Extruder set-up takes years to learn: HR for cable and wire manufacturers

Past midnight, a PVC insulation line finishes one order and has to change over to a heavier stranded conductor. The day setter has gone home. The night operator runs the line well once it is set, but has never done this changeover alone. He picks tip and die from memory and nudges the zone temperatures. For an hour the laser gauge wanders, the concentricity reading swings, the spark tester trips on pinholes and the take-up drum fills with core nobody can sell.

Minding a running line and setting one are separate crafts. Minding it means watching diameter, ovality, the dancer arm and the spark tester. Setting it means bringing all of that right from cold, for a cable the line has not made this week. Few plants have more than a couple of people who can, which is the sharpest strain on a cable floor.

• Tooling: choosing tip and die, pressure or tubing style, and checking the breaker plate and screen pack.
• Temperature profile: barrel zones, crosshead and die set for the compound and its lot, PVC behaving very differently from XLPE.
• Speeds: screw speed matched to line speed and capstan, so thickness holds without surging.
• Conductor preheat and cooling: enough preheat for adhesion, enough trough length for the sheath or insulation to set.
• Centring: adjusting the crosshead until the concentricity gauge and a cut sample agree the wall is even.
• Purging: flushing old compound or colour masterbatch through the crosshead with as little waste as possible.

Each compound and size behaves a little differently, and even the same compound varies between lots. A setter learns how a slightly cold melt looks leaving the die. He learns the sound of a core rubbing in the tip, and when to wait rather than adjust. That judgement comes from many changeovers. Yet a given size may return rarely, and often on a night or a Sunday. A learner on day shift may go months without seeing a particular set-up, so the education is slow and patchy.

• Scrap drums and wasted compound after changeovers done by someone still guessing.
• Lines standing on nights and Sundays until a setter drives in, which often costs more than the scrap.
• Changeovers bunched onto day shift, so planning bends around a few people's rosters.
• Setters working long stretches and fielding calls on their day off.
• Real bargaining power for the two who can set, and neighbouring plants know their names.

Setters are judged on fast changeovers, so they do them alone and quickly. Temperatures and tooling sit in a dog-eared notebook or on a phone. Operators have no grade above line operator, so learning to set brings no visible reward. Rosters keep setters on days because that is when management is present, which leaves nights to cope. None of this is anyone's fault. It is simply how a plant runs when nobody has decided to grow setters.

1. 1

   Write a setting card for every product

   Tooling, zone temperatures, speeds, preheat and cooling that worked last time, plus warnings in the setter's own words. Store cards at the line, not in an office.

2. 2

   Plan changeovers with a learner present

   Production planning schedules key changeovers when an apprentice setter is on shift, and allows a little extra time for explanation.

3. 3

   Log every changeover

   Date, product, who set it, scrap metres to first good core and what was adjusted. The log shows who is improving and which products are hardest.

4. 4

   Sign off setters by product family

   An apprentice is cleared for a family of sizes after setting it alone, witnessed, with scrap within the agreed allowance. Add families one at a time.

5. 5

   Create a setter grade and pay it

   Line operator, apprentice setter and setter, each with pay that reflects the skill. Without the grade, operators have no reason to take on the stress.

6. 6

   Aim for a cleared setter on every shift

   Even an apprentice cleared for the common sizes means nights can change over the routine products without a phone call.

PRODUCT: ______  CONDUCTOR SIZE AND TYPE: ______  COMPOUND AND GRADE: ______  LINE: ______.
TOOLING: tip ______  die ______  style: pressure / tubing.  Screen pack: ______.
ZONE TEMPERATURES: barrel zones ______  crosshead ______  die ______.
SPEEDS: screw ______  line ______  capstan setting ______.
PREHEAT AND COOLING: preheat setting ______  trough sections in use ______.
CENTRING NOTES: which way the core drifts on this product and how the setter corrects it.
WATCH FOR: setter's own words on known traps, with phone photos of an even wall and a lopsided one.
LAST SET BY: ______  DATE: ______  SCRAP TO FIRST GOOD CORE: ______.

Cards go stale when a new compound supplier arrives or a die is reground. Make the setter who completes each changeover update the card at the line before the shift ends, and date the change. A card with last year's zone temperatures is worse than none, because a learner will trust it.

List, shift by shift, who could set each extruder for an unfamiliar size tonight. Lay last month's scrap metres beside the changeover log. Then ask your strongest setter which operator he would trust with a crosshead. The cable plant learning path lays out a helper-to-setter route, and the cable plant pay benchmarking page helps price the setter grade. Night rosters and written line handovers appear in the rostering guide for cable lines. Drum handling, overhead cranes and other strains sit on the cable and wire manufacturers page, while HR for electrical equipment manufacturing compares cable with winding and panel shops.