Filter Cloths for Tower Press Filters

Wide selection to best suit your filtration process

A wide selection of filter cloths enables you to choose the right type of cloth for individual application, minimizing costs and maximizing production. Roxia filtration professionals will provide you with the best long-term solutions.

Filter cloth: the essence of dewatering

The filter cloth is an important component in all tower press filters in the world. The solid-liquid separation is done by the filter cloth. Later on, the cloth acts as a conveyor belt and discharges the cake from the chambers. These two different functions require a number of special properties from the fabric. In the filtration process, the permeability of the fabric and other filtration technical properties are important. In the disassembly phase of the filter cake, while the fabric acts as a conveyor, its strength properties are decisive.

Thanks to Roxia’s expertise on tower filter press cloths, our professionals can help select the most suitable type of filter cloth for a certain application.

If the filter cloth does not fit the application, it does not help if the tower press has the latest hydraulic or PLC automation systems. The filter cannot reach the maximum production level with the wrong type of filter cloth. Let us assist you to choose the optimum cloth for each application.

Tower press filter cloth duties

In tower press filters, the filter cloth has several different duties. The entire pressure filtration cycle has numerous phases and each of them affects the cloth.

1. The first duty of a tower press filter cloth is to hold and wait for all filter chambers to fill up with slurry. During the feeding phase, a filter cake forms on top of the filter cloth. This would not happen if the selection of the cloth is wrong or if there are many holes in the cloth.
2. In the diaphragm pressing phase, the filter cloth is subject to immense pressures up to 16 bar. The filter cloth is pushed deep into the polypropylene grids while carrying a heavy cake.
3. During the air drying stage, the pressurized air flows into the chamber above the cake. Air passes through the cake and dries it. In this phase it is important that air permeability of the cloth correlates to the filter application.
4. Then the filter cloth changes its role from filtration to discharge. Heavy cakes can weigh up to 20 tons/cycle. Filter cloth acts as a conveyor belt and simultaneously discharges the cakes from each chamber in 30 seconds. The cloth is then cleaned by the scrapers and washed from both sides before the next cycle repeats. At this point, cloth tracking needs to be impeccable, otherwise it can cause problems and interrupts the filter cycle.

Evaluation of filter cloth’s properties is performed with an electron microscope.

Strength

One of the biggest differences between regular filter press cloths and tower press filter cloths is strength. As described above, the tower press filter cloth also works as a belt. It has to be strong enough to carry heavy cakes out from the filter and withstand being pressed deep into the supporting grids, over and over again.

The strength of the filter cloth also affects its tracking. If the fabric is not strong enough, it can deform over time and cause tracking problems. Eventually, this can lead to premature filter cloth damage.

To showcase how strong are the tower press filter cloths, let’s look at an example. The production of big tower press filters in mining concentrate applications is often 20 tonnes per cycle. On average, the filter cloth is in use for 6000 cycles. This means that during its lifetime, a filter cloth discharges 120 million kilos!

Air permeability – how to choose the most optimal filter cloth?

The mining industry’s milling technology keeps improving and is reaching better and better ore recovery. Consequently, the particle size has decreased and nowadays filter cloths tend to blind too early. In lots of applications using a cloth with higher air permeability can solve this issue.

But take extreme care when deciding upon air permeability. Using a filter cloth with too high permeability can cause more solids will appear in the filtrate which can lead to tears, holes and overall loss of cloth’s mechanical strength.

Choosing the optimal filter cloth for each application is important because it can:

• Increase filter’s capacity
• Reduce blinding problems
• Shorten the tower press filter cycles

Roxia filtration test team provides you with all the data to make an informed decision for the best long-term solution.

Cloth blinding

How to know when is the filter cloth blinding? One of the most common signs are:

• Thinner filter cake
• Wetter filter cake
• Increased cycle time

With use, every tower press filter cloth will eventually start to blind. But since the filter cloth is an expensive and essential part of the tower press, it should not happen too early! To avoid blinding problems, start at the beginning with the correct filter cloth selection. Other factors which affect the blinding are particle size distribution of the slurry and chemical changes in the process.

Roxia can help you select the correct cloth to avoid such issues. We offer laboratory services for used cloths where we perform a full analysis and give professional recommendations for the most suitable filter press cloths for each process. Our experts assist in eliminating your process challenges and find better solutions.

Filter cloth quality

The quality of a tower press filter cloth is directly connected to the consistency of its air permeability. It must be equal at every point of the cloth, even in the largest sizes (148 m long and 1,7 m wide).

Ensuring equal air permeability is related to quality control, specific for the tower press filter cloth manufacturing process. This is a demanding job but Roxia understands the importance of high quality and eliminating possibilities of weaving errors. All our tower press filter cloths are manufactured with the latest technology textile industry machinery with integrated quality check procedures.

Seams for tower press filter cloths

Tower press filter cloths are usually longer than 100 meters they are delivered in a roll. The correct installation requires to first run the entire filter cloth through the tower press  At the same time, the old cloth is run out from under the filter. Then both ends of the new filter cloth are connected with metallic seams and seam wires and form a continuous belt.

Special metallic hooks are already installed on both ends of the cloth in the factory. There are several different seam hook types that are specially designed based on the applications.

Seam challenges

Metallic seams are run out of filtration chambers with the help of sensors of tower press filters. Unfortunately, sometimes this can cause seam damages and then too many solids are passing through the filter cloth seam.

Roxia has a solution to easily replace damaged seams. With the Roxia seaming machine, it is fast and much more efficient to make a new seam on the spot, right after the issue is identified. In this way, the tower press filter cloth’s lifetime is maximized and can be used until it is completely worn out.

Reinforced edges by Roxia

Roxia tower press filter cloths have special, strong edge reinforcement to prevent them from fraying when tracking is not completely correct. Improper tracking occurs when rollers are worn out or not aligned. Built up rollers can also cause tracking problems to the cloth. This happens when the cloth is not properly cleaned and slurry builds up between the cloth and rollers.

When the filter cloth is not properly tracked, it starts to touch metal parts of the filter (eg.  roller brackets) and the cloth can fray.

Frayed cloth has a shorter lifetime and means increased filter spare part costs. To prevent this from happening, Roxia offers tower press filter cloths with extra strong edges able to withstand the most demanding applications.

How to fix holes in the filter cloth?

Roxia tower press filter cloths are super strong –   have a tensile strength of more than 400 kN/m. However, this does not mean they cannot tear. Filter cloth and other technical textiles can still be damaged by sharp pieces or corners which create a hole (also known as a mechanical hole).

Tower press filters should be not used if there is even one hole in the filter cloth. Why? When there is a hole, it means the solids are passing through and wear down the other filter spares. The hole is gradually getting bigger and bigger and causes more and more problems to the tower press.

Industrial Filter Cloth Patches

This does not mean the entire filter cloths should be changed immediately. There is a better and more cost-efficient solution developed by Roxia: Industrial Filter Cloth Patches. The patches are 2-sided and design to cover the most common shapes and hole sizes. Patching is fast and follows only one installation principle. It is easy to learn and it can be done on the spot by filter operators or other selected staff. There is no need to worry patched will be scraped off by the scrapers as they become one with the cloth’s surface.

Nevertheless, keep in mind patches are only a fast solution to a bigger problem. The real reason for these holes should be found and fixed as soon as possible. Roxia filter service engineers can perform a filter audit and discover the reasons for filter’s issues and suggest solutions. Roxia has a wide selection of all spare parts for tower presses. From plate seals and all other consumable spares, to complete plate packs.

Roxia filter cloth categories are based on different needs:

Light-Duty – lighter applications

• Open and thinner structure, perform better against blinding
•  5 different permeabilities

Standard – common applications

• More durable than widely used filter cloths.
• 9 different permeabilities

Heavy-Duty – the most demanding applications

• The most durable filter cloth on the market, engineered to handle the heaviest cakes in toughest conditions
• 3 different permeabilities