US2362528A

US2362528A - Preparation of fine cellulose flour

Info

Publication number: US2362528A
Application number: US445656A
Authority: US
Inventors: Emil H Balz; Andrew W Kassay; William D Williams
Original assignee: Libbey Owens Ford Glass Co
Current assignee: Libbey Owens Ford Glass Co
Priority date: 1942-06-03
Filing date: 1942-06-03
Publication date: 1944-11-14
Anticipated expiration: 1961-11-14

Description

1944' E. H BALZ ET AL 2,362,528

PREPARATION OF FINE CELLULOSE FLOUR Filed June 3. 1942 Em/7 A. 50/2 ATTORNEYS Andrew W Aassay NTOR:

Patented Nov. 14,1944

, zssaszs raaraaa'rron or me caLL Losn nova Emil a. mu, Andrew w. Kailay, and wmismn. Williams, Toledo, Ohio, aeeignors. by meme assignments to Hblny-(lwens-Ford pony, a corporation of Ohio Glass Com.-

Application 3, i942, Serialhlo. 445,656 I 2 Claims.

The invention relates to the preparation of fine cellulose flour that is useful as a filler for synthetic resin compositions, such as molding compounds and adhesives, and other products, such as insecticides, for which fine cellulose fiour is now used.

Wood and other forms of cellulose are difilcult to reduce to a fine powder because of the fibrous nature of cellulose. Cellulose is a tough and flexible material, and the individual cellulose fibers are believed to have a higher tensile strength than steel. For many applications extremely fine cellulose fiour is desirable, and such cellulose flour is diflicult to produce by grinding because of the toughness of the cellulose fibers. H

Cellulose can be reduced to a fine flour by prowhich the cellulose is ground by the impact of tumbling members, such as a ball mill or a tube mill. cylinder containing steel or porcelain balls which tumble as the cylinder rotates and exert a grinding action upon material contained in the cylin- A ball mill consists essentially of a rotary longed grinding in a tumbling impact mill in put of cellulose flour. I advantages are apparent from the description in Y which reference is had to theaccompanying drawing. I

Figure I of the drawing illustrates a preferred form of apparatus for carrying out the invention.

Figure 11 is a vertical section taken on the line II-II of FigureI.

This specific drawing and the specific description that. follows merely disclose and illustrate, the invention, and are not intended to impose limitations upon the claims.

After cellulose has been ground in a ball mill or other tumbling impact mill for several hours. only a small proportion of particles finer than the meshes in a 2'10 mesh screen can be recovered, and it is necessary to prolong the grinding in the tumbling impact mill for an unreasonable length of time in order to reduce the greater proportion of the cellulose to a fiour of such fineness.

In accordance with the invention, it has been discovered that fine cellulose particles cannot beder. In a continuous process a grinding operation of this character is ordinarily performed by a tube mill. Tumbling members in the form of tubesor rods may be employed in place of balls in such a mill. A continuous mill of this type is an elongated cylinder rotating on its longitudinal axis, which is inclined slightly so that when material is fed at thehigher end, the ground product will flow at the lower end.

satisfactorily separated from coarser cellulose particles by screening. Cellulose particles which are fine enough to pass through the meshes of a. screen, because of their fibrous nature, interlock together and bridge over the meshes of the screen. Dry screening thusprovides an unsatisfactory separation of the desired fine particles. l Eifective separation by screenlng'can be accomplished if the ground cellulose is made up in a Such a tumbling impact mill must be of relatively large size in order to provides. reasonable out-put because the material passes through they mill quite slowly. Thus a tumbling impact mill is a very expensive piece of production equipment.

However, a tumbling impact mill .is the only type oflf mill in which cellulose can be groundto a fine our.

A common form of commercial mill, known as an attrition mill, is ordinarily employed for the operation of reducing a fine saw-dust to the form of coarse wood flour. The finest wood flour that slurry with water and screened wet. Such satisfactory screening is not an economical operation, however, because of the expense of making up the slurry and subsequently drying the product.

In accordance with the invention, therefore,

' the desired fine particles are'removed from the ground mass in each step by air separation. The invention is based upon the-discovery that even air separation does'not provide satisfactoryremoval of the fine particles. It has been discovered that because of static charges on the fine I particles or because of enmeshing fibrous ten-' tacles on the particles, there is a tendency for can be produced by means of anattrition mill 45 groups of fine particles to cling together in is so coarse that less than 5 per cent of it will clumps. Such clumps do not go of! with the fine pass through a 100 mesh screen. The fine wood particles when air separation is carried out, but fiour that is desired for most applications of the are removed with the coarse particles or tailings. type mentioned above is wood flour so fine that It has been discovered that if the tailings from. substantially all of it will pass through-a 270 mesh 50 such an air separation are subjected to a simple screen. grinding operation, the clumps of fine particles The principal object of the invention is to probecome separated so that a large yield of addivide a method of producing cellulose flour by tional fines can be obtained by a further air sepwhich a tumbling impact mill of relatively small a aration. Thus when a yield of 20 per cent fines size can be used to provide a relatively large outis obtained by air separation of cellulose that has More specific objects and I -is a simple type of rotor impact mill, and the ,tailings irom the second air separation arereturned to the tumbling impact mill.

The principalapplication oi the invention is in the production of fine wood flour. In the production of wood flour by the present method, fine sawdust, obtained by passing chips, shavings and coarse sawdust through a rotary cutter, is ground in an attrition mill to produce coarse wood flour which is in turn led to the tumbling impact mill used in carrying out the present invention.

The present method can b used for comminuting any form of cellulose, such aswalnut shelhfiax shives, a bleached sulflte pulp, such as alpha cellulose, or any other cellulosic material.

When the method is carried out by means of the apparatus illustrated in the drawing, wood waste, usually in the form oi. a mixture of chips, shavings and coarse saw-dust, is passed through a rotary cutter-l which convertsit to fine sawdust. The fine saw-dust is suitable for processing in an attrition mill 2 to which it is conducted by a chute I. The attrition mill reduces the fine saw-dust to a coarse wood ilou'r, The attrition mill is used to eflect a preliminary grinding oi the material in order to make possible a more rapid out-put from the tube mill 4 to which the coarse wood flour'is fed from th attrition mill through an inclined chute 5. Although the attrition' mill is capable of carrying out'only a pre-j liminary and relatively coarse grinding oi the material, the out-put ofa small attrition mill in pounds per houris 'sreater than the out-put of a large tubemill costing 20 to 30 times as much as the attrition mill.

The tube mm 4, should be provided with a jacket of the usual type. for cooling water.

The ground product is discharged from the tube mill 4 into a storage hopper provided with a gate 1. From time to time. the gets I is opened slishtly to cause the contents oi the hopper O to be emptied slowly into a chute from which the product is conveyed pneumatically by a blower I through a conduit I. to an air separator II. The surplus air from the air separator ll returns through ducts I 2 and II to the blower.9. A bag 5 Ill is used to collect the fines, which are the finished product. After each emptying of the storage hopper 6, the gate 1 is closed, a'gate ii in a tailings hopper I8 is opened and a divertin vane 11 is turned to the left in order to cause the trailings from the hopper It to be fed to a small imp mill it, having an impact rotor l8. By

means of a blower I! the product from the imp mill I8 is conveyed pneumatically through a vertical conduit to the air separator H, and

the surplus air from the air separator is returned to the blower l9 through the return air ducts I2 and ii. A gate 22 in the discharge chute 23 for the fines is provided in order to permit the discharge of the fines to be shut ofi momentarily while an empty bag is substituted ior a 'full bag.

The re-grinding of the tailings in the imp mill l8 and the air separation of the resulting product are continued, the taillngs from the second air separation being returned to the imp mill, until the discharge of fines from the air separator has substantially ceased. Then the diverting vane II is turned to the right and the grinding of the talllngs in the imp mill and air separation of the resulting product are continued until all of the so tailliigs have been fed back to the tube mill 4. The gate ll of the tailings hopper I8 is then closed, and the system is ready for another emptying oi the storage hopper.

Various embodiments may be devised to meet various requirements.

Having described the invention, we claim: a a p 1. A method oi producing cellulose flour that comprises grinding cellulose in a tumbling impact mill, air-separating the fines from the resulting- Product, resrlnding the tailings from the air separation in a rotor impact mill, and air-separatin in: to said tumbling impact mill the tailings, from the second air separation.

msmneanz.

ANDREW w. KABSAY. wnmmu p. WILLIAMS.