Filter press cloth production, press filtering

Filter presses are used in many fields of industrial processes for liquid filtration, where a physical operation (in this case, pressure) is used to separate water, the liquid phase, from the feed. One of the commonest forms of filter press is the wide range of sludge filters, which are used to remove water from various types of sludges, including usage in sewage treatment.

The sludge fed into the system generally has a water content of 50-60%. Following the operating principle of the installation, the wet sludge enters filter cassettes that slide along a rod and are lined with a filter medium or filter fabric. During the filtration cycle, a pressure of 10-20 bars is applied to the filter cassettes, the filtered water is drained into collection channels, then the resulting sludge cakes fall out of the appliance in the evacuation phase.

This procedure can be operated in stages, though the cycle time is relatively long and a comparatively low filtration efficiency can be achieved. Belt press filters have been developed for the same purpose, but they operate continuously rather than in stages. In addition, belt filters use a combination of physical effects (gravity, vacuum and pressing) to remove water from the feed.

The filtering materials used in these types of frame filter presses and recessed plate filter presses are textile-based filter cloths, press cloths or belt filters. The press cloths we provide are designed and configured in accordance with the geometrical features of the press and the press plate.

The press cloth is usually made of a durable, woven industrial fabric, such as:

• polyester
• polypropylene
• polyamide
• cotton
• etc.

In the fabrics used for press cloths, the filament structure (monofilament or multi-filament), relative density, weight, weave pattern and surface treatment are determinative.

The basic materials used in various types of press cloths and belt filters perform well under different conditions. The most important factors to be taken into account are as follows:

• the highest temperature of the sludge feed
• the maximum pressure during filtering
• physical effects, forces, and the erosive effects of the filtered feed
• the chemical properties of the sludge

When producing filter press cloths, it is important that accessories suitable for usage conditions be incorporated. Seals are used in many cases to ensure watertight connections, with stainless or galvanised steel rings included to hold the press cloth in place. Care must also be taken that the thread used for sewing has similar properties to the cloth.

In other respects, filter press cloths are made in a similar way to clothing: a pattern template is first made from an existing press cloth or using the dimensions of the filter appliance, then the filter textile is cut to size with the help of the pattern. These processes are naturally performed digitally nowadays, allowing all data to be stored and subsequently retrieved for any post-orders. The fabric is cut into shape using a thermal technique in order to prevent unravelling. After cutting, the product is sewn together and accessories are attached.

More information on » Belt filters and filter press cloths for filter presses

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