Depending on the size of either the tubes, or the production lot, Mera Bellows uses two versions of deep-drawing the tubes: comparatively small precision tubes in large production lots can be produced in a multi-stage deep-drawing technique using oil as a lubricant. The advantage of this process is the significant decrease in the number of cleaning and annealing steps but also requires usage of very expensive tools.
Smaller production lots or larger tubes are deep-drawn in a step-by-step methodology using soap as lubricant. Soap is water soluble, therefore it can be washed from the tubes in a comparatively simple way. In addition, soap is very eco-friendly. The tools can be made of regular and less expensive tooling-steel. Thus, the tooling costs are reduced.
At Mera Bellows oil is washed off the intermediate products by eco-friendly paraffin. After the cleaning process, the paraffin is vacuum-distilled and thus it can be used directly and with only a small loss for the next washing process. Soap is removed by using a new washing automat. The recycled water is constantly taken off the basin, cleaned by vacuum distillation and later recirculated to the washing process. The concentration of the detergent remains at optimal levels automatically.
Due to the plastic deformation of the metal, it becomes very hard, so it has to be annealed before continuing the process. To do this, Mera Bellows uses vacuum-furnaces, that work at pressures between 10-2 to 10-4 mbar. The depression protects the surface of our products against oxidation. As an alternative solution. Mera Bellows uses inert-gas furnaces. To avoid oxidation, the products are annealed in a protective-gas atmosphere.
To form the convolutions of the bellows, tubes are placed into a very special tool – called a cassette – which is produced individually for every type of bellow. Depending on the size of the bellows and the wall-thickness, water pressure of up to 250 bar is pressed inside of the tubes. The cassette is then compressed axially to the tube and subsequently the corrugations are formed.
Thermal Stress Relieving
Before the final quality control, one last working-step has to be completed – the thermal stress relieving. The bellows are heated under protective atmosphere and afterwards cooled down very slowly to room temperature.