Simple Solutions That Work! Issue 6

Contact: JOHN HALL jhall@cmhmfg.com all fluid must return. However, designers of electronic circuits have more flexibility in defining ground than hydraulic systems designers have in defining where the reservoir is located. Improper return to tank creates a potential for cavitation because no means has been provided to keep the lowest pressure above that which will result in cavitation. An electrical circuit cannot cavitate. Voltages can go as far negative as is necessary to satisfy the laws of electricity, and there is no such thing as absolute zero voltage. However, there is an absolute zero pressure: a perfect vacuum. Even though a perfect vacuum cannot be achieved, if the pressure in a hydraulic system falls a small amount below atmospheric pressure, dissolved gasses come out of solution (outgassing), which leads to cavitation damage. Unlike ground location, which might be anywhere in the circuit, only one reservoir location can be chosen, Such is not the case in placing the reservoir of a hydraulic circuit. The reason? Pressure anywhere in the system cannot be allowed to fall below atmospheric, otherwise cavitation may occur. Other hydraulic to electric analogies include: • Electric • Hydraulic • Amperage • GPM • Switch • Valve • Wire • Hose • Pump/Accumulator • Power Source (generator, alternator, battery, solar cell, transducer) Hydraulic safety and electrical safety procedures also have a strong analogy. Hydraulic systems are mandatory in gravity die casting because there is no more cost effective method to provide linear mold clamping pressure. Since molds are clamped together with stored hydraulic pressure, many types of injuries can occur. These include soft tissue injury or crushing, burns, fractures, dislocations, lacerations or shin punctures/fluid injection. Not only can injury or death occur but also environmental damage property/ equipment loss. The most common problem associated with permanent mold casting machines in the high temperature foundry environment is pinhole leaks in hoses. If atomized oil comes in contact with an open flame or extreme heat source an uncontrollable fire will result. In order to bring the fire under control the fuel source must be stopped by turning the pump off. Once the fuel source has been terminated the fire can be brought under control with an ABC rated fire extinguisher. Water is not recommended because of the explosion risk of water coming in contact with liquid aluminum. Pinhole leaks are difficult to locate. When an oily spot is noticed do not run your hand or finger along the hose. The oil can be injected directly under the skin. If hypodermic injection of oil does occur it may not be immediately recognized but hours later throbbing and severe pain will occur. If untreated, amputation may be required. In order to prevent hypodermic injection use a piece of wood or cardboard to locate leaks. Another hydraulic hazard is improper coupling. Do not cross a pressure hose with a tank circuit as a high-pressure rupture can occur. CMH includes a pressure relief valve on each machine to avoid pressure spikes. Keep them clean and periodically test them for correct operation. All permanent mold casting machines must be properly maintained for safe operation. Always refer to the CMH handbook for that serial number. Items to ensure include: • Power off pump and lock out tag out • Relieve all stored energy • Block up any over hung loads (ram) prior to reaching inside mold • Ensure fittings are tight and hoses are not damaged • Maintain fluid cleanliness at the rating for proportional valves • Change filters as indicated on gage • Do not exceed recommended operating pressure When properly maintained, a permanent mold casting machine and its hydraulic system is not dangerous. Tilt pour hoses are flexing hundreds of time per day and hoses have a shelf life. Maintenance is the key to safe operation and increased profitability. 13