Impact Resistance BS 3900-E3 BS 3900-E7 BS EN ISO 6272: BS 3900-E13 ASTM D 2794

Scope and Field of Application

BS 3900-E3 is a method used to assess the resistance to the impact of a falling weight of a single coat film or multicoat systems of paint, varnish or related products. Although this standard has been superceded by BS EN ISO 6272: BS 3900-E13, we find it is still requested by those who are following old specifications or who wish to correlate the results with data obtained previously.

BS 3900-E7 is a method used to assess the resistance to the impact of a falling ball of a single coat film or multicoat systems of paint, varnish or related products.

BS EN ISO 6272 and BS 3900-E13 are alternative names for the same method which is used to assess the resistance of a dry film of paint, varnish or related product to cracking or disbondment from a substrate when it is subjected to deformation by a falling weight dropped under standard conditions.

ASTM D 3363 is a method of rapidly deforming by impact a coating film and its substrate and for evaluating the effect of the deformation.

The temperature and humidity conditions of the test are specified in the standards.

There are no pass/fail criteria defined in the standards. This is a matter of agreement between the parties concerned.

The actual standards are copyright-protected documents and we are not able to provide you with copies. If required however, you can easily obtain copies from either the British Standards Institution or the American Society for Testing and Materials.

Summary of Methods

BS 3900-E3

The equipment used for this test can be likened to a small guillotine where the blade has been replaced by an indenter which weighs 4.75 Kg. and which is fitted with a 14 mm diameter hemispherical tip. This falls 570 mm to strike a coated test panel which is sandwiched between two die blocks each of which have 18 mm diameter central holes. The indenter is constructed so that its stroke can be lengthened. In the non-lengthened position the indenter passes through the hole in the upper die block and just touches the test panel before stopping.

The standard does not give any advice regarding by how much the indenter should be lengthened but we find that 2.5 mm extension produces a suitable dent in the test panel.

The standard does not state whether the indenter should strike the coated side or the reverse side of the test panel. Unless specified otherwise, we mount the panel so that the coated side is struck. In our experience reverse impact is a more severe test.

After testing, the coated surface is inspected visually for cracking and loss of adhesion. A precisely defined fabric is the used to wipe the deformed area of the panel before a second visual inspection is carried out.

BS 3900-E7

The only equipment required for this test is a 900 g hardened steel ball. This is dropped onto the test sample from a height of 3 metres.

The standard does not state whether the ball should strike the coated side or the reverse side of the test panel. Unless specified otherwise, we mount the panel so that the coated side is struck. In our experience reverse impact is a more severe test.

After testing the coating is examined for signs of cracking, flaking and detachment from the substrate.

BS EN ISO 6272: BS 3900-E13

The equipment consists of a vertical guide tube down which falls a 1 Kg indenter fitted with 20 mm diameter hemispherical tip. The indenter can be loaded with an additional 1 Kg weight if required. A coated test panel is sandwiched between two die blocks each of which have 27 mm diameter central holes and the indentation depth of the falling weight is limited by variable stops.

The standard states that indenter loading, drop height and indentation depth are a matters for agreement between interested parties. If no indentation depth is specified, we use 5 mm. In our experience this ensures that the resistance of the test panel to deformation is the limiting factor.

The standard does not state whether the indenter should strike the coated side or the reverse side of the test panel. Unless specified otherwise, we mount the panel so that the coated side is struck. In our experience reverse impact is a more severe test.

After testing the coated surface is examined using a x 10 lens and any cracking or peeling from the substrate or cracking of the substrate itself is reported.

The equipment can be used in two modes:-

• Pass/Fail Mode where the test is carried out using agreed values for the panel orientation, indenter loading, drop height and indentation depth.

• Classification Mode where the test is carried out using agreed values for the panel orientation, indenter loading and indentation depth. Panels are tested using progressively increasing drop heights in order to determine the minimum drop height that gives rise to any cracking or peeling from the substrate or cracking of the substrate itself.

ASTM D 2794

The equipment consists of a vertical guide tube down which falls a weight fitted with a handle which protrudes through a vertical slot in the tube. A graduated inch-pound scale is marked along the length of the slot. The standard specifies a number of variants of the equipment with guide tube lengths between 24 and 48 inches. The weight drops on to an indenter fitted with either a 0.5 inch or a 0.625 inch diameter hemispherical tip. The indenter tip rest against the test panel which is mounted on a die which has a 0.64 diameter central hole.

The standard does not state whether the indenter should strike the coated side or the reverse side of the test panel. Unless specified otherwise, we mount the panel so that the coated side is struck. In our experience reverse impact is a more severe test.

The test involves choosing the indenter size and panel orientation and then raising the weight to a height where it is expected that no failure will occur and allowing it to drop. The standard specifies three methods of examining the impacted area for cracking:-

• visual using unspecified magnification.
• treating with copper sulphate solution and examining for copper deposition and/or rust staining.
• use of an electronic pin hole detector.

The test is continued using progressively increasing drop heights in order to determine the minimum drop height that gives rise to cracking.

Sample Requirements

Our sample requirements are as follows:-

If you wish, we can prepare the test panels. The quantity of liquid paint we needs depends on the method of application. We will be pleased to advise you regarding our requirements.

Accreditation

PRA is accredited to ISO 17025 by the United Kingdom Accreditation Service (UKAS) to carry out these tests.

Please contact Peter Collins for further details.

Back to Paint Testing Laboratory Page

Back to Testing Applied Paint Films Page

Back to top of page