Gill Box

Objective of Gill Box

In the textile industry, a “gill box” refers to a machine called a gilling machine or gill box. The primary objective of a gill box is to prepare fibers for spinning by aligning and blending them. Here are the main objectives of a gill box in textiles:

1. Fiber Opening: The gill box opens up compressed fiber bales or tufts, ensuring that the fibers are separated and ready for further processing.
2. Fiber Blending: Different types of fibers may be blended together in the gill box to create desired properties or characteristics in the final yarn or fabric. The machine helps in achieving uniform blending by passing the fibers through a series of rollers and comb-like devices.
3. Fiber Alignment: The gill box aligns the fibers in a parallel and uniform manner, which is crucial for the subsequent spinning process. Proper alignment enhances the strength, quality, and appearance of the spun yarn.
4. Fiber Drafting: The gill box also performs a drafting action, which involves drawing out the fibers and reducing their weight per unit length. This process helps in achieving consistent and desired yarn properties, such as fineness, evenness, and strength.
5. Fiber Cleaning: Some gill boxes may incorporate cleaning mechanisms to remove impurities, short fibers, or contaminants from the fiber mass, ensuring cleaner and higher-quality yarn production.

By achieving these objectives, the gill box plays a significant role in the overall textile manufacturing process, facilitating the production of high-quality yarns that can be further processed into fabrics, garments, or other textile products.

Functions of Gill Box

A number of slivers (doublings) pass between the back rollers (or feed rollers), merge into one sliver and are progressively penetrated and held between pins mounted on the fallers. Upper and lower sets of intersecting fallers move forward towards the front rollers (or delivery rollers) at a slightly higher linear speed than the surface speed of the back rollers. This speed difference applies a tension to the sliver.

At the end of its travel each faller is withdrawn and transported back to the starting point where it gradually re-penetrates the fibres as it moves forward again. The front rollers operate at a faster surface speed than the back rollers so the sliver is drafted to produce a sliver of the required linear density. Typical drafts of 5 – 15 are used.

The length of the drafting zone, the distance between the nip lines of the front and back rollers, is called the ratch. The shortest distance of a line of pines from the back roller nip line is called the back ratch while the front ratch is the closest distance of a line of pins to the front roller nip line. The group of fallers penetrating the sliver between the back and front rollers is often referred to as a bed of fallers. The total ratch is set so that the longest fibre in the back beard (the fibres nipped by the back roller) does not extend beyond half the distance of the faller bed. During the drafting action, each faller moves from near the back rollers towards the front rollers at a speed of around 5% faster than the back roller surface speed. Consequently, the pins gently comb the back beard and this assists in minimising the effects of sliver extension, the removal of hooks leading into the faller bed, and the straightening and aligning of fibres. Fibres released by the back rollers are transported by the fallers to the front roller nip line where, once nipped, the sliver is fully drafted. The large different between the surface speed of the front roller and the fallers is very effective in straightening and removing trailing fibre hooks. Pulling fibres from between the pins gives far more straightening than does combing the fibres with pins.

 Although the back ratch draft gives only a small amount of straightening, it is still important. If the draft in this zone is too high, the combing action of the faller pins may result in fibre breakage, and irregularities may occur because of the uncontrolled motion of the short lengths of broken fibres. On the other hand, if the draft in the back ratch drafting zone is too low, the fibres may not be sufficiently extended to remove their natural crimp. The drafting force in the front ratch zone then reaches a level that is sufficient to break fibres, owing to the greater frictional resistance caused by the crimp retained by the fibres. The pins are used in fibre control in that they assist in maintaining inter-fibre friction. This function, in conjunction with their restrictive effect, minimises any forward, out-of-turn movement not gripped by the front rollers. In addition, the fibres being withdrawn have their trailing ends combed by the pins, greatly accelerating the straightening and parallelisation action.The actions of the faller pins and front rollers in straightening a fibre that is hooked at its trailing end. Because the surface speed of the front rollers is much higher than the speed at which the faller advances, the fibre is drawn through the teeth of the faller and it is thus straightened.

In order to provide straightening on both ends of a fibre a reversal of the direction of drafting is required in the next process (e.g. the second gilling step). Reversal of sliver direction is achieved simply by coiling the sliver into a can and then uncoiling the sliver from the top of the can at the next stage. This means that the leading hooks remaining after the first gilling step become trailing hooks at the second gilling step.

Since trailing hooks cause less fibre breakage in combing, ideally the hooks that remain after gilling should be trailing hooks. This will be achieved if there is an odd number of gilling operations between carding and combing. Three gillings are normally carried out before combing. Increasing the pin densities in later gilling steps provides a progressive straightening and parallelisation. The initial gilling steps have lower pin densities to reduce the severity of the action so that fibre breakage is minimised.

Working of Gill Box

In worsted top making the card sliver is subjected to a number of preparatory gilling or pin drafting operations prior to combing, in order to straighten and improve the parallelisation of the fibres, to provide further mixing and to reduce the fluctuations in linear density of the sliver. These steps are called preparer gilling. Further gilling steps, called finisher gilling, also occur after combing, to give a highly uniform sliver called top. Combing aligns the leading ends of the fibres, which adversely affects the sliver cohesion and subsequent processing. Gill boxes are used in the place of draw frame and comber.

One of the main objectives of finisher gilling is to again randomize the leading fibre ends by drafting. Finisher gilling also provides further

• Blending, 
• Straightening and 
• Aligning of the fibres, 
• The addition of moisture and oil

to produce a top of the required linear density and evenness. The first finisher operation generally involves up to 30 doublings and drafts between 5 and 10, while the second operation involves only 4 or 5 doublings.

Gilling plays a similar role in the preparation of semi worsted card sliver for spinning.

The fallers are metal bars with up to about 100 sharp steel pins projecting from their working surfaces and equally spaced along the length of the bars. The pins may be round or flat; round pins are more robust but flat pins give better fibre control. This is because for the same number per unit length they have a larger free space within which a greater number of fibres can be held. The faller lengths are parallel to the nip lines of the front and back roller and penetrate the sliver vertically.

Gill boxes can be equipped with either mechanical or electronic autolevellers and can also be fitted with spraying devices. Adding moisture during high speed gilling is important to achieve the desired regain for subsequent processing. A lubricant (0.1-0.3%) may also be sprayed onto the sliver during the first or second gilling operations to assist in maintaining (or increasing) regain, minimizing static effects and modifying the fibre-to-fibre cohesion. Integrated suction and blowing systems keep the heads clean.

Gill Box: Calculations

Calculations in a gill box involve various parameters and settings to achieve desired processing outcomes. Here are some key calculations involved:

1. Drafting Ratio: The drafting ratio is the ratio of the linear speed of the front roller to the linear speed of the delivery roller. It determines the amount of fiber stretching and attenuation that occurs during processing.
2. Production Speed: The production speed is the linear speed at which the fiber mass is fed into the gill box. It is typically measured in meters per minute (m/min) or yards per minute (yd/min).
3. Number of Pins: The number of pins on the fallers plays a crucial role in determining the combing and straightening efficiency. Higher pin density can provide better control over the fiber and yield improved results.
4. Tension Control: Tension plays a vital role in fiber processing. Calculations are done to determine the appropriate tension settings for the front roller, delivery roller, and fallers to achieve the desired fiber handling and processing characteristics.
5. Roller Diameter: The diameter of the front roller and delivery roller affects the drafting ratio and the amount of fiber compression or stretching during processing. It can be calculated based on the desired drafting ratio and other process requirements.

These calculations are essential for optimizing the gill box operation, achieving consistent fiber processing, and ensuring high-quality yarn production. However, specific calculations and settings may vary depending on the specific machine, fiber type, and desired end product requirements.

Irregularities in Gilling

Gilled slivers are subject to the same periodic faults as occur in roller drafting, but the presence of the pinned fallers introduces further opportunities for periodic faults to occur. With pin control, fibres that are released by the back rollers are compressed between lines of adjacent pins and therefore become constrained to move at the faller speed until they are nipped and accelerated by the front rollers. However, as fallers move within reach of the front rollers they lose some control of the fibres and the front bed (fibres nipped by the front roller) is then able to pull some un-nipped fibres forward. Also, as the front-most faller is removed from the faller bed, it may disturb the motion of fibre ends and cause a periodic fault known as faller bar marks in the output sliver. The wavelength of the periodic fault present in a sliver equals the product of the draft and the distance between successive lines of faller pins (the pitch of the fallers). The amplitude of faller bar markings increases with short fibre content, the size of the front ratch and, most importantly, the level of draft. The effect of faller bar markings on yarn quality is diminished when a repeat drafting passage is used; the associated reverse feed of the sliver is beneficial.

It is clear from the above that the interaction between fibre and pin strongly influences the quality of the drafted sliver. As a general rule, the distribution of the fibre mass between the pins must be as uniform as possible, to maintain constant friction and drafting forces. The cleanliness and irregularity of the input sliver are therefore important factors. Impurities and thin and thin places in the feed sliver will alter the fibre packing densities between the pins, which, if too high can cause fibre breakage and if too low, a pronounced drafting wave. Finer fibres should be processed with a narrower pin spacing, which prevents the entry of impurities. 

The optimal input count of the doubled slivers is directly related to their fibre fineness, i.e. fineness in microns = count in ktex, 19 µm = 19 ktex.

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