Wednesday, Nov 05, 2014 at 15:44
You need to get this straight.
equipment for industrial lifting is rated in working load limit (W.W.L.)or safe working load( S.W.L.)
Lifting equipment is rated with very generous safety margins.
This is not the case with towing equipment or recovery equipment, height safety equipment or mountaineering equipment....all these are in general rated at failure or breakage.
BUT we do interchange equipment across disciplines.
Because we are not we are not talking about a trailer being lifting equipment we in general resolve everything into minimum breaking strain or minimum failure load ( which may not mean breakage)
ALL shackles rated for industrial lifting purposes MUST by law and standard have at least a 4 to 1 safety factor...and that is minimum failure load..distortion is failure.
Where this 6:1 came from as something youcan rely on..I do not know.
SO a 1 tonne lifting industry shackle must by law and standard have a minimum falure loading of 4 tonnes.
Fact is most reputable lifting equipment manufacturers work on, at least 5 or 6 to one safety factors and the better ones 7 and 8 to one safety factors....a realy nice 1 tonne shackle may be good for 7 or 8 tonnes.
BUT not being able to know the brand for sure and thus the safety factor we must work on is 4:1.
The ADRs specify the minumim breaking strain of the safety chain and the attchment points..( not in those words)....not the SWL or WWL.
The ADRs do not specifically nominate the strength of the shackle
BUT
By inference it would be an "attachment point" or must be equal or greater than the attachment point on the drawbar.
quote VSB01
16.3 Drawbar Safety Chain Attachment Points
Safety chain attachment points are the means by which the safety chains are attached to the drawbar. These points must be located as near as practicable to the tow coupling. Where two points of attachment are required, they must be mounted one on either side of the centreline of the drawbar.
Each safety chain attachment point must be capable of withstanding the following minimum forces without incurring either any residual deformation that would interfere or degrade the function of the assembly, or any breaks, cracks or separation of components:
Longitudinal tension and compression (N) 1.5 x 9.81 x ATM (in kg)
Vertical tension and compression (N) 0.5 x 9.81 x ATM (in kg).
in the equasion the 9.81 is to convert Kg to Neutons
so the attachment point must be able to withstand 1.5 times the ATM of the trailer..
THUS
if it is a 2 tonne trailer ( 3 tonne requirement)....a 1 tonne shackle will be sufficient ( having at least a 4 tonne capacity)
There may be some that should know better and say other wise.
But you may not get a 2 tonne WWL shackle thru 3 tonne breaking strain chain......particulary if it is either transport or lifting grade chain
without any reference to regulations or tables....you should be using the largest shackle that will fit thu the chain fitted
If you are in doubt about anything trailer..start with VSB01 here
http://www.infrastructure.gov.au/roads/vehicle_regulation/bulletin/vsb1/vsb_01_b.aspx#anc_16
cheers
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