HOT ROLLING
Hot rolled tubing has a surface finish comparable to hot rolled bars, plates or sheets of equal thickness. Light mill oxide covers both the outside and inside surfaces. Hot rolled tubing can be produced to outside diameter and wall dimensions with stated tolerances.
When a quotation for this highly specialized product is requested, we work closely with the customer to gain as much knowledge as possible about the end use. This enables us to apply materials with optimum dimensions to reduce costs.
COLD DRAWING
Cold drawn tubing is produced from hot rolled tubes that have been carefully inspected and properly surface-conditioned. Cold drawing consists of pulling a tube through a die and over a mandrel, reducing the diameter and wall thickness. Tubing is cold drawn for one or more of the following reasons: closer dimensional accuracy, better surface finish, smaller sizes than can be hot rolled, or to achieve certain mechanical properties. Cold working also imparts higher strength to the tubing and tends to improve machinability of carbon and lean-alloy steel.
ROTOROLLING®(Cold Pilgered)
Rotorolled tubing is produced from hot rolled tube shells that are conditioned for further reducing. Rotorolled tubes are produced on a machine designed to make large reductions of the cross-sectional area in one pass of the tube. The machine operates by cold swaging the tube between semicircular dies containing tapering grooves. The dies rock back and forth while the tube is advanced and rotated between rocking cycles over a long tapering mandrel. The developed contour of the die grooves forms a tapering circular pass that ends in a constant-diameter ironing section that establishes the OD of the finished tube.
Rotorolled tubing is a premium product with a surface condition superior to those obtained by cold drawing. Machinability is excellent. Dimensional tolerances are very uniform. Our ability to obtain large reduction ratios allows superior mechanical properties to be achieved.
Wall thickness of up to one-third of the outside diameter can be produced.
ROUGH TURNING
Turned tubing is produced by machining the outside surface of the hot rolled tubing. This process removes surface defects and decarburization from the outside, but the inside diameter surface retains the hot rolled finish. This is accomplished in a machine where the tools are mounted in a ring and rotated around the tube. The only motion of the tube is lateral, through the ring and past the rotating tools. Turned tubing is used extensively in automatic screw machines for manufacture into ball and roller bearing races and for special applications where advantages can be taken of the close outside tolerance or clean outside surface. Any hot rolled size up to 8 inches OD can be rough turned. Surface finish approaches 125 RMS or better.
THERMAL TREATMENT PROCESSES
ANNEALING
Annealing is heating uniformly to a temperature within or above the critical range and cooling at a controlled rate to a temperature under the critical range. This treatment is used to produce a definite microstructure, usually one designed for best machinability. It is also used to remove stresses; induce softness; and alter ductility, toughness or other mechanical properties.
HOT BED COOLING
This is the standard process of air cooling the tubing immediately following piercing on a special table or hot bed that continuously advances the tubing as additional tubes are finished. Tubing that is hot bed cooled may require additional thermal treatment to obtain optimum machinability or required mechanical properties.
MILL ANNEALING
Mill annealing is a controlled cooling of the tubing immediately following piercing which produces – in some low and medium carbon alloy grades – the optimum hardness and microstructure for machinability.
NORMALIZING
In this process, steel is heated uniformly to a temperature at least 99° F (37° C) above the critical range and cooling in air to room temperature. This treatment produces a recrystallization and refinement of the grain structure and gives the product uniformity in hardness and structure.
PROCESS TEMPERING
Process tempering is performed to improve subsequent fabrication of the material (machining, cold working, etc.). See Tempering.
QUENCHING (QUENCH HARDENING)
This processes heats steel uniformly to a temperature above the critical range and cools it rapidly in a liquid medium.
SPHEROIDIZE ANNEALING
This special type of annealing requires an extremely long cycle. Spheroidize annealing is used to produce a globular condition of the carbide and maximum softness for best machinability in some analyses or to maximize cold formability.
STRESS FREE
This designates tubing that has been hot rotary straightened. Minimal straightening stresses develop in hot rotary straightening, so stress relief tempering is not needed. Cold rotary straightening and stress relieving can substitute for hot rotary straightening.
STRESS RELIEVING
Stress relieving is a final thermal treatment used when stress-free material is desired. Its purpose is to restore elastic properties and minimize distortion on subsequent machining or hardening operations. This treatment is usually applied on material that has been heat treated (quenched and tempered). Normal practice is to heat to a temperature 99° F (37° C) lower than the tempering temperature used to establish mechanical properties and hardness.
TEMPERING
Tempering heats uniformly to a temperature under the critical range, holding at that temperature for a designated period of time and cooling in air. This treatment is used to produce one or more of the following end results:
- To soften material for later machining or cold working. Also referred to as a Process Temper.
- To improve ductility and relieve stresses resulting from prior treatment or cold working.
- To produce the desired mechanical properties or structure in the second step of a double