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