What is Ribbon Lap Machine?
Ribbon lap machine is used to produce the lap by doubling several numbers of slivers and webs, respectively. This machine plays a crucial role in the cotton spinning process by ensuring that fiber laps are uniform and well-prepared for the comber machine. Its primary function is to convert loose, fluffy cotton fibres into a uniform, continuous, and compact sheet called a ribbon lap. Six sliver laps are then doubled and drafted in the ribbon lap machine and the resulting lap sheet is wound onto the cylindrical spool, which is termed as “ribbon lap.” Laps from the sliver lap machine are taken to the ribbon lap machine and thin sheets from the heads are led down over a curved plate, which turns at right angles, inverts them, and superimposes one upon the other. The draft given in the ribbon lap machine is commonly in the range of 2–4. The ribbon lap produced is fed to the comber consisting normally of eight heads. The web from eight ribbon laps are fed, combed, detached, doubled, and drafted in the comber machine and delivered as a single combed sliver. Variation between the slivers can cause drafting errors, so it is important to use quality slivers. It is also important that the fiber web is wrapped on the lap at the correct tension.
Working Principle of Ribbon Lap Machine
This machine had been always coupled with the Sliver Lap machine to work as a pair. The object of this machine is to finally prepare suitable laps for the comber from the feed material (a lap) supplied by the Sliver Lap machine. The laps prepared on the Sliver Lap machine, have some shortcomings. The constituting slivers in the sliver lap do not get fully merged into the lap. The fibre parallelization is inadequate; although, 22 doublings of slivers forming a lap at the Sliver Lap try to compensate for the irregularity in constituent slivers along the lap length. However, for a comber lap, its regularity and uniformity across its width are as important as its regularity along its length. This is because; the same comber lap is required to be gripped across its width during combing by nippers (Figure 1). If the thickness of the lap across its width varies, the gripping of the lap during combing would not be uniform. The combing operation, in this case, would be seriously impaired. Uneven gripping during combing would also lead to the loss of good fibres.
As shown in Figure 3, the machine has six heads and hence six laps made at the Sliver Lap are placed on fluted wooden lap rollers. The flutes hold the lap surface firmly and ensure the unwinding of the lap at the desired rate. Thus, for six heads, there are six drafting systems and all the laps are passed on to corresponding four-over-four drafting systems placed in front of corresponding heads. With a draft of around six, each lap is finally delivered by a corresponding drafting system onto six different curved plates (Figure 2). The draft of six is only arbitrary and a small variation, depending upon the final desired lap weight could always be made. As the drafting rollers carry out a similar function and controls a similar mass of cotton as in the Sliver Lap, the magnitude of the roller pressure is almost the same as applied to the drafting rollers of the Sliver Lap machine.
The curved plate on which thinned out drafted lap sheet is led is very smooth. Further it is so curved as to change the direction of delivery at right angles to that delivered by drafting rollers. The drafted sheets from the other drafting heads (Figure 3) are similarly passed on to the corresponding curved plates and then turned at right angles. The thinned-out lap sheet from each plate is guided on a smooth extended table with the help of corresponding pairs of table calendar rollers. Thus, six sheets are superimposed on their way along the table so as to improve upon the lap regularity across the width and along its length. Finally, a compact lap comprising six layers is once again heavily calendered and wound on the wooden spools to make a comber lap.
The machine is provided with an arrangement for changing the draft in the drafting systems. The lap width is also selected so as to match with that required at the comber. Usually, this width varies from 10.5 to 11 in. A pair of Sliver Lap and Ribbon Lap machines normally feeds 6–7 Nasmith combers. As mentioned earlier, this old and conventional lap system almost lost its popularity with the introduction of modern high-speed combers. However, in some mills where old and slow-speed combers were still working under the same roof, the system then continued to meet the requirement of conventional combers. In such cases, the system of Sliver Lap–Ribbon Lap was worked to produce much lighter laps (less than 600 grains/yard or 40 g/meter) for processing fine and super fine mixings only.
Even then, it needs to be mentioned that the concept of doubling a thin, drafted web sheet from each head has its potential advantage in improving lap uniformity both along and across its width.
Improvements in Ribbon Lap Machine
The new model introduced by Rieters has a three-over-four drafting system (Figure 4). The nipping distance in the main drafting zone is adjustable from 30 mm to 54 mm, while that in the back zone can be varied from 32 mm to 56 mm. The total draft in the machine can be varied from 4 to 9. The fluted bottom rollers and synthetic covered top rollers are made with high-precision, anti-friction bearings.
The slow-moving parts such as the feed equipment and backline rollers are fitted with Teflon bushes which require little maintenance. On the older Ribbon Lap machine, the loading on the drafting system was very much inadequate as compared to the heavy weight of the material that was processed.
In modern sequence, a wide range of drafts and much higher loading on the drafting rollers are possible. This is certainly helpful when the laps of varying weight per unit length are processed. The most modern and advanced drafting system on the Sliver Lap and Ribbon Lap (S.L.–R.L.) offers excellent fibre control and gives ideal lap drafting conditions (Figure 5). Very high lap weights up to 75 g/m (1,060 grains/yard) with production speeds up to 60 m/min are possible.
The signal-lamp system provided on the new sequence is very efficient. It helps in better supervision and easy location of the causes of machine stoppages. A yellow lamp indicating the machine is in running condition, a red lamp pointing out lapping around the calendar roller or any other drafting roller, a green lamp showing the machine is ready for doffing (with manual doffing) – all help in improving the operating efficiency. The switches for starting or stopping the machine are very conveniently located so the operatives to reach them easily from all sides of the machine.
The safety switches ensure that the doors for the headstock and hood are fully closed before starting the machine. This minimizes the risk of accidents. Inching motions* are provided for piecing-up operations. The pressure variation on drafting rollers is sensed by the control switches so that at any time, when the pressure falls below a certain level, the machine is automatically stopped. This avoids any deterioration in the quality of the material drafted.
The lap, before winding on the spool is very heavily calendered so as to make it compact. The full-lap weight up to 20 kg is possible and the laps when doffed are automatically weighed so as to indicate variations. An earlier version had manual doffing whereas; the automatic doffing using pneumatic pressure is the striking feature of later modern versions.
Gearing Diagram of a Lap Ribbon Machine
Draft calculations:
…………………Surface speed of delivery roller
Total draft = —————————————————
…………………..Surface speed of feed roller
…………………………………………Surface speed of front roller
Total draft in drafting zone = ————————————————–
………………………………………….Surface speed of back roller
Conclusion:
The Ribbon Lap Machine plays a vital role in the textile manufacturing process, particularly in producing high-quality combed yarns. By transforming loose carded slivers into uniform ribbon laps, it ensures better fiber alignment and consistency, ultimately enhancing the quality of the final yarn.
References:
[1] Khare, A. R. (2023). Principles of spinning: Combing in Spinning. CRC Press.
[2] Gokarneshan, N., Varadarajan, B., & Kumar, C. B. S. (2012). Mechanics and calculations of textile machinery. In Woodhead Publishing India Pvt. Ltd eBooks. https://doi.org/10.1533/9780857095527
[3] Kumar, R. S. (2014). Process management in spinning. CRC Press.
