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A calculation of transmission is a screw-nut with the friction of sliding At planning to the transmission set the size of moving of nut or screw of L(M), time of moving of t(c) and force on a nut or screw of F(a). Forward speed of moving of nut about even v = 60L = Pzn₁. (11.1) As by the basic type of destruction in transmissions a screw-nut with the friction of sliding is wear of screw-thread, then as a criterion of capacity of such transmissions is accepted wearproofness. Pressure of q between the coils of screw- thread of screw and nut does not must possible [q], dependency upon material of spiral pair and her external environments. At a design calculation a middle diameter is determined: d₂ = (11.2) where y is a coefficient of height of nut, y choose on the structural considering within the limits of 1,2... 1,5; large values in appoint for the screw-threads of less diameters. Choice of possible [q]: - [q]= 10... 13 MPa - at the friction of hard-tempered steel on a bronze; - [q]=8... 10 MPa - at unhard-tempered steel on a bronze; - [q]=4...6 MPa - at diminishing worn down of screw-thread in the process of work of transmission. By found value of middle diameter of screw-thread d2 for TOCT 24705-2004 find the sizes of all parameters of screw-thread: d1(D1); d2(D2); d(D); P. Set the value of height of nut Hr=of 0.01 M and determine z is a number of coils of screw-thread of nut: 2Fa ny[9] Z₂ = 4/ (11.3) Dependence between moving, sometimes, by frequency of rotation of screw n, and looks like the parameters of screw-thread: Pzn₂t L = 60 from where find frequency of rotation of screw : 60L ng = Pzt The corner of getting up of screw-thread is determined on a formula: ₁ = tan = Тстг. Pz nd₂ = atan (1). After the choice of parameters produce the checking calculations of screw- thread of nut on a cut, and bar of screw on durability at the action of axial force and turning moment. Durability of coils of screw-thread of nut on a cut is checked up on correlation <[Terr.]; (11.5) Fa *DĘH, (11.4)
where Terr. is calculation tension on a cut in the coils of nut; - KoediniЄHT plenitude of screw-thread which shows the relation of height of coil in a dangerous cut to the step of screw-thread (for metrical screw-threads {=0,65); [Terr.]T.r. is possible tension on the cut of screw-thread of nut, [T CT.r.]=(0.2 - 0.3)σT, OT-355MPa for structural steels. Transmissions a screw is a nut in the mechanisms of management of AC work in the reversible mode, the number of cycles of change of tension in these transmissions arrives at the values of N=104..105. It gives basis to conduct a calculation on durability of bar of screw taking into account tireless character of destruction. In this case determine the coefficient of margin of safety of screw in a dangerous cut on a formula nont n = ≥ [n] (11.6) where [n] it is a possible coefficient of margin of safety, for the feed-screws of AC [n] = 1,3... 1,5; no иn - coefficient of the reserve of minerality according to normal and dotic pressure no = olim A/op(CX) n₂ = Tlim A/TK where lima and Tima is maximum tension for the calculation cut of screw; Olima 50MPa and Tlima 5MPa; op(CK) and TK, is working tension of stretch (compression) and twisting 4Fa op(cx) = nd² 0.5Fad₂ tan(+r) (11.7) (11.8) 0.2d² where is a corner of getting up of screw-thread, 4-2... 20°; p' - corner of friction, '-arctan(f) - the brought coefficient over of friction, f'=f/cos(a/2); f it is a coefficient of friction in a screw-thread; for a pair steel is a bronze at plastic butter f-0,08 ... 0,10. On the formula of Euler at λ=μl/i>[np] n²EJ F₁ xp = (μl)² (11.9) where E is the module of resiliency of material of screw, for steel of E=2-10¹¹ Pa; J-given moment of inertia of cut of screw J = (ndt/64)(0.4+ 0.6d/d₁) μ- coefficient coersion of length of screw, case sensitive fixing of screw (table. 11.1); 1- length of the compressed area of screw; 1=10*10-³M, A, Anp - flexibility and maximum flexibility of screw; for carbon and alloyed steels λпp=90, i-a gyradius of cut of screw (i=d1/4). Efficiency of spiral pair in the case of converting of rotatory motion into forward even n = tan/tan(y + p') (11.10)
Efficiency of transmissions is a screw-nut with the friction of sliding not high. At =2... 20° and ¹=5.. 6° -0,25... 0,70. 3 8 20 Chart of fixing Tasks: to expect the parameters of transmission screw-nut. Ne pitch. L(M) t(c) 26 0.35 0.32 0.24 H 0.3 1 0,7 Chart of fixing 15 14 10 H 2 0,5 Table 11.1 Fa(N) 400 480 530 520