US2279486A - Segmental abrasive wheel for pulp grinding - Google Patents

Description

April 1 4, 1942.

L. A. PATT 'SEGMENTAL ABRASIVE WHEEL FOR PULP GRINDING 4 Sheets-Sheet 1 Filed Dec. 14, 1939 jz a . INVENTOR. LEON A. PATT ATTORNEY.

April 14, 1942; v 1.. A.VPATT SEGMENTAL ABRASIVE WHEEL FOR PULP GRINDING 4 Sheets-Sheet 2 Filed Dec. 14, 1959 LEON A. PATT BY ATTORNEY April 14, 1942". PATT 2,279,486

SEGMENTAL ABRASIVE WHEEL FOR PULP GRINDING Filed Dec. 14, 1939 4 Sheets-Sheet 3 It 4, A

, mvmon LEON A. PATT ATTORNEY.

April 14, 1942. PATT v 2,279,486

SEGMENTAL ABRASIVE WHEEL FOR PULP GRINDING Filed Dec. 14, 1939 4 Sheets-Sheet 4 INVENTOR.

LEON A. PATT BY .ammmg ATTORNEY.

Patented Apr. 14, 1942 Q SEGMENTAL ABRASIVE WHEEL FOR PULP GRINDING Leon A. Patt, Sanborn, N. Y., assignor to The Carborundum Company, Niagara Falls, N. Y., a corporation of Delaware Application December 14; 1939, Serial No. 309,217

7 Claims.

This invention relates to the manufacture of segmental abrasive wheels and particularly to segmental abrasive wheels which, are used for the manufacture of wood pulp.

One of the objects of the present invention is Y to anchor the abrasive segments as strongly as possible to a metal. hub whose mean radius or mean distance from the axis of rotation of the wheel is smaller than the mean radius of the abrasive segments.

It has been a common expedient to clamp abrasive segments on a steel drum or reinforced concrete center by means of clamping members which press on shoulders of the abrasive segments and which extend through the hub where nuts are used on the inside surface of the hub to apply the necessary clamping pressure. Such methods of mounting the abrasive segments usually involve extensive reduction of size of the segmental bases with consequent danger of breakage of the segments under the stresses caused by the work of grinding, by changes of temperature, and by the pressure of the clamping means on shoulders disposed in the bases of the segments. If the supporting drum is close to the bases of the abrasive segments the mounting for the abrasive annulus is made correspondingly heavy. On this account reinforced concrete centers are frequently provided for segmental wheels, and clamping means are extended from shoulders on the bases of the segments through the concrete to steel hubs or supports of comparatively small radius. One object of the present abrasive segments are illustrated by means of the accompanying drawings in which:

I Figure 1 is a perspective view of an abrasive annulus assembly prior to the pouring of the concrete between the abrasive annulus and the metal hub;

Figure 2 is a perspective view of an abrasive segment with clamping hooks assembled in the segment; I

Figure 3 includes two fragmentary sections of an abrasive annulus taken in planes perpendicular to the axis of rotation, the smaller section being in a plane spaced from the clamping hooks;

Figure 4 is a section of the abrasive wheel on the line IV-IV of Figure 3;

Figure 5 is a side view of an abrasive segment,

' showing a face whichis perpendicular to the axis invention is to provide a set of .very strong anchors for each segment in wheels of this type.

Another object is to provide connections be tween the segments and the hub or drivingsupport, which connections are substantially free' from stress fluctuations due to temperature vari-- ations in the normal operation of the wheel; These connections are obtained by using a metallic anchor hook or an anchor hook composed of a combination of metals to connect the abrasive segments to the driving hub. These metallic connections are designed so that the accumulated thermal elongation of the metallic connection is J substantially equal to the accumulated thermal elongation of the surrounding material that extends between the seat of the hook in the segment and the driving hub of the abrasive wheel.

Improved means are also provided for transmitting torque from a concrete center to the segments in the abrasive annulus.

The improvements in the mounting for the of rotation whenthe segment is placed in position on the wheel mounting; v v

Figure 6 shows a radial face of an abrasive segment with two anchor hooks in position;

Figure '7 is a perspective view of an anchor I hook;

Figure 7a is a similar view of a modified form of anchor hook;

Figure 8 is a perspective view of a completed abrasive wheel containing a plurality of abrasive annuli;

Figure 9 shows a completed abrasive wheel mounted on a driving shaft;

Figure 10 is a fragmentary section taken in a plane perpendicular to the axis and showing modified anchor hook connections between the concrete core andan abrasive segment;

Figure 11 is a fragmentary section on the line XB-XI of Figure-10 and Figure 12 is a view similar in part to Figure 10, showing a slight modification of the latter.

Referringto the drawings in detail, abrasive segments 2 are assembled-on a horizontal surface .as shown in Figure 1 to form an abrasive annulus 3. Each segment 2 is a bonded abrasive mass whose base is cut away to form grooves as indicated at 4 in Figure 2. Before the segments 2 are laid in the position shown in Figure 1 their lower surfaces are sealed against water penetration from the concrete center by means of a coating of a suitable sizing material, and they are provided with a number of anchor hooks 5. These hooks may be made of a nickel-steel alloy which has approximately the same coefficient of thermalexpansion as the abrasive segments to which the hooks are attached. The hooks are bent (as shown at 6 in Figures 3 and 7) so that the short arm 'I of each hook is substantially parallel to the base of the abrasive segment in which it is seated. The short arm of the hook is inserted-in a slightly larger opening 8 in its abrasive segment. One or more strips of resilient material 9 are inserted in the openings 8 between the hooks 6 and the wall of the opening 8 in the abrasive segment as indicated in Figures 2, 3 and 4. These resilient strips may be made of felt or of rubber-bonded fibrous material. ample of fibrous material which may be used. The object of these strips is to prevent the accumulation of destructive stresses between the anchor hook and the segment in which it is subsequently seated in the following manner.

into the openings 8 to'form seats for the short arms of the hooks 5. The location of the hooks with respect to the segments and of the seats for the short arms of the hooks is illustrated in Figure 3, where seats are indicated at 8.

In the abrasive annulus shown in Figure 1 the joints l between the segments are composed of a resilient composition which can be' made by inserting one or more sheets of fibrous material that has been impregnated with rubber and vulcanized. These resilient sheets are cemented to the adjacent surfaces of the segments which are being joined. As shown in Figure 2, the ends of the hooks which extend from the abrasive segment toward the concrete center are threaded. Internally threaded sleeves II are screwed onto the projecting ends of the hooks and are used to couple extension rods I2 to the hooks as shown particularly in Figures 3 and 4. The extension rods l2 pass through plates H which are disposed in contact with the inside surface of the hub rings ll. Nuts I5 on the threaded ends of the rods [2 are used to hold the plates i3 against the rings H. The sleeves it are covered with yieldable tubes 2|, and portions of the extension rods I 2 are covered with similar tubes 2| in the view shown in Figure 1 which illustrates the mounting of an abrasive annulus prior'to the pouring of the concrete within the ring of segments. Tubes 2|" surround the long arms of the hooks 5.

Sisal is an ex- O -Q melting metal, such as Babbitt metal, is poured The grooves 4 in the bases of adjacent abrasive segments are combined in pairs to permit the forupper left-hand corner of the drawings. Metal plates I! are indicated in Figures 1 and 3 as disposed in the-grooves lying between the bases of adjacent segments and as extended between the sleeves II. These plates I] serve to reinforce the portion of the concrete which is poured into the grooves I and around the projecting stems of the hooks and their extensions. The concrete core is shown in Figure 3 as extending not only between the abrasive segments and the ring l4 but also inside the ring and around the nuts l5 which are thus held in locked position.

Before the concrete is poured, each of the nuts I5 is tightened by means of a calibrated torque indicating wrench to give a definite predetermined compression on the seat that separates the short arm 1 of the anchor hook 5 from the segment to which the anchor hook is connected. Thus each ring of segments is tightly secured before the concrete core is poured. This method of assembly therefore distinguishes it from certain methods known in the prior art where clamping rods extending through a concrete core are tightened up, after the concrete core has been poured. In the case of a pulpjwheel manufactured by the applicant's method, the setting of the concrete core takes place under favorable conditions for obtaining a balanced condition of the segmental wheel.

' Also, before thepouring of the concrete core, the bases of the abrasive segments are coated with a layer of waterproofing material which prevents the water from leaching into the abrasive segments in that region of the concrete core which is adjacent to the abrasive segments. This arrangement has the general effect of preserving the solidity and strength of the concrete adjacent the abrasive segments, as well as preventing shrinkage of the concrete. This waterproofing material impregnates a layer of each abrasive segment adjacent the coated surface.

The concrete core is reinforced by means of metal rings or hoops 22 as shown in Figures 1 and 4. Suflicient metal reinforcement is used to adequately restrain the concrete core from appreciable or destructive expansion due to centrifugal stresses when in operation. In this way the segments in the abrasive annuli are .not required to in any way restrain the concrete core from bursting.

Towardthe left of Figure 3 a small section removed from but parallel to the main section is shown. The small section shows particularly the' driving key 6 reinforced with the metal plate IT. The resilient layer I0 is shown only on the trailing face of the key 16. The leading face of the key I6 is in contact with the adjacent segment 2. The arrow A in Figure 3 shows the direction in which the wheel is operated. The concrete projections l6 reinforced by the radially disposed plates I! have an important'function in transmitting torque from the concrete core to the abrasive annulus which is made up of the abrasive segments 2.

In Figure 8 there is shown in perspective an abrasive wheel made up of three abrasive annuli. These annuli are separated by resilient annular joints indicated by the reference character I8. Theseare similar to the joints I0 described in some detail above. A plurality of abrasive annuli can be assembled by providing them with a common ring or tube formed by joining the. rings l4 in an axial direction. The abrasive annuli can also be provided with a common core, in which case the concrete is not poured until all the annuli have been assembled, along with the ring and-the anchor hook connections.

In the view shown in Figure 8 the segmental abrasive annuli are so assembled that the joints between the segments of the first annulus are offset from those in the second annulus, while 4 the joints between the segments in the third annulus are offset from the joints of the second annulus and also from those of the first annulus. This same progressive offset relationship between segments in adjacent and successive abrasive annuli can be maintained in assemblies that require a larger number for convenience in construction.

It is also distinctlyadvantageous to have the planes between the intermediate annulus (or annuli) and the end annuli inclined at a slight angle to the end planes of the wheel as illustrated in Figure 9. The interannular planes are therefore not quite perpendicular to the axis of the wheel.

This arrangement tends to prevent the formation of grooves between the segments and to reduce the localized wear on the wheel. In Figure 9 there is also shown meansfor driving the completed abrasive wheel. The driving shaft 23 has a left-hand threaded engagement with the driving flange 24 and a right-hand threaded engagement with the oppositely disposed driving flange 25.

Increase of load on the wheel therefore tends to screw the driving flanges more tightly against the wheel.

A resilient material is provided between all adjacent faces of the abrasive segments. These resilient joints afford a compensating factor for gaged therewith to obtain a reliable assembly.

differential expansion ofthe concrete core with respect to the abrasive segments. These resilient joints also afford a compensating factorfor expansion of the abrasive segments when they are subjected to the operating temperatures produced Rings 14 confine all plates l3 as indicated in the drawing and hold them in definite position. The

working loads which are imposed on the segment anchorage will.be transmitted back to the rings M. This transmission of forces to the rings will by heat generated byabrasion at the periphery of the stone when in use. The temperatures of the outer parts of the abrasive segments may approximate those of boiling water. I

One of the principal advantages ofthe anchor hook attachments to a segment (illustratedpan ticularly in Figures 2 and 7) is found in the fact that only a small amount of material is removed from the segments to provide for the insertion of the hooks. The thickness of the abrasive between the seat of the hook (which may be made of Babbitt metal) and the base of the abrasive segment may vary nearly half an inch without seriously weakening the abrasive segment. The radial thickness of one of the abrasive segments such as is shown in Figure 8 may be seven inches or more. The applicant has made a number of tests of the tensile strength of such an anchorage,

the outer portion of an abrasive segment being gripped and pulled in one direction while the four hook-arms that extend from the base of the segment are simultaneously pulled in the be readily appreciated on inspection of Figure 1, from which it can be seen that, when the assembled annulus is rotating, the various forces acting on the abrasive segments are transmitted to and borne by the strong rings l4. Consequently th size and proportioning of these rings are vital and basic factors which can be adjusted to meet' the"variations in speed or other operating are controlled principally by the size of the assembled grinding wheel, as well as by the speed and other operating conditions to which it may be subjected. In the design of thereinfaces as is shown clearly inF-igure 3. This 10- cation of the segment anchorage is quite advantageous as it places the anchoring means at the best geometrical points in the abrasive segment to effective'y resist centrifugal forces and to secure each segment against the forces produced by the work load of grinding. These forces tend to twist or'rotate the segments out of their assembled positions within the grinding wheel. These forces. are often far in excess of the centrifugal forces acting on the segments since they are the resultants of the centrifugal forces and the reactions of the materials that are being ground and crushed. It is apparent, therefore, that the combination of a strong means of anchorage and the best mechanical application of that anchorage to individual segments in the abrasive annuli is such'as to provide a distinct improvement in the design and construction of segmental grinding wheels; forwhen so made they will withstand to an unusual degree the stresses incident to normal operation. It is evident, therefore, that the applicants segmental anchorage is of such a character that it can resist very great centrifugal forces when the abrasive wheel is in operation.

The segment anchorage means in this new and improved construction of abrasive wheels consists of a plurality of units which are here shown and described as bimetallic members. Each bimetallic member consists of a special nickel steel alloy anchor hcok 5 connected to an extension rod l2 by means of a threaded sleeve forcing structure of this pulp wheel, the actual amount of reinforcing of the concrete center will be principally that required to prevent the concrete center from any bursting caused by centrifugal stresses which occur in normal operation of the wheel. The concrete center could be rotated safely at operating speeds without the abrasiv segments. The wheel is designed'so that in the completed. assembly normal operation of the wheel will not cause rotational expan'sion of the center that would produce undue outward pressure on the abrasive segments.

Another important feature of the wheel design is to be found in the outside layer of steel coils or rings 31 which are located very close to the outer surface of the concrete center for a purpose which will now be explained The disposition of these rings or coils 31 is very important since they actually act as compression members which have been found to effectively prevent appreciable shrinkage of the concrete while it is curing or setting. This is believed to be a novel feature of the design. Others have built concret centered pulp stones, but have found it necessary to tighten the abrasive segments onto the center after the concrete had cured and shrunk. The compression of rings of the present design eleminate any loosening up of the final assembly, as well as any tightening or adjusting such as has just been described in connection with prior practice.

The segmental abrasive annular assembly shown in Figure l is essentially a self-sustaining member, as is also the concrete center. The concrete center is indicated in Figures 3 and 4. When a grinding wheel so assembled is mounted as shown in Figures 8 and 9, the flanges 24 and 25 grip the ends of the concrete center with sufllcient pressur to cause it to revolve. The

reinforced driving keys l6, being integral with N the concrete center, exert a driving torque on the abrasive segments 2, each of which is in contact with the. leading edge of a corresponding key l6 as shown in the upper left portion of Figure 3, wher the arrow A above the abrasive segments indicates clockwise rotation.

Work load pressures in pulp grinding are applied (for example, by means of a hydraulic piston) in a direction toward the axis of the wheel. Friction of the logs (being ground) against the grinding surface tends to move the abrasive seg ments 2 in a direction opposite to the rotation of the wheel. The lugs I6, being in contact with portion of the long arm of the anchor hook 5. It has been found thatwhen approximately onehalf of the combined length of the sleeve II and the rod l2 are encased in the tubes 2| and 2|,

the segments, prevent such dislocation and transmit driving torque from the concrete center to the abrasive annulus or annuli. The principal function of the anchoring means is to hold the abrasive segments tightly on the surface of the concrete center. The anchoring means is pro- 1 sity for compensating in any way for differences in thermal expansion between the abrasive segments and the concrete center. The abrasive segments have a lower coeflicient of thermal expansion than the concrete center. Assuming uniform increase of temperature, the abrasive segments will expand radially at the same rate as the anchor hooks 5, and the concrete center will expand radially at the sam rate as the extension rods l2. This arrangement in which the anchor hooks 5 have the same coefficlent of thermal expansion as the surrounding abrasive segments and in which the extension rods |2 have the same coefllcient of thermal expansion as the surrounding concrete center therefore protects the abrasive segments and the anchoring means from radial stresses during change of temperature. During increase of temperature there will be a tendency for the abrasive segments to separate in both axial and circumferential directions. It is desirable, therefore, that the combined member l2 and 5 should be able to bend slightly. To accomplish this result, .the long arm of the anchor hook 5, the sleeve H and the radially outward portions of the rod |2 are mounted within yieldable tubes 2|", 2|, and 2| as shown in Figures 1, 3 and. 4 so as to actually separate these metal parts from rigid surrounding materials. The tubes 2|, 2|, and 2|" may be made of paper or other compressible material as their function is to permit the rods |2 to remain in a straight line or to bend slightly so that undue stresses will not be built up in the abrasive segments or in the anchoring means during changes of temperature.

The actual length of the tube-encased portion of the anchorage means is only such as to avoid dangerous stress concentration in the anchorage means. Even though the encasing tubes will eliminate actual contact between the concrete and the sleeve N, there is another factor that must be recognized. The length of the encased portion of the anchoragev means is related to the stress concentration at the ends of the threaded portions of the hooks 5 and rods 2. If nearly the entire length of the rod |2 were free to move laterally, the flexural stresses within the anchorage means would be small.

On the other hand, if the rods I2 and the sleeves I were to be embedded directly within the concrete for their entire length, then the fiexural stresses in the anchorage means would reach such high values as to be unsafe, since there would be excessive stress concentration at the threaded as shown in the drawings, the flexu'ral stresses within the anchorage means remain within the limits usually considered safe for mechanical members of this class. Factors such a the size of the assembled wheel, fluctuations in the operating temperature, and the thermal expansion or other physical characteristics of the construction materials must all be considered and evaluated when determining the actual lengths of the tubes 2| and 2|. For the purpose of elimination of vibration, it is preferred to embed the inner portions of the rods l2 substantially as shown in the drawings. In any case the long arm of the hook 5 is partially encased within a tube made of yieldable material. Due to the relatively short length of the hook in the member 5 it is essential that freedom for lateral movement be'provided for the hook within the recess in the abrasive and particularly where it passes through the driving key |6. Hence the tube 2|" surrounds this portion of the hook.

It will be noted that in the case of pulp wheel structures of the type disclosed in this application, thermal stresses within an assembly may build up to destructive values in the absence of suitable means for reducing such stresses. The magnitude of such stresses is often far greater than the purely mechanical stresses incident to normal operation. Such stresses are likely to cause failure, especially near the junction of the abrasive segments and of the concrete center. The use of yieldable tubes to greatly reduce or to prevent the building up of such stresses to a dangerous point is therefore considered a vital part of the invention.

In the modification illustrated, in Figures 10 and 11 the anchor hooks 5' are integral with the bolts I 2'. Each bolt I2 is surrounded by a strong metal sleeve 3|. The sleeve 3| extends between a shoulder 32 on the anchor hook and a plate 33. By tightening the nut 34 the bolt |2' can be put under tension. I

While the segments (with the attached anchor hooks, bolts, plates and nuts) are being assembled into an abrasive annulus, preloading of radial jointsis accomplishedby external application of radial pressure by means of clamping bands, etc. The bolts |2 are placed under tension by means of the nuts 34. The concrete is poured within the abrasive annulus and around the inwardly projecting sleeves 3| and the annular reinforcements 35. The external pressure is removed after the concrete has set. The hooks 5 project into openings 8 in the sides of the segments in the same manner as shown in Figure 3. The hook is seated on the abrasive segment by means of Babbitt metal or the like at 36. Resilient strips 9 are used as described in connection with Figures 2 and 3.

In the modification shown in Figure 12 .the

sleeves 3| project beyond the concrete to the bends in the anchor hooks.

Other advantages of the applicant's improved segmental wheel will be apparent from the foregoing description taken in connection with the drawings. The invention is defined within the a of the a substantially larger coemcient of thermal expansion than the abrasive segments, a plurality of anchor hooks each having a curved end that is seated in an opening in the side of an abrasive segment and having the opposite end adapted for supporting said abrasive segments, and a plurality ofbimetallic anchor hooks in each of which a short arm rests on a seat in a corresponding abrasive segment while the long arm forms an angle with said short arm andis at-o tached to a strong support embedded in the conwhile the traiiing iace of the key is connected to the rim by means 01', a resilient layer, and anchor hooks connecting the abrasive segments with the wheel hub ring, each of said hooks having a bent portion seated in a lateral face of a segment and an inwardly extended portion which is clamped. to the wheel hub ring and surrounded by the concrete core.

'5. A segmental abrasive wheel comprising a plurality of segments forming an abrasive rim, a concrete core for said abrasive rim, an annular hub coaxial with said abrasive rim and separated therefrom by the bulk of the concrete core, a plurality-'91 hookswhich grip each segment in positions distributed symmetrically about the segment by insertion incylindrical openings in radial races of the segments, said hooks being comcrete center, the stresses in the hook due to changes in temperature being rendered substantially tree from fluctuation by making the hook oftwo materials, one of which has approximately the same coeflicient oi. thermal expansion as the surrounding abrasive segments while the other part has substantially the same coeflicient or expansion as the surrounding concrete, and the I intermediate portion or the anchor book being separated irom its rigid surroundings by means of tubes of yieldable material.

3. A segmental wheel comprising a plurality of abrasive segments, a concrete center for supporting said abrasive segments, and a plurality of bimetallic anchor hooks for holding each segment to the concrete support, each of said hooks havingashortarmseatedinanopeninginits abrasive segment, the opening being only slightly larger than the enclosed portion of the hook and of small dimensions as compared with the dimensions of the segment, and the portion of the hook which is surrounded by the segment having substantially the same coemcient of expansion as the segment while the remainder of the hook has substantially the same coeiiicient of expansion as the surrounding concrete.

4. A segmental abrasive wheel having a rim comprised of a plurality of abrasive segments connected by means or resilient joints, a hub ring for the abrasive wheel sive rim, a concrete core connecting the abrasive rim with the wheel hub rim, one or more reini'orced concrete keys projecting from the concrete core into the abrasive rim,

key being in direct contact with the rim disposed within the abrathe leading lace posed of material having substantially the same coeflicient oi expansion as the abrasive segments and extending to the concrete core, connecting rods attached to the gripping hooks near the bases of the segments and extending through the concrete core and the annular hub, said connecting rods having about the same coeiiicient of expansion as the concrete, and means for placing 'said'connecting rods under tension to draw the gripping hooks tightly against seats in the cylindrical openings in the faces 01' the abrasive segments.

6. A segmental abrasive wheel having a rim comprised of a plurality of abrasive segments connected by means of resilient joints, a hub ring for anchoring the abrasive rim, and a plurality of anchor hooks connecting ,the abrasive segments with the hub ring, each of said anchor hooks having a bent portion seated in an opening in a lateraliace or a segment and an inward extension which is connected to the supporting hub ring, the portion oi the anchor hook which is seated in and adjacent to any abrasive segment having approximately the same coefllcient of expansion as the abrasive segment.

7. A segmental. abrasive wheel having a rim comprised of a plurality of abrasive segments connected by means of resilient joints, a hub ring for the abrasive wheel disposed within the abrasive rim, a concrete core connecting the abrasive.

the concrete. v LEONAPA'I'I.

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