Benefits of a Vacuum

Vacuum bags made of silicone increase the efficiency of making parts from fiber-reinforced plastics, especially in small-series production. The French company Durisotti uses the process to make floor panels for handicapped-accessible buses.

Of all materials, a great deal of hope is being pinned on fiber-reinforced plastics, which offer a compelling mix of stability, low weight and huge design latitude. They therefore have the ideal properties for automotive and aircraft makers. Their special properties are more than just the sum of their two parts, however. Fiber-reinforced plastics are much more stable than the combination of the stability conferred by pure fiber and plastic encasement would lead one to expect. In the direction of the fiber, they are especially rugged because the fibers are firmly embedded in the structure by the surrounding plastic matrix. This high stability is the reason that fiber-reinforced plastics find application in Formula 1 racing, the aviation industry and the rotors of wind turbines. Not only that, but they are relatively easy to process, which is why small runs needed for these applications can be made economically.

Durisotti employees need just five minutes to exactly position the silicone vacuum bag on the workpiece. The former production process required over an hour for positioning and sealing of the plastic sheeting.

It is precisely all these qualities that appeal to Durisotti, a French company. This family-run business specializes in converting mass-produced vehicles to meet special purposes. It adapts vehicles to suit the needs of emergency services, transport and bus companies, craftsmen and commercial companies. The company, based in Sallaumines on the Belgian border, has by now adapted more than 27,000 vehicles. Customers include the French postal service and police, Air France and the city authorities in Paris.

The use of heavy materials should be avoided in retrofitting work, as they would reduce the available payload and increase fuel consumption. Nonetheless, there may be no compromises on stability either – which could jeopardize the vehicles’ roadworthiness And with special superstructures and modifications, it is often the case that unusual, complex parts are required that meet the customers’ specific needs. Large production runs of these special-purpose vehicles are generally unlikely.

Durisotti has been working with composites since the 1970s, and some of its structures have been as voluminous as 20 cubic meters. For a long time, its typical working process for making the composite workpieces consisted of charging the fiber component, resin and hardener into a half-mold, which was then covered with plastic sheeting that had to be laboriously taped all around the edges. A vacuum pump then extracted the remaining air from the mold and at thesame time ensured that the still-liquid resin was evenly distributed. When the resin hardened, the plastic sheeting was removed and disposed of. They then removed the finished workpiece from the mold. The disadvantage of this process was that it generated a great deal of waste and sealing the molds before the vacuum was applied was a tedious, labor-intensive task.