The Complete Guide to Chain

# 2.3.7 Take-Up

Conveyor chains need proper tension, which is why take-up is added to a system. You have to position take-up where the chain's tension will be minimal. If you can remove two links from the chain, the adjusting length of take-up is:

L = chain pitch + spare length

If you can't remove links from the chain, use this formula:

L = length of machine × 0.02 + spare length

In this formula, 0.02 represents the allowable wear value (2 percent). There are two portions of the spare length: one is the maximum and minimum range of variation in length for new chains; the other portion is the length to loosen the chain's connecting link when the chain's total length has been set as tight as possible. For example: the machine length is 10 m, the length for maximum and minimum range of variation is 0.25 percent, assuming the length needed to connect chain is 25 mm, then:

L = 10,000 × (0.02 + 0.0025) + 25 = 225 + 25 = 250 (mm)

If the chain expands and contracts with temperature, the system needs some means to absorb it. When you use a chain in a high-temperature environment or to convey high-temperature objects, the chain becomes hotter and the length increases at about the same ratio as its coefficient of linear expansion. When the temperature is between 0° and 300°C, and 1 m of chain is heated by a value of 100°C, the chain elongates by about 1 mm. If you want to allow for this elongation with take-up, you must be careful about the following points or the chain may fail:

• In the case of chain temperature increase, adjust take-up after the temperature increase.
• In the case of chain temperature decrease, adjust take-up before the decrease.

In the case of chain temperature change, the take-up should be designed to absorb the elongation or the contraction of the chain.

If you don't drive the chain in reverse, it is more convenient to design a catenary section and collect the elongation in that part. In that case, it is also beneficial to design a take-up. Figure 2.25 shows an example of a design with catenary and take-up.

It is very annoying to continuously adjust take-up. Sometimes it is possible to use self-adjusting take-ups by hanging a weight or using a hydraulic power cylinder instead of adjusting the take-up. However, the chain receives additional tension by doing this (sometimes the motor capacity is also influenced), so don't forget to check the chain strength as well as the motor capacity.

Another point about take-up is that if you drive the chain in reverse while carrying objects, the take-up receives the load as if it were a driving part. In this situation, you must select and design take-up with consideration for its strength.