Gears can be classified according to tooth shape, gear shape, tooth line shape, surface where the teeth are located, and manufacturing methods. The tooth shape of the gear includes tooth profile curve, pressure angle, tooth height and displacement. Involute gears are relatively easy to manufacture, so among the gears used in modern times, involute gears account for the absolute majority, while cycloid gears and arc gears are less used. In terms of pressure angle, gears with small pressure angles have a smaller load-carrying capacity; gears with large pressure angles have higher load-carrying capacity, but the load on the bearing increases under the same transmission torque, so it is only used in special cases. The tooth height of the gear has been standardized, and the standard tooth height is generally adopted. Displacement gears have many advantages and have been widely used in gear processing of various mechanical equipment.
In addition, gears can also be divided into cylindrical gears, bevel gears, non-circular gears, racks, and worm gears according to their shapes; they can be divided into spur gears, helical gears, herringbone gears, and curved gears according to the shape of their tooth lines; they can be divided into external gears and internal gears according to the surface where the teeth are located; The manufacturing material and heat treatment process of the gear have a great influence on the load-carrying capacity and dimensional weight of the gear.
Before the 1950s, carbon steel was mostly used for gears, alloy steel was used in the 1960s, and case-hardened steel was mostly used in the 1970s. According to the hardness, the tooth surface can be divided into soft tooth surface and hard tooth surface. Gears with soft tooth surfaces have low load-bearing capacity, but are easier to manufacture and have good running-in performance. They are mostly used in general machinery with no strict restrictions on transmission size and weight, and small-scale production. Because the small wheel bears the heavier burden among the paired gears, in order to make the working life of the large and small gears roughly equal, the hardness of the tooth surface of the small wheel is generally higher than that of the large wheel.
When processing external gears, the teeth and grooves of the tooth roots of non-ground gears must be pre-machined by pre-grinding hobs
The difference between pre-grinding hobs and ordinary hobs is that the top of the teeth of the pre-grinding hob adopts the tip of the tentacles, and a certain amount of undercut will be generated during the generating process of the tooth root circle of the gear.
In the same way as above, the pre-grinding gear shaper cutter must be used to pre-process the tooth profile when machining the non-grinding tooth root circle part of the inner ring gear.
For the selection of pre-grinding hobs, pre-grinding hobs can be divided into single-arc and double-arc. The processing quality of tooth root fillet, grinding boss and tooth root surface has a great influence on the bending fatigue strength of the gear. When conditions permit, it is recommended to use a single-arc tooth root, that is, use a single-arc pre-grinding hob for tooth profile preprocessing.
For the selection of pre-grinding gear shaper cutters, pre-grinding gear shaper cutters and pre-grinding hobs are the same, so I won’t repeat them here.