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Woco relies on DESMA technology

Material saving and energy efficient O ring production with new high tech injection moulding

The Woco group is well known as a company which develops and manufactures demanding components as well as complete subassemblies for automotive engineering and industrial applications. Woco develops its functional solutions to improve comfort and safety of vehicles, to reduce vibrations and to seal and separate gaseous and liquid media in the industrial sector by using various kinds of elastomer and plastic material, however, focus is set on polymers.   

During the tour through production at the headquarters in Bad Soden-Salmünster, many complex and filigree elastomer and 2-component parts can be seen that require a lot of know-how, and which partly are produced in sophisticated, linked processes or production cells. But of all rubber injection moulding machines, it is just the new one of Klöckner DESMA Elastomertechnik GmbH, the horizontal D 969.300 of the current S 3 series, fitted with state-of-the-art technology and all refinements, on which O rings are produced, an article which strike as simple at first sight. The initial thought that in this case they would possibly use a steamroller to crack a nut very quickly turns out to be false.   

„The O ring is famous for being the most difficult part to be produced, because it always has parting in the wrong place“, says Dr. Fritz Buschhaus, member of Woco management and Executive Vice President of the Business Unit Polymer Automotive – Engineering, smilingly but referring to a quite serious background. The break of one single O ring may eventually cause the failure of a complete motor or of machines. Buschhaus explains: „With such piece parts, we have to guarantee important functions of the total assembly.“ And this encompasses, so Buschhaus, not only reliable tightness but also uncomplicated mounting. „And something that is easy to plug in can easily drop out if geometry is one hundred percent not totally correct“, says Buschhaus. Therefore the least faults have to be avoided on such simple parts, too, and what is more, this O ring has to endure a lot. It serves as a seal on a plug connection between two plastic parts for turbo-chargers. There it is exposed to strong pressure, aggressive exhaust fumes and high temperatures. This is where even commercial fluororubber is touching its limits. „Due to today's lean motor management, the resulting cocktail becomes increasingly aggressive“, knows Buschhaus. For this reason Woco has developed a rubber compound which is resistant to these extreme conditions. Buschhaus identifies this material competence to be a clear market advantage. 

Production start of the O rings which are manufactured in several different nominal widths was first realized by using standard rubber injection moulding technology. However, very soon it became obvious to the people in charge that the customary hot runner technique would reach a dead end. The waste of material that cropped up due to the fully cured runner spiders could not be justified commercially in the light of such an expensive rubber compound. As a result, it was decided to launch simultaneously a project to produce O rings by using the material saving cold runner technology. 

„When looking back, I can only recommend to add an optimizing project as series production launch to the running production“, says Buschhaus. „When the customer wants to have parts, optimizing works are no longer feasible.“ And as soon as the series has begun, and the piece numbers are rising, it is also getting hard to optimize moulds/processes. 

With DESMA, Woco has brought in a supplier and pioneer of hydraulic valve gated cold runner technology. Together they developed runners aiming at saving material and carried out tests on various DESMA-built sample moulds with hydraulic valve gated standard cold runner block in the process engineering center at Fridingen/Germany headquarters. „We did not start with a production mould at once, but first tested several versions“, explains Buschhaus, „and spare no expenses.“ But it was worth it: as against the standard production, material waste could be reduced by 35 to 40%.  

After the successful test runs, DESMA built the production mould followed by another two moulds for other ring nominal width. „Our in-house moulds shop could have done this, too“, says Buschhaus, „but in this case we decided in favor of DESMA, so that everything is matching.“ In the meantime, all three O rings have been run in and are producing for half a year. Buschhaus reports: „This was one of our first projects with DESMA in the course of which we cooperated very closely.“ In view of the many operative daily tasks, one does not have to and neither is able to tackle such a project on one's own. „And the result definitely deserves praise“, says the delighted Buschhaus. The planned performance data have been achieved and were partly even succeeded. Thus, Buschhaus already regards the DESMA technology as future standard for Woco: „We have already identified new applications for it, and I hope to have three, four or five machines of them here in the very near future.“   

„To us, DESMA was not only machine supplier, but also mould builder and concept provider“, summarizes Buschhaus once again the essential role of the machine manufacturer. The combination of mould shop and cold runner know-how has already proved successful with other moulders, so that advantage could be taken from their experiences as well. „The technical support was excellent“, emphasizes Buschhaus.“ Especially the developing and testing phase in the Fridingen process engineering center represents a big advantage: „Otherwise, we would have had to buy the machine and the cold runner block and to gain our own experiences in operating them by ourselves. This cannot be done casually.“

DESMA was very satisfied with this cooperation as well. Peter Hurrle who took care of the project on the part of the machine manufacturer underlines: „With Norbert Seipel, the manufacturing engineer, we had a competent partner with expertise who was able to provide us with the required input at any time.“ That one is especially glad about this success: „We have once made a negative experience with cold runner blocks. When this issue was raised again because of the expensive compound, some colleagues were sceptical about it. It was a challenge which we solved together with DESMA. The cold runner runs perfectly and is easy to control. It is real fun working with this machine.“ 

The old hand Seipel shows his real pleasure in this project. They also experimented with demoulding. Unlike the procedure we used before, the O rings are brushed out fully automatically. „The brushes are a book with seven seals“, stresses Seipel and reports in depth about different lengths, bristle diameters and material. Eventually, there is an individual brush solution for all different nominal widths and bristle thicknesses of the O rings. 

But the DESMA SEALMASTER at Woco has a lot more to offer yet. „We have not yet brought so much attention to the topic energy efficiency“, admits Buschhaus, „but we have to and will now be increasingly dealing with it.“ But without measuring and differentiated examination of the individual consumer levels, this will remain superficial only. Therefore Woco has the machine equipped with almost every option for energy efficiency offered by DESMA. ServoGear, the first hydraulics concept with servo-drive allows for hydraulic energy to be saved by 45% thanks to the two-pump system. „The longer the cure times, the more this system pays off related to the total energy consumption“, explains Hurrle. They are very short in O ring production replied Buschhaus but stated that they would scrutinize it systematically. In this context the EcoSilence temperature-control units are used as well. In addition to noise emission reduced by 6 dB/A, these units lower energy consumption by 2,000 kWh per year and machine because of their optimized degree of efficiency. Especially the insulated ISO+ heating platens tackle the biggest energy consumer in rubber injection moulding, the heating. Apart from reducing the expensive heat dissipation considerably, they ensure a more even temperature distribution. 

A special highlight for Buschhaus is the EnergyControl option which avoids current peaks by delaying the individual consumers and enables an energy efficient starting up of the machine. „This should be standard in the future.“

The process control Propter which is integrated in DESMA machines as PropterLight as a standard in a 60-day mode has convinced Woco as well. According to Buschhaus, they have gained nice experiences with such systems for two years already and thus they know that this is working with O rings. For this reason they had the Propter full version activated. This opportunity of compound-depending automated re-adjusting of the process appears to Buschhaus to be extremely important. 

And Buschhaus identifies further potential: „Many people mainly look at cure time reduction. But the question is: where lies the optimum operating point and how can I reach it? The short cure time does not have to be optimal.“ But such questions have to be attended by application engineers. Someone has to deal with it, otherwise the expenses of such systems does not pay. „Today's machine technology enables to have a deep insight into the process. We are now able to do so with the new machine and its comprehensive equipment. We will use it! But one should also have staff with time to deal with it in detail“, continues Buschhaus. „For example such a guy like Mr. Seipel who adopted the project as his baby and who ambitiously implemented it“, he praises his manufacturing engineer. Of the same importance to Buschhaus is the process support from the machine manufacturers, just like DESMA perfectly provided it.

For more information see the informative website of Woco Industrietechnik GmbH
www.wocogroup.com