Can anyone explain, how to make moulded commutator?

Question

Commutator is used in DC motor's armature. Moulded commutator are mostly used in small motors, like mixture etc.

Answer 1

A commutator typically consists of a set of copper segments, fixed around part of the circumference of the rotating part of the machine (the rotor), and a set of spring-loaded brushes fixed to the stationary frame of the machine. The external source of current (for a motor) or electrical load (for a generator) is connected to the brushes. For small equipment the commutator segments can be stamped from sheet metal. For very large equipment the segments are made from a copper casting that is then machined into the final shape.

Another important application that often uses a traditional slip ring assembly is packaging machinery. Most packaging machines use some type of commutator or slip ring as a connection to the moving parts that are heated to seal the packages closed after they are filled. Some machines use heated rollers while others use heated crimpers. In addition to passing current to the heater elements, temperature must be maintained by reading data back to a controller, and it's important to conduct the signal with minimal electrical noise. It is desirable to pass the power and the signal through the same rotating electrical connector in order to minimize the number of connector parts that must be built into the machine. The Mercotac Modular Series provides the ideal low cost slip ring for these types of applications. Both power and signal are passed through a single connector with near zero electrical noise. Thus providing accurate temperature control and reliable power transmission.

Another form of slip ring assembly is the signal slip ring. One of the more popular uses of this type of slipring is in video cable inspection reels. In order to inspect underground pipes, a video camera must be attached to the end of a cable that is fed into the pipe for inspection. These cables are stored on reels which feed the signal back to a video monitor. At the junction of the stationary wires feeding the monitor and the rotating cable on the reel there must be a rotating electrical connector with superior transmission capabilities to provide a clean video signal. Many companies that manufacture cable reel inspection systems rely on Mercotac connectors for their slipring needs. The near zero electrical noise and superior transmission of Mercotac sliprings is the ideal solution for cable reel inspection systems.

Each conducting segment on the armature of the commutator is insulated from adjacent segments. Initially when the technology was first developed, mica was used as an insulator between commutation segments. Later materials research into polymers brought the development of plastic spacers which are more durable and less prone to cracking, and have a higher and more uniform breakdown voltage than mica.

The segments are held onto the shaft using a dovetail shape on the edges or underside of each segment, using insulating wedges around the perimeter of each commutation segment. Due to the high cost of repairs, for small appliance and tool motors the segments are typically crimped permanently in place and cannot be removed; when the motor fails it is simply discarded and replaced. On very large industrial motors it is economical to be able to replace individual damaged segments, and so the end-wedge can be unscrewed and individual segments removed and replaced.

Commutator segments are connected to the coils of the armature, with the number of coils (and commutator segments) depending on the speed and voltage of the machine. Large motors may have hundreds of segments.

Friction between the segments and the brushes eventually causes wear to both surfaces. Carbon brushes, being made of a softer material, wear faster and may be designed to be replaced easily without dismantling the machine. Older copper brushes caused more wear to the commutator, causing deep grooving and notching of the surface over time. The commutator on small motors (say, less than a kilowatt rating) is not designed to be repaired through the life of the device. On large industrial equipment, the commutator may be re-surfaced with abrasives, or the rotor may be removed from the frame, mounted in a large metal lathe, and the commutator resurfaced by cutting it down to a smaller diameter. The largest of equipment can include a lathe turning attachment directly over the commutator.

Answer 2

That kind of part is normally manufactured in high volume. With high volume manufacturing, the cost of the required equipment is not high in comparison the total cost of the products made using the equipment. Molds, fixtures and automatic machining equipment is used. The equipment may be designed and constructed by the commutator manufacturer. It might also be designed and/or manufactured by someone else working under contract under the direction of the commutator manufacturer. In either case, the equipment and its design would be considered proprietary to the commutator manufacturer and perhaps a trade secret. An outsider can not easily learn the details of such a process.