Cold Drawn Seamless tubing (also known as CDS). Cold Drawn Seamless tubes offer tight tolerances compared to Hot Finished Seamless tube, and offers stronger physical properties compared to other mechanical tubing. CDS is popular in the hydraulics, being used to make hollowed chrome plated telescopic cylinders and hydraulic rods. It is also popular for large bore, heavy walled, high pressure hydraulic cylinders. Cold Drawn Seamless tubes also find uses in heavy equipment manufacturing such as cranes and garbage trucks.
BARREL TYPE CROSS ROLL PIERCING PROCESS
In this process, rounds are heated in the rotary hearth furnace/ slope type fixed bed heating furnace to a forming temperature of approximately 1280 degree C. This is followed by a high pressure water jet descaling, prior to which the bloom is pierced in the cross roll piercing mill to produce a thin-walled hollow shell which is elongated to between 3 and 4.5 times its original length. The elongation corresponds to a deformation level between 65 % and 75%. Owing to the relatively large angle of roll inclination, and higher rolling speeds, stock exit speed in the case of barrel-type piercer is considerably faster than in Mannesmann piercing mills.
General process of cold drawing
A considerable proportion of the seamless tubes and pipes manufactured through the cold roll piercing technology undergo subsequent cold forming. The principal reasons behind cold drawing are:
- Achievement of closer wall thickness and diameter tolerance
- Improvement in surface finish
- To enhance serviceability
- No premature failure
- Suitable for critical forming Such as 180˚ Bends
- Enhancement of mechanical properties of the tube
- Expansion of product mix towards the lower end of the OD and wall thickness scales.
There are three basic processes employed for the cold drawing of tube:
- Hollow drawing
- Stationery drawing or floating plug drawing and
- Drawing over a mandrel (also known as drawing on-the-bar)
After the goods are cold drawn to sizes, the tubes are put on annealing furnace for heat treatment and normalising.
Post annealing, the goods are passed through a seven roller straightening machine to achieve proper straightening of the tubes.
Post straightening, each tube is passed through eddy current machine to detect for surface cracks and other defects . Only the tubes that pass eddy current are fit for delivery to customers.
Each tube is either oiled with corrosion resistant oil or varnished for surface protection and corrosion resistant as per customers requirement, each tube end is covered by plastic end caps to avoid damage in transit, the marking and specs are put and the goods are ready for dispatch.