Screw Press Description | Vincent Corp

The Vincent horizontal continuous press is a dewatering machine with a conveying screw rotating inside a perforated cylinder. Incoming material is forced the length of the machine, liquid “press liquor”) is expelled through the cylinder wall. The remaining solids (“press cake”) are discharged at the far end.

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The press is available in sizes with screws ranging from 4″ to 30″ in diameter. The screw has a graduated pitch, interrupted flight design. This screw interacts with stationary resistor teeth. These teeth assure that the material to be pressed (1) does not turn (co-rotate) with the screw and (2) is intermixed during passage through the press. Because of this, more material is exposed to the screening surface.

The graduated pitch screw gradually compresses the material as it passes through the main screen cylinder of the press. The press liquor is forced through the perforations in the screen.

The press cake encounters resistance at the discharge of the cylinder in the form of a cone mounted on a ram. As the material reaches the discharge point, the cone exerts final pressing action to achieve maximum dewatering. The cone system allows easy adjustment of the resistance to cake discharge.

This cone assembly may incorporate a unique discharge pinch point, described in a patent as a frustum, the converging angle formed by the cone face and main screen section. The change in direction as the press cake enters this area assures fresh material contact with screen surface. This converging pinch area has proven to give excellent final pressing action.

Air cylinders, springs, or counterweights actuate the cone assembly, depending on the model. It is available in both rotating and non-rotating versions. The standard, non-rotating cone is used for pulpy, fibrous and less slippery materials, while the revolving cone model is required to permit pressing of slippery, low fiber content materials that tend to “channel” in a standard screw press.

The design features of the Vincent Series VP Presses give greater screen areas than found in conventional presses. The hopper section has a screen area covering 180º of the periphery of the screw to allow drainage of free water. The main screen section has a full 360° screen area, approximately four screw diameters in length. The cone assembly also has a screen area with a separate drain pan.

The standard drive arrangement for the Vincent Press is a gear reducer directly coupled to the screw shaft. Variable speed drive arrangements, although rarely used, are available to allow maximizing capacity as feed characteristics change. This type of drive is recommended either when different products are to be processed or when major seasonal variations occur.

The press is fed from the top at the drive end through a rectangular flanged hopper. The press cake discharges at the far end, between the bedframe beams below the cone section. Press liquor drainage is through standard or sanitary pipe connections; these are attached to the pan under the screen section.

CAPACITY:

The rated capacity of the Vincent Continuous Screw Press is proportional to the bulk density of the material to be pressed, as well as the slippage characteristic of the material. The ability of the material to give up its moisture, its particle size, and its fibrous content are factors to be considered. The high capacity of this machine, its low head room requirement, as well as low horsepower factor, are some of its many advantages.

The capacity and the water removed during pressing can be varied by adjusting the cone pressure. Adjusting this pressure assures maximum dewatering over a wide range of feed rates, permitting good turndown from rated capacity.

SCREENS:

The screen frames can be readily opened or removed for ease of cleaning and screen maintenance. The screens of the Vincent Press are available in a variety of arrangements and screen perforation sizes, commonly in the 0.023″ to 0.095″ diameter range. With wedge wire screens, 0.012″ to 0.030″ slots are commonly used. Selection is determined by the material being pressed and the desired pressing results.

MAINTENANCE:

The Vincent press has been recognized for the exceptionally low maintenance costs associated with it. Easy access to all component parts keeps maintenance time to a minimum. Use of off-the-shelf components (gearbox, bearings, air cylinder, etc.) reduces maintenance costs and assures trouble-free operation. The all-fabricated design facilitates in-plant repairs should they become necessary.

MATERIALS OF CONSTRUCTION:

All press models are of fabricated steel design. They are available in all stainless construction, partial stainless, and carbon steel, as follows:

• H style presses are carbon steel construction, except for the perforated screening, covers, and drain pans, which are made of Type 304 stainless steel.
• P style construction has (in addition to stainless steel covers, drain pans and perforated screening) a Type 304 stainless steel screw-spindle assembly.
• K style construction has all contact parts, i.e. screw-spindle assembly, resistor-stop bars, screen frames, hopper and cone sections, of Type 304 stainless steel.
• Special construction of Type 316 stainless steel is available. The bedframe is of carbon steel.
• SERIES: There are four Series of Vincent presses available: the TSP, VP, CP, and KP.

The newest Vincent Press is the TSP Series. These have two overlapping screws. This design offers positive feeding of even very slippery materials. The best dewatering performance over the widest operating range is available in this press. The capacity and performance of the press is sensitive to changes in screw rpm, so the use of a VFD is recommended.

The traditional Vincent Press is the VP. These are differentiated by having screens in the inlet hoppers; a flared section in the main screen just ahead of the discharge cone; a single air cylinder cone actuator; and (usually) a belt drive between the motor and gearbox.

The Series CP (Compact Press) features a hollow shaft gearbox and a simplified cone drive, both of which shorten the frame of the machine. There is no screen in the inlet hopper, and profile bars screens are almost always used. These presses are available only in stainless steel construction.

The Series KP presses are designed for a “soft” squeeze. They dewater high throughputs of easily dewatered materials. Instead of a discharge cone, they use a lever actuated stopper plate. Perforated screens are used in almost all cases. Only stainless steel construction is available.

TEST FACILITIES

To conduct tests Vincent Corporation maintains laboratory and pilot equipment. Feed rates, moisture contents, percent solids, effluent characteristics, and horsepower requirements can be determined from test data.

A large fleet of rental machines are available for in-plant trials.

Screw press

A dewatering screw press is a screw press that separates liquids from solids. A screw press can be used in place of a belt press, centrifuge, or filter paper. It is a simple, slow moving device that accomplishes dewatering by continuous gravitational drainage. Screw presses are often used for materials that are difficult to press, for example those that tend to pack together. The screw press squeezes the material against a screen or filter and the liquid is collected through the screen for collection and use.

History

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An example of a dewatering press is a wine press. Dating back to Roman times, these machines worked similarly to the modern screw press but possessed some disadvantages which have been corrected and improved within modern presses. The ancient wine press only allowed for grapes to be juiced in batches and often a thick cake would form against the screen, making it difficult for the juice to flow through the screen and be collected for wine. Most modern screw presses allow for a continuous flow of material by surrounding the screw with a screen, which also helps to avoid the build up of a layer of solid material on the screen. One modern approach even removes the screen in favor of a system of fixed and moving rings, which often eliminates solids buildup entirely.[1]

The most commonly known screw press of this design is said to have been invented by famous Greek mathematician Archimedes and is known as the screw conveyor. The screw conveyor consists of a shaft, which is surrounded by a spiral steel plate, similar in design and appearance to a corkscrew. This design is used in a multitude of screw presses. There are some machines of this and also of similar design that are not screw presses at all - they do not separate solids from liquids but are instead used to fuse them together. An example of this is a mold-filling machine. Plastic pellets are inserted at one end and heat is applied, melting the pellets and discharging them into a mold. Another example is known as a cooker-extruder and is used in the production of snack foods such as pretzels and more.

Design

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Most screw presses can have dilute materials pumped directly into the screw press, although pre-thickening sometimes improves the performance of the press. This is typically done with a static or sidehill screen, a rotating drum screen, belt press, or a gravity table.

Patented in 1900, Valerius Anderson's interrupted flight design is most commonly used as opposed to the continuous flight design. Anderson, upon studying the continuous flight design, noticed that it led to co-rotation and a less efficient job being done dewatering, especially with softer materials. He solved this by putting interruptions on the flights of the screw. The interruptions allowed for the materials to stop moving forward between interruptions along the shaft and also allows for an adequate buildup of the material before it is pushed through the screw press to container that catches the material. This allowed for a better job at the dewatering and a consistent cake material being released.

The interrupted flight design screw presses uses were broadened from just soft or mushy materials to include most materials screw presses were used for because unlike the continuous design screw presses the interrupted flight design did not require constant feed or consistency of material. If either were diminished in the continuous design so would production of the dewatered product, in order to avoid this while maintaining the continuous flight design a larger and heavier press with variable speed settings was a necessity; the press also entailed the need of an operator.

The interrupted flight design eliminated the need for consistency as the compression of the screw did not change as the material did not progress through the screw until a sufficient amount of the material had formed, as described above. This also eliminates the need for changing speed and an operator. The design allows for self-correction and efficiency that is unavailable with the continuous design. It allowed for a more economically effective screw press that has been used for more than just slimy or slippery materials.

After a period of time and its initial patent, resistor teeth were added to the presses where there was no flighting in order to increase the agitation of the materials adding to the limitation of the tendencies of co-rotation within the press

Options

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The buildup of press cake moisture is controlled by a discharge door or cone. Screw presses possess different options that include perforated/slotted screens, a rotating cone, hard surfacing on the screw, and supplemental screen surface in the inlet hopper on the face of the cone. The standard construction for screw presses is of stainless steel with a carbon steel frame on the larger presses.

Capacity

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The specific details of the design of a screw press depend on the material however. The configurations, screw speeds, screens for maximum outlet consistency, including an excellent capture rate vary per material. Most screw presses are designed to feed material that has a 40-60% water make up. The length and diameter ratio of the screw press also depends on the material. The range of the capacity of a screw press

Drive

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Larger presses use a foot-mounted gearbox while smaller presses use a hollow-shaft gearbox. Currently, nearly all presses are driven by electric motors due to their reliable and low cost frequency drives. The electric motors replaced the previously popular hydraulic motor drives. A vertical design was popular in the 1800s through the 1950s but they are no longer made. Most screw presses are currently built with the screws in a horizontal configuration. One newer version uses an angled screw design to reduce floor footprint and press cake moisture.[2]

Compressive Mechanisms

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Compression is created within the screw press by increasing the inner shaft diameter of the screw. For example, if a 16" screw press has a 6" shaft at the start, the flights on the screw will be 5" tall. If this 6" shaft diameter is then increased to 12" at the discharge, the fights will be only 2" tall at this point. Thus compression is applied as the material is being pressed from a 5" opening through a 2" space.

This compression can also be achieved tightening the separation of the flights of the screw. If at the inlet, the pitch is 16", the material thus will move 16" with each revolution. If it is then decreased to 8" at the point of discharge, the material will move 8" per revolution. This results in there being more volume forced into the press than there is being forced out of the press at a time. This creates the desired compression and pushes the liquid through the screen.

Another way to achieve compression is to place a cone at the point of discharge. This can also be called a choke, stopper, or door. In many designs it is bolted into a fixed position, making a fixed, smaller opening which the material must pass through. More commonly found however, the screw press has the cone pushed into the point of discharge via a hydraulic or air cylinder.

Specialized types

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Some other types of presses are vapor-tight presses, and twin-screw presses. Vapor-tight presses are used during the production of soybean protein concentrate (SPC), citrus and apple pectin, bioresin, and Xanthan gum. Twin-screw presses contain two overlapping compression screws. This is more complicated on a mechanical level because the screws must remain synchronized in order for them to work properly. These are often used for slippery materials and feature an internal shredding action.

Classification

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There are two major kinds of screw presses of this design. One type, known as Expellers ®, removes water from fibrous material, while the other removes free liquid from a material.

Expellers

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Oil expellers are used to squeeze the fat out of soybeans, peanuts, sunflower seeds, canola (rape seeds), and other oil seeds. The expeller works by exerting extremely high pressures which convert the fat in seeds into a liquid oil. Once the oil is liquefied the oil flows through the screen and is collected.

Removal of free liquid

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Screw presses that are used to free liquid from material are commonly used in the pulp and paper industries, municipal biosolids, septage and grease trap sludge, food production, food waste, manure, and also within the chemical industry.

Applications

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Pulp and paper industries

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Pulp and paper industries remove water within cellulose fiber.

Sewage disposal

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Biosolids are dewatered and heated through a specific process which includes raising the pH to a level of 12. Septage and grease trap sludge is dewatered with a simple screw press of the above stated design. Nutrient management programs dewater hog and cow manure for sale and commercial use.

Food processing

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Alcohol solutions are squeezed from foods with screw presses (such as soybeans, protein, pectin, and xanthan gum.) Food processing factories use screw presses to separate water from waste streams and convert the solid into animal feeds. For example, sugar beet pulp, orange peel, and spent grain.

Fish and orange peel dewatering often provide maximum yield when dewatered within a press of the interrupted flight design and with the addition of steam begin injected into the material. Commonly steam injection holes are drilled into the resistor teeth of the press close to the screw's shaft.

PET bottles "polyethylene terephthalate" is the preferred packaging for soft drinks, fizzy drinks, juice and water. This results in large waste problems. For breweries, large volumes of discharged products need to be destroyed regularly in order to eliminate the risks of the bottles being resold again. For waste collectors handling and transport is difficult and expensive, as there is a large discrepancy between weight and volume[3]

Manufacturers of ice-cream have a need to destroy returned goods with expired date and faulty manufacture to prevent the products being sold by mistake.[4]

Dairies destroy returned goods such as yogurt and other dairy products with expired date and faulty manufacture.[5]

Chemical industry

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Within the chemical industry screw presses are used for "ABS, sodium alginate and carrageenan, synthetic rubber, synthetic resin, hydrated polymer, naphthalene, elastomeric adhesive, color film emulsion, CmC, pharmaceuticals" and more.[6]

Cosmetics: To many manufacturers and brands the challenge is often that they have large amounts of discarded products, that needs 100% destruction to ensure no reselling on the black market.[7]

References

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