Tumble belt blast machine for coating preparation

Blast cleaning of springs prior to coating
Shot blasting is the most common pre-treatment technology to prepare the surface of technical springs for subsequent coating operations. In a newly established manufacturing line for compression springs this cleaning operation takes place in a Rösler tumble belt blast machine. Within short cycle times the custom-engineered RMBC 4.2-HD produces surfaces that are perfectly prepared for the subsequent coating operation. Oil carried into the shot blast process, is neutralized and, through the media cleaning system, separated from the blast media.

The Baumann Springs Ltd., located in Ermenswil, Switzerland, is a global leader in the production of springs and all kinds of stampings. This family-owned company was founded in 1886 and ever since has been managed by the family, today in the fifth generation. Baumann Springs is specialized in the development and production of custom-engineered products with tight dimensional tolerances and high demands for process stability in the automobile industry, medical engineering and other markets. The products are manufactured in 11 plants in Europe, Asia and North-America.

Shot blasting solution for a new production line
In 2021 the plant in Stare Mesto in the Czech Republic established a new production line for different types of long compression springs made from spring steel EN 10270-2. For cleaning and texturing (roughening) the surface of the springs prior to coating, the company purchased a tumble belt blast machine, model RMBC 4.2-HD, from Rösler. Claudio Hertig, project manager global operations at Baumann Springs, explains: „For this challenging task we had discussions with several equipment manufacturers and requested quotes from three of the suppliers“. “The Rösler solution impressed us not only because of the design of the equipment but also its functionality. Another positive factor was the sturdy machine construction. To familiarize myself with the suppliers, I visited all three companies and prepared a detailed technical comparison. Last-but-not-least, our good experience with Rösler equipment already running at some of our facilities and the global presence of the company, also played a role in our decision for Rösler”, continues Mr. Hertig.

Equipped for short cycle times and clean results
The RMBC 4.2-HD was painted per customer specifications and is equipped with special technical features. It allows the blast cleaning of complete batches of loosely tumbling compression springs with batch weights of up to 1,000 kg. Two Gamma 300G turbines, each equipped with a power of 11 kW, ensure a high shot blast intensity. These high performance turbines, developed by Rösler, are equipped with curved throwing blades in “Y” design. Compared to conventional turbines the specially calculated blade curvature generates very high media throwing speeds resulting in an up to 20% higher blast performance and, consequently, shorter cycle times. All this is achieved with a lower energy consumption. Moreover, the special “Y” design of the throwing blades allows the use of both blade sides. This practically doubles the usable life of the throwing blades. A quick-change system permits a quick blade change without the need for dismounting the turbine from its housing.
The blast process is further intensified and accelerated by the integrated blast media deflectors. These special compressed air nozzles are causing an additional blast media movement. The automatic blast media flow control allows not only the monitoring but also the precise adjustment of the media flow to the respective work pieces. The media replenishment takes also place fully automatically. An additional automatic dosing system allows the application of a powder cleaning compound in the blast chamber to catch and discharge any oil that may be carried into the shot blast machine by the work pieces. It should be noted that the powder compound does not affect the functionality of the blast media: In the air wash separator of the media cleaning system the powder is completely separated from the blast media. Since the machine was also intended for stripping the coating buildup from the work piece carriers used for the coating operation, the dry dust collector is equipped with explosion protection features.

In order to minimize machine downtimes due to wear, the inside of the blast chamber is lined with easily replaceable 6 mm thick highly wear-resistant manganese plates. The left and right side of the media discharge opening of the turbines is equipped with additional wear plates. These bundle the media stream and prevent this section of the blast chamber to be attacked by the blast media. Finally, the barrel heads, also made from manganese steel, are equipped with a PU coating providing an additional wear protection in the primary blast zone. This helps to further extend the equipment uptime. Claudio Hertig concludes: „The comprehensive experience and know-how of Rösler with the production of such machines is an invaluable advantage that helps improve the overall efficiency of the equipment. In addition, the global Rösler technical service allows us to work in other plants with the same processes and machinery and have them maintained by local Rösler service engineers”.