doris schulz

Topic: Clean pressing rollers to give wheels an immaculate surface

Wheels play an important role in the overall appearance of an automobile – especially when it comes to light alloy wheels to give a car racy lines. The manufacturer BBS has integrated CO2 snow jet cleaning into its flow forming process to achieve an optimum finish for its wheels which have become a legend on racing circuits and roads the world over.

Driven by the vision to construct lighter weight components for motorsport, in 1970 Heinrich Baumgartner and Klaus Brand founded BBS in Schiltach, Germany. To start with, the company made body parts out of plastic which helped fast cars become even faster. In 1972, it started manufacturing innovative three-component racing wheel rims. Even back then, stars and wheel rims were made of aluminium and magnesium. Eleven years later, BBS brought out a road version made of forged aluminium onto the market which was a great success. Meanwhile, not only are numerous world champions from all racing disciplines driving on BBS wheels to attain their titles – among others, Michael Schumacher – but the company is also one of the most sought after original equipment manufacturers in the automotive industry. Nearly all of the world’s top manufacturers buy wheels made in Schiltach. The recipe for success in this industry has been innovative developments such as the air inside technology for high-quality aluminium wheels. This technique enables wheels to be constructed using a cavity principle and reduces the weight of the wheel anything up to several kilos whilst simultaneously increasing stability and resistance to flange deformation.

Clean pressing rollers – a must for sooth, pressed surfaces

With this technique, the spokes and inner and/or outer shoulder of the wheel rim are hollow molded. To achieve this, during the flow forming step aluminium flanges fabricated in the casting process are shaped on a rotating cylinder using special tools to create a cavity and then joined together using the latest laser welding techniques. “To prevent aluminium from adhering in the reshaping process, we use a mixture of oil and graphite as a separating agent, but that’s not always enough. As a result, from time to time aluminium sticks to the pressing rollers. These residues meant that the manufacturing process had to be stopped immediately to avoid producing defective parts,” explained Lutz Langner, manager of mechanical processing at BBS.

Series tests to obtain the desired result

In consequence, for a long time the Schiltach wheel manufacturer searched for an appropriate technique which could be used to clean the pressing rollers during the production process. “We tried out dry ice in tests but couldn’t obtain a usable result,” said Lutz Langner. He stumbled on the answer by chance: a colleague from the painting industry who had attended PaintExpo 2008 gave him the visiting card of a member of staff working at acp – advanced clean production GmbH, a company which develops, manufactures and sells CO2 snow jet cleaning systems. “I then found out some information about the technique – also from a company which implements the process. As the information was very positive, we carried out cleaning tests in cooperation with acp and were able to achieve the cleaning effect we’d been looking for,” the divisional manager stated.

Effective cleaning with liquid carbon dioxide

In contrast with CO2 pellet cleaning, the snow jet cleaning process developed by acp utilizes liquid carbon dioxide as a blasting agent. “Using liquid carbon dioxide for the jet has a great advantage. It’s much easier to handle, store and feed than ice pellets,” remarked Langner.

The core of the system is the patented cleaning head which is a supersonic two-component nozzle. The liquid carbon dioxide expands on exiting the nozzle to form a mixture of snow and gas which is the core jet. Compressed air is added as a jacketed jet and this accelerates the CO2 crystals to supersonic speed. This gives a much better cleaning result that that obtained using a single-component nozzle and also requires considerably less carbon dioxide.

CO2 snow is non-toxic and non-combustible and removes solid and filmy contamination through a combination of mechanical, chemical and thermal properties. It is a dry process which leaves no residues. On impacting on the surface to be cleaned, the snow crystals turn into a liquid state and then sublimate. The resulting sublimation impulse detaches the fine particulate contamination present and carries it away. In the liquid phase, the environmentally-neutral carbon dioxide works like a solvent and removes filmy coatings or contamination. Additionally, the tiny snow crystals have a low degree of hardness, making this a very gentle cleaning process.

Easy integration into the flow forming machine

Lutz Langner sees a further advantage in that the cleaning system can be integrated problem-free into the processing machine. Two cleaning heads are installed inside the machine using magnetic holders and hose lines added for compressed air and carbon dioxide. “To enable the cleaning process to run automatically, we’ve coupled the cleaning module controls with our machine controls. “Not only was it easy to integrate the system into our production line, it’s also very user-friendly”, Langner concluded.

photo BBS Radschnitt:

During the flow forming step, aluminium flanges fabricated in the casting process are shaped on a rotating cylinder using special tools to create a cavity and then joined together using the latest laser welding techniques.

photo: acp_BBS machine

Aluminium adhering to the pressing rollers is cleaned off by two CO2 snow jet nozzles integrated into the machine while production is running to avoid having to stop the wheel manufacturing process.

photo BBS Rad klomplett:

The air inside technology developed by BBS reduces weight significantly, in some cases by several kilos per wheel. At the same time, resistance to flange deformation increases by up to 60 percent.