Designers at Alfa Laval Agri, selected a magnetic plastic for the company’s latest milking machines
Engineers at Alfa Laval Agri have developed a new pulsator – the element at the core of modern cow milking systems – which has at its heart injection-moulded polymer magnets.
Designed by Hans Olofsson – the agricultural company’s master engineer – the pulsator uses valves around the outer wall of the suction cup to create the required vacuum for milking by introducing a series of plastic strips back and forth over the air chambers within the pulsator.
In order to generate the reciprocating movement on the valve axle, some form of magnet was required at the end of the axle. However, conventional metal industrial magnets were considered unsuitable by the design team for a number of reasons.
The main problem was that a great deal of precision work would be required during assembly to fit a metal magnet into a cut-out on the axle of the vacuum-generating ribbon holder in the pulsator.
Olofsson and his colleagues thus settled on an injection moulded magnet material from Sura Magnets.
The team discovered that Sura’s material possessed the required characteristics without the need for adding precision assembly to the manufacturing process. By means of a double injection of the ‘normal’ material used for the valve axle, complemented by the magnetised plastic at the end of the trunnion, a complete finished product was made in a single production process.
The injection moulding of the magnetic plastic material does impose demands on the moulding sequence. The magnetic material in the liquid plastic must be given a particular orientation in order to create the north and south magnetic poles. Sura’s solution is expected to have spin-off applications Firstly, material A is injected in the first cavity, the tool opens and the semi-finished part is moved (by rotation of the tool) to the second cavity and material B is injected on/over the material A. The magnetic material is orientated by a magnetic field in the cavity, which is created by an external field.
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