APPLICATION STORY
    

RDP takes a load off Ratcliff's mind. As the originator of the vehicle-mounted tail lift, and the UK’s market leader for over 40 years, Ratcliff prides itself on its innovation and build quality. Whilst the Company's engineers design their lifts using finite-element stress analysis, they need to verify statutory overload capability by carrying out physical tests. Ratcliff establish the yield strength of each model, and retain the records in the lift's CE Technical File. The traditional method of determining the ultimate strength of a lift has been to apply calibrated weights – huge steel blocks - stacked one by one on the tail lift’s platform until the yield point was reached. But Alan Barsby, Engineering Director at Ratcliff Tail Lifts Ltd, was not satisfied. Not only was this method a time-consuming and often destructive procedure, it was, particularly with high payload lifts, potentially dangerous. After the test, there was no clear indication of the primary failure mechanism. Again, comparative tests of central, distributed and off-set loading were impractical and the method was not sophisticated enough for Ratcliff’s new generation of lightweight all-aluminium tail lifts. Ratcliff devised a test rig made from a rigid steel cage incorporating a hydraulic ram capable of exerting up to 125,000 N of load at any point on a platform through a pressure pad, matched to the footprint of the intended load. The equipment will handle the full range of the Company's products, from the smallest passenger lift to the biggest column and cantilever models. One phrase “Displacement transducers” typed into an Internet search engine brought Alan to the virtual front door of RDP Electronics. As he explained, “I looked through the website and found, from one company, everything I needed. Displacement transducers, load cells, amplifiers and displays. The most important requirement was the ability to plot a load / displacement curve in real time. In that way we could view the approaching yield point without destroying the test sample. So I made a call and spoke to Fred.” RDP’s Fred Thorneycroft worked with their Southern Area Sales Engineer, Ken Irvine, on a solution. “Ken visited us, discussed the problem and the solution was relatively simple.” explained Alan. An ACT6000 300mm LVDT and E725 AC conditioner/indicator were chosen to measure the deflection caused by the increasing load, and a 53-20,000lb load cell in an articulated knuckle joint with another E725 DC (calibrated to read in tonnes) was fitted to the base of the ram to measure the load. He continued, “The two E725s were connected to a PC via the RS485/RS232 option to provide a stress/strain plot and Ken then set up RDP’s Excel-based spreadsheet and chart software for us. We could not have asked for a better service.” “The test rig works exceedingly well, and we are delighted with the performance. We are able to explore the ultimate strength limits of prototype lifts without causing damage." "Currently, we are using the equipment to establish the yield point of a heavy-duty platform with a concentrated load of more than nine tonnes. This would have been out of the question using dead-weight methods." _________________________________________________________ For sales and technical information contact:- RDP Electronics Limited Grove Street, Heath Town, Wolverhampton WV10 0PY. UK. Tel: +44(0) 1902 457512. Fax: +44(0) 1902 452000 E-mail: sales@rdpelectronics.com Website: www.rdpelectronics.com November 2002
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