Finish roll

Strip is produced as wide as 2 m and in thicknesses as low as 0.1 mm in regular mills. FoU in thicknesses of 0.025 mm or less is produced in special mills. To obtain strip with a bright surface, high ductUity, and low hardness, finish rolling is performed hot at 120—150°C. 

Lubrication of sheet and strip is necessary for aU operations. Although for special operations vegetable and mineral oUs maybe employed, a mixture of paraffin and taUow oU is normally preferred in rough rolling. Requirements for finish-roll lubricant are more strict because of staining caused by breakdown of the oU or reaction with the zinc. Strip zinc is usuaUy finish-rolled with cotton seed or mineral oU. 

Polymer coatings on stiffer substrates can be measured by time-resolved techniques (Sinton et al. 1989). Often in these cases it is not convenient to measure a direct reflection from an uncoated part of the substrate at more or less the same time, and anyway the substrate may not be flat, but this may not matter if it can be assumed that either the thickness or the longitudinal velocity of the coating does not vary. The time interval between the echoes from the top and bottom surfaces of the coating can then be used to determine the unknown quantity. An example of the kind of signal that can be obtained is shown in Fig. 10.5. The specimen was a coating of PET (polyethylene terephthalate) 15 m thick on a stone-finish rolled steel substrate. Although there is some overlap of the two echoes, there is no difficulty in... 

Fig. 10.5. Signals reflected from the top and bottom surfaces of a 15 ym thick coating of polyethylene terephthalate on a stone-finish rolled steel substrate, using a short pulse of centre frequency 230 MHz and half-power bandwidth 110 MHz z = +40 (with the top surface of the polymer as datum) (Sinton etal. 1989).

The rapid-water-quenching system produces good optical properties, has low equipment cost, but can be difficult to use to get precise control over the water temperature. Vibrations and currents can cause little marks on the film. A critical point is the necessity for maintaining a smooth surface in the water quench tank where the melt first enters. Different devices are used to control the flow of water such as baffles with openings. It has serious limitations when high production speeds are attempted the water must be kept from carrying over into any on-line pretreatment and the finished roll. However, these problems can be controlled. This liquid bath system has been used for blown tubular film inside the blown film to improve... 

The final step is the extrusion of the ETFE-foil. In this step granules are processed to the finished rolled foil. The granules will be filled, e.g. into a single-screw extruder. Inside the extruder the granules melt. The screw transports the semi-fluid material with defined velocity, temperature and pressure. The forming tool at the end of the extruder consists of a nozzle with a defined gap. The thickness of the produced film depends on that gap. The width is defined by the length of the nozzles. Standard thicknesses of ETFE-foils are today 12 pm to 300 pm (0.012 mm to 0.30 mm). The width... 

Static steel-wheel rollers were developed first and are used in all rolling (compaction) phases (initial or breakdown rolling, intermediate rolling and finish rolling). Static steel-wheel rollers are available in two basic types, the tandem steel-wheel rollers (also called double-drum rollers) and the three-steel-wheel rollers (also called steel drum rollers). The tandem steel-wheel roller bears a steel drum at the front and a steel drum at the back, while the three-steel-wheel roller, shown in Figure 8.16, bears two steel wheels at the front and a steel drum at the back. 

Rolling consists of three consecutive phases the initial or breakdown rolling, the intermediate rolling and the finish rolling. 

Most of the compaction is achieved during breakdown rolling. Intermediate rolling increases the density of the mix further and minimises all surface pores. During finish rolling, all roller traces and other surface deficiencies are removed. Between the three phases, there should be no time delay. 

Breakdown rolling is recommended to be carried out with static or vibratory steel drum rollers, and finish rolling, with pneumatic rollers or static steel drum rollers. 

Sheet thickness is controlled by the speed of the drum, the depth of immersion, the temperature of the molten lead bath and the intensity of water cooling applied to the inside of the drum. The sheet is usually mn through a set of finishing rolls to provide a smooth surface and a precise gauge. Standard gauges are expressed as weight per unit area and are shown in Table 14.2. Width of the sheet is normally 900 to 1000 mm and is usually produced as a roll on a mandrel containing 1500 to 2000 kg of lead. 

The distance from the die to the finishing roll nip must be kept as short as possible to avoid any premature freezing of the molten extrudate. A drawdown ratio (die gap/ film thickness) of 2.0 is followed for thin film (less than 0.25 mm), and a drawdown ratio of 1.1 to 1.2 is usually used for thicker film and sheet. 

Application of finish requires special applicators. Fairly old-fashioned is a finish roll, a porous ceramic roll which constantly takes up finish from a bath, which is then transferred to the yarn that just touches the surface of the roll (see Figure 17.11a). More modern applicators accurately supply the required amount of finish via a small gear pump, to stift or block applicators, through a hole or slit. The yarn is spread as a ribbon over the applicator and takes up the finish (Figure 17.11b,c). At higher yarn speeds the even distribution of finish becomes increasingly difficult. An applicator with multiple slits or a finish wheel (a roll with small holes under the yarn path) may then be applied. 

With the winding concepts, where the nip between drum and finished roll is opened, the web can be cut with a web-wide knife operated in the open draw. As the new spool is already wrapped by the web, the system is self-threading. The system has a very high tum-up efficiency and is mainly applied for lower and medium basis weights up to about 120 g nT. ... 

Fig. 8.8 Single-drum winder - finished rolls at 11 and 1 o clock positions (source Voith).

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