1. General Information
The ST 30 is a scratch tester intended to assess the adhesion of thin coatings deposited on flat substrates by measuring the critical load at which the coating first shows signs of failure.
The sample is mounted on a sloping table that can be driven in the scratch direction by a stepper motor. The speed can be adjusted via a potentiometer; the sloping angle can be adjusted via a micrometer.
The hemi-spherically ended diamond is held in a cylindrical housing, which slides vertically in an aluminium block; this block houses the miniature load cell used to measure the load applied on the diamond. The load is displayed on the front panel digital display.
The method is as follows. The sample is positioned under the diamond, the table drive speed is selected, the sloping angle is selected, the final load is selected, the indenter is loaded onto the sample until the chosen initial load is reached, the table is driven against the diamond, because of the slope, the load applied on the diamond increases until the selected final load is reached. The resulting scratch is examined under an optical microscope. The total length of the scratch is measured to determine the loading rate, the distance along the scratch at which failure first occurs is measured. The load at this point can be calculated because of the linear increase in the loading, this load is the critical load Lc.
Note, the loading rate depends on the combination of substrate and coating hardness. This scratch tester is well suited for comparison of adhesion levels between coatings of the same type on the same substrate, making it a powerful Quality Control tool.
2. Specification
Diamond: Rockwell 'C' Spherical cone, Cone Angle 120 degrees, Tip Radius 0.2mm
Load Range: 1 Newton to 200 Newtons, Load cell non linearity: <0.25% Full Scale output
