Lifting chain sling components / hooks 3

[tigermoth]

Hi

Can anyone offer advice on the machining of lifting hooks from solid steel plate (instead of forging). Obviously, grain direction is not optimal but is it actually a terrible idea? (provided detailed fatigue analysis is carried out, the steel properties are well characterised, grain direction and surface finish specified and the analysis validated by appropriate Break Force, Proof Force and fatigue type tests?) Must be better than non-forged castings which are historically the only other way of attaining the required finished shape.The only standards around seem to be those covering forged hooks.

Thanks

 

[ishvaaag]

You are providing a layout for the fabrication of these items. It doesn't sound unpractical since you are ready to study an proof it theoretically and by tests, that should be extensive and then see to what level and cycles you can load your fabricated items. It may turn not economically interesting since your fabrication is material-intensive, you need a lot of machining for every single part.

 

[cntw1953]

I have seen lifting hooks made out of steel plates - 4 or more plates machined and groove welded together. No idea on aspect of design though.

 

[bridgebuster]

I'm not up on chains, but here's a paper I had in my files by an engineer with the USACOE; perhaps it will be some help.

 

[tigermoth]

ishvaaag - The particular hook design I am thinking of is difficult to forge and produced in small quantities so 5-axis CNC machining makes it cost-effective.

cnt1953 - yes I've seen these too for very large one-off hooks

bridgebuster - thanks for the paper: a good case study, however it concentrates more on the chain itself than the terminal or hook aspect. Same design principles should apply though I guess.

 

[dvd]

http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=INTERPRETATIONS&p_id=24769

 

[SEwannaB]

That OSHA is a good reference.

Design I've used is based on ASME B30.20 and BTH-1 (Dave Duerr is a good consultant on this) latest editions and met requirements of OSHA. Made beam grabs with machined hooks from an rough bending and shear design and then FEM analysis. Then load tested to 125%. Not sure of the metallurgy, but we didn't have problems.

 

[Ron]

tigermoth...have seen it numerous times as cntw1953 noted...also seen flame-cut plate used as field expedient method...not recommended, but it worked.

 

[dhengr]

Tigermoth:

Let’s see what you think this hook will look like, I can’t see it from here. What lifting apparatus (terminal hardware) is going to exist above and below the hook? What will the hooks be used for?

You may want to start your design by picking the weldless oblong alloy links, pear shaped links, shackles, or wire rope slings you’ll be using, as they will determine your minimum machined shape in various areas. And, although the hook may not look too elegant, I wouldn’t machine where I didn’t have to, except to fair in various surfaces and shapes. A nice radius on the four corners of a rectangular shape in the area of max. stress may not be all bad.

Obviously, ASME and OSHA should be followed. You have the advantage of FEA, assuming you model the hook correctly. Years ago we didn’t have this advantage, it was all long hand, closed form analysis with some testing and a big F.S. Looking at the side of the hook, with the upper eye at about 12 o’clock, and the lower sling bearing at about 5:30 to 6:30; the max. stress will be btwn. 8 & 10 o’clock, due to bending and axial loading. The C.G. and the N.A. of the section are not at the same location, the N.A. moves toward the center of curvature.

Proof testing to 125% of rated load, is not a big problem. A good sound analysis both to yield and to ultimate, watching out for high combined stresses, which can include some significant radial stresses, and principle stresses, etc. makes complete sense. So does a reasonable shot at some fatigue analysis; and generous corner radii and fairing from surface to surface. What is your F.S. or Margin of Safety? I would not talk about fatigue testing for a few-of-a-kind, unless you want to be at it for the rest of your life. I would increase the M.S. to avoid any fatigue testing, but have a nice discussion of fatigue considerations in my analysis packet.

 

[tigermoth]

Thanks guys

Unfortunately I can't describe the 'hook' in detail for commercial reasons, however it incorporates a clevis for pinning to the lifting chain as per a conventional hook.
I'm basically trying to ensure the hook/lug/'lump of metal' has similar margins to standard chain and terminal hardware ie 4:1 on break, 2:1 or 2.5:1 on yield, fatigue cycles same as the lifting equipment it is permanently attached to. The only area I feel I'm potentially out on a limb is the machined-from-solid aspect. Some chain sling standards seem to insist on forged terminal fittings (with their nice grain flow etc), but whether this based on historical experience or is leftover from before the advent of CNC machining, FEA etc I don't know.