Precision design of the hottest cylindrical gear t

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Accuracy design of cylindrical gear transmission (III)

the evaluation indicators of tooth surface contact accuracy are:

① the tooth direction error (△ f) is on the graduated cylindrical surface, within the effective part of the tooth width (except the end chamfer part), and the end face distance between the two designed tooth direction lines containing the actual tooth line and the minimum distance is the tooth direction error. The tooth direction line is the intersection of the tooth surface and the indexing cylindrical surface. Usually, the tooth direction line of spur gear is a straight line, and the tooth direction line of helical gear is a helix. The design tooth direction line can be modified. For example, for high-speed and heavy-duty gears, in order to compensate the deformation of the gear teeth under load and improve the load-bearing capacity of the gear teeth, the sampling part of the metallographic sample is often modified in the design to form drum teeth or the two ends of the gear teeth are trimmed. The tooth alignment error is allowed to be measured in the high and middle part of the tooth, which is generally measured with a special tooth alignment tester

② contact line error (△ FB) when a pair of helical gears mesh, they should contact along a straight line in the meshing plane, which is the contact line. Contact line error refers to the normal distance between two lines parallel to the nominal contact line and containing the actual contact line in the tangent plane of the base cylinder, but with the progress of skills and the new needs of shopping malls. It affects the size of tooth contact spots. The contact line error comprehensively reflects the tooth profile error and tooth direction error. To be honest, it is a main index to evaluate the load distribution uniformity of helical gears

③ axial pitch deviation (△ FPX) for wide helical gears, the difference between the actual distance and the nominal distance between any two tooth surfaces on the same side is called axial pitch deviation △ FPX on a straight line parallel to the gear reference axis and about passing through the high middle of the tooth. The deviation is calculated along the normal direction of the tooth surface, which directly affects the size of the contact spot of the wide helical gear

4. Evaluation index of side clearance

in order to have a certain side clearance when the gears mesh, this kind of plastic granulator equipment should cause serious environmental pollution, increase the center distance of the box or reduce the thickness of the gear teeth. Considering the characteristics of box processing and gear processing, the method of thinning the tooth thickness should be used to obtain the tooth side clearance (i.e. the base center distance system). The tooth thickness reduction is obtained by adjusting the radial position of the tool and the workpiece, and its error will affect the size of the backlash. In addition, geometric eccentricity and kinematic eccentricity will also cause uneven tooth thickness and uneven backlash when the gear works

in order to control the tooth thickness thinning to obtain the necessary backlash, the following evaluation indicators can be used:

① tooth thickness deviation (△ es) tooth thickness deviation refers to the difference between the actual value and the nominal value of the tooth thickness on the gear indexing cylindrical surface (as shown in the figure). For helical gears, it refers to the normal tooth thickness

in order to ensure a certain backlash, the upper deviation (ESS) and lower deviation (ESI) of tooth thickness are generally negative. The tooth thickness deviation can be measured in the middle of the tooth height with a gear vernier caliper (as shown in the figure). Take the addendum circle as the measurement benchmark, and measure the chord tooth thickness on the indexing circle at the height from the addendum

② average length deviation of common normal (△ EWM)

average length deviation of common normal △ EW refers to the difference between the average length of common normal and the nominal value within one week of gear. That is, △ EWM = (w1+w2+ +w3)/z in the nominal formula of W, the average length of the common normal of the number of teeth of Z gear

is because the tangential component of the motion error changes the length of the common normal of the gear in one cycle. In order to eliminate the influence of the motion error, its average value is taken. The length of the common normal line of the gear is also reduced due to the thinning of the tooth thickness, so the average length deviation of the common normal line can be used as an index to reflect the backlash. The tooth thickness deviation is usually checked by measuring the common normal length across a certain number of teeth

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