Ingot Tong 250 ton: what about weight?

[maxpcc]

Ingot Tong 250 ton: what about weight?
I'm budgetting an ingot tong, capacity 250 ton, maximum open width 3500 mm,
minimum open width 1500 mm, ingot temperature 1300°C (just for sample:

http://hoists-crane.com/lifting-devices/lifting-devices-ingot-tong.html)

At the moment I need to know the weight and the material. I'm designing
it made of DILLIMAX 690. The weight is about 42.000 kg. My customer says
that our competitors can build it in S355 with a weight of about 33.000
kg.

Is there someone that can confirm me these data? I can't understand where I'm in mistake.....

 

[boo1]

Consider if the two tongs use the same design criteria, example: designed and manufactured in conformance with the ASME B30.20 standard (“A lifter (tong) shall be designed to withstand the forces imposed by its rated load with a minimum design factor of 3") based on yield strength, for load bearing structural members.”. Many variable can be used, including heat, shock loading, and cycle time, increase the design factor to as high as 5, with consideration of shock loading of 150% or more.

 

[rb1957]

a quick google on "S355 strength" got ... Grade S355 hot rolled structural steel also suffers losses in residual yield and tensile strength when subjected to temperature over 600ºC in fire. High strength steels, of which grade S355 is typical, obtain their characteristics as the result of the addition of strengthening elements, typically vanadium and niobium. At high temperatures these elements tend to precipitate out of the matrix creating a coarse distribution. As a result the reduction in yield strength at room temperature after the steel has been heated to temperatures above 600ºC, may be proportionately greater than for unalloyed mild steels.

doesn't sound real good for 1300deg ...

 

[racookpe1978]

Even if only the tong "tips" contact the ingot itself, they - being thinner than the main body of the part, and in very close contact with the hottest part of the furnace right as they lift the load, and under the bending highest stress where they contact the load - will be the most affect ed by both the heat and the highest duty cycle of your application. Further back, away from hot furnace and away from the ingot, this steel maybe OK .....

 

[boo1]

Some of the variables when considering a below-the-hook lifting device are:

Maximum weight
Single or multiple pieces per lift
Temperature
Shear strength of the material
Maximum / minimum dimensions
Surface finish requirements
Crane limitations (rated capacity, available headroom)

 

[boo1]

design link:

http://www.bushmanavontec.com/userfiles/media/Applications for Tong Grabs.pdf

 

[racookpe1978]

You had another good series of photo's about riveting hooks under the "hot rivet" thread.

 

[maxpcc]

Thanks to all.
Some more specifications:
I don't know design (rules and so on) of my competitors, of course I'm giving all the best in my design, that's the why I'm trying to know if my result is quite good and my competitors are in mistake or the opposite!

About temperature: I made a calculation of thermal impact (radiaton, convection, conduction) and I think that the temperature of my tong will be about 150°C: in the contact point I use inox steel, in the rest of the ton I use thermal shields (inox plate not in contact, to reduce radiation effect).

I'm using UNI 13155 rule: max vertical force is double of ingot weight, max stress is yield stress when I consider a capacity double of the maximum (so say italian rules).

I ask again: does someone used a tong of this capacity or similar (2000/300 tons) and know the weight? Or my customer is making fun of me??

 

[rb1957]

"Or my customer is making fun of me??"

that's my take ! tell him that's this is your best design, and if he prefers the other, then that's the free market (capitalism) at work. but don't compromise your design (maybe take out some conservatism).

 

[maxpcc]

Of course rb1957,
my design is this and I don't want to change anything against rules and safety.

But my customer (that will build the tong) is choosing his partner in engineering, and if my competitor is lighter than me he will prefer him, even if (my customer can't know that...) my competitor is in mistake!!

 

[boo1]

Lighter, cheaper may not met requirements.

 

[rb1957]

cavet emptor ... (buyer beware)

maybe your competitor is compliant, maybe he isn't.
maybe he's hoping to change the design later, at a design review.

it does seem "odd" ... your material is significantly superior (yes?), and presumably more expensive (per lb). typically you'd think that better material properties are off-set with a lighter component.