A wood chip maker thought they needed a new oil cooler for a chronic problem it was having with a hydraulic power unit. After evaluating the application, Kaman recommended changing the process, not just the part. The approach involved upgrading to a new fully integrated hydraulic, mechanical and electrical system. The strategy solved the problem and produced significant savings for the company.
As most people know, processed wood chips are frequently used by pet stores and medical research labs as bedding material for small caged animals. What might surprise you however is the fact that these chips are actually manufactured from full-sized logs rather than salvaged as a byproduct from other manufacturing operations. One such wood chip maker was experiencing significant downtime due to problems with an outdated hydraulic system.
The company recycles logs deemed unsuitable for other types of wood products such as plywood and furniture. Converting logs into properly sized chips requires a special milling machine equipped with two, high-powered multi-blade shaving heads and a moving carriage. Logs being processed are placed on the carriage which travels 10' laterally using a hydraulic cylinder. The milling heads below the carriage chew away at the logs as they are pulled back and forth by the hydraulic system. The operation must be perfectly timed to produce the proper chip size, grade and quality.
Over the course of a day's production, oil temperature would rise - often exceeding 275°F - thus altering oil viscosity which, in turn, was affecting cylinder pressure and speed. High oil temperatures were also considered a potential fire hazard.
Machine operators were forced to stop production for 15 minutes of every hour to re-adjust the flow control valves in order to maintain consistent carriage speed so logs could be moved over the cutting blades at the required feed rate. Because the operation involved handling tons of dead weight and the use of extreme force, it put severe demands on valves, bearings, pumps and seals resulting in chronic oil leaks and occasional component failure. Energy consumption was also very high.
The manufacturer called Kaman to see about adding a cooler to their existing power unit in order to cool the 100 gallons of oil that was driving the system's hydraulics. Because of the various types of problems the company was experiencing, however, Kaman representatives suggested taking a different approach using state-of-the-art technology to circumvent the old hydraulic system's inherent design weaknesses.
Instead, a special Kadant/AES Unigy hydraulic pump, motor and drive system with a custom-designed, PLC based control system was recommended. The Unigy technology provides a much higher level of position, force and speed control, and an efficiency rating previously unattainable from the hydraulic system. Using a positive displacement pump with a "smart" drive and PLC, the system automatically modulates the torque and speed of the motor to compensate for (and eliminate) ripple effects caused by the cycle of fluid displacement.
The system processes 8,000 data points with every shaft revolution, while proprietary algorithms control the power and speed of the motor to optimize flow and pressure. By keeping track of where the piston is at all times, and by monitoring the rotation of the pump, the system governs the speed of the carriage in both directions without the need for flow control valves. Velocity is accomplished by the pump dispensing oil at different rates in the forward and reverse directions to compensate for piston rod displacement. The carriage/piston assembly decelerates to "creep" speed a fraction of an inch from the proximity sensor, making the switch at low speed. As a result, there is no more "hydraulic shock" when the carriage direction is reversed. All of these functions are controlled by the Unigy system, PLC and a single solenoid control valve - no additional hydraulic control equipment is required.
The new precision operating system has provided some impressive results: