EHD (Ultra Thin Film Measurement System)

Part code: EHD
Main product features
  • Evaluation of film forming and frictional properties of oils and greases.
  • Starvation and reflow characteristics of grease lubricated components.
  • Fuel economy prediction of candidate crankcase oils.
  • Performance prediction of oil in water emulsion rolling mill lubricants.
  • Fundamental investigations of the high pressure/high shear behaviour of fluids such as liquid crystals.
  • Investigation of boundary additive performance.
  • Technical Specs
  • Description
  • Accessories
  • Knowledge
Film Thickness 1 to 1000nm
Load 0 to 50 N
Contact Pressure 0 to 0.7 GPa (Steel ball on glass disc)
0 to 3 GPa (WC on sapphire)
Speeds 0 to 4 m/s
Temperature Range Ambient to 150°C
Test Sample Volume 120 ml
PC Custom software running Windows 7 (32 bit)
Safety Checks Dual Platinum RTD's for temperature measurement Emergency stop on front cover
Power Supply 100-240V. 50/60 Hz, 750 VA
Mechanical Unit 50 x 50 x 30 cm, 25 kg
Electronics Unit 50 x 44 x 23 cm, 19 kg

The EHD2 Ultra Thin Film Measurement System is the latest evolution of the successful EHD instrument. It is now a fully automated computer controlled instrument for measuring the film thickness and traction coefficient (friction coefficient) of lubricants in the elastohydrodynamic (EHD) lubricating regime. The instrument can measure lubricant film thickness down to 1 nm with a precision of +/- 1 nm. The contact pressures and shear rates in this contact are similar to those found in, for example, gears, rolling element bearings and cams. In addition to film thickness measurements, traction coefficients can be measured at any slide/roll ratio from pure rolling up to 100%.

The instrument measures the lubricant film thickness properties in the contact formed between a ¾“ (19.05mm) diameter steel ball and a rotating glass disc by optical interferometry. The lubricant film thickness at any point in the image can be accurately calculated by measuring the wavelength of light at that point. Normally the system measures the wavelength of the light returned from the central plateau of the contact and hence calculates the central film thickness.

Automated testing
The control software runs on a standard PC and allows the user to easily define a test profile containing a sequence of temperatures, loads and speeds. After setting the initial film thickness, the selected profile steps the instrument through the test sequence, recording data as required, without any intervention by the user.

EHD2 Method

1) The contact is illuminated by a white light source directed down a microscope through a glass disc on to the contact.
2) Part of the light is reflected from the Cr layer and part travels through the SiO2 layer and fluid film and is reflected back from the steel ball.
3) Recombining the two light paths forms an interference image which is passed into a spectrometer and high resolution black and white CCD (charge-coupled device) camera.
4) The camera image is captured by a video frame grabber and analysed by the control software to determine the film thickness.

EHD2 Brochure