Terry fabrics are used in various fields because of their water absorption properties. Looms for the production of terry fabrics operate with two warp systems. The highly tensioned warp for the base fabric is processed in conjunction with loosely running warp pile, which is fed to the base warp at a certain ratio. As an additional warp yarn is inserted into the base fabric, a third dimension, the pile height is formed. The fabric volume increased in this manner leads on the one hand to a bulky and soft handle and, on the other hand, to an increased surface area of the fabric. Absorbancy and heat retaining capacity are thus improved and are, among other factors, decisive for the further processing into bath robes, leisure, sports & baby wear.

Weaving is a critical process in terry manufacturing as it requires a well prepared material, trained personnel, and a complex weaving mechanism. A well structured quality control system which gives due importance to the above requirements can only ensure the production of a fabric of expected quality consistently. In this paper, various quality control measures that are required in different stages of terry fabric production are discussed in detail.

Strip of three pix.

Weaving preparatory

Yarns for terry weaving

Yarns for weaving may be:
(i) Grey yarns
(ii) Processed yarns (bleached yarns, mercerised yarn, dyed yarn)
Terry fabrics must be produced at a certain weight per square metre, using mostly 100% cotton yarns as Pile, ground and weft. Yarn counts that are normally used for pile warp yarns are: Ne 10, Ne12, Ne16, Ne 2/20, Ne 2/24, Ne10 + Ne 60 PVA, etc.
Yarns made out of PVA fibres can be doubled with cotton yarns for the production of super soft Terry fabrics. PVA fibres will be dissolved out at processing stage, leaving a fluffy soft terry structure.
Count ranges used for ground warp yarns are:
Ne10, Ne11, Ne 2/20, Ne2/24 etc.
Count range for weft yarns are:
Ne 2/20, Ne1/14, Ne1/12, Ne 2/24, Ne 2/16, etc.
It is the pile yarns that contribute to more than 60% of total fabric weight. Mostly ring spun yarns are used as pile yarns. OE yarns also can be used as pile yarns and it depends upon customer requirements. Typical yarn quality requirements for pile warp yarn are given in Table 1.

Table - 1

(Data given above shows only the minimum quality requirement. However, a mill can set its own quality standards as per its achievable quality level.)

Warping

Beam warping or direct warping is the preferred route for producing piece dyed terry fabrics while sectional warping is opted for yarn dyed fabric production.

(a) Control on incoming material (cones)

To ensure the production of a quality beam at sizing it is very essential to have a strict control on the incoming material. Apart from testing the cones for quality parameters (Table 1), the following measures have to be adopted.

A regular check on the lot number of cones in the carton boxes and the presence/absence of identification mark on cones shall be established. Mixing up of yarns of different counts and cones of different lot numbers will lead to shade variation after dyeing.
Check the weight of cones on sample basis and find out the weight variation of cones. A report on Cone weight variation shall be maintained.
Cone density may also be checked periodically
Proper material handling procedures has to be set and should be followed strictly.

(b) Warping stage

Quality control measures:
Speed of warping should be almost constant throughout the winding of the beam. Of course, running the machine at slower speeds during the initial and final phase to control end breaks is allowable. Sort details (count, type of yarn, no. of ends/creel) and labeling on beam is to be checked for identification and traceability.
Proper working of stop motions has to be checked to avoid missing ends in the beam. An end break study has to be done for each lot of material and the reason for end breaks has to be recorded and investigated.
Packages causing repeated machine stops should be immediately replaced by the worker. Single end tension can be measured at different positions in the creel, ie. near the headstock, at the farthest creel position, in the left side of the m/c, and in the right side of the m/c.
Beam density can be checked at the left, centre and right side of the beam.
Percentage of bottoms generated (Remnant %) has to be calculated for every creeling. For efficient warping operation, the remnant should be less than 1%.
Temperature & RH conditions are to be maintained inside the department.
Though the present day machines have mechanisms that automatically regulate the yarn tension, pressure on drum for beam density as per requirements, a random check on these parameters is must to produce a quality warpers beam.

Sizing

The importance of sizing is well known and a proper sizing only can ensure loom efficiency and production of quality fabric. The percentage of size add-on depends on quality of yarn, ends/inch in the fabric, loom speed, etc. But the real performance of sized yarn is assessed by the incidence of end breaks in loom. End break study in the loom shed will give a clear picture on the quality of sizing. Sizing of pile yarns for terry weaving usually requires a low size add-on of 1 to 5% compared to 8 -14% of warp yarn for ordinary weaving. Ground yarns also require low size add-on especially if they are doubled yarns.

Still, the operation of sizing is very critical as poor sizing causes variety of production and quality problems in loom shed. If yarns are not properly covered by the size, on exposure to abrasive actions in loom, the fibres from the yarn body will be pulled out, leading to the problem of “linting” in terry fabrics. Linting is a major quality problem.

Nowadays, pre-blended sizes are used as sizing material which may contain, modified starch, PVA, wetting agents, antifoaming agent, etc. Application of more size or other secondary ingredients to yarn is based on the performance of yarns in weaving.

Quality control measures at sizing

Check the quality of size materials
Check the viscosity (using viscosity cup) and solid content (using refractometre) of size paste in both the cooking stage and also in sow box.
Sizing quality study has to be done for full beam, at least once in a shift for every machine and the incidence of lappers and migratory ends has to be recorded.
Check the creel tension, braking pressure of creel beam, feed tension of yarn before sow box, sow box temperature, nip pressure (squeezing), drying zone temperature, beam pressing pressure, winding tension and % stretch. These parameters are automatically regulated in automatic sizing machines as per requirements.
A random check on % moisture in the sized beam is essential even for automatic sizing machines that have automatic control.
Every sized beam has to be weighed and % size add-on is to be calculated & recorded. Tensile testing of sized yarn may also be carried out to ascertain the improvement in strength.

Terry weaving

As mentioned earlier, the production of terry fabrics require the use of two beams, one beam for the ground structure and the other for pile structure. Generally warp density varies between 10-15 ends/cm in ground and as well as pile. In denser construction it ranges between 15-18 ends/cm. The pile ratio of 1:4 to 1:8 is used depending on the end use of terry fabrics. Pile ratio is the length of pile yarn to the length of terry fabric.

Quality control measures at loom shed

A typical loom card data for production of a terry towel fabric is shown in Table 2 and the formation of a three pick terry structure is shown in Figure 1.

Table 2

a) First Piece Inspection

For every new sort, on production of few metres of fabric, the fabric has to be inspected for the following against the customer requirements.
Weight per square metre (GSM)
Pile ratio
Dimensions (length, width, size of design portion, etc)
End/inch, picks/inch
Loops/sq inch, and
Any defects

(b) Control on weight per square metre of terry fabrics

Terry fabrics are sold on weight basis and hence a control on fabric weight is of paramount importance. Weight/square metre (GSM) of terry fabrics are generally in the range of 360-670 grams. Companies mainly use standard warp and weft yarn counts as well as warp density. For required terry weight per square metre, the weft density and pile length are the parameters to be adjusted. The length of pile in relation to the length of terry fabric is measured in terms of pile ratio.
The pile ratio, pile height and weft density (picks/cm) are related by the expression,

Pile height (in cm) = (Pile ratio/Picks per cm) x 0.5 x Type of terry

(c) Online and offline inspections

On-line inspection in looms should ensure that defects are identified and rectified in the loom stage itself. In fact, on loom inspection gives a clear idea not only on the defects, but also on the quality of warp beams, quality of weft yarn, condition of m/c, operator skill, etc.
Off-line inspection, which is grey inspection of fabrics, is normally carried out on sample basis and the defects are to be properly identified and recorded. 100% Grey inspection is necessary only if the online inspections are not effective in controlling the defects. The doff weight and dimensions of relaxed fabrics are checked in grey inspection stage.

The list of mendable and non-mendable terry weaving defects is given in Table 3.

Defects can also be classified as Major and Minor depending on its intensity.
For example, temple mark that is visible as thin lines in grey inspection stage may not show up after processing stage. This can be considered as a minor defect. However, if the lines are very prominent and had disturbed the loop structure, it is certain that they will show up well after processing. Then it should be considered as a major defect. In this regard, training of quality personnel about various types of defects in fabrics and its implication on the final quality of the product is a must.

Conclusion

Identification of quality elements, developing it into system, effective system implementation, and continual improvement of the system are the ingredients of a successful Quality Management System. Since the market of terry fabrics has undergone a phenomenal change in recent years, a comprehensive and stringent quality control system is very essential to deliver a product that consistently meets the ever-increasing customer expectations.

Note: For detailed version of this article please refer the print version of The Indian Textile Journal July 2008 issue.

R Guruprasad.
Lecturer
K S R College of Technology,
Tiruchengode, Tamil Nadu.