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MTM (Mini Traction Machine)
/ Specimens
On this page: Overview | Specimens available & material choice
Overview
The Mini Traction Machine is a bench top precision traction measurement instrument. It provides fully automated traction mapping of lubricants and other fluids. 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 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. Below is information on some of the existing specimens. Please contact PCS to discuss alternative material composition, finish or hardness.
Specimen
MTM Standard Specimen Pack
(Part code: MTMSSP)
Barrel Specimen
(Part code: MTMBARREL)
½" Diameter Tungsten Carbide Ball
(Part code: MTMWC1/2DBALL)
¾" Diameter Tungsten Carbide Ball
(Part code: MTMWC3/4DBALL)
Highly Polished ¾" Diameter Drilled Steel Ball
(Part code: BALLD)
Flat Tungsten Carbide Lower Specimen Disc
(Part code: MTMWCDISC)
MTM Steel Disc with Rough Finish
(Part code: MTMDSA)
Standard Highly Polished MTM Steel Disc
(Part code: MTMPD)
Description
The standard specimen pack is made up out of 10 drilled balls (BALLD)
and 10 standard highly polished disks (MTMPD).
Flat rotating disk specimen giving a different contact geometry (ellipse)
and contact pressures. Pressure 3.2 GPa.
This is a ½" diameter tungsten carbide ball for use with the MTM in
½" ball mode. The smaller diameter and its greater hardness allows
higher contact pressures to be achieved. Pressure 1.85 GPa.
This is a ¾" diameter tungsten carbide ball for use with the MTM in
¾" ball mode (normal). The hardness of the material allows higher
contact pressures to be achieved.
Pressure 1.25 GPa.
This flat tungsten carbide lower specimen disk can be used as a
lower specimen for the MTM in both ½" diameter and ¾" diameter
ball modes. The hardness of the material allows a higher range of
pressures to be achieved for a given load.
This is a MTM steel disc with rough finish (0.15 micron Ra).
This is our standard highly polished MTM steel disc.
Roughness approximately 0.01 micron Ra.
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
AISI 52100 (EN31)
AISI 8620
AISI 1015 (EN32)
AISI 316
AISI 440C
AISI 420S29
Tool steel M2
Indicative available hardness
185 to 760 HV
200 to 760 HV
200 to 760 HV
150 HV
200 to 650 HV
Up to 800 HV
Comments
Bearing steel, through hardened
Low alloy steel suitable for case hardening
Contains no chrome. Suitable for case hardening
Austenitic stainless steel
Heat treatable martensitic stainless steels
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
Bronze
Copper
Brass
Aluminium alloy
Other Materials
Tungsten carbide WC
Glass
Elastomer discs
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
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.
