Chain Sling Design
Chain Sling Design
(OP)
Hi,
I'm just a simple Materials engineer.
Can anyone please advise as to whether to include for acceleration/deceleration forces in detrmining the acceptability of Chain slings using simple ratings from SWL(or WLL)?
Thanks
A
I'm just a simple Materials engineer.
Can anyone please advise as to whether to include for acceleration/deceleration forces in detrmining the acceptability of Chain slings using simple ratings from SWL(or WLL)?
Thanks
A






RE: Chain Sling Design
I never did, but my lifting devices were not subjected to extreme lifting conditions. It is standard practice to NOT jerk loads when lifting, and major lifts should be done by experienced personnel. But it depends on your industry and the 'culture' regarding safety in your facility. Some industries by nature have more severe requirements than others. And some companies have a serious concern about safety, and others don't.
As a general rule I wouldn't select a chain sling for the exact load required. Just a little bit extra would cover minor impact conditions and makes sense because the unknowns present when making a lift on the shop floor. Many times you don't know th exact weight of the lift, the sling angle, etc. A good material handling vendor might be able to assist.
High speed hoists however, can can cause lifting forces to be greater than the static load. Formulas for this can be found in the monorail specs by MMA and overhead crane specs by CMAA. If you are interested in more info about cranes and monorails try here.
http://www.mhiastore.org/category.cfm?Category=39
Regards,
-Mike
RE: Chain Sling Design
ASME B30.20a-2001 Structural and Mechanical Lifting devices.
main section Requires sf=3
padeye Requires sf=5
CMAA crane requirements
AASHO 1.6.17
Steel Construction Manual-AISC
Occupational Safety and Health Administration (OSHA) 29 CFR standard 1926.753(e)(2) and 1926.251
American Society of Testing and Materials Specifications A391
Naval Facility Command NAVFAC-307
American National Standards Institute, "Below The Hook Lifting Devices"
ASME B30.20-2003 20-1.2.2
"The load-bearing structure components of a lifter shall be designed to withstand the stresses imposed by its rated load plus the weight of the lifter, with a minimum design factor of three, based on yield strength of the material, and the stress ranges that do not exceed the values given in ANSI/AWS D14.1 for the applicable condition. ...."
This paragraph determines the maximum allowable stress for materials used as load-bearing structural components. Analysis or actual max working stresses must be determined based upon working conditions including impact or other factors pertinent to the application. Actual max working stress must be equal to or less than the allowable stress.
The intent of Section 20-1.2.2 is that the load suspension parts of a lifter shall be designed so that the static stress calculation for the rated load shall not exceed 33% of the yield strength.
The following paper has numerous examples:
"Design and Construction of Lifting Beams" David Ricker, Structural Engineering Journal, Fourth Quarter/1991 of AISC
www.aisc.org <http://www.aisc.org>.
RE: Chain Sling Design
The 3 to 1 and 5 to 1 factors of safety are sometimes confusing. When designing lifting devices I would use an allowable stress that was either 1/3 the material yield or 1/5 the ultimate strength, whichever was less. This range helps insure ductility in overloaded devices to avoid dropping loads. When purchasing lifting equipment you usually don't have this information so you depend on the manufacturers expertise.
-Mike
RE: Chain Sling Design
"When purchasing lifting equipment you usually don't have this information so you depend on the manufacturers expertise."
That's a rather odd position, isn't it ? I guess mike means that you can't be sure how the supplier has factored your specified load, unless you specify it in the PO, and this is the experience your depending on. Surely, tho' the supplier is responsible (and accountable) for ensuring the supplier goods meet the specification. sure, if there's a problem i'd be willing to bet that there'd be two groups of lawyers getting rich over "he said, she said".
RE: Chain Sling Design
Since many companies don't have the expertise in their maintenance or plant engineering depatments to do these calculations, they need to work with vendors that do.
-Mike
RE: Chain Sling Design
Many thanks for your excellent posts.
It is stated to have a minimum safety factor of 5 on UTS.
When we do the actual calculations however it is actually about 65% of yield. The acceleration/deceleration loadings are about another 20%, so quite appreciable.
This is not what you would classically describe as a shock loading application either.
My view is that potentially some allowance should be made in SWL for these loads.
john