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."
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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
