DESIGN OF V-BET TRANSMISSION (STAS 1163 71 & ISO R 155). Design Data inut ower (at the driving sheave), P 1 inut rotational seed (of the driving sheave), n 1 (rot/min), transmission ratio, i BD. center distance, A. alication (service) factor c f (K s ). γ/ β 1 F F β A Fig. 1. Geometry of belt drives Fig.. Power rating chart for V-Belt selection Select the V-belt (cross-section) sie function of the ower and rotation seed at the inut, using the diagram from Figure. If the oint is close to a demarcation line, it is recommended to select the belt sie under this line (with greater load caacity). Table 1 gives data for all dimensions of the belt cross-section. Machine Design 3-4 1
Select the working diameter of the driving sheave, D 1. It is recommended to select a normalied value (STAS 116-67). The range of normalied diameters is in accordance with the sie of the belt (see Table ). Sheave diameters below minimum values recommended for the belt sie in question should not be used because the higher bending stress materially reduces the belt life. Calculate the working diameter of the driven sheave: D = i D (1) BD 1 If there are no restrictions for the transmission ratio, the diameter can be normalied to the closest value (see Table 4 STAS 116 67) Included angle: where normally D A ( D + D ) 3 1 D D1 γ = arcsin () A Shaft distances that are too short (short belts) result in higher frequencies, causing excessive heating and thus remature failure of the belt. Shaft center distances that are too long (long belts) may result in belt vibrations, esecially of the slack side, also causing higher belt stress. Angle of wra (arc of contact): Working length: o on driving sheave β1 = 18 γ, on driven sheave β = 18 + γ o γ π = Acos + ( β1 D 36 1 + β D π ( D ) A + 1 + D ) ( D + D 4A 1) (3) A normalied value of the working length should be selected from vendors catalogues (usually the closest value is selected). Standard values are given in Table 3. Periheral velocity: D1 n1 v = π [ m / s] (4) 6 It is recommended a maximum eriheral velocity v max =4 m/s. Preliminary number of belts: (a) c f Pc = c c P β (5) l h b max Fig. 3. V-Belt Dimensions (STAS 719-83) Machine Design 3-4
Sie Cross section dimensions l h h ± δ h Table 1. - V-Belt sies D max [ ] Working length Minim Maxim D min SPZ 8.5 8. 8±.4. 63 355 71 SPA 11. 1 1±.5.8 8 45 1 SPB 14. 13 13±.5 3.5 4±.1 15 8 16 16 15 16. 15 15±.5 4. 16 1 SPC 19. 18 18±.6 4.8 15 4 Table. - Normalied values for working length Working length 4 5 63 8 1 15 16 5 315 4 5 6 8 1 15 Examle of notation: SPA ; STAS 719-83 (V-Belt sie SPA, with working length = mm) Table 3. - Normalied values for working diameters, D 63 71 8 9 11 15 14 16 18 4 5 8 315 4 45 5 56 63 71 8 9 11 15 14 16 18 5 where c - length correction factor (Table 4) function of the working length. c β - wraing factor: ( ) c = 1.3 18 β (6) β 1 P - nominal ower transmitted by one belt is given by vendors Tables 6...9 give values from STAS 1163-71. inear interolation should be used for intermediary values. - may should not be rounded off. Final number of belts: = (6) c where c is belt load reartition factor (see Table 5). The result should be rounded to the uer integer. It is recommended that 8. Bending frequency: f v[m/s] = 1 3 x [ H] (7) where: x number of sheaves. Machine Design 3-4 3
Bending frequency should not be greater than 4 H. Periheral force: F u 3 P1 ] 1 [ kw = [ N] (8) v[ m / s] Belt tensioning (Preload) force: F = (1,5...) F [ ] (9) u N Note that the belt tensioning force is the radial force loading the shaft (suorted by the bearings). Adjustment of shaft center distance (Minimum take-u allowance): X>.3 Y>.15 The dimensions of the grooves for V-belts are standardied (STAS 116 84) see Figure 5 and Table 1. Working length,. Table 4. ength correction factor c Belt sie SPZ SPA SPB SPC 4 45 5 56 63.8 71.84 8.86.81 9.88.83 1.9.85 11.93.87 15.94.89.8 14.96.91.84 16 1..93.86 17 1.1.94.87 18 1.1.95.88 1..96.9 4 1.5.98.9.8 5 1.7 1..94.86 8 1.9 1..96.88 315 1.11 1.4.98.9 355 1.13 1.6 1..9 375-1.7 1.1.93 4-1.8 1..94 Machine Design 3-4 4
Table 5 - V-Belt load reartition factor, c Number of belts, c 3.95 4.6.9 over 6.85 B f e l r D e D n m α Fig. 5. Standard dimensions of V-belt grooves Table 1. - V-belts groove dimensions Groove sie Z A B C Belt sie SPZ SPA SPB SPC l 8.5 11 14 19 n min.5 3.3 4. 5.7 m min 9 11 14 19 f 8 ± 1 1 + 1 1 1.5 + 17 + 1 e 1±.3 15±.3 19±.4.5±.5 38 ±1 38 ±1 38 ±1 38 ±3 α 34 ±1 34 ±1 34 ±1 36 ±3 r.5 1. 1. 1.5 Sheave width: B = ( 1) e + f Remark. Sometimes, working diameter is called datum diameter. Working length is also called nominal length or length in datum system. Machine Design 3-4 5