US3572595A

US3572595A - Attrition mill

Info

Publication number: US3572595A
Application number: US664578A
Authority: US
Inventors: Charles R Lyon
Original assignee: Celanese Corp
Current assignee: Celanese Corp
Priority date: 1965-03-02
Filing date: 1967-06-26
Publication date: 1971-03-30
Anticipated expiration: 1988-03-30

Abstract

An apparatus for the separation of fibers of cellulose pulp sheet material including an attrition mill having a stationary and an opposing rotary disc, the stationary disc having a central aperture for reception of sheet material, the apparatus further including an impact zone, a driven roll extending across the width of the sheet material for feeding the pulp sheet in unfolded state to the impact zone, a series of spaced hammers mounted in the impact zone on a driven shaft for hitting the sheet material adjacent to its leading edge, with repeated impact spaced across its width to break the pulp material at its leading edge into chips, the hammer elements adapted to coact in interfitting relation with a set of stationary spaced cutter teeth on a stationary bar, a series of spaced supporting elements staggered with respect to the hammers for supporting the sheet material adjacent to its leading edge, the construction being such that the chips fall between the spaced supporting members, a conveyor mounted below the supporting elements for receiving the chips and for continuously feeding the chips to the aperture.

Description

United States Patent {72} Inventor CharlesR.Ly0n

Fort Mill, so. 211 Appl.No. 664,578 122 Filed June26, 1967 [73] Assignee Celanese Corporation [54] ATTRlTlON MILL 5 Claims, 7 Drawing Figs. [52] U.S.Cl 241/152 [51] Int. Cl B02c 7/06, BOZc 13/06, B02c 21/00 [50] Field of Search 241/28, 29,

152,152(.5),157,158,160,186,247; 225/(lnquiry); 83/906 FORElGN PATENTS 68,832 10/1891 Germany 241/152 I Primary ExaminerDonald G. Kelly Art0rneysLeonard Horn, S. D. Murphy and Andrew F.

Saybo, Jr

ABSTRACT: An apparatus for the separation of fibers of cellulose pulp sheet material including an attrition mill having a stationary and an opposing rotary disc, the stationary disc having a central aperture for reception of sheet material, the apparatus further including an impact zone, a driven roll extending across the width of the sheet material for feeding the pulp sheet in unfolded state to the impact zone, a series of spaced hammers mounted in the impact zone on a driven shaft for hitting the sheet material adjacent to its leading edge, with repeated impact spaced across its width to break the pulp material at its leading edge into chips, the hammer elements adapted to coact in interfitting relation with a set of stationary spaced cutter teeth on a stationary bar, a series of spaced supporting elements staggered with respect to the hammers for supporting the sheet material adjacent to its leading edge, the construction being such that the chips fall between the spaced supporting members, a conveyor mounted below the supporting elements for receiving the chips and for continuously feeding the chips to the aperture.

Patented March 30, 1971 6 Sheets-Sheet 1 AWL INVENTUR CHARLES R. LYON )1? W 4 nrramr Patented March 30, 1971 3,512,595

6 Sheets-Sheet 2 INVENTOR CHARLES R. LYON er L ATTORNEY Patented March 30,1971 3,512,595

' 6 Sheets-Sheet 5 INVENTOR CHARLES R; LYON ATTORNEY Patented March 30, 1971 6 Sheets-Sheet 4 INVENTOR CHARLES R. LYON ATTORNEY Patentecl' March 30, 1971 6 Sheets-Sheet 5 INVENTOR CHARLES R. LYON arrakwsr Pa tent ed Marc so, 1971 3,512,595

6 Sheets-Sheet- 6 "we/won CHARLES R. LYON ATTORNEY I A'I'IRI'I'ION MILL This application is a division of application Ser. No. 436,579, filed March 2, 1965, now U.S. Pat. No. 3,406,916.

This invention relates to the attrition of woodpulp for use in the production of cellulose derivatives.

In the manufacture of cellulose derivatives it is customary to employ, as one of the starting materials, fibers of bleached woodpulp of high alpha cellulose content (so-called chemical pulp"). The pulp is supplied, by the pulp manufacturer, in

the form of sheet material prepared by drying a wet mass of individual fibers. Before this pulp is converted chemically to the desired cellulose derivative (e.g. to an ester such as cellulose acetate) it is common practice to pass the sheet material to an attrition mill to separate the individual cellulose fibers, which may for example be on the order of /s--%-inch in length. One conventional attrition mill used for this purpose employs two concentric discs one of which is rotating at high speed relative to the other, which is usually stationary. The discs have opposing teeth which project into the attrition zone, between the discs, and which engage the dry pulp material as it passes through this zone. The stationary disc has a central hole through which the pulp sheet material is fed to "the attrition zone, while the rotating disc is provided with knife elements facing this central hole and arranged in a more or less random pattern; these knife elements serve to cut the pulp material into smaller pieces which are thrown outward eentrifugally through the space between the two discs. The resulting individual fibers which pass out from the e periphery of the discs are taken up by a current of air, produced by the action of a suction fan, and delivered to a storage zone for conversion into the desired cellulose derivative. 1

The pulp sheet material, as furnished by the supplier, generally has a width of about 2 to 3 feet and a thickness of about one-eighth inch, and is supplied in roll form or in large individual sheets. The feed hole in the stationary disc of the attrition mill is, for example, about I8 inches in diameter. In feeding the sheet material to the attrition mill, it has for many years been the practice for an operator to bend the edges of the sheet material upwardly, pass the material into the larger end of a conical chute leading to the intake opening of the attrition mill, and thereby urge the resulting folded or partially rolled sheet against against the knife elements of the rotating disc.

It is an object of this invention to increase the rate of production of pulp fibers in the attritionmill.

. Another object of this invention is to improve the operation of the attrition mills used for the production of pulp fibers.

Other objects of this invention'will be apparent from the following detailed description and claims. In this description and claims, all proportions are by weight unless otherwise indicated.

A device for use in one aspect of this invention is illustrated in the accompanying drawing in which:

FIG. 1 is a side view showing the attrition mill coupled to a device for supplying the pulp material thereto;

FIG. 2 is a view taken from the right'end of FIG. I;

' FIG. 3 is a view of the right end of FIG. 1 with portions in cross section;

FIG. 4 is a view of the right end of FIG. 1 showing the opposite side of the pulp-supplying device;

FIG. 5 is a view taken from the same end as in FIG.2 and showing portions in cross section;

FIG. 6 is a cross-sectional view of the pulp-supplying device showing details of the construction; and

FIG. 7 is a perspective view of details of hammer elements and sheet-supporting elements.

In the drawing reference numeral 11 (FIG. I) designates an attrition mill of conventional type (Sprout, Waldron) having a casing I12 and a pair of opposed toothed discs 13 and 14 (FIG. 3), the stationary disc 13 having a central opening 16 and the driven rotating disc 14 having cutter knife elements 17; the disc 14 is driven by a motor 18, whose drive shaft 18a is supported on bearings 18b (FIG. 1).

In the embodiment of the invention illustrated in the drawing there is mounted, in position to feed cellulose pulp material 19 (as from a roll 19a, FIG. 1) to the inlet opening 16, a combined hammer mill and conveying device, indicated generally as 21, comprising a hammer mill portion 22 (FIGS. 3 and 4) mounted on a vertical plate 23 arising from a base 24, which base also supports a conveyor portion 26 located just below the hammer mill portion 22.

At the inlet end of the hammer mill portion 22, there is mounted a pair of feed rolls 28, 29 (FIGS. 3 and 4) of sufficient length to accommodate the full width of the woodpulp sheet material, the lower feed roll 28 being suitably driven, as through a belt 31 fitted over a pulley 32 and driven by an electric motor 33 which may be mounted on the base 24. The upper feed roll 29, which is an idler roll, is biased downward, in any suitable fashion, as by a spring or weight (not shown) to press the sheet material, fed to the nip of these two rolls, against the driven roll 28. Advantageously, the rolls 28 are rubber-covered rolls.

Within the hammer mill portion 22 a series of spaced parallel hammers 36 are mounted on, and keyed to, a rotatable hammer shaft 37 which is driven in any suitable fashion, as by an electric motor 38 supported atop the hammer mill portion and connected to the hammer shaft 37 through a belt 39 engaging a pulley at the end of that shaft. The hammers 36 have central bearing areas 41 (FIG. 5) projecting on both sides of each hammer to provide for their rigid support and to act as spacers;

The hammers 36 are adapted to coact, in interfitting relation, with a set of spaced stationary cutter teeth 42 mounted on a stationary bar 43 and so positioned thatthe pulp sheet material, as it passes from the feed rolls, is supported on the cutter teeth and is struck and penetrated by the downwardly moving hammers, which then pass between the cutter teeth.

The hammers 36 in the embodiment illustrated in the drawing, are tapered, being of parallelogram disposed at about 45 to the other two edges to fonrr sharp corners and are so mounted that, on rotation of the hammer shaft 37, their long flat edges strike the top of the pulp sheet material. The tapered construction of the hammers provides adequate strength while limiting the masses of the hammers at their outer edges, thus facilitating high speed rotation of the hammer shaft. Adjacent hammers, although in parallel planes, are mounted'at an angle to each other; as shown in the drawing this angle is so that alternate hammers are parallel to each other. In one preferred embodiment the hammers 36 and the teeth 42 are uniformly spaced and are each about one-half inch wide, with straight flat vertical sides, and the hammertooth clearance, on each side of each hammer, is about onefourth inch.

The action of' the hammers 36 which may be rotated at, for example, 1800 r.p.m. with a tip velocity of 4500 feet per minute, breaks the sheet material into more or less rectangular chips or pieces, e.g. /wiinch squares or Aid-inch rectangles, depending on the relative preset, constant speeds of hammer rotation and of sheet feeding. For best results the sheet material being fed is struck by the operative ends of each h'ammer no later than it is struck by that portion of the hammer which is closer to the center of rotation of the hammer; in this way the pieces of pulp are chipped off from the forward end of the advancing sheet without cutting the sheet material into ribbons.

The chips of sheet material fall between the cutter teeth 42 through the large open top of a tapered conveyor housing 46 having a circular bottom 47 in which there is mounted a rotatable helical feed screw 48 whose axis is concentric with that of the center of the curvature of the circular bottom 47. The screw 48 is suitably driven, as by an electric motor at mounted on the base 24 connected to the center shaft 52 of the feed screw d8 by means of a belt. The chips are delivered, by the action of the feed screw 48, directly to the inlet 16 of the attrition mill Ill, which inlet is concentric with the feed screw 48.

it is found that the use of the arrangement described above makes it possible to triple the maximum practical continuous rate of feed of the sheet material to the attrition mill, without changing the speed of operation of the attrition mill, and with the use of substantially less power in the mill. The load on the attrition mill is found to be much more uniform, the mill operates with little, if any, of the bumping and grinding observed with the previous method, and maintenance costs are considerably reduced. Also, this invention eliminates the difficulties resulting from breaking of the cutter elements of the rotating disc and the need to sharpen these elements often. The usual frequent interruptions of operation due to breaking or tearing of the relatively weak pulp sheet material as it was fed to the attrition mill are also avoided.

In addition the use of this invention has been found to improve the properties (eg filtration characteristics) of cellulose acetate spinning solutions produced in conventional manner from the pulp, despite the tripled rate of operation. This effect is observed, for example, in solutions made, in the conventional manner, by acetylating the pulp fibers, ripening the acetylated product to produce secondary cellulose acetate and dissolving this cellulose acetate in acetone to form a viscous spinning solution, or dope, for use in the formation of continuous filaments.

It is to be understood that the foregoing detailed description is given merely by way of illustration, and that variations may be made therein without departing from the spirit of out invention.

lclaim:

1. In an apparatus for the separation of fibers of cellulose pulp sheet material which includes an attrition mill having a stationary toothed disc and opposing rotary toothed disc, said stationary disc having a central aperture for the reception of said sheet material, the improvement which comprises means providing an impact zone, a driven roll extending across the width of said sheet material for continuously positively feeding said pulp sheet material in unfolded state to said impact zone. a series of spaced tapered parallelogram shaped hammer elements mounted in said impact zone on a driven rotary shaft for hitting said sheet material, adjacent to its leading edge; with repeated impacts spaced across the width of said sheet material to break the pulp material at said leading edge into chips, said hammer elements adapted to coact in interfitting relation with a set of spaced stationary cutter, teeth on a stationary bar, a series of spaced supporting elements, between said hammer elements, for supporting and spacing said hammer elements, the construction and arrangement being such that the chips fall between the spaced hammer elements, a conveyor mounted below said hammer elements for receiving said chips and for continuously feeding said chips to said aperture.

2. Apparatus as set forth in claim 1 in which said hammer elements are so disposed on said shaft that adjacent elements hit said sheet material at different times, and said cutter teeth are so disposed in relation to said hammer elements that said hammer elements strike said sheet material at points upstream of said leading edge no later than they strike said edge, and said conveyor is a screw conveyor having an outlet directly abutting said central aperture.

3. Apparatus as set forth in claim 2 in which said hammer elements are parallelogram-shaped and are mounted on said shaft between their operative ends to hit the said sheet material twice with each rotation of said shaft and are tapered toward said ends.

4. Apparatus as set forth in claim 3 in which the parallelogram-shaped hammer elements have two edges of the parallelogram each disposed at about 45 to one of the other two edges and the hammer elements are mounted so that their long flat edges strike the top of the sheet material.

5. Apparatus as set forth in claim 2 in which adjacent hammer elements are mounted in parallel planes and said hammer elements are at an angle to each other.

UNITED STATES PATENT OFFICE P0-105U (5/69) CERTIFICATE OF CORRECTION Patent No. 3,572,595 Dated March 30. 1971 Inventor(s) Charles R. Lyon It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, first line, after "of", insert U. S.-

. Column 1, line 29, delete "e" between "the periphery" Column 2, line 38, after the word "parallelogram", insert shape, with two of the edges of the parallelogram-- Column 3, line 27, "out" should be ---our- Signed and sealed this l). .th day of December 1971.

(SEAL) Attest: I

EDWARD M.FLETCHER,JR. Atteating Officer ROBERT GO'ITSCHALK Acting Commissioner of Pete:

Claims

1. In an apparatus for the separation of fibers of cellulose pulp sheet material which includes an attrition mill having a stationary toothed disc and opposing rotary toothed disc, said stationary disc having a central aperture for the reception of said sheet material, the improvement which comprises means providing an impact zone, a driven roll extending across the width of said sheet material for continuously positively feeding said pulp sheet material in unfolded state to said impact zone, a series of spaced tapered parallelogram shaped hammer elements mounted in said impact zone on a driven rotary shaft for hitting said sheet material, adjacent to its leading edge; with repeated impacts spaced across the width of said sheet material to break the pulp material at said leading edge into chips, said hammer elements adapted to coact in interfitting relation with a set of spaced stationary cutter teeth on a stationary bar, a series of spaced supporting elements, between said hammer elements, for supporting and spacing said hammer elements, the construction and arrangement being such that the chips fall between the spaced hammer elements, a conveyor mounted below said hammer elements for receiving said chips and for continuously feeding said chips to said aperture.

4. Apparatus as set forth in claim 3 in which the parallelogram-shaped hammer elements have two edges of the parallelogram each disposed at about 45* to one of the other two edges and the hammer elements are mounted so that their long flat edges strike the top of the sheet material.