Bundesmann Water Repellency Test:
Water repellency test is done by Bundesmann test. The Bundesmann test determines the resistance to simulated rain for fabrics that are being contacted during use such as rain jackets. The Bundesmann test aims to produce the effect of a rainstorm on a fabric in the laboratory. This test is done by Bundesmann water repellency tester. In the test shown in below figure the fabric is subjected to a shower of water from a head fitted with a large number of standard nozzles. During the shower the back of the fabric is rubbed by a special mechanism which is intended to simulate the flexing effect which takes place when the fabric is worn.
Bundesmann water repellency test is used to determine resistance to wetting and resistance to penetration of water repellent fabrics which are permeable to air. In this test, four test specimens taken from the fabric under test are simultaneously exposed to a simulated heavy shower of controlled intensity while the lower surface of each specimen is subjected to a rubbing action. The increase in mass of specimen during exposure to shower is determined and any water passing through the fabric is collected and its volume is determined.
The method is not currently a British standard because considerable variation has been found between different machines, although when tests are carried out on the same machine the variability can be reduced to acceptable levels.
In the test four specimens are mounted over cups in which a spring loaded wiper rubs the back of the cloth while the whole cup assembly slowly rotates. They are subjected for 10 min to a heavy shower whose rate has been adjusted so as to deliver 65ml of water per minute to each cup. The water flow is maintained at 20°C and between pH 6 and 8. Because of the large amount of water consumed the equipment has to be connected to the mains water supply which leads to difficulties in keeping the water temperature constant. The shower is calculated to have a kinetic energy 5.8 times that of a cloudburst, 90 times which for heavy rain, 480 times that for moderate rain and 21,000 times that for light rain.
Two fabric parameters are determined from the test:
- Penetration of water through the fabric: The water collected in the cups is measured to the nearest ml.
- Absorption of water by the fabric: In order to do this the specimen is weighed before the test and then after the shower.
To remove excess water the fabric is shaken ten times using a mechanical shaker and then weighed in an airtight container:
Absorption% = (Mass of water absorbed / original mass) × 100
In each case the mean of four values is calculated.
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Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. He is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.
