Filter Yarn Selection
Proper yarn selection is critical in the design of filtration fabrics as both the warp and fill yarns contribute specific properties to the filter fabric. Both yarns must be compatible for optimum cover uniformity producing a quality defect free fabric which when finished will be stable and uniform in filter efficiency as well as flow rate.
Warp yarns provide the tensile strength in the vertical direction as well as establishing the cake release characteristics. Warp yarns are generally smaller in size and woven closer per inch than fill yarn. They will generally have more twist per inch. It is the combination of the higher twist per inch and higher thread count that create the cake release characteristic. This also establishes the higher tensile strength in this direction.
The fill yarns establish the filtration (retention) qualities. These yarns may be larger and have less twists per inch. Decreasing the twist will increase the yarn "cover" and improve filtration efficiency. When designing the fabric warp and fill yarns, it is important that the ratio of warp and fill yarn sizes, as well as twists, be considered as they must complement each other and not distract from each other's performance contribution. For example: extremely large fill yarns could reduce the cake release qualities of significantly smaller warp yarns.
Proper filter media selection is a critical factor in the overall filtration performance in any liquid filtration application. The chemical and physical conditions of the slurry as it reaches the filtration machinery, and any subsequent operations that may be carried out, such as washing or steam blowing determines the type of material to be used. Resistance to acids, alkalis and solvents is relative. It is commonly greater with low concentrations and temperatures, and it most often decreases as those measures rise. To determine the best filter media for a specific application, the mechanical and physical forces to be applied as well as the desired characteristics of the final product must be carefully analyzed.