Getting the most out of your extrusion systems.

by Roger A.P. Fielding, BENCHMARKS

The author’s first contribution to this newsletter appeared in April 1996. Many years’ of experience working in, and auditing the operation of numerous extrusion plants had showed that, even when equipped with what was then state-of-the-art equipment, few extruders achieved benchmark performance.

The Double Puller System was a case in point. Some will recall the interest generated at the Third International Extrusion Technology Seminar, ET’84, when Granco’s Charles Gentry introduced “The Exciting Double Puller from Norway.” However, subsequent operational audits of, and visits to, extrusion plants equipped with double pullers revealed that few made effective use of its numerous working cycles, and many press operators were not inclined, or instructed, to change their familiar operating practices.

Clearly, the potential impact of the double puller on the profitability of an extrusion plant had to be explained. This was done by focusing on recovery, and in the event, three articles: “The Cost of Recovery,” “Recovery: The Impact of Modern Handling Systems,” and “Applying Continuous Improvement to Reduce Waste in Metal Recovery,” preceded a fourth, with a complete description of the double puller operating cycles: “Understanding the Operation of the Granco Clark Double Puller System,” appeared in “Hot off the Press,” Volume 4, Issue 1.

The following is adapted from the first three articles:

The Cost of Recovery

Take a group of extruders to visit any extrusion plant, and within ten minutes they’ll have dispersed all over the plant as each indulges their particular interests, or looks for the solution to their own particular problems. Watch what happens as they disperse and you’ll see each individual pausing to study the butt discards, the stretching allowances and the scrap at the finish cut saw; they’ll look at the alignment of stop marks on the tables; and they’ll each invariably take a long hard look at any loose or baled scrap awaiting shipment to the remelt and casting plant. They’ll demonstrate interest in any equipment to compress saw chips or to compact and bale extruded lengths.

The interest in what is after all “waste,” is driven by each extruder’s understanding of the problems that cause the scrap, and the added problems caused by handling and disposing of scrap material in the extrusion plant. But, take a look at the financial records for any extrusion plant and you’ll find numbers recording the cost of this waste which may not reflect the intensity our visitors’ interest in it.

Take a look at an extruder’s accounting records and you’ll find an item variously called “recovery” or “scrap” or “recycling cost.”  The sums entered against these headings will include credits which vary, depending on whether the scrap is sold on the open market, recycled through a third party, or recycled in the company’s own remelt and casting facility. The “costs” incurred in generating the scrap will vary significantly from extruder to extruder, depending on the efficiency of the extrusion plant and how they are calculated.

The costs are minimized if the recovery from billet or log is maximized in accordance with a pre-determined “plan.” However, much of the aluminum which ends up as scrap is not planned, and is often higher (rarely lower) than that allowed for by the extruder’s planners and schedulers.

The true cost to the extruder of “recovery,” “scrap,” or “recycling” is invariably higher, and often much higher than that which appears in the company’s financial records. Much of the difference between the true cost and the recorded cost of recovery is buried in the labor, materials and energy used to produce the waste in the first place, and in the cost of the additional labor, materials and energy required to dispose of the scrap and “do it right” the second time. The reported cost of “recovery” rarely—if ever—reflects the cost of the disruption created by deviations from plan, and I have never seen an accounting entry for the cost of the “lost opportunity” caused by the deviation from the company’s production plan.

To improve profitability, unplanned scrap must be eliminated, and planned scrap minimized by measuring, understanding, controlling and improving the production planning, extrusion equipment and operating systems.

The Impact of Modern Handling Systems

How do we minimize losses? 

• Use the production planning and control system to record the performance of every extrusion die, using feedback from the puller and press to measure die wear and the run-out of each billet.
• Use the production planning and control system to record the stretcher scrap and the requirements for sample material for every extrusion die.
• Use equipment which ensures tight control of the die, billet, and container temperatures. Control the extrusion process to ensure the production of extrusions with good surface finishes which meets the required properties.
• Use double pullers and cut on the fly to eliminate the die stop mark, and thus incorporate the transverse weld scrap into the stretcher scrap.
• Use double pullers and cut on the fly at the stop-mark to “recover” the metal between the platen and the die.
• Use double pullers and cut on the fly to eliminate the time which is wasted waiting for the puller and restarting the press when “double-pushing.”
• Use belt handling systems with rectilinear motions to eliminate the damage to extrusions which is common with the use of lift-offs and walking beams.
• Use automatic batching and belt handling to move extrusions into and out of stretchers.
• Use automatic batching and handling to move extrusions into and out of under-table finish-cut saws to improve safety and remove another source of scrap.!!!

Measuring and understanding the production planning, the extrusion equipment and operating systems shows where losses occur and how to control and improve extrusion operations. Understanding the true cost of recovery provides justification for expenditures on modern handling systems

Applying “Continuous Improvement” to Reduce Waste

Kaisen: the Japanese word which covers all actions resulting in the continuous improvement of a production system.

How do we start on the road to continuous improvement?

Start by improving metal recovery. And, measure, understand, control and improve all parts of the extrusion production system.

One: Measure the waste to find where it comes from. Measure and record the butt discards, the stretcher scrap, and the scrap at the finish cut saw. Studying the scrap will show how much aluminum is wasted due to poor planning, and how much is scrapped due to poor process control. Measurement will show that we incur losses starting a new die, that we damage extrusions on the run-out conveyor, with the lift-offs and walking beams, and again when handling extrusions into and out of stretchers. That we use too much stretcher scrap, and don’t plan for sample material. Scrap analysis shows where we damage extrusions in ageing ovens, and on the way to shipping.

Don’t cut scrap till you know where it came from. Account for all the metal supplied to the extrusion press during each shift. Make the scrap analysis part of every shift report.

Two: Understand the reasons for scrapping metal. Record the reasons: “Wrong billet size,” “dents from the lift-offs,” “too much stretcher allowance,” “too little stretcher allowance,” “twists at the stretcher,” “scratching from seized rollers on the saw table,” “didn’t make properties,” etc.. Note the quantity of scrap which can be attributed to
each cause.

Record the reasons for scrapping aluminum and rank them in order of importance. Display the scrap analysis for all to see.

Use the information to plan improvements.

Three: Find out why the wrong billet was used, why the stretcher allowance was wrong, and why the rollers on the saw table are seized. Control the operating practices and processes to reduce the waste. Maintain the equipment to eliminate damage. Check the production planning procedures, and ensure that the plan is followed. Control the aluminum log and billet inventory. Control the die, billet and container temperatures, monitor and control the extrusion exit temperature, and quench the sections properly.

Start by controlling the most frequent and the biggest reasons for scrapping metal. Ensure that documented best practices are in place, and are used all the time. Continually reinforce the use of best practices.

Four: Use the resulting understanding of planning, equipment and process to develop better working practices and processes.

Plan and implement the improvements to working practices and processes. Reinforce the changes.

Five: Measure the waste from the improved production system.

Go back to one!

“Understanding the Operation of the Granco Clark Double Puller System,” will be updated and appear in the next edition of Granco Clark Profiles.