The following laminated safety glass tests for windscreens are carried out in practice in keeping with the afore-mentioned standards and the customary laminated glass specific testing procedures:

• Moisture measurement of laminated safety glass
• Ball-drop test according to ECE R43
• Determining glass adhesion/pummel test
• Determining glass adhesion/compressive shear test
• Boil test according to ECE R43
• Bake test
• Humidity test according to ece R43/ edge stability of laminated safety glass

The individual tests and the partial inter-dependence of the test values are subsequently described.

Preparing the test samples

Quality assessment of the finished windscreens is carried out with test samples which are prepared from series-produced W/S in the following manner:

The 30 x 30 cm test specimens identified as D-G in the figure are used for the ball-drop test according to ECE R43, while the remaining specimens A-C are used for the aforementioned and subsequently described tests. The glass orientation in relation to the film, i.e. the manner the film was laid, must be established and identified on all specimens. This can be determined with a UV lamp: The bath or tin side (Sn) gleams in bluish/white, while the air side (F) of the glass does not have this gleam. The identification of the glass side is essential with laminated safety glass from separately laminated sheets or that have not been taken from windscreens. The glass orientation is particularly important with penetration test (ball-drop test - see below) to determine the impact side and/or to establish test deviations attributable to differing PVB adhesion to the respective glass side.

The measurement of laminated glass produced with TROSIFOL VG - in this case test glass samples A-C produced from windscreens - is carried out by the IR transmission method. The specimens for measurement should be preferably produced from clear float-glass and colourless PVB film. If coloured float-glass is used then correspondingly calibrated laminated safety glass samples should be used. The measured moisture values must fulfill the given specification values for TROSIFOL VG. The subsequent figure shows the dependency of the film moisture within the laminated safety glass on the ambient moisture prevailing in the lay-up room.

Moisture absorption of the outside film layers of stretched film sections within a film stack will be faster than the inner film layers. The film thickness is less when the (colour band) films are already stretched. The modern IR measuring instruments indicate both the moisture value as well as the film thickness.

The following figure shows the moisture absorption of TROSIFOL VG - measured on a freely suspended film sample - in relation to the ambient moisture.

The most important laminated glass test for automotive glazing is the ball-drop test according to ECE R43/ANSI Z26.1. This test establishes the penetration resistance of 30 x 30 cm laminated glass specimens to a 2.26 kg steel ball (5 lb) at a temperature of 20 ± 5°C (68 ± 9°F) during the test. A falling height of 4 m must be withstood without ball penetration. The test glass specimens are mounted in a supporting frame.

Normally, for safety reasons, the tests are carried out from a higher falling level. In addition to the absolute falling height, it is also usual to determine the mean break height (MBH). The latter defines the falling height at which 50% of the test glass specimens withstand the ball, while the other 50% are penetrated by the ball.

At higher and lower testing temperatures the mean/absolute break height declines. According to ECE R43 (or equivalent standards), a 227 g (0.5 lb) steel ball is used at temperatures of -20°C (-4°F), and the test is carried out from a falling height of 8.5 - 12.0 m (28-39 ft.), depending on the thickness of the windscreen.

 

The purpose of the test is to determine the adhesion of the PVB film to the glass. Adhesion is controlled to prevent possible glass separation due to insufficient adhesion and possible problems during the ball drop test (to DIN 52338) due to excessively high adhesion.

LSG specimen
The specimen measuring approx. 8 x 20 cm with a maximum thickness of 2 x 4 mm is cooled for ≥ 2 hours to -18°C (0ÅãF) and then pummelled with the (automatic) hammer, as shown in the picture. The glass specimen is put at a small angle in relation to the steel plate. Each specimen must be inspected from both sides (see illustration left). For assessment, the specimen is warmed up to room temperature. Test samples measuring 8 x 30 cm taken from central areas of windscreens are tested in the same way. A rough distinction is made between high and medium glass adhesion in accordance with the mode of assignment in the bottom diagram. From one laboratory to the next, the assessment can vary by up to 3 grades up or down with this method due to equipment, impact force and frequency, side of the glass and experience of the testers. The dependence of pummel adhesion on film moisture can be seen in the graph below.

As is the case with the pummel test, the measurement of glass adhesion of PVB with the compressive shear test is not standardised. Several 25 x 25 mm (1 x 1 in) test glass specimens are compression shear tested at 23°C (73°F) in a modified tensile testing machine. The maximum shearing force until the test specimen breaks is a measure of the adhesion of TROSIFOL to glass. The thickness and dimension of the glass piece is also a deciding factor for establishing glass adhesion. The glass industry also uses (drilled) round testing glass samples.

 

 

 

The boil test according to ECE R43 is carried out in the same manner as described under "Tests Architecture". The purpose is to determine the laminated glass stability when exposed to heat and moisture and the association with possible bubble formation. 30 x 30 cm samples (C or D-G) cut out of windscreens are boiled for 2 hours in water and then visually inspected. Possible deviations are listed under "Trouble-shooting". A similar test is also specified by the standard EN DIN 12543 for building laminated safety glass.

Bake testing of test glass specimens in a minimum size of 30 x 30 cm (about 1 sqft.) are carried out in the same manner as described under "Tests Architecture". Similar to the boil test the stability of laminated glass when exposed to heat is established, except without the additional moisture effect. After the test has been carried out the specimens are visually inspected. The number and type of bubbles are an indication of the degree of deairing and the moisture of PVB during the laminated safety glass production process. Possible deviations are listed under "Trouble-shooting".

In the humidity test according to ECE R43, 30 x 30 cm test glass specimens (specimens D-F from a windscreen) are placed in a climate of 50°C/ 98% rel. humidity for 14 days, and then dried again at room temperature for another 14 days. The test is passed if there are no visible changes outside 10 mm from the uncut edge, and 15 mm from the cut edge of the laminated safety glass. Laminated safety glass with TROSIFOL VG fully fulfils the demands: There is no visible whitish discolouration in the edge area at the end of the test. A repeat test with at least another 2 test cycles confirms the excellent edge stability of TROSIFOL VG. In addition to the humidity test, there are a number of other alternating climate tests in both laboratory longterm simulations (accelerated ageing test) as well as under natural weathering conditions. These tests are then followed by additional adhesion tests in the edge area and center of the glass and, if necessary, light fading of the samples is also measured.
All the listed tests reveal that the laminated glass with TROSIFOL VG has outstanding ageing and edge stability (test results upon request).