ISO 9981-2020 pdf download.Belt drives一Pulleys and V-ribbed belts for the automotive industry – PK profile: Dimensions.
5.2 Minimum effective diameter
The minimum recommended effective diameter, de, for PK pulleys is 45 mm.
5.3 Tolerances on finished pulley
5.3.1 Checking conditions
Profile, diameter and run-out tolerances shall be checked on the finished pulley without surface coating.
5.3.2 Groove-to-groove diameter tolerances
The variation in diameters between the grooves in any one pulley shall not exceed 0,15 mm. This variation is obtained by comparing the diameters over balls or rods.
5.3.3 Radial and axial circular run-out
Radial and axial circular run-outs shall not exceed 0,25 mm full indicator movement (FIM). Run-out in the two directions is measured separately with a ball mounted under spring pressure to ensure contact with the groove as the pulley is rotated.
5.3.4 Diameter over balls
The tolerances on the diameters over balls, K, shall not exceed +0,6 mm.
5.3.5 Groove finish
The pulley grooves shall have a surface roughness Ra≤3,2 um. See ISO 254 and ISO 4287 for definitions and the method of measurement.
5.4 Pitch diameter, dp
The fit of a V-ribbed belt in the corresponding pulley is shown in Figure 3. The true pitch diameter of a V-ribbed pulley is slightly larger than the effective diameter and its exact value is determined with the particular belt being used.
A nominal value of the effective line differential, ber of 2 mm may be used to calculate the speed ratio. If more precision is required, the belt manufacturer should be consulted.
Further information is given in the ISO 8370 series.
5.5 Designation of pulleys
A V-ribbed pulley for the automotive industry is characterized by the number of grooves, the profile and the effective diameter. It is designated by a series of numbers and letters as follows:
a) the first letter “P” means “Pulley”;
b) the first set of numbers indicates the number of grooves;ISO 9981 pdf download.