PLC Brings Precision and Versatility to Portable Car Crusher
To some moviegoers, the phrase car crusher brings memories of innovative - but macabre - methods of body disposal in the plots of spy and gangster films. To the more technical minded, the phrase highlights the brute power that hydraulics can deliver. Discarded automobiles are flattened in seconds for more convenience and economical shipment of their scrap metal to steel mills. Because the high power level has the potential to damage the basic structure, control of car crushers is just as important as control of more delicate hydraulic applications.
Al-jon Inc. Ottumwa, Iowa, manufactures portable and stationary car crushers. The operation of these machines appears simple. A large forklift picks up the automobile and puts it into the open side of a box built of heavy-duty lids and plates. Running on a programmed automatic cycle, vertical hydraulic cylinders extend in a 51-sec rocking sequence to flatten the car with the top plate-- like a huge press. The rocking sequence involves Al-jon's patented Quad-Post design that allows the machine to lock one cylinder while pressurizing the other to take advantage of the 20-ft lever arm formed by the plate between them. When the cycle is finished, the first crushed car is 15 in. high-- even less after subsequent cars are stacked on top of it and crushed.
A 100-hp diesel engine powers the portable crusher, driving a double gear pump that can flow 70gpm. The pump supplies two 8-in. bore crushing cylinders in a 3000-psi circuit. The vertically mounted, guided cylinders stroke 81 in. as they push the crusher's top plate down against the car.
When Al-jon redesigned the remote control system for a portable model, they sought to reduce the space requirements of the relay circuits in the existing design while increasing the reliability of the timer. It was apparent that a programmable logic controller could make the new system more compact and simpler, yet more versatile, with lower component and installation costs.
Al-jon chose a 12-V DC version of the SK-1600 low-profile PLC manufactured by Entertron Industries, Inc. of Gasport, NY to meet its specific needs. The SK-1600, designed for industrial applications, provides the capabilities Al-jon wanted, without any costly extras that were unnecessary yo this custom application. The solid-state board has no moving parts, which translates into longer service life.
The availability of a 12-V DC model allowed the PLC to be powered directly from the crusher's battery. Entertron modified its standard product to provide a higher transistor current rating. This high-amperage output rating ensures sufficient power for reliable performance in which all timer, counter, and external relay functions are transferred to the single controller. There is no possibility of operator error.
Another bonus in the low-cost package is that all Entertron PLC's include free software for relay ladder logic programming using IBM PCs or compatibles. This software allows program editing, off-line simulation, and on-screen documentation specific to the application. Al-jon used Entertron's optional EPROM with a simple serial interface, giving them program security.
Many of Entertron's PLCs include a full-duplex RS232 serial port. With this arrangement, users can download the PLC directly and then monitor the program on-line while it is running.
October 1997 /
Hydraulics & Pneumatics
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