 Ratcheting Straps
The ratchet tie downs are the assembly of webbing and ratcheting buckle , it’s a well recognized fact, if we use cam buckle instead of ratchet buckle then it’s cam buckle tie down, it’s pretty straight forward, isn’t it? Due the low strength of the cam buckle, we usually see these cam buckle tie downs being used on pick up trucks, 1” cams are all over the place while 2” cams are being used in box trucks. Ratchet buckles are different, there are 1” to 4” ratchets, and they can be quite heavy duty and can stand all kinds of abuse, the most commonly used on commercial trucks are 2”, 3” and 4” ratchet tie downs, they have working load limit of 3,333lbs, 5,400lbs and 5,400lbs respectively, these assemblies have design factor of 3:1, thus the minimum breaking strength is 10,000lbs, 16,200lbs and 16,200lbs respectively.
So far we talked about tie down devices for flatbed trucks or similar transportation vehicles, we will see there are other kind of trucks, the typical one is box truck, and most of them have E Track installed inside the truck, for these rigs we use e track straps. By estimation, there are almost 80% trucks on the road are box trucks, so these e track straps are supposed to the most popular ones by volume. The e track straps usually have working load limit of 1000lbs, which is only 30% of the 2” flatbed tie downs, and the breaking strength is only 3,000lbs based on design factor 3:1. It’s easy to understand that why e track straps are not as strong as regular ratchet tie down straps, inside the box truck the loads already have strong support, at least there is no risk of falling off, all the e track straps will do is to fixate the loads more than tie them down.
We already discussed the design factor of ratchet straps, it is 3:1 and for the record all this says is that safe load limit of tie down straps is 1/3 of it’s breaking strength, while grade 70 chains which have a design factor of 4:1, that means the transport chains will work in more tough environment than tie down straps, which usually are chose for regular loads. The most common materials in making tie down webbing are nylon and polyester, which serve different tie down applications. The typical application for nylon webbing is motorcycle tie down, while polyester webbing is ideal for tying down concrete pipes. When making the webbing, we have to take following characteristics in to consideration, the breaking strength, elongation, abrasion and the environment. Breaking strength has to reach the recommendation level no matter what, and elongation has to meet the requirement, abrasion and environment sometimes are not that clear cut, when designing tie downs we may have to consider the most extreme conditions these tie down straps may be in, or we may just consider the normal transportation environment.
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