in Vol. 4 - July Issue - Year 2003
Photo 1: The wire mesh belt blasting machine by R
Photo 2: The wire mesh belt is a decisive element of the system concept. In order to minimize wear, the wire links are made from a special alloy.
Photo 3: Large volume die cast part (oil sumps) undergo an all-round deburring process in a wire mesh belt
Photo 4: Aluminium die cast component that had to undergo all-round processing but could not be processed whilst hanging.
Photo 5: The RDGE system can be ideally integrated into fully automatic manufacturing with robot support.
Rösler Oberflächentechnik GmbH is an international leading all-round supplier of surface finishing and shot blasting systems located in Untermerzbach and Hausen, Germany. The manufacturing programme also includes the media (chips + compounds) for the surface finishing as well as process technology and environmental technology (recycling, processing, recycling of waste and process water + high-performance centrifuges). Besides the German plants the Rösler Group has branches in Great Britain, France, Italy, The Netherlands, Austria, Switzerland, Spain, Singapore, Brazil, South Africa and USA. All in all, the Rösler Group employs 990 staff worldwide.
Wire mesh shotblasting systems are the better solution for many application areas
Heavy and sticky scale is normally scoured off forged parts and then descaled in a shotblasting system. However, there is another way: In the wire mesh belt-blasting machine (RDGE) the surface of forged parts are shotblasted complete in one operation. In order to descale the components evenly on all sides, high descaling performance is necessary. The required intensity is achieved by means of several blast wheels that act on the components from all sides. In order to balance expected loss due to „blasting through“ the belt, more energy is supplied from below. At the same time the position of the components is shifted minimally, thus preventing even the slightest formation of shadows.
The descaling of forged parts is only one possibility from the extensive processing range that Rösler Oberflächentechnik envisages for RDGE. Systems of this kind are the better and more economic solution for many application areas.
For instance for applications where components are treated in one continuous process, for components that cannot or should not be processed whilst hanging, as well as for components that cannot be transported on a roller conveyor system due to their small size and/or too delicate for batch-by-batch processing. Preferred application fields are the deburring and surface finishing of light metal parts of aluminum and magnesium, the descaling of forged parts or the deburring and roughing of torch-cut parts. In order to be able to deal with the most varying characteristics of components and capacities accordingly, Rösler has designed the system concept of the RDGE to be variable. Depending on the processing task the system is available in processing widths (800, 1000 1250 and 1500 mm) and is equipped with a varying number of blast wheels (from 2 up to a maximum of 8).
Performance and Order of the Blast Wheels
The selection and number of the blast wheels as well as their exact performance and their order in the shotblasting chamber are determined on the basis of component geometry, type of component, and the required capacity. The higher the capacity, the wider the system or the faster the speed of the continuous flow has to be. However, if the continuous flow is higher the components will be under the stream of shotblasting media for a considerably shorter time. Therefore, more shotblasting fields must be available.
Generally, the blast wheels are located at the top and bottom of the shotblasting chamber in offset positions, so that they do not blast against each other. The angle of inclination of the individual turbines is decisive for uniform, shadow-free processing. The ideal angle is determined by means of tests with the parts to be processed, which ensures that edges or undercut areas are also reached by the stream of shotblasting media. The selection of the blast wheel type depends on the necessary blasting energy and the material of the component to be blasted. A further important factor is the throughput of shotblasting media. The bigger the blast wheel, the more kinetic energy will be available. The higher the drive performance, the more shotblasting media will flow. Generally Rösler uses blast wheels of the Hurricane 28 and 32 type with drive performance of 5.5 to 11 Kilowatts for the RDGE – systems. In special cases – e.g. if the system is used for the surface finishing of components with a large surface or for compression blasting – double turbines are used– i.e. blast wheels with a hot spot, an especially large and even flow stream of shotblasting media.
Wear-resistant Wire Mesh Belt, solid Construction
The wire mesh link belt plays a decisive role for the function and performance of the RDGE. This used to be a critical point with former system concepts, because it is a fundamental wear part of the system.
In order to increase its operating time considerably, the wires of the belt used consist of a wear-resistant alloy. Wire thickness and mesh size are precisely adapted to the processing task. The wire mesh link belts chiefly used have a mesh size of 50 to 60 millimeters and wire thickness of 5 to 6 millimeters. The system construction is solid, with massive blasting booth walls, lined inside with additional sheets of manganese steel. Because of wear protection there are no screws and bolts inside the steel booth, or in the preliminary and finishing booths.
Ideal cell solutions and further options
Especially in the area of die casting there is a trend to process large-volume components in a continuous flow system placed on a wire mesh link belt, rather than hanging. The fundamental reason is that this process saves time and personnel; at the same time a wire mesh continuous flow system can be much more easily integrated into a fully automated production process with robot support. The components can be placed on the large-size wire mesh belt by a handling system (robot). After blasting process is completed the same or a different handling system can take them off again. The RDGE is this way adapting ideally to modern cell production concepts. Handling systems can of course also load and unload hanging conveyor systems.
However, the technical expenditure is higher, since the hanging components must be placed very precisely. In this case and if components cannot be processed whilst hanging due to their size the wire mesh continuous flow system is the better solution. For a user in Spain, Rösler constructed a RDGE 800 -2, which is successfully used to process node sheets. Those components cannot be processed whilst hanging and at the same time are too delicate for batch-by-batch processing. Tests have shown that an ideal processing result can be achieved in a wire mesh belt-blasting machine with two blast wheels.
Generally this type of system provides a wide processing range, the areas of light metal and die cast showing the biggest demand. A RDGE 800 – 4 is used very successfully for filter deburring and finishing of aluminium die cast oil sumps. In this system, the hollow parts are blasted in a continuous flow system shadow-free and absolutely clean, so that they comply with the strict requirements of the car industry.
Best processing results are also achieved when blasting long and bulky components of magnesium. The low weight of magnesium components leads to problems and additional expenditure when they are processed whilst hanging, since the components must be firmly fixed for processing.
They would otherwise begin to sway when exposed to the stream of shot and move outside the blast pattern. Processing in a wire mesh belt – the shotblasting system provides a clearly more effective and more economic alternative. As more and more magnesium components are used, especially in the automobile industry, this type of processing and system has a high potential for the future.
Another area of use for the RDGE can be found in traditional iron and steel foundries where heavy sand-cast components are de-sanded and de-scaled. This field almost exclusively uses automatic handling systems because of the size and weight of the cast components. The RDGE can be easily integrated into a manufacturing line of this kind. And finally, in many cases the RDGE also provides a better and more effective solution for comprehensive de-scaling and cleaning of laser-cut components than other types of systems, especially for automated manufacturing processes.