When plant personnel tried to run maximum size, hardened angle iron in a hydraulic cut-off machine, they either needed newly sharpened dies or multiple strokes to handle the hardened metal. By adjusting the relief valve’s spring, they determined that a pressure setting of 2650 psi would cut the hardened angle iron consistently with average tooling. This pressure requirement not only exceeded the maximum operating pressure capability of the pump, but also overloaded the electric motor by almost 100%. The original system was designed for 1500 psi.
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Intensifier circuit
At first they considered buying a new, higher-pressure pump and a higher power electric motor. However, because the hardened angle iron was cut only about 10% of the time and at random intervals, they decided to add an intensifier circuit instead. This simple circuit, assembled with readily-available components, proved to be economical and required few piping changes. The machine’s press cylinder had an 8-in. bore, and high pressure was needed for only about 114 in. of the stroke. They calculated needing 63 in.3 of oil at 2650 psi and ensured that the cut-off machine’s press cylinder could handle higher pressures.
For an intensifier, they used a nonshock service hydraulic cylinder with an oversize rod rated at 5000 psi. A cylinder with a 6-in. bore and a 4-in. rod provided an intensification ratio of 1.8:1. This translated to an output of 2700 psi from 1500-psi-input and a volume of 78 in.3 of oil from a 5-in. stroke. This cylinder intensification circuit can be used for systems requiring less than a 2:1 pressure boost and is inexpensive because it uses stock components.
Sequence of operations
To operate the cut-off machine’s press cylinder, the operator energizes solenoid 1 of directional control valve A. Oil flows to the primary port of sequence valve B and through the bypass check of sequence valve C to the cap end of pressure cylinder D and to the rod end of intensifier cylinder E.
Sequence valve B is set at 1400 psi. As long as the cutoff force needed can be generated by system pressure of less than 1400 psi, sequence valve B remains closed, and the cut-off operation is performed with the original circuit, with no time delay.
When more than 1400 psi is needed, sequence valve B opens, oil flows to the cap end of intensifier cylinder E, and intensified oil from its head end is forced into the cap end of press cylinder D, providing the force needed to perform the cut-off smoothly and quickly.
Retracting
To retract press cylinder D, solenoid 2 of valve A is energized, and oil flows to the rod end of press cylinder D, which retracts. Oil from the cap end of press cylinder D first flows to the cap end of intensifier cylinder E, which retracts without needed oil from the pump.
After cylinder E is fully retracted, pressure buildup in the cap end of press cylinder D opens remote pilot-operated sequence valve C. This allows oil from the cap end of press cylinder D to return to tank. Once cylinder D has retracted, the work cycle is complete.
This article is from the archives of Bud Trinkel, deceased, a frequent contributor to Hydraulics & Pneumatics.