Technical Manual for Ribbed Belt Drives

Design HintsRibbed Belt TensionII. Belt Tensioning using a ”Length AdditionalValue”It has become evident that span deflection methods are notalways the ideal checking procedures for ribbed belts. Thefollowing very simple method for the determination of the belttension is therefore recommended:1. Calculate the static belt tension “T”.500 · (2.03 – cT ≈ 1 ) · P B+ k · v 2c 1 · z · v2. The outside length L a of the Ribbed Belt should be measured onthe top surface with the belt slack prior to fitting it to the drive.Measurement may also be taken on the drive itself, but withouttension.Example::P B = 23.4 kWc 1 = 1.0v= 16.6 m/sDrive specification with Optibelt-RB Ribbed Belt 12 PL 1075T ≈500 · (2.03 – 1.0) · 23.41.0 · 12 · 16.6+ 0.036 · 16.6 2 ≈ 70 NWhen fitted for the first time, the tension should bemultiplied by a factor of 1.3.T ≈ 1,3 · 70 ≈ 91 N3. Calculate the length additional value “A” by using the formula:A ≈ L est · RLength measured on the back of the belt whilst slackA ≈ 1075 · 0.00264 ≈ 3 mmR = Stretch factor from table 19 page 43.4. This length additional value A should then be added to themeasured outside length (from step 2).L a ∗ ≈ L a + ATighten the belt until the length measured around the outside is1103 mm. The belt is then correctly tensioned.L a ∗ ≈ 1100 + 3 = 1103 mm5. The ribbed belt should then be tensioned until the outside lengthL a * calculated in step 4 is obtained. The belt tension will then becorrect.6. If the drive is to be retensioned, the ribbed belt must first beslackened off so that it can be measured in a stress freecondition. The procedure as detailed in steps 4. and 5. is thenrepeated.IV.Checking the Belt Tension by Speed MeasurementIn this method, the belt tension is checked using the theoreticalslip. The speeds of the driver and driven pulleys are measuredfirst in an unloaded and then in a loaded condition.III. Checking the Ribbed Belt Tension by Measurement ofthe Static Shaft LoadingA very accurate method for the setting of the correct belt tensionis by direct measurement of the static shaft loadingusing the formula:S = Slip (%)n 1L = Speed of driver pulley, unloaded(r.p.m.) (min -1 )n 2L = Speed of driven pulley, unloaded(r.p.m.) (min -1 )n 1B = Speed of driver pulley,under load (r.p.m.) (min -1 )n 2B = Speed of driven pulley,under load (r.p.m.) (min -1 )Formula for the calculation of slip:S a ≈ 2 T · sinβ2· zn 1L /n 2LS = (1 – ) · 100n 1B /n 2B42This checking method, however, does call for specialisedmeasuring instruments.At the rated loading, the slip should not exceed 1%. The beltservice is considerably shortened due to excessive flank wearwith an unacceptably low initial tension or under extremeloading conditions, with slip in excess of 2%.