Resistance to impact by large diameter ball

 

 

Principle
A specimen from the laminate under test (bonded to wood chipboard if specified) is covered with a sheet of carbon paper and subjected to the impact of a steel ball which is allowed to fall from a known height. Impact resistance is expressed as the maximum drop height which can be achieved without incurring visible surface cracking or producing an imprint greater than a specified maximum diameter.

Materials
1. Fine-faced wood particleboard, complying with EN 312 (for interior fitments), (230 ± 5) mm square, with a nominal thickness of 18 to 20 mm (± 0,3 mm), a density of (680 ± 20) kg/m3, and moisture content (10 ± 3) %. Where the specimen is bonded to chipboard, the test actually measures the impact resistance of the
whole composite material, i.e. laminate, adhesive and substrate. (The correct choice of chipboard quality is very important in achieving good reproducibility with this test).

2. Urea-formaldehyde adhesive, containing approximately 15 % filler, or an equivalent adhesive.

Apparatus
1. Free-fall test apparatus, of the type shown in Figure 9, or an equivalent which will produce the same results.
2. Polished steel ball, of mass (324 ± 5) g and diameter (42,8 ± 0,2) mm, having no damaged or flattened areas on its surface.
3. Specimen clamping frame.
4. Conditioning chamber, in accordance with EN ISO 291, with a standard atmosphere of (23 ± 2) °C and relative humidity (50 ± 5) %.

Test specimens
Specimens shall be (230 ± 5) mm square. For laminates of thickness less than 2,0 mm, specimens shall be prepared by uniformly bonding a piece of the laminate under test to the wood chipboard using the specified adhesive evenly spread at 80 to 120 g/m2. The bonded specimens shall be preconditioned for at least 72 h at (23 ± 2) °C and (50 ± 5) % relative humidity before being used for the test.
For laminates of thickness ≥ 2,0 mm and < 6,0 mm, the effect of bonding the specimen is insignificant and the test may be conducted with the laminate clamped in the frame in contact with the chipboard.
Laminates of thickness ≥ 6,0 mm shall be tested clamped in the frame without the chipboard support. Sufficient specimens shall be prepared to obtain a final result (about five is usually sufficient).

Procedure
The test shall be carried out in the laboratory atmosphere.
Clamp the specimen in the clamping frame and place the assembly on the solid base of the free-fall test apparatus. Cover the specimen with a sheet of carbon paper with its coated face in contact with the decorative surface. Adjust the height scale so that its base is touching
the face of the specimen.
Position the electromagnet at any arbitrary height (the specification limit for the material under test is a useful starting point).
Place the steel ball on the energized electromagnet. Operate the release mechanism so that the ball fails on the specimen, catching the ball on the first rebound so that multiple impacts do not occur.
Examine the surface tested for damage at the point of impact. If cracking is evident, or the carbon imprint is greater than the diameter specified, lower the electromagnet and repeat the test. If no cracking is evident and the imprint is smaller than the specified diameter, raise the electromagnet and repeat the test. The distance between points of impact, and between points of impact and the edge of the specimen, shall be at least 50 mm. For referee purposes, only one impact per specimen shall be made, with the point of impact as near as possible to the center of the specimen. Repeat the above procedure, as necessary, to determine the impact resistance of the laminate under test.

Expression of results
The impact resistance of the laminate under test is defined as the maximum height for which no visible surface cracking, or imprint greater than the specified diameter, occurs in five successive strikes.
To prove compliance with a specified limit value it is only necessary to carry out the test at the specified drop height.