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The Open Loop Two/Three Roller Test Machine is a research machine for the study of highly loaded lubricated power transmitting contacts and rolling contact fatigue of materials.
The successful operation of machine elements such as gears, rolling bearings, cam/follower systems and traction drives is vital to industry. The common feature to all these is that fact that power or motion is transmitted through highly loaded lubricated contacts with rolling or combined rolling and sliding motion.
The high loads (or contact pressures) result in elastic deformation of the surfaces in contact and the components operate under elastohydrodynamic lubrication. The performance of the gear, cam or bearing is dependent on both the material and the lubricant withstanding the highly stressed conditions in the contact.
In the case of gears, the motion of rolling and sliding at a given instant in the meshing cycle can be reproduced by two circular rollers of radii equal to the pitch circle rotating with equal and opposite angular velocity about fixed centres. This is the basis of the two roller machine first developed by Merritt in 1935 to simulate conditions in the gear contact. Since the radii of curvature of the teeth at the contact point are the same as the rollers the contact stresses under a given contact load are also simulated by the roller machine.
For gear contacts, the obvious departure from complete similarity arises from replacing the cyclic behaviour of tooth meshing by a steady motion which reproduces the conditions at only one instant in the meshing cycle. However this does at least mean that one condition can be studied at a time and only transient effects are ignored.
In traction drives even more attention is focused on the lubricant since the power transmitted by the drive is limited by the coefficient of traction of the fluid. Petroleum based oils possess neither the lubricating power at high pressures nor the chemical stability for the high temperature/stress conditions in the contact. Therefore new lubricants with piezo-viscous properties and good molecular stability are being developed.
The traditional method of studying the performance of such fluids under controlled conditions is by using a two roller machine. In the Plint TE 73, the two rollers are driven at different speeds through a back-to-back gear arrangement to give fixed percentage slip in the contact and therefore to transmit increasing amounts of traction. The maximum traction coefficient is obtained at a particular value of slip and this is a characteristic of an individual fluid. With the TE 103, infinitely variable percentage slip between 0 - 50% is provided by the use of twin drive motors and digitally locked drives.
In variable ratio gear systems there is an additional complication. It is an inherent property of this kind of mechanism that there is a velocity gradient across the width of the contact zone in a direction perpendicular to the rolling direction. In other words there is spin in the contact zone. The effect of spin is to modify the traction-slip characteristic. The distinction between the high and low slip regions is lost and instead there is a more gradual growth in traction as slip increases.
This phenomenon can be studied by introducing a third disc between the two rollers that is free to rotate about a vertical axis. This is the TE 73/S Contact Spin Adapter.
In the TE 103 roller specimens are mounted on the ends of parallel test shafts which are connected to separate ac machines each rated at 65kW up to 6000rpm. One shaft is connected directly to the ac machine, the other is connected via a special 0.99:1 ratio gearbox. The ac machines are driven by two digitally locked vector drives and controlled using the COMPEND 2000 control and data acquisition system.
Slip percentages from 0% (pure rolling) to 50% are selected by entering the required master ac machine speed (compensating for the gearbox ratio) and slip ratio set points. Each machine incorporates digital feedback to provide absolute speed holding.
The lower shaft housing is fixed while the upper housing is hinged to allow motion in the transverse and vertical directions only, guidance being provide to ensure that the rollers do not skew relative to one another. A static compressive load is applied to the rollers using an hydraulic actuator under feedback control, hydraulic power being provided by a small integral power pack. A lever technique is employed to apply the set point load to the roller contact and the applied load is measured by an in-line strain gauge load cell. A separate load cell mounted in the transverse direction measures the traction forces in the contact of the upper test roller.
The upper shaft/casing are insulated electrically from the rest of the machine. This allows a small potential to be applied across the roller contact via integral slip rings. Variations in this voltage can be used to give an indication of the frequency of inter-metallic contact between the rollers.
All rotating parts of the machine are guarded for worker safety. Further, the COMPEND 2000 software incorporates Alarm Level checking features that are switchable from step to step to take account of changing load conditions. There are two types of alarm, for warning and for machine shutdown.
The machine may be used in several modes:
As a Two Roller Machine with 152 mm diameter rollers
As a Three Roller Machine with 60 mm diameter rollers on the main shafts and a free rotating third roller of mm diameter in between. The lower roller is then driven in reverse.
As a Slide/Roll/Spin tester with the TE 73/S Contact Spin Adapter and 120mm diameter rollers
As a Slide/Roll/Spin tester with 60 mm diameter rollers and other spin disc sizes
The 152 mm Two Roller Mode and TE 73/S Spin Mode are standard.
The test rollers run inside an aluminium housing fitted with heating elements to allow control of the housing temperature above ambient up to 120 degrees C. A recirculating cooling fluid is used in conjunction with a cooling plate within the roller housing when testing with dip lubrication and the large 152 mm rollers. Cooling of the fluid is provided using a Recirculating Coolant Service Module.
Pumped sample fluid lubrication is required at high rolling speeds and with the TE 73/S spin adapter. This is provided by jets in a series of locations within the housing. The temperature and flow rate of the sample fluid is controlled by a separate Recirculating Sample Fluid Service Module and thus allows some control of the roller temperature. Bulk temperature of the upper roller is measured using a trailing thermocouple.
The TE 103 has COMPEND 2000 PC based sequence control and data acquisition resources incorporating an integrated SLIM 2000 Serial Link Interface Module.
| Speed Range: | 100 to 6000 rpm |
| Rolling Velocity: | 0.75 to 48 m/s (For 152 mm diameter rollers) |
| Load Range: | 0.25 to 15 kN |
| Maximum Peak Hertz Stress: | 2.8 GPa (Steel rollers 152 mm diameter) |
| Contact Pattern: | Elliptical |
| Slip Rate: | Infinitely variable +/- 20% |
| Motor Power: | 65 kW each of two ac machines |
| Rotational Speed of the Test Rollers | |
| Slip Ratio | |
| Load | |
| Temperatures: | |
| Sample fluid supply | |
| Roller housing | |
| Test Duration |
| Rotational Speed of Rollers and Spin Disc | |
| Load | |
| Slip Ratio | |
| Traction Force | |
| Temperatures: | |
| Roller surface (side) | |
| Bulk oil | |
| Sample fluid supply | |
| Sample fluid return | |
| Roller housing | |
| Bearing housing | |
| Contact Resistance | |
| Test Duration |
| Roller Diameter: | 120 mm |
| Crown Radius: | 20 mm |
| Spin/Roll Ratio Capability: | 0.8-1.33 |
| Maximum Peak Hertz Stress: | 2.5 GPa (Steel rollers 120mm diameter) |
| Contact Pattern: | Elliptical (2.36 ellipticity) |
| Sump Capacity: | 5 litres |
| Feed/Scavenge Pumps: | Positive displacement gear pump |
| Pump Power: | 0.37 kW |
| Flow Rate: | 4 litres/minute maximum |
| Flow Sensor: | Gearwheel type for high viscosities |
| Turbine type for low viscosities (up to 20 cSt) | |
| Rated Feed Temperature: | 120°C |
| Rated Return Temperature: | 180°C |
| Heater Power: | 3 kW (surfaces in contact with test fluid <150°C) |
| Circulating Fluid: | Heat transfer oil |
| Feed Pump: | Positive displacement gear pump |
| Pump Power: | 0.37 kW |
| Flow Rate: | 4 litres/minute maximum |
| Control Valve: | 3-way electric |
| Electricity: | 460V, three phase, 50/60 Hz, with neutral, earth and isolator, 120A |
| Water: | mains water and drain, 15 litres/minute at 20°C |
| Compressed Air: | clean, dry air at 8 bar supply pressure, 1 micron filtered |
| PC and Printer: | Minimum Specification |
| Machine: | 960 mm x 2400 mm x 2200 mm |
| Control Cabinet: | 600 mm x 800 mm x 1950 mm |
| Power Module: | 1200 mm x 600 mm x 1800 mm |
| Sample Fluid Module: | 525 mm x 925 mm x 500 mm |
| Heat/Cool Module: | 525 mm x 925 mm x 500 mm |
Copyright © 2003 Phoenix Tribology Ltd.