Improving Plant Performance

Part 2

by Roger A.P. Fielding, BENCHMARKS

In the last issue, we described analyses that have been demonstrated to enable understanding of the factors affecting the perform-ance of an extrusion press. The data describing lost time and—in the case of press recovery—lost aluminum, can readily be associated with the responsi-bilities of plant managers and supervisors, maintenance and process engineers, die correctors, and press operators. Realistic targets for improvement can be set, and progress can be monitored. No more references to vague targets of “5% per annum” or the like!

To get a better understanding of the achievements of the “benchmark” extruders, the author devised two additional measures:

1) The Utilization of Men, Machines, and Metal

The recovery of aluminum, measured at the finish cut saw, is the measure of the utilization of the aluminum billet delivered to the extrusion press. Contact utilization or machine efficiency is the ratio of contact time to total production time, and is therefore a measure of productive utilization of the extrusion press and its press crew.

The effect of improving the recovery and the contact utilization (or machine efficiency) can easily be calculated.

Productivity increased from 15 to 18 million pounds per year by increasing recovery from 82 to 84%, and increasing machine efficiency from 65 to 77%.

2) The “Consistency” of Extrusion Operations

The average extrusion speed achieved at the press is a function of the extrusion dies, the billet quality, and—above all—the control of the extrusion “process” parameters. The extrusion process parameters—the temperature of billet, container, and dies—must be controlled to maximize ram speed.

Dead production time is the sum of the mechanical dead cycle, the average die change time, and the time wasteddue to minor delays at the extrusion press: waiting for billet, lubricating the tooling, etc.

A comparison of “benchmark” extrusion press operations shows the effect of increasing the effective extrusion speed and reducing the dead production time: Productivity is increased from one to two million pounds per month by doubling the effective extrusion speed and reducing the dead production time from 50 to 35 seconds.

Discussion

While correctly focusing on the operation of the extrusion press, it is essential to ensure that the subsequent—downstream—operations of handling, sawing, aging, and packing are con-figured so that they (or the manner in which they are operated) do not delay the extrusion press.

In the recent past, it could be shown that handling systems (including the press run-out, cooling tables, and stretching), together with the finish cut saw and their collective operation, were often the cause of “full tables”. And, although press crews could be trained to work together to minimize the incidence of delays, delays did occur.

In the extrusion plant, the prime production device—the extrusion press—must define the ultimate output from the plant. It must be the “bottleneck”. Belt handling systems, automatic or semi-automatic stretchers, wide saw tables,

and automatic or semi-automatic racking systems have been combined to minimize or eliminate full tables. But, at considerable cost, automatic handling systems cannot be justified on many of the presses currently extruding less than 2500 pounds per hour of AA6063 or AA6060 type alloy extrusions.

Rightly or wrongly (it was not always the correct solution), the wide saw table was probably the first attempt to remove a downstream bottleneck, thereby allowing the extrusion press to reach its full potential. The development of a practical run-out table puller followed. Automatic racking of sawn extrusions and the development of automatic stretching systems came next. But improvements to aging systems have been slow to follow, with many extrusion plants still relying on batch age ovens, loaded (and unloaded) every six to eight hours.

Conclusion

Although most extruders monitor recovery and average productivity, few monitor every element of the extrusion cycle to identify opportunities for improvement. Many extruders accept a level of recovery and productivity that is within the capability of the press crew to consistently deliver. There are few improvement programs in place, and when upgrades or replacements to key equipment—for example, the extrusion press—are made, the lack of under-standing of the factors that control productivity at the press results in sub-optimal performance.

The specific performance data contained in this paper covers the range reported by numerous extrusion presses. The numbers exceed those of many, many presses, and were only achieved after considerable development of process and equipment, combined with rigorous operator training.

Improvement to benchmark performance can only be achieved following a program that sets out to measure, understand, control, improve, and optimize production—before automating!

Improving Plant Performance - Part 3

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Abridged from “Managing the Performance of an Extrusion Plant,” Proceedings of the Eighth International Extrusion Technology Seminar ET ’04 Orlando, Florida, May 18-21, 2004, pp. 565-570