Case Study AZUD Filter in Plastic Extrusion
In 2009, Pfeffer Filtertechnik, as AZUD Distributor for Germany, was asked to supply automatic backflush filter to a PVC profile extrusion company in Germany.
The task was to filter particles out of the cooling water of the extrusion line. The target particle size was determined by the customer at 20 microns. PVC profiles are extruded and then pushed through a caliber to achieve exact outside dimensions of the product. If hard particles are getting in between the product and the caliber, scratches on the surface are the result and the product can be considered wastage. As the profile is extruded under vacuum, it is very important that the supply of cooling water is continuous and without great variation of pressure and flow in order to not affect the state of vacuum in the cooling tunnel.
As the factory was in full production and the filters had to be added to the lines during the lines being in operation, it was not possible to connect the lines to a common water circulation and filtration system. As result, each line in the factory (25 lines in total) was equipped with an AZUD 202 Air Assist Filter at 20 micron filter grade.
With a cooling water tank of minimal size, it was mandatory to use a filtration system that does not require much backflush volume as the backflush would drain the tank at each cycle. AZUD AIR ASSIST with a backflush volume of 10 ltr/backflush/ element only, did match this requirement perfectly.
A further reason to choose AIR ASSIST was the low design flow of 12 m³/h and the low pressure of 1,6 bar. No other filtration system could do an efficient and automatic backflush at 12m³/h and 1,6 bar of pressure and would require additional pumps and other equipment .
After some month of operation, it was obvious that the filtration at 20 µm was a perfect solution, however the AZUD filter discs removed so much fine organic particles (plaques of soft biofilm) that the filter was backflushing very often and the loss of water was considerable, even with the highly efficient AIR ASSIST technology. As this soft biofilm particles do not affect the quality of the product nor interfere with the technical process, the customer decided to switch to a 50 micron filtration, simply by exchanging the set of filter discs, which is neither a complicated, nor an expensive task. The biofilm was then eliminated by a combination of UV – treatment in full flow and dosing of chemicals. After many years we can confirm that 50 µm filtration is a perfect match for this application. And again, the question must be: how clean is clean enough?
In the following years, other and bigger, centralized filtration systems were installed in other factories where a central cooling water treatment was possible.
AZUD Series 500 AA, Model 506 (discontinued - succeeded by Series 200 AA)
AZUD AIR ASSIST Filters are a standard solution now for the extrusion of PVC profiles, pipes and the production of batches, as well as for PP and PE, etc. products.
50 micron has proved to be the most suitable filter grade, a perfect and reasonable compromise to avoid blocking of heat exchangers, valves, guarantees the cleanliness of calibers and therefore keeping quality high in extrusion lines but also keep backflush water loss at a reasonable and economic scale. Minimal operation pressure and backwash pressure requirements of 0,8 bars allow low pressure systems and ensure lower energy bill.
After 8 years of continuous operation in this specific company, AZUD HELIX AUTOMATIC filters have shown to be a perfect solution for the filtration of process water in the plastic industry, whether it is extrusion or injection molding for much more than a decade. Perfect water quality, just clean enough, but also filtered safely and economically, with minimal downtime, long lifetime of filter discs, minimal maintenance cost and highest process safety can be provided by AZUD Filtration.
Azud filters are made for that purpose.