Accumulator bank breathes new life into core machine

Typical of core blowers, this was a pneumatic machine with an air-over-hydraulic drive system to close its clamp and an intensifier to create the required 1100-psi hydraulic clamping pressure. The machine had two 7-in. bore, 30-in. stroke, ram-type clamp cylinders. The design velocity specified that the clamp cylinders should extend 18 in. within 2 sec, which required a large amount of compressed air during this part of the cycle.

Operating problems that the manufacturer was having seemed related to the fact that compressed air demand at the Tennessee plant had grown to the point where it often exceeded the facility’s capacity. The resulting pressure fluctuations were limiting the cylinder speeds that the air/oil system could produce. Additionally, because of the dirty foundry environment, the intensifier was a high maintenance item, and the original circuit was a plumbing nightmare for the maintenance department.

Reviewing the total machine sequence of operation, the core-machine clamp seemed ideal for a small hydraulic system augmented by accumulators. The accumulators could store and provide the high flows — about 180 gpm — needed for rapid extension to close the clamp, and there was plenty of time to recharge them during the blow and gassing portions of the cycle.

We designed a simple system consisting of a 20-gpm piston-type pump to supply the main circuit — which included five 5-gal accumulators and a piggybacked gear pump to provide about 17 gpm of flow through a cooling and filtration loop. (Because the clamp is a single-acting ram, conventional return-line filtration could not be used.) Both pumps were manufactured by the Bosch Rexroth.

The power unit was protected from the generally dirty environment and mounted on a mezzanine away from the actual core machine. Bosch Rexroth also designed a remote manifold incorporating logic-cartridge valve technology that helped clean up the plumbing.

This new hydraulic system also had sufficient capacity to drive a 40-in.-stroke magazine cylinder that shuttles a blow or gas head on top of the press. Originally, this cylinder was pneumatic. By converting to a smaller-bore hydraulic cylinder, we saved more air and space and actually sliced off a little more cycle time by achieving higher velocity. To control this new, high-speed cylinder, we added a proportional valve with inherent braking.

The new arrangement met all its objectives immediately. Cycle times on the core blower were reduced by 20% to help meet production schedules, and the overall plant air pressure was more stable once the huge consumption was eliminated. The cast aluminum component manufacturer has purchased three such accumulator systems and is planning more in the future.

This summary was provided by Tim Gillig, CFPS, vice president of sales at Livingston & Haven, Charlotte, N. C. For more information, visit www.livhaven.com.