LOCKED AND LOADED
Load testing of power transmission units is a proven cost saving tool as any problems can be easily identified and rectified prior to onsite installation. Loaded and unloaded testing of critical gear drives proves that individual components and complete assemblies are fit for service before expensive transport, labour and downtime is incurred.
The AMR visited Gear Drive Services (GDS), in Wangara, WA, to look at the process of disassembling, checking, refurbishing and load testing gearboxes and drives commonly used in mining applications.
Gear Drive Services specialise in industrial power transmission service and repair. The company recently designed and built a 6000m2 workshop specifically to accommodate overhaul, refurbish, load test and engineer all types of industrial reducers, speed increasers, wind turbines and fluid couplings.
STRIP AND ASSESS
The first step in the process is to strip down the drive unit and assess its condition. This step is completed on every component which comes in for overhaul.
A detailed report is completed on the gearbox to include a minimum of gear mesh contact, gear mesh backlash, bearing/shaft end floats, visual inspection on every component, dimensional inspection on every component and nondestructive testing (crack detection) on gearing, shafts, couplings and housing.
The condition of all components is photographed and a detailed written report completed.
All components must adhere with OEM tolerances and specifications.
The quality of repaired or manufactured components meets or exceeds OEM specifications.
Assembly on every component is carried out following stringent procedures and a very high standard of workmanship. Bearing/shaft end floats are checked and set to OEM specifications.
Spiral bevel gear sets are setup to achieve the optimum blue contact/ gear mesh and the correct backlash, always while considering things such as thermal growth, the type of bearings installed and the direction of thrust caused by a combination of left or righthand gearing and direction of rotation.
Helical gearing backlash and blue contact is checked, while considering gear tooth profile corrections such as crowning and tip relief.
All dimensional measurements and settings are recorded, photographed and double-checked by another technician.
Load testing is completed on all overhauled drives and fluid couplings. Gear Drive Services have a highly advanced testing facility and some of the most rigorous testing procedures in Australia, with the capability of testing industrial reducers, speed increasers, wind turbines and fluid couplings.
Their advanced control system can test different styles of power transmission gearboxes and simulate exact operating conditions onsite, with the ability to test gearboxes with a power range from 10kW to 3500kW ranging from ratios of 5:1 to 900:1.
Testing such a broad spectrum of power and ratios has its challenges. Every setup must be carefully thought out considering that some load tests exceed 250,000Nm of torque at the gearbox output shaft.
Load test tooling, adaptions, test shafts, couplings and mounting brackets need to be specifically engineered for every load test with expected power and torque figures kept in mind. The latest upgrade to the facility will permit the testing of full drive assemblies. This means that a complete drive assembly, such as a ship loader or bucket wheel drive, can be load tested utilising the final installed motor and coupling arrangement.
The customer’s motor will be connected and tuned to our control system so a load test can be carried out on the entire assembly.
Load testing has proven to be a vital and critical step of the overhaul process as any minor problems can be captured and rectified prior to installation onsite, thus saving transportation costs, installation and removal costs onsite and ultimately unexpected down time and loss of production. Our latest upgrade will furthermore prove that all components are fit for service prior to arriving onsite and improve the reliability of customers’ core components.
Gear Drive Services have assisted in developing a control system specifically for load testing industrial drives. The main objective for the control system is to simulate the exact operating conditions any drive would see while in service.
The way in which different types of industrial drives experience loaded conditions in service is actually very different with different types of drives. For example, when looking at a conveyor drive, the input shaft/highspeed shaft is driven by the installed motor.
When considering a wind turbine gearbox or power generator, the highspeed shaft is actually the output shaft and is driving the generator, therefore operating in a braking type scenario. These different scenarios require different programming and different control measures to accurately simulate each test.
GDS’s system operates in torque control mode, which means the torque on the high-speed shaft is maintained and will not fluctuate more than 1 Newtonmeter (Nm) for any test carried out.
The system has the flexibility to maintain the driving torque or the braking torque. This is how the system has the capability to accurately test a conveyor drive as well as a wind turbine gearbox.
With any given test, one motor will fluctuate power/torque to achieve accurate torque control on either the driving motor or the braking motor. The same accuracy is maintained in relation to the speed (RPM) of the highspeed shaft.
The system has 100pc control of the rpm “ramp” rates and torque “ramp” rates. This means GDS can program how fast the torque is applied and how quickly the drive reaches the desired rpm.
Having this flexibility makes it possible to simulate the torque/power fluctuations a drive might see while in service. This has been a very valuable control measure on certain load tests. GDS have set up strain gauges for certain load tests and simulated a load spike coming onto a gearbox to record exactly how the gearbox is acting.
Testing such a variance of different size drives means the system needs to have advanced safety measures in place to ensure no damage is incurred during any load test.
The control system has several pages where the gearbox parameters must be programmed before a test can start, as well as a test program which is customised to suit every different gearbox tested.
All the different setup pages work to insure that the customer’s gearbox is never overloaded. The safety limits are controlled via four main criteria: torque; power; speed and temperature. If any of the programmed values are exceeded, the test will automatically shut down.
While any test is running, the load test cell is logging the data and collecting it in 1-second intervals for the duration of the test. The main data streams collected include motor speed, torque, power and gearbox temperature.
It also captures all the parameters which were entered on every setup page as well as the testing program written for the test. When a load test is complete, there is also an option to create a test report.
The load test cell takes the recorded data and generates a condensed PDF report. This report includes the test program, the gearbox temperatures reached and the power and speed figures which were attained. The data is translated into colour-coded graphs for a visual representation of the test results. The load test report is then submitted to the customer.