CA1153287A

CA1153287A - Screw press with continuous slope feed screw

Info

Publication number: CA1153287A
Application number: CA000377249A
Authority: CA
Inventors: Arthur J. Hunt, Jr.; Arthur J. Hunt
Original assignee: Individual
Current assignee: Individual
Priority date: 1981-05-08
Filing date: 1981-05-08
Publication date: 1983-09-06

Abstract

SCREW PRESS WITH CONTINUOUS SLOPE FEED SCREW

Abstract A screw press for extraction of liquids from solids or semi-solids haying a feed screw (22, 24) disposed in a cylindrical cage (41) formed from filter screens (42). The feed screw has a body portion (22) that increases in diameter over the full length of the screw in a linear fashion forming a gradual slope providing a gentle pressing action on the materials being pressed. A variable speed drive (60) is used to optimize the rotational speed of the feed screw for maximum liquid extraction versus material throughput. The cylindrical cage (41) comprises at least-one pair of semi-circular sections connected along a lower edge by a set of offset hinges (46) and bolted together along an upper edge. For cleaning of the press or changing of filter screens, the sections open with the off-set hinges causing the sections to move downward and outward, completely clear of the feed screw. The screw press is especially suitable for predraining of grape must prior to final pressing, dejuicing fragile fruits such as apples, and dewatering of materials having a high liquid content.

Description

`` :llS32~37 - SCREW PRESS WITH C~:)NTINUOUS SLOP~ FEED SCRE~I

BACI~G~OUND OF THE INVENTION

1. Field of the Invention.

The present invention relates to screw presses for extracting liquids from fruits or vegetables or the like~ and more particularly to a screw press for extracting the free liquid in such fruits and vege-tables prior to final pressing.

2. Description of the Prior Art.
Screw presses have been widely used for the extraction of liquids from solids or semi~solids in the food industry. A primary application of such - presses is the grape and wine industry. It is common practice to introduce harvested grapes into a destemmer or precrusher which serves to free the grapes from their stems. The destemmer in operation causes rupture damage to a large proportion of the incoming fruit which results in a free run of juice in the mass of grapes, or must, as the mass is termed.
Before pressing the must to remove the remainder of the juice from the grapes, the must is predrained of this free running juice. Several methods are in common use. For example, the must containing the free run ~uice is transferred fro~ the destemmer to settling tanks, where the free run juice is allowed to settle out. A typical settling time may be on the order of two hours. After settling t the free juice is drawn off and carried to a separator to remove solids which have collected from the crushing or destemming operation. The remaining must is dumped into feed troughs for transport to the final . . ..

- l~S328~

pressing operation. A typical time for the dumping and feeding operation may be on the order of one-half hour. The must delivered to the final press still contains free run juice since the settling tank can-not completely drain the original must in the allottedtime. Th.e extreme wetness of the must often causes difficulty in the conveyors and other predrainers which may ke utilized prior to the final pressing.
Other systems utilize drag screens disposed along the conveyors from the destemmer to the presses which allow the free run juice to drain off and ~e collected in drain pans beneath the conveyors. This approach is also slow since the transport time must he long to provide sufficient draining time. Even with pre-draining, the wet must delivered to the pressescauses difficulty in feeding due to slippage of the wet mass of grapes. Thi.s problem varies with.the type of grapes. being handled.
In the wine i.ndustry, great effort is expended to get a crop harvested at the proper time, with.
picke.rs working night and day until harvesting is complete. However, when trucks carrying the harvested crop arrive at the winery, i.t is common to have long waiting periods for unloading This delay i.s ~ener-ally due to the long times required for predrainingand conveying of the must after destemming. Thus, the. throughput of th.e winery is essentially limited ky this operation.
Attempts have been made in the past to reduce the predrain time and to deliver a much dryer must to the final press. For example, U S. Patent No.
4,117,776 to H.unt describes a screw press apparatus having a two-section press The first section receives the must di.rectly from the destemmer without requi.ring settling tanks, drag screens~ or the like.

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` ~532~7 The feed screw of the first section includes a seg-mented body havins a straight section, a sharply tapered section and a final straight section. ~ust is introduced into the first flights of the feed screw and carried along to the tapered body, thereby re-ducing the volume of the must producing a squeezing action. Further draining is then accomplished in the final straight section. The feed screw operates within a conventional chamber or cage formed from filter lQ screens such that the free run juice squeezed from the must passes through the screens and is collected.
The speed of rotation of the feed screw is adjusta~le in the order of SQ to 30Q rpm. After the predraining operation, the resulting pulp is passed directly to the second section of the apparatus which operates as a conventional screw press compressing the predrained must to a final dry cake, The screw feed for the second section of the apparatus is separately rotated and desi~ned to rotate on the order of 10 to 50 rpm.
Although an improvement over the prior art and useful for many applications, in predraining grapes and pressing ~rapes~ a number of problems has been found.
First, the extremely wet undrained must, when intro-duced into the inlet of the predrainer section of the apparatua, caused slippage between the mass of grapes and the spiraling feed screw. Next, the relatively acute taper of the feed screw body contributed further to the slippage and caused difficulty in controlling the percentages of juices obtained in the predraining phase, Difficulty has also heen encountered in attempting to independently adjust the rotational speeds of the feed screw in the predrainer section and in the press section to obtain optimum throughput.
Another difficulty in the predrainer section involves the cleaning of the filter screens which requires . .
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~ ~ ' ~:~L53287 excessive time and labor. In accordance with the present invention, the difficulties encountered in the predrainer of the previous Hunt patent have been solved, and a screw press provided which operates as a high speed-predrainer for grapes and the like.
In addition to the wine and grape industry, many products require dewatering at certain stages in processing. Examples are: sugar beets; kelp;
vegetables; spent ~rainsi citrus pulps; pineapple lQ peels; industrial sludges; animal stomachs; alfalfa, plastics~; and cranberries. Many of these are wastes from food processin~ and the like to be completely dried and utilized for animal feeds. Such drying commonly requires high BTU burners which use large amounts of energy. Efficient screw presses, in accordance with the present invention, can predrain or remove a large percentage of liquids from such products quickly and at low cost. Thus, the energy requirements for final drying are greatly reduced.
Screw presses and other types of presses avail-able in the prior art often use star wheels or breaker bars to mascerate ~rape skins and seeds, lmpartin~ a "~rassy" taste to the juice or wine.
When such presses are used with tobacco or paper sludges, these devices cause hard spots in the finished product called "fish eyes". Our invention advantageously dispenses with the need for star wheel~ or brea~er bars.

SU~MARY OF T~IE rNVENTION

mhe present invention is a screw press type liquid e~tractor especially adapted to extraction of free run juice from grape~ and similar fruit.
In such application of our invention the press will " ' . ~' ' ~ ' ,' ~1~i"32~7 be referred to as a predrainer. The press utilizes a feed screw having a body which increases in dia-meter over the full length of the screw in a linear fashion forming a gradual slope in conjunction with a drive system providin a high speed of rotation.
The invention thus utilizes a gentle pressing action due to the gradual reduction in volume in the screw feed flights and a positive ejection of the liquids by virtue of centrifugal force generated from the high rotary speed of the feed screw, The feed screw is surrounded by filter screen cages through which the juice iæ ejected from the fruit. The juice is then collected in an appropriate drain system.
A key feature of the invention lies in the design of the inlet chamher. When used as a pre-drainer~ the incoming must contains a large amount of free run juice and preæents 2 wet, slippery mass to th.e feed screw~ In prior art screw type presses, it i.s common to utilize a large inlet covering several flights of the feed screw and having tapering side portions such that a large volume of must can enter the inlet area in an attempt to maximize throughput, ~owe~er, the result is that only the must closest to the cage portion of the press is positively fed into th.e pressing region, The must at the front end of the feed screw tends to slip and to thus limit the amount of must th.at can be fed.
~e have discovered experimentally that a ~aximum throughput in a screw press may be obtained by observing an optimum mathematical relationæhip between tn.e pitch of the feed screw and the size of the inlet opening, and by limiting the open area around the front end of the feed screw. ~ccordingly, the invention uti.lizes an inlet having a longitudinal throat dimension of 1.5 times the pitch of the 532~7 feed screw. We have also found for the predrainer application o~ the invention that the optimum ratio of the diameter of the feed screw to its pitch ls 2 to 1, We have also found it advantageous to limit the opening of the inlet area of the sides encircling the front end of the feed screw to approximately SQ% of the circumference~ In other words, the first flight of the lead screw is enclosed by cylindrical sides for at least half of its circumference and preferably for about 75% of its circumference, In operation with this novel inlet structure, a hopper is provided above the inlet and the free run liquid-containing must introduced into the hopper. To obtain the maximum throughput, that is, to insure that the must entering the first flight of the feed screw is transported forward and does not slip, requires a certain mass of must in the hopper.
If less than this mass is present then slippage is possib,le, and if more mass is in the hopper, the density of the incoming must may be excessive. We have also found a relationship between the speed of rotation of the feed screw and the head formed by the must in the hopper for proper optimum feeding.
For a given head, there is an optimum rpm required for the feed screw. Thus~ we provide a variable speed drive unit for the feed screw such that the operator may maintain this optimum speed in accor-dance with the rate of incoming must to the hopper.
On start-up of a predraining operation before the flow of must has begun, the operator may speed up the screw feed system to start the movement of must through the predrainer. Once this flow has begun the speed of the shaft can then be dropped to the normal operating rpm. Once the predrainer is filled and the hopper has reached its ~esired head, it may : ., .

1153~37 be noted that a pumping action occurs as the feed screw moves the must through the predrainer, in effect sucking the must into the inlet positively in addition to th.e normal tendency of gravity to feed the must.
As the must moves through the predrainer, the decreasing volume of space hetween successive flights of the feed screw combined with the gradual slope of the body causes a gentle pressing of the must to force the free run juice toward the outside of the mass aided by the centrifugal force generated by the relatively high.speed rotation of the feed screw which may vary from 6Q to 360 rpm. The free run juice thus extracted flows through the surrounding screens and is drained into jui.ce collecting pans disposed below the cage.
As the must arrives at the end of the feed screw r it is ejected into a must collector for subsequent press-ing to recover the remaining juice. In predraining grapes, it is common to ohtain approximately 80% of the available juice ïn the apparatus of our invention.
The operator may determine the optimum operating conditions for parti.cular varieties of grapes and other fruits utilizi.ng the two variables of the head of the must in the hopper and the rotational speed of the feed screw. The high.er the feed screw rotation, th.e more rapidly the must will he transported through the predrainer and the greater the amount of the juice that will he. removed by centrifugal force. Il.oweverr the faster the feed, the lower the head will be main-tained in the hopper and the less efficient the feeding action will be. Thus, the operator must balance the rotational speed against the requirement for a certain head of must in the hopper and the proportion of juice removed. Once these parameters are determined experimentally and set for a given incoming must rate, the predrainer can operate with a minimum of attention.

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~lS~Z~7 If the rate of incoming must drops, then the operator can reduce the rate of rotation of the feed screw sufficient to maintain the predetermined head, while an increase in incoming must will permit a higher rotational speed.
It is desired in wine making and other liquid extraction systems to minimize the amount of solids in the juices. In wine maki.ng, the destemming opera-tion generally introduces a significant amount of solids whi.ch appear in the free run juice. It i5 therefore important that the predrainer and pressing operations do not add appreciably to these solids to minimize time and e~pense in separating the juice from the solids. The gentle squeezing and centrifugal force action in the predrainer of the invention advantageously prevents significant amounts of addi-tional solids from occurring. The screen mesh may also be sele.cted to provide some filtering action with.respect to solids; however, a tendency of solids to clog the screens must be avoided, It is also important after a run to ~e able to easily and efficiently clean the filter screens.
Additionally~ it is desirable to be able to change filter screens for the optimum filter mesh design for th.e variety of grape or the type of fruit being processed, In prior art machines, disassem~ly of the screens has been necessary to accomplish such changes. In accordance with our invention, we have provided a hin~ing structure in which screens can be 30. very easily and quickly cleaned and the predrainer made ready for the next run. Similarly, the hinging method permits easy interchange of screens when desired.
The filter screens of the invention comprise a pair of semi-circular se.ctions of a cylindrical cage ~l3L53;~137 g having a screen frame consisting of a plurality of circumferential ribs arranged to support the screens.
The screen frames thus represent halves of a cylinder with attachment strips along the outer edges. A
pivot shaft is disposed parallel with the drive shaft of the feed screw having a series of hinge blocks pivoted thereto. One edge of each screen frame is attached to a set of interleaved hinge ~locks, The screen cage is split lengthwise forming two semi-cylindrical sections. The two sections are hinged at the bottom with the hinge ~locks forming offset hinges such that opening of the two screen cage sections causes th~ sections to moYe downward and outward completely clear of the feed screw. The screen halves are normally secured at the top when the unit is in operation. ~hen cleaning is required, the bolts holdin~ the top edges of the screen sections together are removed and the two halves opened. At this point the inner surfaces of the screens are readily accessible for rinsing, scrub~ing and clean-ing, as is the feed screw. The screens are attached to the screen frames by attachment strips fastened to the frame edges. Wlth the screens in the open position, the screens are readily remova~le and replacea~le, The preferred drive system for the invention utilizes a hydraulic system powered from an electric motor. The drive motor or the feed screw is there-fore a hydraulic unit with control of the hydraulic pressure utilized to provide speed control. Thus, the electric motor serves only to operate the hydrau-lic pump to provide hydraulic pressure. Advantage-ously, the hydraulic motor transfers this energy at constant torque regardless of the speed.
It is therefore a principal o~ject of the 11S32l~7 invention to provic~e a screw type press particularly suitable for use as a predrainer in removing free run juice ~rom grapes and the like.
In its broadest form the present invention provides a method of extracting clear juice from applies or the like comprising the steps of: a) introducing the fruit into the input of a first screw type press having a gradual continuous slope of the feed screw of the body; b) gently compressing the fruit in the screw type press to express juice and solids from the fruit; c) filtering the expressed juice and solids;
d) separating and collecting the clear juice from the expressed solids; and e) reintroducing the separated expressed solids into the input of the screw type press.
The above method may be carried out by way of the present invention which also provides a screw press for extract-ing liquids from wet or slippery materials, the press having an inlet end, an outlet end, and a base comprising: a cylindrical cage formed from-at least one pair of semi-cylindrical frames, the frames supporting filter screens - serving to pass extracted liquids from the materials there-through; a rotatable feed screw having a body with a sloping frusto-conical shape, and a screw thread disposed helically around the surface of the body, the feed screw disposed con-centrically .in the cylindrical cage and the screw thread having an outside diameter essentially equal to the inside diameter of the cage, the slope of the body selected to provide a gradual reduction in volume of the flights of the screw thread from the inlet end to the outlet end of the screw press to gently and progressively squeeze the materials against the filter ~ --10--.... . . ............... . .
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:115328'7 screells as tile materials are fed from lhe in]et end to the outlet end of the press by rotation of the Eeed screw; and adjustable drive means attached to the feed screw for rotating the feed screw at a rate wh,ch will produce centrifugal force on ~he materials to maximize the amount of extracted liquids from the materials.
These and other features and advantages of the invention may be determined from the detailed description below when read in conjunction with the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS

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Figure 1 is a cross-sectional view of the frame of the invention showing the feed screw;
Figure 2 is a cross-sectional view through the plane 2-2 of Figure 1 showing a preferred inlet section of the screw press of the invention and showing a minimum and maximum throat opening;
Figure 3 is a cross-sectional view of an inlet section of the invention utilizing and offset throat;
Figure 4 is a partial perspective view of the screw press showing the filter screen cage in its normal operating position via a cutaway view and another cage section in its open position for cleaning or changing of screens;
Figure 5 is a greatly simplified schematic diagram of the drive system of the screw press;
Figure 6 is a cross-sectional top view of the output end of an alternative embodiment of the invention;
Figure 7 is a simplified schematic diagram of the door pressure system of the alternative embodiment of the invention; and Figure 8 is a functional block diagram of a tandem juice extraction system utilizing the invention.

1~32~'7 DETAILED DESCRIPTION OF THE PREFERRED ElYBODIMENT

Referring first to Figure 1, a longitudinal cross-section of the preferred e~hodiment of the screw press is shown. The framework of the screw consists of four transverse bulkh.eads mounted on a bed or base 5:
front bulkhead lQ having a front bearing 27 mounted therethrough for shaft 26; rear bulkhead 14 having opening 11 therein; inlet bulkhead 17 utilized to support inlet housing 32 between front bulkhead 10 and inlet bulkhead 17; and intermediate bulkhead 12 provided between inlet bulkhead 17 and rear bulk-head 14 serving to divide a cage section shown generally at 40 into a front and rear section, Cage section 4a is formed ~y screen frames 41 (.see Figure 4) consisting of a series of circumferential ribs 49 supporting stainless steel screens 42 which form the inner walls of cage 40. Details of the cage con-struction are discussed below. Thus, the essentially cylindrical inlet housing 32 and cage section 40 form an elongated c~linder housing a feed and cam-2~ pressing screw shown generally at 20. Screw 2nconsists of a base or body portion 22 mounted to and concentric wi.th dri.ve shaft 26 as may be noted in Figure 2~ Drive shaft 26 is supported at its rear end by bearing 13 in pillow block 25. P.ody portion 22 has a small diameter at its front end and a large diameter at its rear end with its surface forming a frusto-conical shape having a continuous slope.
Spiral screw threads 24 are affixed to the surface of body portion 22 and have a constant diameter with sufficient clearance to turn within the walls of the cage 40 and inlet housing 32 without interference therewith~ ~s may be noted from Figure l! the volume or space between body portion 22, screen walls 42 - ' . -.

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and the faces of threads 24 diminishe.s from the front end of the press to th.e rear end. The degree of slope of body portion 22, the pitch and diameter of spiral threads 24 and the length of the press are all parameters which may be selected in accordance with the material to be pressed, the characteristics of the li.quids to be ex2ressed! the volumes of material to be handled, and the throughput required.
However, we have determined experimentally, for use with grapes, that the optimum ratio of the length of the feed screw to the diameter of the screw threads is ahout 4 to 1, ~hen a smaller ratio (shorter press) is used the slope of the screw body 22 is greater and the materials tend to pack and require excessive driving power, If the ratio is larger, the through-put is reduced without an increase in extracted liquids, As shaft 26 is rotated in the direction shown by the arrow D, material in the spaces between threads 24 ~ill tend to he moved longitudinally along the press and ejected at the rear end as shown by solid arrow C. Assuming that the flights between threads 24 are essentïally filled with material. it may he noted that the material will be gradually reduced in volume due to the taper of body portion 22. Thereore~ liquid contained in the material will be squeezed out and will pass through screens 42 between ribs 49. Such liquids will be callected by ~an 54 in the hase 5 and may be withdrawn via an outlet as shown by solid arrow ~. As may be seen in Figure 4~ stainless steel covers 56 are used over bulkheads 17~ 12 and 14 e~tending down and connecting to base 5 to prevent loss of liquids and to direct such liquids into pan 54. As the liquid is removed from the material~ the remainder is carried through ~ ' .

i32~7 the opening in rear bulkhead 14 into collector 53 for collection and further processing as indicated hy solid arrows C. Feed and compression screw 20 is driven via shaft 26 from a hydraulic drive unit 60 which includes a manually variable speed control indicated at 62, While the rotational speed of feed screw 20 is a design parameter and may be selected in accordance with the materials to be pressed and the desired throughput, we prefer to utilize a range of 6Q to 360 rpm which is eminently suitable for extracting juice from grapes.
When utilizing the press of the invention ~ith grapes or similar fruits which tend to be slippery when wet, problems are encountered in prior art screw presses in obtaining positive feeds~ The wet mass of such fruit tends to slip at the inlet portion of the press with a resulting reduction in throughput. To overcome this problem we have determined opti~.um parameters of inlet section 32 and inlet throat 30. In accordance with our inven-tlon~ the longitudinal length of the opening of inlet throat 30 i5 limited to not more than 1.5 times the pitch of spiral screw threads 24. Re-ferring to Figure 2~ it is also necessary that inlet housing 32 enclose the lower portion of threads 24 to at least half of their circumference as indicated at 30' representing an opening. For very wet materials, the opening may be narrowed to enclose 85 to 90% of the circumference as indicated by inlet 30'. For most applications~ however, we prefer about 75% of the circu~ference enclosed as shown at 3a. ~s the fruit, such as grape must, is fe,d into hopper 50 the must will enter through inlet throat 30 and flow into the totally enclosed region of inlet housing 32. As feed screw 20 rotates, an~

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tendency of the must to slip rather than to be carried by the threads 24 and body 22 is essentially prevented. As a portion of the must is carried into the completely enclosed circumference beyond the throat 30, a pumping or suction effect results operative on the following must and a continuous flow of mus,t alon~ the press results, assuming that the must in hopper sa is maintained at an appropriate level, In some instances where a large amount of 10 free run juice may be present in the must, the operator may run shaft 26 at a higher than normal speed to assist in start of the feed, however, as soon as positive feed begins~ the pumping and suction effect is self sustaining in accordance with 15 the invention. An alternative throat design that we have found very effective offsets the inlet in the direction of rotation of the feed screw. Figure 3 shows inlet 81 having a side 82 tangent with inlet housing 8Q. Thus~ material input as indicated by 20 the solid arrow is carried by gravity in the direc-tion of rotation of feed screw 2Q as shown by the rotational arrow, assisting in starting and main-taining positive feedings.
Having hereinabove explained the basic functional 25 elements of the screw press of our invention, a typical application will now be described. As previously mentioned~ in the wine industry free run juice or liquid generated during destemming opera-tions is required to be re~oved from the must before 30 final pressin~. The invention is admirably suited to perform this predrainina operation quickly and efficiently at high throughputs. For example, in a predrainer, in accordance with the invention, havina a screw diameter of .06 meters and a feed 35 screw length of 2.4 meters, 6800a kilograms to ~S,~2~ 7 13600 kilograms per hour of grapes can be predrained to approximately 8Q% of the total available juice as compared to prior art systems using settling tanks and the like in whlch predraining of must from deste~mers operating at 450Q0 tons per hour is predrained typically at a rate of 6800 to 7700 tons per hour.
The destemmed and precrushed grapes directly from the destemmer are fed into hopper S0 as shown by solid arrow A (~ig. 1). The must enters inlet housing 32 via throat 30 as previously described and the operator sets the desired feed and compres-sion screw speed by control 62~ This speed is pre-determined for particular varieties o~ grapes such that the ejected must at C has been pressed to remove about 80% of the a~ailable juice. The required speed of rotation is also affected by the must head in hopper sa ~ If insufficient head is present, difficulty is encountered in maintaining positive feed at high rotational speeds Therefore, it i5 desirable to have a flow rate from the de-stemmer sufficient to maintain an optimum head.
I~Jith a higher velocity of feed screw 20, the centrifugal force on the must beins squeezed is greater and more juice will be ejected for a given distance traversed through the press by the must.
An increase in rotational velocity will thus cause increased throughput without sacrificing the per-centage of liquid removed as long as the head in hopper 50 is not excessively reduced. If the velocity is too high such that the head is lost, only partial feeding occurs, and the flights are not completely filled. Thus, the must will travel rapidly through the press, will be only partially pressed, and will be ejected with excessive juice 2~'~

remaining. As may now be seen, the operator can re.adily maintain the predrainer at its optimum throughput by observing the head in hopper S0 and adjusting speed control 62 to compensate for varia-tions in the head.
Turni.ng now to Figure 4 certain aspects of ourinvention will be described which greatly simplify day to day maintenance of the press~ and provide flexibility of applications. Figure 4 is a partial perspective view of the press of the invention with certain parts omitted and others cut away for clarity.
The improvements disclosed are in reference to screen cage 4Q. The rear section of the press between intermediate. bulkhead 12 and rear bulkhead 14 is shown in operating condition with stainless steel cover 56 partially cut away to reveal the exterior of cage 4Q. The forward cage section 40 is shown with cover 56 removed and ca~e 40a, b opened for cleaning or screen replacement. As may be noted, cage 4~ comprises two semi-cylindrical sections thereof hinged at their lower edges. When in the clos.ed or operating condition as noted with respect to the rear section, the two halves are joined to screen frame mountin~ bar 15 through mounting strips 43 with.bolts 47 To open the screen cage, holts 47 are removed and the screen sections opened in a book-like fashion. In order to completely clear feed screw 20., the hinges are formed by hingee~ten-cion blocks 46 and pivot shaft 48. As may be noted hinge extension blocks 46 extend the pivot line a short distance below the. cage 40 so that the cage halves 40a and 40b move downward and outward when opened as shown by arrows E. This design advan-tageously completely exposes the inner wall surfaces of ~creens 42 to allow rinsing~ scrubbing, and otherwlse cleaning of the mesh. If the press is to 13L~.-3~ 7 be next used with a different material or a different variety of fruit requiring a different mesh size or type, screens 42 may be easily changed by removing the screws holding screen attachment strips 44 to frame 41. New screens with the required mesh design may then be readily re-installed. While a variety of screen materials may be used ~ependent upon the material to be pressed, we prefer material known as KLEENSLOT screen manufactured by WEDGE-WIRE
Corporation which is available in a wide variety of meshes and designs. We have found that the use of slotted screens greatly minimizes clogging as compared to perforated screens~ The novel cage design also permits ease of cleaning of feed screw 2Q since all areas of the feed screw are readily accessible when the cages 4Q are in their open position. Thus~ very little down time is required for the pres~ of the invention for cleaning of the screens and feed screw prior to another run.
As previously described, we prefer to use a hydraulic drive unit for powering the press.
Figure 5 shows ~enerally a greatly simplified block diagram of the drive system. Basically electric motor 66 is utilized to drive hydraulic pump 61 with reservoir 65 providin~ hydraulic fluid.
~Iydraulic drive unit 60 includes a hydraulic motor with motor speed control 63 controlled by knob 62.
The primary advantage of the hydraulic drive system is that constant torque is provided over the normal ran~e of speed variation of the hydraulic motor.

~5~ 7 ALTERNATIVE E~IBODIMENT

The preferred emhodiment of the invention des-cribed hereinabove contemplates the use of the press for predraining of grapes and the like and for extracting juice from other fruits and vegetables and the like. In such applications the squeezing of the material is due to the diminution of the volume between the screw feed and the screen cage walls. However, the invention may also ~e utilized for dewatering of materials with very low con-centrations of solids such as sludges, sewage, and the like. An alternative emhodiment of the inven-tion will enable materials having from one-half to 6% or so of solids to be efficiently dewatered.
Turning now to Figure 6, a cross-sectional view of the output end of an alternative embodiment of the invention is shown. It is to be understood that the forward portions of the screw press of this emhodiment are in all respects identical to the press shown in Figure 1 and subsequent figures. Rear bulkhead 14 is provided with a circular opening 21 which may be tapered as indicated in Figure 6. A
circular door 16 is slida~ly engaged with drive shaft 26, which can move along shaft 26 on bushing 19. Rear pillow block 25 which supports the outer end of shaft 26 also supports a pair of hydraulic actuators 72 having actuator rods 71. Actuator rods 71 are attached to the outer face of circular door 16 and the inlet lines of actuator 72 connected to a source of hydraulic pressure as indicated in the simplified schematic diagram of Figure 7. ~ydraulic pressure Ph is applied to actuator 72 from the hydraulic system so as to force door 16 which has its outer edges tapered into the matching taper 21 in the opening in bulkhead 14. This pressure, as shown by arrow Ph, serves to hold door 16 closed when no material is present in the screw press.
However, as material is input to the press of Figure 6 such that the screw flights become filled with material ! continued rotation of feed screw 20 will force the material in the last flight against the exposed outer rim portion of the inner face of door 16 producing pressure indicated by the arrow Pm.
Thus, in addition to pressing or squeezing of the material due to the reduction in volume of the screw flights, the faces of the last screw flights will exert pressure on the material against the inner face of door 16, creating pressure Pm. This addi-tional pressure, due to the force of the feed screw,will, of course, express additional moisture or liquid from the material through screens 42. The required hydraulic pressure Ph is a system adjust-ment parameter dependent on the type of material being pressed. Referring to Figure 7 ! it ~ay be noted that hydraulic actuators 72 are supplied hydraulic pressure from the hydraulic system of Figure 5 via pressure controller 92. Thus, the operator may, by adjusting pressure controller 92, set the pressure required for door 16 to open.
pressure relief or bypass valve 94 is disposed across the input and output lines of actuators 72 such that when the pressure Pm on the inside face of door 16 exceeds the external pressure Ph the door will be pushed rearward in the direction as indicated by arrow F and bypass 94 will relieve the back pressure in actuators 72. As door 16 opens the material will be extruded between the edges of door 16 and the opening 21 as indicated by flow arrow G in Fisure 7~ This flow reduces pressure ~S~ 8'7 Pm resulting in an opening such that Pm and Ph are balanced. As may be understood, the dryness of the pressed material exiting from the press is a function of the type of material, the speed of rctation of feed screw 20, the type of and areas of the mesh openings ln screen 42 f and the pressure Ph exerted by the hydraulic actuators. The optimum parameters may be determined experimentally to produce maximum throughput for each of a variety of materials, and the press adjusted prior to operation for a given material, SYSTEM APPLICATIOWS OF THE INVENTION

As discussed above, the predrainer press in accordance with the invention may have the length, diameter! slope and pitch of the spiral threads varied in accordance with the type of material to be dewatered. Similarly, the filter screens may use a variety of mesh designs and degrees of fine-ness according to the solids to be held back. In the dewatering of many materials, it is not practical to select these parameters such that a total de-watering can be performed in one machine. In such cases, two or more predrainers of the invention may be used in tandem, with variations in the variable parameters from machine to machine such that the maximum llquid extraction may be obtained while maximizing throughput or production of the system.
A system in accordance ~ith the invention utilizing for exemplary purposes three predrainers in tandem will be described here below. To illustrate such an application! the production of clear apple juice will be described.
It is generally agreed that the best method of ~S~.12~

producing clear apple juice is by the well-known rack and cloth method. In this ~ethod, the apples are spread in thin layers, for exa~.ple 50.8 centi-meters thick, with burlap fabric between layers.
During pressing, the burlap acts as a filter to minimize solids in the juice. A flat, even pressure is then applied downward on the layers of apples, generally by a hydraulic type press. While pro-ducing excellent juice, the rack and cloth method is slow and a low volume process. Modern screw presses have been used to dejuice apples and, due to the consistency of the apple stock, it has been necessary to add bulking agents such as paper, ~ood, or rice hulls. However~ most screw presses have too great a volume between the screw flights and do not produce enough pressure against the mass for a long enough period to sufficiently dejuice the apples.
Since the predralner press of the invention produces a uniform pressure against the screens from the gentle rise in diameter of the screw body and the fact that the apples are in a relatively thin layer, the action closely resembles the rack and cloth method, eliminating the necessity for additives in the press. T~e have discovered that the long, gradual 25 510pe of the feed screw of the invention also reduces excessive back pressures and prevents excessive solids in the juice. For e~ample, a feed screw having a lCl.6 centimeters depth of the thread at the feed end, a .9 centimeters depth at the exit end, and a slope length of about 2.4 meters is ideal for dejuicing apples.
A much greater yield of clear apple juice may be obtained with the predrainer press of the invention by utiliz.ing a system of predrainer presses operated in series in which the variab~e parameters 2~ ~

of each successive press are selected to specifically match or adapt to the consistency and remaining liquid content of its input. We have determined that a three-stage system is well suited to clear apple juice production.
Turning now to Fiqure 8, a three-sta~e system utilizing predrainer 100 as a first stage, pre-drainer 102 as a second stage and predrainer 104 as a third sta~e is illustrated. ~lhile we show here three stages, it may be understood that some types of fruit may require only two stages, others may effectlvely utilize additional stages. The para-meters of each stage, such as feed screw pitch, feed screw slope~ screen amplitude size and form, speed of rotation of the feed screw, and the optimum head in hoppers 101, lQ3 and lOS may be determined experimentally for the particular types of apples to be processed.
Also shown is a novel separator and recycling 2Q system which increases the yield of clear juice over known sy5tems.
In operation the apples are introduced in the first stage in hopper lQl as shown by input arrow A.
The apples are pressed through the operatïon of the predrainer 100 and, combined with the centrifugal force of the relatively high speeds of the feed screw of predrainer 100, produce expressed juice B from drain 115. The centrifugal force action minimizes the solids which may pass through the ~ilter screens by permitting smaller screen aper-tures; however, the output of the juice is maximi2ed hy allowing some such solids to pass, Advantageously, a separator 116 is utilized to filter off clear juice D which appears in Qutlet pipe 106. The solids remaining are indicated ~y flow arrow C and are carried by conveyor 117 back to the input hopper lOl and recycled through first stage predrainer 100.
The pulp E, which exits from the ~achine into output tray 110, is carried ~y conveyor 120 to hopper 103 of second stage predrainer 102 and is pressed for a se.cond time therein, The output juice F from drain line lQ7 is directed to separator 118 which separates the clear juice D in line 106 and directs the separated solids G via conveyor 119 bac.k to input hopper 103 to he recycled through predrainer 102.
The drier puLp H after its second pressing is collected in output pan 112 at H and carried by conveyor 122 to hopper 105 of third stage pre-drainer lQ4. The operation is repeated in this stage with juice J at drain outlet 108 being s.eparated in separator 109 with clear juice D
joining the clear juice from the previous stages to the juice collection system. Again, separated solids K are reintroduced into hopper 105 by con-2Q veyor 12Q. Finally~ the completely dry pulp L iscollected in tray 114 for disposal.
The high efficiency and rapid though gentle pressing of the apples in thin layers through the various stages of the system! and the recycling of the separated soli.ds from the juice provides an apple dejuicing system having clear apple juice of the quality associated with the rack and cloth method but with.production at a much higher rate.
Although the system of Figure 8 ha~ been described with reference to apples, it is to be understood that many types of fruit and vegetables lend them-selves to the described process with greatly reduced processing costs by the elimination of ~dditives, the increase in throughputs, and increased volume of liquids produced, ., 1~.5.~2~7 As may now be recognized, we have disclosed a novel screw press for extracting liquids from liquid-containing materials which has a positive feed system, a continuously sloping feed screw that pro-vides a gentle pressing operation, a variahle speeddrive permitting optimization of throughputs and easily cleanable and changeable filter screens.
Although a specific preferred embocliment has been shown, various modifications and changes will be o~vious to those of skill in the art. Therefore, the disclosed embodiments are to be considered for example only and we are not to he limited thereto.
The invention has also heen described in relation to specific materials but many other materials may be lS handled by the disclosed press.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A screw press for extracting liquids from wet or slippery materials, said press having an inlet end, an outlet end, and a base comprising:
a cylindrical cage formed from at least one pair of semi-cylindrical frames, said frames supporting filter screens serving to pass extracted liquids from said materials there-through;
a rotatable feed screw having a body with a sloping frusto-conical shape, and a screw thread disposed helically around the surface of said body, said feed screw disposed con-centrically in said cylindrical cage and said screw thread having an outside diameter essentially equal to the inside diameter of said cage, the slope of said body selected to provide a gradual reduction in volume of the flights of said screw thread from the inlet end to the outlet end of said screw press to gently and progressively squeeze said materials against said filter screens as said materials are fed from said inlet end to said outlet end of said press by rotation of said feed screw; and adjustable drive means attached to said feed screw for rotating said feed screw at a rate which will produce centrifugal force on said materials to maximize the amount of extracted liquids from said materials.

2. The press as defined in claim 1 in which said adjustable drive means is adjustable over a range of 50 to 360 rpm.

3. The press as defined in claim 2 in which said drive means is a hydraulic drive motor producing constant torque over its adjustable range of speeds.

4. The press as defined in claim 1 in which said cylindrical cage comprises:
at least one pair of semi-circular frames having a plurality of semi-circumferential ribs;
replaceable filter screens adapted to be changeably attached to said semi-circular frames, said filter screens forming said screen-like walls of said cylindrical cage; and a plurality of interleaved hinged blocks disposed longitudinally along a lower portion of said cage and hingedly attached to said base, with one set of said blocks connected to one of said semi-circular frames of said pair and another set of said hinged blocks connected to the other of said semi-circular frames of said pair, said hinged blocks forming offset hinges said hinges causing said semi-circular frames in a closed position to form said cylindrical cage during operation of said press, and permitting said semi-circular frames to move downward and outward completely clear of said feed screw during non-operation of said press in an open position for cleaning or replacement of said filter screens.

5. The press as defined in claim 1 which further comprises door means disposed at said outlet end of said press, said door being connected to means for applying a closing force thereto, said door adapted to open when pressure on the inner surface of said door from pressure of said material caused by rotation of said feed screw exceeds said external door closing force.

6. The press as defined in claim 5 in which said door closing force is produced by at least one hydraulic actuator cylinder having a fixed element connected to said base and a movable element attached to said door whereby hydraulic pressure operates against the outside surface of said door.

7. The press as defined in claim 6 in which said hydraulic pressure is adjustable.

8. The press as defined in claim 6 in which said door is slidably engaged with a shaft concentric with said feed screw whereby opening of said door by said internal pressure causes said door to move rearwardly along said shaft.

9. A predrainer screw press for extracting free run and other juice from destemmed grape must, said press having an inlet end and an outlet end, comprising:
a cylindrical cage formed from at least one pair of semi-cylindrical frames, said frames supporting filter screens serving to pass extracted juice from said must therethrough, said pair of semi-cylindrical frames attached to offset hinges along the lower edges thereof and removeably attached along the upper edges thereof, whereby said cylindrical cage may be opened for cleaning of said screens or replacement of said screens;
a rotatable feed screw having a body with a sloping frusto-conical shape, and a screw thread disposed helically around the surface of said body, said feed screw disposed con-centrically in said cylindrical cage and said screw thread having an outside diameter essentially equal to the inside diameter of said cage, the slope of said body selected to provide a gradual reduction in volume of the flights of said screw thread from the inlet end to the outlet end of said screw press to gently and progressively squeeze said must against said filter screens as said must is fed by a head of said must from said inlet end to said outlet end of said press by rotation of said feed screw; and adjustable drive means attached to said feed screw for rotating said feed screw at a rate which will produce centrifugal force on said must to maximize the amount of extracted juice from said must.

10. In a screw press for extracting liquids from wet or slippery materials, said press having an inlet end, an outlet end, a cylindrical cage having filter screen walls, and a base, the improvement comprising:
a rotatable feed screw having a body with a sloping frusto-conical shape, and a screw thread disposed helically around the surface of said body, the outside diameter of said screw thread having a ratio to the pitch of said frusto-conical shape not exceeding two-to-one, said feed screw dis-posed concentrically in said cylindrical cage and said screw thread having an outside diameter essentially equal to the inside diameter of said cage, the slope of said body selected to provide a gradual reduction in volume of the flights of said screw thread from the inlet end to the outlet end of said screw press to gently and progressively squeeze said materials against said filter screen walls as said materials are fed from said inlet end to said outlet end of said press by rotation of said feed screw; and adjustable drive means attached to said feed screw for rotating said feed screw at a rate which will produce sufficient centrifugal force on the liquids in said materials to increase the amount of extracted liquids from said materials over the amount extracted by such squeezing of said materials.

11. A predrainer screw press for extracting free run an other juice from destemmed grape must by pressing and by centrifugal force, said press having an inlet end, a hopper for feeding must into the inlet end, and an outlet end, comprising:
a cylindrical cage formed from at least one pair of semi-cylindrical frames, said frames supporting filter screens serving to pass extracted juice from said must therethrough, said pair of semi-cylindrical frames attached to offset hinges along the lower edges thereof and removeably attached along the upper edges thereof, whereby said cylindrical cage may be opened for cleaning of said screens or replacement of said screens;
a rotatable feed screw having a body with a sloping frusto-conical shape, and a screw thread disposed helically around the surface of said body, the outside diameter of said screw thread having a ratio to the pitch of said frusto-conical shape not exceeding two-to-one, said feed screw disposed con-centrically in said cylindrical cage and said screw thread having an outside diameter essentially equal to the inside diameter of said cage, the slope of said body selected to provide a gradual reduction in volume of the flights of said screw thread from the inlet end to the outlet end of said screw press to gently and progressively squeeze said must against said filter screens as said must is fed by a head of said must in said hopper from said inlet end to said outlet end of said press by rotation of said feed screw;
adjustable drive means attached to said feed screw for rotating said feed screw at a rate which will produce sufficient centrifugal force on the juice in said must to maximize the amount of extracted juice from said must for a selected throughput of said must.

12. A dewatering system for liquid-containing materials comprising:
1) At least one predrainer screw press having a) a cylindrical cage having an input for materials and having filter screen walls, b) a rotatable feed screw having a body with a sloping frusto-conical shape and a screw thread disposed helically around the surface of said body, the ratio between the diameter of said screw thread to the pitch of said body being 2 to 1 or less, c) adjustable drive means for rotating said feed screw at a rate sufficient to produce sufficient centrifugal force on the liquid in the material being dewatered to extract a portion of said liquid by such centrifugal force, d) a drain outlet associated with said cage for receiving liquid extracted from the material, and e) a pulp outlet for expression of material after extraction of liquid, 2) Separator means connected to said drain for receiving extracted liquid and separating remaining solid matter therein from the liquid; and 3) Conveyor means associated with said separator means for transporting the separated solid matter from said separator and feeding the same into said input.

13. The system as defined in claim 12 which further comprises:
a plurality of said predrainer screw presses having pulp conveyor means for transporting material from said pulp outlet of each of said presses to the input of each succeeding press except for the last one of said presses wherein the speed of each of said adjustable drive means is selected to maintain a continuous flow of materials through said system to thereby optimize the percentage of liquid extraction.

14. A method of extracting clear juice from apples or the like comprising the steps of:
a) introducing the fruit into the input of a first screw type press having a gradual continuous slope of the feed screw of the body;
b) gently compressing the fruit in the screw type press to express juice and solids from the fruit;
c) filtering the expressed juice and solids;
d) separating and collecting the clear juice from the expressed solids; and e) reintroducing the separated expressed solids into the input of the screw type press.

15. The method as defined in claim 14 com-prising the further steps of:
f) collecting the pressed fruit pulp from the output of said screw type press;
g) introducing the collected compressed pulp into a second screw type press; and h) repeating steps (a) through (f) in the second screw type press.

16. The method of claim 15 comprising the further steps of combining the separated and collected clear juices from the first and second screw type presses.