Pullback cylinder

The press is suitably of the down-stroking two-column type, as shown in Fig. 7. The two columns are connected to the cylinder- and bottom platens by split nuts and check nuts. The pullback cylinder is suspended in the main cylinder so as to reduce the overall height. The pullback plunger acts on a crosshead which is connected to the plunger crosshead by two tie-rods. The plunger head carries the extrusion ram, on the bottom of which is fixed the die. The ram is bored out and provided at its bottom end with a curved outlet, through w hich it is possible to push out the die w ith the help of a rod. 

Also in this design the pullback cylinders a and h for the main cross-head and the piercer crosshead are suspended in the main- and piercer cylinders to keep the length of the press to a minimum. The pullback... 

The stripper cylinders incorporated in the piercer plungers k permit of using a common pullback device for main crosshead and piercer crosshead. The two pullback cylinders r are arranged on the front and back sides of the frame and the pullback plungers s are of the differential type. They may just as well be simple plunger pistons provided with a reversing linkage. 

A two-valve control also answers the purpose when, for example, the pullback cylinders of an auxiliary device of the press are connected directly to the pressure conduit. In such case the main piston, while advancing, has to overcome the constantly acting pullback power and must... 

Fig. 10 shows a solder wire press of the horizontal type. The main cylinder is connected to the counterplaten by two columns. The plunger, which is sealed by a stuffing box and packing collars, presses on a crosshead guided in its travel on the columns, and is retracted by a pullback... 

Fig. 61. Cylinder end of extrusion press with main- ami pullback plungers being sealed by stuffing boxes...

During the idle stroke the oil flows from the filling tank through the filler valve into the cylinder and forces the main piston of the press forward at a pressure of about 5 atmospheres. The oil which is forced out of the pullback chamber of the cylinder, is fed back into the filling tank by the pump. The idle speed may therefore be adjusted at random by simply changing the pump stroke. 

The die used for the extrusion of sections is lifted by means of a tube which passes through the container support and is set on a sleeve which is connected to the ejector crosshead. The crosshead is moved up by the two bottom plungers being so designed to form at the same time the cylinders for the two stationary top pullback plungers which are bolted to the frame by two tie-rods each. In order to facilitate dismounting of the sleeves in the dowmward direction, the pistons can perform an excess stroke after the bolts, which hold the sleeve in the crosshead, have first been released. 

In most cases the pullback power chosen for the extrusion ram amounts to 10% of the extrusion power the counterpressure in the main cylinder should not exceed about 10 to 12 atmospheres if the plunger area was designed for a hydraulic pressure of 300 to 400 atmospheres. Under these circumstances idle speeds of about 200 to 300 mm/sec are attained in either direction. With a hydraulic pressure of 200 to 300 atmospheres the permissible counterpressure is 6 to 8 atmospheres. 

When extruding machined billets on the without shell method with the ram moving close-fitting in the container bore, it is recommended to increase the pullback power by 25%. If the press is equipped with advance- or piercer cylinders, the plungers of which move the main cross-head, as shown in Fig. 88, the maximum counterpressure occurring in the main cylinder is 2 to 3 atmospheres thus the pullback power required is decreased correspondingly. 

In many rod and tube extrusion presses the main cylinder is combined with the pullback and piercer cylinders in one piece of steel casting to form a cylinder-platen which is provided with integrally cast lugs for the columns (see Fig. 88 and 89). The number of the auxiliary cylinders and their arrangement around the main cylinder have lead to a great variety in cylinder-platen designs. 

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