Hydraulic Clamping Fundamentals

GENERAL INFORMATION In general, it is recommended that the load applied to the work piece be made over a rigid stop or a work support to avoid part deflection.

POSITIONING TIME / CYLINDERS Positioning time is the time to position from retracted to extend. This time is controlled by the power unit output, and is related to stroke and end function, but as a general rule should be limited to a minimum of .25 seconds. The actual time in which the cylinder can be positioned will vary by, available flow and end function requirements and may require customer testing of their specific application to establish limits. SIZING THE CYLINDER The cylinders nominal load rating is at 5,000 psi. The force being applied is a function of: A. The effective piston area. B. The hydraulic pressure applied to the clamp In order to find the size of cylinder needed, you must first determine the total load the cylinder must develop. This load is based on the following factors: The anticipated force from the operation being performed (as the work-piece retention forces are anticipated, some margin of safety should be incorporated) The direction of the force vectors as a result of the operation being preformed The weight of the part may also be an issue, depending on work piece orientation. If the load is to be applied in the extend mode (push) or the retract mode (pull). To calculate output force multiply the hydraulic pressure by the piston area from the Vektek catalog for the model number cylinder being used. Note that on a double acting cylinder the retract area (rod end) is different than the extend area (blank end). Therefore, the retracting force (pulling) will be less than

Typically, the cylinder should be installed so that when the rod engages a nominal work- piece, it is not at full stroke. This will allow for compensation of work piece dimensional variables and will assure that required force is being applied. The maximum functional system backpressure a single acting cylinder can readily overcome is 10 psi. If the backpressure during the return is greater than this, the cylinder will be slow to return, or possibly not return at all. In automated or robotic load and unload applications, double acting cylinders should be used when ever possible. The hydraulic pressure applied to the return side of the piston (as opposed to a mechanical spring) will help insure that the cylinder is returned, or “out of the way”. Double acting systems also permit the use of devices such as pressure switches in the return line to convey feedback information to a computer, or controller. Cylinders, like swing clamps are subject to a reduction of force due to friction from side (kick) loading of piston rod.

Hydraulic Clamping Fundamentals Rev - D

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