Case study:- Film
Description

This Dutch company produces film in different colours, with LDPE and LLDPE. Most of the extruders have screw-diameters of 80-90 mm. Up until now a cleaning compound that uses mechanics to clean the extruder has been used. The company is interested in having a cleaning compound that works quicker, easier and more economical.

Problem analysis

Burning of polymer takes place when material comes into contact with oxygen, but also in zones where the flow of the material is slowed, f.i. in the die of a blown film extruder. This is especially true for multilayer film production, where several polymers with different melt behaviour are brought into contact, like EVA, PA and EVOH. Most dies are, rheologically speaking, not optimal. Initially a thin layer of gel forms in these "low-flow" zones, but this layer builds up, and carbonises in time. The surface becomes rougher, and allows f.i. pigment particles to get stuck in it.

Target

Our target is two-fold: to get to the source of the problem, and to get control over the source of the problem in future. All polymers burn, but this burning process should be controlled before the residues get a chance to carbonise. In other words: the forming of layers of gel should be broken off at an early stage, when this is relatively easy to do, and with minimal loss of (machine-)time and cleaning material. Preventive maintenance is important !

Solution

A three-way test was carried out:
1.   Cleaning of a "dirty" extruder for a colour change.
2.   Cleaning of a problem extruder.
3.   Establish over a longer period of time (4-6 weeks) what the optimal cleaning frequency would be for removing the residues in the gel-phase, thereby keeping the cleaning periods as short as possible.

The test was carried out with Econoclean 100-c, as this company had enough carrier resin available. In all mentioned test the optimal result was achieved regarding cleaning, but more important, also in minimising costs through preventive maintenance.


Costcalculation

1.  A. current cleaning material:chalk filled PE
     B. Used quantity (kgs)100
     C. Price/kg:2,95 Euro
                Total material costs:295,00 Euro
     D. Cleaning time (hours):2
     E. Costs/hour:115,00 Euro
                Total costs machine time:230,00 Euro

      TOTAL COSTS CLEANING:
525,00 Euro

2.       A. ECONOCLEAN blend 
     B. Used quantity (kgs)5
     C. price/kg of blend:5,10 Euro
                Total material costs:25,50 Euro
     D. Cleaning time :15 mins.
     E. Costs/hour:115,00 Euro
                Total costs machine time:28,75 Euro
      TOTAL COSTS CLEANING:54,25 Euro

      Difference between 1 and 2:       470,75 Euro = 89.7% cost reduction !

Note:

By applying preventive maintenance this way, not only are costs reduced, but also production hours gained, flexibility increased, and pulling the screw has been reduced to an absolute minimum!