The SATRA STM 439 lace abrasion machine
Describing the application of this valuable piece of test equipment.
Despite the introduction of other methods of fastening footwear, the shoe lace still remains popular, and it is easy to see why. The lace – often viewed as a simple component – actually plays an important role in the footwear's success. Not only does the lace perform its primary function extremely well, but also, in combination with its carrier, provides a wide range of design options for shoemakers.
Whatever the choice of lace and carrier, the basic requirements remain the same – the lace should not break, it should remain knotted once tied, not stain another part of the shoe or other objects and not change colour. In addition, any tags on the ends should stay in place. As all wearers of laced footwear know, it is common to encounter laces that do not meet all of these requirements.
Resistance to breakage
Lace breakage typically occurs when the shoe is being fastened, rather than during wear. The forces involved in this process, particularly when pulling the ends of a lace to tighten footwear with many pairs of eyelets, can be extremely high. A lace must have sufficient strength to withstand these high forces and also be capable of retaining that level of strength long enough to satisfy reasonable expectations of wearers. Two factors determine whether a lace will meet the second of these requirements – the breaking strength of the lace when new and the rate at which strength is lost over time. Abrasion is the main cause of strength loss. This takes place both where the lace is in contact with the carriers and also where it is in contact with itself. Therefore, when assessing whether a lace will be sufficiently durable, both its breaking strength and abrasion resistance must be considered.
Abrasion resistance tests
SATRA TM154:2018 – ‘Shoe lace to shoe lace and shoe lace to lace carrier abrasion’ is the SATRA test method widely used for assessing the resistance of shoe laces to abrasion caused where the lace rubs against itself and where the lace rubs against the lace carrier in the shoe. Both of these assessments can be made on the SATRA STM 439 lace abrasion machine. Prior to testing, the laces should be stored in a standard controlled atmosphere for at least 48 hours. One of the two laces used at each of the six stations has both ends of the lace clamped in the carrier provided. The second lace is threaded through the loop created by the first lace. One end of the second lace is fixed to a moving carrier, while the other is attached to a weight that tensions the lace to 2.45 N.
When the machine is started, the action of the moving carrier causes the two laces to abrade. The machine moves each lace a distance of 35 mm at a frequency of 60 cycles per minute. Each station has a separate counter and, when a lace breaks, the count is stopped on that station. When all six laces have broken, the machine will stop. SATRA STM 439 is provided with hand control for ease of setting and is fully guarded in order to comply with European health and safety requirements.
The same machine can be used to test the abrasion effects of rubbing the lace through a lace carrier or hook, for example eyelets, D-rings, ski hooks and other components.
How can we help?
Please contact firstname.lastname@example.org for further information on the SATRA STM 439 lace abrasion machine and email@example.com to discuss the test methods used.
This article was originally published on page 36 of the October 2021 issue of SATRA Bulletin.