A company that fabricates oil-field pipes starts with flat steel, rolls it into a round tubular shape, and simultaneously welds the inside and outside surfaces of the joined ends. Tooling removes excess weld material, creating a round pipe that actually looks like seamless pipe. A cutoff station then cuts the pipe coming off the production line to 21-ft lengths. When 12 cut pieces of pipe are collected in a saddle, a hydraulic cylinder quickly extends and dumps all 12 pieces onto a conveyor that takes them to a banding station.
The schematic shows the dump cylinder, control valves, and hydraulic power unit, which is about 50-ft away from the cylinder. The cycle time for the cylinder is quick, and once the gas pressure in the accumulator reaches 2,000 psi, the directional valve shifts to dump the batch of pipes. Again referring to the schematic, flow-control valves are mounted close to the cylinder, and the directional valve is mounted on the power unit.
The dump cylinder started failing after 1 to 1½ months of running two shifts, five days a week. The repair shop reported contamination and dirty, overheated oil as the problem. However, temperatures at the power unit do not exceed 135°F and the oil samples show an acceptable ISO cleanliness code for the components.
Any idea what was causing the problem and how to fix it?
ROBERT J. SHEAF JR., is founder and president of CFC Industrial Training, a Div. of CFC Solar, which provides technical training, consulting, and field services to any industry using fluid-power technology. Visit www.cfc-solar.com for more information.
Solution to Cylinder failures on a pipe-fabrication machine
The excessive heat and contamination problem — which only appears in the dump cylinder — is caused by the oil going across the meter oil flow controls that generate heat. The long lines going back to the power unit don’t allow this heated oil to return to the reservoir and is then pushed back into the cylinder only to exit over the flow control again. If the flow controls would be re-located at the power unit, the heated oil could return to the reservoir. This would greatly help the oil over-heating problem. However, the same oil would be recycling in and out of the cylinder.
This condition could be fixed by adding a small, 1/8-gpm fixed pressure control flow control with an outlet check in series mounted close to the cylinders plumbed from the cap to the rod outlets. This would allow a small amount of oil to migrate every cycle from one side to the other always adding fresh oil to one port and returning dirty oil back to tank.