Renault D24 1699 Impact Resistance of Paint Using Rough Surface Balls

The "Renault D24 1699 Impact Resistance of Paint Using Rough Surface Balls" standard, developed by the French automobile company Renault , describes a test method for determining the impact effect of gravel on vehicles.

The purpose of this test method is to determine the peel resistance of paint coatings applied to any substrate, preferably made of smooth plastic material. This test method should be performed on all layers constituting the paint film, but can also be performed on each layer independently to determine the specific properties of each layer.

In principle, the test consists of throwing a silicon carbide-coated ball at the surface of a coating applied to a support, reproducing a surface deterioration (flaking) equivalent to that produced by throwing a pebble at a vehicle.

The average fragmentation size is determined for a certain bullet speed, as prescribed in regulatory documents.

The general scheme of the apparatus used in these tests is included in the standard annex (Annex 1). It has a barrel with an inner diameter of 3,5 mm, and the bullets are fed by means of a cylinder or any suitable feeding system. In order to limit the wear caused by friction from rough balls, the main elements (barrel, barrel, plate) must be subjected to nitriding treatment.

This device can move vertically by means of two adjustable supports. The ejection of the balls is carried out using compressed air, the pressure of which can be adjusted by means of a pressure regulator equipped with a control pressure gauge. An optical device is used to determine the velocity of the projectile as it leaves the barrel. The fixing of the bottom of the test tube by means of four screws is provided by a movable plate. This plate, placed in a housing, makes it possible to change the angle of impact of the projectile with respect to the test piece and possibly the distance between the point of impact and the barrel of the gun (from 0 degrees to 90 degrees). Unless otherwise specified in the verification plan, the angle of impact is maintained at 45 degrees and the distance between the point of impact and the barrel at 25 cm. The spent balls are directed into a removable chamber. In short, these devices reproduce the impact effects of gravel on the polished or painted surfaces of vehicles.

When calibrating these devices, the launch velocity is measured at the muzzle exit. Deceleration due to air resistance is neglected. Two photoelectric cells, 25 mm plus/minus 0,01 mm apart, are placed at the end of the barrel and their beams intersect the ball's trajectory. They are connected to a low-voltage constant power supply and a time counter (optical fiber) as per the diagram. The time it takes for the ball to travel the distance between the two photoelectric cells is indicated in milliseconds by the time counter. The apparatus used shows the time required for the ball to travel 25 mm in milliseconds. The ball's exit velocity can be easily calculated using the formula given in the standard.

The tests are carried out at room temperature. When setting up the test tube, the plate is set at 45 degrees and the test piece is fixed on this plate using screws. The barrel is placed in a horizontal position and its height is adjusted so that the impact of the bullet is in the upper region of the test tube.

The holes in the barrel, plate and cylinder are connected together. The pressure is adjusted to obtain the projection speed set in the standard documents (the obtained projection speed should be equal to the set speed plus/minus 5 percent).

A bullet is placed in the loading channel. Before firing the next bullet, the barrel is rotated one notch. These two operations are repeated until the desired number of impacts (minimum 10) are obtained on the test piece to be tested. In order to eliminate the risk of overlapping the two impacts, the barrel must be moved approximately 4 mm in the vertical plane after each protrusion.

When processing the tested sample, the adhesive tape is slowly applied to the impact area, rubbing it with a finger to avoid air bubbles between the tape and the paint coating. Finally, an equal amount of pressure is applied to the entire surface of the tape. This tape is then torn off with a rapid and continuous movement at a 90-degree angle.

Our organization, which has been trying to support businesses from every sector with its wide range of testing, measurement, analysis and evaluation studies for years, has a strong staff that closely follows the developments in the world in the field of science and technology and constantly improves itself. In this context, testing services are also provided to businesses in accordance with the standard of “Renault D24 1699 Impact resistance of paint using rough surface balls”.