Basics
2.3.4 Strength of Attachments Bending and twisting forces can affect the attachments. For the A attach- ment, which is a common type, the allowable load calculation indicated in cat- alogs is based on the bending strength. When a tall fixture is added onto the attachment, you must study the strength of the entire configuration. When the attachment is subject to forces other than those explained, you also must calculate the twisting forces. If the attachment receives bending forces at the same time, make sure to combine the bending forces with the twisting forces. When calculating the strength of attachments such as A-type, K-type, SA- type, and SK-type, which are extensions of a standard steel chain’s plate, use the values shown below as their ultimate tensile strength, and choose a proper safety factor. Nonheat-treated plate: 490 MPa (50 kgf/mm 2 ) Heat-treated plate: 1,078 MPa (110 kgf/mm 2 ) 2.3.5 Stick Slip When using an extra-long conveyor system (more than 15 m) and slow chain speed (less than 10 m/min.), you may notice longitudinal vibration in the line, which is called stick slip, or jerking. The basis for this phenomenon can be seen in Figure 2.24. Here the coeffi- cient of friction is plotted against the speed of the chain. When operating a long conveyor at slow speeds, the coefficient of friction for sliding surfaces (in top chains, between top plates and rails; in R-rollers, between the outer sur- face of the bushing and inner surface of the roller) decreases as speed increas- es. This causes the chain to jerk or stick slip. Usually, you can’t solve this problem by adding lubrication or by increasing the number of sprocket teeth. There are, however, things you can do to pre-
vent or reduce stick slip: 1. Increase chain speed.
Chain Speed
Figure 2.24 How Chain Speed Impacts the Friction Coefficient
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