US2618471A - Churn for the production of viscose - Google Patents

Description

1952 w. R. WEIGHAM ETAL CHURN FOR THE'PRODUCTION 0F VISCOSE 2 SHEETS-SHEET 1 Filed Sept. 17, 1951 INVENTORS WILLIAM REGINALD WEIGHAM WILLIAM HENRY STOKES BY THEIR ATTORNEYS 1952 w. R. WEIGHAM ETAL CHURN FOR THE PRODUCTION OF VISCOSE 2 SHEETSSHEET 2 Filed Sept. 17, 1951 S 2 2 mm //7ven/0rs Vl /'///0m R Wag/20m I l /'///'0m H. 5/0 kes By/h e/r affomeys Patented Nov. 18, 1952 2,618,471 CHURN FOR THE PRODUCTION OF VISCOSE William R. Weigliam, Coventry, and William H.

Stokes, Balsall Common, near Coventry, England, minors to Courtaulds Limited, London, England, a British company Application September 17, 1951, Serial No. 246,942 In Great Britain October 11, 1950 2 Claims. 1

This invention relates to churns for use in the production of viscose.

Customary steps in the production of viscose include the treatment of alkali cellulose with carbon disulphide to produce cellulose xanthate and the dissolution of the cellulose xanthate in dilute alkali to form the viscose. The carbon disulphide provides serious fire and health hazards against which stringent precautions are taken. One-well known method involves mixing the alkali cellulose with carbon disulphide in a hermetically sealed rotating churn (a so-called dry churn) from which the dry cellulose xanthate is removed and passed to a separate mixer in which the dissolution in dilute alkali is effected. One drawback of this process is that the churn has to be cleaned out after each xanthation; normally the cleaning is carried out by an operative brushing and scraping the inside of the churn. By another known method the two steps of xanthation and dissolution are effected consecutively in a single sealed churn (a so-called wet churn) the dilute alkali being admitted on the completion of the xanthation. This second method has the advantage of facilitating the clearance of the churn, but on the other hand it involves the use of considerably more power than the first method as it is normally carried out in a fixed churn with stirring paddles rotated slowly during the xanthation stage and more rapidly after the admission of the dilute alkali. In addition the fire hazard within the churn is greater due to the moving parts.

It is the object of the present invention to obtain the advantages of the second method without its main disadvantages.

According to the present invention a churn for the production of viscose comprising a shaft, a container mounted on said shaft and stirring mechanism also mounted on said shaft and extending within the container over at least half of the internal capacity of the container, is provided with the combination of locking mechanism whereby, when the container is rotated, the stirring mechanism is also rotated so that there is no relative motion between the container and the stirring mechanism, and free-wheel mechanism whereby the stirring mechanism can be rotated relative to the container. The container is preferably surrounded by a jacket so that the contents of the churn may be heated or cooled as desired.

In the preferred method of operating the churn according to the invention the container is charged with alkali cellulose, sealed, evacuated and then rotated with the stirring mechanism locked relative to the container whilst the carbon disulphide is admitted and the xanthation efiected; the container is then stopped, dilute alkali is admitted and the stirring mechanism is set in motion relative to the container to effect dissolution; the solution is then removed and the churn washed out with further dilute alkali 2 which is added to the viscose solution removed from the churn. Before re-charging with alkali cellulose the churn is preferably washed with caustic soda of approximately mercerising strength to avoid wetting of the alkali cellulose. A specific example of a churn constructed in accordance with the present invention is illustrated in the accompanying drawings, in which Fig. 1 is a front elevation partly in section; Fig. 2 is a section through the free wheel mechanism of Fig. l; and

Fig. 3 is a rear elevation of part of Fig. 1. A churn indicated generally at l comprises a container 2 surrounded by a jacket 3. The churn I has a free wheel 4 at one end and a hollow shaft 5 at the other end. A shaft 6, held in two bearings 1, 8 in frames 9, l0 respectively, protrudes through the free wheel 4 into the container 2 and the shaft 5 is held in a bearing H in a third frame I! so that the churn l is capable of rotation about its horizontal axis.

A paddle I3 is mounted at the end of the shaft 6 within the container 2 and may be rotated by a pulley l4 splined to the shaft 6'. The pulley I4 is capable of being driven from an overhead drive (not shown) through a driving belt I5, which is shifted off an idler pulley 25 by a belt shifting fork 16 when required.

The churn I may be rotated by shifting the belt l5 by means of the belt-shifting fork I6 on to a third pulley I! mounted on a sleeve I8 surrounding the left-hand end of the shaft 6. A gear-wheel 19, also mounted on the sleeve l8, drives the free wheel 4 through a reduction gear chain 20 and an idler gear-wheel 2|.

Referring to Fig. 2, the shaft 6 having a collar splined to it passes through a ring 5| fixed centrally to. the free wheel 4. Four slots 52 are cut in the internal surface of the ring 5| which lies in contact with the collar 50, thus defining four passages 53 which are parallel to the shaft 6. Each passage 53 encloses a roller 54 lying parallel to the shaft 6 and is tapered in a clockwise direction about the axis of the shaft 6 so that its maximum width is greater and its minimum width smaller than the diameter of each roller 54.

Each roller 54 is spring pressed by means of a spring 55, enclosed by a cap 56, into the tapered part of each passage 53, so that it is in contact with both the ring 5| and the collar 50. The spring 55 is housed in a bore 51 opening into the wider part of each passage 53 and is held in position by a screw 58.

During the xanthation stage, the free wheel 4 is rotated in an anticlockwise direction and the rollers 54 are forced into the tapered parts of the passages 53 by the action of the rotation. The rollers 54 act as wedges and the collar 50 is locked to the ring 5| so that the collar 50 together with the shaft 6 are made to rotate with the free wheel 4. Consequently, the paddle l3 is locked to the churn I and is caused to rotate with the churn I.

During the dissolution stage, the shaft 3 together with its associated collar 33 is rotated in a clockwise direction by the pulley I4. The rollers 54 now tend to move out of the tapered parts of the passages 53 against the action of the springs 55 to a position where the width of the passages 53 is greater than the diameter of the rollers 54. Consequently there is no driving contact between the collar 53 and the ring II, and the collar 50 rotates freely within the ring that is, a free wheeling effect" is obtained and the free wheel 4 receives no drive. When the rotation of the collar 53 stops, the rollers 54 are again urged into the tapered parts of the passages 53 by the springs 55.

To prevent the churn creeping" during the dissolution stage, a brake 22 is applied when shifting the driving belt I5 on to the pulley I4 by means of the belt shifting fork l3.

As shown in Fig. 3, the fork I3 is mounted on a screw 60 which is rotatable by a handle 3|. A cam 62 is fixed to the lower side of the fork I6 and is free to slide in a slot 63 in the frame 9 as the fork I6 is moved along the screw 33 by the rotation of the handle 3|. A cam follower 34 mounted on one end of an arm 35 rides against the cam 62. The arm 85 is attached, at its other end, to a cam member (not shown) which is capable of expanding a brake band 36 against the internal surface of a brake drum 51 of the brake 22. Normally, the band 63 is held in a contracted state out of contact with the drum 61 by means of a spring (not shown) within the brake 22. The cam 62 is so shaped that when the belt I5 is driving the pulley H or rotating the idler pulley the brake 22 is inoperative, but when the belt I5 is moved on to the pulley I4, the cam follower 64 is pressed down against the spring within the brake 22 and the brake 22 is operated, thus preventing the sleeve I8, and consequently the churn I, from rotating. The brake 22 may also be operated by a foot-pedal 23 through a rod 68 connecting the pedal 23 and the arm 65. A hand-wheel 24 is fitted to the .end of the sleeve I8 for manual rotation of the churn during loading operations.

In a typical churning operation in the manufacture of viscose, alkali cellulose crumbs are charged into the churn I through a charging door 26 from a chute 21. The door 26 is then closed and air is evacuated from the container 2 through a pipe 28 passing through the centre of the shaft 5, communicating with a chamber 29 in a column 33 having an opening 3i.

Carbon disulphide, delivered to the container 2 by means of a second pipe 32, is now passed through the pipe 28 and through a second chamber 33 in the column 33 to a nozzle 34.

When the churn contains the alkali cellulose and the carbon disulphide the driving belt I5 is shifted from the pulley 25 on to the pulley II so that the churn I and the paddle l3 are rotated for the duration of the xanthation period. The belt I5 is then shifted back to the pulley 25 and the churn I braked by the brake pedal 23.

A quantity of dilute aqueous sodium hydroxide solution rather less than the total volume ultimately required is now admitted to the container 2 through a third pipe passing through the pipe 28, to the chamber 33 and the nozzle 34. The belt I5 is then shifted on to the pulley l4 and the paddle I3 rotated while the churn I is held stationary by the brake 22.

when the cellulose xanthaie has been dissolved, the belt I3 is shifted back on to the pulley 23 and the churn I rotated by means of the handwheel 24, until the door 23 is positioned over a discharge chute 33 in the churn room floor 31. The door 23 is removed and the solution discharged into the chute 33. dilute sodium hydroxide solution is now passed into the churn I through the nozzle 34 to wash out the residual cellulose xanthate solution and this also passes down the chute 33. The churn I is now ready for the cycle to be repeated.

The temperature of the container 2 is controlled by passing a heated fluid continually into a space 33 between the container 2 and the jacket 3 by means of an inlet pipe 33 communicating with an internal pipe 43 within the wall 4| of the hollow shaft 5 which opens into the space 33. The fluid passes out of the space 33 by a second internal pipe 42 communicating with an outlet pipe 43.

If desired the churn can be modified to permit a continuous supply of carbon disulphide in a manner similar to that adopted with known "wet churns but this requires more complex packing glands.

A churn constructed in accordance with the invention requires small power only to rotate it during the xanthation, and the fire hazard is low owing to the absence of parts moving relatively to one another.

What we claim is:

1. A churn for the production of viscose comprising in combination, a container, a free wheel secured to the container, a driving shaft passing through the free wheel, extending into one end of the container and supporting the container, a stirring mechanism mounted on the driving shaft within the container, said mechanism extending over at least half of the internal capacity of the container, a hollow shaft passing into the other end of the container for introducing fluids into the container co-aligned with the driving shaft and also supporting the container, a support for the driving shaft, a second support for the hollow shaft, two independent driving wheels mounted on the driving shaft, one of the said driving wheels being freely mounted on the driving shaft and geared to the free wheel so that when a drive is directed to the said driving wheel the container and the stirring mechanism are locked and rotated together so that there is no relative motion between the container and the stirring mechanism and when the drive is directed to the second driving wheel which is fixed to the driving shaft, the stirring mechanism is rotated while the container remains substantially stationary.

2. A churn as claimed in claim 1 wherein there is a jacket surrounding the container so that the temperature of the contents may be controlled by a fluid circulating in the jacket, and a pipe accommodated within the hollow shaft to pass in the fluid.

W. R. WEIGHAM. WILLIAM H. STOKES.

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

UNITED STATES PATENTS Number Name Date 1,504,832 Pouget Aug. 12, 1924 1,750,558 Zettergren Mar. 11, 1930 2,267,898 Cornell Dec. 30, 1941 The remainder of the

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