Motor Selection For My First Project Motorised Tong

We would need some prior detail in order to formulate an answer. What is the proposed geometry of the jaw and its actuator? How fast does the system need to operate? Why a lead screw rather than a hydraulic cylinder? What other movements does this lifter perform after the jaws grab the 50-ton roll?

So here i have attached the image of my project.Now you can easily understand the application.It is going to lift the rolls and place it at the desired location. The speed of the lead screw used to move this jaw is 7-8 rpm so that the time taken by jaw to move to close position that is as shown in image will be approximately 2 minutes.

Now the answer to why we have used the lead screw is because we want to go for lighter design and simplest mechanism as well as it is to be completed in the limited budget. Hydraulic will not serve our requirements. So tell me now how i can proceed for selecting motor.

Thanks.

Why not use four 15-ton fabric slings made to lengths that suit the two rolls?

Right now we are using the same but before few days one accident has occured and our top management decided to go for a safe option and that is Tong.

If the controls are not in place to look after the certified lifting equipment that is already in place, what is there to say that this motorised tong thing will:

• Be tested and certified for lifting?
• Maintain its certification at periodic inspections?

After all, that is what the fabric slings have to go through to satisfy the insurance company's Engineer/Surveyor's requirements.

A fabric sling is tested and certified for the purpose. The tong thing isn't. There will be numerous hoops to jump through before it is. Can management wait that long <rhetorical question>?

I agree with tornado...

The cylindrical shape of you lift begs for the plain-vanilla solution....load-certified slings. or slings with a strongback.

IMHO, A custom designed tong, that will require certification and testing does not seem to bethe best solution.

There are ASME standards incorporated into OSHA requirements (and state law) that govern "below the hook" lifting devices.

I take it this is for lifting the stand rolls in a mill?

There's one major problem whith your design, the outward thrust on the tongs as they lift will cause them to splay outwards. I worked on one designed in the 1970's. That was only holding 2Tonne. It was a pain in the backside to try and keep working safely.

I'd think again.

Better still get a lifting design company to do it for you and then it's their problem to get it approved and certified.

I am not interested on the certification part, that is the head ache of my top management. I just want to go for safe design. So for the same design do you have any suggestions.Hey and what about the motor. No body is advising me about motor selection.

Tony now to avoid the outward thrust i haved used the taper roller bearing, so it will not effect the equipment and it has been approved by my boss who is technically sound.

To lift the rolls this way, you will face lots of problems as others have mentioned.

It is inherently unsafe, clamping of the rolls will depend on the friction between the tongs and roll and there is danger of the roll slipping away. The tongs also can leave mark on the rolls because of clamping force, damaging the surface. Lead screw design would also be very important apart from tongs and other part of the mechanism. Every part in the mechanism is stressed and the chances of failure are great if not designed properly, which looks like a clear possibility since the safety aspect is not realised. The regulations say you must get all your lifting tackles certified from authorities and testing needs to be carried out with certification every year.

The design is too complicated and unsafe, it is not a good choice. Best option would be go for fabric slings.

Rajesh

Rajesh, There is no question of slippling of the rolls because, we are going to use Nylon and copper pads. Now about lead screw design, ya it is very important but we will take care of it. About mechanisms ,we are going to use track rollers for movement of jaw, and movement is occuring very slowly so our design experts are approving the design. Do you have any suggestion other than Fabric slings because we are using the same.

You can see that everybody is suggesting to not to go for the design of motorised tongs. You can either use the fabric slings or go for the solution suggested by Mr. Suresh Sharma. Safety can not be overlooked and it is responsibility of everybody concerned. The product design should take care of the safety factor first, all other considerations are secondary.

I worked in a multinational for 27 years and the first thing an employee goes through after joining is "Safety training" before he starts working. This is true even for temporary workers or contractors workers. But unfortunately in our country, this awareness is very poor in most of the local companies.

The pickup tongs I worked on used curved shoes to clamp on to a 2tone ring. It still managed to drop them due to the arms of the tongs splaying outwards as the weight was taken up. If you proceed with the design be prepared to allow a considerable budget for its maintenance. The stresses at the top of the arms will be immense causing bearing failure. One bearing failure will result in the roller on the floor if your lucky. The risk of damage and injury is just not worth it.

I worked in an iron foundry altering PLC programs. I had a sign above my desk.

If I kill some by my mistake, who's got to look his widow in the eye and say, "I'm sorry".

Follow suresh sharma's advise, go for a lifting frame with slings.

Thanks TonyS.

Suresh Sharma

Don't thank me, it's you that gave the sensible solution to the problem.

I just hope we can nip this madcap idea in the bud before someone gets hurt.

I suggest that you should design a lifting beam with two ends provided with wire rope slings which are detachable from one end of the loop. Rolls should be protected with nylon pads (removeable) so that rolls are not damaged at area of contact with rope slings. This would be simple device and requiring minimum maintenance.

Hello Hiren,

I agree with the others about your design, But your question is about the motor size. a few more questions for you.

1, what is the clamping force?

2, what is the inertia?

3, what is the stopping speed and rate?

4, what is the duty cycle?

5, what safety factor have you determined?

One other note about your design to be considered, if you're going to be using a screw, The coupling between the screws is going to be a major weak spot.

Dave

I'm sorry, but you and your company seem to be in a position that is asking for a lot of trouble.

Disregard ANY possibility of issues, people saying it's "not my problem", and someone could get hurt or killed. Then, managers and engineers lose their jobs and everything else, including their freedom. This type of attitude has led to many well known engineering failures.

I would advise you and your organization to seriously reflect upon what you are trying to do and the possible consequences, and review the advice provided to you.

The fact is, if your name is associated in any way with this, then you will be held responsible for any engineering failures, even if it is not of your doing.

Mr guest, its not the question of attitude, you have taken me in wrong manner, i am saying that getting certified is not my job its my organisation top management responsibility. And even i give safety as the prime and first importance.The organisation to which i belongs will never permit an unsafe design. And the reason behind this project is also to go one step ahead towards safety.we consider our labourers as our family.Right now we are using slings and we still doubt on slings. So we want to go for Motorised Tong.Do you have any suggestions for designing a motorised tong.

Our "Guest" is making salient points, you and your company will be liable in a court of law for any mishap. In the UK any lifting gear failure whether it results in injury or not is reportable the Health & Safety Executive, they can prosecute for unsafe working practices.

The design is fundamentally flawed!

I wonder if we'll hear the outcome of this from the OP