The insulating paint of the rotor is mainly used for curing. Generally, when the temperature exceeds 180°, it will melt and become soft. The bungee of the rotor commutator has a critical point of use temperature of less than 200 degrees. Generally, the temperature resistance of the bakelite does not exceed 300°.
We have done an experiment, the starter rotor, when it is not more than 180 degrees, or close to this temperature, the speed reaches 31000 rpm, and the commutator with bad reinforcement will break up.
During the use of the starter, if the start-up time is too long, or the start-up difficult current is too large, the rotor can easily exceed this temperature. It will even be higher.
In addition, the user will find that the vehicle did not respond when it was started for the second time. In fact, the commutator has been broken at that time. That is to say, the engine has been started before the commutator is broken.
Why is this happening?
When the rotor temperature has exceeded 200 degrees, although it has not burned, the insulating paint has become soft and the degree of solidification has weakened. At this time, the commutator bakelite is already in an overheated state, and the firmness is also decreasing. In addition, the temperature of the rotor commutator is the highest due to brush friction. However, when the load of the starter is working, the rotor generally does not rotate more than seven thousand revolutions, which is not enough to break up the rotor with bad reinforcement.