# Professional Calculation and Selection of Timing Belts and Pulleys, a Must-have for Mechanical Engineers.

Timing belt pulleys are a novel transmission method that uses teeth on a belt to engage with teeth on pulleys to transfer power. They provide precise synchronous transmission, require no lubrication, have no slip or pollution, and produce minimal noise. The transmission efficiency can reach 0.98, the speed ratio range can be up to 1:10, allowing linear speeds of up to 50m/s. They are capable of transmitting power from a few watts to several kilowatts and are suitable for multi-axis transmission. They find widespread applications in industries such as textiles, automotive, chemical fibers, tobacco, papermaking, printing, and chemical machinery. In recent years, there has been an increasing demand in the mining and metallurgy, steel machinery, and medical equipment sectors.

I. Selection Calculation for Vertical Timing Belt and Pulleys:

Below is an example illustrating the calculation steps for a vertical application: Vertical design requirements: Tray and goods weight 20kg (196N), slider movement distance 1250mm, required time 6s.

1.Design power:

Based on the working conditions, look up and select 1.5 from the table.

2.Belt type selection:

Based on

belt speed and pulley speed (n = 100 r/min), choose 5M curved-tooth belt from the table.

3.Number of teeth (z) and pitch circle diameter (PCD) of the pulleys:

Choose the largest possible value for z based on belt speed and allowable installation dimensions from the table. For 5M belt, z = 26, pitch circle diameter

outer diameter

4.Belt speed (v):

5.Transmission ratio：

Since the driving and driven pulleys are the same, the transmission ratio (i) is 1, and both pulleys are of the same type.
6.Preliminary center distance.

7.Preliminary belt pitch length and number of teeth.

8: Actual center distance (a):

9.Basic rated power: Obtain from the table。

10.Belt width (bs)。

11.Setting of flange：
For 5M pulleys, the minimum height of the flange is K = 2.5 ~ 3.5, R = 1.5, and the flange thickness t = 1.5 ~ 2。

Diameter of the bend of the retaining ring

Outer diameter of retaining ring

Vertical Direction Timing Belt Pulley：

Pulley Type: 5M curved-tooth, pitch circle diameter 41.38mm, number of teeth 26, outer diameter 40.24mm, total width 13.3mm, flange outer diameter 48.24mm, pulley bore 10mm, fixed using set screws (two screws placed 90 degrees apart on a 7mm wide side, threaded hole M3).

Vertical Direction Timing Belt:

Belt Type: 5M curved-tooth belt, belt width 10.3mm, pitch length approximately 3418mm.

Note: When selecting timing belt pulleys, pay attention to parameters such as tooth profile, number of teeth, material, surface treatment, and pulley shape.

I. Tooth Profile:

Timing belt pulley tooth profiles can be classified into English (ordinary torque) MXL, XL, L, H, and metric (high torque) S2M, S3M, S4M, S5M, S8M, and (ordinary torque) T5, T10.

The selection of tooth profile can be referred to the table below:

II. Number of Teeth:

The number of teeth is an important parameter for timing belt pulleys. The pitch circle diameter of the pulley is equal to the number of teeth multiplied by the pitch/π.

III. Material and Surface Treatment:

Timing belt pulleys are commonly made of aluminum alloy or 45# steel. The surface treatment options are:

Aluminum pulley: Natural oxidation, black oxidation; Steel pulley: Ferric oxide protection, no electrolytic nickel plating.

IV. Pulley Shape:

K-shaped pulley.

A-shaped pulley.

B-shaped pulley.

D-shaped pulley.

Specifications of the pulley shaft bore.

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