Machines for EU safety footwear testing – part 8
Continuing a series on SATRA test equipment that can be used to conduct the tests specified in the European safety footwear standard EN ISO 20345:2011.
by Peter Allen
The first five articles in this series covered ‘basic requirements’, and subsequent articles explored the test equipment which can be used to conduct the tests, as set out in clause 6 of EN ISO 20345:2011 – ‘Additional requirements for safety footwear’. In this issue, we are investigating additional requirements for ‘whole footwear’ (clause 6.2) and, in particular, ‘heat insulation of sole complex’ (clause 220.127.116.11), ‘cold insulation of sole complex’ (clause 18.104.22.168), ‘energy absorption of seat region’ (clause 6.2.4), and ‘water resistance’ (clause 6.2.5). These tests are applicable to both Class I footwear (leather and other materials but excluding all-rubber or all-polymeric) and Class II footwear – all-rubber (entirely vulcanised) or all-polymeric (entirely moulded) as defined in EN ISO 20345:2011, except for the water resistance test, which is only applicable to Class I. Class II footwear requires a leakproof test within ‘basic requirements’ (clause 5.3.3), and is covered in part 2 of this series.
Additional testing requirements may be necessary for safety footwear, depending on the risks to be encountered at the workplace. In such cases, safety footwear must conform to the appropriate additional requirements and can be marked with the codes shown in table 18 of EN ISO 20345. These codes allow the customer to identify the additional hazards for which the footwear is appropriate.
Heat insulation of sole complex
The requirements for assessing the ‘heat insulation of sole complex’ are set out in clause 22.214.171.124 of EN ISO 20345. This specifies, when tested in accordance with ISO 20344:2011 clause 5.12, that the temperature increase on the upper surface of the insole after 30 minutes must be not greater than 20°C, when the temperature of the hot plate on which the footwear sample is standing is 150°C. The SATRA STM 471 heated sandbath test equipment (figure 1) allows this test to be conducted. It comprises a temperature-controlled, heated hot plate on which the footwear sample is placed, and a containment wall which allows the 5L of sand required for the test to be retained over the hot plate. Also included is 4kg of 5mm diameter stainless steel balls which act as a thermal transfer medium and are used to fill the footwear test sample, as well as a temperature probe which is used to measure the temperature of the insole. The footwear sample is conditioned until the temperature of the insole is constant at 23°C.
When conducting a test, the temperature probe is placed in contact with the inside top surface of the insole and surrounded with the stainless steel balls. If all 4kg of the balls cannot be contained in the footwear, a collar should be used to extend the height at the opening so all the balls can be used. Prior to a test, the sandbath is heated for two hours, as specified in the test method, and with the hotplate set to a temperature of 150°C.
The sample is worked through the sand until it is in contact with the hotplate at the heel and forepart, and then the sand is levelled off around the sample’s sole. The machine displays the hotplate temperature and the probe temperature. In addition to meeting the temperature requirement at the probe position, after 30 minutes of testing there is also a requirement for a visual inspection of the sample against criteria set out in annex ‘B’ of EN ISO 20344:2011. Footwear which meets the requirements of this test can be marked with the code ‘HI’.
Cold insulation of sole complex
The requirements for assessing the ‘cold insulation of sole complex’ is set out in clause 126.96.36.199 of EN ISO 20345. This specifies, when tested in accordance with ISO 20344:2011 clause 5.13, that the temperature decrease on the upper surface of the insole shall not be more than 10°C. The test is conducted within an insulated cabinet with the temperature regulated to -17°C. The footwear sample is supported on a copper plate within the cold chamber. The same type of temperature probe and thermal transfer medium (5mm stainless steel balls) as specified for the heat insulation test are used in the cold insulation test, with the probe positioned on the top surface of the footwear sample insole and the sample filled with 4kg of steel balls. The method describes how a foam collar can be used to extend the height at the opening to the footwear to allow all 4kg of the stainless steel balls to be used.
Prior to the test, the footwear sample is conditioned at 23°C until the temperature of the insole is constant at 23°C which, in this case, the standard states should be ‘for at least three hours’. The temperature of the test chamber is reduced to -17°C and held at that temperature for the duration of the test. The conditioned test sample is placed on the copper support plate in the test chamber with the temperature probe connected to the measuring equipment. The temperature of the insole is monitored during the 30 minutes specified for the test and reported to the nearest 0.5°C. The test is passed if the fall in temperature measured at the probe is not more than 10°C. This test can be conducted using SATRA’s STM 472 cold insulation test machine (figure 2). Footwear which meets the requirements of this test can be marked with the code ‘CI’.
Energy absorption of the seat region
The requirement for determining the energy absorption of the seat region is set out in clause 6.2.4 of EN ISO 20345:2011. This states that, when tested in accordance with ISO 20344:2011 clause 5.14, the energy absorption of the seat region shall not be less than 20J. The test can be carried out with the SATRA STM 766 tensile tester fitted with STM 766BP (a set of six backpart punches made from standardised lasts). Clause 188.8.131.52 defines some key dimensions of the last punches which cover a wide range of footwear sizes. When conducting a test, the footwear sample is placed on the tensile tester’s lower jaw base plate, and a backpart punch is selected for the top jaw in accordance with the footwear sample size as set out in table 6 of EN ISO 20344:2011.
The upper punch is brought down to just contact the inside of the footwear sample at the centre of the heel area. A compressive load is applied at a rate of loading of 10mm/min until a force of 5,000N is obtained. A plot is obtained for the load versus deflection up to the maximum load applied (5,000N). A determination of the energy absorption is made by integrating the load deflection curve between 50 to 5,000N, and this is calculated using the tensile tester software. The result in Joules should be reported to the nearest 1J. Footwear which meets the requirements of this test can be marked with the code ‘E’.
Two methods are set out in clause 6.2.5 of EN ISO 20345:2011 for determining the water resistance of footwear. Either of these can be followed to meet the requirements. One option is a human subject trough test in accordance with EN ISO 20344:2011 clause 5.15.1. The alternative option is a mechanised test in line with EN ISO 20344:2011 clause 5.15.2.
A SATRA STM 505 dynamic water resistance test machine (figure 3) can be used when conducting a test to clause 5.15.2. This is a two-station machine which allows two footwear samples to be tested independently.
The machine comprises a footform which is flexed by a pneumatically-activated mechanism inside the footwear sample. The footwear is clamped in place during the test, and the toe is flexed through an angle of 22 degrees at a rate of 60 flexes per minute, in line with the test requirements.
Each station has its own water tank into which the sample and its associated flexing mechanism is lowed at the start of the test (figure 4). The test method sets out the distance from the test machine heel piece to the centre of the flexing pivot, and this depends on the footwear size. The water level in the tank is adjusted so that when the sample is lowered into the flexing position, the water level is 20mm above the featherline. A total of 80 minutes is specified for the test which, at a flexing rate of 60 flexes per minute, is equivalent to 4,800 steps. After completion of the required number of flexes, the footwear is removed and inspected for signs of internal leakage. If no obvious water penetration has occurred, absorbent paper is used to determine if and where water penetration has occurred. Areas of dampness should not be greater than 3cm² in order to meet the requirements of clause 6.2.5 of EN ISO 20345;2011. Footwear which meets the requirements of this test can be marked with the code ‘WR’.
The ‘trough test’ option requires a human subject with a foot size appropriate to the footwear under test. He or she walks to and fro in a 9-10m long shallow trough of water for 100 lengths, which gives about 5,000 steps for each footwear sample.
An advantage of a mechanised test is that many more cycles can be undertaken without extensive human subject time being required. For product development of performance footwear, 100,000 – or even 300,000 flexes (step equivalents) – could be appropriate, which is much more demanding than the 4,800 flexes which are needed to meet the requirements of clause 6.2.5 of EN ISO 20345:2011. SATRA STM 505 is a valuable test machine which not only meets the requirements of this safety footwear standard, but can be used to evaluate the water resistance of a wide range of everyday footwear, performance footwear or military footwear.
SATRA test equipment is designed and manufactured in the UK and supplied to a global market. The range of over 300 test machines and devices draws on the experience gained over its 99 years’ history, from fundamental research, development of over 400 test methods and the extensive use of SATRA machines in our own commercial laboratories.
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This article was originally published on page 36 of the September 2018 issue of SATRA Bulletin.