Balancing is the process of determining the values and angles of roller imbalances and reducing them by adjusting the masses. Balancing is performed both with the help of balancing machines and directly during operation.
Vibration from unbalance reduces the service life of the rubber/polyurethane roller coating, damages bearings and other machine parts, and has a significant negative impact on the quality of the final product.
Roller balancing is the process of changing the position of the centre of gravity so that it is on the axis of rotation.
Static balancing
If a frictionlessly mounted roller remains at rest, regardless of the position in which its rotation is stopped, all local deviations will self-compensate, and in this case, static balance is achieved. If the roller is not statically balanced, it is necessary to add enough mass to its "light" side to achieve balance. This is usually done by drilling a hole and adding a balancer to the rubber covering of the roller. Static balancing is mainly used for rollers operating at rotational speeds of less than 180 m/min. However, rollers that are balanced for one speed are not necessarily in balance at another speed.
Dynamic balancing
Even if a roller is statically balanced, the centre of gravity of one of its ends may be off-centre, in which case a correction must be made on the other end. This change cannot be detected during static balancing and becomes noticeable when the roller is accelerated. This results in oscillations (known as dynamic or momentary imbalance), which can be analysed to determine whether one end of the roller or both ends need to be balanced (counterbalanced).
In such a situation, each end may require its own counterweight so that the sum of the two produces a static balance. The rubber coating of an unbalanced pressure roller may develop a flat area or a coating that has come loose from the rod. Lagging can also occur if the upper roller is unbalanced.
Kinematic balancing
When a roller is made of pipe, its walls can have different thicknesses along the surface of the roller as well as around the circumference of the pipe. When such a roller is statically and dynamically balanced, and then set into rotation at high speed, localised imbalances occur along the surface, with the heavier sections of the shell moving away from the centre. When the shape of a roller changes due to uneven distribution of its mass, a condition called kinematic imbalance occurs. To avoid this problem, it is recommended to use a machined rod (both inside and outside) that is balanced at the operating speed prior to coating.
Static unbalance is expressed in kilograms per work surface, while dynamic unbalance can be expressed in kilogram-centimetres and is a measure of one or more forces that cause vibration when the shaft rotates.
Vibration is measured as a linear motion at the shaft ends. The requirements for dynamic balancing must be expressed in terms of the vibration amplitude at the shaft ends at a given speed measured by a vibration recording device. For shafts with a specified dynamic balance, the minimum amplitude is 0.13 mm at the shaft ends, twice as large as in the centre of the shaft at a given speed.
The main stages of balancing:
- Preparing the appropriate tools and the product itself.
- Determination of the initial vibration indicators by means of precise measurements.
- Determining the masses and angles of the correction weights.
- Installation of the correction weights. Last measurement of the residual vibration for the final check of the roller balancing process.
- Completion of the process (filling in the balancing protocol).
Balancing must be carried out for all cylindrical or symmetrical rollers with respect to the axis of rotation.
Shaft balancing should always be performed on new rollers or after repair.
Today, Dessa-NV can perform dynamic shaft balancing:
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up to 3 m long
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weighing up to 700 kg
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diameters up to 700 mm
