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Many production lines of VW engine plant in Salzgitter are equipped with integrated stations for partscleaning. A vacuum drying system is part of each cleaning station. Vacuum in the vacuum chamber isgenerated by Elmo Rietschle screw vacuum pump – a cost-effective and proven solution.
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 requirementsfor modern combustion enginesand the associated components, achievinghigher environmental objectives forproductand manufacturing and energysaving strategies of the group requirecontinueddevelopment of productiontechnologies in mechanical processing.The component cleanliness of enginecomponents plays a very important role.
VW Group has defined very high standardsfor component cleanliness, which areapplicablefor each component and adherenceto these standard is possible onlywith corresponding cleaning technologyand techniques.
The core cleaning technique used inSalzgitter plant is based on cleaning withliquid media. More than 130 cleaning systemsbased on liquid media are used here.Many of these cleaning systems are usedfor washing processes, wherein 100%component drying must be achieved afterwet cleaning.
In very demanding components such ascylinder heads and cylinder crankshafts,this requirement can be achieved only byusing vacuum drying - from a technicaland process perspective - due to complexexternal geometry with numerous hollowspaces, holes in the component.
The design of the vacuum drying stationsis standardised just like the cleaning systems.Vacuum pumps are used to generatethe required vacuum in the chamber.During the vacuum drying process, thecomponent, which has residual moistureon the surface as well as in holes andthreads, is exposed to vacuum pressure ina closed and sealed chamber.
This vacuumpressure lowers the boiling temperatureof water. The water residues on the componentare vaporised even at lowtemperatures.Holes and surfaces on thecomponent are thus freed of water (dried).With the vaporisation of water residues,thermal energy is removed from thecomponent,which also has a secondaryeffectof cooling the component.
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.
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
After intensive market research and longtest phases supported intensively by GardnerDenver, the decision was made to buyoil-free screw vacuum pump S-VSI 300from Elmo Rietschle/Gardner Denver.
Asdry running pump it can do the job withoutany oil supply and delivers maximumfinal vacuum of 0.1 mbar (absolute) with avacuum capacity of up to 360 m3/h. Thiscreates good conditions for shorter evacuationtimes, which is absolutelynecessaryin In-Line drying.
Significant improvements and savings canbe achieved with the screw vacuum pumptechnology. The number of required vacuumpumps was reduced to one pump per systeminstead of earlier two pumps, because thescrew vacuum pump is more effective andsafer. This also resulted in reduced energyrequirement of approx. 7.5 kW engine outputfor each washing system.
Even the overall service life of the pumpsis very satisfactory. Higher initial investmentsare amortised due to fewer systemdowntime and heavily reduced maintenance requirements. The screw vacuum pumpshave a maintenance interval of 7500 operatinghours and this is three times morethan conventional rotary vane pumps.
Peter Tomaschewski also mentions anotherbenefit of the new pump standard:“Oil-free pump operation is much morepositive from an environmental perspective,because we do not have to dispose largequantities of used oil and oil separationelements.Even air quality in the plant hasimproved significantly with oil-free pumps,because there are no oil vapours whichwas often the case with conventionalrotaryvane pumps”.
Collaboration was so good that Elmo Rietschlealso developed customer-specific variantof S-VSI 300 based on request from Volkswagen.Sven Finger, Planning CleaningTechnology in VW engine planning divisionat Salzgitter location, says: “We are alwayslooking for improvement opportunities.Normally pumps require a coolant connection. However, it is very difficult to implementin some cases. There we are using pumpswith circulation cooling”.
For this variant,Elmo Rietschle has installed an air/watercooler so that the pump can be used as“Plug and Play” solution without externalcoolant supply.
As the Volkswagen works on “Best Practice”principle across all its plants, “Twister”pumps from Elmo Rietschle is not onlyinstalledin parts cleaning system in Salzgitter.The screw vacuum pumps arealsoused in VW plants in China, Mexico andPoland.
