Over-Speed (Proof)
Spin Test Systems
Technical Description
Over-speed spin pits are predominately used to perform a few specific spin tests. Over-speed or proof tests are typically run to prove component integrity, following preliminary machining or component repair, or for pre-stressing rotors prior to final machining. This model of spin test system incorporates all of the basic spin pit modules and provides an efficient and cost effective means to proof test high speed rotating components.
The over-speed spin test model system includes the following modules:
1.0 SPIN TEST CHAMBER
The containment system is purposefully designed to insure containment in case of a burst. It has the ability to contain the energy of even higher energy rotors than those for which it is designed. A well designed and robust spin chamber is the most important component in a safe spin test system..
1.1 CASING
The casing is fabricated from high strength steel and is intended to enclose the entire test chamber and sustain a vacuum using airtight seals. The inside of the casing is larger than the outside diameter of the containment cylinder (Armor Cylinder, see 1.1.6) to allow the inner safety liner to expand if it is overloaded. This extra room is important because it allows the containment cylinder to stretch and absorb energy without ruining the vacuum chamber during an exceptionally high energy burst.
Figure 1 - Spin Chamber Layout
1.2 COVER AND LID
The cover is constructed of 3” thick, high-strength alloy steel, and is bolted to the casing with one-inch dia. grade 8 fasteners, providing robust cover retention capacity. There is an O-ring vacuum seal between the casing and the cover, and the cover is removable for access to the entire chamber.
The lid is piloted precisely in the inner diameter of the cover and is sealed with a generously sized O-ring retained in a dovetail groove. The drive is mounted in a center bore with a bolt pattern designed to accommodate all industry standard turbines and drives. The lid opening is determined by the size of the rotors which will be tested and come in standard size of 18, 24, 36, and 48 inches, with additional sizes available.
1.3 LID DOGS
The lid is held in place by four servo-actuated, high-strength cover locks (lid dogs). The lid dogs are a mechanical safeguard to insure the lid remains in place in case of a high energy rotor failure with a strong axial component. Intrinsically, one readily recognizes the risk of a rotor failing in a radial fashion, but containment of burst fragments presented in an axial fashion can easily be overlooked in the design of a spin chamber. Consequently, the most dangerous spin chamber failure can be the result of axial force exerted on the lid of a poorly designed spin chamber.
The lid dogs are controlled by a special closing and interlocking system to prevent operation of the spin system without the cover locks in place. The lid dogs can only be opened if the drive turbine is not rotating and the vacuum has been vented. This feature is important because the highest risk of a deflagration is when air is being introduced through the vent to the dust or oil mist in the chamber.
1.4 LID ELEVATOR
The test article is hung vertically from a spindle that extends below the bottom of the lid. The elevator system is designed to offer quick and convenient manipulation of the lid and test article in and out of the spin chamber. This is important for high-throughput production systems, especially when large or heavy test articles are involved. Once the lid and test specimen clear the top of the chamber, the elevator system can rotate the assembly by as much as 180° in either direction. The entire system is hydraulically powered with the controls located away from the heavy test article to protect the operator from injury.
This system is particularly important in a production application where articles must be changed rapidly and routinely. The elevator system maintains alignment, especially while lowering into the chamber, and allows smooth coupling and uncoupling. This protects the test specimen from touching the sides of the chamber and avoids damage of the drive spindle when the test rotor is being changed out.
Figure 2 - Spin Chamber Lid With Lid Dogs and Turbine
1.5 AIR FLOAT COUNTERBALANCE (OPTIONAL)
Small parts are easily attached or removed from the spindle manually. An elevating die cart with a hydraulic lift mechanism is convenient for parts too heavy to be lifted manually.
An Air Float Counter-Balance (see Figure 3) is installed on the side of the spin chamber for handling heavy rotors. The test rotor is placed on the top of the small pneumatic lift, which is constructed around a very low friction rolling diaphragm cylinder. The weight of the rotor is exactly balanced by adjustment of the high-resolution pressure regulator so that the heaviest rotor can be moved up to the spindle with only finger pressure. This system allows easy coupling and uncoupling of test parts to the drive system. The centerline of the counterbalance is located exactly on the centerline of the lid when it is moved into position.
Figure 3 - Optional Air Float Counterbalnace
1.6 LEAD BRICK LINER
Test Devices uses a soft lead liner inside the forged steel armor cylinder (see 1.1.6). The lead is a soft material that:
- Catches fragments to prevent their ricochet internally, especially against the cover;
- Limits formation of explosive metal dust (an especially serious problem for rotors containing aluminum and/or titanium);
- Spreads out the time of force application (F= m* v /Dt) to reduce the impact force significantly; and
- Damps resonant vibration of the liner during the impact event. These vibrations have been calculated to double the stress in the armor cylinder without damping.
Figure 4 - Lead Bricks and Retention Ledge
1.7 ARMOR CYLINDER – PRIMARY CONTAINMENT
The steel armor cylinder used for the primary containment of an uncontrolled burst is forged, heat treated, and machined to a thickness of nine inches. The single piece forging eliminates welds reducing stress concentration and strength issues. It is designed to yield only under overload conditions, with an 18% elongation. Test Devices designs its armor cylinders so that they will be fully elastic in both shear and tension, and they are reinforced at the top and bottom by a retention ledge. This feature strengthens the ends of the cylinder and prevents the extrusion of the soft lead inner liner against the covers.
Test Devices’ philosophy for containment is that a burst is always possible and the spin test system must survive burst without damage to the primary containment. A robust armor cylinder is mandatory for long-term safety of the machine and the operator. To read more about Test Devices’ philosophy on spin test safety please see http://www.testdevices.com/anatomy1.htm.
2.0 CONTROL AND MONITORING CONSOLE
The control console is specifically designed to be the most productive in the industry. Listed below are its major elements and features.
Multi-function digital tachometer, including fast response overspeed trip. The tachometer displays six digits and includes a high-speed computer communications interface. The tachometer is a microprocessor-based instrument developed by Test Devices specifically for spin test applications. It includes dual sensor input with crosscheck comparison to protect against sensor failure, as well as quadrature detection for sensing the rotation of direction of the drive. The over-speed trip system includes a relay for direct control of the system safety trip valve.
The tachometer includes an internal calibration standard oscillator periodically measured by the internal processor to continuously verify accuracy.
Liquid-damped pressure gauges indicating air supply, drive nozzle, brake nozzle, and oil pressure.
Figure 5 - Control Console
Electronic vacuum gauge with limit relay for safety interlock.
Spin stability monitor (vibration meter) using a non-contact proximity probe to measure the vibration of the test piece mounting arbor. The measured eccentricity is displayed on a panel meter in thousandths of an inch, and automatic shutdown is provided. An automatic bypass prevents shutdown at the low speed resonance.
Turbine speed control system for accurate regulation of steady-state test protocols, including proof tests, burst tests, overspeed tests, etc. Acting in conjunction with the high-speed servo pressure regulating valve, the controller regulates turbine speed within 0.2% of full speed scale throughout the duration of a test.
2.1 SYSTEM SOFTWARE DESCRIPTION
Operator control display. The display is a software and hardware system built on a PC with SVGA high-resolution color graphic display. The computer used is a standard model, easily maintained by local resources. Operator control is through a mouse or keyboard for simple operation. The operator controls the equipment by clicking buttons displayed on the video screen. Several different display screens are used for equipment control and test operation. The display system is carefully designed to give information to the operator when it is needed, but also eliminates confusion by only displaying required screens.
The operator display includes several screens that are rapidly accessible as needed, and each screen includes several programmed "softkeys" to control the various stages of the test operation.
Each rotor to be tested can be listed on the “setup” screen with speed and test duration. The operator sets up the system by using a keyboard and mouse to chose the label with the rotor identifier code, and the machine is then automatically configured to perform the proper test for that rotor. Rotor identifier codes, speeds, and test duration are easily changed by the supervisor using a password to give access to the data to be changed.
The system makes it easy for an operator to run spin tests with very little training. Operating the machine is accomplished by following simple menu commands. In the following section are examples of screens that are part of the operator interface for production testing.
A special software package was developed for the system to provide accurate air turbine control during spin testing.
This regulation is very accurate and eliminates substantial overspeed or underspeed. Special software is included to prevent the turbine from stalling during acceleration and drive control. The amount of energy used for braking during acceleration (and vice-versa) is negligible and it helps maintain a high degree of speed regulation.
Software screens have been developed to transfer input data from the display screen inputs to the PLC (programmable logic controller), and to transfer output data from the PLC to the screen control functions.
2.1.1 EXAMPLES OF CONTROL SCREENS
The following screens are examples of the control software which the operator interacts with through the Human Machine Interface (HMI).
The same Main menu (Figure 6) stays in place at the top of each display screen. Individual buttons on Main are selected by clicking to toggle between screens.
Figure 6 - MAIN Menu
SELECT TURBINE Display
To set up the control system the operator must first select a turbine. Press SELECT TURBINE in the upper left portion of the screen. The SELECT TURBINE screen will then appear as shown below:
Figure 7 - SELECT TURBINE Display Screen
Press one or two under "Turbine Selection" and the selected turbine model and maximum speed will be highlighted. The turbine must be confirmed by the operator by pressing the CONFIRM TURBINE SELECTION flashing button box.
After a few seconds the message box will change to a green colored CONFIRMED TURBINE MAXIMUM SPEED. (This is the screen format shown above.)
Turbine selection can be made only when the vacuum pump is off. As well as being first in the setup procedure, this operation is the most important. The operator must input the correct turbine selection to avoid turbine operation outside of the maximum speed range.
Figure 8 - SETUP TEST Screen for Proof Test
General Test Data - Enter Disk Part No., Device Serial Number and Operator Identification by entering the appropriate information into each of these data fields using the screen keyboard.
The data is then entered into the system PLC by pressing screen button GENERAL.
| Disk Part No. |
Target test speed in RPM (0-60,000 RPM) |
| Disk Serial No. |
Further serial number identification of test rotor |
| Operator |
Identification of the person operating the test. |
Speed Performance Mode - Enter information about Test Speed, Test Time and Speed Tolerance. After data has been entered inside related field, press the PERFORMANCE screen button to send the data to the PLC.
| Test Speed |
Target test speed in RPM (0-60,000 RPM) |
| Test Time |
Length of test time required within the test speed tolerance band |
| Speed Tolerance |
Upper and lower limits on the test speed |
ACCEL DISPLAY Screen
Figure 9 - ACCEL DISPLAY Screen
The ACCEL DISPLAY screen is the core of the system and is central to the turbine service and turbine protection logic during all kinds of tests. It allows the operator to monitor all major test functions easily. Under normal operating conditions, the ACCEL DISPLAY appears as shown above (Figure 9).
The test parameters are displayed in the upper left. The current date and time, taken from the system clock, are shown on the lower left. Be sure they are correctly set, as they will appear on the printed output page from each test.
The speed set point is shown on the ACCEL DISPLAY screen in the upper graph as a straight line (see Figure 9). This graph will be calibrated from 0 to 60,000 RPM. The lower graph is the vibration monitor; it is calibrated from 0 - 10 mils.
All ACCEL DISPLAY window data are entered through the SETUP TEST screen. If any one of the parameters are not properly entered, then red blinking text will appear to highlight the problem. During setup and operation a few small windows will be superimposed on the ACCEL DISPLAY Screen.
Figure 10 - High Resolution SPEED Display Superimposed on ACCEL DISPLAY
This screen displays: the tolerance band, the actual speed and a box containing the remaining test time. The test time clock is only incremented when the rotor speed falls within the tolerance band. (Tolerance is defined in the SETUP Screen.) When the low speed tolerance is crossed: time scanning begins, the system accumulates testing time, and the time remaining for the test is shown in the window. When the test is complete, (time remaining is 0 sec,) the system brakes the rotor automatically.
Figure 11 - Test Setup Screen
Figure 11 shows the “Test Setup Screen” which displays the following parameters:
General Data
- Disk Part No. = Part number of test piece
- Disk Serial No. = Serial number of test piece
- Operator = Technician/Engineer who is running the test
Proof Testing
- Test Speed = Ultimate maximum over-speed (37,800 RPM)
- Test Time = Time in seconds to complete proof-Test Devices (420 seconds)
- Speed Tolerance = Accuracy of maximum test speed (+/-)
System Control PLC - The system is controlled and supervised by a high-reliability industrial computer called a Programmable Logic Controller (PLC). The PLC is designed for use in an industrial setting and is protected against errors caused by electrical interference, etc. All switches, contacts, and actuator coils are connected as inputs to or outputs from the PLC which is programmed to control all system functions in response to operator commands. The PLC helps the operator control the system safely, preventing inadvertent errors that could endanger the equipment or the operator. The PLC provides control in three primary areas: Drive, Lubrication, and Vacuum. The PLC monitors each function listed below and links the data into the safety interlocks and onto the alarm and fault displays:
All system fault contacts must be in a safe condition for the turbine to run. When no fault exists, the interlock indicator will turn on.
If any system fault interlock is in an unsafe condition, the interlock fail indicator is displayed and the drive will not start. If the drive is running when the fault occurs, the auto brake function is enabled, and brings the drive to a stop rapidly and automatically.
Printer - The printer is used to make a permanent record of each test by printing an image of the operator control screen at the end of the test. A data block on the screen allows the operator to input the serial number of the rotor which has been tested, then the document can be printed and stored as a permanent part of the production record for each rotor.
Non-interruptible power supply - A battery-backed inverter power supply is installed in the system to operate all controls and instruments during a power failure. The capacity of the battery backup system is sufficient to maintain operation for 10 minutes after failure of the main supply. If a test is being run in automatic mode, power failure will cause the application of the brake until the rotor has stopped or until main air supply is exhausted.
3.0 DRIVE SYSTEM
Figure 12 - Test Devices Air Turbines
3.1 HIGH PERFORMANCE DRIVE ASSEMBLIES
A variety of drives are available and can be installed to suit specific testing requirements, covering the complete speed range of up to 160,000 rpm. The 600 series air turbines are robust and reliable drive systems well suited to overspeed spin testing requirements. These models deliver high horsepower output despite their comparatively small and compact packages. The compact design of these turbines permit easy mounting and removal from the spin chamber, requiring only a few connections or dis-connections. The 600 series air turbines come in the following standard models: 608 – 30,000 rpm, 606 – 40,000 rpm, 604 – 60,000 rpm, and 602 – 100,000 rpm. Many customers purchase more than one turbine model to satisfy the speed range requirements of the variety of parts they test.
For example purposes, shown below is the performance curve for the Model 604-20 (60,000 rpm) turbine.
3.1.1 Model 604-20 Turbine
| Peak Horsepower |
20 |
| Stall Torque |
67 lb-in |
| Air Flow |
342 scfm at 90 psig |
| Maximum Speed |
60,000 rpm |
The figure below shows the drive and brake characteristics of the 604-20 turbine.
Figure 13 - 604-20 Turbine Perfromance
3.2 DAMPING SYSTEM
Test Devices uses a unique, squeeze-film spindle damper on its spin test turbines and motors. These robust, innovative damping systems have solved serious vibration problems common with other spin test spindles. Without robust damping, many test articles are lost during testing due to inadequate performance of the non-linear damping mechanisms used by other suppliers. Test Devices operates a high volume spin test service business using its own spin chambers, turbines and dampers. Since development of the damping system, TDI has avoided ruining test rotors countless times due to a broken spindle.
Figure 14 - Drive Spindle Successfully Damped
Figure 14 shows a drive spindle attached to a composite flywheel which underwent high vibration nearly causing failure during the test. The test piece was saved due to Test Devices’ robust damper. This allowed the operator to slow the rotor to 0 rpm without snapping the spindle and dropping the flywheel.
4.0 VACUUM SYSTEM AND LUBRICATION MODULE
Operating in and maintaining a constant vacuum is necessary for several reasons:
- It reduces the loading and increases the stability of the rotating components and bearings by eliminating aerodynamic forces (both radial and thrust).
- The absence of oxygen eliminates a fire or explosion hazard in the event of a burst that combines oil mist, reactive metals or other combustible residue.
- Removing the air from the chamber prevents air drag (resulting in the ability to use a smaller drive system and reduced energy demand) and eliminates parasitic heating of high-speed components.
Figure 15 - Vacuum System Connection to Console and Containment
Spin pit and turbine support systems are combined on one skid for simplicity and space conservation. Included in the module is all of the lubrication, scavenge, filtering and vacuum modules as follows:
- Oil Mist Generator for lubrication
- Vacuum Pump and motor capable of a drawing a vacuum of 100 millitorr in. This is a dual-pump vacuum system incorporating an oil-sealed reciprocating pump in series with a positive displacement blower.
- Automatic vacuum valve to isolate the vacuum chamber and prevent loss of vacuum during a power failure.
- Lid lift hydraulic system including a hydraulic pump.
- Dual section hydraulic pump system for turbine bearings and spindle damper lubrication/scavenge.
- Safety interlock system for protection against failure of system support equipment, including oil flow, oil pressure, oil tank level, vacuum, lid dog closure, mist pressure, mist tank level, motor overload, and excess acceleration.
- High-performance, turbine speed regulating valve assembly, including 50 millisecond response time control servo valve, and high capacity slave regulator valve to control airflow to the turbine.
5.0 SPARE PARTS & SOFTWARE UPDATES
5.1 SPARE PARTS
Delivery of an over-speed spin test system will include an initial inventory of spare parts and consumables for all systems and subsystems.
5.2 SOFTWARE UPDATES
Updates of all application software will be provided when available during the warranty period of 12 months after commissioning.
6.0 DATA ACQUISITION SYSTEM (optional)
The data acquisition system has been designed for use in a spin test system environment, and is fully integrated with the control system. The dedicated PC continuously records test parameters including speed and vibration. The application software is based on screen control buttons which are intuitive and user friendly. All recorded test data is stored on the hard drive and can be printed and/or copied to a compact disk.
Figure 16 - Data Acquisition System
For more information, please contact one of our sales engineers at:
| 
