Primary Processes

 

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 only to outside diameter and wall dimensions. Within our production capability, any decimal or fractional outside diameter or wall thickness can be specified. Metric dimensions are acceptable. When a quotation for this highly specialized product is requested, it will benefit the customer if we are given as much knowledge of the end use as possible.

 

 

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®
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 that obtained by cold drawing. Machinability is excellent. Dimensional tolerances are very uniform.

 

Wall thicknesses of up to one-third of the outside diameter can be produced.

 

 

Rough Turning
Turned tubing is produced by machining the outside surface of hot rolled tubing. All surface defects and decarburization are removed from the outside, but the inside 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 advantage can be taken of the close outside diameter 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.

 

 

Secondary Processes

 

Annealing:

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, and/or to remove stresses, induce softness and alter ductility, toughness or other mechanical properties.

 

Cold Straightening:
A process used to achieve straightness tolerances by deflecting the product until plastic deformation occurs. Cold straightening may be achieved either on rotary straightening equipment or by press straightening.

 

 

Cut Off:
An operation used primarily to:

 

• Cut the tubing to the length required by the customer.
• Obtain metallurgical samples to provide material for testing required by the customer's specifications.

 

 

Hot Bed Cooling:
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:
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:
Heating uniformly to a temperature at least 100°F 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.

 

 

Pickling:
An operation by which the scale formed on the surface of the tube during piercing or heat treatment is removed by the chemical action in sulfuric acid. After the acid bath, the tubing is rinsed in water.

 

 

Process Tempering:
A tempering operation performed to improve subsequent fabrication of the material (machining, cold working, etc.). See Tempering.

 

 

Quenching (Quench Hardening):
Heating uniformly to a temperature above the critical range and cooling rapidly in a liquid medium.

 

 

Scale-Free:
The absence of loose scale on a hot finished tube, typically achieved through pickling or blasting.

 

 

Spheroidize Annealing:
A special type of annealing that differs only in the extremely long cycle required. This treatment 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:
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:
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 100°F lower than the tempering temperature used to establish mechanical properties and hardness.

 

Tempering:
Heating 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 treatment.