Balancing Machine

a machine for the determination of the point and value (degree) of static or dynamic imbalance of rotating machine parts such as rotors of electrical machinery and turbines, shafts, pulleys, and so on. The balancing machine usually consists of bearings accommodating the article to be balanced (for example, a rotor), a power drive to rotate the article, and measuring devices with indicating instruments.

A distinction is made between balancing machines with pliant and rigid bearings. Pliant bearings execute oscillations in response to the unbalanced rotating article (rotor). The amplitudes and phases of the bearing vibrations provide information on the imbalance. Rigid bearings hinder vibrations of the rotor and experience pressure as a consequence. In this case the pressure exerted by the rotor on the bearings and the phase variation of the pressure are measured in order to obtain information on the imbalance.

The bearings in a balancing machine are equipped with sensors that transform the vibrations (or pressure owing to centrifugal forces) into electrical signals. The electrical signals in the sensor output are sent to a measuring device. The structure of the measuring device and the form of information on the imbalance depend on the purpose of the balancing machine. A diagram of a balancing machine designed for dynamic balancing with a wattmeter measuring device is shown in Figure 1. The imbalance is measured first in one plane and then in another with the aids of switches. Balancing machines are driven by a double-hinged shaft, a slip-on transmission belt, an air jet, or other device. Correction of an imbalance—that is, positioning of counterweights or removal of excess material (by drilling, milling, and so on)—is done manually either on or off the balancing machine.

Figure 1. Balancing machine for dynamic balancing, with wattmeter measuring device: (1) rotor to be balanced; (2) bearing; (3) sensor; (4) angle-magnitude switch; (5) wattmeter indicator; (6) double-hinged shaft; (7) power drive; (I, II) correction planes; (A, B) axes in planes of measurement.

Types of balancing machines are available for static and dynamic balancing and with a horizontal or vertical axis of rotation. Balancing machines are manufactured with different degrees of automation—for example, automatic machines including devices for establishing the amount and point of the imbalance, devices for removing the imbalance, and (when needed) devices for repeat inspection. In some particular cases where parts of complex configuration are to be balanced—such as crankshafts of internal-combustion engines—a special automatic transfer line takes care of balancing.