The physic of Slacklining and its variations, is different compared to any other sport. A properly set up and tensioned longline has a static load equivalent to 500-1200 kg and on top of it there is an additional dynamic stress when somebody is walking or jumping on the webbing.
In many cases people tend to use inappropriate equipment, which is not produced and/or tested for slackline use, such as aluminium carabiners and pulleys often used for climbing. These are rated for one person weight only and usually exclude the additional tension load of a longline, even though their tested tensile strength is over the expected load.
Aluminium is a rigid material. Once you drop an aluminium equipment from a larger height you cannot fully trust it any more, as the stress from a drop can cause invisible cracks in its structure.
Yield strength of aluminium (the stress at which a material begins deforming plastically) is close to its ultimate tensile strength (the force under which the material brakes) and its elongation before break is just about 11%. In a case like this, it’s not possible to note if your equipment is overloaded before it fails.
For your safety we have decided not to use aluminium parts in cases where these parts are continuously exposed to heavy loads and additional dynamic loads.
Stainless steel’s tensile strength is pretty much the same as the 7075 aluminium but its yield strength is much lower, therefore the elongation at break is about 50-70%. This means that when you overload your system the deformation would be noticeable, as a result of the system not being used properly. Visible deformation appears much before it fails so you can note that. This way, it’s easier and safer to follow the history of the equipment and make the decision about trusting it in the future.
Aluminium has been used in cases, where there are no big dynamic forces. We use 7075 high strength aluminium alloy, used in climbing equipment, as well as aircraft construction and bicycle parts. All of these aluminium parts are hard anodized which adds more durability to them and brings their properties closer to those of hard faced or case hardened steel.
The main parts which will be exposed to heavy loads are constructed from high strength stainless steel (1.4301 and 1.4571). These are durable, and everlasting materials that match the outdoor use and increase safety.
The combination of these high-tech materials makes ZERGE outdoor equipment perfect for slacklining.