Bonding of the windings

Bonding of the windings

The “bonding of the windings” by Joule heating is performed in order to eliminate impregnation with paints or resins and to block and better insulate the windings of small-medium stators of electric motors, with considerable savings in terms of costs and time.

Indeed, the bonding of the windings relies on the use of enameled wires coated with an additional layer of thermosetting paint which softens when heated. Thus allowing bonding with the adjacent wires, and polymerizes when the required temperature is reached, therefore stabilizing the process.

This operation allows considerable savings, in terms of

  • material (paints or resins)
  • equipment (ovens and impregnation tanks)
  • energy (since only the copper wire is heated, rather than the entire stator and the air for heating)
  • time, since the operation takes only a few seconds: 15 – 30” (compared to a few hours required for impregnation and cooking in the furnace) and the possibility to proceed with assembly immediately after winding.

Obviously, some precautions are needed in order to avoid quality issues:

  • Use of insulation suitable for the temperature: cables, tubing and binding wires
  • Slot insulation and between windings, made of material impregnated with self-bonding paint to allow total adhesion with the winding and avoid sliding which, due to the effect of magnetostriction, may cause failures in the long run
  • Final head molding, since no changes can be made after bonding. In this regard, after molding, it is necessary to block the windings with suitable systems like: heat-resistant cages, binding with heat-shrinkable wire (preferred system), or, at minimum, molding press during the operation. The molding press, however, can be removed only after the windings have cooled.
  • Another point to consider is the type of terminals that allow good contact (which our machines guarantee). For example: wires, FASTON or dedicated terminals, given the high circulating current.

Standards associated with this test

The list of standards available by using our equipments.
Non ci sono normative per questa macchina.

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Avantages of bonding of the windings

In economic terms, compared to traditional impregnation systems the total savings can range from 20 to 35%, depending upon the types of stators.

Indicative values for small motors (these data may vary slightly depending on the type of wire used):

  • Current density: 80 A/mmq.
  • Maximum temperature: 200°C+/- 15 %.
  • Required time: 15 – 30 sec.
  • Control of the current rising ramp: in the event of interruption or short-circuit, the voltage varies in an abnormal manner and the cycle stops instantaneously
  • As a general rule, the maximum bonding voltage must not exceed 2 – 2.5 times the nominal voltage of the winding, in order not to subject it to excessive stress and generate unnecessary waste
  • Another factor to take into account is the presence of the thermal overload protector connected with the windings of single-phase stators. In this case, our machines leverage a particular system that allows cementing equally, without the activation of the thermal overload protector in order to stop the process, or its damage by excessive circulating current
  • For three-phase stators, depending on currents and resistances, the windings, when possible, can be placed in series or parallel, allowing the use of a single current generator
  • Generally, direct current generators are used, since the current is not affected by the inductance of the windings (as it would happen in the case of alternating current) and, therefore, a lower voltage is required to circulate the same current, with less stress on the wire

Bonding takes place by the JOULE effect for the passage of current, which can have the following characteristics:

  • Constant current: in this case, the current is always kept constant with the increase in voltage, proportionately to the increase in the resistance of the wire due to temperature increase. This system, which is a little more complex from the point of view of the power supply, allows saving a fair amount of time
  • Constant voltage: simpler as a power supply, but with longer bonding times, as the current progressively decreases due to the increase in resistance

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