Batch pressing

Expression Dewaterings of Fibrous Materials. Fibrous materials are frequently dewatered in belt-filter, screw, disk, and roU presses and in batch pot and cage presses. Table 1 Hsts appHcations of screw, roU, and pot presses. Screw and high pressure belt presses are continuous and have replaced batch pot and cage presses in most appHcations. Traditionally, however, batch presses have been used for squee2ing cocoa butter from cocoa beans, which require pressures up to 41 MPa (6000 psi) (39). A description of many types of batch presses is included in Reference 40. 

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. 

Presses are of two basic types hydraulic batch presses and screw presses. Hydraulic presses are used for extracting fruit juices, and screw presses for dewatering materials such as paper pulp, rubbish and manure. The equipment used is described in the handbooks Perry et al. (1997). 

Rowley, G. 2004. Filling of liquids and semi-solids into hard two-piece capsulSSidrmaceutical Capsules, eds. F. Podczeck, and B. E. Jones, 2nd ed. 169-194. Bath The Batch Press. 

Hydraulic Pressing. Batch pressing was the earliest commercial method of oil extraction. Hydraulic equipment replaced the mechanical operations and the method became known as hydraulic pressing (49). In open presses, oilseed meals were wrapped in cloths and placed between plates, which were then gradually... 

The processing of soybeans has been described in more detail elsewhere than can be done here (132-134). Oil is recovered today by either mechanical means or through the use of organic solvents. In the preindustrial revolution period, soybeans were merely pressed with lever or animal-driven screw-operated batch presses. Around the turn of the Twentieth Century, when soybeans became a viable commercial crop in the United States, steam-powered hydraulic batch presses were used. Today, electric-powered continuous screw-presses, often referred to as expellers (but this is a trademarked name for screw presses manufactured by one supplier), or continuous countercurrent solvent extractors are used. 

Around 1890, oilseeds were pressed in manually loaded batch presses. Workers stacked layers of oilseed, separated by filter cloths and hollow pressing plates, into the press and applied pressure through a manually operated jack screw or a hydraulic cylinder. Oil flowed from the compressed material into the hollow plates and then out through the side walls of the press. After the oil stopped flowing, workers opened the press, placed the deoiled solids in a hopper, and recharged the press with fresh material. 

Batch presses can be divided into two main types open type, where the oily material is wrapped in press-cloths, and closed type that, omitting press-cloths, confine the material in a metal chamber that holds the oilseed under pressure. Open-type presses can be subdivided into plate presses and box presses. Closed-type presses can also be subdivided into two varieties cage presses that confine the material in a cylindrical cage with slotted walls and pot presses that confine the material in potlike chambers with perforated bottoms. 

Hydraulically operated open-type presses generally had a 40.6-cm (16-in) cylinder operating at 27,580-31,027 kPa (4000-4500 psi) hence, the pressure on the oilseed was 11,376-12,755 kPa (1650-1850 psi). It is important on batch presses to build up pressure gradually. A typical press cycle is 2 min to charge the press, 6 min to attain maximum pressure, 20 min to drain, and 2 min to remove the solids total time, 30 min. 

The rate of press closing, particularly under the high pressures that develop in the initial compression of the mat, has an important impact on the development of the density profile through the thickness of the panel. For a batch press the hydraulic pump capacity determines the closing rate. Increasing this rate reduces the quantity of material in which the resin has cured before the required face density has been achieved, and which must be removed in sanding. 

Continuous presses also have no dead time associated with loading the mat and unloading the panel after the press, and are thus able to manufacture thin panel more economically than batch presses. There are at least four manufacturers of continuous presses, and today this type of press would normally be selected for a particleboard or MDF plant. 

Various types of equipments are available. The principal batch presses are the box, platen, pot, curb, cage [5], and tube press. A filter press with a compression device is widely used in various fields. For continuous operation, the screw press, the roller mills, and the belt press are in common use. In connection with drying operations, the following devices are explained. 

The transformation of grapes into juice can be obtained by different methods. Juice extraction can be immediate or preceded by a skin maceration phase. It can be continuous or in batches, with or without crushing and destemming. Continuous and immediate juice extraction processes (very widespread until recently in high-volume wineries, despite its disastrous consequences on juice quality) are fortunately being abandoned they will therefore be covered only briefly. Immediate whole or crushed grape batch pressing and skin maceration will be described in more detail. 

Three principal types of batch presses are nsed vertical presses, moving head presses and pneumatic presses. These same presses are used for red winemaking (Section 12.6.4, Fignre 12.11). Press operating conditions have a greater inflnence on the quality of fresh grapes than fermented skins, which contain only approximately 15% of the total wine prodnced. 

Juice exdaction methods have a prime influence on the formation of suspended solids. Slow batch pressing while minimizing crumbling obtains the clearest juices (Section 13.3.3). 

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