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IT IS one of the unfortunate characteristics of the trailer

24th July 1982, Page 28
24th July 1982
Page 28
Page 29
Page 28, 24th July 1982 — IT IS one of the unfortunate characteristics of the trailer
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industry that many operators take the equipment for granted. To some extent this is justified in the sense that more research and development goes into a lorry by virtue of its complexity but a trailer, and in particular a refrigerated van, nevertheless needs a lot of careful thought. For apart from the structural requirements, it also needs to meet the various hygiene and insulation conditions.

I recently spent a day at the MIRA proving ground to talk to David Bowman, product coordinator at Crane Fruehauf and to witness some pave-testing of a CF reefer.

The particular testing that I witnessed at MIRA was with a payload of approximately 25 tonnes to give a gross weight of 38 tonnes. Whereas most vehicle and trailer manufacturers use concrete blocks as test weights with these being bolted to the floor (as with the CM/Crane Fruehauf dry freight van), the procedure for reefers is somewhat different.

The weight is the same and so is the material but as the worst loading occurs when hanging meat is carried, the CF test procedure sets out to simulate this, so the 25 tonnes of payload is in the form of small concrete "pillars" suspended from the roof using conventional meat hooks.

As David Bowman explained: "Using hanging weight is critical. We actually prove something during the tests as we are putting the load through the sidewalls. Having the weight on the floor does not give us much information for a van."

There is no British Standard for a hanging carcass so the height of the test weights is set very much by rule of the thumb.

The Crane Fruehauf target for pave-testing is 800km (500 miles). It is often a source of discussion as to how one can equate distance on pave to distance covered during "normal" road operation. Suffice to say that CF experience equates 500 miles of pave work to one million miles on the road.

The aim is to reach the 500 miles with the test vehicle in one continuous programme, which means no stops other than for when the drivers are changed. It is not a question of doing 100 miles, going back to Norfolk, inspecting the trailor, returning to MIRA and clocking up another 100 miles.

Bouncing up and down on the pave tests the driver even more than it tests the structural integrity of the van so CF switches drivers after every four laps. At the 17 to 20mph target speed this means a driver change every half-hour. With an inspection at each driver change taking about 15 minutes, the test team target is 50 pave miles per day.

During the panel testing that I watched, nothing happened — a situation which CF obviously hoped would continue! If anything structurally untoward occurs during the test, the CF depot at nearby Tamworth is used for minor repairs.

As far as this particular pave test was concerned, the object of it all was to prove the integrity of the box. Nothing else. David explained: "We don't think we have anything to prove on the running gear but we still check it as we go along."

Not very long ago, pave testing involved pounding round and round until something cracked or, in extreme cases, broke off altogether. Things are more sophisticated now. Although testing to destruction is still part of the programme, strain gauges are used more and more to plot the pattern of failure.

This CF van had strain gauge mounted internally at floor love up the side panels and at the roof/wall junction. They were mounted at the nearside only, a experience has shown that this is the area which takes most of the loadings during operation thanks to road camber and the position of drains.

Strain gauges were also mounted on the outside walls with one batch in particular being secured above the suspension. Temperature compensation is provided by having a dummy unit mounted alongside the particular test gauge.

About five working days is th4 average time that it takes to strain gauge a reefer. The CF technicians prefer working on grp as opposed to aluminium eca use it is easier with the irmer to get the strain gauges adhere.

The results are monitored in nits of six. The CF equipment llows more than this, in fact, ut as David Bowman said: "It ets complicated to analyse the aces. We end up with them oming out of our ears."

All the strain gauges are wired p to one junction box which is onnected by an electrical mbilical cord to the test ngineer's car. The equipment an be carried in the cab but here it receives the same ■ attering as the driver and the test railer. The layout of the MIRA ircuit means that, at the 17!Omph test speed, it is easy for he car to keep pace with the ruck/trailer combination on the mooth road around the outside )f the pave circuit.

The Scania tractive unit used )y Crane Fruehauf is a 6x2 which vas chosen not only for its lexibility of kingpin position but ilso because it gave the drivers better ride. And as I mentioned )efore, testing the driver is not eally part of the exercise!

Before a complete reefer is )uilt for test purposes, many static tests are carried out on iifferent panel materials to 91iminate the obvious nonstarters and to test the structural omposition. In David

Bowman's words: "We eliminate the daft ideas before we start the serious testing."

The purpose of my MIRA test was to monitor performance of a grp panel using structural foam in the sandwich rather than ply. Ply is a heavy material and it can also become un-laminated. It also makes things marginal on internal width because of the thickness needed to achieve the required insulation standards.

Crane Fruehauf in fact makes reefers in both aluminium and grp with the current split being about 50/50 but showing a definite trend towards grp. Both materials have their advantages and disadvantages with the question of price being somewhat clouded by the dependence of grp on oil for its production.

The test grp/foam sandwich was just a part of the overall Crane Fruehauf development programme. As you would expect, the company tests every material the engineers can get their hands on. "This particular foam is just one on our list," said a very non-committal David Bowman. "It's not necessarily the one we will be using in the future."

Crane Fruehauf is, of course, part of the giant Fruehauf Corporation and Fruehauf Europe is actually run from the UK. Test information collected at any of the Fruehauf divisions is made available automatically to the others to avoid duplication of testing. The research and development centre of Fruehauf is based in Detroit and the evaluated test results are circulated to all the other divisions worldwide.

Fruehauf Europe recently carried out a suspension exercise for all its member companies with all the testing being carried out in the UK.

Refrigerated trailer design is more specialised than the other parts of the trailer business with the possible exception of tankers. Attention to detail is all important with the method of construction as there is more heat loss through the joints than through the material itself.

The K factor for the wall• material will be known from the samples but is still double checked when the full size reefer is built. (The K factor is the overall coefficient of heat transfer for the material.) It is worth mentioning here that CF was the first body manufacturer to install a test chamber for testing insulated bodies to the standards of the European agreement, Accord Transport Perissables, or ATP for short. The very first chamber in the UK was the one used by the Shipowners Refrigerated Cargo Research Association at Cambridge.

The purpose of the test is to enable a type approval certificate to be granted for a particular range of body. In the case of Crane Fruehauf because of the facilities just mentioned, the company is allowed to perform its own type approval test — under the SRCRA supervision.


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