In the past, except for the use of electric winding machines, winding manufacturing was mostly done manually, which was labor-intensive, inefficient, and costly. In recent years, countries have been actively researching and improving these methods. Various winding machines, slot insulation machines, slot mold insertion machines, end forming machines, and binding machines for small motors , as well as coil forming machines and wrapping machines for medium and large motors, have been put into production. Many countries have also developed automated production lines for small motor winding manufacturing.
Insulation processes have also seen significant improvements. Ms. Can has compiled some information she has gathered today and will share it with you.
Coil manufacturing
In coil manufacturing, the speed and automation of winding machines are constantly improving. Foreign automatic winding machines can reach a winding speed of up to 2500 turns/minute and can wind two types of conductors simultaneously. They can automatically count turns, cut wire, and wrap insulation tape. They can also automatically stop when a wire breaks or a malfunction occurs. To match the pull-in automatic coil unwinding machine, the wound coils are changed to a single row, and the winding die structure is also changed accordingly. It can wind multiple sets of coils simultaneously without disassembling the winding die, and the wound coils can be directly pulled into the stator slots.
Slot insulation and slot mold processing
In terms of slot insulation and slot mold processing, many countries have adopted automated processing and automated slot insulation machines, which can insert 2 to 3 slots per second; slot mold machines can insert 1 slot per second. Some small motors use epoxy powder welded slot insulation, which is produced on automated lines, and each unit only takes 6 to 8 seconds.
Winding Embedding
In recent years, pull-in type automatic stator winding machines have been developed for winding insertion. Initially used for single-layer windings, they can now be used for double-layer windings. For example, there is a horizontal two-station automatic winding machine where the stator core is mounted on a slide plate. After the lower layer coil is pulled in and the interlayer insulation is inserted at the first station, the slide plate sends the stator core to the second station. A shaping die is used to press the end of the winding near the pull-in head outward into a flared shape, and then it returns to the first station to pull in the upper layer coil and insert the slot die.
In recent years, electromagnetic impulse winding machines have been under development both domestically and internationally. This type of machine utilizes capacitor discharge to generate a large pulse current within the stator coil. Through electromagnetic force, the conductor is pressed tightly against the bottom of the slot, while the coil ends simultaneously open outwards. By appropriately controlling the pulse energy, the conductors can be wedged together after being stretched, preventing loosening and increasing the slot fill factor to 90%. This method is suitable for embedding three-phase double-layer windings and single-phase main and auxiliary windings; that is, the lower layer coil or main winding is first pressed tightly against the bottom of the slot, and then the upper layer coil or auxiliary winding is inserted.
Mechanized winding end shaping: In addition to the electromagnetic impact method, mechanical shaping devices can also be used. A bowl-shaped molding mold covers the outer periphery of the winding end, and a rubber expansion tire is placed inside. A press is used to apply axial pressure from both ends, and the expansion tire expands outward to press the end into the required size and shape.
Mechanized winding end binding: One type of foreign end binding machine uses a lead wire awl for interlocking knitting, capable of threading 100 needles per minute. Some binding machines are equipped with an integral program control device, allowing for multi-layer binding according to a predetermined pattern; other automatic end binding machines utilize two needle bars for descending and ascending, and two knotting rods for advancing and retracting, enabling simultaneous binding of both ends of the winding.
Insulation treatment
In recent years, in terms of insulation treatment, countries have conducted a lot of research and reform on motor winding insulation treatment processes, based on comprehensive requirements such as saving impregnation materials, shortening impregnation and drying time, and striving to improve insulation quality, working conditions and environmental hygiene.
Currently, the drip impregnation process for small motors is relatively mature and widely used. Other impregnation methods include spray impregnation, where the motor stator is mounted on a special rotating device, heated to 115-120°C for 2 minutes, and resin is sprayed from a pressure cylinder onto the rotating stator windings. This process takes approximately 1-2 minutes, during which the resin penetrates the windings under pressure and overflows into the stator's inner diameter. A rotating rubber wheel is then used to evenly coat the inner wall of the stator with a thin layer of resin, ensuring adhesion to the slot mold. Finally, heating is applied to cure the resin. Its main advantages are relatively simple equipment and short impregnation time. It can be used to process stator windings for motors of several hundred kilowatts.
Another method is centrifugal impregnation. This uses fast-drying solvent-free polyester varnish. To impregnate the stator windings, special clamps seal the winding ends and hold the core in place. The system is rotated at high speed, allowing the resin to penetrate the stator slots and winding ends, and then rapidly cure under heat. The impregnation temperature is room temperature or 50-70°C. The entire impregnation process takes only 5-8 minutes. The powerful centrifugal force removes all air bubbles, resulting in a dense, void-free filling. It also eliminates the need for slot film and interphase insulation. For motors below 2 kW, this method is more economical than vacuum impregnation. For motors above 2 kW, while the cost savings are not significant, labor productivity is greatly improved. Another method is funnel casting. When used for DC armature windings, the armature is held upright, a funnel is placed on top, and the required solvent-free resin varnish is poured in. The hardener content is adjusted so that the resin begins to gel within the armature as soon as it is completely poured in. The armature is then rotated horizontally to achieve curing, preventing resin accumulation on one side and maintaining balance.
Thermoplastic winding manufacturing
The thermoplastic winding manufacturing process is characterized by the use of self-adhesive enameled wire with a thermoplastic coating, approximately 0.023 mm thick. Phase insulation, interlayer insulation, and phase mold are also coated with thermoplastic coatings, approximately 0.015 mm thick. During baking, pressure mechanisms are applied to both ends of the stator and the inner hole to press the conductors within the slots tightly. After heating, the thermoplastic coating on the enameled wire and slot insulation melts, making the winding a single unit. Before cooling, a layer of polyester coating is applied to provide moisture and chemical corrosion resistance, suitable for winding insulation below 5 kW. Baking time is 10-45 minutes. This process reportedly saves 8% in cost compared to the impregnation method and 14% compared to the drip impregnation method.
High-voltage coil insulation improvement
Improvements to high-voltage coil insulation tend to replace general epoxy with heat-resistant epoxy, and significant progress has been made in the application of Class F insulating adhesives. The main focus is on developing insulating materials with excellent processability (long shelf life, wide range of process parameters, and good processing performance), and adopting new baking and curing technologies (such as far-infrared heating). For medium-sized high-voltage motors, the use of a continuous, integral impregnation process with low-adhesion mica tape insulation has become a global trend.
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