Presses – Automatic or material triggered control – Of actuating means
Patent
1993-05-17
1994-10-25
Gerrity, Stephen F.
Presses
Automatic or material triggered control
Of actuating means
100112, 100117, 100127, 100145, B30B 914
Patent
active
053578554
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates in general to screw presses, and relates in particular to a screw press which dehydrates slurry to produce sludge and discharges the sludge.
BACKGROUND OF THE INVENTION
A conventional screw press generally has a screw shaft mounted inside an outer screen casing. Slurry is supplied between the screw shaft and the outer screen casing. Slurry is then dehydrated and pressed by rotating the screw shaft subject the slurry to a solid-liquid separation, and the produced sludge is discharged as a cake.
When the cake is formed gradually during the dehydrating operation by the screw press, the load on a drive unit rotating the screw shaft becomes too heavy to press the slurry sufficiently.
The above mentioned outer screen casing mounted on the screen press is not capable of bearing a large pressure. This is because the outer screen casing is mainly formed from a metal screen. The screw press for dehydrating viscous waste water requires a pressure tightness in order to receive a large pressure. Therefore, the metal screen of the outer screen casing mounted on the press is rigidly reinforced by rings, flanges, and so on. The screen of the screw press processing the viscous slurry usually has a fine mesh. As a result, the screen tends to clog and then needs to be cleaned. Conventionally, although the clogged screen is cleaned with a brush, it is very difficult to clean the clogged screen to a good condition because the screen has a very fine mesh and the above mentioned reinforced flange and related structure prevent the brush contacting the entire screen. In an alternative method of cleaning the screen by spraying compressed air onto the screen, that method also is unable to thoroughly remove the clogging.
SUMMARY OF INVENTION
It is a primary object of this invention to provide a screw press which has an improved capability of dehydration and is capable of reducing an overload on a drive unit rotating a screw shaft during the dehydration, and has a screen from which the clogging of the mesh can be easily cleaned.
It is another object of this invention to provide a method for driving the screw press, comprising a first step of detecting the overload produced in a drive unit driving the screw press during processing of slurry, and a second step of returning to the slurry process again after reducing the overload, thereby performing the slurry process continuously and efficiently.
This invention is based on the discovery that the slurry process is effectively performed by rotating an outer screen casing simultaneously with the rotation of the screw shaft at a rotating speed within a predetermined range, in the opposite rotational direction of the screw shaft. The screw press of this invention is characterized by a drive unit for rotating the screw shaft in one rotational direction and for rotating the outer screen casing in the opposite rotational direction at the same time. The drive unit has a transmission which changes the rotational speed of at least one of the outer screen casing or the screw shaft.
The effectiveness of dehydration by the screw press is especially obtained by setting the rotational speed of the outer screen casing in the ratio 0.1-1.2 to that of the screw shaft. Therefore, the transmission is characterized by the capability of rotating the outer screen casing and the screw shaft in accordance with the above ratio.
The above-mentioned screw shaft is characterized by a hollow shaft having an outer screenlike surface for filtering the slurry. Therefore, the dehydration efficiency becomes higher by performing a double filtration.
The above-mentioned screw press comprises a device for detecting overload when it occurs in the drive unit, and a device for rotating at least one of the outer screen casing and the screw shaft in a rotational direction opposite to their present rotational direction for a predetermined period of time against said overload. Therefore, the load of the drive unit is reduced.
In the screw press above described, a high pressure cle
REFERENCES:
patent: 1876064 (1932-09-01), Lang
patent: 2419545 (1947-04-01), Gray et al.
patent: 2709957 (1955-06-01), Armstrong
patent: 4286512 (1981-09-01), Berggren
patent: 4844799 (1989-07-01), Lee
Ishigaki Eiichi
Mitani Yukitoshi
Gerrity Stephen F.
Ishigaki Mechanical Industry Co., Ltd.
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