The Electric Motor

DOCUMENTATION OF THE PRODUCTION PROCESS OF ELECTRIC MOTOR COMPONENT PARTS INCLUDING MACHINES USED AND PROBLEMS FACED

FRAME

This is produced either by rolling or casting.

ROLLED FRAME

Mild steel sheets of required thickness (3mm; 5mm) are cut to the required size (eg 10mm?)

The sheets are then rolled in a rolling machine to form the casing. Research institutes and manufacturing companies and establishments with good machine shops, like PRODA, Railways, etc. have rolling machines which can be used to produce this.

After rolling, there could be a problem of putting the laminations in the frame as has been experienced by some motor producers. The laminations are clamped together and are put in the frame and the frame welded at the bottom. Stoppers are welded in order to hold the laminations.

The laminations already in the frame are shellacked thinly by pouring shallack over the laminations.

CAST FRAME

This is useful where companies want to copy, reproduce or adapt a particular product. The motor frame to be copied is taken to the ceramic production mould making section where available, and using a p.o.p. based mixture (p.o.p., cement and talc) sections of the frame are moulded. These sections are later joined together to form the mould for the frame. The frame is then cast in aluminum or cast iron as the case may be using the mould. Heat treatment and machining should then follow. This method has been tried and tested.  

Laminations are then forced into the cast frame. The Laminations are pushed into the frame and pined on three sides.

STATOR/ROTOR LAMINATIONS

The production process is in this order; A die is first produced. Using a press, the required laminations are stamped out. Scrap Laminations purchased from the scarp market can also be procured if they meet your design specifications. Alternatively you can order laminations from manufacturers giving them your design and your specifications to meet your objectives. Depending on the size and design of the motor, approximately 180 -200 laminations or more will be enough for a motor of about 5hp or less. If you are recycling laminations, they have to be cleaned using steel brush or metal brush or iron brush. This will help remove any dirt or  rust. These laminations are shellacked (Vanished) individually by dipping them in a thick shallack. They are left to dry. It is usually to dry both sides alternately. It is possible to produce the rotor laminations ourselves using basic machine shop equipment. Although it may not look very flashy, It will work electrically once the design is correct.

 

SHAFT PRODUCTION

A shaft is produced to the required dimension in the Machine shop to fit the rotor bore. A similar sized shaft could be copied. Remember to use the right material preferably carbon steel to make sure that the motor can drive a load. Remember to put key and pulley extractor grip. The shaft should be heat treated for safety.

ROTOR PRODUCTION

Conductor Embedding

Stack the Lam inations on the Shaft. Clamp, shallack (thinly ie pour the shallack over the assembly). Allow to dry for about 2 hrs. Using masking tape cover the teeth so that the slots will be free for conductor embedding.

End Rings

Dip in sand mould  - in the  foundry

Remember the POP mould made for the end rings

Make POP mould for the end rings. It is good to copy straight from a similar size of rotor or you can make a design of your own or produce a prototype from a material which is easier to handle which can then be copied.

In making the POP mould, remember to account for the gate ie where the metal will be poured into and from where it will flow. This is a basic foundry practice. Make provision for air bobbles and escaping air. Pressure die casting is preferred; but were not available, gravity casting can be used. The aluminum is superheated and then poured (gravity) and left to cool. The rotor is dressed and skimmed to make it look nice and fit appropriately as designed and specified.

STATOR / ROTOR LAMINATION

To stack the stator Laminations, we use the following method:

Use 3 (three) bent rods to fit into three slots at 120^o apart

For the rotor laminations, we use a scriber to guide it onto the shaft. All these can be automated using precision machines. The guided laminations have to be aligned. These are then clamped using two clamps at both ends. Wood is used at each end to protect the metallic laminations from the vice. The clamping is necessary for binding. Remember that the shallack is poured on this assembly and allowed to dry. Again clamping will reduce air gaps and air bobbles between the laminations and increase efficiency. Dynamic balancing is important

STATOR WINDINGS

The winding design, former design and winding specifications and diagram have been made. The coils are made to specifications using a coil winding machine. We have a manual winding machine incorporating a counter.

The Foundation NOMEX ie base NOMEX (is cut and used to line the stator slots) this shape has been found better than the rectangular shape                                          This is used to line the slots and provide insulation between the coils and the                                                 laminations, at the base of the slots. The coils are slotted in with the terminal block                                    in mind. The end and start wires are to be positioned at the (end) Face of the motor having the terminal block.

Leadroid is put in again on top of the coils for insulation from the top of the stator teeth. All this is to prevent earth leakage. The coils are slotted in carefully in a coil of 170 turns, about 20 turns may be put in at a time using a stick for dressing the coils.

The Overhang of the other end is bound (ie. the end not having start or end wires) Paper myler or thin Leadroid is used to insulate each group of coils from the other before binding.   The connections are made usually end – end, start to start.

With 2 leads brought out in each group of coils. The above is a 4 pole motor.

For  2 poles:

Connecting:

For Connecting, we first scrape off the resin used to insulate the wires and then use solder. Sleeves are used for further insulation of the connected portions.

Cables:

Cables are connected to the relevant wires and brought out to the terminal block.

The motor is tested. Using a mega we test for continuity, and insulation of one phase from another, earth leakage etc.

When all faults are cleared, we test the motor. It runs and then we disassemble and shallack the windings.

Shallacking:

Pour thin shallack over the windings and allow to dry in an oven for 6hrs ~ 50^oC. In our own case the oven was bad so we dried in sunlight ~ 35oC for 2 days. Assemble for test run. Is the motor heating? No. Why?