The white silicone cover on the feeder protects the electronics –
without interfering with the vibrations conveying the dry bulk.
The German company Coperion operates worldwide and has a manufacturing base in Switzerland. Coperion makes extruders for the plastics and food-processing industries and provides end-to-end material handling solutions. Its subsidiary, Coperion K-Tron, in turn, specialises in process feeding and pneumatic conveying. In addition to the plastics and food-processing industries these systems have applications in pharmaceutical companies. The product range includes vibratory feeders, “These feeders are designed for high-precision dosing of free-flowing dry bulk - for example, for extruders,” explains Coperion engineer Urs Helfenstein.
New solutions found together
Coperion came to Angst+Pfister for a moulding to cover a feeder drive – and already had a clear concept of what the part should look like, and provided a sketch for the part. It had to be silicone and attached on the underside by means of a metal plate to provide a tight seal. The walls of the silicone cover needed to be transparent or at least semi-transparent – and therefore thin. The serial number and construction year plate had to be easy to read through the silicone so that during servicing the cover would not have to be removed and replaced in a time-intensive procedure. In general, the thicker the silicone the milkier it becomes. In other words, the walls could not exceed about two millimetres in thickness. A further function of the integrated metal plate was to stop the thin protective cover from slipping off, or shaking like jelly, when the dry bulk is moved forwards by means of vibration. The design for the silicone part involved two of Angst+Pfister’s specialities: sealing technology and antivibration technology.
This was a hard nut to crack for Angst+Pfister’s engineers: the complex structure, a length over fifty centimetres, the specification for transparency and the United States Food and Drug Administration special approval requirement. “The thing that really caused us a headache during the feasibility study was the integrated metal plate and the rubber-metal connection,” says Marcello Gisler, Product Application Engineer for Angst+Pfister’s Sealing Technology department. He knew solutions could be found for all the other issues. In fact, it is virtually impossible to find a manufacturer for such a large and complex silicone moulding. It requires massive tools and the right sort of machinery. “But we found what we were looking for in our vast network of first-class contacts,” continues Marcello Gisler. The moulding not only had to be large but also of exceptional quality. Firstly, it could not have any tiny air bubbles that might diminish transparency. Secondly, the surface had to fulfil strict hygiene specifications. The cover also needed to protect from dirt and spills so the equipment could be cleaned correctly.
“From our point of view, the challenge was to design a vibrating machine with as little damping as possible that prevented a build- up of dirt and could be cleaned easily,” recalls Urs Helfenstein.
Alternatives that pay-off
“Our idea was to lose the metal plate – for reasons of cost and ease of manufacture. Instead, the cover could be fixed to the metal sheet underneath by means of silicone plugs. At the same time we proposed a silicone that is so transparent that the plate underneath could still be read regardless of the thick walls,” says Tugba Bilgic Tune, Engineer Sealing Technology at Angst+Pfister. In turn, the customer carried out a vibration simulation on this design and positioned the silicone plugs – with good results and the metal insert component really could be omitted.
The engineers chose a translucent silicone rubber (VMQ) for this design with a Shore A Hardness of 50. It has FDA approval in accordance with Title 21 CFR (Code of Federal Regulations) 177.266 a) to f) for elastomer articles. This means it is included on a positive list and has passed migration testing. This material with its superior transparency enabled Marcello Gisler and Tugba Bilgic Tune to increase the silicone wall thickness and dispense with the metal plate.
Coperion tested the design first with a prototype produced using the vacuum casting process. The customer gave the go- ahead for the idea – without the metal plate, the cover could be made at a significant cost reduction. “We are very happy with the outcome,” says Urs Helfenstein. The dialogue-based approach produced good, workable solutions.
Design and hygiene regulations
Tugba Bilgic Tune und Marcello Gisler even came up with a convincing solution for the hygiene and cleaning issue in the design. “The cover was pressed onto the feeder under tension so that the internal electronics remained hermetically sealed,” reveals Tugba Bilgic Tune. As a result, a closed system was created. The silicone cover prevents ingress of dirt to the grooves. This keeps cleaning to a minimum. Coperion verified with tests that no liquids entered the equipment and, as such, that it complies with the strict hygiene design stipulations of the food and pharmaceutical industry. “The cover envelopes the whole drive mechanism without gaps or cracks,” observes Urs Helfenstein. For customers, this means a more efficient cleaning cycle and the hygiene risk, which can have serious consequences, is minimised. “Coperion and Angst+Pfister are both members of EHEDG and have the required expertise for hygiene applications,” says Marcello Gisler. EHEDG is a European trade association that promotes hygiene in the food processing industry.”
Ultimately, Angst+Pfister was able to supply the three-dimensional silicone cover between 30 and 54 centimetres in size. “We are delighted by the good and cost-efficient solution to the challenge we faced.” – concludes Urs Helfenstein.
«The cover was pressed onto the feeder under tension so that the internal electronics remained hermetically sealed.»
Tugba Bilgic Tune, Engineer Sealing Technology, Angst+Pfister Group
«Coperion and Angst+Pfister are both members of EHEDG and have the required expertise for hygiene applications.»
Marcello Gisler, Product Application Engineer Sealing Technology, Angst+Pfister Group
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published: Feb 8, 2021, 9:18:00 AM by: Angst+Pfister Group