Design Procedurei

Considerations and calculations required to dimension the hydraulic power plant for a hydraulic press are given in Table 1. A standardized procedure for determining the basic design features of the power plant for a hydraulic press is offered in the left column. The right column gives an example of how the standard procedure should be used. The press selected for the example is an open die press for forging ingots into billets or bars through gradual reduction of cross section on narrow, flat dies that, at each stroke, penetrate several inches into the hot metal (cogging). The ingot is advanced and rotated, and, when it is close to the desired size, the surface is made smooth by the application of shallow-penetration—to 2-in (0.32- to 1.27-cm)—fast strokes (planishing) of the press (Figure 5).

FIGURE 5 Vertical forging press with double-acting cylinder

TABLE 1 Example of power plant design for a hydraulic press

Standard Procedure

1. Water or oil can be used as the liquid in a hydraulic system of a vertical or horizontal press. The decision can be made in accordance with the general discussion in this section. The generation of full pressure during planishing is not required; because of rapid stroking, there would not be enough time to pressurize the liquid iully and expand the cylinder fully. The pull-back cylinders are kept continuously under pressure during planishing, thus reducing the time required for valving. The generation of about 10% of nominally rated pressure is considered sufficient for planishing.

2. Select operating pressure p in pounds per square inch (megapascals) of the hydraulic system.

3. Determine the required effective pressing area A in square inches (square centimeters) of the main plunger of the press: T X 2000

where T is the rated power in tons (newtons).

Requirements:

Press rating T = 6000 tons (53 MN) Pull-back rating TR = 600 tons (5.3 MN) Total stroke St = 48 in (122 cm) Maximum pressing stroke Sp = 12 in (30 cm) Fast advance speed va = 360 in/min = 6 in/s (5 cm/s) minimum Fast return speed ur = 360 in/min = 6 in/s (15 cm/s) minimum Pressing speed Vp required: At full 6000-ton (53-MN) rating: 120 in/min 2 in/s (5 cm/s) maximum At § = 4000-ton (36-MN) rating: 180 in/min = 3 in/s (8 cm/s) maximum At i = 2000-ton (18-MN) rating: 360 in/min = 6 in/s (15 cm/s) maximum Rated operating cycles: Cogging: 15 c/min, each cycle consisting of Fast advance—4 in (10 cm) Pressing—4 in (10 cm) Return—8 in (20 cm) Planishing: 80 c/min, each cycle consisting of Advance—\ in (0.64 cm) Pressing—\ in (0.64 cm) Return—\ in (1.3 cm)

1. Selected: oil hydraulic system

3. in USCS units

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