What is Sliver Lap Machine?
Sliver lap machine is a preparatory machine used in spinning mill, particularly in the combing process. This machine is used to produce the lap by doubling several numbers of slivers. Its primary purpose is to process multiple carded slivers, condensing and preparing them into a lap for efficient feeding into a comber machine. This is a conventional machine and has the combined features of both, the drawing frame and lap-making part. Thus, the first half up to the drafting rollers almost resembles the draw frame; whereas the second half is a lap-making unit. It may be mentioned here that the drafting system, unlike the one on a conventional draw frame, plays a different role and therefore the drafting capacity of the system is very limited. In the combing preparation, several card slivers are drawn and wound up parallel as comber rolls on a sliver lap machine. The card slivers in the range of 16–32 numbers are doubled and drafted in the sliver lap machine and the delivered lap sheet is wound onto the cylindrical spool, which is termed as “sliver lap.”
The dimension details of sliver lap are given as follows:
- Lap grams per square meter (GSM) of 50–70 g/m
- Width of 230–300 mm
- Diameter of 500 mm
- Weight of up to 27 kg
The draft given in the sliver lap machine is commonly in the range of 1.5–2.5. As there is no waste removed in the sliver lap machine, the actual and mechanical drafts are theoretically the same. 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.
Objects of Sliver Lap Former Machine
- Uniform lap formation by combining multiple slivers.
- Removal of short fibers below a predetermined length.
- Improvement of fiber parallelization by reducing entanglement and disorientation.
- Improvement of fiber alignment for better yarn quality.
- Reduction of sliver irregularities.
- Minimization of fiber waste during combing.
- Enhanced productivity in the combing process.
- Elimination of neps and foreign matter.
- Enhancement of mean fiber length by removing noil and maintaining the degree of combing.
- Preparation of laps for efficient combing.
Working Principle of Sliver Lap Machine
The sliver from card cans (Figure 1) are kept behind the machine and the slivers from these cans are guided through a single preventer roller or lifting roller system. There are usually 20–22 card slivers fed at a time to the sliver lap machine. The slivers are passed over suitable guides and led through the nips of a single preventer system (Figure 2). The function of the lifting or single preventing system (Figure 1 (A)) is basically to see that sliver breaks in the feed zone are sensed and detected. Immediately, thereafter, the machine is stopped. The functioning of this sliver break-stop motion is very simple. Both the top and the bottom rollers are given electrical connections. The bottom roller is continuous and extends over the full width of the machine; whereas the top rollers are split into pairs of two. As long as the slivers run through the nip, there is no contact between the top and bottom rollers. But when any of the slivers breaks, the respective top roller makes the contact with the bottom roller and thus completes the electrical circuit which ultimately stops the machine.

Much earlier versions of this machine had mechanical sliver break sensing and stopping arrangement where, in place of a single preventer roller, there used to be sliver guiding spoons (Figure 3). The slivers, in this case, were guided over these spoons and then led on to lifting rollers. The lifting rollers, in this case, were merely made to act as a device to lift the slivers; whereas the sensing of the sliver break was done by the spoons. With the slivers continuing their journey over the spoons and in the process pressing them a little, the tail end of the spoon remained lifted up.

When the sliver broke, the tail end of the spoon used to turn around the pivot edge and fall down. The tail of the spoon used to be then picked by the vibrating bar on its way. This finally resulted in stopping the machine. The great disadvantage of the spoon-type of motion was that being purely mechanical, there was a marked delay in sensing the sliver break and conveying it further to the shifting of the main driving belt to stop the machine.

Further, its functional efficiency also depended upon the smooth turning over of the spoons when the sliver broke. Therefore, as compared to the mechanical sliver break-stop motion, electrical sensing and conveying, as done by the single preventer roller, is much faster and almost instantaneous. It may be noted here that the electrical sensing system assumes one very important thing and that is the non-conductivity of cotton material passing through sensing preventer rollers. This is true when the moisture content in the cotton material is lower. But with higher humidity in the department, especially in rainy seasons or wet nights in winter, the moisture content in cotton also increases and it partially starts conducting the electricity. Hence, in such situations, faulty sensing of the absence of a sliver is registered and the machine frequently stops. In extreme cases, the worker operating the machine finds the machine stopped even when there is no sliver break at the creel. If this is repeated frequently, he feels irritated and thus tends to tamper with the electrical connections, which again is worse.
The condenser (B) (Figure 1 and 4) has several guide plates which provide channels for the slivers coming through a single preventer system. The basic object of the condenser is to restrict the width of the slivers as they enter the drafting system.

This is essential as not only the slivers are laid side-by-side before they enter the drafting system, but also the width to which the slivers are restricted decides the width of the lap sheet that the slivers are going to form after they emerge from the drafting system. This gives the precise width to the lap formed later. While guiding the slivers over the condenser, care must be taken to avoid any folding or overriding of slivers which form the sheet; otherwise, it will lead to uneven thickness of the lap sheet.
The drafting system placed subsequent to the condenser consists of traditional four-over-four rollers. As compared to the drafting system on the draw frame, the pressures on the top rollers in the sliver lap machine are much higher. This is because the material controlled and processed during drafting is much heavier. The draft employed, however, is limited to only 1.5–2.0.
Thus, there is not much drafting and hence parallelization is not the main object of this machine. The basic purpose of this low draft is mainly to provide a little flexibility for small adjustments to obtain the desired lap weight per unit length. It also provides some loosening of slivers so that when they come out of the drafting system, there is a good merging of adjoining slivers with their neighbours.
This helps in obtaining a little more homogeneous lap structure. This again is very important as the slivers lose their separate identity that they have before drafting. It results in a well-textured lap.
The amount of draft that the machine can use is very low, only a little adjustment in the lap weight is possible. Hence, when a major variation in the lap weight is required, it is customary to vary the number of slivers fed to the machine. Here again, too much reduction in the number of slivers to arrive at the required lap weight is likely to affect the lap uniformity owing to variation in the number of doublings. It is therefore advisable to suitably produce the appropriate hank of card sliver so that by keeping the same number of doublings, the required lap weight can be arrived at. The drafted sheet in the form of a thick web comes out of the front pair of drafting rollers. It then passes through a nip of pair of calender rollers which are bigger in size and are heavily loaded. The sheet is compressed to consolidate the sliver lap and is made more compact (Figure 5). This is essential as the lap when wound in this sheet form has to be free from any lap-licking tendency during subsequent unwinding.

A compact lap sheet also helps in reducing the full-lap volume for a given lap weight. However, when this machine is used in the traditional sequence (Sliver Lap – Ribbon Lap), a very high pressure to consolidate the lap is also not beneficial. This is because first the lap formed on the Sliver Lap is not the final lap. Second, this lap is again required to be drafted at the Ribbon Lap, the next machine in the sequence. Nevertheless, the compacting pressure should be adequate enough so as to avoid any lap licking at the feed end of the Ribbon Lap machine. The lap is wound on wooden or metallic spools (Figure 6). The spool is hollow and a lap spindle is made to pass through it. As the width of the comber lap, in comparison to that made in the blow room is much smaller; the lap spindle is also much shorter in length.

Whenever the lap is full, the spools are required to be replaced. At this time, by using the turning handle (A’ of the handle to be engaged with A of the rack pinion – Figure 7), the racks holding the spool and the spindle are raised. This releases the pressure on the spindle (Figure 7). The lap spindle can then be partially withdrawn so as to take out the full spool. At the same time, the spindle is again passed through another empty spool. By again using the handle, the spindle holding the spool is lowered and the empty spool is made to rest on the fluted lap rollers. There is an arrangement provided to level the spindle. This ensures perfect seating of the spool on the lap rollers with even and uniform contact and pressure across its width.

Importance of Lap Preparation in Sliver Lap Machine
The importance of lap preparation is as follows:
- Fibers from carded sliver are not well oriented and may lie in all directions.
- Most of the fibers arc hooked.
- To avoid excessive strain on comber needles.
- To avoid loss of good fibers in the nods.
- To get high degree of evenness in transverse direction.
Technical Specifications of Sliver Lap Machine
- No. of ends up →24 or 36
- Feed sliver weight → 0.12 to 0.18 for 24 slivers
- Weight of feed sliver → 75 g/m to 120 g/m
- Draft → 1.5 to 2.0
- Lap weight → 50–70 g/m
- Total lap weight → 12 kg
- Working speed → Up to 65 m/mm
- No. of heads → 6
- No. of doublings → 6
- Width of lap → 230 mm or 250 mm
- Weight/m fed → 44 to 75 g/m
- Mechanical draft → 4–9
- Width of lap delivered → 265 mm or 300 mm
- Weight/m delivered → 50 g/m
- Total lap weight → 13 kg or 15 kg
- Delivery speed → Up to 65 m/min
Different Formulas of Sliver Lap Machine
……………………………………………………Weight of silver lap
1. Silver weight/yard in a silver lap = ——————————————-
…………………………………………………..No. of silver ends fed
…………………………………………8.33
2. Creel silver hank = ———————————————————-
……………………………Creel silver weight/yard
……………………………….1 × (lap drum rpm × drum circumference in inches × efficiency)
3. Silver laps/Machine = ————————————————————————————————–
…………………………………………………………..63 × hank of lap
Draft calculations
……………………..Surface speed of shell roller
1. Actual draft = —————————————————————-
……………………..Surface speed of feed roller
………………………………..Surface speed of first roller
2. Front zone draft = ———————————————————
………………………………Surface speed of second roller
……………………………Surface speed of fifth roller
3. Back zone draft = ———————————————————–
…………………………..Surface speed of sixth roller
…………………………………Surface speed of third roller
4. Middle zone draft = ———————————————————
……………………………….Surface speed of fourth roller
5. Total draft = Front zone draft × Middle zone draft × Back zone draft
Conclusion
Sliver lap former machine is responsible for developing the laps that feed the comber. It is an essential link in the spinning process, bridging carding and combing operations. By preparing uniform and consistent laps, sliver lap machine plays a crucial role in achieving high-quality yarn, making it indispensable in fine cotton spinning processes.
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.
[4] Gries, T., Veit, D., & Wulfhorst, B. (2015a). Textile Technology: An Introduction. Hanser Pub Incorporated.
[5] Kiron, M. I. (2022a, February 17). LAP Former Machine: features, types, functions and working principle. Textile Learner. https://textilelearner.net/lap-former-machine-features-functions/