US2544632A - Repair of pulpstones - Google Patents

Description

March 6, 1951 N. F. HOLTER ETAL REPAIR OF PULPS TONES 2 Sheets-Sheet 1 Filed Feb. 16, 1948 Inventors AbRMA/v F Hows/a WALTER BETH fit orneg March 6, 1951 N. F. HOLTER ETAL 2,

REPAIR OF PULPSTONES Filed Feb. 16, 1948 2 Sheets-Sheet 2 Fig.3

Inventors F 4 Noam/w E Houm WALTER BETH Httarngy Patented Mar. 6, 1,951

REPAIR OF PULPSTON ES Norman F. Holter and Walter F. Beth, Worcester,

Mass., assignors to Norton Company, Worcester, Mas s., a corporation of Massachusetts Application February 16, 1948, Serial No. 8,488

The invention relates to pulpstones and the repair thereof.

One object of the invention is to repair a pulpstone one or more blocks of which have broken or come out. Another object of the invention is to provide a repaired pulpstone, that is to produce a satisfactory pulpstone from one in which one or more blocks are broken or missing. Another object is to provide a method and repaired structure for a pulpstone of the type disclosed in U. S. Letters Patent No. 2,421,885 to Wallace L. Howe and Lorenzo S. Washburn, patented June 10, 1947.

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

The invention accordingly consists in the features of construction, combinations of elements, arrangements of parts, and in the several steps and relation and order of each of said steps to one or more of the others thereof, all as will be illustratively described herein and the scope of the application of which will be indicated in the following claims.

In the accompanying drawings illustrating one of many possible embodiments of the mechanical features of this invention,

Figure 1 is a fragmentary cross sectional view of a pulpstone with one block missing, the rubber filler or joint material having been scraped off and the concrete of the center having been chipn ped away to a depth of one half inch, more 'or less,

Figure 2 is a bottom plan view of a replacement block,

Figure 3 is a fragmentary sectional view of the block of Figure 2 taken on the line 33 thereof,v

Figure 4 is a view similar to Figure 1 showing the replacement block in place.

Pulpstones constructed in accordance with the aforesaid patent to Howe and Washburn have proved superior in practical use to any other pulpstones heretofore known and breakage thereof in normal use has been practically nonexistent. That is to say, we understand that in no case has a block or segment broken or come loose from a Howe and Washburn pulpstone attributable to weakness of or defect in the pulpstone itself or the block or segment. But, in the paper mills, the pulp grinders still occasionally malfunction, usually by way of failure of the water supply. In such cases'differential thermal conditions can be created which no large stone couldwithstand. In such cases one or more blocks or segments cracks,

2 .Claims. (Cl. 51-206. 1)

breaks or comes loose thus making the stone useless for the time being.

Each pulpstone represents a large investment and it is therefore highly desirable to repair a pulpstone which :has lost one or a few blocks. In fact, it is always desirable to repair pulpstones when feasible. In accordance with this invention we provide a method for the repair of a Howe and Washburn pulpstone which may also be applicable to other pulpstones and we provide pulpstones so repaired.

Referring now to Figure 1, the pulpstone of the Howe and Washburn patent comprises blocks I0 secured to a concrete center II by bolts [2 embedded in the concrete H which bolts l2 have screw heads l3 which are screwed into threaded holes in the blocks Ill. The threads of the screw heads l3 are massive with a large pitch as shown. The concrete center H may be reinforced'with steel hoops It.

The blocks H] are made of bonded abrasive material composed of any desired type of abrasive such as quartz, silicon carbide or fused alumina, the latter two being preferred, bonded together with suitable bonding material, vitrified ceramic bond being-preferred. Each block is preferably formed from a mixture of clay or frit with abrasive, suitably plasticized as by the provision of a suitable plastic clay and the addition of water, then molded in a'suitable mold and pressed under high pressure to cause the block to have sufficient green strength for handling. After this, the block is vitrified in a kiln.

Between the blocks l0 and on all faces of each block In excepting the marginal faces which form the side faces of the pulpstone, are sheets [5 of filler or joint material such as described in U. S. Letters Patent No. 2,054,771 to Thure Larsson. These sheets [5 may comprise hard rubber containing cork granules vulcanized to the blocks [0, but other material might be used. The pulpstone according to the Howe and Washburn patent has integral key ridges IS of concrete fitting in reentrant grooves I1 formed in the blocks l 0 so that the pulpstone will not be torn apart by the stresses resulting from the high power input. The manner of making a pulpstone such as above described is fully set forth in the aforesaid patent to Howe and Washburn and hence will not be repeated herein.

Assuming now that a block ID of suchpulpstone has cracked or broken, the first step is to remove the cracked or broken block if it or any part of it still remains in the cavity 20. Thenext step is thoroughly to clean away all partly inside of the holes 2I.

joint or filler material I5 on blocks surrounding the cavity 20 and also to remove the phe-' nolic resin or other adhesive upon the screw heads I3 of the bolts I2. (In the Howe and Washburn patent it is explained that phenolformaldehyde A stage resin plasticized to the consistency of a heavy cream by means of liquid furfural is brushed. onto the screw heads I3. It is further explained that after assembly of the blocks I and insertion of the bolts I2, the entire assembly is heated to cure the sheets I and the resin on the screw heads I3.) the first step is to make a thoroughly clean cavity 20, removing organic material and leaving only the stone-like blocks II! with clean faces and the stony concrete II at the bottom of the cavity and clean iron or steel screw heads I3 (usually four of them) upstanding in the cavity 20. I

The next step is to chip away the concrete of the center II at thebottom of the cavity 20 to a depth of the order of half an inch. This includes chipping away some of the integral key ridges I6. At some time the sides of the blocks Ill around the cavity should preferably be grooved or roughened. This will materially aid in cementing the new block in place.

"A replacement block Ida is shown in Figure 2. This should preferably be, as to abrasive and bond, grade and structure, size and shape and temperature at which matured, the same as other blocks I8 of the pulpstone but differences in any specifications other than size and shape and strength will make little difierence in the grinding qualities of the repaired stone. There are, however, some specific features to the block Illa not shared by the other blocks III. Instead; ofrhaving threaded holes to receive the screw heads I3 as do the blocks I0. the blocks Ilia have oversized. holes 2I with roughened or grooved walls 22 as shown in Figure 3.. The holes 2i do not go completely through the blocks Illa any more than do the corresponding holes in the blocks Ill, but bores 24 are formed through the .blocks [Ila parallel to the axis of the holes 2| and, as clearly shown in Figures 2 and 3, overlapping the holes 2|, that is to say the circles of thebores 24 are partly outside and Preferably as shown in Figures 2 and 3 the bores 24 have smaller diameters than the holes 2|.

Just before setting the replacement block IIJa, it should be soaked in water. A minute is usually suficient time for soaking and the block Ida should be clean prior to soaking. The cavity 2!! should likewise be thoroughly wetted prior to setting the replacement block Illa.

Sometime prior to setting a replacement block la, a grouting mixture is prepared from quicksetting Portland cement and iron chips or filings. We have found that eight pounds of Portland cement mixed with eight and one-half pounds of so-called iron hardener which is around No. 46 to No. 60grit size cast iron makes a good grouting mixture. Sufficient water should be added to give the mixture about the consistency of a heavy paste. This grouting mixture should be made up just prior to use since it is cold-setting. H

With a trowel or similar tool a quantity of the grouting mixture is placed in the cavity 20 to fill the cavity to a level about higher than the concrete of the center II which was chipped away. In so trowelling the grouting-mixture,

Thus,

4 the bottom of the cavity is brought to a shape very close to that which it originally had.

Now the surface of each screw head I3 and the inside of each hole 2I are coated with sufficient groutin approximately to fill the hole 2| then the block is placed in position. This should be done quickly after trowelling the grouting onto the bottom of the cavity 20 and coating the inside of the hole 2I and the surface of the screw heads I3. The replacement block IIla should be well bedded on the grouting at the bottom of the cavity 20 which can be done by tapping the block IDa with a mallet. In setting the block Ina, the holes 2I fit onto the screw heads I3 being oversize with respect to such screw heads. This approximately positions theblock lBa; it should then be carefully adremainder of the stone.

justed to leave joint spaces all around the block of approximately equal size. These joint spaces will then be found to be about A to wide. ---Now grouting is forced down through the bores 24 usin a rod which loosely fits the bores and then a plunger which closely fits the bores, tapping the latter slightly to insure complete filling of the holes 2i around the screw heads I3. 'Grouting should be forced into the bores 24 until the bores 24 are full of grouting to the level of the outer surface of the block Ifla.

Now more grouting is used to fill the joints between the replacement block Ilia and the original block I0 around the cavity 2!]. Thin metal strips or like tools can be used to force the grouting into position. These joint spaces are filled to the level of the cylindrical periphery of the pulpstone.

'Now the replacement block IGa and the area right around it are covered with damp bags which are allowed to stay in place for about forty-eight hours. At the end of this time the bags are removed and the grouting is allowed to cure in air for twenty-four hours more before use. At any time after removing the damp bags, the replacement block Ida is chipped to bring its outer cylindrical surface even with the It will be understood that the pulpstone has presumably been in use for some time and therefore its diameter is probably a little less than when it was originally made. If the replacement block is the same size asthe original blocks and the original blocks have worn down some, the replacement block 100. will stand up above the level of the other blocks, wherefor it is chipped to make it level. Chipping should be done from the outside edges to the center of the block Illa to avoid breakage. The surface of the replacement block I00; can be finished by rubbing it with an abrasive block, for example, one of the same kind as itself.

Figure 4 shows the repaired pulpstone. It is the same pulpstone as is shown in Figure 1 except that the block Ida is in place in the cavity 20. The cavity 20 around the block Ifla is lined with grouting 30 which strongly adheres to the concrete center II and to the sides of the adjacent blocks III. In the holes 2I, grouting 32 is in contact with the roughened or grooved walls 22 and also with the threads of the screw heads I3 thus locking these screw heads to the block Ilia. The bores 24 are likewise full of grouting 34 thus to make the surface of the repaired pulpstone continuous.

Should severalblocks of a pulpstone not contiguous to each other become broken, each one can be replaced as herein described. Should a. number of contiguous blocksof a pulpstone be? come broken, the entire number can be replaced as herein described up to at least four contiguous or adjacent blocks and probably more.

The sheets l5 of filler or joint material are compressible and absorb considerable expansion of the blocks due to overheating. In the repaired pulpstone the compressible joint material It is replaced by substantially rigid grouting 33 around the replacement block. However it is found that the compressibility of the joint material 1% beyond the blocks IS adjacent to the block lfla is suificient to provide for expansion under any normal conditions. At all events, pulpstones according to the Howe and Washburn patent have had blocks replaced according to this invention with entirely satisfactory results in that no further breakage has occurred.

It will thus be seen that there has been provided by this invention a method of repairing a pulpstone and a pulpstone so repaired in which the various objects hereinabove set forth together with many thoroughly practical advantages are successfully achieved. As many possible embodiments may be made of the above invention and as many changes might be made in the embodiment above set forth, 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.

We claim:

1. Method of repairing a pulpstone of the type having a concrete center, a plurality of holding bolts embedded in said concrete center, abrasive blocks held to said concrete center by said holding bolts, and sheets of filler material between said blocks, said pulpstone having at least one block missing or broken, comprising forming a cavity by removing any broken parts of the broken block, removing the sheets of filler material around said cavity, chipping concrete from the bottom of said cavity to increase the depth of the cavity, providing a replacement block with oversize holes fitting over the upper ends of said holding bolts and with ofiset holes extending from the oversize holes to the outer surface of said replacement block, placing cementitious grouting material at the bottom of said cavity, placing the block inthe cavity over said upper ends, ramming cementitious grouting material in said offset holes and from them into said oversize holes, and ramming grouting material around said replacement block.

2. Method of repairing a pulpstone of the type having a concrete center, a plurality of holding bolts embedded in said concrete center, abrasive blocks held to said concrete center by said holding bolts, and sheets of filler material between said blocks, said pulpstone having at least one block missing or broken, comprising forming a cavity by removing the filler material and the parts of the broken block, if any, providing a replacement block with oversized holes fitting over the upper ends of said holding bolts and with offset holes extending from the ovensized holes to the outer surface of said replacement block, placing the block in the cavity over said upper ends, ramming cementitious grout- 111g material in said offset holes and from them into said oversized holes, and ramming cementitious grouting material around said replacement block.

NORMAN F. I-IOLTER. WALTER F. BETH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,032,484 Jeppson Mar. 3, 1936 2,074,114 Larsson Mar. 16, 1937 2,433,814 Holter Dec. 30, 1947 cementitious

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