Designing worm wheels
The basic geometric dimensions of the worm wheel are determined from the calculation (Section 3.2.3). Most often, the worm wheels are made up of components: the center is made of gray cast iron or steel, and the ring gear is made of bronze. The connection of the crown to the center should ensure the transmission of a large torque and a relatively small axial force. The design of the worm wheel and the method of connecting the crown to the center depend on the output volume.
For single and small-scale production, when the annual output is less than 50 pcs. and with small wheel sizes (< ae2 less than 400 mm), the gear rims are centered with interference fit.
With a constant direction of rotation of the worm wheel, a shoulder is applied to the outer surface of the center, to which the axial force is directed (Figure 3.60).
If the wheels are large (1 ae2 & gt; 350 mm), the crown can be attached to the center by bolts without a gap (Figure 3.61, a) or rivets (Figure 3.61, b) In this case, the crown is centered along the diameter O. The conjugation of the centering surfaces is performed by a transitional fit.
In this design, it is necessary to provide reliable locking of the nut from self-unscrewing.
The fixing bolts (3-4) have the following dimensions:
Worm wheels rotate at low speed and, as a rule, do not require balancing, so the non-working surfaces of the rim, disc, wheel hub are left unworked and made conical with large radiuses of curvatures. Sharp edges on the ends of the crown blunted with basques
where m is the linkage module with rounding to the standard value (Table 3.27).
The dimensions of the other basic constructive elements are taken from the ratios
The rest of the worm wheel design elements should be assumed to be the same as for external external gears (Section 188.8.131.52).
With any gear design, machining & gt; and the teeth are cut after the crowning with the center.
Worms, as a rule, perform steel and, more often, at the same time with the shaft. The geometric dimensions of the worm, including the length of the cut portion L and the reference distance/between the supports, are determined from the calculations and the sketch of the gear unit. Therefore, when designing a worm shaft, this data is the original data.
The dimensions of the end of the worm shaft protruding from the reducer, the diameter of the shaft at the bearing installation site and its other diameters are determined according to the recommendations given in Sec. 5.
In Fig. 3.62 shows possible worm designs.
One of the main requirements for them is to ensure high rigidity of the worm. For this, the distance between the supports is trying to do as little as possible. The diameter of the worm shaft in the unsharpped part is designated so as to ensure, if possible, the free exit of the tool when processing the turns and the necessary amount of the stop shoulder for the bearing.
In Fig. 3.62, a, b diameter of the worm shaft in front of the chopped part satisfies the condition of free exit of the tool when processing the turns. In Fig. 3.62, and the height of the shoulder is sufficient for the bearing stop, and
Fig. 3.62, it is small. Therefore, a bearing is provided for the bearing stop. With a small diameter, the worm must be carried out according to Fig. 3.62, c. In this case, the stop shoulder at the bearing installation is performed as in Fig. 3.62, b, and according to Fig. 3.62, in.
Globoid worms (Figure 3.63) are structurally different from the cylindrical shape of the cutting area and the diameter of the neck for bearing, commensurate with the diameter of the worm.
The rest of the worm elements of this type are constructed in the same way as cylindrical ones.
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