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Vacuum drying: It all depends on the pump

Many production lines of VW engine plant in Salzgitter are equipped with integrated stations for parts cleaning. A vacuum drying system is part of each cleaning station. Vacuum in the vacuum chamber is generated by Elmo Rietschle screw vacuum pump – a cost-effective and proven solution.

Elmo Rietschle case study VW image 1

The engine plant in Salzgitter is the main engine plant. The employees assemble up to 7000 Otto and diesel engines for cars and utility vehicles in a day. The engine range covers three cylinders to 16-cylinder engines in series, V and W engine design with engine output starting from 55 kW.

The mechanical production of the plants includes processing core engine components such as cylinder head, cylinder crankcase, crankshaft, camshaft and piston rods as well as production of mounting parts, modules and small components for the engines.


Increasingly higher performance requirements for modern combustion engines and the associated components, achieving higher environmental objectives for product and manufacturing and energy saving strategies of the group require continued development of production technologies in mechanical processing. The component cleanliness of engine components plays a very important role.

High requirements for component cleanliness

VW Group has defined very high standards for component cleanliness, which are applicable for each component and adherence to these standard is possible only with corresponding cleaning technology and techniques.

The core cleaning technique used in Salzgitter plant is based on cleaning with liquid media. More than 130 cleaning systems based on liquid media are used here. Many of these cleaning systems are used for washing processes, wherein 100% component drying must be achieved after wet cleaning.

In very demanding components such as cylinder heads and cylinder crankshafts, this requirement can be achieved only by using vacuum drying - from a technical and process perspective - due to complex external geometry with numerous hollow spaces, holes in the component.

The design of the vacuum drying stations is standardised just like the cleaning systems. Vacuum pumps are used to generate the required vacuum in the chamber. During the vacuum drying process, the component, which has residual moisture on the surface as well as in holes and threads, is exposed to vacuum pressure in a closed and sealed chamber.

This vacuum pressure lowers the boiling temperature of water. The water residues on the component are vaporised even at low temperatures. Holes and surfaces on the component are thus freed of water (dried). With the vaporisation of water residues, thermal energy is removed from the component, which also has a secondary effect of cooling the component.

Elmo Rietschle case study VW image 2

From oil-lubricated rotary vanes to screw vacuum pump

Originally rotary vane pumps were used for vacuum processes in washing systems to generate vacuum. In a cleaning system for cylinder head or cylinder crankshaft, two rotary vane vacuum pumps with approx. 7.5 kW pump output each must be used due to component geometry and size and due to short cycle times of the system in each washing system.

Peter Tomaschewski from the maintenance department of Salzgitter plant: "This required heavy investment in time and costs, which we wanted to reduce - especially when some of the wear parts such as oil separator element require separate disposal. In addition, each maintenance activity also required complete shutdown of the system to carry out maintenance".

Rotary vane vacuum pumps were in focus even with regard to lower service life and unachievable process safety. Therefore, an alternative pump system was checked and tested in Salzgitter plant in 2007 and it was found to be very efficient.


Performance of S-VSI

Due to very good vacuum performance of S-VSI,
time required to dry the cleaned parts is reduced
by 25%.

Comparative costs of dry running screw vacuum pump and oil-lubricated vacuum pump

Comparative costs of dry running screw
vacuum pump and oil-lubricated vacuum pump

Shorter drying time, lower energy requirement

After intensive market research and long test phases supported intensively by Gardner Denver, the decision was made to buy oil-free screw vacuum pump S-VSI 300 from Elmo Rietschle/Gardner Denver.

As dry running pump it can do the job without any oil supply and delivers maximum final vacuum of 0.1 mbar (absolute) with a vacuum capacity of up to 360 m3/h. This creates good conditions for shorter evacuation times, which is absolutely necessary in In-Line drying.

Significant improvements and savings can be achieved with the screw vacuum pump technology. The number of required vacuum pumps was reduced to one pump per system instead of earlier two pumps, because the screw vacuum pump is more effective and safer. This also resulted in reduced energy requirement of approx. 7.5 kW engine output for each washing system.

Even the overall service life of the pumps is very satisfactory. Higher initial investments are amortised due to fewer system downtime and heavily reduced maintenance requirements. The screw vacuum pumps have a maintenance interval of 7500 operating hours and this is three times more than conventional rotary vane pumps.

 

Peter Tomaschewski also mentions another benefit of the new pump standard: “Oil-free pump operation is much more positive from an environmental perspective, because we do not have to dispose large quantities of used oil and oil separation elements. Even air quality in the plant has improved significantly with oil-free pumps, because there are no oil vapours which was often the case with conventional rotary vane pumps”.

Joint improvement initiative: Pump with recirculation cooling

Pump S-VSI 300 with integrated recirculation cooling


Collaboration was so good that Elmo Rietschle also developed customer-specific variant of S-VSI 300 based on request from Volkswagen. Sven Finger, Planning Cleaning Technology in VW engine planning division at Salzgitter location, says: “We are always looking for improvement opportunities. Normally pumps require a coolant connection. However, it is very difficult to implement in some cases. There we are using pumps with circulation cooling”.

For this variant, Elmo Rietschle has installed an air/ water cooler so that the pump can be used as “Plug and Play” solution without external coolant supply.

 

As the Volkswagen works on “Best Practice” principle across all its plants, “Twister” pumps from Elmo Rietschle is not only installed in parts cleaning system in Salzgitter. The screw vacuum pumps are also used in VW plants in China, Mexico and Poland.

Overview of added value

  • Dry running vacuum pumps without oil supply with adequate vacuum capacity and final vacuum for shorter evacuation times in In-Line drying
  • Only 1 screw vacuum pump instead of 2 pumps per system reduces electricity requirements and maintenance costs
  • Longer maintenance intervals, demonstrably fewer failures and higher service life of the new pumps
  • Customer-specific modification by installing a recirculation cooling with Elmo Rietschle as “Plug and Play” solution without external coolant supply
  • Models with integrated cooling have become standard across the company in accordance with “ Best Practice” principle and they are also used in other plants
en-UY