presents Model 703/704 hardness rocker and levelling tables by Sheen Instruments.
Designed to determine the hardness of organic coatings, the hardness rocker and levelling table operates on the principle that the amplitude of oscillation of the rocking device decreases more rapidly, the softer the surface on which the test is conducted.
The performance of the hardness testers is sensitive to the surface condition of the coating or test piece and may be influenced by the thickness of the coating and the nature of the substrate.
It is important that the test piece is level and free from movement or vibration and the test is carried out in a controlled draught-free atmosphere. The test procedure is fully described in ASTM D2134.
Method of use
The levelling table with the test plates is levelled carefully and the surface of the glass test plate thoroughly cleaned. The underside rings of the rocker should be examined critically and cleaned with a suitable solvent to remove any sticky deposits.
The rocker is placed carefully onto the test surface, and the instrument rolled to the right until bubbles are in view. Once the rocker is released and the left-hand bubbles disappear, the counting of the number of ‘rocks’ (complete oscillations) should be started. The count is stopped when the right-hand bubble disappears.
The rocker is set before despatch to make 50 oscillations on a standard glass plate with the period of oscillation being set at 60+0.5 seconds by means of the adjustable knurled nuts. A frequent check should be made on the number of oscillations the apparatus makes on the standard glass plate.
The change of state for rocker hardness can be monitored against time, provided that the coating is smooth, free from blemishes, and has its thickness controlled.