Fabric friction-test

An inclined plane method is specified for coated fabrics in BS342439. The test piece is attached to a sled resting on an inclined plane which is covered with the other surface to be tested. The inclination of the plane is varied until sliding takes place. This is probably the simplest form of friction test but not an accurate one and, of course, cannot operate at any given velocity. 

Table 11.2 shows a comparison of common pill test methods. The best correlation between test method and actnal wear is fonnd when a variety of mechanical forces act npon the fabric dnring testing. For anti-pilling tests of a new article with strange pilling behavionr, the combination of at least two different methods is recommended. They shonld be based on different principles, for example a friction test (e.g. Martindale) and a shock or impact dominated test as RTPT or the shake box test."... 

Since softening is inherently subjective because human sensory perception is involved, no instrumental method has been identified to date as the perfect one to quantitatively relate human perception of softening to instrumental data. The Kawabata method measures the mechanical properties of fabrics [2], These properties are used to quantify the effects of fabric softeners. Softening is associated with lubrication, flexural rigidity, and compressibility of whole fabrics. Fabric lubricity is related to fabric friction, which can be measured by Instron tests. 

A major area of negotiation in the development of the specification concerned the Drum Friction Test. This is a test which simulates a stalled belt. The NCB test in force had evolved after the Creswell Colliery disaster of 1953. A stalled rubber belt had remained in contact with its drive drum which continued to run for several hours. The frictional heat caused a fire which resulted in several fatalities. The drum friction test to emerge afterwards stipulated that the belt shall break, in addition to drum temperature and belt flow limitations. In effect this meant a textile-reinforced PVC belt in which the frictional heat melts the PVC and then melt-breaks the synthetic-fibre fabric as it makes contact with the drum. Such a belt meets the drum friction requirements and the NCB used this type of belt for many years. The steel-cable reinforced rubber-belt needed for the single-belt installation, first at Cadley Hill, and then at... 

Gamache, L. (2007), The design and implementation of a friction test apparatus based on the thermostamping process of woven-fabric composites , MS Thesis, Department of Mechanical Engineering, University of Massachusetts Lowell. 

Diverse appHcations for the fabric sometimes demand specialized tests such as for moisture vapor, Hquid transport barrier to fluids, coefficient of friction, seam strength, resistance to sunlight, oxidation and burning, and/or comparative aesthetic properties. Most properties can be deterrnined using standardized test procedures which have been pubHshed as nonwoven standards by INDA (9). A comparison of typical physical properties for selected spunbonded products is shown in Table 2. 

Empirical attempts have been made to relate strip and grab test results, particularly for cotton fabrics, so that if one strength is known, the other can be calculated. The relationship is complex, depending on fiber strength and modulus, yam size and crimp, yam-to-yam friction, fabric cover factor, weave, weight, and other factors (19). 

Years of development have led to a standardized system for objective evaluation of fabric hand (129). This, the Kawabata evaluation system (KES), consists of four basic testing machines a tensile and shear tester, a bending tester, a compression tester, and a surface tester for measuring friction and surface roughness. To complete the evaluation, fabric weight and thickness are determined. The measurements result in 16 different hand parameters or characteristic values, which have been correlated to appraisals of fabric hand by panels of experts (121). Translation formulas have also been developed based on required levels of each hand property for specific end uses (129). The properties include stiffness, smoothness, and fullness levels as well as the total hand value. In more recent years, abundant research has been documented concerning hand assessment (130—133). 

Friction coefficients will vary for a particular material from the value just as motion starts to the value it attains in motion. The coefficient depends on the surface of the material, whether rough or smooth, as well as the composition of the material. Frequently the surface of a particular plastics will exhibit significantly different friction characteristics from that of a cut surface of the same smoothness. These variations and others that are reviewed make it necessary to do careful testing for an application which relies on the friction characteristics of plastics. Once the friction characteristics are defined, however, they are stable for a particular material fabricated in a stated manner. 

Plunkett and his assistant decided to cut open the containers. When they did, they found a white, waxy powder inside. Plunkett tested the powder. He found that it was chemically inert and heat resistant. He also found out that it had a very low surface friction. Because of this low surface friction, most things would not stick to the powder. The TFE gas in the container had polymerized to produce this new substance. The new substance s chemical name is polytetrafluoroethylene (PTFE). It was later named Teflon. Teflon is used to protect fabrics and in bakeware to prevent food from sticking to pots and pans. 

FAST (Fabric Assurance by Simple Testing) is another well known system. It was developed for quality assessment in the wool garment industry. FAST is less expensive and much quicker than the KES-F because it measures only some aspects of the fabric hand such as compression, bending, extension and dimensional stability at a few given points in a simplified form. The first three parameters correlate fairly well with the perceived softness but no quantitative hand values are calculated. For the evaluation of yam softness, there are several other devices in use, for example the p-Meter (Zweigle), a frictional balance (Reibwertwaage from Schlafhorst) and the F-meter. 

The Linear Intersecting Vane Machine test device will be fabricated and used with selected seals, ports, and low friction materials to provide basic performance data applicable to the TTVM and to further down-select options. 

More simple test methods for certain polymer types have been standardized for many years the inclined plane for fabrics and the simple towed sled for plastic films. But it is only fairly recently that more comprehensive procedures have been recognized in standards. There is no reason why such a comprehensive method should not be written for use with all materials, but the tendency has been for standardization to be carried out within particular industries. One reason for this is that there are a considerable number of tests for particular products, mostly developed with the aim of simulating the particular conditions of use. The measurement of friction is comprehensively covered in Chapter 23. 

Pullout test is also a method, providing useful information about fabric tearing, its ability to absorb energy especially in ballistic applications, lllnishing efCbiency, bending, and shearing hysteresis of the fabric and Qially the frictional behavior of the fabric. 

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