Haul-off equipment

The past 25 years have seen a tremendous improvement in the extrusion process (19). Productivity has increased 250-300% in this time. The process has evolved from an art to a science. The increased output is attributed to improvements in screw design and haul off equipment for increased cost effectiveness (70-80% lower than in the fifties). Processing costs have decreased due to energy efficiency. Plastic processing energy efficiency has increased 300-... 

This operation requires the personal skill of the startup person. That person is required to integrate/interrelate extruder and down-stream equipment. Extruder screw speeds and haul-off rates may then be increased. Downstream equipment is adjusted to meet their maximum operating performance, such as having the vacuum tank water operate with its proper level and vacuum applied. The extruder can be fine-tuned to obtain the final required setting for meeting the desired output rate and product size. 

The production of rigid PVC profiles is described with reference to state-of-the-art twin screw profile extruders and downstream equipment from Battenfeld. Features of the machinery are described, and particular details are given of the profile dies, calibration block, calibration table, haul off and profile saw. 

In this process, the melt film contacts (as quickly as possible, vertically or at an angle) the first water-cooled highly polished (to 1 ptm) chrome-plated roll. An air knife can be used its placement parallel to the die makes it possible to press the film smoothly onto the first cooling roll by means of a cold air stream. Lubricant plate-out on the cooling rolls is avoided by operation with contact rolls. At haul-off rates of up to 60 m/min, reel change is carried out by hand. At higher rates, automatic changeover equipment is required. 

Smooth and glossy finish of the end products requires the use of high-quality belts, polishing rolls, or rubber rolls. Rubber rolls are used in pipe, profile, and sheet extrusion. Either polished roUs or rubber rolls are used, which depend on the end product finish. These haul-off should be equipped with accurate speed controls for better results. In film or... 

Water Quench. The water queneh east film process (Fig. 8.9) is similar in concept to the chill roll process and uses similar downstream equipment. A water bath takes the place of the chill roll for film cooling, and by cooling both sides of the film equally, it produces a film with slightly different properties compared to chill roll cast film. The extruder s slit-die is arranged vertically and extrudes a melt web directly into the water bath at elose range. The film passes under a pair of idler rollers in the bath and, for any given rate of extrusion, it is the rate of downstream haul-off that regulates film drawdown and finished thickness. 

The monofilament process (Fig. 8.13) includes aspects of both the melt spinning and slit film processes. The extmder is equipped with a melt pump immediately upstream of a spinneret that extmdes relatively thick filaments ranging from 0.08 mm to 3.0 mm in diameter. The filaments are quenched in a water bath and are hauled offby godet rolls. Orientation is performed by reheating and stretching in an oven under tension applied by a second haul-off. An alternative orientation process uses heated godet rolls in place of the oven. 

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