Quenching

Part 1

by Roger A.P. Fielding, BENCHMARKS

Although we can all agree that the extrusion of aluminum is a “conversion process”—during which an aluminum billet, forced at high pressure and temperature through a steel die, is converted into a three-dimensional shape—the complexity of this process is often overlooked. This is never more true than during the specification of a new press installation or the upgrading of an existing press.

When invited to comment on the plans for a new aluminum extrusion press, or, for that matter, the upgrade of an existing press, the response to the question of “product mix” is invariably:

“The press will be used to extrude AA6060 and AA6063 type alloys. And 10 to 15 percent of the mix will be AA6061 and other press-quenchable alloys.”

The reference to “press quenchability” is often left unstated! But the 10 to 15 percent of AA6061 (and other alloys)—which by implication constitutes a “small” proportion of the product mix and will invariably be quenched at the extrusion press—has a major impact on the design of the extrusion press facility, from the log or billet storage to the finish-cut saw and age ovens.

The extrusion of aluminum employs known thermal and metallurgical processes to achieve accurate three-dimensional shapes (the width and height of the extrusion and the extruded length), and these processes are found in all stages of the conversion process. The ultimate productivity of an extrusion press installation is governed by the degree of control exercised over the processes: The heating of the billet, the die, and the container. The quenching of the billet in a taper quench. The quenching of the extrudate as it leaves the press and passes down the runout table, the cooling, and stretching. And finally the aging process. All are specific to the alloy, and, to some extent, the geometry of the extrudate.

Anyone contemplating a new extrusion press installation or the upgrading of an existing installation is well advised to focus—in the first instance—on the processes which will be employed to convert the aluminum log or billet to extrudate. The thermal and metallurgical process: heating billet and log, dies, and container; the taper quenching (or heating) of billet; the press quenching and cooling; the stretching and aging systems. These define the ultimate productivity and quality which can be derived from a particular press system.(1)

The metallurgical requirements of the press quench system have been discussed by Bryant.(2) And the principles of “press quenching” were set out by Peterson and Dore in their paper to the first International Extrusion Technology Seminar in 1969.(3) The problems which can be encountered if things are not done properly were described by Bryant et al.(4)

Planning for a new press quench system must integrate the quench with the press platen opening and, specifically, the dimensions of the extrudate. Planning must integrate the quench with the operation of pullers. Planning must incorporate features to maximize recovery during the press dead cycle and other minor delays. The press quench must not be the limiting factor in maximizing press productivity and recovery.

In this writer’s experience, those planning a new extrusion press installation, or the upgrading of an existing installation, most often fail to account for the water quality, quantity, and pressure required. The supply is undersized, the capacity of the system too small, and maintenance of quality—both temperature and cleanliness—inadequate to efficiently quench the extrudate, where “efficiency” includes measures of dimensional stability, metallurgical properties, press productivity, and recovery.

Quenching - Part 2

References

1. Fielding, Roger A.P., “Integrated Extrusion Systems,” Light Metal Age, vol. 58, nos. 5, 6, June 2000, pp. 10-24

2. Bryant, A.J., “An Interpretation of The American National Standards Institute Temper Designations for Extruded Aluminum Alloys,” Light Metal Age, vol. 59, nos. 3, 4

3. Peterson, W.S., and J.E. Dore, “Super Quenching of Aluminum Extrusions,” First International Extrusion Technology Seminar, New Orleans, March 3-5, 1969, Paper No. 26

4. Bryant, A.J., W. Dixon, R.A.P. Fielding, and G.E. Macey, “Defects in Medium and High Strength Extrusion Alloys,” Light Metal Age, vol. 57, nos. 5, 6. June 1999, pp. 30-54