Rösler Oberflächentechnik GmbH

Innovative shot blasting solutions for descaling crankshafts

After annealing, the crankshaft surface is contaminated with scale. This, combined with the short distance between the shaft flanks, pose a considerable challenge for shot blasting.

To ensure a scale-free surface, crankshafts forged at ThyssenKrupp Gerlach must undergo a blast cleaning process. ThyssenKrupp purchased a system for descaling these shafts from the world’s leader in shot blasting, Rösler Oberflächentechnik GmbH. The Rösler blast machine is used to descale 150 different crank shaft designs and was easily integrated into ThyssenKrupp’s existing automated line.

ThyssenKrupp Gerlach GmbH, located in Homburg, Germany, is also supported by a globally operating sister company: ThyssenKrupp Forging Group. Together the two form one of the world’s market-leaders for forged and machined crankshafts. The R&D focus of ThyssenKrupp Gerlach GmbH has been on using high tensile strength steel and alternative manufacturing methods to reduce the weight of their components. This lowers both fuel consumption and exhaust gas emissions. The six million crankshafts produced annually in the Homburg facility are installed into in-line, boxer, V, VR, and W engines for passenger cars, industrial vehicles, motor bikes, etc.

Scale-free surfaces

Once forged, the shafts undergo a special tempering (annealing) process, which produces a thick, difficult to remove layer of scale on their surface. However, the micro-crack testing that follows this tempering process requires a surface that is totally scale-free. This presented a problem for ThyssenKrupp. Stefan Nussbaum, Manager of Tempering Operations, explained, “With our previous shot blasting machine, the handling of crankshafts was very labor-intensive and posed a significant risk for accidents. We wanted to optimize the process and decided to purchase a new system.” The ability to produce a scale-free surface finish and to blast various crank shaft types were the most important technical requirements for this new system. The customer also required that the new system could fit into the existing building without any modifications (i.e. foundation pit or roofing changes). Mr. Nussbaum continued, “In the beginning, we conferred with ten different equipment suppliers before narrowing the field to the four top competitors. We chose the RKWS 2x2 machine from Rösler because of the machine’s compact nature and high degree of automation.”

Determining optimum processing

To achieve this high level of automation across the component range, the Rösler engineers started out by developing part-specific PLC programs for the four most complex designs. They made their selections based on differing lengths, complex geometries, and smallest crank shaft flank spacing, because these characteristics pose the greatest challenge for achieving a scale-free finish.

To ensure the greatest results, the PLC programs were set to control blast time, speed, rotational RPM, oscillation distance, and blast angle. These parameters were determined by extensive computer simulations and blast trials. An integrated measuring system ensures that the parts are precisely positioned below the turbines and in-line with the programmed values. The blast pattern can be continuously adjusted by rotating the control cage with a linear motor. The RKWS is equipped with two workstations that can be automatically adjusted to the crank shaft type, thus further automating the system and eliminating the need for operator intervention.

Full automation

Following forging, annealing, and cooling, the finished crankshafts are transported via overhead conveyor to the RKWS 2x2 blast machine. Then a parts-handling system places the components into a calibration unit to determine the part specifications. After the two workstations have been calibrated based on this information, a robot picks up the crankshafts and places them on the preset work stations. This design allows processing of either two small, simple crankshafts in once cycle, or one complex crank shaft placed across the workstations.

After the blast chamber doors close, the media flow is initiated to the blast turbines. Simultaneously the crank shaft(s) on the work piece carrier start rotating and oscillating, ensuring scale removal from all surface areas; even the most critical areas between the crankshaft flanks.

“We really liked the automatic adjustment of the blast pattern, as well as the rotation and oscillation of the parts during the blast process. None of the other equipment suppliers offered these features,” commented Nussbaum.

Four, Long-Life Gamma 520 blast turbines, 37 kW (50 hp) each, generate the required blast intensity, throwing up to 4.5 metric tons of blast media per minute at the work pieces. These high-performance turbines are equipped with throwing blades that feature double-sided work areas, allowing the shot blast process to run with two rotational turbine directions. The rotational direction (specific to each crank shaft type) is also controlled by the PLC program. Compared to conventional blast turbines, the Gamma turbines generate up to 30% higher blasting speed and offer exceptionally higher wear-resistance.

Excellent wear-protection and easy maintenance

The wear-protection of the Rösler RKWS 2x2 machine reflects the high blast media throughput. The blast chamber is fabricated from 10 mm (.4 in) thick manganese steel, while the areas directly exposed to the blast stream are lined with highly wear-resistant, exchangeable protective plates made from 10 mm (.4 in) thick manganese or 20 mm (.8 in) thick hardened tool steel . The work piece carriers are also made from hardened tool steel. Containers filled with blast media are placed on the floor of the blast chamber in the “hot spot” area to prevent direct exposure of the wear liners to the blast stream. This significantly contributes to wear reduction and, as a result, high equipment uptime. The media transport and classification systems were also designed to cope with the high blast media throughput.

The Rösler engineers focused especially on facilitating the maintenance of the RKWS machine. This is reflected in the easy access to all service-relevant machine components. In addition, the system is equipped with a crane-and-cable lift system, allowing for simple and quick maintenance of blast turbines.