Adjustable reaction tubs for cellulose

An adjustable reaction tub for making tubular cellulosic casings from viscose, the tub having upper rollers mounted to a frame and lower rollers on a roll support mounted to the same frame for adjustable positioning of the lower rollers at any of a range of depths within the tub.

TECHNICAL FIELD 
The present invention relates generally to the manufacture of tubular 
cellulosic casings for food, and more particularly to the tubs used in 
making regenerated cellulosic casing from extruded viscose (sodium 
cellulose xanthate, sodium hydroxide, and water). 
BACKGROUND ART 
The procedure for making regenerated cellulosic casings from extruded 
viscose is well-known. Viscose is described in U.K. Patent No. 8700 and in 
U.S. Pat. No. 1,036,282, and its manufacture is described in U.S. Pat. No. 
3,835,113. U.S. Pat. Nos. 1,070,776; 1,158,400; and 1,163,740; describe 
the use of viscose to manufacture a tubular cellulosic casing, and 
processes for doing so are described in U.S. Pat. Nos. 1,601,686; 
1,612,508; 1,645,050; 1,654,253; 2,901,358; and 5,451,364. 
The modern process of making regenerated cellulose casings by extruding 
viscose through an annular die into a bath of coagulating and regenerating 
liquid held in a reaction tub is described in U.S. Pat. Nos. 1,898,400; 
2,271,932; 2,999,756; 2,999,757; 4,590,107. Generally, the casing after 
extrusion dips into and out of the tub by winding between upper rollers 
mounted above the tub and lower rollers mounted within the tub, below a 
liquid level. As explained in U.S. Pat. No. 1,887,446, the casing passes 
through the air between dips into the liquid, at which time the casing 
cools and gases are evolved, internally and externally from the casing 
surfaces. The internal gases are contained within the casing. 
Conventionally, the casing-making process involves a series of reactions 
tubs. As explained in U.S. Pat. No. 1,903,622, some tubs contain acid 
necessary for cellulose regeneration, while others include washwater. 
Examples of such systems are described in U.S. Pat. Nos. 1,898,400; 
1,903,622; 1,937,225; 1,958,181; 2,144,899; 4,778,639; 4,790,044; and 
5,358,765. 
Conventional systems suffer from several problems. 
In conventional systems, hydraulic pressure created by the liquid contents 
of a tub can cause dimensional distortion of the tub walls on which the 
lower rollers are mounted. Distortion can be aggravated by thermal 
expansion of the tub walls caused by high temperatures of the liquid. 
These distortions tend to skew the alignment and positioning of the lower 
rollers with respect to the upper rollers. Slight misalignments of the 
rollers can cause the extruded casing to mis-track at high line-speeds. 
Thus, in conventional systems, line-speeds are limited to approximately 40 
meters per second, much due to poor tracking of adjacent casings. 
Conventional systems also offer relatively little flexibility. If the time 
of submergence in an acid needs to be reduced, for example, the only 
practical way to achieve a significant reduction in time is to "re-lace" 
the line to omit a pair (or more) of rollers. Doing so reduces the volume 
within the casing in which the evolved gases may be contained and 
distributed, requiring more frequent slitting of the casing to release 
such gases. Re-placing is also inefficient because it requires each line 
of casings to be cut and subsequently re-taped. 
Because of their positioning within the tank, the lower rollers (which are 
typically made of glass) are difficult to maintain without breakage. 
Maintenance is also time-consuming, because it requires the tub to be 
drained of its liquid in order to provide access to the lower rollers. 
SUMMARY OF THE INVENTION 
The present invention solves all of these problems, allowing improved 
alignment of the rollers and, with it, greater line-speeds; fine-tuning of 
submergence times without any need for re-lacing or any reduction in air 
residence time; and a simplified maintenance procedure for the lower 
rollers that does not require draining the tub. 
These dramatic improvements are realized by replacing the conventional 
lower roller mountings within the tank with an adjustable roll support 
attached to the same frame on which the upper rollers are attached. The 
roll support can be adjusted by raising it or lowering it with respect to 
the tank walls, and can even be positioned so that the lower rollers are 
completely above the liquid level in the tanks, allowing the rollers to be 
serviced without draining the tank and with minimal risk of damage to the 
rollers.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the FIGS., FIG. 1 shows an adjustable reaction tub 10 for use 
in making regenerated cellulosic casings. 
The tub 10 has a series of tank walls 15 and 20 that form a reservoir for 
acid or washwater. The walls are attached to a tubular frame 25 that 
includes uprights 26 and crosspieces 27 and 28. In the embodiment 
illustrated in FIG. 1, the walls are preferably constructed of homopolymer 
polypropylene and are approximately 105 cm high. The tub is designed to 
hold liquid up to a liquid level 30 (FIGS. 4 and 5) about 85 to 95 cm 
above the bottom 35 of the tub. Because some of the cross pieces 28 
support the walls when they deflect under the pressure of the liquid in 
the tub (see FIG. 4), the walls need be only approximately 4 cm thick. 
Thus, the proportional thickness of the tub walls to their height to the 
liquid level is approximately 1:22. The tank walls 15 and 20 are thus 
proportionally thinner than in conventional plastic tubs, and thus less 
expensive. Alternatively, the walls could be made of other non-metallic 
materials, such as PVC, PRC, or fiberglass; or of rubber-lined steel, or 
other anti-corrosive materials, with similar reductions in required 
thickness. 
While the deflection of the thin walls 15 and 20 would cause problems in 
the alignment of lower and upper rollers in a conventional tub, it causes 
no problem in the illustrated tub 10 because the lower rollers are not 
mounted to the tub walls. 
In the embodiment shown in FIG. 2, the long walls 15 of the tub 10 are 
approximately 508 cm long, accommodating two end-m-end racks of lower 
rollers 40 (FIGS. 3 and 5). The lower rollers are preferably made of 
glass. Preferably, each roller is approximately 3" in diameter and 468 cm 
in length. The rollers are arranged side-by-side on a horizontal plane, 
with each roller positioned approximately six inches on center from each 
adjacent roller. The short walls 20 of the tub 10 are approximately 200 cm 
wide, accommodating six lower rollers arranged side-by-side. The lower 
rollers do not rotate; they are fixed. 
As seen in FIG. 3, lower roller brackets 45 accommodate ends of each of the 
lower rollers 40. The lower roller brackets are mounted to a roll support 
50. As illustrated in FIG. 1, the roll support has a collar 52 that is 
slotted to one of the cross-pieces 27 of the frame 25 for adjustable 
positioning of the lower roller brackets at various horizontal planes 
within the walls 15 and 20 of the tub 10. The lower roller brackets are 
preferably locked into position by horizontal locking pins (not shown) 
that lock into pre-drilled holes in the frame 25. The roll support is 
raised and lowered with respect to the frame by a pair of screw shafts 53 
powered by electric motors 54. Alternatively, the roll support could be 
lifted by, for example, an overhead crane, winches, ratchets, air 
cylinders, or hydraulic cylinders. 
A set of upper rollers 55 is mounted at the top of the frame 25 above the 
lower rollers 40. The upper rollers preferably are of the same general 
dimensions as the lower rollers, but are covered with a rubber outer 
surface. As is conventionally known, the upper rollers rotate about their 
axis, and are driven by motors. The upper rollers are positioned on a 
horizontal plane, parallel with the lower rollers. 
Casing 60 (best seen in FIG. 5) winds in a path 65 (FIGS. 1 and 4) between 
the upper rollers 55 and the lower rollers 40. Submerged portions 70 of 
the path, below the liquid level 30, are within the liquid 75. By raising 
the roll support 50, the submerged portions of the path are shortened 
while the remainder of the path, above the liquid level, remains 
unchanged. Since casing on the path moves at the same line-speed at all 
points on the path, adjusting the horizontal positioning of the roll 
support 50 allows the submergence times of the casing to be adjusted 
without the need for re-lacing the line or changing the amount of time 
that the casing is exposed to the air between submerged portions of the 
path. 
By lengthening the screw shafts 53 and mounting the electric motors 54 in a 
higher position than illustrated in FIG. 1, the tub 10 can be designed so 
that the roll support 50 can be raised high enough so that the lower 
rollers 40 are completely above the liquid level 30. Raising the lower 
rollers above the liquid level allows the lower rollers to be serviced 
without the need to drain the liquid 75 from the tub 10. 
As is conventionally known, liquid can be added to the tub 10 through an 
inlet 80 (FIG. 5) and drained through a drain 85 (FIG. 4) on the bottom 35 
of the tub. An overflow pipe 90 (FIG. 5) includes an insert 95 that can be 
adjusted to different liquid levels. 
Numerous modifications and alternative embodiments of the invention will be 
apparent to those skilled in the art upon review of this description. 
Accordingly, this description should be construed as illustrative only and 
is for the purpose of teaching those skilled in the art the best mode of 
carrying out the invention. The details of the structure may be varied 
substantially without departing from the spirit of the invention.