2. Chain Dynamics
The tension ( T ) in a horizontal conveyor, like that in Figure 2.22, is basically calculated by this formula: T = M 1 3 g 3 f 1 3 1.1 + M 1 3 g 3 f 2 + M 2 3 g 3 f 3 Where: T = total chain tension M 1 = weight of the chain, etc. M 2 = weight of conveyed objects f 1 = coefficient of friction when chain, etc., are returning f 2 = coefficient of friction when chain, etc., are conveying f 3 = coefficient of friction when conveyed objects are moving g = gravitational constant 1.1 = sprocket losses due to directional changes of the chain NOTE: “chain, etc.,” in the above formula includes chain and the parts moving with the chain, such as attachments and slats. In this formula, a coefficient of friction is multiplied by every term in the equation. Therefore, if the coefficient of friction is high, the tension increases and larger chain is required. Also, the necessary motor power, which is calculat- ed as tension 3 speed 3 coefficient, increases. A more powerful motor is need- ed when the coefficient of friction is high. Reduce the coefficient of friction and you can reduce the tension, too. This allows you to choose a more economical chain and motor, and decrease the ini- tial and running costs for conveyor equipment. The chain’s coefficient of friction differs by type of chain, by material, and by type of roller; it is shown in the manufacturer’s catalog. To illustrate this con- cept, two examples are included. The coefficient of friction for different types of top chain and guide rails is shown in Table 2.3. The coefficient of friction when large R-roller chain rotates on rails (rail material: steel) is shown in Table 2.4.
Table 2.3 Friction Coefficients for Top Plate and Guide Rails
Friction Coefficient
Top Plate Material
Guide Rail Material Stainless Steel or Steel
Unlubricated
Lubricated
Stainless Steel or Steel Stainless Steel or Steel
0.35 0.25 0.25 0.25 0.17 0.18
0.20 0.15 0.15 0.12 0.12 0.12
UHMW
Engineered Plastic Engineered Plastic
Stainless Steel or Steel
UHMW
Engineered Plastic (Low Friction) Engineered Plastic (Low Friction)
Stainless Steel or Steel
UHMW
Table 2.4 Friction Coefficients for Different Types of Rollers
Friction Coefficient
Chain Type
Roller Type
Unlubricated
Lubricated
RF Double Pitch Chain
Steel
0.12 0.08
0.08
Engineered Plastic
—
Large Pitch Conveyor Chain
Steel
0.13 ~ 0.15
0.08
Engineered Plastic
0.08 0.03
— —
Bearing Roller
25
Made with FlippingBook Digital Proposal Creator