The traction is generated between a upper specimen (ball or barrel) in contact against a rotating disc. The upper specimen can be either rotating or stationary.
Standard MTM test setup
MTM Traction disc
This is a disposable, highly polished steel disc and during the test the ball is loaded onto its upper polished surface. It is attached to the vertical driveshaft in the lubricant pot.
This is a super finished AISI 52100 (535A99) test ball. The highly polished surface finish of the ball plays an important role in the repeatability of test results and in reducing disc wear during each test. Each ball should be used only once. The balls are supplied with a drilled hole to allow them to be attached to the ball drive stub shaft for the traction measurements. The test ball can be interchanged with alternative upper specimens.
Standard specimen configurations
The standard MTM specimens are made of AISI 52100 steel. Several sizes of specimens are available, giving the user access to a wide range of contact pressures.
MTM Specimen configurations
Contact shapes and pressures
The most commonly used configuration, the ¾" ball on disc, creates a point contact, allowing contact pressures up to 1.25GPa. The ½" ball generates a higher contact pressure and the smaller size makes it compatible with the PCS mini-pot and with some surface analysers . The small radius of the barrel creates a high pressure elliptical contact. This specimen has recently been used to investigate scuffing. Contact pressures available (load range 5-75N) for each steel specimen configuration:
Contact shape and pressure at 37N - Scale 1/100
MTM Specimen contact pressures
Hardness and surface finish
The MTM steel discs can be tailored to your needs with a choice of surface finish from rough (Ra > 0.5 μm) to mirror finish (Ra < 0.01 μm). The discs can be heat treated to achieve various hardness, from fully annealed (185HV) to through hardened (760 HV).
Measuring the specimen surface finish
Specimen material choice
MTM balls and discs have been manufactured in a wide selection of materials, in response to specific customer requirements.
Selection of steels
The selection of steels has been recently broadened to include M2 tool steel. Its high tempering temperature means it can be heated up to 550°C without softening. This property makes the M2 specimens suitable for most coating processes such as sputtering, PVD and CVD.
|Material||Indicative available hardness||Comments|
|AISI 52100 (EN31)||185 to 760 HV||Bearing steel, through hardened|
|AISI 8620||200 to 760 HV||Low alloy steel suitable for case hardening|
|AISI 1015 (EN32)||200 to 760 HV||Contains no chrome. Suitable for case hardening|
|AISI 316||150 HV||Austenitic stainless steel|
|200 to 650 HV||Heat treatable martensitic stainless steels|
|Tool steel M2||Up to 800 HV||Suitable for coating (DLC for example)|
Non ferrous metals and others materials
While the surface finish influences the lubrication regime, the material components affect the surface chemistry in the contact (additives reaction). Studying specific applications is possible with the MTM as the specimens can be manufactured from a range of materials.
|Non Ferrous metals||Other Materials|
|Bronze||Tungsten carbide WC|
|Aluminium alloy||Elastomer O rings|
Assortment of MTM discs manufactured from different materials
Using a material with different mechanical properties allows a wider range of contact pressures (up to 4.1 GPa between a steel barrel and a tungsten carbide disc). Non ferrous metals have typically a low hardness (<200HV), whereas WC specimens are much harder (>1500 HV). This hardness enables a very fine surface finish.
Mirror finish on WC disc
PCS can supply DLC (diamond like carbon) coated 52100 steel specimens [a-C:H coating, sp3 ~ 50%, H ~ 40%]. The coating process runs at a temperature low enough to not significantly soften the specimens. For coating processes involving a temperature greater than 200°C, the specimens can be made of M2 tool steel. These specimens are sold uncoated or coated as required. Specimens can also be supplied coated using a chemical process. For example, electroless nickel plating can deposit a layer of nickel-phosporous alloy of various percentage of phosphorus.
Below is information on some of the existing specimens. Please contact PCS to discuss alternative material composition, finish or hardness.
Test Specimen Packs
|MTMSSP||MTM standard specimen pack (10 discs + 10 x ¾” balls)|
|MTMRSP||MTM rough specimen pack (10 discs + 10 x ¾” balls)|
|MTM1/2SSP||1/2" MTM specimen pack (10 0.5" discs + 10 0.5" balls)|
|MTMPPAK||MTM pin pack (10 rough discs + 10 pins)|
|MTMMINISSP||Mini-Pot MTM specimen pack (10 4mm thick 0.5" discs + 10 0.5" balls)|
Test Specimens – Balls
|BALLD||Drilled 3/4" AISI 52100 precision steel ball|
|BALLD1/2||Drilled 1/2" AISI 52100 precision steel ball|
|MTMWC3/4DBALL||MTM 3/4" drilled tungsten carbide ball|
|MTMWC1/2DBALL||MTM 1/2" drilled tungsten carbide ball|
|MTMGBALL||Drilled 3/4" glass ball|
|MTMB3/4AL2O3||Drilled Aluminium oxide 3/4" ball|
|MTMB1/2AL2O3||Drilled Aluminium oxide 1/2" ball|
|BALLDM2||M2 tool steel drilled balls|
|MTMCB||MTM Copper Ball|
|MTM1BALL||1" AISI 52100 steel ball|
|MTM1BALLB||1" bronze ball|
|MTMDLCBP||MTM 3/4'' ball coated with pure DLC|
|MTMDLCBD||MTM 3/4'' ball coated with Cr doped DLC|
|MTMBPDMS||MTM Drilled Balls from PDMS|
Test Specimens – Discs
|MTMPD||MTM polished disc (standard) (Ra ~ 0.01 μm)|
|MTMDSA||MTM disc steel rough finish (0.15 micron)|
|MTMPD1/2||MTM polished disc (standard) for 1/2" ball|
|MTMMINDISC||Disc for Mini-pot|
|MTMWCDISC||MTM tungsten carbide disc|
|MTMPDM2||M2 tool steel polished discs|
|MTMUPDM2||M2 tool steel (unpolished) discs|
|MTMBRD||MTM bronze disc|
|MTMCD||MTM Copper Disc|
|MTMGD||MTM Glass Disc|
|MTMCD||MTM clutch disc (smooth)|
|MTMBD||MTM brake disc (rough)|
|MTMAD||MTM Aluminium disc|
|MTMD440C||Stainless MTM disc (440C)|
|MTMD3/4AL2O3||MTM disc for 3/4" ball in AI203|
|MTMD1/2AL2O3||MTM disc for 1/2" ball in AI203|
|MTMDLCDP||MTM disc coated with pure DLC|
|MTMDLCDD||MTM disc coated with Cr doped DLC|
|MTMSDS||MTM steel discs - 185HV|
|MTMCMD||MTM clutch material discs|