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Rotor Spin Testing:

Proof Testing

The Issue

Computer modeling is an essential tool in the design of high speed rotating components, but its success depends on the accuracy of assumptions made by the designer. While computer modeling can help reduce design risk, it cannot test unpredictable parameters such as variations in the manufacturing process. Quite simply, there is no substitute for testing the integrity of actual rotating components under controlled conditions while measuring and recording outcomes.

Why It Matters

High speed turbomachinery components carry an inherent risk of failure due to design errors or manufacturing anomalies. Each high speed rotating component contains a large amount of kinetic energy which, should a component fail, presents a danger to surrounding equipment and personnel. In addition, manufacturers can enhance component performance in the field by ensuring that rotating parts have undergone plastic radial expansion as part of the production process, prior to final machining.

What You Can Do

Manufacturers can mitigate the risk associated with the design and production of high speed components with Proof Testing (also known as Integrity Testing). Test Devices offers component manufactures two methods of Proof Testing, each of which offers a range of situation-specific variations:

1. Overhead Spin testing verifies high speed component integrity and provides objective evidence regarding the capabilities of a component at design limits and beyond.
2. Production Spin (also known as Pre-Spin) testing elicits a specified amount of plastic radial growth to the residual stress state of rotor forgings prior to final machining.

Test Devices has expertise and experience in the specialized field of Proof Testing. We have invested in top-flight equipment, instrumentation processes, data recording, and personnel to provide our customers with the crucial information they require to ensure that their high speed rotating components perform as designed.

Applications for Proof Testing

Jet engine components	Gears	Compressor rotors
Turbine rotors	Centrifuge rotors	HVAC fans
Turbofans	Impellers	Metallic flywheels
High speed fans	Turbochargers	Composite flywheels
High speed machine tools	Electric motor rotors	Grinding wheels

Advantage of Proof Testing

1. Verified Integrity: Components that are Proof Tested are typically accelerated to between 120% - 150% of operating speed, and then held at speed as briefly as several seconds or as long as a few minutes. During one excursion above the normal operating speed, the integrity of a finished component can be thoroughly tested. Design and analysis, material selection, manufacture and inspection all can be examined in detail. In addition, information needed to meet ISO9001 / AS9100 quality requirements to validate that a component design actually meets its intended performance can be measured and recorded.
2. Higher Quality Components: By spinning a rotor forging past its design limits prior to final machining, centrifugal stress is imparted on the rotor to preferentially yield lower strength areas and equalize global material properties. The result is a more homogeneous rotor. Spinning is also used to “pre-grow" rotors to achieve a desired degree of plastic radial growth before final machining. This pre-growth helps to avoid in-engine plastic rotor growth, which can lead to problems including excess vibration and unintended contact between parts.
3. Dedicated Spin Chambers: Due to the large amount of kinetic energy stored in high speed components, and the risk of damage from a component failure, Test Devices conducts Proof Tests within vertical spin chambers designed for this application. Spin chambers are robust steel vessels that provide containment in the event of a high speed component failure. An air turbine or electric motor, mounted on top of the spin chamber, drives the test piece within the spin chamber. A vacuum system reduces frictional drag in the spin chamber, reducing test cycle time and improving drive efficiency while testing bladed components.
4. Data Acquisition: Test Devices uses an on-line, high speed, digital data acquisition system to record all test parameters throughout the duration of all Proof Test procedures. This system replaces paper data recorders traditionally used in the industry, allowing large amounts of data to be stored, transferred and analyzed easily. All test data are included in the final report together with all other project paperwork, including certificates of conformance, balance, heat calibrations, and tooling material certificates. Test data is also archived at Test Devices for the customer’s future reference.