Assessing footwear water resistance

Reporting on SATRA test equipment designed to determine the ability of footwear to avoid the ingress of water.

by Peter Allen

It is vital for any manufacturer or supplier of footwear, which is claimed to offer a level of water resistance, to have this ability assessed before the product is placed on the market. The SATRA STM 505 Dynamic Water Resistance Test machine allows for water penetration resistance to be accurately determined.

Testing conducted using STM 505 provides an alternative to the ‘trough test’ (SATRA TM81), in which a wearer repeatedly walks along a water-filled trough to determine the resistance of the footwear to water ingress. SATRA TM230 is a whole-shoe test designed to assess the completed footwear for resistance to water penetration into the volume occupied by the foot. It was developed for use with the STM 505 test machine with the results correlated against the trough test.

The SATRA STM 505 Dynamic Water Resistance Test machine simulates the effects of walking by flexing the footwear by means of a pneumatically operated mechanical foot (see photograph at top of page). The test is conducted with the footwear immersed to a set level in a water bath. SATRA TM230 has become our preferred laboratory objective test method for water resistance testing. A mechanised test is more controllable and more objective than the trough test, and can be run continuously, which is more practical for the longer-duration tests and requires a reduced labour content compared to trough testing. SATRA TM230 is now specified in UK military footwear specifications.

In addition to SATRA TM230, a number of other SATRA tests can be used to assess materials prior to selecting them for a particular footwear product – for example, tests used to assess upper leathers or synthetic materials for water resistance when they are flexed. However, a whole-shoe test enables a wide range of aspects to be assessed, such as the effectiveness of sealing on cut edges and seams, wicking effects and preservation of the integrity of membranes. Importantly, it is also a good test for sole bond integrity which can affect water resistance due, for example, to poor quality caused by over-roughing, under-roughing and a poor-quality adhesive bond.

Depending on the intended use for the footwear, different water levels relative to the footwear featherline can be set, in addition to a varying number of flexing cycles. This allows the tests to assess a wide range of footwear types, from everyday footwear to demanding outdoor performance and military products, where immersion over the vamp and an extended number of flexes (typically 300,000) gives a severe yet realistic test for a wet weather boot. For these longer duration tests, the effects of wicking can also be assessed. Wicking along seams, laces or in the materials of the upper can result in water ingress into the footwear at some height above the water immersion level.

A key characteristic of the SATRA STM 505 Dynamic Water Resistance Test machine is its control of applied flexing load. Due to the geometry of the mechanism and the pneumatic actuation, the maximum applied load is controlled. This is an advantage over other types of machine, in which a flexing mechanism forces a set angle of flex, irrespective of the load required to produce the flexing. For footwear with a high sole stiffness, forcing a fixed angle of flex is unrealistic, as this degree of flexing would not be encountered when in use.

Using the STM 505 machine

The STM 505 is a twin station, tabletop mounted machine, which allows two tests to be conducted completely independently. A single station can also be used on its own. The tabletop operating height offers ease of setting up and monitoring of the test. Samples are attached to the pneumatically-driven foot, which has a hinged toe piece section that flexes the footwear at a pre-determined rate, as specified in SATRA TM230. The foot has adjustable sections to allow different sizes of footwear to be fitted, as well as to allow positioning of the flexing point.

The footwear is lowered into position and the water level adjusted, depending on the test to be conducted. The number of cycles required for the test is set and, once initiated, the flexing cycles commence. On completion of the set number of cycles, the sample is automatically raised out of the water. Periodic manual checks can be carried out during the test to identify any leaks and, importantly, to determine the initial position of any leaks. To carry out these checks, the footwear is raised and removed from the test station before absorbent paper is pressed against the inner face of the footwear and the position of any leaks identified. A major failure will result in the footwear sample filling with water.

A more recent development is the availability of alternative toe and heel shapes, which can be obtained from the SATRA equipment sales team (test.equipment@satra.com).

The SATRA STM 505 Dynamic Footwear Water Resistance Test machine is a valuable, more consistent and time-saving alternative to trough testing, that allows footwear to be assessed for fitness for purpose with respect to prevention of water penetration across a wide range of footwear types. This includes footwear required for demanding applications with significant exposure to water. The advantage of a whole-shoe test is that aspects of construction and the quality of production as well as the materials used are evaluated. The SATRA STM 505 machine has a proven track record of yielding consistent results, with high levels of reliability and ease of use.

Click here for comprehensive information on SATRA's range of test equipment.

Publishing Data

This article was originally published on page 36 of the June 2011 issue of SATRA Bulletin.

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