Abrasion, rub and scuff resistance testing
The complexity of wear processes has led to the development of numerous standard test methods and test apparatus. Correlation between these methods is not generally possible, although materials are often ranked in the same order.
Pira testing facilities include the Taber abrader, the Gavarti CAT, the Pira rub tester, the Crockmeter and the Satra rub tester.
The Taber Abrader is primarily used to evaluate the resistance of surfaces to rubbing abrasion. Specimens are mounted on a rotating turntable and subjected to the wearing action of two abrasive wheels, which are applied at a specific pressure. The severity of the test can be altered by using different wheels under different loads. The end point is either a visual change in appearance or a weight loss associated with material removed by abrasion.
Standard methods include Tappi Standard T476 covering the abrasion loss of paper and board, British Standard BS 3900 for the determination of resistance to abrasion applicable to paints and varnishes, and ANSI Standard INCITS 322 applicable to card durability. A Taber abrasion test is specified by the Book Manufacturing Institute (BMI).
The Gavarti comprehensive abrasion tester or Gavarti CAT was originally designed to test the abrasion resistance of inks and coatings on aluminium beverage cans. The device simulates the motion of a truck or train during shipping and is used by Pira for assessing the transit scuff resistance of printed cartons and book covers as well as cans.
The printed sheet is sandwiched between oblong blocks of polyurethane rubber. A plain or printed sheet of the same stock is placed in with it and then hydraulic rams push the blocks from the side in a wave motion to simulate transit vibration. At the end of the test, the print-to-print or the print-to-plain-paper can be examined for scuffing.
The Gavarti CAT conforms to ASTM D5181-91.
The Pira (PATRA) rub tester rubs two printed surfaces against each other (face-to-face) in the same plane, at the same speed (60 rpm), under a constant rubbing pressure. The rub test equipment can also be used to evaluate colour transfer from printed or coated surfaces during rubbing and is used by Pira to evaluate the rub resistance of labels and general printed matter.
The Pira rub tester conforms to British Standard BS 3110.
The Crockmeter is used to assess the transfer from the surface of coloured materials to other surfaces by rubbing. The machine takes its name from the term 'crocking' meaning the transfer of colouring matter or other substances from the test sample to a wet or dry cloth rubbed against it.
The Crockmeter is used in testing against ASTM F1319 and International Standard ISO 105-X12.
The Satra rub tester is a circular rub fastness tester which can also be used for testing the rub/abrasion resistance of inks on printed films, such as plastic carrier bags, under dry, wet or sweaty conditions. The machine has a rotating head holding a circular felt pad under load.