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We further subdivide the geometry of worm and wheel gearing by classifying the tooth form. We use a two-letter designator to define tooth form geometry. In addition to the various designations of contact, there are five active profile designations typically used worldwide. They are classified as ZA, ZK, ZC, ZN, and ZI. The various profiles are a function of both design application and manufacturing. The tooth form in part defines the interaction between the teeth. It is generally accepted that one would not mix any of the ‘Z’ designates with any other.
ZA: Worm gear with straight-line (trapezoidal) tooth profile in axial section. The tooth sides are slightly convex in the normal section; the cross-section results in the spiral of Archimedes. The elements in the axial section are usually standardized (i.e. mx=m, ax=a). The gearing is produced using lathes or thread-cutting machines (the worm resembles a motion screw with trapezoidal threads). A tool shaped as the basic profile is applied onto the workpiece in the axial plane. With larger γ angles, different cutting angles occur in the forming tool on the lateral edges, which results in unequal cutting-edge loading and blunting. The lateral worm areas can only be sharpened using a special form grinding wheel. Therefore, spiral gearing is used in worms with a low pitch angle (γ<10°) in those cases when tooth sides are not treated thermally and do not require regrinding.
ZN: Worm with a straight-line tooth profile in normal tooth section, namely; a) On the mean helix of space. b) On the mean helix of tooth. In the axial section, tooth sides are slightly convex and the cross-section results in a general evolvent curve (in an extended or shortened evolvent). The elements in the normal plane are standardized, (i.e. mn=m, an=a). The gearing is worked in case with one and in case and with two forming in the normal plane. The cutting angles are identical with great angles γ. Thermally treated sides can be ground using a grinding wheel with straight-line bevel areas on thread grinding machines. This grinding process results in non-straight-line lateral areas which, however, rather approximate the theoretical ones. If also the screw milling cutter used to produce worm gear toothing is subject to this grinding process, the worm and the worm gear create a theoretically proper pair. The common gearing is also suitable for worms with greater angles γ and for worms with thermally treated tooth sides that require regrinding.
ZI: Worm with an evolvent profile (a straight-line tooth profile in a plane tangential to the main cylinder). The tooth sides are convex in both the centerline and normal sections and the cross-section results in an evolvent. The elements in the normal plane are standardized (i.e. mn=m, an=a). The gearing is worked using two tools applied onto the workpiece. The tool cutting edge lies in the tangent direction toward the helix on the main cylinder. The evolvent gearing is used in worms with a higher number of teeth (e.g. z1 > 4); the worm resembles a cylindrical gear with helical teeth. Tooth sides can be ground with the flat side of the grinding wheel. Special grinding machines must be used given the relatively small angle γ.
ZK: Profile formed by a cone ground using a wheel and / or shank tool.
ZH: Concave tooth profile (highest accuracy / precision and most expensive).
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发表于 2023-1-30 11:13
