1. Types of test methods for fabric water permeability

At present, there are two kinds of testing methods for fabric water permeability in laboratory.The first type is the inside-out test mechanism, namely hydrostatic test method, which fixes the fabric on one side of the sealed container, fills it with water under the condition of standard atmospheric pressure and continuously adds the water pressure, observes and records how much water droplets seep out on the back of the fabric, and the water pressure measured at this time is hydrostatic pressure.The greater the hydrostatic pressure, the better the water resistance.The second type is the outwards and inward test mechanism, namely the spraying test, that is, continuous dripping or spraying water to the fabric to be tested from a certain height and Angle, which can determine the time needed for the water to be soaked to the other side of the fabric by the leaching test.It can also measure the amount of water absorbed by the sample after a certain period of time or observe the water stain morphology of the sample.

2. Control of pressure rise rate in fabric permeability test

In the hydrostatic test method, which is one of the testing methods of fabric permeability, there are strict requirements on the rate of water pressure rise.For example, GB/T 4744-2013 requires a pressure boost rate of 6.0kpa /min± 0.3kpa /min. In hydrostatic testing of fabrics, it is difficult to maintain the pressure boost rate of the above accuracy.Because under a certain pressure, the surface of the fabric will produce abnormal deformation, and is suddenly increased, so that the original stable pressure boost rate suddenly reduced.Unless a pressure detection and control system is composed of computers, the accuracy of the rate of water pressure rise specified in national standards cannot be achieved.

3. Analysis of the influence of pressure boost rate on hydrostatic test of fabric

There are many factors affecting the hydrostatic properties of fabric, which are mainly related to the structural parameters and technical indexes of the fabric itself.

3.1 tightness of fabric

The increase of distance between yarns will directly affect the level of water pressure.Generally, the tighter the fabric structure is, the better the impermeability.

3.2 size of coating film hole

The larger the aperture of coating film hole, the worse the hydrostatic performance of coating fabric.

3.3 the size of the theta contacts

When theta > is 90°, the fabric has water resistance, and the water pressure resistance of the fabric increases with the increase of theta.

3.4 coating thickness

The coating is too thin on the surface and is not easy to form continuous film, which reduces the water pressure resistance of the coated fabric.The coating is thick and the water resistance of the fabric is improved.

3.5 fabric thickness

The thicker the fabric, the greater the wet resistance and the greater the water pressure resistance.

3.6 yarn thickness

For the compact fabric with good hygroscopicity, the yarn radius can be reduced due to the presence of capillary effect, which can improve the impermeability of the fabric.

3.7 the performance of warp and weft yarns

Under the action of water pressure, the warp and weft yarns with good elasticity are easy to elongate, which leads to the formation of adjacent warp and weft yarns gap, and the water droplets are easy to penetrate through, thus reducing the hydrostatic pressure of the fabric.

3.8 coating quality

Require the entire cloth uniform, with a certain fastness.The better the coating quality, the better the impermeability.In the experiment, it is found that when the boost speed changes too fast or the change value is too large, a kind of water pressure impact is formed on the fabric.This kind of impact will cause the rapid seepage of water droplets on the surface of the fabric, resulting in the loss of hydrostatic pressure of the fabric.However, it is found that the static pressure of the same fabric does not change much when the boost rate is controlled at a constant difference.

Hydrostatic Head Tester is an instrument that can test the water permeability of fabrics to improve work efficiency. Want to know more, contact us!

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