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Heat shrink containement tubes to fix and protect against corrosion magnets in BLDC brushless motors

Heat shrink containement sleeves for fixing the permanent magnets of BLDC  brushless motors and protecting them from corrosion


In recent years brushless motors have come to represent an important innovation in the field of electric motors. Through the introduction of permanent magnets made with alloys containing rare earths such as Neodymium and Iron Boron, despite their small size, these motors are able to develop 50% more torque than conventional motors of the same size.


Moreover, brushless motors enable a reduction in energy consumption, have higher speeds, require less maintenance, dissipate heat better, have a lower moment of inertia, can be overloaded and are more reliable.


SPM (surface permanent magnet) brushless motors also have an inertia that is 20-30% lower than IPM (interior permanent magnet) brushless motors and their only real drawback was their increased cost.


This higher cost was due to the complexity of fastening the magnets and the difficulty in automating fixing of the permanent magnets externally to the rotor, also due to the fact that they are made of a material that cannot be welded.




To overcome these problems Politubes, in collaboration with DuPont, developed a special spiral-wound tube made of heat-shrink polyester (Mylar HS) covered by patent EP 2763283 B1, which makes it possible to automate fixing of the magnets, reducing the production costs of these motors and making them much more competitive.


Our sleeve retainer is fitted over the rotor with the magnets in position and heat-shrunk instantly, to obtain firm cohesion of the magnets to the rotor even at high rotation speeds.


It must be stressed that, unlike more costly steel or brass rings, our spiral-wound tube also covers and protects the ends of the magnets, which are also subject to corrosion and which, if chipped, can cause the motor to seize.

In motors that use annular magnets obtained by compression molding of Nd-Fe-B with the addition of thermosetting resins (plasto ferrite) Neodymium Iron Borum , our tube also protects the magnet from corrosion, in view of the fragile nature of the alloys used, preventing the motor from seizing.

Our tubes delay as well the moment when the glue used to fix the annular magnets to the rotors, begins to work and oppose to the radial force.


The special polyester used reaches the point of maximum hardness upon completing the heat-shrinking process, thereby guaranteeing an excellent mechanical seal.

The spiral-wound polyester film is perfectly suited to this application, also due to the fact that brushless motors usually do not operate at very high temperatures, as the majority of permanent magnets would become de-magnetized. Our tube is used at operating temperatures of around 130-135°C, with peaks of up to 155°C.


The fact that the tube is perfectly round also guarantees balancing of the rotor.

This special tube has internal diameters ranging from 15 to 131 mm; thicknesses are very low and vary from 100 to 250 microns.

Even after heat-shrinking, the tube does not interfere with the air gap and with the magnetic flux of the motor, allowing it to achieve the maximum performance for which it was designed.

This simple, rapid and efficient solution is patented and has already been well and successfully received throughout the world by many leading companies in the field, after years of rigorous stress testing.


The adhesives, carefully selected during our forty years of expertise, comply with all REACH and ROHS standards and ensure that the films used maintain their original properties.


The Politubes technical department is at your service to listen to your needs and offer made-to-measure innovative solutions.



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