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O C KLEIESS

8th April 1999, Page 40
8th April 1999
Page 40
Page 41
Page 40, 8th April 1999 — O C KLEIESS
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There have been significant advances in curtainsider engineering over the years such as bolted rather than welded construction, and improvements in unladen weight and corrosion protection. The actual curtains and curtain-fastening system themselves though have remained largely unchanged since Boalloy invented the concept with the Tautliner. Now the designers are turning their thoughts to curtains without buckles.

Faster turnround and a clutter-free surface that is easier to clean and livery are the main benefits of buckleless curtainsiders, but eliminating the buckles is not simply a cosmetic change. Much of the load-retention capabilities of the curtain come from the vertical tension produced when the driver tightens each vertical webbing strap and locks it in. Any design that removes buckles still has to deliver vertical tension.

• Curtain systems

Most manufacturers are using pneumatic power for vertical tensioning, including Boalloy, Cartwright, Don-Bur. Mirofret and SDC Trailers. It may be more complicated to install and maintain, but the positive tensioning of the curtain that results relieves concerns about adequate load security especially on longer trailer bodies.

The bodies have a lateral bar under the chassis along each side, which the rave hooks are attached to. The bar is connected to an air supply from the vehide or trailer air reservoir and is pulled and retracted either by pistons or by modified versions of spring brake cham

bers. The driver actuates the system by pressing a button on the bulkhead or at the rear. As the bar swivels, it either increases or releases the tension in the curtain.

On most bodies, the driver must manually release the hooks, although SDC has designed its system so that the bar travels out far enough to release the hooks.

Don-Bur's BC buckleless curtain has a slightly different arrangement. The original BC curtain, first seen on the CM Trailer of the Year award-winning Palletmaster 2002, has a cable system that runs laterally along the body, retained in roller guides at the end of each vertical strap. There is one cable for the front part of the trailer, and another at the rear. Turning a ratchet handle in the centre of the rave tightens the cables, which in turn pulls the curtains against the rave. The twin-cable system makes it easier to open part of the curtain in the event of a load shift.

The latest Evolution version uses modified Neway Anchorlok spring brake chambers to pull the cable taut. The curtains are tensioned when the spring brake is on so they will remain taut even if the air supply fails.

Don-Bur put its BC trailer through a tilt test to demonstrate its load retention capabilities. The trailer was tilted to 27.50 and the curtain had a r6-tonne load resting on it.

Boalloy's Vitesse buckleless curtainsider spent 18 months on test in Eddie Stobart's fleet before going on general sale early this year. The Congleton manufacturer wanted a design proven in practice.

The exception in buckle

less design is Lawrence David's Fast Strap system which simply eliminates the buckle. A piece of elasticated webbing attached to the main straps allows the rave hook to be pulled beneath the side rave, tensioning the curtain. Lawrence David says because the driver is not pulling hard on the strap to tension it, there is less wear on the webbing and the roof rail and the use of pre-shrunk webbing minimises any stretch. It also points out that the buckle or rave hook is often the weakest point in a conventional curtain assembly.

Spanish reefer manufacturer Mirofret has developed a buckleless version of its insulated curtainsider. The lateral rave is further under the chassis to produce a positive temperature seal. The curtain has a flexible tube running up the rear vertical edge and along the top. When the button to tension the curtains is pressed, it also sends air up the tube, forcing the curtain against the top pelmet and creating a tighter seal. The trailer has a Class A ATP certification.

Grahams of Gildersome offers a solution to operators wanting to smooth the vehicle sides while retaining the traditional buckle tensioning system. The buckle is moved from partway up the curtain to the end of the webbing strap where it is combined with the rave hook.

• Air-smoothing side skirts

The full side skirts that are starting to appear on more trailers not only look good; they have a streamlining effect that can reduce fuel consumption, albeit by small amounts. Some skirts, such as Boalloy's Vitesse and DonBur's Palletmaster 2002, wrap round under the trailer in front of the landing legs and at the rear, encompassing the wheels.

Cartwright, which took part in the research into vehicle aerodynamics done by the Department of Energy in the early 19905, reckons the roof-scoop on its aerodynamic trailer is as important as the tapering side skirts in smoothing air flow. And some operators are certainly worried that skirts are vulnerable to damage.

• Weight saving

The acceptable weight for a maximum-length curtainsider is now 6.5 tonnes or less, compared to around 7.0 tonnes just a few years ago. But manufacturers are not stopping there. Floors are the latest component to lose weight. Montracon is one of the first trailer builders to use a new plastic flooring from Bonnington Plastics called Top Dek. It is made from extruded plastics planks, has a depth of z8mm and comes in two widths and continuous lengths up to 53.5 metres. It is claimed to be 40% lighter than Keruing flooring, with a weight of 395kg per 3 om2 of floor, compared with 6604 for Keruing, and 595kg for birch ply laminate.

German trailer builder Krone has saved weight by redesigning the floor so that the material forms part of the structural strength. Modern materials don't shrink, warp or crack, says Krone, reducing the need for supportive cross-members, Removing the cross-members allows a thicker 3omm floor to be used, increasing the point-loading capability to 7.1-tonne per forklift truck axle.

Moulded composite plastics, as used by Don-Bur on its Evolution trailer, have the benefit of lightness and strength. The 9.7-metre prototype weighs less than 5.5 tonnes. Plastics are used for the pillarless roof, rear doors and front. The mouldings incorporate fixings such as curtain tracks and door-locking mechanisms that are needed.

• Corrosion protection

There have been huge strides in corrosion protection in the 199os. Galvanised or zinccoating of rear frames and shotblasting and two-pack painting of chassis have become almost universal. Environmental pressures forced European manufacturers to look at their painting processes, which they say now also deliver improved corrosion protection. Axle manufacturer BPW and trailer builder Krone are using a steel treatment process similar to that used for car body shells. Components are immersed in a series of baths, which include a cathodic iron or zinc phosphate corrosion protection coating. A top powder paint coat is then applied and baked on. The major benefit is that every nook and cranny gets the same level of coating.

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Organisations: Department of Energy

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