Measurement of Yarn Hairiness | Shirley Yarn Hairiness Tester

Yarn Hairiness
Yarn hairiness is in most circumstances an undesirable property, giving rise to problems in fabric production. Therefore it is important to be able to measure it in order to control it. However, it is not possible to representhairiness with a single parameter because the number of hairs and the length of hairs both vary independently. Theoretically a yarn may have a small number of long hairs or a large number of short hairs or indeed any combination in between. The problem is then which combination should be given a higher hairiness rating.
 
Fig: A. A yarn with a low number of hairs X13 
Fig: B. A plot of number of hairs against hair length.
It has been found that the number of hairs of different lengths protruding from a yarn is distributed according to an exponential law . That is there are far more short hairs than long ones and the number of hairs falls off exponentially as the hair length increases. It is considered that there are two different exponential mechanisms in operation, one for hairs above 3mm long and one for those below; this is shown in Fig. B where the two parts of the plot of the log of the number of hairs against hair length can be approximated by a straight line. The hairiness index devised by assumes a straight line on the plot of the log of the number of hairs against hair length. The number of hairs exceeding 3 mm in length as a percentage of the total number of hairs is found to be linearly related to the count of the yarn, that is there are more hairs in a fine yarn than there are in a coarse one of the same type. The overall number of hairs is influenced among other things by the spinning system and by the fiber length. Measurements of hairiness are very dependent on the experimental configuration used such as the number and type of guides the yarn passes over and also the method chosen for detecting the hairs.

Shirley Yarn Hairiness Tester
The Shirley yarn hairiness tester consists of a light beam shining on a small diameter photoreceptor opposite to it. The yarn under test is run between the light and the receptor at a constant speed. As a hair passes between the light and receptor the light beam is momentarily broken and an electronic circuit counts the interruption as one hair. The instrument has two sets of yarn guides as shown in Fig. C. The lower set leads the yarn over a guide at a fixed distance of 3 mm from the receptor. The upper set leads the yarn over a movable guide which can be set at a distance of between 1 and 10mm from the receptor. The total number of hairs in a fixed length of yarn is counted by counting for a given time, the yarn running at a known speed. 
 
Fig:C. Shirley yarn hairiness
Zweigle G565
This apparatus counts the number of hairs at distances from 1 to 25mm from the yarn edge. The hairs are counted simultaneously by a set of photocells which are arranged at 1, 2, 3, 4, 6, 8,10,12,15,18,21 and 25mm from the yarn as is shown diagrammatically in Fig.D. The yarn is illuminated from the opposite side from the photocells and as the yarn runs past the measuring station the hairs cut the light off momentarily from the photocells, which causes the electrical circuits to count in a similar manner to that of the Shirley instrument. The instrument measures the total number of hairs in each length category for the set test length. The yarn speed is fixed at 50m/min but the length of yarn tested may be varied. The zero point, that is the position of the yarn edge relative to the photocells, is adjusted while the yarn is running by moving the yarn guides relative to the photocells. A further set of photocells is used to locate the edge of the yarn during the setting up procedure. The instrument calculates the total number of hairs above 3 mm in length which can be used as a comparison with the Shirley instrument. It also computes a hairiness index which has been especially devised for this instrument and which is intended to combine all of the information measured by it.
Fig:D. Zweigle yarn hairiness
Uster Tester 3 Hairiness Meter Attachment
This device is produced as an attachment for the Uster evenness tester and is connected in place of the normal measuring capacitor. However, it makes use of the full statistical result collection capabilities of the evenness instrument. The principle of the measurement is quite different from the above instruments and therefore the results from the two types of instrument are not comparable. In this instrument the yarn is illuminated by a parallel beam of infra-red light as it runs through the measuring head. Only the light that is scattered by fibres protruding from the main body of the yarn reaches the detector as is shown in Fig. E. The direct light is blocked from reaching the detector by an opaque stop. The amount of scattered light is then a measure of hairiness and it is converted to an electrical signal by the apparatus. The instrument is thus monitoring only total hairiness, but using the Uster evenness data collection system can monitor changes in hairiness along the yarn by means of a diagram, spectrogram, CV of hairiness, and mean hairiness in a manner similar to that used in evenness testing.

Yarn Bulk
The WRONZ Bulkometer test gives an indication of the covering power of a yarn when it is incorporated into finished products such as knitwear or carpets.
Fig:E. The measurement of hairiness by scattered light
Fig:F. The Wronz bulkometer.
Yarn bulk is denned for the purpose of this test as the volume occupied by 1 g of yarn at a given pressure, measured in cnrVg. To carry out the test a hank of yarn containing a known number of turns is placed in a channel 10cm long by 5cm wide so that all the strands of the hank are aligned as shown in Fig. F. A load of 50Og is then placed on the sample, so compressing the yarn. When the load comes to rest the height of it above the base is measured. From the area of the channel (50cm2) and the height of the load, the volume occupied by the yarn can then be calculated. The size of hank used in the test depends on the linear density of the yarn; a suitable size can be calculated from the formula:

Number of turns = 90,000 ÷ linear density in tex

It is preferable when comparing similar yarns to keep to the same number of turns. 
 
 

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