BS 5441:1988 download.British Standard Methods of test for Knitted fabrics.
1 Scope
BS 5441 describes methods of test for knitted fabrics. Section one gives general information relevant to both warp and weft knitted fabrics; section two specifies methods appropriate for wet t knitted fabrics and section three specifies methods appropriate for warp knitted fabrics.
NOTE. The titles of the publications referred to in BS 5441 are listed on the inside back cover.
2 Definitions
For the purposes of BS 5441 the following definitions apply.
2.1 barriness or barrJ. Regularly repeating stripiness in textiles.
2.2 barry. Exhibiting barriness.
2.3 grade. One of five members of the scale (see 3.7), each exhibiting a different degree of bar/background contrast.
2.4 half-grade. An imaginary contrast midway between those exhibited by two adjacent grades.
2.5 rating or barriness rating. The number of the grade or half-grade assessed visually as exhibiting a degree of contrast between bars and background similar to that on the fabric being compared with the scale.
3 Apparatus
3.1 Counting glass, the aperture width of which shall be 2 ± 0.005 cm at all places. The thickness of the base plate at the edges of the aperture shall not exceed 0.1 cm. Other suitable apparatus may be used.
3.2 Ruler.
3.3 Dissecting needles, scissors and razor blades.
3.4 Balance, capable of weighing to an accuracy of 0.1 mg.
3.5 Crimp tester.
3.6 Course length tester, consisting of a weighted clamp and a rigid base-board adapted for mounting vertically on which are mounted an appropriate number of freely rotating pulleys so positioned that the yarn can be wound round them in a zigzag manner, and a series of locations for a yarn clamp labelled to show the distance from the clamp to the zero point of a metric ruler. When the yarn is attached to the clamp and wound round the pulleys, the length indicated on the ruler by the weighted clamp
is added to that indicated on the appropriate location in use to give the total length of yarn.
Alternatively an electronic course length tester consisting of a measuring wheel with electronic pick ups, a digital display and a tensioning device as well as a hold down device for the specimen of circular knitted fabric may be used.
3.7 The Hatra barriness scale1 which consists of five numbered black frames, each with a grey card and a hole of equal size. Grade 5 is bar-free, grades 4 to 1 are progressively more barrlV. A grade is illustrated in figure 1 and information on the precision of the method and care of the scale is given in appendix A.
The external dimensions of the black frames are 355 mm x 250 mm. The grey cards (i.e. the actual photographs illustrating the various degrees of contrast between bars and background) are 100 mm x 118 mm and the adjacent holes are the same dimensions. Each grey card has parallel lines 0.75 mm thick and 9 mm apart’.
3.8 Light source, preferably artificial daylight fluorescent tubest. The tubes shall be changed after 2000 h to 3000 h use because of diminished ultraviolet emission.
NOTE. The preferred light intensity is at least 810 lux, likely to be available approximately 300mm from one or 1000mm from two 65/80 W tubes of the previously mentioned type.
A preferred viewing arrangement is illustrated in figure 2, in which the tubes are at such an angle that the fabric receives most of the light from the tube areas nearest to it at an angle of 450 and the fabric is viewed from a distance of 300 mm. Although the frames of the barriness scale shield the eyes from the surrounding field, it is good policy for viewing areas to be matt neutral grey. Too much black can be depressing and tiring; gloss paint causes glare and fatigue.
Table and tube mounting (650 mm above it) are both at 22.5 0 to the horizontal. The two tubes are within 180 mm of the rear. The ‘stop on the table is 500 mm from the rear and 130 mm from the front, which is 850 mm from the floor. At the front of the mountir there is a 140 mm high vertical antiglare shield, 300 mm proud of the wall. The whole area is well shielded from daylight.
6.2 Principle
A sample of fabric, regarded as representative of the
textile to be assessed for barriness, is compared visually
under specified conditions with grades of a specified scale
that differ in the degree of bar/background contrast.
6.3 Procedure
6.3.1 Fabric position. Rotate fabric, use-surface uppermost, to decide the orientation of greatest apparent barriness. In the event of uncertainty as to which face of the fabric will be seen in use, consider both faces. Record the orientation showing greatest barriness.
6.3.2 Comparison with scale grades. Put scale frames in turn on the fabric, with the bars on the card and the fabric parallel, and compare bar-background contrasts.
6.3.3 Comparisons of rated fabrics. Place together fabrics identically rated and recheck against scale.
NOTE. Errors become prominent and fabrics differing in bar! background contrast from most in the group can be compared with adjacent groups and rechecked against the scale.
When a number of fabrics have been assessed and there are. for example, three groups of samples rated 3—4, 3. and 2—3 respectively, it is useful to look at all the ones in the ‘3’ group together, without the scales, and check whether they show similar contrast. If one fabric looks worse than the others, take it out and compare it with the contrasts in the ‘2—3’ group and rerate it against the scale. If another
Since special provision of the preferred conditions is required, it may prove convenient to use other conditions, and these should be reported. For instance, it is possible to use commercial colour matching equipmentt. This reverses the angles in figure 2 and it is supplied with the recommended tube. Alternative light. ing is also possible. This could be an ultraviolet tube, perhaps usefu if gross yarn mixing, for instance polyester with nylon, is suspected and ecru fabric is being assessed. Daylight can be used, but is more variable than the tube, even if north light only is used, and it may not always be bright enough for reliable assessments.
CAUTION. Ratings may vary with conditions of use. The recommendations in this standard give maximum agreement between observers. Other conditions can be used in special circumstances. If this is the case. these should be agreed, specified and recorded.
(c) the orientation used and whether it had been selected by rotation as the orientation of greatest apparent barriness;
Cd) the fabric area visible through any black mask used with a small specimen or any departure from the preferred procedure;
Ce) the barriness rating.
NOTE. In routine inspection operations one consistent observer may suffice. In arrangements between different parties the opinion of one observer may be acceptable to both, or two observers, one from each party, may assess and decide. In complaint investigation and in development work, it ii preferable to have multiple assessments. One observer can make repeated assessments, three or five observers can make one assessment each, or both methods may be combined. The implications for precision of a rating are discussed in appendix A.