Case study:- Compounding
Description

A Dutch compounder of masterbatches has a number of single-screw extruders, mostly with a screw diameter of 60 mm. The company has specialised in the production of small runs on customer specification and just-in-time deliveries. These small runs make purging on the extruder a frequent necessity, while the time needed to clean the extruder is coming out of production time. Until now they purged with a chalk-filled PP. The masterbatches are based on carrier resins such as PC, SAN, PS, PE and PP.

Problem analysis

All polymers burn, even if they are hardly thermally treated, like in compounding of masterbatches. In places where the flow of material is lower, like , f.i. on the backside of the flights, burning of polymer will occur. Initially a gel-layer is deposited, which carbonises over time. Regularly small particles break of, which are recognised as black specks. The carbonised layer also has a rougher surface than metal, and pigment particles will easily get stuck. This can be clearly seen when a colourchange is made.
Mechanical purging, like with chalk filled PP, cannot remove this layer efficiently, and certainly not prevent 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

The test was carried out with Econoclean 100-c, as this company has sufficient suitable carrier resin in-house, on one of the smaller extruders. The extruder was cleaned out in a very short time, whereby the previous colour runs where coming out in reverse order. More important, however, is the costcalculation that they carried out, which forms the basis of a regular preventive maintenance routine.


Costcalculation

1.  A. current cleaning material:chalk filled PP
     B. Used quantity (kgs)8
     C. Price/kg:1,00 Euro
                Total material costs:8,00 Euro
     D. Cleaning time (hours):1
     E. Costs/hour:86,00 Euro
                Total costs machine time:86,00 Euro

      TOTAL COSTS CLEANING:
94,00 Euro

2.       A. ECONOCLEAN blend 
     B. Used quantity (kgs)2.5
     C. price/kg of blend:4.72 Euro
                Total material costs:11,80 Euro
     D. Cleaning time:30 mins.
     E. Costs/hour:86,00 Euro
                Total costs machine time:43,00 Euro
      TOTAL COSTS CLEANING:54,80 Euro

      Difference between 1 and 2:       39,20 Euro = 41.7% 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 !