Powder Coating Extruders: An insight from Xtrutech
The powder coatings customer base continues to demand products for thinner film application with tighter specification, on faster delivery deadlines and improved service… it goes on, but many readers would say that this is no different from any other sectors of the coatings industry. Companies making powder coatings may find themselves at times short of help to enable them to keep on hitting these requirements. This might be because their own in-house expertise has been streamlined and more widely spread and the recent spate of mergers and acquisitions will not have helped in this respect. It has been said that many modern production facilities have efficiencies in the region of only 50-60%
This has three main causes
1) Maintenance demands (planned and unplanned)
2) Down-time for cleaning
3) Older machines that perform below their original production output
To some extent, this production gap has been met by European machine designers. Xtrutech has incorporated a number of equipment and processing developments to boost output and mixing efficiency by new designs of extruder with longer extruder barrels, and operate at higher speeds. This not only increases the output of any give size of extruder, but improves processing performance on newer more demanding formulations.
Price versus quality
The emergence of Chinese built extruders over the past ten years or so has further complicated the choice of extruder. Although the gap in price is clear to see the gap in build and processing quality is not so apparent at first. Xtrutech designs, manufactures and sources components for its extruders in the UK and Europe highlighting the need for buyers to review more closely the new process innovations and technology improvements.
Xtrutech uses a high volume 1.8D/d screw geometry which originates from the early 1980’s closely matching the mega volume geometry now promoted by Coperion. Couples with a high torque AC drive system; this provides the optimum blend of screw volume to processing powder for Powder Coating materials. Issues related to the intake of the extruder are dealt with by a combination of optimising the feed port and feed screw design and possible use of a side feeder to minimise air entrainment with the premixed raw materials.
Wide range of processing capabilities
The XTS has been designed with a wide range of processing capabilities and can be configured for optimal mixing of products as diverse in their mixing requirements as Acrylics, clearcoats, thin film and textured or leatherette finishes and the capability to recycle 100% fines with one simple change of screws.
Xtrutech has the clamshell barrel which has been further developed by incorporating the stuffing box into the barrel and opens with the tip barrel half, to expose the shaft couplings. This makes the removal of the shafts that much easier and simpler. The traditional gland packing and followers have been replaced with oil impregnated split bushes, which prevent find feed powders from leaking into the shaft coupling area and eliminate the need for regular maintenance.
The new barrel has been designed with a single-piece, robust, backing block and fewer clamping bolts to save barrel opening times, offering quick access to the screws during cleaning or maintenance. This barrel is also fitted with a split chilled discharge arrangement that also improves the barrel opening time. Temperature control is achieved through optimising the screw profile and the highly-efficient water cooling channels located in the barrel backing blocks.
A combination of wear-resistant steels and strategically- designed lengths of insert type liners, maximise the wear life of the XTS barrel and minimise future replacement costs.
The mechanical heart of the extruder (the gearbox) is sourced from Germany. It is identical in design to those used in huge numbers for thermoplastic compounding. Thus transmits power via a pair of quick release, positive locking couplings to 24 tooth splined extruder shafts. This gives a matched drive train of impressive strength, but protection against overload is vital and is provided by an ‘autoguard’ coupling. The control system provides an electrical reset of the coupling, avoiding removal of machine guarding to reset the system, if the coupling trip is activated.
The XTS features the latest barrel design from Xtrutech, which is also available as a standalone retrofit for use on almost any existing twin screw extruder. It is aimed to minimise abrasive wear and to place the user in the best possible position to economically maintain the screws and barrel with the decided tolerances through its production life.
In addition, Xtrutech offers wear solutions for all other makes of twin screw extruder alongside an inspection service which can be part of a preventative maintenance plan.