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News / Innovations
Continuous production of stator tubes without joint lines.
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The special pump stator machines in the DESMA D 969 Z2 series have successfully gained a global niche market in recent years. The production of these pump stators involves the continuous production of up to ten metre long steel tubes: they have virtually unlimited injection volumes and are continuously filled with a rubber compound to line the tubes.
In order to pump highly viscous or high solid content media, for example oil, slurries and highly viscous pasty masses, a common solution in industry is to use eccentric screw pumps. The material is transported along the pipe (the stator) by a rotating screw-like rotor. The stator is made up of a steel pipe lined with a rubber compound, the inner contour of which is also spiralled.
In the oil industry, these stators are often up to ten metres in length, with diameters of up to 23 cm. In order to fill pipes of this size, injection volumes of up to several hundred kg rubber compound are sometimes necessary. DESMA 962 /2 series machines are designed to satisfy these kinds of specifications, they feature Twin-inject units. The stator machines have two injection units, arranged using a central temperature controlled nozzle system. The filling of the tubes is on the FIFO principle requiring precision synchronisation by the controller - they are the key factor in ultimate stator quality. This is because the quality of the plastified rubber compound is kept to a high quality throughout because the material is nowhere heated any longer than necessary, nor is it subjected to additional frictional heat.
The production of stators requires the rubber compound to be injected at high pressure into the steel pipe around a clamped steel core followed by sealing. The profile of the core matches that of the spiralled rotor. Once the rubber compound has fully vulcanised - which because of the size of the pipe usually takes place outside the machine (in an autoclave), the core is removed using an extractor.
Perhaps the key factor determining stator quality is the continuous interruption-free injection of the rubber compound having a virtually unlimited injection volume, during which joint lines in the compound inside the pipe are to be avoided and minimised. These weak points, also known as "weld seams", result if flow fronts meet of injected masses which are of different quality and in a different degree of hardness. Such weak points can not only reduce the service life of a stator but also impact on pump performance capacity.
A further advantage of DESMA stator machines is their extremely high injection pressures, which allow the compound to be evenly, continuously and quickly forced into the pipe. In connection with the DESMA-FIFO concept, the fill time is minimised even when processing very demanding and ultra-hard polymers.
 
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