Innovative solutions for the blasting of cast products

Topic of the month - April 2015

Photo © Rösler Oberflächentechnik GmbH

The RHBE 27/32-F was set up for the particular requirements of coring. This also includes blasting abrasive preparation with double magnetic separators and the filter system equipped with special cartridges. Photo © Rösler Oberflächentechnik GmbH

In the foundry business, blasting technology is amongst the indispensable processes to produce the necessary surface and/or product characteristics. Thereby, new developments for automated blasting supplement the range of use, and they enable significantly more economical and high quality processing of cast products.

More efficiency for surface processing

When it comes to processing and surface finishing of cast parts for the automotive industry, the requirements for quality, economic viability and throughput are extremely high.

These were also the requirements of a South German automotive manufacturer for various blasting machine manufacturers, when selecting a blasting system for residual desanding and surface finishing of cylinder heads. The 510 x 320 x 150mm (L x W x H) and 18.8 kg workpieces are produced in gravity chilled casting.

Rösler developed a plant concept, which corresponded to the customer requirements on the basis of a roboblaster - a combination of blasting plant and 6 axle robot that can be used for various blasting technology processing procedures, from deburring, desanding to compression blasting (shot blasting). The car manufacturer's good experiences with a previously used roboblaster blasting system from Untermerzbach, and the adherence to the specified workpiece throughput volume, were crucial in the decision in favour of this system RROB 800/750-4.
Photo © Rösler Oberflächentechnik GmbH

The pump parts are blasted individually or as a batch. The maximum part dimensions are 2.5 x 3.0 m (W x H), the hook load is 5 tonnes. Photo © Rösler Oberflächentechnik GmbH

Blasting at 16 second intervals

With this solution, a robot alternately loads two blasting plants. This procedure enables the required redundant design of the blasting process, and it prevents production standstill in the case of a plant breakdown.

The plant manufacturer achieves the specified, short cycle time of just 16 seconds per workpiece with a double gripper, with which the robot can accept two workpieces at once. The cylinder heads are delivered to the robot cell via a roller conveyor with side transfer unit. The cylinder heads are prepared in the precise position by an alignment system for acceptance by the robotic gripper.

In the blasting plant, the duplex gripper positions the cylinder heads on part-specific, designed workpiece mountings and then pulls out of the blasting chamber again. After closing the chamber door, the turbine bulkhead releases the inflow of blasting abrasive, and at the same time the cast parts are set in rotation via the workpiece mountings.

This continual changing of position guarantees that the cylinder heads are blasted on all sides, evenly and without shadow effects. Stainless steel is used as a blasting abrasive, in a grain size of 0.5 to 0.8mm. After the specified blasting time, the bulkheads close the turbines again, while the workpiece mountings continue to rotate until the blasting chamber is completely open. This means that the workpieces are pre-emptied in the blasting chamber.

Each blasting plant is fitted with a total of four high power turbines, type Hurricane H42 with a diameter of 420 mm and a drive power of 15kW each. Rösler determined the optimum placement and required inclination angle of the turbines in the construction phase, through 3D simulations of the blasting process.

In order to prevent extreme strain due to the high blasting intensity, the plant casings and workpiece mountings are made from extremely hard wearing manganese steel. In addition, the work chambers are clad with 12mm thick, gap-free laid manganese steel plates.
Photo © Rösler Oberflächentechnik GmbH

The optimised wear protection of the blasting chamber made from 10mm manganese steel consists of interchangeable 25mm thick chilled casting plates in the direct blasting area, and on the sides there are 10mm thick manganese steel plates. Photo © Rösler Oberflächentechnik GmbH

Challenge of emptying blasting abrasive

However, there are not only high requirements to be fulfilled regarding cycle time and precision, but also regarding waste sand / blasting abrasive content.

The specification of just 0.5 grams per workpiece makes a very clever solution equally necessary here: After blasting, the robot transfers the cylinder heads to an emptying unit in pairs - similarly designed to a Rhönrad motor. The workpieces move in a precisely determined channel, whereby they are rotated in the defined directions.

Via an unbalance motor on the bogie, vibrations are conducted into the workpiece, so that the blasting abrasive can be shaken out of even hard to reach places of the water chamber.
Photo © Rösler Oberflächentechnik GmbH

Due to its Y design, the mechanical shovels of the new universally usable Gamma® 400 G can be used from two sides, and therefore offer double the tool life compared to the usual blasting machines. Photo © Rösler Oberflächentechnik GmbH

Efficient blasting abrasive cleaning with double cascade air separation

The low waste sand content with this plant means that a magnetic separator is not required, and the blasting abrasive preparation can be carried out using more cost effective double cascade air separation.

It guarantees that both the required residual soiling value of <0.1 volume% in the blasting abrasive flow, and the specification regarding the blasting abrasive output of <1% in the preparation, are adhered to.

The roboblaster blasting system also shows high economic viability regarding the necessary space requirements: It has been housed in an area of just 10.40 x 8.60 m and is completely enclosed in a soundproof cabin.

In order to carry out maintenance work on the blasting plant during 3 shift operation, the working area of the robot is also marked off with a protective grille. The whole concept was set up on the first floor of the foundry of the car manufacturer, and it was so flexible that it could be transported in the freight lift (6m x 4m x 3m).