Chain Hoist Tripod in MEW 264

[richardandtracyParticipant @richardandtracy]

Ian,

Sorry, I got the number wrong, must be a sign of old age. The horizontal lift is not 10% lateral, but a 15 degree angled lift to the nominal vertical down (which also has to be considered), and equates to a 25.8% horizontal load. This is based on Def Stan 07-85 parts 1 & 2 requirements. There was a defence standard for lifting equipment (Def Stan 04-14, Interim 1992) but that was withdrawn before being fully implemented. Def Stan 07-85 is now withdrawn as British & European Standards seem to be considered 'good enough' to require the same quality levels. The current crane design document is BS EN 13001:2015 ( **LINK**&nbsp which supersedes BS 2573 (apparently its status is 'Current, superseded' ) .

Most of the Def Stans (inc 07-85/1 & 07-85/2) are available on the web as zero cost downloads, unlike the BS EN.

Regards,

Richard.

[Ian AustinParticipant @ianaustin]

Richard, unfortunately I am locked out of these Def Stans by a paywall. As is the BS2573 and for that matter AS 1418.1 (the local one here). I guess we will just have to take your word for it unless someone has a standard to hand, to check.

In googling I did find this handy snippet:

"In summary

SWL has been phased out and should no longer be used, and all reasonable practicable efforts should be made to replace SWL with MRC.
MRC should be used for all cranes, hoists and winches. The MRC must be clearly labelled on both sides of the crane beam or boom.
WLL should be used for all for all lifting devices below the crane hook. Allowance must be taken into consideration for the arrangement of the lifting devices by derating the WLL."

source: https://asseteng.com.au/do-you-know-the-difference-between-swl-wll-mrc-and-when-they-should-be-used/

[duncan webster 1Participant @duncanwebster1]

I don't recall the BS requiring a load test at all, that was an insurance company requirement, and I think it was different for various load capacities, but it's getting a bit far in the past. I could dig it out, but prefer not to, life's too short. We used to inspect all welds, and load test the crane, but not the lifting lugs on the load, they just got NDT on the welds. This on the basis that any one load would only be lifted a few times in its life. If it was something that was lifted often we'd load test that as well.

BS2573 does not require anything like a factor of 4 on yield, for straight tension it was 1.7, even less for bending. However for something like a tripod which is likely to be abused or unevenly loaded I'd go for more, and 4 on yield is as good as anything else, especially as we don't have coded welders or NDT of the finished product. If you do the sums by BS2573 and the latest BS EN you get the same results, ie if it was acceptable to the old standard it is acceptable to the new one, just a different approach to calculation. The old one de-rated the allowable stress, the new one uprates the loads. In both there are further factors for frequency of use, how often you lift the maximum weight, consequences of dropping it (ladles full of molten metal, nuclear fuel flasks etc) which need not trouble us here. If you are proposing to work up the the allowable stresses you need to be pretty sure you've done the sums in enough detail, but I've never had to resort to FE analysis. It is entierly likely that there is a different spec for stuff like tripods, I think 2573 is aimed more at overhead cranes and the like. There certainly was one for runway beams.

MRC is 'Manufacturer's Rated Capacity', which means much the same as Safe Working Load, but I assume it has some legal wormhole.

[Neil WyattModerator @neilwyatt]

Posted by duncan webster on 08/08/2018 17:03:43:

MRC is 'Manufacturer's Rated Capacity', which means much the same as Safe Working Load, but I assume it has some legal wormhole.

In Australia MRC applies to a lifting configuration rather than being an overall rating.

Presumably this is to reflect things like how a wire sling can be used at different angles or doubled up.

N.

[MeunierParticipant @meunier]

Having carefully considered all the above-mentioned analyses and standards (n.b I said considered – not worked through!) and knowing little of FEA, I sent off for a 2-ton hydraulic lifting crane with max extension of boom at 500kg for lifting ML7 on its welded steel table and the WM18 mill. It performed admirably with only a little difficulty concerning head-room with the lifting straps available. When I can clear some floor space it will be used to re-mount them. When the WM18 was originally lifted up onto its stand I used 2x parallel scaffold tubes with 4ft clear between two oak beams and a chain hoist. The scaffold poles showed a distinct downwards set subsequently.
At GBP180 incl shipping to SW France, the peace of mind more than justified its price.
DaveD

[Author]

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