in some cases to char the wood being ground. This is done almost instantaneously and develops high temperature on the surface of the pulpstone which due to the low conductivity of the abrasive structure does not penetrate too rapidly and develops stresses because the outer layer expands ahead of the inner layers or increments of the segment. When this strain thus developed exceeds the strength of the structure of the segment, spalling and cracking may occur. In former pulpstones, for example a 62" by 54" stone, occasionally some trouble has been experienced by spalling and breaking as the result of thermal shock developed in grinding. The segments in these particular stones were arranged in five rows of segments across the face of the pulpstone and segments around the periphery thereof. The segments were hexagonal in shape but Were somewhat longer in the dimension crosswise of the stone so that there was approximately 9 inches of stone per joint circumferentially and approximately 13 /2 inches per joint across the face of the stone.

Within reason the smaller the size and the more equidimensional the shape of the abrasive segment, the greater the resistance to thermal shock. I have found that with any construction, particularly the one referred to, the most equidimensional unit that can be geometrically nested together is an equilateral hexagon with the angles of all corners 120 as the nearest approach to the ideal possible. In order to eliminate one of the causes of spalling and cracking of the segments, I have reduced the size and shape of the segment to approximate an equilateral hexagon in shape as shown in Fig. 5, so that in a pulpstone 62 by 54" I have eight rows of segments across the face of the stone and 20 segments around the stone thereby decreasing the inches of abrasive per joint across the face of the stone thus increasing the flexibility across the face of the stone so as to make it more resistant to thermal shock so as to eliminate or minimize spalling and cracking of the segments. .By shaping thesegments 10 as equilateral hexagons, the sheets of joint material 13 therebetween are of uniform shape and size. The amount of abrasive material per joint is equal all directions at right angles to the sides of the hexagon, consequently any expansion of the abrasive segment is uniformly taken up by compression of the joint material 13.

As shown in Fig. 5, a pulpstone has been illustrated which is formed by eight rows of segments superimposed upon each other in an axial direction. The marginal rows of segments preferably have one side formed as a plane surface so that the side faces of the stone are in true radial planes.

It will thus be seen that there has been provided by this invention a pulpstone in which the various objects hereinabove set forth together with many thoroughly practical advantages are successfully achieved. As many possible embodiments might be made of the mechanical features of this invention and as the art herein described might be varied in various parts, all without departing from the scope of the invention, it is to be understood that all matter hereinbefore set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

I claim:

1. A pulpstone in the shape of a body of revolution, the curved surface of which is the outer surface of a plurality of bonded abrasive segments, comprising a plurality of said bonded abrasive segments, a reinforced central concrete core, and a U-shaped clamping member prestressed onto opposite side face of each of said segments, the open ends of said clamping members having inwardly projecting hooks engageable with pockets formed in the opposite sides of said segments, the inner ends of said clamping members being embedded in the concrete core to anchor the segments therein.

2. In a pulpstone, an abrasive segment having an outer abrading surface, a V-shaped inner surface, a plurality of faces between said surfaces, at least two of said faces being opposed substantially radial faces, a pocket formed in each of said faces, a groove on each of said faces extending from the pocket to the inner face of the segment, and a substantially U-shaped clamping unit, a pair of inwardly projecting hooks formed integral with the outer ends of said unit, the hooks and side portions of said unit being arranged to fit in said pockets and grooves respectively on opposite sides of said segment, and adjustable connections between the sides of said unit adjacent to the inner surface of said segment whereby the unit may be pre-stressed to said segment.

3. In a pulpstone, an abrasive segment having an outer abrading surface, an inner surface, a plurality of faces between said surfaces, at least two of said faces being opposed substantially radial faces, a pocket formed in each of said radial faces, a groove on each of said faces extending from the pocket to the inner face of the segment, and a substantially U-shaped clamping unit comprising a pair of radially arranged brackets, inwardly projecting hooks at the outer end of each of said brackets which are arranged to engage said pockets from the opposite sides of said segment, inwardly projecting arms of the inner ends of said brackets, the inner ends of said arms bearing against each other to form the inner end of said unit, and adjustable connections between said brackets adjacent to the inner surface of said segment to facilitate pre-stressing said clamping unit to said segment.

4. In a pulpstone, an abrasive segment, as claimed in claim 3, in combination with the parts and features therein specified in which the adjustable connections include a tie bar extending between said brackets adjacent to the inner surface of said segment, and adjustable connections between the ends of said tie bar and said brackets whereby said unit may be pie-stressed to said segment.

5.1m a pulpstone, an abrasive segment, as claimed in claim 3, in combination with the parts and features therein specified in which the inner portion of said U-shaped clamping unit is embedded in the concrete core securely to anchor the segment to the core.

6. In a pulpstone, an abrasive segment for an outer abrading surface, a V-shaped inner surface, a plurality of faces between said surfaces, at least two of said faces being opposed substantially radial faces, a pocket formed on each of said faces, a groove on each of said faces extending from the pocket to the inner face of said segment, and a substantially U-shaped clamping unit, a pair of inwardly projecting hooks formed integral with the outer ends of said unit, the hooks and side portions of said unit being arranged to fit within said pockets and grooves respectively on opposite sides of said segment, a resilient gasket between said pocket and grooves and said hooks and side portions, and a tie bar adjustably connected between the sides of said unit whereby said unit may be pre-stressed to said segment.

References Cited in the file of this patent UNITED STATES PATENTS

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