Continuous press

Screw presses (Fig. 2) do not produce a clear liquid product. Frequendy, the product is further filtered in a filter press to give a clear Hquid product. Press aids are added to feed materials containing fine particles or particles that can deform and plug the slots in the edge of a screw press. Typical press aids include sawdust, rice hulls, perlite, and diatomaceous earth (see Diatomite). A vertical screw press is a continuous press that has been used for dewatering sewage sludge (2). 

In the past, expression presses were used in many processes for extracting oil and juice, generally from seeds and fruits such as olives. Batch presses were typically used in these apphcations, and hand unloading of the pressed cake was often required. Batch presses that require hand unloading or extensive cleaning between pressings are rarely used now descriptions of various types are presented in earlier editions of this handbook. This section, therefore, describes mainly continuous presses. 

The press temperature influences the possible press time and therefore the capacity of the production line. The minimal press time has to guarantee that the bond strength of the still hot board can withstand the internal steam pressure as well as the elastic spring back of the board when the press opens or when the board leaves the continuous press. 

In cold pressing pulp for white wines, present practices vary considerably within the industry. Some processors using continuous presses have found it an advantage to treat pulp with pectolytic enzymes prior to pressing. However, with the Willmes press, cold pulp to which cellulose fibers have been added press with no difficulty, and juice yields have been considered satisfactory. A general practice has been to add pectolytic enzymes to white must before yeast inoculation as an aid to rapid clarification of the new wine. 

Chaiken et al.24,37,38 proposed using Raman spectroscopy to measure glucose in vivo with a technique called tissue modulation, that is, continuously press/unpress the measurement site with a mechanical apparatus. The basic principle is that during the press phase, blood is expelled from the measuring site and thus the spectrum is considered as nearly devoid of blood. During the unpress phase, the spectrum is considered to be a sum of both blood and other tissue constituents. 

In the North Coast, four basic types of presses are used horizontal basket presses, vertical basket presses, bladder presses, and continuous presses. They... 

Figure 5. A battery of modern dejuicers and continuous presses. Note the multiple outlets for separating different qualities of press juice.

Also, today in the Interior Valley, the must may be pumped directly to juice predrainers (Figure 2), which rapidly separate the juice, primarily from white grapes. The drained pomace is conveyed to continuous presses (Figure 6) for further pressing of the remainder of the juice. In this type of separation, many winemakers claim that more suspended solids (pulp and skin material) pass through draining screens, usually with 3/32-inch-diameter perforations with the various juice fraction. In some screen systems, it is possible to get up to 8-10 percent suspended solids by volume. 

Depending upon the requirements of the product, direct-faced boards may be produced at high or low pressures on static or continuous presses. One of the best-known types is melamine-faced chipboard ( MFC ), which is covered by... 

A screw-press is a mechanical device that accepts a continuous stream of fatbearing material, compresses it under very high pressure to squeeze out the fat, and then discharges a continuous stream of squeezed solids. Considerable effort was made in the late 1800s to develop a continuous press that would work. The batch-operated hydraulic presses of that era were already considered too labor intensive. 

Commonly, LVL is produced in 0.6 to 1.2 m (2-4 ft) widths in a thickness of 38 mm (1.5 in.). New plants with continuous presses form a potentially endless sheet that is cut to the desired length. Various widths of product can be manufactured or recut in the retail facility. 

Strands are coated with a waterproof structural adhesive, e.g. phenol-resorcinol formaldehyde, and laid-up using special equipment to ensure proper orientation and distribution. The microwave continuous press both densifies the material and cures the adhesive. LVL is commonly produced in 0.28 by 0.48 m (11 by 19 in.) section -much thicker than that of LVL. Final product can be sawn into smaller dimension, if desired, while the length is limited only by freight and handling restrictions. 

Technically, there is no length limit for parallel strand lumber since a continuous pressing operation is used. However, considering handling restrictions, PSL billets are usually cut to 20 m lengths, by up to 280 x 480 mm in section. The billets are recut to desired dimensions for use as beams, headers, columns, and studs. 

Figure 11.13. A 300 x 375 mm continuous press, for the manufacture of parallel strand lumber (Churchland, 1988). Four drive drums draw the strands into the press. The throat acts as a prepress reducing the thickness of the loose mat to 35-40% of its imconsolidated thickness. Both platens and side dams apply compressive forces to the mat that is ciued by microwave energy admitted through ceramic windows in the side dams. These are transparent to microwave energy and yet sustain the full compressive forces on the edge of the product.

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