Cylindrical Mandrel Bending Tester

1. Scope of Application

The Cylindrical Mandrel Bending Tester is mainly used to evaluate the flexibility of coating films for paints and varnishes. Flexibility is one of the key indicators in determining coating performance and is highly valuable for product selection.

This instrument is designed to evaluate the resistance of coatings (paints, varnishes, and related products) to cracking or detachment from a metal substrate when bent around cylindrical mandrels under standard conditions. It complies with GB/T 6742 and other relevant international standards.

2. Structure, Principle, and Parameters

Working Principle

Coatings exhibit different levels of extensibility depending on the bending radius. By observing whether a coating cracks or peels when bent around mandrels of different diameters, the flexibility of the film can be determined.

Main Parameters

Mandrel diameters: 2, 3, 4, 5, 6, 8, 10, 12, 14, 18, 20, 25, and 32 mm

Mandrel shaft adjustment range: >17 mm; gap with test bar ≤0.1 mm when pressed tightly

Applicable specimen thickness: ≤1.0 mm metal test panels

3. Operation Instructions

Prepare test panels according to product standards (apply, dry, and measure film thickness).

Place the tester at the edge of a workbench to allow free handle operation.

Select the appropriate mandrel and insert it into the base, then secure it with the locking nut.

Lower the support plate using the adjustment handwheel, insert the test panel (coating side facing downward), and tighten with screws and a pressing strip.

Raise the support plate until the panel is pressed tightly against the mandrel.

Lower the handle fully, then adjust the pressing shaft so it contacts the specimen.

Raise the handle smoothly within 1–2 seconds to bend the test panel 180°.

Lower the support plate to release and remove the bent specimen.

Inspect the specimen immediately after bending, using normal vision or a 10× magnifier to check for cracking or peeling (excluding <10 mm from the edge).

Identify the smallest mandrel diameter at which coating failure (cracking/peeling) occurs. Repeat with a fresh specimen to confirm. If no failure occurs even at the smallest mandrel, record that result accordingly.

Recommended test environment: 23 ± 2°C, 50 ± 5% RH.

4. Notes & Precautions

To prevent coating damage during bending, a thin sheet of paper may be placed between the coating and pressing surface.

If a 10× magnifier is used for evaluation, this should be clearly stated in the test report.

If no failure occurs at the smallest mandrel diameter, note the exact diameter used.

For aluminum test panels, the long side should be parallel to the rolling direction.

When the tester is not in use for extended periods, apply anhydrous Vaseline to all mandrels for protection.