Batch type filter system

Disclosed herein is a batch type filter system including a cover provided with a supply pipe for supplying raw liquid and air, a plate having a filter medium support on an upper surface thereof and a filtrate exhaust pipe, said cover being vertically separable from said plate, a plurality of filter medium moving rollers provided on both sides of said cover and said plate, and a sheet-like long filter medium stretched over said rollers and adapted to be moved by a predetermined length per one batch of filtration, said filter medium being temporarily fixedly held between the circumferential portion of said cover and the curcumferential portion of said plate. The improvement in the batch type filter system comprises arcuately curved tension bars provided at such positions where a moving direction of the filter medium is changed and on downstream sides of said filter medium moving rollers, so as to apply a larger tensile force to a central portion of said filter medium than to both edge portions thereof.

BACKGROUND OF THE INVENTION 
The present invention relates to a filter for filtering a suspension under 
pressure and uncontinuously exhausting a filter cake having a low content 
of a mother liquor. 
In a well-known filter system, a filter cloth is disposed on a filter plate 
provided on the upper surface of a flat filter medium support, and a cover 
arranged above the filter plate is brought into tight contact with the 
circumferential portion of the filter plate. Then, a suspension is 
supplied under pressure to a space defined between the cover and the 
filter cloth to carry out filtration. When filtration efficiency is 
reduced because of stacking of a filter cake on the filter cloth, supply 
of the suspension is stopped, and pressurized air is supplied to reduce 
mother liquor content of the filter cake. Then, the cover is separated 
from the filter plate to remove the filter cake as well as the filter 
cloth. Further, in another well-known filter system, a long filter cloth 
is used, and a predetermined length of the filter cloth is moved every 
time a filtering operation is carried out to thereby remove the filter 
cake. While the drawn filter cloth on which the filter cake is deposited 
is sometimes abandoned after one use, it is economically preferred to wash 
and regenerate the filter cloth for reuse. Therefore, a soft cloth such as 
non-woven fabric cloth is widely used as the filter cloth from the 
viewpoints of filtration efficiency and economy. However, when a fixed 
length of such a soft filter cloth is moved by a filter cloth feeding 
roller and a filter cloth drawing roller, ununiform expansion and 
contraction of the filter cloth is apt to occur to create lateral 
deviation. Even if such deviation is intended to be restricted by guides 
provided on both sides of the filter cloth, there are only created 
wrinkles of the filter cloth, and the guides cannot return the filter 
cloth to a normal position. 
To this end, when there occurs deviation of a moving position of the filter 
cloth, the deviation is conventionally corrected by changing the 
inclination of the filter cloth drawing roll or friction bars provided on 
front and rear sides of a filtering position. In a conventional control 
system, such correction of the deviation is automatically carried out by 
using a photoelectric sensor for detection of an end portion of the filter 
cloth to control the inclination of the friciton bars. However, it is 
impossible to eliminate generation of meandering causing the expansion and 
contraction of the filter cloth. As a result, an excessive width of the 
filter cloth is required, and a narrow filtering surface only is 
unavoidably used, which results in economical disadvantages. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an economical automatic 
adjusting mechanism for a filter system which may prevent meandering of a 
filter medium in moving a soft long sheet-like filter cloth as the filter 
medium. 
It is another object of the present invention to provide an economical 
filter system which has a large capacity of filtration by utilizing the 
entire width of the filter medium for filtration. 
According to the present invention, in a batch type filter system including 
a cover provided with a supply pipe for supplying raw liquid and air, a 
plate having a filter medium support on an upper surface thereof and a 
filtrate exhaust pipe, said cover being vertically separatable from said 
plate, a plurality of filter medium moving rollers provided on both sides 
of said cover and said plate, and a sheet-like long filter medium 
stretched over said rollers and adapted to be moved by a predetermined 
length per one batch of filtration, said filter medium being temporarily 
fixedly held between the circumferential portion of said cover and the 
circumferential portion of said plate; the improvement comprises arcuately 
curved tension bars provided at such positions where a moving direction of 
said filter medium is changed on downstream sides of said filter medium 
moving rollers, so as to apply a larger tensile force to a central portion 
of said filter medium than to both edge portions thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1, the filter system of a preferred embodiment according 
to the present invention includes a cover 1, an annular packing 2 attached 
to the lower surface of a circumferential portion 1a of the cover 1, a 
plate 3, a filter medium support 4 mounted on the upper recessed portion 
of the plate 3, an air cylinder 5 and a filter paper 6. The filter paper 6 
is fed from a new filter paper roll 6a through a feed roller 8a and a 
pinch roller 8b and a tension bar 8c onto the filter medium support 4. A 
feeding direction of the filter paper 6 is converted at the tension bar 8c 
by about 90 degrees. 
The cover 1 is provided with a supply pipe 1b for supplying raw liquid and 
air, and is designed to be vertically moved by the air cylinder 5. When 
the cover 1 is lowered, the filter paper 6 is fixedly held between a 
circumferential portion 3a of the plate 3 and the annular packing 2. As 
the filter paper 6 is supported by the filter medium support 4, the raw 
liquid is supplied from the supply pipe 1b into a raw liquid chamber 1c, 
and is filtered through the filter paper 6 and the filter medium support 
4. Then, the filtrate is discharged from a filtrate chamber 3c through an 
exhaust pipe 3b. 
On the other hand, when an amount of filter cake 7 deposited on the filter 
paper increases, supply of the raw liquid is stopped at an appropriate 
time, and pressurized air is supplied, so as to eliminate the difficulty 
of filtration due to an increase in pressure in the raw liquid chamber 1c. 
As a result, the raw liquid contained in the filter cake is wholly 
recovered as the filtrate, and the dewatered filter cake 7 only remains on 
the filter paper 6. Then, the cover 1 is upwardly moved by the air 
cylinder 5 to release the filter paper 6. 
The filter paper 6 is fed through a drawing roller 8d, and then the filter 
cake 7 is separated off by a scraper 8f. Then, a feeding direction of the 
filter paper 6 is converted at a tension bar 8e by about 90 degrees, and 
finally the filter paper 6 is wound around a roll 6b. 
Referring to FIG. 2 showing a route of the filter paper 6, the filter paper 
6 advances downwardly from the feed roll 8a, and changes its advancing 
direction horizontally at the position of the tension bar 8c. The tension 
bar 8c is downwardly curved in an arcuate fashion, and the degree of 
curvature thereof is such that the radius of curvature is preferably about 
1 to 10 meters. 
The filter paper 6 as horizontally advanced is used for filtration, and is 
then turned back along the drawing roller 8d to horizontally reversely 
move. Then, the filter paper 6 changes its advancing direction downwardly 
again at the position of the tension bar 8e, and finally reaches the roll 
6b. As similar to the tension bar 8c, the tension bar 8e is arcuately 
curved to such a degree that the radius of curvature is about 1 to 10 
meters, and the direction of curvature is rightward. In other words, both 
the tension bars 8c and 8e are designed to apply a large tensile force to 
the central portion of the filter paper. 
Even when the radius of curvature of the tension bars is more than 10 
meters, it is effected to suppress meandering of the filter paper 6. 
However, an excessively small degree of curvature is less effective. 
Conversely, when the radius of curvature is less than one meter, the 
filter paper 6 advances with the side edge portions thereof separated or 
floating from the tension bars, which adversely affects prevention of 
meandering. 
For the comparative purpose, a centrally expanded roller was used in 
substitution for the tension bars of the invention, but it was less 
effective in preventing meandering of the filter paper. 
Having thus described the preferred embodiment of the invention, it should 
be understood that numerous structural modifications and adaptions may be 
made without departing from the spirit of the invention.