Although worm gears of high enough ratio MAY be self-locking, there is no absolute guarantee of that. Good practice suggests using a brake also, and safety regulations may require a brake, especially if persons could walk beneath the load.

Also can be sensitive to lubrication - will lock with standard lube, but put moly or other lube it is possible for them to become non locking (theoretically).

A brake will fix this problem.

Discuss the issue with specialised lifting equipment suppliers with a view to farming out the design. These specialists will be able to come up with solutions that will satisfy the Engineer/Surveyor from the company that supplies lifting equipment failure indemnity insurance.

Yes. As mentioned, find one that fits your specific application.

http://www.joycedayton.com/products/machine-screw-jacks/5-ton-machine-screw-jack

You Can go for Spiralock threads , Visit www.Spiralock.com

Self-locking gears are well-known in the gear industry.

You should read this little article first,

then hand the project over to someone who knows more than a layman about the principles involved, and the advantages and disadvantages of various methods of eliminating back-driving. In the short run you will save money. A properly-designed and constructed hoist will do the job you require and you will only need to fabricate or buy one. In the long run you will avoid the risk of serious or fatal injury to your personnel. You will also avoid costly damage to the hoist and whatever it is you are lifting or whatever it might fall onto.

On my wife's wheelchair the motor is attached to a worm drive, and when this is engaged it is impossible for the wheelchair to roll backwards, even on a steep incline (12%). But I wouldn't trust this on a winch or crane that lifts up to five tons, I would always add a brake, one that locks on when movement ceases!

Spencer

If you are thinking of making 5 Ton winch without brake then it is risky decision. As per I.S you are supposed to provide E.M Brake for safety purpose.

Totally agree!!!

Simply buy a 5 ton hoist. The brakes and gearbox are built in and you won't have to deal with legal requirements.

I am not sure what codes you are dealing with but here in the state it is clearly defined that what you are looking to do is NOT permitted in the elevator, hoist or crane standards. You must use either a brake motor or shaft brake. Personally I prefer a shaft brake.