The polyster cords are replacing the conventional rayon cords as reinforcement members of industrial V-belt drives due to their higher power transmission capacity, lower belt stretch and higher dimensional stability. Another development in V-belt technology is the polychloropre (Neoprene, Bayprene etc) covering given to the base rubber belt. This jacket offers improved oil, heat and water resistance. The following is the typical data about polyster cord reinforced V-belts:
|Section||Nominal dimension (mm)||Angle||Size range||Recommended minimum pulley dia (mm)|
|A||13||8||40°||20.0 – 180.0||80|
|B||17||11||40°||24.0 – 275.6||125|
|C||22||14||40°||40.0 – 418.0||200|
|D||32||19||40°||75.0 – 598.0||315|
|E||38||23||40°||180.0 – 598.0|
The designation of V-belt drive as A1550/A60 indicates that belt is of cross section ‘A’ having a pitch of 1550 mm and inside length of 60 inches. For easy calculation of difference (in mm) between pitch length and inside length, following can be used:
For obtaining the length required for the given pulley diameters and center distance following formulae is used:
L = 2C + (D – d)2 / 4C + 1.57 (D + d), where L is pitch length in mm, C is center distance in mm, D and d are diameters of large and small pulley respectively.
For selecting pulley for electric motors (TEFC), the following table is used to select standard pitch diameter: (All dimensions are in mm)
|Nominal speed (rpm)||3||4||5.5||7.5||11||15||18.5||22||30||37||45||55||75||93||112||130||150|
GRADING OF LENGTH: Many of the V-belt drives use more than one belt to transmit the power. It is therefore necessary to ensure that each of the belts share the load uniformly. This requires the belt lengths to be within the specified tolerances. The specification of length variation is done by way of a grading system where a symbol 50 represents a belt of exactly the same length as the nominal inside length. Every number above or below 50 represents a + 2.5 mm variation from the nominal inside length in case of Dunlop and +2 mm in case of Fenner. The manufacturers recommend certain consecutive grading numbers which may be used to make a matched set.
DESIGN AND SELECTION: The design and selection of a V-belt drive requires details of driver, driven equipment, speed of driver and driven equipment in rpm, power to be transmitted, center to center distance of pulleys and service duty etc. During installation of V-belt drives it must be insured that an initial tension is prevailed in the belt to begin transmission of power. In order to get the initial tension the belts may be stretched to 0.5 to 1% of the length of the belt.