Overview

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.

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.

Test ball

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.

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:

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).

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
AISI 440C AISI 420S29	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
Copper	Glass
Brass	Elastomer discs
Aluminium alloy	Elastomer O rings

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.

Coatings

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.

Available specimens

Below is information on some of the existing specimens. Please contact PCS to discuss alternative material composition, finish or hardness.

Test Specimen Packs

Part Code	Description
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

Part Code	Description
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

Part Code	Description
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