The filter cloth plays a very important role in the operation of filter presses. In both chamber filter presses and frame filter presses, it is the textile-based filter cloth that separates the different materials, based on the particle size.
The filtration process
When initiating the filtration process, the first step is the loading of the material itself, the sludge, into the equipment. If necessary, pre-filtration is carried out, followed by washing and post-pressing. This involves the introduction of high-pressure air or water into the membranes of the filter press, which causes the plate to expand and compress the sludge collected in the chambers of the filter sheets.
A high-pressure blow-off removes the filtrate collected in the filter sheet bundles and the layers of the channels. This is followed by draining, which means that the excess water, the unwanted liquid, is removed from the system using a pump. The complexity of the process depends on the situation, if it is a simple filtration, pre-pressing, washing and post-pressing can be omitted.
What do you need to know about filter cloths?
The filter cloth's role in this process is the filtration itself. The properties and parameters of the filter cloth determine fundamentally which elements it filters out, i.e. what becomes sludge and what leaves the filter.
The filter cloth is held in place by the filter sheet, which is shaped to allow the formation of sludge deposits and has holes to help the material flow away. The filter sheets form the filter sheet bundles, which are called head sheets, end sheets and intermediate sheets, depending on where the filter sheet is located.
Filter sheets can also be grouped by function. These include chamber flaps, membrane flaps, wash flaps and other special solutions. The usability of filter sheets is determined by various parameters, such as their dimensions, the location of the drainage channels, the chamber volume, the maximum pressure, the dimensions of the filter surface and the quality of the material.
The filter cloth thus creates a filter surface on both sides of the press plate, and these materials can therefore be produced in both fold-over and fold-through versions.
What are filter cloths made of?
Filter cloths are typically made from woven industrial fabrics, which can be polypropylene-, polyester-, cotton-, polyamide- or fluoropolymer-based.
The properties of the filter cloth are determined by the material itself. For example, the fibre structure, which can be mono- or multifilament, the fibre thickness, the weaving method, the production technology, the density, the pattern, the surface design and finally the breathability is essential. To obtain a satisfactory final filtration result, the above parameters must be combined.
Filtration fabrics can also be used in specific situations. If, for example, extremely high temperatures or extreme PH are to be expected, a fabric made of heat-resistant fibres should be chosen as the material for the cloth. All fabrics are prepared to withstand high temperatures and are treated with a thermofixing process to ensure that the size of the canvas does not change.
It is also essential that the flaking process is carried out with the appropriate efficiency. To achieve this, the filter fabrics are smoothed and calendered, i.e. pressed between two rollers, but it is also possible to weave monofilament fibres between the multifilament fibres.
Makrofilt also offers a solution for filter cloths: filter cloths in flow meters, filter cloths tailored to narrow plates, and customised filter cloths.
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