1. Introduction


The use of nonwoven filter fabrics is growing steadily in applications like separating industrial dust in cement, coal mines and fertilizer industry, purifying air, fumes from the kitchen and colour industry (Naik 1983). Nonwoven fabrics are successful in capturing fine particles with little pressure drop and are cheaper to produce. The random distribution of fibres, punch density and the contraction during finishing is responsible for the formation of pores (Midha 2003). A good filter should have high compactness, low air permeability, reasonable strength and low elongation (Balasubramanian et al 1993). A proper understanding on the role of the process parameters is required for designing a suitable filter fabric. In this paper, the effect of machine parameters like depth of penetration and punch density, process parameter i.e. calendaring, along with multiple layers of needled fabrics on fabric density, air permeability, breaking force and breaking elongation has been discussed.


2. Experimental


Crosslaid fabric samples of 200 g/m2 were prepared on a 3m wide needle punching machine using 15x18x36x3.5 RB needle board. First set of samples (Needled fabrics) was prepared from 6 denier hollow polyester fibres of 65 mm fibre length. Second set (Multilayered fabrics) was prepared by layering 100 g/m2 of 6 denier hollow polyester fibres between two layers of 50 g/m2 of 1.2 denier polyester fibres of 38 mm fibre length after preneedling at a punch density of 50 punches/cm2 and 8mm depth of penetration. Both set of samples were then calendared at a temperature 180oC with delivery speed of 1m/min. The samples were tested for fabric weight per unit area, fabric thickness, air permeability, breaking force and breaking elongation as per ASTM standards. Fabric density was calculated as the ratio of fabric weight per unit area and fabric thickness.


3. Results and Discussion


Table 1 shows the properties of needled and multilayered needlepunched filter fabric.


Table 1: Properties of needled and multilayered needled fabric filters



 

3.1 Fabric density


Fabric density increases with increase in depth of penetration, but punch density does not have any significant influence on the fabric density. A decrease in fabric thickness with increased depth of penetration is observed, due to Parameters Needled fabric Multilayered needled fabric the reorientation of fibres and the greater pressure exerted on fibres remaining in horizontal plane by the fibrous arcs between adjacent tufts as they are pulled further into the web. This causes compression of the web and increase in fabric density. Fabric density is highest for the multilayered needled fabric and lowest for the needled fabric, because more number of fine fibres at the surface are pulled deep into the structure leading to increased compactness. The fabric density increases significantly after calendaring for needled fabric samples, but fabric density decreases after calendaring for multilayered needled fabric samples, as shown in Figure 1(a).


3.2 Air permeability


Air permeability is not at all influenced by punch density but slightly increases with increase in depth of penetration. Multilayered needled fabric shows significantly lower air permeability as shown in Figure 1(b), because of increased compactness of the fabric. The air permeability decreases after calendaring for needled fabric, and increases after calendaring for multilayered needled fabric.



3.3 Breaking force


Breaking force increases initially and then decreases, as depth of penetration or punch density increase. Multilayered needled fabric shows lowest breaking force, however no clear cut effect of calendaring is observed on the breaking force of the fabric as shown in Figure 2 (a).


3.4 Breaking elongation


Breaking elongation decreases with increase in depth of penetration and punch density. Multilayered needled fabric shows significantly lower breaking elongation as shown in Figure 2 (b). Calendaring has a different effect on breaking elongation for needled and multilayered fabrics, breaking elongation decreases after calendaring for needled fabric and slightly increases for multilayered fabric.



 

4. Conclusions


As depth of penetration increases, fabric density and air permeability increase, breaking elongation decreases. Punch density does not have any influence on fabric density and air permeability, whereas breaking elongation decreases as punch density increases. Breaking force and breaking elongation decreases after initial increase as depth of penetration or punch density increases. Fabric density increases, air permeability and breaking elongation decreases on calendaring. Multilayered needled fabric shows higher fabric density, lower air permeability and low breaking elongation as compared to needled nonwoven fabric filters.


5. Acknowledgment


This research was funded in part through a grant by MINISTRY OF HUMAN RESOURCE DEVELOPMENT, GOVERNMENT OF INDIA. The author wishes his sincere thanks for the same.


6. References


1)    Balasubramanian, N., Rakshit, A.K. & Patil, V.K. (1994), Some critical manufacturing parameters affecting the properties of nonwoven dust filters, Indian Journal of Fibre & Textile Research 18 (1994) 209-215.

2)    Midha, V.K. & Kothari, V.K. (2003), Gas filtration using textile Filters, The Indian Textile Journal 113, 9-17.

3)    Naik, A. (1983), Textile filter media-II, The Indian Textile Journal 93, 73-77.


About the Author:


The author is associated with the Department of Textile Technology, National Institute of Technology, Jalandhar, India.



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