Water Repellency Test | Bundesmann Water Repellency Test

Water Repellency:
Water repellent is a state of a textile material. In contact with water, water repellent materials form drops that can be easily removed from the fabric surface but for longer contact with water or with a higher pressure difference, the material will absorb water. Water repellent textiles are often high density woven materials made of very fine yarns or common materials with hydrophobic surface treatment. This method of test is especially suitable for screening if any textile has been given a water-repellency finishes. Water repellent materials are currently used in the three major textile areas (clothing, home and outdoor products and technical textiles). There are a large number of possible applications, from rain garments to medical and military equipment.

Bundesmann Water Repellency Test
The Bundesmann test aims to produce the effect of a rainstorm on a fabric in the laboratory. Water repellency test is done by Bundesmann test.   In the test shown in Fig. 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. 

The Bundesmann shower test.
Fig: The Bundesmann shower test.
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 l0 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 2O 0C 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 that 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:

1 Penetration of water through the fabric: the water collected in the cups is measured to the nearest ml.
2 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: 

In each case the mean of four values is calculated.
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Mazharul Islam Kiron is a textile consultant and researcher on online business promotion. He is working with one European textile machinery company as a country agent. He is also a contributor of Wikipedia.

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