Hydraulic extrusion press

At one time the small fragments of amber produced during the fabrication and machining operations were used to produce varnishes. In 1880 they were first used in the production of Ambroid. This is made by pressing the fragments in a hydraulic press at temperatures somewhat above 160°C. The moulded product has a close resemblance to amber. A form of extrusion has also been used to produce amber rods for subsequent conversion into pipe and cigarette-holder mouthpieces. 

Mixing of the crystalline ingredients of oxidant, fuel elastomer binder (butadiene-2-methyl-5 vinyl-pyridine copolymer plasticized with the formal of diethylene glycol monobutyl ether) 26% by vol is done in a sigma blade mixer. The completed mix is blocked in a hydraulic press to form a chge suitable for extrusion. The extruded strand is cut into grain blanks which are cured at... 

Recently a new technique of extrusion of solventless powder dough was introduced, in which extrusion is effected by a worm screw extruder instead of a hydraulic press. 

Extrusion can fall into one of two categories direct extrusion and indirect extrusion (Figure 7.17). In direct extrusion a metal billet is placed into a container and driven though a die by a ram, usually attached to a hydraulic press. In indirect extrusion the billet is again placed in a container, but the container end is closed. A hollow ram, carrying a die of the desired shape, is forced into the billet, with the extrusion exiting through the ram Indirect extrusion may occur as a result of die movement or container movement. Because there is no movement between the container wall and billet surface, frictional forces are lower in this method, which reduces the force needed to extrade. There are, however, some limitations on the load that can be applied by the hollow ram. 

The modernized clas.sical extrusion method of double base i>owder by mearrs of a heated hydraulic press Werner and Pflcidcrer is sho w in Fig. 124. 

In some sectors, the extruder has now been replaced more or less by other forming technologies. This applies to the field of tableware in which, today, plates and cups are mostly isostatically pressed extruders are only for special applications and in manufactories. The situation is similar in the refractory industry where hydraulic pressing has almost completely ousted extrusion. 

Figure 18.7. Hydraulic pressing device installed in a universal testing machine for solid state extrusion...

It is on this account that in the course of time numerous experiments were carried out with other materials with a view to improving the properties of the sheathing and at the present time sheathing is even made of synthetic materials, steel and aluminum. However, in the manufacture of such sheathing, the use of hydraulic presses is limited to the extrusion of aluminum sheathing only. 

The design of oil-hydraulic tube extrusion presses is simpler and cheaper than that of water-hydraulic presses due to the fact that doubleacting pistons are employed in the former. They have found wide application in light metal works since the ram speeds required in such works are very low and in most cases less than 25 mm/sec., thus requiring small horsepowers only. A further plus is that pumps and motors may be arranged in close proximity of the main cylinder (see pp. 203 and 208). 

In tube and rod extrusion presses, stepless remote-controls are employed almost exclusively for the regulation of the pressing speed. In presses which are driven by a hydraulic accumulator with a constantly operative and rather uniform pressure potential, regulation is done by means of a throttle gate valve or a throttle valve. The speed of directly driven oil-hydraulic presses is controlled by the infinite regulation of the delivery of the pumps. 

Cocoa butter (also called cacao butter and theobroma oil) is produced commonly by three methods hydraulic pressing, extrusion or expeller pressing, and solvent extraction. Cocoa butter produced by the first two methods has a faint chocolate flavor and aroma that can be removed by steam distillation under vacuum it is brittle at temperatures below 25°C and melts at 34-35°C. ... 

An extrusion is comprised of a basket (cylinder) to contain the mix and a hydraulically actuated piston to press the mass through multiple extrusion dies. The baskets are jacketed for temperature control and contain internal screens to retain large agglomerates. Since the casting powder strands are unperforated, the dies are simple cylindrical barrels with conical lead-in sections. Extrusion rates are normally controlled by orifices in the hydraulic supply line however, constant-rate positive displacement devices are also used. As they extrude, the strands are collected separately in suitable containers. 

The hot, homogeneous mass is shaped in a hydraulically-operated extrusion press of the type used for smokeless powder (Fig. 121). It is usually cruciform. A guillotine cuts the extruded material to the required length. The outer surfaces of the limbs of the cross are covered by a substance which does not burn readily (e.g. strips of plasticized cellulose acetate or polystyrene 1.5-5 mm thick), and cemented in place, to prevent uneven burning at the surface. 

The dried powder blend is pressed to desired shapes in hydraulic or mechanical presses. In special cases, a presintering followed by shaping to final form may be required. Large components and tools may require cold isostatic pressing followed by green forming. Rods and wires are formed by the extrusion process. 

This product, which is thermoplastic, can now be geometrically shaped as desired, in accordance with the type of the powder, using finishing rollers, cutting and punching machines, or hydraulic extrusion presses. 

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