Ruf Maschinenbau GmbH & Co. KG

Recovering oil from grinding sludge - Case Study


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Zahnradfertigung Ott uses RUF briquetting unit

A large volume of sludge is produced in the grinding of high-precision gears. In most cases, this grinding sludge is disposed of at high costs. Zahnradfertigung Ott, a specialist manufacturer of gears, found a better solution: since 2005, the company is using a briquetting unit from RUF to recover 500 litres of grinding oil per day from the sludge. Through this measure, it could drastically reduce the disposal costs and also reduce the labour involved in the disposal process.

Zahnradfertigung Ott based in Bodelshausen, is an industry leader as regards know-how, experience, technical expertise and product range. Apart from the worm gear set with patented Ott gearbox for the machine tool industry, the workers at the plant in Bodelshausen mill, plane and grind gears and hollow wheels, which are designed for 5 to 10 MW and classified in the top bracket. They are for example used in large gear systems in ships and wind turbines, ensuring reliable force transmission. Zahnradfertigung Ott has experienced a huge growth over the last few years, especially in the wind energy sector. This does not come as a surprise to Erwin Haag, managing director of the company: 'Wind energy has become a significant technology for today and the future. We identified its potential many years ago and have for the last decade been producing hollow wheels and other components for this industry. As a result, we have acquired a lot of know-how in this field and invested in the relevant technology.'

Manufacturers of wind turbines – and also other customers of Zahnradfertigung Ott – require high-precision products. Apart from milling and planing, gears must thus be processed by grinding. At the moment, the company operates four large-scale profile grinding machines, catering for diameters of up to 3200 mm. They are run 24 hours a day in three shifts, seven days a week. Due to the increase in demand, Erwin Haag has already ordered another profile grinding unit.

While grinding is indispensible to achieve the necessary precision and surface finish, the company would gladly do away with the grinding sludge produced in the process, admits Erwin Haag. This sludge consists of minute metal chips and grinding oil. Depending on its consistency, disposal of the sludge can be very expensive.

'In the past, we attempted to recover oil by processing the sludge in a hand-operated centrifuge. The metal wool of the mixture was then thrown by hand into a container and disposed of against a charge. Nobody liked to do this work, which occupied two people full-time every day“, remembers the manager.

Pay-back time of the RUF briquetting unit: about one year

Just about three years ago, things changed radically: the company invested in a RB 4/2800/60S briquetting unit from RUF, who now deals with the difficult sludge. Zahnradfertigung Ott now saves money in more than one way, as Erwin Haag explains: 'In the old days, we needed two full-time staff to deal with the grinding sludge. With the briquetting unit, all work can be done by a single worker, who fills the sludge into the press, handles the recovered oil and disposes of the metal briquettes, while having ample time to deal with other supply and disposal tasks at the plant. The machine does not need continuous supervision and the recovered grinding oil can be used again. We need less storage space, as the metal briquettes can be easily stacked and we even get some money for our metal scrap instead of paying for its disposal. Taking all this into account, the RB 4 paid for itself within one year.'

The currently used four grinding machines produce about seven tons of grinding sludge per week, as they are operated around the clock. The sludge is continuously transferred to the centrally located briquetting press, which is equipped with a 4 kW hydraulic unit generating pressures of more than 2800 kg/cm². The sludge produced during a day can thus be compacted into convenient briquettes within about a shift an a half.

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