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Nonwovens – Batt Formation

N.Balasubramanian*

Retired Joint Director & Consultant,Tel 022 25280767 mail to Balasubramanian.N
Nonwoven textiles represent a unique way of forming a fabric which has many advantages over woven textiles. There is a great potential for expansion in this technology in India as the government is committed to increase manufacturing area at an accelerated rate. China's nonwoven production is 10-12 times that of India. Not only nonwoven manufacturing plants but also nonwoven machinery manufacturing units based on latest technology have come up in good measure there. On the other hand, there are only 5-8 good nonwoven manufacturing units in India. Most of them are geared to meeting the need of meeting moulded carpets and trunk liners of automobile units, blankets, waddings and interlinings. There are several other products like filters, disposables, wipes, resinated felts, hygiene products, synthetic leather, building materials, medical textiles, technical textiles, agricultural textiles and geotextiles where there is considerable scope for nonwovens.

In making nonwovens many processes like spinning of fibres into yarn, winding, warping sizing and weaving are omitted. The raw material is opened and made into a batt with directionally or randomly oriented fibres by a variety of means and the fibres are entangled or bonded by mechanical(friction or cohesion) or thermal(adhesion) or chemical(adhesion) means to form a fabric. Nonwoven manufacture consists essentially of 2 stages.

• Batt formation
• Bonding

The present article discusses about the first part viz; batt formation. The various methods of batt formation are enumerated in detail and their relative merits, scope for application and critical quality and process control measures to get better performance are discussed.
Merits and Limitations of Nonwovens against Wovens.
The chief merits and limitations of Nonwovens against traditional woven material is broadly tabulated below.

Table 1: Merits and Limitations of Nonwovens against Wovens
Merits	Limitations
Lower Labour Employment	High Cost of Equipments
Shorter processing sequence	Few Indigenous manufacturers of repute
High Production rates	Need to develop market
Ability to process recycled and waste fibres	Lower Tensile and Tear strength
Wider width of fabrics up to 10-25m possible	Low Abrasion Resistance
Non directional properties of fabric due to random orientation of fibres	Lower life (Very enhanced in blankets and carpets)
Higher In-plane Water permeability (especially with needle punched)	Pilling tendency and boll formation
Higher filtration Efficiency (especially with needle punched)	Low strength utilisation of fibres
Ability to take the shape of the surface on which it is laid	Lack of technical and marketing personnel with adequate knowledge and experience
Higher Friction to soil	Lack of trained operatives and fitters
Less expensive, hygienic and more versatile especially in wipes	Low strength and unsuitability for rough usage
Ability to utilise the properties of fibres in a better way	Difficulty in getting spare parts

The relative merits of woven and nonwoven geotextiles is discussed elsewhere1,2. Parikh et al3 compare woven gauze with spunlace nonwoven for medical and surgical applictions3. The above comparisons do not mean that nonwoven is a substitute for woven Rather nonwoven represents a means for exploiting he properties of fibres to meet the unique needs of certain applications. Nonwoven should be considered as a supplement for enrichment of existing textiles. Jute fabric backing under a nonwoven felt gives dimensional stability to floor carpet. Package tray and seat covers made by punching nonwoven on a HDPE woven fabric have strength, comfort and dimensional stability. Woven scrim cloth is sandwiched between needle punched nonwoven felts in filters and blankets. The purpose of scrim cloth is to provide dimensional stability to the product. In some geotextile applications, woven fabric has to be sandwiched between needle punched nonwovens to meet the diverse requirements of strength and permeability. Improved canal liner is made by a composite made out of LDPE film sandwiched between a HDPE woven tape and a nonwoven fabric. Nonwoven fabric minimises damage to film caused by gravel and reduces slippage of cement laid on it4 while HDPE woven tape gives strength to it.

Two basic methods of batt formation are wet and dry laid technology. Later spun bonding and meltblown technology were developed as alternative methods of batt formation.
Wet Laid Nonwovens
Wet laid technology makes use of very short fibres laid on a traversing perforated lattice in water in a manner similar to making paper. The wet laid nonwoven is distinguished from paper by one of the following criterions as defined by INDA5.

More than 50% of the material is made of fibres (excluding chemically digested vegetable fibres) with a length to diameter ratio greater than 300
if the above condition does not apply and if the following condition is fulfilled. More than 30% of material is made of fibres (excluding chemically digested vegetable fibres) with a length to diameter ratio more than 300 and density is less than 0.4 g/cm3.

The main advantage of wet laid technology is high production rates going up to 1.5 tons/hr on 50 gsm fabric or delivery rates up to 350 m/min. Disposable fabrics like baby diaper cover, sanitary napkins, surgical clothing, table cloths, bed linen and liners, household cloth, protective clothing and sterile packs in medical fields are made using this technology.
Raw Materials
Wood pulp is invariably a component because of its cheapness and ease of application. Other component is made of cotton linters, cut cellulosic staple fibres, manila hemp or bast fibres. Sometimes synthetic fibres and glass fibres are also used for special end use. Fibre length is short ranging from 2 – 10 mm mainly for getting uniform dispersion of fibres in aqueous medium. Weight percent of fibre in suspension is known as 'dilution'. This is kept at 0.005 to .05%. Higher levels of dilution result in flocculation.
Method of Manufacture
A uniform dispersion of fibres and wood pulp in the form of aqueous suspension is first made and fed to a Head box or Dispenser. The aqueous suspension is then fed uniformly through a regulator on to a screen. (Fig 1 ).The liquid is filtered out by means of vacuum or water pumps under the screen. Suction is applied on the emerging nonwoven sheet to remove excess water. The material is then dried and bonded by means of application of latex binders like polyacrylate or sterene butidene rubber. The binder can be applied as a liquid or foam or by spraying or by dot printing.

Fig1: Method of manufacture of wet laid Nonwoven
Major products are filters, coverstock for diapers and hygienic products, sanitary napkins, surgical materials, wipes, table cloths, towels, and shoe upper material.
Process control measures
1. Uniformity of dispersion and freedom from flocculation should be checked
2. Variation in gsm and isotropy should be checked
Dry Laid Nonwovens
Major Raw materials
All fibres natural, man made and special fibres can be processed. Natural fibres like jute, wool and cotton can be needle punched. But needling of cotton is difficult because of its short staple length and high resistance to needling. Special needles have to be used for cotton. Cotton nonwovens can however be prepared by hydroentanglement, thermal bonding and chemical bonding. Among synthetic fibres viscose has a major share especially in thermal and chemical bonding. Polyester, polypropylene and nylon are widely used in nonwovens with all the methods of bonding. Relative merits of polypropylene and polyester has been discussed by Balasubramanian6. Coarser denier fibre gives higher thickness to the product of given gsm. High crimp fibre gives more loftiness and is preferred in wadding7 and paddings. Nonwoven geotextiles made from finer fibres have lower opening size, higher strength, less air and water permeability than that made from coarser fibres8. Use of dope dyed fibres are preferred in needle punched nonwovens because of the colour resistance to abrasion, light and washing. Since dope dyed polypropylene is available in a large number of shades, use of this fibre is more common particularly in carpets. Further low density and inert characteristics of this fibre has also contributed to its wider application though low UV stability and lower melting point limit its use in certain applications.. However cost of the fibre plays an important part in its selection and usage. Problem fibres like glass, carbon, rock wool can be easily converted into felts by needle punching. Special high temperature resistant and high tenacity fibres like nomex, Kevlar, bicomponent fibres can be made into felts by needle punching or thermal bonded to make composites and special products.
Batt Formation
Opening and Mixing
Opening is the first stage in batt preparation. Opening lines vary depending upon whether it is synthetic fibre or cotton. The mixing line for synthetic fibre usually consists of a Hopper bale opener or a pair of bale openers feeding to a cross lattice. Metered flow of material is achieved by weighing systems at the delivery end of Hopper bale opener. Hergeth employs gravimetric continuous fibre metering system, Optimeter (Fig 2 ) to ensure uniform feed.

Fig 2: Optmimeter
In the Optimeter, fibres sucked from the bale plucker fall on a condenser and thereafter drop into a chute. Photocells placed in the chute ensure a constant level of material. The fibres from the chute are withdrawn by feed rollers to an opening roller which opens them and drop them on a weighing belt. A set of load cells measure the mass of fibres on the belt. The weighed fibres are then fed to a chute. The system can be used for controlling the variations in mass of fibre flow in forming a mixing or can be used to ensure accuracy in blending two or more components. Baltromix weighing Hopper by Temafa has a weighing accuracy of ±1%. The material is afterwards taken forward by a step cleaner followed by a kirschner beater. Sometimes two kirschner beaters may be used in tandem or a single 6 lag kirschner beater to get better opening. Afterwards the material is laid in a mixing bin in a number of layers by means of a traversing cyclone for conditioning. Antistatic spray is also applied to fibre as it is laid on the bin. Automatic spraying of known amounts of spray on to the fibres as they are laid to and fro by a traversing lattice with the help of circular sprayers is found in some automixers like Hergeth emptomix.. This helps to achieve uniform spraying of antistat. An oiling apparatus is used for preparing the emulsion containing antistat. The quantum of antistat can be easily adjusted by means of controls After conditioning, the fibres are removed by a vertical lattice with spikes and fed to a chute. Two or more bins are normally used. While fibres are laid in one bin and conditioned, material from other bin is taken to card by pneumatic means. The delivery chute moves automatically from the bin where fibres are laid to the one which is being emptied. Fig 3 shows how an automixer like emptomix works.

Fig 3: Automixer
When two or more fibres or colours are to be blended, the components are pre weighed and opened by Hopper bale opener. A stack is made of the opened material and conditioned. Vertical cuts are taken from the stack and given a second passage through the bale opener. For intimate mixing a stack is again made of the opened material and passed through the Bale opener. Gravimetric fibre metering systems with the help of weighing pans is useful to ensure uniform blending. Temafa employs a Mixmaster to achieve uniform blending of components automatically. Material from sandwich blend after opening through hopper feeder and step cleaner is laid in a number of layers one over other in Automixer bin by a telescopic arm with rotary separator. After conditioning the material is removed by a discharger and fed back to the front section of the same unit in a similar manner. The material is conditioned and removed vertically and fed to next stage. In this way blend uniformity up to ±1% is achieved. The mixmaster can be divided into 2 bins by means of a separator partition. In this way while one batch is laid on one chamber, the conditioned material from other chamber is fed to card thereby reducing card detention time for change of lots. A typical layout of Mixing room of Nonwoven is given in Fig . 4.

Fig 4: Mixing room layout
In the case of cotton, the opening line is similar to that found in blow rooms of cotton spinning with 3 to 4 beaters depending upon the % of trash and impurities.
Batt Formation
Two major processes are used for batt formation though some hybrid types involving both have been later developed.
1. Carding and Crosslapping or carding and parallel laying. The former is widely used while the latter is used for limited applications
2. Air laying
The merits and limitations of the Carding - Crosslapping and Air laying are given in Table 2.

Table 2 :Merits and Limitations of Card – Crosslapping and Air laying
Carding Crosslapping	Air Laying
Very wide widths of fabrics up to 15-20 metres are possible	Width is limited up to 2-3 metres
A wide range of fabric weights from 75 to 2500gsm are possible by varying take-off speed of laying lattice in relation to speed of delivery lattice	GSM lower than 150 are not normally possible
Highly uniform Fabrics can be made in respect of weight per unit length. Variations in weight per unit length in longitudinal and lateral directions are within 5%	It is difficult to achieve good uniformity in weight/unit length particularly in low weight nonwovens
Ability to process a wide range of staple lengths	Mainly suitable for short fibres. With long fibres it is difficult to get satisfactory uniformity
There is no randomisation between lateral and vertical planes. Anisotropy in strength is also present in the lateral plane. Strength is generally higher in cross direction than longitudinal direction though this is minimised to some extent by the use of randomising rollers in carding and web drafting prior to bonding	Fibre orientation is random in all the 3 dimensions though longitudinal direction strength is slightly higher than cross direction strength. The isotropic distribution gives a high degree of insulation properties. But strength is reduced as fibres in the vertical direction do not contribute to strength. Further anisotropic material cannot be made Batt formation involving carding

Batt forming from web coming out of card can be done either by parallel laying or crosslapping.
Parallel Laying
A number of cards up to a maximum of 10 are laid in tandem over a platform as shown in Fig. 5

Fig 5: : Parallel Laying
Usually cotton cards are used in this method. Web from each card is taken down and laid on a conveyor lattice underneath, which runs full length under the cards. Webs from successive cards are laid one over the other so as to form a batt of desired weight. The conveyor lattice moves forward slowly and the batt is then taken for bonding by chemical or other means. As fibres in the card web are preferentially oriented in the longitudinal direction, the strength of nonwoven is about 8-10 times higher in longitudinal direction than cross direction. This method is usually followed in making interlinings, belts where longitudinal strength is more important.
Card - Crosslapping
This is more widely used method of batt formation. Card web coming out of card is passed through a cross lapper. The web is taken forward by a fast moving laying lattice, changed in direction by 900 and laid on a slow moving draw off lattice in a zig- zag manner to form a batt. The weight of batt depends upon ratio of laying speed and draw off speed and laying width. The relative merits and limitations of the two methods are given in Table 3

Table 3 : Relative merits of card - crosslapper cross laying and parallel laying
Cross laying	Parallel Laying
Very wide widths of nonwovens up to 30m can be formed	Width is restricted by card width. as a result widths beyond 2 – 4 m are not possible
Greater uniformity in strength between longitudinal and cross direction. CD/MD ratio up to 1 : 1.3 can be obtained by use of randomising and condensing rollers in card and web drafting	Cross direction strength is very low in relation to longitudinal direction. MD/CD ratio is 8-10 times
A wide range of weights are possible from 50 to 1500gsm	Only light weights can be made.Weights beyond 100 gsm are not possible
Investment is high as Machinery costs are high	Investment is low and second hand cards disposed by spinning mils are easily available

Batt Uniformity
Weight uniformity of batt is very important in nonwovens, as it affects the appearance, strength and all other properties. A good nonwoven should have weight uniformity of ±2.5%.Batt uniformity is largely dependent upon web uniformity though the number doublings in crosslapping has also influence over it. Web uniformity in card is improved by the use of
1. Continuous volumetric feeding
2. Non continuous feed from weighing hopper and micro weighing systems
3. Autolevelling
Continuous Volumetric Feed
Weight of material in chute (feeding to card) is maintained constant by photo cells or pressure transducers in feed trunk. Variations in filling across the width of trunk is equalised by automatic adjustment of flow of material. The density of material across the width is measured by ultrasonic sensors in Hergeth and based on the signals, frequency of joggle units is varied to achieve uniform density across the width Vibrating arrangement to chute is provided in Hergeth and Spinnbau cards to minimise air pockets and filling height variations across the width.(Fig 6 )

Fig 6 : Vibrating Chute
Ultrasonic control system is used in Thiebeau card and Hergeth to improve uniformity. Ultrasonic signals placed across the width measure the density which is used to control the frequency of joggle units to get uniform density in cross and longitudinal directions. Hergeth further employs a gravimetric fibre metering system in the opening sequence to ensure uniform flow rate. Web profile integrated tuft feeder system is developed by Truetschler (Fig 7).

Fig 7 : Scan Feed Tuft Feeder
The tufts from opening roller section is drawn by a fan into an upper trunk. The filling height is maintained constant by pneumatic pressure controlled by combs covering air inlet. Feed roller at the lower end of trunk feeds the material through a spring weighted feed plate to an opening roller. Opened tufts are fed to lower trunk. The fibres are blown by air into lower trunk and as air takes line of least resistance, uniformity across the width is maintained. The fibre mass in lower trunk is pneumatically compressed and the sheet is fed to a feed roller through a spring weighted segment. Material thickness is automatically adjusted by the spring pressure on the segments of feed plate. An optimal supplement is the Web profile unit which improves uniformity both in longitudinal and cross directions. Selective web profile across the width can also be obtained with web profile unit.
Weight Control
Heigh chandwick and Temafa have developed a micro weigh system to minimise variations in feed sheet to card (Fig 8 )

Fig 8: Micro-Weigh
The system employs a sensitive weigh pan with pneumatically activated shutters and doors/solenoids, mounted on transducers and controlled by a micro processor. Small tufts are dropped into the pan with an accuracy of ±2g. Microprocessor memory compares each mass with the required mass and opens the weigh pan and opens the weigh pan to drop the material into the chute. This system ensures batch to batch variation within ±1%
Autoleveller
Following systems are in vogue

• Feed sheet thickness to card is measured by a sensitive load beam transducer as it passes over a balance scale. Based on the force on the beam a signal is generated to control speed of feed rollers.
Fig 9: Scanning of feed weight
NSC Nonwovens employs 4 weighing gauges on the batt feeding to card and varies the front roller speed as per the weight. They also have another system where batt density measured with constant thickness is used to vary feed roller speed. Spinbau uses an electronic belt weigher to determine weight of the batt and vary the feed roller speed as per the same
• Web monitor The delivered web from card is passed through a pair of rollers in WIRA Web monitor, the small top roller being a measuring one. The vertical movement of top roller as per the thickness variation in web is measured by a transducer. The deviation from standard is used to vary the speed of feed roller.

Carding
Nonwoven cards are usually of roller and clearer type though in parallel laying, revolving flat cards are used. Nonwoven cards are wider in width from 2 - 5m. Usually they consist of a breast roller followed by a main cylinder. Nonwoven cards of Tandem type with breaker and finisher cylinders are also common.
A typical Nonwoven Card is shown in Fig .10.

Fig 10: Nonwoven single card
The main difference between Nonwoven card and roller and roller and clearer card is the use of randomising roller between cylinder and doffer. The purpose of randomising roller is to alter the preferential longitudinal orientation of fibres to a more random one. Randomising roller rotates in a direction opposite to the main cylinder.(See Fig 11)

Fig 11 : Direction of rotation of randomising roller in relation to cylinder and doffer
Further wire on this roller has a unique angle. Transfer of fibres from main cylinder to randomising roller is largely by aerodynamic forces. Part of the fibres on randomising roller is also fed back to main cylinder. As a result of these factors, the fibre orientation is changed from longitudinal to a more random direction. The extent of randomisation can be varied by varying speed ratio between randomising roller and main cylinder. A certain amount of randomising is also achieved by use of condensing rollers between doffer and transfer roller. The condensing action increases web weight/sq meter and randomises the fibre orientation to some extent. With randomising roller and condensing rollers, cross direction to machine direction strength, usually denoted by CD/MD, is reduced from 5:1 to 1.5:1.. Direct doffing without condensing rollers is used while making products with pronounced fibre orientation in longitudinal direction. Changeover from direct doffing to condensing system is usually automatically done
Nonwoven cards are usually of tandem type to get better opening and fibre individualisation. A typical Nonwoven Tandem card is shown in Fig . 12. Tandem card improves the individualisation of fibres and opens up the clusters and neps. Presence of neps and clusters is a major defect in blankets, automobile furnishings particularly made out of reclaimed fibres. And use of Tandem card will help overcome such problems.

Fig 12 : Nonwoven Tandem Card
To increase the web thickness and card productivity, Double doffer cards have been developed and all manufacturers offer this (Fig 13 ). Most manufacturers offer this type of card. Oerlikon Neomag offers a card with 3 doffers.In Bremen double doffer card the top and bottom webs can be turned 900, by a web deflector so that the two webs are laid side by side so as to get double the width.

Fig 13 : Double doffer Nonwoven Card
Two sets of randomising rollers and Doffers doff the web from cylinder. The web from top doffer is laid on the web from lower doffer so as to increase the thickness of web. Delta card by Spinnbau has three doffing systems made up of random and condensing rollers. Web is transferred from pre opener to main cylinder by a top transfer roller and a lower doffer and transfer roller. As a result, weight of material to main cylinder is increased and mixing of fibres is improved by the counter rotating action of upper transfer roller. Random orientation ensures uniform properties in longitudinal and cross direction and is essential in applications like geotextiles. Oerlikon Neomag offers injection cards, which uses aerodynamic principle to carry out carding action. 5-7 worker rollers are placed around the main cylinder and the fibres are removed from worker rollers by aerodynamic action caused by specially shaped material. This reduces stress caused on fibre by mechanical in the worker stripper system used in traditional cards. This is claimed to reduce neps and fibre breakages and damage. Erko Truetzschler have developed Rando card EWK413 for production of cotton pads and other cotton products for hygienic applications.
Production rates
In Table 4 card width and production rates claimed by different card manufacturer.

Table 4 : Card Width and Production rates.
Manufacturer	Make	Width mm	Production rate
Spinbau	Universal Super servo double doffer card	1000 – 3500	150m/min
	Delta Card	1000 – 3500	200 m/min
	High capacity Random Card, Hyperspeed card	4000 – 6000	400 m/min
	Alpha Card	2500	80 m/min
Oerlikon Neumag	Injection card with 2 doffers	Up to 3500	250 m/min
	Injection card with 3 doffers	Up to 3500	250 m/min
	Card MM 2+2	Up to 3500	300 m/min
Erko Truetzschler	EK 150 single doffer	1000 – 4200	120 – 240 kg/hr for 1m width
	Ek 150 double doffer	1000 – 4400	80 – 400 kg/hr for 1 m width
	EWK413 Random Card	1000 – 4500	300 kg/hr/m
NSC	CA 21	2500	100 m/min
NSC	Excelle Card	2500 – 3500	250 m/min
Befama	CV641	1800 – 2400	350 kg/hr/1m
	CV661	1800 = 2400	600 kg/hr/1m
	CV691	2200 – 2500	1000 kg/hr/1m
	CV791	2500 – 3500	1250 kg/hr/1m

Actual card production rate, however, depends upon the type of fibre denier, type of wire, condition of wire, humidity and temperature in card room. In general, production rates have to be kept lower with polypropylene compared to polyester. Because of its low melting point, polypropylene forms globules at higher production rates which stick to the wire and cause fibre loading. Production rates have to be kept lower with finer denier because of loading tendency. Static generation also causes fibre loading restricting the doffer speed. Right type of wire has to be used taking into consideration denier. Finer density wires have to be used for finer fibres. Production rates are also restricted with blunt wire points due to long usage. Maintenance of proper humidity and temperature through the use of humidification system is a necessary perquisite for getting satisfactory carding performance and productivity. Too high or too low humidity result in lapping around the wires, former because of sticking tendency and later because of static generation. Relative humidity of 60% and temperature of 900F are normally recommended.
Feed Roller
Standard Feed is one where feed roller is placed over feed plate. A gap of .005" is kept between feed roller and feed plate to prevent wear of feed plate during empty running. The setting is either manually or electrically adjusted. Feed plate positioned over feed plate is a recent development which claims more uniform and easy feeding of fibre. The two feeding systems are shown in Fig : 14 .

Fig: 14 Normal and Overhead Feed plates
Card clothing
Garnett type interlocking wire is usually used in Nonwoven roller and clearer card. The main advantage of this wire is in the event of damage, damaged strips alone can be replaced thereby reducing cost of replacement. Finer type of wire clothing should be used for cylinder and worker for finer fibre. Wire point density used for various parts of card for coarse and fine fibres are given in Table 5.. Wire height for cylinder, worker and doffer are kept lower for finer fibres than coarser fibres. Front angle and height of doffer wire is greater than that of cylinder and random roller to enable easy transfer of fibres.

Table 5 : Wire point density for various parts of card (Points/sqin)
Card part	8 – 30 den	1.5 – 6 den
Feed Roller	25 – 30	35 – 45
Breast Roller	150 – 250	80 – 110
Worker	175 – 250	300 – 350
Stripper	80 – 120	200 – 250
Cylinder	400 –450	250 – 300
Doffer	300 – 350	200 – 250
Random roller	500 – 550	400 – 450
Condensing roller	130 – 150	100 – 120
Take off roller	85 – 95	100 – 110

Dust Removal
Air cleaning dust removal systems are employed and the system is completely sealed contributing to dust free card room. The need for periodic card cleaning used in older cards is no more needed.
Carding quality
Carding quality plays a critical role in determining the quality of final product. Good carding is determined by the extent of opening of fibre clusters and removal of neps. This in turn is achieved by

By using a production rate optimum for the fibre. Increase of card production rate reduces carding quality but the deterioration in quality becomes more prominent beyond a certain optimum level. The optimum in turn depends on the properties of fibre, card condition and atmospheric conditions.
Settings at various points in the card affect quality. In particular the following settings are critical.
1. Setting between feed plate and lickerin roller.
2. Setting between worker and cylinder and between worker and stripper
3. Setting between cylinder and doffer/random roller
Condition of wire points. After a period of working the wire tips tend to become blunt and a proper wire replacement schedule has to be followed to maintain quality.

Another important point to be controlled in carding is web weight uniformity. Web weight uniformity is affected by feed weight variations, functioning of auto leveller and lapping incidences
Process control and Maintenance

Raw material should be checked for presence of molten fibres, undrawn fibres and extraneous materials.
Lags and pins of Hopper Feeder and opener should be checked for damaged and bent points
Uniform application of spinfinish on the material should be checked by random checking of spinfinish content at different places of stack
Thorough cleaning of cards should be done once a week. The wire points of stripper, worker, breast roller, cylinder, doffer and transfer rollers should be cleaned with a wire brush and petrol to remove embedded materials. Interspaces of cylinder/doffer and framings should be thoroughly cleaned
Wire should be checked for damages and damaged strips replaced once in 3 months
Card settings should be checked once in 3 months
The schedule for replacement of wire depends upon the fibre quality, virgin or reclaimed fibre, card production rate and maintenance practices. Normally wire should be replaced between 18 – 24 months.
Web gsm variation should be checked once a week by placing a template of 25 × 25 cm at different places and weighing the material under it and estimating the CV%. CV% should be within 5%.

Air Laying systems
Two types of air laying systems are common Rando Opener

Random Cards Rando Opener
Rando Machine corporation was the first to introduce this system. This is found in many nonwoven plants. The fibres opened through a Blow room line are fed to a saw tooth Opening roller. Fibres picked almost in a single fibre status by the teeth of opening roller are taken round and deposited on a slow moving perforated lattice by means of an air stream blown above to form a batt (Fig 15 ).A powerful fan blows air through a narrow duct at the exit end of opening roller. A suction fan creates suction under the perforations of the conveyer lattice. Net result is randomisation of fibres deposited on lattice.

Fig : 15 Rando Opener
Fibre orientation is nearly random in the horizontal and vertical plane and is fully isotropic. This greatly improves the insulation value and loftiness of the batt. This enhances the quality of such material for wadding, high lofts used in winter clothing and sound insulation material.
Random Card
Fehrer was the first to introduce this system. The random card used in this works on aerodynamic principles. The card consists of a series of small carding cylinders each fitted with a pair of worker and stripper rollers. Part of the fibres from the first card is delivered into a duct while the remaining part is taken forward to the next card. The delivered fibres from each card is transported via individual ducts to a common collecting perforated surface and is transported forward by a conveyor belt.(Fig :16)

Fig : 16 Random Card
As individual fibre layers from each of the ducts is laid one over the other on the conveyor, considerable doubling and randomisation is achieved. This contributes to uniformity of batt. The working width is 1 – 2.5 m. In the next generation batt forming line of Fehrer (Fig : 17), a pre web forming machine V21/R reduces the size of the tufts from the hopper feeder by means of an opening roller to form batt of 300-500 gsm. This is fed to a Random card K12 consisting of a cylinder and a pair of workers and strippers. The delivered fibres from the card is transported to a perforated conveyor supported by lamina air flow produced by a transversal blower. Suction at the high loft device at the delivery end increases the batt height and volume. This system is suitable for producing 'High Loft' material used in insulation. K12 card without "high loft" device is also offered. Production rates up to 50- 100 m/min are obtained with MD/CD ratio of 0.9 – 1.5 : 1 in the model K21 card.

Fig : 17 Random Card K12
Spinnbau offers a Turbo-unit TU for aerodynamic web formation in a weight range 30 - 450 g/m and web speed of 60 m/min with applications in the medical, hygiene and cosmetic applications. They also offer Fiberlofter for the medium and higher gsm products.. In airlaying systems by Oerlikon Neumag and others, fibres and low melt powder material can be transported together to form blended batt or a multi layer product. Fluff pulp, bicomponent low melt fibre or superabsorbent fibre can be mixed with regular fibre to form batts which can be bonded to make products like table top and wipe material, hygienic products, health care, female incontinence. Schirp uses perforated drum linked to a special air system to form batt from the web fed by feed roller. The drum is fitted with steel pins or saw tooth wire. The system claims to make batts of 100 to 200 gsm with a maximum production rate of 14 m/min.Laroche has developed an airlay line for making batts from all types of fibres with weight range 200 – 5000 gsm and thickness up to 250 mm and width up to 4000 mm. They have also a compact resinfelt line for making resinated flts used as under lays of automobile carpets and for acoustic insultation.
Process Control
1. Wire points of the Opening roller and card wires of Random card should be checked for damages once in 3 months 2. Weight per unit area should be checked at 25 different places and CV % worked out every week and at the time of lot change. 3. MD/CD ratio should be checked once a week.
Crosslapping
Cross lappers are of two types

Horizontal cross lapper
Camel back cross lapper

The laying speeds are higher with the former and most of the modern cross lappers are therefore of horizontal type.
In crosslapping card web is laid by a laying/feed lattice on a delivery lattice which runs at 900 of it. Speed of laying lattice is many times that of Feed lattice and as a result, a number of layers of card web are laid one over the other in a zig zag manner as shown in Fig 18 .

Fig 18 Horizontal Crosslapper
Thus a batt of much higher thickness and weight is made from card web. The number of doublings depends upon the relative speed of laying and delivery lattice, web width and laying width. Let
 Laying lattice speed = F m/min
 Delivery lattice speed = D m/min
 Laying width = L m
 Web width = W m  Time taken to lay one layer = L/F
 Distance moved by delivery lattice during laying of one layer = (L/F)×D
 Number of doublings =W/[( L/F) × D].
Production rate of crosslapper therefore depends upon the number of doublings. Since the direction of web is changed by 90⁰, the preferential orientation of fibres in the final batt is in cross direction. As a result, a higher strength is found in cross direction than in longitudinal direction. Laying speed depends upon the type of fibre, fineness and length, crimp, sticking tendency, web weight, spinfinish and humidity and temperature of department. With short and waste fibres lower laying speeds are used. Laying speed with modern cross lappers range between 150 - 270 m/min with card web input speed ranging from 120 to 200 m/min. Control systems are usually incorporated to control the card web as it enters the top carriage. This minimises web control problems encountered when top carriage approaches card and this facilitates higher laying speeds. A major problem in crosslapping is the disturbance caused by removal of air entrapped in the fibres of card leading to unevenness. To overcome this problem NSC has developed a system to remove entrapped air. In addition controls are used to prevent web accumulation at the reversal point. Dilo crosslapper prevents disturbance by air turbulence by guiding the web between two conveyor belts. Laying width in crosslappers can be varied from 1m to 10 m with step wise adjustment of 25 – 50 cm. For paper maker felts laying width go beyond 10 m.
Profiling systems
Profile technology is one of the major developments in cross lapper. Profile technology reduces the weight variations in the cross direction of finished fabric arising out of variable amount of distortions across the width during needling or web drafting. This results from differential shrinkage of material across the width during web bonding. Extent of shrinkage is more at the edges and progressively reduces towards the middle. Without profile technology, weight (gsm) will therefore be higher at the edges than at the centre, as shown in Fig, 19 because of differential shrinkage that takes place at the centre and edges of batt as it passes through bonding like needle loom or through web drafter.

Fig : 19 GSM variation across the width with and without profiling
Profile systems have been developed by most manufacturers like NSC Nonwovens9 and Dilo10. With profile technology, drafting of web takes place exactly at those places which are laid as selvedge in crosslapping. The increase in thickness at selvedges which takes place in needle punching or other bonding systems compensates for the preformed thin selvedge. CV of GSM across the width is reduced as a result from 3-4% to around 1-1.5%. Scanning gauge based on Xray technology is used to scan thickness and the measurements are used to control laying speed to achieve uniform thickness in a closed loop system. A nonwoven manufacturer has to ensure a minimum target weight in his product. With a lower CV in gsm, target weight can be significantly reduced leading to savings in raw material costs. Apart from variation in gsm, MD/CD strength ratio also varies across the width because orientation of fibres takes place to a greater extent at the edges than at the centre. NSC nonwoven has developed ISO Prodyn profile which not only reduces gsm variations but also MD/CD strength ratio variations across the width of the fabric9. Weight is automatically adjusted by speed variations in card and croslapper as per the weight distribution in the final fabric. The extent of improvement in width wise variation of MD/CD strength ratio with such a profiling system is shown in Fig .20

Fig 20 : Variation of MD/CD ratio across the width with and without profiling
Web Drafting
Web drafting is used for reorienting the fibres from cross to machine direction thereby reducing the CD/MD strength ratio of the product and improve isotropy. Further as drafting reduces the weight, card web can be made heavier leading to a higher production. Common types of web drafters used are shown in Fig : 21.

Fig 21 : Web Drafter
Web drafter is used after preneedling. Sometimes it is used between crosslapping and needling. The drafting rollers are clothed with wire to reduce slippage. Draft in each zone is kept low around 1.2 to 1.3 to minimise uneven stretch and fibre breakages.
Spunbonding
In Spunbonding, Nonwoven batt is formed by extruding, drawing and laying the filaments on a moving perforated screen. The process is similar to synthetic filament spinning. The molten polymer is passed through a spinneret and the emerging filaments are drawn and laid on a moving conveyor. Raw materials are synthetic fibres like polypropylene, polyester, nylon, polyethylene and polyurethane. Polypropylene is most widely used because of higher coverage obtained, arising from low density. Further the fibre is available in dope dyed form in a wide range of colours and shades and in recycled form, apart from virgin fibre. The drawback of the fibre is its low UV stability, low creep resistance and lower melting point.

Polyester is the next widely used fibre. Higher strength, better abrasion and resistance to UV are its main merits. Low resistance to alkalis is its drawback.

Nylon 6 and 66 are also used for some applications. Energy costs are however higher with this material. It has a higher moisture regain than polyester and polypropylene which is an advantage in some applications.

Polyethylene has lower strength and low melting point and so cannot be used in applications involving higher temperature. Lower cost is its advantage

Polyurethane has merits in apparels and other products requiring higher stretch and recovery

Bicomponent fibres either of core/sheath or side by side can be used with advantage. By keeping low melt polymer on the surface and high melt fibre on the core thermal bonding can be achieved without adding a low melt fibre. Bycomponent fibre made of polylactic acid (PLA) fibre in the core and polypropylene on the surface enables eco-friendly fabrics to be made in hygiene sector. Two extruders are used to melt the different polymers and are combined at the spin pack to form bicomponent fibre.
Batt manufacture
The polymer chips laid in hopper are melted inside an extruder. The molten material is filtered and is pumped by a spinning pump through a spinneret to form a bunch of filaments. As the fabric is wide two or three spinnerets are laid side by side to increase the number of filaments. The emerging filaments are quenched by a stream of cold air (Fig 22) and are attenuated mechanically or pneumatically to orient the molecules so as o increase the strength. There are two methods of batt formation
1.Partial orientation
2.Full orientation
The strength improvement by partial orientation is adequate for many products like coverstock for diapers and hygiene materials. With partial orientation higher production rates can be achieved. Partial orientation is achieved pneumatically by an air generation unit. However for products like geotextiles, carpet backing, roofings and industrial products, full orientation is achieved by drawing the filaments over heated godets, with draw ratio of 1 : 3 or 4 followed by pneumatic acceleration. The filaments are then passed through a pneumatic air gun where high velocity air is forced through a constricted area of low pressure. This helps to achieve high uniformity and cover. Electrostatic charge is applied to keep the filaments separate. Batt formation takes place by random and uniform deposition of filaments on a moving perforated conveyor. The batt is then taken forward for bonding. Lay down with preferential direction in cross or machine direction is also possible. Suction is provided under the conveyor to improve randomisation. Fig 22 outlines batt formation in spunbonding.

Fig :22 Spunbonding
Recofil system developed by Reifenhauser is the most widely used system of spunbonding. Latest Reicofil model 4 can produce light weight material for hygienic products at speeds of 800 meters/min. Energy consumption of 1 – 1.2 kwh/kg for melting and conveying the raw materials. Other systems are ‘Docan system’ and ‘Lutrafil sysem’. Reiter spunbond system claims a production capacity of 5000 tons/year/beam and energy consumption less than 1kwh/kg Hills and Fre specialise in spunbonding equipment from bi and multi-component material and claim speeds over 5000 metres/min, In the latest developments, special emphasis is laid on energy conservation and reuse of waste made in production.Ratio between he components can be varied from 50 : 50 to 85 : 15. Spunbonding from bi component and multi-component fibres provides products with unique properties. The different components are melted in separate extruders and passed through separate spin assembly and afterwards combined to pass through special spinneret orifices to form bi or multi-component filaments Special spinneret orifices are available to form core/sheath or side by side and segmented pie profile bi-component structures.
The relative merits of spun bonding and staple fibre bonding are given in Table 5 below.

Table 5 : Relative merits of filament bonded and staple fibre bonded Nonwovens
Spun Bonding	Staple fibre bonding
Higher strength	Lower Strength
Lower Elongation	Higher Elongation
Higher Uniformity in thickness and gsm	Lower uniformity in thickness and gsm
Lacking in textile character and feel	Has good textile character and feel
Higher tear strength	Lower tear strength
Products are normally of low to medium gsm (20 – 250)	Wide range of products from low to medium to high gsm are available (20 – 1500)
Less flexibility in regard to raw material. Generally line is suitable for either polypropylene or polyester or Nylon or bicomponent fibre. Some latest models however claim flexibility in regard to fibre All types of raw material can be processed in the same line	All types of fibres, manmade and natural can be made in the same line
High Plant capacity in terms of production	Low to medium capacity in terms of production
High capital investment	Low to Medium capital investment

Major Applications
1.Coverstock for diapers and hygiene products
2.Surgical materials
3.Carpet backing
4.Bedding and furniture
5.Geotextiles
6.Roof Materials and other construction material
7.Filters
8.Industrial products
Meltblown Nonwoven
Melblown nonwoven is batt formed of ultra fine filaments deposited on a screen. Polymer is extruded through a die consisting of several hundred holes.(Fig 23) Streams of hot air at temp of 220 to 3400C, passing from an outer channels of the die, rapidly attenuate the extruded polymer at 0.5 o 0.7 times the speed of sound, to form extremely fine micro filaments. The filaments are quenched by cool air flowing from the contours of the die and blown on to collector screen thus forming a self bonded nonwoven batt. The fibres are bonded together because of interlacing action of deposition and thermal bonding by the hot air. The meltblown material has low strength and is often used in combination with other nonwoven material. Because of the ultra fine size of the filaments and increase in specific surface area, meltblown material has a high filtration efficiency for gas and liquids and particles.
Barrier material is formed by combining meltblown material with spunbonded. Absorbents are made by combining cellulose or wood pulp with meltblown material Meltblown material sandiwiched between two layers of spunbonded materials, known as sms nonwovens are widely used as hospital gowns, hygiene, and filtration products. SMMS are also sometimes made.

Fig 23 Meltblown Process
Process Checkpoints
1. Viscosity of polymer chips should be checked in viscosity meter.
2.The spinnerets and other parts of the spinning system must be thoroughly cleaned of polymer build-up at periodic intervals and at the time pack change. When polymer build up contaminates the parts, production has to be brought down to maintain satisfactory processing. The quality of product also gets adversely affected by presence of defects like stripes, bars and doglegs. Traditional cleaning consists of 1 burning the hardened polymer by placing the spinneret in a furnace 2. Cleaning in an ultrasonic bath of caustic soda and 3. spray bath cleaning. This method is time consuming and there is risk of spinneret damage. The vacuum pyrolysis process of cleaning is much more rapid and ensures defect free thorough cleaning
3. Spinnerets should be examined under magnification for wear and tear. Preferably, an automated spinneret examination system should be used to inspect the spinneret at the time of purchase and during use to ensure that the design specifications are maintained as this speeds up the process. If the holes of the spinneret show signs of wear they should be refurbished.
References
1. Nonwovens – Technoogy of manufacture and properties
A.K. Rakshit, A.N. Desai and N. Balasubramanian, Proceedings of Symposium on Nonwovens, BTRA, 1987, Feb
2. A comparison of woven and nonwoven geotextiles,
J. Perfetti, Meliand Textilber (Eng. Edn.), 1985, March, p207
3.Woven and Nonwoven medical/surgical materials
D.V.Parikh, T.A.Calamari, A.P.S.Sawhney, N.D.Sachinwala, W.R.Goynes, J.M.Hemstreet, and T. Van Hoven, International Nonwovens J, 1999 Spring
4. Development of a geocomposite canal liner – BTRA’S experience
A.N.Desai and N.Balasubramanian, J. Textile Association, 1991 Jan, p187
5. http://www.inda.org/wet-laid.html
6. Relative merits of polypropylene and polyester
N.Balasubramanian, Indian Textile J, 2004, 32, p32
7. Influence of processing conditions on functional properties of high loft structures
A.N.Desai and N.Balasubramanian, Indian J of Fibre and Textile Research, 1990, 15, p169
8. Opening size and water permeability of nonwoven geotextile
A.K.Rakshit and N.Balasubramanian, Indian Textile J., 1991 June, p 26
9. Indian Textile J, 2009, July, p 71
10. http://www.texdata.com/content/0082e.pdf

* Retired Joint Director (BTRA), & Consultant, Tel 022 25280767

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