Hydraulic clamp

Figure 3.47 presents a schematic of a hydraulic clamping unit in the open and closed positions. The advantages of the hydraulic system is that a maximum clamping force is attained at any mold closing position and that the system can take different mold sizes without major system adjustments. 

Several techniques can be used for the clamping unit (1) hydraulic clamps, in which the hydraulic cylinder operates on the movable parts of the mold to open and close it (2) toggle or mechanical clamps, in which the hydraulic cylinder operates through a toggle linkage to open and close the mold and (3) various types of hydraulic mechanical clamps that combine features of (1) and (2). 

An overall view of the basic tensile-test apparatus is shown in Fig. 1. To eliminate any interaction between the 12-T magnet and the surrounding room-temperature structure, the entire load frame of the tester is fabricated from nonmagnetic stainless steel. The crosshead, shown in the fully raised position in Fig. 1, is supported by two 5.3-m-long, 100-mm-diameter columns. It is raised and lowered by two hydraulic pistons and can be hydraulically clamped to the columns at any position. The column height was made sufficient to allow the cryogenic structure to be raised above the cryostat, the cryostat to be removed, and the structure then lowered back down for the sample to be changed. 

To perform the mold movements, the clamping unit needs a drive mechanism. Two fundamentally different systems are used as drives. There is thus a basic distinction between mechanical clamping xmits and hydraulic clamping units. 

For this and other reasons, alternatives to the toggle lever clamping unit are in use. One example of such an alternative is the hydraulic clamping unit. 

Figure 5-6 Hydraulic clamping unit with travel- and clamping cylinder...

It has been shown with the example of the hydraulic clamping unit, how hydraulic modules are employed to execute the mold movements. 

For example, a company in Ohio implemented quick die change on one 400-ton press. After installing rollers and clamping, the company continued to use a fork truck for die exchange. The fork truck tore out some of the hoses for hydraulic clamps several weeks after they were installed. Die rollers were also damaged to the point that they could no longer function correctly. 

While a hydraulic clamp machine requires a very large cylinder in the center of the platen to apply full clamp tonnage with hydraulic pressure, hydraulically actuated toggle clamps (Fig. 5.62i ) use a small cylinder and a mechanical toggle. To close the clamp, the cylinder moves forward, extending the toggle links (Fig. 5.6261" ). Clamp... 

In hydromechanical clamping units, toggles are combined with hydraulic cylinders. The toggle is used to open and close the clamp, but the hydraulic piston builds the clamp pressure. Since this requires small hydraulic cylinders, clamp movement is faster and the clamping units are smaller than comparable hydraulic units. However, hydraulic clamping provides better control of the clamp force. 

A 2CK) ton HPM injection molder base with toggle clamp. A 220 ton hydraulic clamp unit was also considered. The toggle clamp unit is expected to be less costly by approximately... 

Fig. 4. Toggle and hydraulic clamps. Illustrations by Rick J. Bujanowski John W. Bozzelli.

Paper-roll clamp. Specifically designed to carefully grasp and transport rolled materials in the vertical position. It is frequently combined with a rotator which allows the roll to be carried horizontally in the case of loosely rolled or easily damaged materials. Push-pull. Uses a polished platen instead of forks to carry the load. Its purpose is to position loads in dense environments without the use of a pallet. In place of a pallet, a thin shp sheet is used under the load.This sheet is grasped by hydraulic clamps and pulled into the tmck platen for loading and pushed off again into its next position. 

The force requirements ensure that the clamp unit must be engineered very robustly, but this conflicts with the need to open and close the mold rapidly to minimize production time. A variety of clamp mechanisms has evolved in the search for a suitable compromise. The two most common types are the direct hydraulic clamp (Fig. 7.2) and the toggle clamp (Fig. 7.3). Other variants include hybrid toggle/hydraulic types, lock-and-block systems, and electromechanical systems. 

Figure 7.2 Typical direct hydraulic clamp uniU A Actuating plunger, B removable spacer, C mold, D injection nozzle, E fixed platen, F movable platen, G tiebar, H cylinder base plate, I clamping cylinder.

Figure 7.1 Wide-width tensile test on a nonwoven geotextile using hydraulic clamps. Courtesy LGA.

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