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Proof testing, or overspeed testing, is performed by spinning a component above the typical operating ceiling of the machine. For example, a rotor with a speed for which it was designed to operate of up to 20,000 rpm could be tested at speeds over 24,000 rpm. The goal of the test is to confirm the structural integrity of the rotor and ensure that there is an adequate safety margin against a potential catastrophic failure (a rotor burst), even if actual operating conditions exceed the speed for which it was designed.

During the spin testing process, we measure the change in the rotor OD (or inner diameter if accessible). From the measurement, we can observe the average growth or map the growth as a circumferential deformation profile (expansion measurement). The former helps us to understand the bulk material behavior of the rotor, and the latter provides a visualization of the deformation shape of the rotor at speed.

Rotors spinning at high speeds can catastrophically fail (rotor bursting), releasing a large amount of kinetic energy. Because of the danger associated with rotating component failure, it is important to understand the design integrity of the rotor against a burst, testing to validate the engineering model and establish accurate safety margins above the maximum rated operating speed of critical components.

During a burst spin test, the rotor is spun until it ruptures under CF load. A burst test can be performed either at ambient or elevated temperature conditions.

Capturing the Burst Event with High-Speed Video
Within the spin pit, we designed a setup to capture the burst event with high-speed video cameras. By observing how the rotor bursts, the Test Devices by SCHENCK team provides key insights to our customers into where and how the failure happened, enabling the engineers and designers that developed the rotors to make necessary adjustments. The images from the high-speed video will pinpoint the initiation point of the failure, saving many hours of painstaking investigative work involved in a failure investigation.

We can set up spin tests that subject the rotor to its realistic operating temperatures. Temperature can significantly affect the material strength and damage mechanism, making it a key ingredient in performing more realistic testing. Performing a spin test at the rotor’s operating temperature gives a superior demonstration.

Fatigue is common and perhaps one of the most prevalent damage mechanisms. Historically, people have suffered the consequences of fatigue damage that resulted in catastrophic failures of machines and structures.

Low-Cycle Fatigue (LCF) testing is an important method for evaluating the durability of a rotor. Each cycle of an LCF test typically represents an operational cycle. For example, for aircraft engines, each cycle typically represents a take-off to landing cycle.

We perform LCF tests for tens of thousands of cycles for each rotor. Between the cycle segments, the rotor is inspected for signs of fatigue cracking. The criteria for a successful LCF test depends on the anticipated operating life of the machine. When it comes to automotive parts or aerospace propulsion systems, rotors are required to demonstrate a high degree of durability with conservative safety factors.

Learn more about Test Devices by SCHENCK’s LCF testing and Crack Detection system and how it could lower costs, or schedule your low-cycle fatigue testing work here.

Test Devices by SCHENCK offers precision balance checks and dimensional inspections before (pre-test) and after (post-test) spin test runs. The pre-test determines the rotor’s balancing and dimensions before testing begins, whereas the post-test checks to see if the spin testing caused any change to the rotor.

In a spin test, the stress in the rotor could reach its yield limit, and it could lead to unexpected permanent changes in the rotor dimensions. For tightly toleranced features in high-performance machines, such as blade tip clearance in jet engines and air gap clearances in EV and E-Propulsion motors, unwarranted dimensional change could negatively impact performance. Similarly, concerns exist for rotor unbalances – any degradation in the unbalance level after a spin test or over a set of LCF tests is often undesirable. Rotor unbalance is one of the main causes of vibration and noise in vehicles, which could affect anything from ride quality to structural wear and damage.

SCHENCK is the global leader in balancing technologies. By leveraging SCHENCK’s expertise, Test Devices can offer not only spin testing services but also precise dimensional inspection and rotor balance measurements, all under one roof. Our goal is to provide the most relevant engineering data and engineering insights that our customers need to optimize their product designs.