Spin Test Machine Applications For Rotating Components
The image at the top of this post shows one of the fragments of a steam turbine rotor that broke into four pieces during a testing accident in 1970. The fragment was found in Nagasaki Bay, 880 meters away from the test site.
Rotating components in high-speed machinery operate under extreme centrifugal stress. A burst failure can be catastrophic. Components in the hot section of a turbine engine also experience incredible temperatures for extended durations. Spin testing is a critical step in the engine development cycle for verifying the centrifugal strength of rotors, disks, blades, and more in extreme conditions.
What Goes Into a Spin Test Machine?
A modern spin test machine consists of a rotor suspended from a flexible spindle in a heavily armored “spin pit” — a term that’s a relic of a time when these chambers were positioned in a hole in the ground. Today’s testing chambers don’t require this precaution, as the thick steel armor of a modern testing cylinder can withstand enormous forces. Spin chambers are often lined with a layer of lead to further mitigate impact shocks.
Most spin test machines will use a vacuum chamber to eradicate friction losses (from air particles) and maximize the potential speed of rotation. Risks like friction heating and aerodynamic destabilization are also eliminated in a vacuum.
Image: An Aerodyn spin test machine
Spin test machines have diverse purposes and can test many types of components. Here are a few of the most valuable spin testing applications for high-speed rotating components:
5 Spin Test Machine Applications
- Spin Burst Testing: A centrifugal burst disaster can be catastrophic in rotating machinery. Establishing safety for service is especially critical in jet engines and other human-interfacing applications. Verify the strength of rotors and other turbomachinery components to prevent failures with explosive force. Data analysis from spin burst testing will not only establish upper limitations on rotation speed, but the expected fatigue life of high-performance disks or rotors.
- Hot Spin Testing: Gas turbines and compressor rotors operate at extreme temperatures. Any rotating components within the hot section of a turbine must be tested at an appropriate temperature to ensure proper performance. Hot spin test machines are fitted with heat-resistant spindles and seals (and other modifications to control the damper temperature) to enable testing at temperatures of up to 2000 °F. While a vacuum will prevent convective heat transfer (mostly), infrared radiation from resistive heating elements can still heat the rotor.
- Adhesion Testing for On-Blade Sensors: Adhesives must retain strength at high temperatures and show the ability to remain bonded at incredible g-loads. In-situ contact sensors and any other components bonded to rotating components will need spin testing to evaluate bonding materials. Aerodyn heated a spin test machine to 350°C (662°F), for instance, to assess the bonding method for TurboTrack™ sensors from Sensatek. The proprietary bonding materials demonstrated success in extreme environments, remaining adhered at g-loads up to 16,000g and temperatures up to 350°C (662°F).
- Controlled Atmosphere Testing: A vacuum spin test will often show a shorter life for turbine blades than they would exhibit in real-world service conditions. For example, the absence of air is known to accelerate the fretting of a blade fir-tree root (a common blade-to-disc connection style in low-pressure steam turbine blades). An appropriately engineered spin test machine — with careful controls for temperature and aerodynamic losses in place — is capable of safely simulating up to one atmosphere of pressure during a heated spin test.
- Vibration Testing: Vibration during rotation can cause blades and disks to interact in unique ways at different frequencies. Test rotating parts in different vibration conditions to understand the impact of HCF conditions and various resonant frequencies on the operating performance of rotating parts. A bladed rotor can be excited with air or oil jets within the spin testing machine. Analysis of test data will reveal damping parameters, even for individual blades.
Maximize Test Data on Rotating Components
The spin testing rig is a valuable piece of equipment, but the best data will come from continuous monitoring of thermal conditions and strain on rotating components — not one-time, limited datasets from test stands. Consider deploying in-situ RF sensors that survive the life of the turbine for real-time data that will become a life model of engine conditions.
The TurboTrackTM sensor system is the industry’s first in-situ temperature and strain monitoring system for rotating parts. Bring real-time, repeatable trend data to your components beyond the initial heated spin tests in the development cycle. RF sensor data helps you to predict maintenance needs, extend engine life, increase energy production, and reduce the catastrophic risk of failures during service.
Aerodyn spin tests have verified that our sensors remain bonded in the extreme environment of a turbine engine, and OEMs have verified an unparalleled material lifespan of up to 40,000 hours. Our compact, wireless design can be installed without full engine teardowns or time-consuming and costly re-instrumentation. Get in touch with Sensatek for more information on these groundbreaking sensors.
Featured Image: Wikimedia Commons