Pipe Extrusion Line Start-up and Shutdown Procedure

Purpose. This procedure sets out how to start up a pipe extrusion line after a die or material change, bring it to specification, run it and shut it down safely.

1.Before start-up

Confirm the job card, the Process Setting Sheet for the pipe size and material, the die and calibrator fitted match the sheet, the material lot is correct and dried where the sheet requires, the vacuum tank and spray bath are clean and filled, the haul-off, marking, cutter and coiler are set for the pipe size and the extraction is running. Check that all guards on the die head, haul-off and cutter are in place and the emergency stops work.

2.Heating and purging

Set the barrel, adapter and die temperatures from the sheet and allow the die to soak at temperature for the time on the sheet before starting the screw. Start the screw at low speed and purge until clean material flows from the die with no black specks or unmelted material. Purgings must be handled with heat-resistant gloves and placed in the purge station. Never look directly into the die.

3.Threading the line

Draw the melt from the die with the threading tool, through the calibrator with vacuum off, through the spray bath and into the haul-off at threading speed with the haul-off guards closed. Apply calibrator vacuum and cooling and bring the screw and haul-off speeds up together to the values on the sheet. Keep hands clear of the calibrator entry and the haul-off belts at all times.

4.Bringing pipe to specification

Measure outside diameter and wall thickness at four points around the pipe with the ultrasonic gauge and the calipers and compare with the standard and the sheet. Adjust the haul-off speed for wall thickness and the vacuum for outside diameter within the limits on the sheet. Check the marking is legible and complete with the standard, size, class, material, manufacturer and batch. Cut the start-up pipe to scrap until dimensions are within tolerance and record the start-up scrap weight.

• Outside diameter at four points
• Wall thickness at four points, minimum and maximum
• Ovality
• Marking content and legibility
• Length and cut quality

5.Running

Record the dimension checks on the job card at the frequency on the sheet. Take the test samples required by the test plan for the laboratory. Watch melt pressure, barrel and die temperatures, vacuum and bath temperature and report any drift outside the sheet limits to the supervisor. Do not adjust temperatures without the supervisor's agreement.

6.Shutdown

For a short stop, reduce screw speed and stop the haul-off with the pipe in the calibrator. For a full shutdown, run the hopper empty or purge with the purge compound on the sheet, stop the screw, stop the haul-off, release the vacuum and drain the bath, and reduce the heats to the standby setting. For a die change, allow the die to cool to handling temperature and isolate and lock out the extruder before removing the die head bolts.