Sitra News Jan 13

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  • This issue of SITRA NEWScovers the following topics:


    Quality Assurance in spinning mills a case study 1


    Influence of yarn friction on knittability of cottonyarns 5


    Inter-relationships between Deviation Rate inyarn mass (DR%) and variations in yarn tensilecharacteristics 7

    MEDICAL TEXTILES - Series 19 10





  • Jan. - Feb. 2013

    SITRA News

    Quality Assurance in spinning mills a case study

    Quality control is the watchword in the competitive industry like textilesas it affects the user need as well as profitability. It (QC) is generallya procedure or set of procedures intended to ensure that a manufacturedproduct or a performed service adheres to a defined set of qualitycriteria or meets the requirements of the client or customer. Thoughall spinning mills are having a quality control department, nevertheless,in most cases, the activities of QC need to be enhanced with asystematic approach in meeting the quality requirements of a product.This process is known as Quality Assurance (QA).

    QA is the systematic measurement in comparison with a standard,monitoring of processes and an associated feedback loop that conferserror prevention. Two principles are included in QA: Fit for purpose,the product should be suitable for the intended purpose and Rightfirst time, mistakes should be eliminated.

    Of late, the importance of QA has been picking-up in spinning mills.Many mills, more particularly those are largely in export which business/ having a group of mills, have a QA department in the place of QCdepartment.

    To highlight the activities of QA in spinning mills, a typical example isgiven in this note as case study.

    Quality Assurance in a spinning mill a case study

    The activities/functions of Quality Assurance department of a textilemill, having its spinning units working in different places, are givenbelow:

  • Jan. - Feb. 2013

    SITRA News

    Organisation structure

    All the units are having their own testing laboratories with a range oftesting equipment like Uster HVI Spectrum, Uster AFIS Pro2,computerised count balance, Uster Tester 5, Uster Tensorapid 3, UsterTensojet 4, Uster Zweigle Hairiness tester, etc.

    Each unit has a Quality Assurance manager with required supportingstaff including lab assistants. The QA managers of individual unitsreport to the QA manager of the Central Office.

    Activities/functions of individual units QA department

    - Testing of raw material, inter-mediate products and finalproducts.

    - Conducting various process control studies

    - Ensuring that testing instruments are calibrated as perschedules.

    - Analysing customer complaints and replying to the customerswithin a specified time.

    - Acting or assisting as management representative for theimplementation of Quality Management System ISO 9001,Environmental Management System (ISO 14001),Occupational Health and Safety Management System(OHSAS 18001), etc.

    - Analysing causes for abnormality, etc.

    Central QA department

    Some of the unique features of the Central QA department arementioned below:

    1. All the test results from the individual units are directly uploadedto QA server from the testing instruments. Once the authorizedperson in the respective units approves the test results, thesame can be monitored by the Central QA department. Thishelps to check/compare the quality parameters of the differentunits.

  • Jan. - Feb. 2013

    SITRA News

    2. Customer complaints are also uploaded in a separate system,provided for effective handling of customer feedback. If a replyhas not been sent to the customer within a prescribed time, areminder message will be sent to all the persons concerned(Marketing/Production/QA) by marking a copy to the topmanagement.

    3. Based on the requirement of QA/marketing department, thesoftware and servers for handling test results and customerfeedback are created, maintained and updated by the millsown EDP team.

    The following are the main activities of the Central QA departmentother than the routine schedules.

    1. To review periodically the testing schedules, activities andprocedures between units for standardisation.

    2. To co-ordinate with marketing department while finalising theorder regarding technical specifications.

    3. To prepare standards for all in-process testing with controland alarming limits, which are reviewed periodically and revisedwhenever necessary.

    4. To prepare quality standards for end product and get approvalfrom the top management.

    5. To conduct round test between the units at regular intervalsfor ensuring the correct working of various testing equipment.

    6. To share information regarding the trials conducted in therespective units with the other units.

    7. To assist in developing new products.

    8. To co-ordinate with other departments such as Production,Engineering, Maintenance, Human Resource, etc., andorganise management review meeting, group technicalmeeting, etc.

    9. To organise internal and external audits for implementation ofsystems such as ISO 9001, ISO 14001, OHSAS 18001, etc.

  • Jan. - Feb. 2013

    SITRA News

    Customer feedbacks handling procedure

    The mill has fixed a time frame for addressing the customer feedback.The units concerned should send the feedback to the marketingdepartment with a detailed analysis report within 96 hours. In general,the feedback should be addressed to the customer within a span of 7days. Otherwise, a reminder message will be forwarded to all thepersons concerned (Marketing/Production/QA) by marking a copy tothe top management.

    The following flowchart explains about the procedure of handling thecustomer feedback.

    Feedback from customer to marketing department

    Immediate acknowledgement by themarketing department to the customer

    Forwarding the customer message/samples to QAD of the

    respective units

    Circulate the complaint to all the concerned persons in the unit by

    the QA manager

    Aanalyse the feedback based on standard procedure/checkpoints

    Based on the customer priority, nature of

    complaint, etc. make a visit to the customer


  • Jan. - Feb. 2013

    SITRA News

    Flowchart Addressing customer complaints

    - Liaison and Consultation division

    Influence of yarn friction on knittability of cotton yarns

    Yarn friction contributes to difficulties during knitting in two ways firstly, it affects the tension of the yarn supplied to the knitting elementsand secondly, a high friction may increase the abrasion of yarn withknitting elements and guides. Tension in knitting is one of the factorscontrolling the amount of yarn placed round the needles (length ofyarn per stitch) and therefore, it affects the length of knitted goods.The final tension under which the yarn is laid round the needles dependson the take-off tension from the package and the friction at all points ofcontact of the yarn i.e., guides, tensioning devices, needles, etc.

    Detailed reply should be forwarded to the marketing department by the respective units QA department

    Review the various feedbacks in the periodical meetings at Central


    Monitor the effectiveness ofpreventive action in the subsequent lots

    Suitable reply will be sent to the customer

    by the marketing department


  • Jan. - Feb. 2013

    SITRA News

    As per studies conducted at SITRA and elsewhere, the increase inyarn tension is significantly influenced by the co-efficient of dynamicfriction () of yarn with metal surfaces. The increase in tension forvarious yarn values after passing over guides are given in Table 1.

    Table 1 Increase in tension for various values afterpassing over different number of guides

    It is important that the co-efficient of friction should be low and uniform.A sudden increase in take-off tension may produce a break in theyarn, and a press off will be the result. Also, small changes of tensionfor a short duration may produce differences in loop length.

    As per available literature, the variations in the length of yarn in theloop and the total length of knitted goods are often due to the differencesin yarn tension, which depends on the friction between the yarn andobjects with which the yarn comes into contact. The results of a studyconducted at SITRA in this connection are shown in Figure 1.

    Figure 1 Relationship between yarn tensionand yarn length per 1000 stitches

    Factor by which tension increases1 guide 2 guides 3 guides 4 guides 0.15 1.3 1.6 2.0 2.60.25 1.5 2.2 3.2 4.8 0.35 1.0 3.0 5.2 9.10.65 2.8 7.7 21.0 59.0 0.90 >4.0 >17.0 >69.0 >286.0

  • Jan. - Feb. 2013

    SITRA News

    In order to reduce the excessive tension generated during knitting, theco-efficient of dynamic friction () requires to be maintained between0.15 to 0.17. Hence, waxing during cone winding is popular for knittingyarns. For better performance, the wax pick-up during winding may bemaintained in the region of 0.15% so that can be maintainedwithin the required limits.

    - Dr.K.P.Chellamani,Spinning division

    Inter-relationships between Deviation Rate in yarn mass(DR%) and variations in yarn tensile characteristics.

    An uneven yarn gives rise to a patchy fabric. Very high levels ofunevenness also results in loss of yarn strength.

    In the recent past, a new parameter ca