Balancing Services

The Issue

Unbalance in rotating components is caused by the displacement of the mass centerline from the rotor’s axis by an eccentricity in the distribution of the rotor mass. Balancing is the correction of this phenomenon by the removal or addition of mass to the component to compensate for centerline error. In practical terms, balancing “is the process of attempting to improve the mass distribution of a body so that it rotates in its bearings without unbalanced centrifugal forces.” (ISO 1940/1 Mechanical vibration – Balance quality requirements of rigid rotors)

Why It Matters

During rotation, the “heavy” side of an unbalanced rotating component exerts more centrifugal force than the “light” side. This unbalanced condition pulls the entire rotor in the direction of the heavy point and can result in excessive noise, rapid component wear, excessive vibration, and reduction in bearing life. In extreme cases, unbalance can lead to component failure and resulting threats to machinery and personal safety.

What You Can Do

Test Devices offers a full range of balancing services for parts as simple as single plane steel pulleys or as complex as dual plane exotic alloy assemblies of complex geometry. We work with quantities from a single part to full production lots. Test Devices also has in-house capability for design and manufacture of balance tooling to aid our customers in the production of precisely balanced components.

Advantage for Balancing

Properly balanced rotating components minimize vibration and noise, extend the life of bearings and help to ensure a component’s intended levels of safety, reliability and performance. Test Devices offers both static and dynamic balancing services.

Figure 1 - Static / "Single-Plane" Unbalance

Figure 1 – Static / “Single-Plane” Unbalance

Static (single plane): If unbalance occurs at a single axial point on a disk-like rotor, static balancing is typically appropriate. With the part rotating, the heavy point is measured in relation to the component centerline.

Figure 2 -Dynamic / "Dual-Plane" Unbalance

Figure 2 -Dynamic / “Dual-Plane” Unbalance

Dynamic (dual plane): If unbalance occurs on components with significant axial length or with multi-rotor assemblies, dynamic balancing is required. Because two or more heavy points will act independently on the mass centerline, the unbalance must be measured dynamically and corrected in two planes.

Balancing Options

Production Balancing is for customers who fabricate lot size quantities of rotating turbo-machinery components that require balancing prior to delivery or installation. Each rotor is balanced to meet customer specifications and requirements, then either returned to the customer or shipped directly to the end user with Balance Certifications.

Precision Balancing provides extremely accurate balancing of high-speed (greater than 5000 rpm) components. Many customers utilize this service during R&D to ensure very precise balance before installing the component in the turbo-machinery equipment for testing.

At-Speed Balancing (or Operational Speed Balancing) is for high-speed rotating components where standard “low-speed” balancing (less than 3000 rpm) is not sufficient. Typically, at-speed balancing is required when additional vibration modes (critical speeds) or radial growth of components are encountered at operational speed.

Balance Correction

When unbalance is identified, Test Devices can perform balance correction on materials ranging from plastics to aerospace superalloys. Balance correction is done according to customer specifications and can be performed using the following methods:

Drilling or Milling Material Removal

Drills or endmills are used to plunge to specified depths at the appropriate location. In addition, CNC milling equipment can be used to precisely control the depth and arch of the material removal.

Note: For some materials, such as titanium, which are susceptible to spark impingement, it is critically important that the machining methods, rather than abrasive material removal, be used to correct imbalance.

Abrasive Material Removal

Grinding or air-powered sanding equipment is used to remove mass at the appropriate location.

Mass Addition

Mass is added by the addition of epoxy, welding metal strips, or by adding mechanical hardware (set screws, washers, etc.) if provisions are included in the design.

Over-Speed Spin Testing

Some high-speed components must be balanced and over-speed spin tested prior to final installation. Test Devices provides a full range of spin testing services with a quick turnaround. Click for more information on over-speed spin testing.

Applications for Balance

Pulley assemblies Starter armatures Airspace components
High-speed machine tools Composite flywheels Impellers
Centrifuge rotors Electric motor rotors Fan and blowers
Compressor rotors Turborchargers Precision shafts
Turbine rotors

Balancing Services Capabilites

ISO 1940 specifications for high-speed components (G2.5, G1, G0.4) Component diameters up to 45 inches (1,140 mm) Component weights up to 10,200 pounds (4,560 Kg)

Quality

Drawings for many precision parts call out very precise depth and width levels, below which material cannot be removed. To ensure compliance to these requirements, for many precision balanced parts, Test Devices includes a final measurement verification step performed by our quality department.