Why can’t the coal grinder run idle for a long time?

During the commissioning of the coal grinder, when it is stopped to drain out the coal powder, or during startup, it needs to run idle for a period of time. However, according to relevant regulations, the idling time of ball mill coal mills must not exceed 10 minutes ； The idling time for each cycle of a medium-speed coal grinder shall not exceed 1 minute. The reason for this requirement is that when the coal grinder is idling, the grinding components come into direct impact and friction with each other, resulting in increased metal wear ； When steel balls collide with each other or with steel armor, the steel balls may break apart ； When metals collide and rub against each other directly, sparks are easily generated, which can also serve as a source of ignition for coal dust explosions. Therefore, the idling time of the coal grinder must be strictly controlled.

I’m not sure what type of coal grinder the person upstairs is referring to. If it’s a roller-type coal grinder, it is strictly prohibited for the grinding rollers to spin idly after they stop moving; idling, whether for a short period or for an extended time, is not allowed. For example, medium-speed roller coal mills. The grinding components (wear-resistant parts) are made of high-chromium cast iron, a material that is prone to brittleness and thermal cracking. Therefore, collision impacts and heating must be avoided. For this reason, in medium-speed roller coal mills, apart from low-speed cranking, startup is only permitted after the grinding rollers are lifted, or after a predetermined amount of coal has been placed on the grinding disc. It is absolutely not allowed to start the machine and let it run idle with no coal on the mill drum (and with the grinding rollers under load).

What’s said on the third floor makes sense; roller coal mills do work that way indeed