processing feature | Melt filtration
four times larger than similarly sized competitive models, and as a result extend screen life. They are also designed to reduce dwell time, melt pressure and fluctuation rates, as well as accommodating high throughputs. Both models use rectangular flat screens
that attach to clamping grooves on each piston’s curved screen plate. When a piston
German-based Gneuss
Kunststofftechnik. “There is better sorting on one hand, but also more
contamination.” Over the following pages we look at a range of developments from a selection of
Nordson Kreyenborg’s V-Type features an automatic power back- flush to extend screen life
leading melt filtration system suppliers that are designed to meet these evolving market requirements.
Increasing exposure Maag highlights three recent developments: the CSC-BFX, a continuous screen-changer for recycling with automatic back-flushing; the CSC-R for compound- ing, which features curved breaker plates and wrap- around screens for optimum filtration exposure; and the CSC-R/S retrofit version that uses curved breaker plates to increase screen exposure to melt flow. Harald Pohl, product manager of polymer filtration, says that the CSC-BFX provides minimal melt flow fluctuations during the direct extrusion of recyclate into finished products such as profiles and film. Its patented design stores melt for back-flushing in an integrated accumulator under rheologically optimized conditions. “The machine cleans contaminated screen surfaces with no impact on end-product,” Pohl explains. “It does this with only two hydraulic turn-lift cylinders, as opposed to competitive designs with as many as eight.” He adds that the BFX and other models in the com- pany’s new generation of screen-changers are “ex- tremely compact and easy to integrate into existing extrusion lines, with corresponding cost benefits.” Other features of the BFX include: active filtration areas of 250 to 3,250 cm2
; adjustable back-flush volume
and pressure for tailored purging via the maaxBFX controller; an integrated start-up valve and ejection of start-up melt; optimized flow channel geometry to shorten dwell time; and easy replacement of fouled screens.
The CSC-R and retrofit CSC-R/S, meanwhile, each
incorporate a pair of hydraulic pistons with the patented circular breaker plates and wrap-around filters. Maag says that they provide filtration surfaces that are up to
48 COMPOUNDING WORLD | July 2014
and screen are repositioned in the filter housing after changeover, the screen cavity is pre-flooded and vented to eliminate air bubbles from the melt stream. During the “short screen-change process,” the other screen continues to filter polymer.
The CSC-R and CSC-R/S models accept screen
lengths of 160 to 560 mm. The throughput range of the filters is 1,150 to 19,000 kg/hr.
Screening heavy contamination Developments from Nordson Kreyenborg include the V-Type system. Designed for use with most materials, including highly viscous polymers, the system is especially effective when recycling and compounding are combined in one line and the potential for melt contamination is high. Stefan Wöstmann, head of R&D at the company, says that in such a two-step process, where melting and filtering and compounding and pelletizing occur, the V-Type has advantages that improve the efficiency and economics of its use. The unit has two screen-bearing pistons, each with
two filtration cavities. During normal production all four cavities are in use. During the back-flush process or a screen change, one of the four cavities is temporarily removed from operation. Advantages of the screen-changer include the
automatic power back-flush system, which applies high pressure and consistent volume. This extends screen life and eliminates operator involvement. The power back-flush system has four hydraulically-
actuated displacement pistons, one each for the four nitride steel screens that filter melt. Flow channels and screen cavities are rheologically optimized for uniform flow.
When the differential pressure reaches a pre-set limit, the automatic back-flush begins. One of the displacement pistons retracts and moves the contami- nated screen into position for cleaning. This shuts down the affected flow channel but still leaves 75% of the total screen area in operation. Part of the filtered melt is redirected through the rear of the repositioned filter and compressed in a reservoir to purge it of contami- nants. The displacement piston flushes the screen with a fast-forward movement, which forces contaminants
www.compoundingworld.com
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72