Sometime you should watch the blue smoke from a cigarette laze its way through the air, moved about by air currents until it finally disappears. Actually, the fine particles in the smoke settle out to become dust. Certain types of dust such as taconite and cement have particles so fine that they approach the size of smoke particles. Protection against such fine particles is required.
Taconite is a low-grade iron ore found as a hard rock. Before it is transported to steel mills it is concentrated to pellets in processing plants. The amount of airborne taconite dust in these processing plants will vary depending on the amount of dust abatement equipment available. This dust is highly abrasive and harmful to windings and bearings.
Once the iron rich particles enter an electric motor, they become magnetized by the electrical field and cling to the winding and rotor gap. Those particles that find their way into bearings and gears act as a pumice. When such dusts contaminate equipment the road to failure is under construction. Oil offers no protection since fine particles become suspended in the oil and continuously cycle through bearings.
Inherently an excellent seal, grease traps the particles before they can reach bearings. In a large grease reservoir, bearing protection is effective, however, extremely large quantities of such dusts fill the grease fairly rapidly and frequent re-lubrication is required for optimum protection.
Preventive maintenance may not be performed faithfully, hence it becomes necessary to provide seals which will give protection in the severe dust atmosphere. There are several practical sealing methods which are used depending upon the application and mounting position of drive equipment.
Our position on combating dust atmospheres is to provide "Taconite Duty". For general taconite duty applications items below must be met:
Note: If the application is severe duty (high concentrations of ore) Inpro-Seals™† must be used.
†All non-Nidec Motor Corporation marks shown within this document are properties of their respective owners.