Presses – With drain means for expressed liquid – Drainage through or along pressure surface
Patent
1982-02-03
1984-03-27
Feldman, Peter
Presses
With drain means for expressed liquid
Drainage through or along pressure surface
100146, B30B 912
Patent
active
044386915
DESCRIPTION:
BRIEF SUMMARY
This invention relates to screw press arrangements.
A screw press which effects a continuous expelling of fluid from various moist material masses, is described in Norwegian Patent Specification No. 56,471 (from 1935) and in the main features the screw presses are built continuously as is described in said patent specification.
Gradually as screw presses have found application in new areas, it has been found that when materials are concerned which give good squeezing out of fluid--and with this also a compact and hard press cake with great friction between the material and the screw surface--there is obtained with the construction of the screw element described in the aforementioned Norwegian patent specification, an insufficient thread engagement between the screw elements over a large portion of the length of the screw element so that the press cake rotates to too great a degree together with the screw elements. As a result the advancement of material is reduced and the effect of squeezing out of fluid is reduced. As a consequence of the material rotating to a large degree with the screw element the pressure which is built up internally in the press basket already begins to decrease strongly at a distance from the discharge end of approximately 30% of the total length of the screw element. This situation is determined by means of special pressure measuring cells which are mounted at suitable mutual distances along the press basket.
An object of the present invention is to eliminte the afore-mentioned disadvantages with these types of presses and particularly the objective is a screw press arrangement where the forward feeding of the material, the squeezing out of fluid and the build up of pressure in the screw press can be improved.
Accordingly the present invention residues in a screw press arrangement having at least two screw elements in side-by-side relation provided with threads having a pitch at least three times greater than their thickness in the axial direction and projecting inwards between threads of an adjacent screw element into intermediate spaces defined thereby and a relatively tightly fitting press basket surrounding the screw elements and having openings for drainage of fluid. Each screw element it is provided with a feed portion having a small core diameter and large thread diameter, a discharge portion with a large core diameter and small thread diameter or without threads and an intermediate portion forming a transition between the feed portion and discharge portion where the press basket is substantially cylindrical in shape. The discharge portion has a length of between 10 and 30% of the total length of a screw element with a core diameter increasing uniformly towards the discharge end and with a uniformly decreasing press basket inner diameter. The sum of the internal press basket radius and core radius in any radial plane in the discharge portion is constant and substantially corresponds to the center distance between the screw elements.
When it is stated above that the sum of internal press basket radius and core radius substantially corresponds to the center distance between the screw elements, it is meant that the screw threads--in the instances the discharge portion is provided with screw threads--substantially form a sliding abutment against the core surface of the adjacent screw element.
In the two-screwed presses hitherto used, one has been heavily committed to maintaining a particular press cake thickness when, for the screw presses of a particular press size and press capacity, there is first determined the core diameter of the screw element and the thread diameter and with this also the center distance between the screw elements. According to Norwegian Patent Specification No. 106,253, it has been found possible to reduce the press cake thickness by cutting in grooves in the core of the screw element for the reception of the threads of the adjacent screw element. An increase of the press cake thickness has been able to be effected relatively easily but then with the con
REFERENCES:
patent: 2567219 (1951-09-01), Lesniak
Feldman Peter
Stord Bartz A/S
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