U Bolt

PRODUCTION CAPACITIES

At present we have capacities to produce 3.5 lakh U Bolts per annum on two shift basis.

The various activities involved in manufacturing U Bolts are:
Incoming raw material inspection using Brinell cum Rockwell hardness tester.
Cutting to size of alloy steel bars.
Chamfering of ends.
Centreless grinding of pre roll diameter. This operation ensures accuracy of threads formed subsequently.
Thread rolling on Hydraulic thread rolling machine. Rolled threads are stronger than machined threads and hence essential for this component.
Cold bending on special purpose hydraulic cold bending machine
Zinc plating using Acid Zinc Plating process. This process ensures negligible hydrogen embrittlement. This is a metallurgically desirable attribute in a high tensile steel component such as U Bolt.
Final inspection
Identification marking and packaging.

1.Increase in cost
2.Decarburisation and hence softening of threads if the furnace atmosphere is not completely inert.

MANUFACTURING PROCESS

Cold Bent U-Bolts are made from ground Alloy steel bright bars having a UTS of 80-95 kg/mm². These U Bolts are cold formed and
hence the need for post bending heat treatment is eliminated. On the other hand, the bends in a hot bent U Bolt become weak as the steel at the bends gets normalized due to heating and subsequent air cooling. Thus there exists a UTS gradient at the bends. Concentration of stress also occurs at the bends due to change of shape of cross section.
A combination of UTS gradient and stress concentration at the bends makes the Hot Bent U Bolt susceptible to failure under dynamic loading.
In order to regain the strength of the parent material and to relieve stresses, heat treatment of the U Bolt is required. This leads to:

WHY COLD BENT U BOLTS?

Application:
  
U Bolt is a safety component in an automobile as it is used to clamp leaf spring with axle. As such this component is subjected to heavy dynamic loading. U Bolts are also used in body building of trucks, buses, tippers and trailers. Hence both - dimensional and metallurgical quality is of prime importance in manufacturing of u bolts

U Bolt: