Dust Less Blends

Dust Less Blends, normally cylinders of diameter 2.5 mm and length 5 - 10 mm, have very good flow properties compared to the respective powder physical form. Although DLB's have 'good' flow properties relative to the 'poor' flow characteristics of powders, the granulated form is even better. This is a simple reflection of the more suitable particle size of granules.

Apart from all of the expected advantages their improved flow brings to operations such as packing and unloading. DLB's also reduce the potential for problems during feeding into the extruder. Typical problems associated with the feeding of powders which are non-existent, or dramatically reduced, with DLB's are bridging, tunnelling, clumping, plugging at critical points in the feeding system and even melting and sticking in the feed region. Such problems with powder feeding and conveying can lead to segregation of the additive mix and subsequently to concentration variations in the polymer. This may well result in a higher level of 'off spec' polymer, where the additive levels are too low, and overdosed polymer where the additive concentration is too high. Both of these considerations have a direct cost penalty associated with them.

In the case of 'off spec' polymer it is quite common to sell it a discount price of approximately US $ 220/T. This is a cost which comes directly from the profits of the company as all of the fixed and variable costs of the polymer production have been paid.

Consider a 500,000 TPA plant running at capacity and operation at 98 % within specification. This means that 2 %, or 10,000 TPA, of polymer are 'off spec'. If this is sold at a discount of US $ 200/T there is a los of US $ 2,000,000 directly from the bottom line of profits. Whilst it is clear that not all 'off spec' product arises due to errors or problems with additive feeding, a significant amount does. For the example given above, the savings in 'off spe' product due to the use of DLB's could be expected to be in the region of US $ 1,000,000 per annum.

Taking into account this potential for 'off spec' due to segregation and feeding problems, some polymer producers will deliberately raise the set point by more than 10 - 20 % in order to avoid producing 'off spec' product. This of course, is a direct cost, made unnecessary by the use of DLB's.

The dosing accuracy of powder feeders is commonly in the region of 15 %, however, can be up to 30 %. This errors are multiplied due to the feeding of more than one additive. In the case of DLB's the feeding accuracy is typically in the range of 1 - 2 %. When a DLB is used, thanks to its more consistent feeding properties, the amount of 'off spec' product due to feeding fluctuations and difficulties is minimised.

Apart from the advantages of consistent polymer quality and reduced 'off spec' product, the feeding of DLB's also requires less overdosing to account for feeder accuracy. This means that the set point of the feeder can be reduced when using DLB's instead of powders hence a direct saving in raw materials is achieved.