SLC Testing Services, Inc. provides tribological testing services for industrial lubricants and

additive technologies through the use of a machine called a Twist Compression Test (TCT).

Our experts are able to evaluate the performance of your products under specific conditions

with various metallurgical tools or surfaces. Primarily designed to assist lubricant and additive

manufacturers, testing has been performed for customers in many different industries,

including but not limited to, automotive, transportation, mining, steel, and coatings.

Tribological testing services for industrial lubricants and additive technologies.

Twist Compression Test (TCT)

The Twist Compression Test (TCT) equipment was originally used to evaluate lubricants and die materials for application in metal forming processes. This test measures the transmitted torque between a rotating annular cylinder and a lubricated flat sheet specimen. The 25mm (1”) diameter annual cylinder is driven by a hydraulic motor for smooth delivery of the applied torque at speeds up to 30 RPM (90 inches/minute). The pressure may be adjusted to 35,000 psi to best duplicate the tribological conditions of the metal forming process being studied.

Data is collected electronically and the coefficient of friction is calculated from the ratio of transmitted torque to applied pressure. The TCT is best used as a comparative rather than an absolute test. The simplicity of the TCT and good laboratory practices minimize variations.

Lubricant Performance Indicators in the Twist Compression Test

Friction: Indicates the effectiveness of the lubricant at reducing the interfacial shear stress. Interfacial shear prevents movement of sheet material into a die or distribution of material over a punch.

Time to Breakdown: Indicates ability of the lubricant to prevent adhesion between the tool and the work-piece. This is a function of the lubricant film strength and additive efficacy including extreme pressure (EP) lubricants.

Pick-up/Galling: The nature of metal in the TCT has been found to be an excellent indicator of tool wear.

Testing Services

The frictional force transmitted by the tool to the work-piece changes as the lubricated interface changes with the tool rotation under the applied load. In the typical test, the following stages can be identified:

Stage 1: Initial Contact – The rotating tool contacts the lubricated sheet. The transmitted torque increases rapidly as pressure at the interface builds and the lubricant is displaced. This stage is governed by the following parameters:

• Sheet and tool characteristics• Lubricant viscosity• Contact pressure• Speed of rotation

If determining the static coefficient of friction, the load is applied before beginning rotation.

Stage 2: Primary Lubricant Mechanism – In most cases, the interface will reach a period of stability and exhibit a stable frictional force. This period of stability may be brief or continue for several revolutions depending on test conditions.

• Hydrodynamic lubrication – may occur briefly in TCT results, usually involving viscous lubricants at low pressure.

• Boundary lubrication – common in TCT results, the full load of the tool is carried by the points of contact with the sheet. Viscosity will have little effect on boundary lubrication.

• Mixed lubrication – also common in TCT results, pockets of lubricant trapped in the sheet surface are pressurized. The pressurized pockets replenish the lubricant at the sheet/tool interface.

• Solid film lubrication – the sheet and tool are separated by a solid film.

Stage 3: Lubricant Depletion – With continued sliding contact the lubricant is depleted and the mechanism may fail. In the presence of EP additives, the heat generated at the contact points may be sufficient to cause a reaction between the additive and the metal surfaces. In such cases, low shear strength reaction products will form on the surface(s) preventing or delaying breakdown.

Stage 4: Lubricant Breakdown – When lubricant mechanism failure occurs, friction rises dramatically and becomes unstable as pickup and galling form. The test is usually stopped at this point to preserve the tool.

Contact Us

Need help with your next project? Do you have a new product or additive you need tested? Don’t have enough lab time or equipment to perform the tests you need to properly evaluate your products’ performance? No problem, SLC Testing Services can help!

For more information about SLC Testing Services, Inc., please contact Ted McClure by phone at 440-871-7887 or by email at: ted.mcclure@slctesting.com.

Test Results

Common measurement results include:

• Time Until Lubricant Breakdown (TBD)• Static-initial coefficient of friction (COF)• Average coefficient of friction• Coefficient of friction at specific time• Friction Factor• Sheet Damage• Tool Damage / Galling• Tribochemical Residues

Typical Test Graphs