VW PV 3974 Plastic Components - Determination of Mar Resistance of Unfinished Surfaces in Vehicle Interiors and Exteriors

The standard “VW PV 3974 Plastic components - Determination of mar resistance of unfinished surfaces in vehicle interiors and exteriors”, developed by the Volkswagen automobile company, specifies the requirements for determining the surface resistance of granular, untreated plastic interior and exterior parts with respect to traces of irreversible deterioration.

Mar resistance is the resistance of an unfinished granular component surface to the mechanical impact of a rounded-edge disc. Such a load is applied, for example, when nails scratch decorative surfaces with a small amount of force. The resulting scratches and mars are irreversible and visibly noticeable.

In this test method, a machine-guided metal disk is used to create parallel lines 0,5 mm apart on a grained, unfinished plastic surface using the rounded edge of a reference disk. The reference disk is clamped at right angles to the push/pull direction perpendicular to the specimen. For evaluation, the resulting distorted surface is monitored for gloss change compared to the unstressed surface.

The following equipment should be used in the tests:

• Scribing device (motor-driven cross-cutting device)
• To determine the mar resistance, the hard metal disc has the following requirements:
  • Material: G30F hard metal
  • Diameter: 16,0 plus/minus 0,1 mm
  • Thickness: 1,0 plus/minus 0,1 mm
  • Test edge: 0,5 mm rounded
  • Surface quality: on the test edge, finely machined with an average roughness depth of 2,0 μm to 3,0 μm

Optical measurement is carried out to determine the surface roughness parameters based on the DIN EN ISO 364 standard with a measuring field size of approximately 270 µm x 38,5 µm and a wavelength limit (cut-off) of 4287 µm.

• Gloss level meter in accordance with DIN EN ISO 2813 (measuring angle 60 degrees, measuring area 9 mm × 15 mm (other measuring areas only available after consultation with the relevant department)).
• Illuminating for visual assessment.

Prior to testing, samples must be stored in standard atmosphere for at least 50554 hours in accordance with the VW 48 standard.

When testing grains that do not show any directional dependence on mar resistance:

• The test is performed at 23 degrees plus/minus 5 degrees.
• The test area is created using a reference disk (parallel test lines are given in the figure within the standard).
• Each line is applied with 1× tension in one direction only (i.e. not twice or in a crisscross pattern).
• The following test parameters are applied: contact force 3 N, speed 1 000 mm/min, line spacing 0,5 mm.
• The reference margins are adjusted after the disc is installed and the sample is compressed. When doing this, no additional weight (e.g. metal disc) is placed on the sample. In the zero position, the reference disc should not touch the sample and should be lifted very slightly from the sample.
• When setting the weight force required to perform the marring test (3 N), only suitably calibrated additional weights are used.

When testing grains that show directional dependence on mar resistance:

• This test should be performed if the plate containing the original sample of the grain shows the directional dependence of the grain.
• The test is performed as described above.
• A test is performed in the direction of travel and a test is performed with a new sample taken from the same position but rotated 90 degrees.
• The gloss level measurement is performed parallel to the push/pull direction.

At the end of the test, the gloss change on the damaged surface compared to the unstressed surface is monitored. In addition, the initial gloss level of the unstressed test surface is specified. The gloss level measuring device must be positioned precisely. The gloss level measurement is carried out parallel to the push/pull direction. The measurement result is the average of three measurements.

Among the numerous tests, measurements, analyses and evaluation studies that our organization has carried out for businesses in various sectors, our organization also provides testing services defined in the standard “VW PV 3974 Plastic components - Determination of mar resistance of unfinished surfaces in vehicle interiors and exteriors” with its trained and expert staff and advanced technological equipment.