TRAPEZOIDAL SCREW-THREAD

A trapezoidal screw-threadis motion (translating). It is mainly used for transformation of motion rotation on straight line motion. The sizes of a single trapezoidal screw-thread regulate State Standard 9484-81, and a multiple-thread is State Standard 2439-81. The thread profile is shown in fig. 4.8.

Figure 4.8 - A trapezoidal thread profile

а) б)

Figure 4.9 - Conventional drawing of a trapezoidal thread:

a) on a pipe; b) in an opening.

Denotation of a thread (fig.4.9) consists of the the Latin letters T_r , external (nominal) diameter and other parameters in accordance with the general rules of marking the threads.

The example of the conventional denotation of threads is with the nominal diameter 36 mm:

1. Tr36x18(P6)LH-8H – triple thread with a thread lead 18mm and a pitch 6mm, internal, with the tolerance band 8Н, left-hand;

2. Tr36x6-6g – a external thread with the tolerance band 6g and a pitch 6mm, right-hand.

BUTTRESS THREAD

A buttress thread is used as leading. It is used to transmit great power in one direction for example in jacks, presses, etc. Profile of a buttress thread is shown in fig. 4.10 according to State Standard 10177-82. The sizes of nominal diameters and pitches coincide with the proper parameters of a trapezoidal thread.

Thread denotations consists of the Latin letter S, external (nominal) diameter and other parameters according to the general rules of marking the threads.

Example of conventional denotation of a buttress screw-thread with the nominal diameter 80mm, the pitch 10mm, an external thread with the tolerance band 7h: S80x10-7h.

Figure 4.10 - A buttress thread profile

а) b)

Figure 4.11 - Conventional drawing of a buttress thread:

a) on the outside; b) in an opening.