An introduction - the basics

Bend Tests

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Basics

Adhesion is considered being the summation of all interfacial forces. Furthermore ASTM D 907 gives a definition for adhesion:

"The state in which two surfaces are held together by interfacial forces which may consist of valence forces or interlocking forces or both."

During the process of applying a film to a substrate bonding energy will be generated. Energy, therefore, is needed to separate the two phases again; the so-called "Work of adhesion". For a typical situation the maximum theoretical adhesive strength (force per unit area) is 100 mPa.

Obviously this value can never be obtained in practice as other mechanisms are involved in keeping the two phases together. The nature of the bound will never be purely physically but also chemical processes might be involved. Furthermore the rheological properties of the coating will certainly influence the experimental determination of the adhesive strength.

Several theories have been developed to explain why this value will never be obtained in practical measurements.

Bend Tests

Description

Test instrument to determine the elasticity, adhesion and elongation ability of a dry paint film applied on a flat metal support.

It contains a holder for a mandrel, a bending lever fitted with height adjustable rollers, and sliding tongs for fastening the sample. Mandrels supplied in a case.

• 14 stainless steel mandrels of 2-3-4-5-6-8-10-12-13-16-19-20-25-32 mm diameter
• The instrument can be adjusted to the diameter of the mandrel and the thickness of the sample support

Samples

• Max. Width: 70 mm
• Max. Length: ranging between 80 mm (2 mm mandrel) and 100 mm (32 mm mandrel)
• Max. Thickness: 1 mm

Advantages

• Easy to bent samples at a steady speed
• The position of the sample clamp can be adjusted for the sample thickness
• The gliding rollers are treated to avoid damaging the surface of the sample during bending

Maintenance

User's Guide

Products, Options & Accessories

• Elcometer 1500 Cylindrical Mandrels on Stand
• Elcometer 1510 Bending Tester with Conical Mandrel
• Elcometer 1506 Cylindrical Mandrel Bend Tester
• Elcometer Adhesion Gauges
• Elcometer 1535 Multifunction Scratch Tester

Literature

• Paint and Coating testing Manual - J.V. Koleske, Editor - 1995 - Chapter 47 - Flexibility and Toughness - Robert D. Athey, Jr
• DIN EN ISO NF 1519, Paints and varnishes - Bend test (cylindrical mandrel)
• ECCA T7[1996], Resistance to Cracking on Bending