1、 Filter type

There are many types of liquid filtration filters, which can be basically divided into two types: surface filtration filters and deep filtration filters.

1. Surface filtration type filter cartridge

Surface filtration type filter cartridges capture pollutants on the surface of the filter cartridge. Once the surface of the filter cartridge is blocked by pollutants, it cannot continue to be used, so the service life of surface filtration type filter cartridges is short. Although surface filtration type filter cartridges are often considered to be able to be backwashed and reused by mixing liquid and compressed air together, this method cannot completely flush the filter cartridge. Because during backwashing, the flushing fluid always passes through the area with low resistance on the filter element first. When a certain part of the filter element is flushed clean and unobstructed by the flushing fluid, this part of the channel on the filter element becomes the channel with low resistance. Then all the flushing fluid will flow through these channels, and other parts will become more tightly blocked, resulting in smaller pores. A good way to completely rinse the filter element is to use ultrasonic cleaning, using pure water as the cleaning solution, but ultrasonic cleaning is more expensive; Chemical dissolution method can also be used, for example, when the pollutant is acid soluble, dilute acid cleaning can be used. However, this method may cause corrosion and expansion of the filter aperture. Therefore, the filter element cleaned by this method needs to be rinsed with pure water and inspected to be qualified before it can continue to be used. Among the filter cartridges used for electroplating solution filtration, the earlier sintered polyvinyl chloride filter rods, as well as the currently used polypropylene melt blown filter cartridges, polypropylene PP filter paper, pure wood pulp filter paper, etc., are all surface filtration filter cartridges.

2. Deep filter element

Cleaning the filter element is very troublesome, but increasing the filter element's dirt holding capacity and extending its usage time can reduce the frequency of cleaning the filter element. Deep filtration type filters can achieve this. During the use of deep filtration type filter cartridges, pollutants are intercepted in layers according to particle size inside the filter cartridge, so the filter cartridge has a high slag load capacity, a long service life, and can maintain the nominal filtration accuracy of the filter cartridge for a relatively long time. There are many materials used to make filter cartridge structures, so this type of filter cartridge can be almost suitable for filtering liquids and gases of various properties. The main filter used for electroplating solution filtration is a wire wound filter made of polypropylene, commonly known as a cotton core. Its advantages include: a smaller pressure difference can achieve a larger flow rate, high filtration accuracy, long service life, and the ability to maintain the accuracy of the filter element for a longer period of time during the filtration process.

2、 Structural characteristics of wire wound filter element

When making a wire wound filter element, cross wrap the specially made coarse yarn with fluff on the porous skeleton and roll it layer by layer to the required specified diameter. The rovings are continuously cross wound on the skeleton, forming a filter layer containing thousands of diamond shaped holes. The diamond shaped holes on the filter layer near the skeleton on the filter element are smaller, and the larger the diamond shaped holes, the larger the diamond shaped holes on the outer layer. The diamond shaped holes are connected inside and outside to form a channel. In order to increase the flow of liquid in the filter element, the diamond shaped hole channels are curved and scattered, but the diamond shaped holes in each layer are still connected. The curvature prolongs the diamond shaped hole channels, which is equivalent to increasing the thickness of the filter layer and improving the filtration effect. This is where the deep filtration of the filter element lies. The yarn is wrapped with certain parameters, and a diamond shaped curved filtration channel is formed inside the filter element from the surface to the inside and from large to small. The size of the diamond shaped holes in the inner layer of the filter element is the key to determining the accuracy of the filter element. The smaller the diamond shaped holes, the higher the accuracy of the filter element produced; The larger the diamond shaped hole, the lower the precision of the filter element produced. Legitimate filter production enterprises have specific filter precision and diamond hole quantity comparison tables, where different channel numbers represent different filter precision. Normally, the accuracy of 8-channel is 100 μ m, 15 channel is 20 μ m, and 19 channel is 10 μ m.

image

3、 Characteristics of wire wound filter element filtration

Another characteristic of the wire wound filter element is that it can pass through a larger flow rate. Each type of wire wound filter element with different filtration accuracies has a fixed number of channels D. After the filtration accuracy is determined, the number of channels L increases or decreases according to the length of the filter element.

The formula for the total number of channels is: Total number of channels=D × L × 2.

Taking a filter element with a length of 250 mm as an example, its filtration accuracy is 20 μ m, and the number of channels on its diameter is 15, while the number of channels along the longitudinal length of the filter element is 51. Therefore, the total number of channels on the filter element is 15 × 51 × 2=1530, which means there are 1530 independent channels on the filter element. If the filtration flow rate is 0.5m ³/h (taking clean water as an example), which is 8.3 L/min, the liquid is dispersed and flows into 1530 independent channels for filtration, and the flow rate in each channel has actually decreased to 5.4 mL/min.

If the filtering accuracy is 3 μ m, the number of channels is 27, and the number of channels is 91, then the total number of channels on the filter element is 27 × 91 × 2=4914 (pieces). Therefore, for a filter cartridge with a precision of 3 μ m, although the filtering medium (i.e. fiber fluff) becomes denser, the number of filtering channels increases to 4914, and the flow rate inside the channels is only 1.7 mL/min. At this time, the flow rate can be called "siphon flow".

It can be seen that the wire wound filter element can pass through the filter element with a large flow rate, but the filter element can still maintain its * * * filtering performance under a small pressure difference in a decentralized flow structure. This structure of the filter element is also conducive to filtering out colloidal or gel substances in the liquid. Wire wound filter element can filter out particles much smaller than the pore size with larger filter holes, so it is often referred to as precision filter element.

4、 Selection of wire wound filter element

Due to fierce competition, most filter manufacturers are competing to reduce costs, and their main methods and adverse effects include:

1. Simplify the winding method. Although it has improved production efficiency, it has caused a large number of blockages in the filter channels of the filter element, resulting in blind holes (simplifying the winding method will cause the surface diamond holes to be intercepted by the lower layer of yarn, forming blind holes), causing the wire wound filter element to degrade into a surface filtration type filter element.

2. Change the inner and outer diameter standards and reduce the thickness of the filter element. Although this can save yarn raw materials, it will lead to thinning of the filter layer, shortening of the filter channel, deterioration of the filtering effect, and reduced stability.

3. Use inferior raw materials. Although this can reduce costs, it can cause corrosion of the filter element. Therefore, when choosing a filter cartridge supplier, it is necessary to examine whether they have a complete filter cartridge quality management mechanism and the ability to ensure filter cartridge quality. When selecting a wire wound filter element, the following issues should be noted:

A、 Check if the filter holes of the filter element are fully connected. The filter element with a large number of clogged holes and blind holes has lost the effect of a wound filter element.

B、 Check the inner and outer diameters of the filter element to see if the filtering layers have been reduced.

C、 After using for a period of time, observe whether the yarn and skeleton of the filter element are corroded. Corrosion not only weakens the filtering effect, but also causes contamination of the electroplating solution.

5、 Application fields of wire wound filter element

Due to its high flow rate, low pressure difference, suitability for low viscosity media, and strong corrosion resistance, wire wound filter cartridges are often used as pre filters for high flow pure water systems, for the treatment of wastewater and circulating water in power plants and steel plants, in the food industry such as the filtration of edible oil and vegetable oil, and for the filtration of various slurries such as syrup and chocolate. In addition, in the treatment of chemical industry preparations, such as the filtration of electroplating solutions, paints, oils, coatings, mechanical oils, cutting oils, heavy oils, and fuels, high viscosity resins and oils, and pharmaceuticals, they also have efficient applications.   

Due to the structure of the wire wound filter element being designed to prevent fibers from wrapping around the skeleton, it has a higher filtering pressure bearing capacity compared to general filter elements, while not losing pressure and having a longer service life. The non-toxic and harmless nature of polypropylene fibers, as well as the non adhesive processing technology of hot melt, make this filter element very suitable for the food and beverage industry.   

The production of mineral water, syrup, alcohol, edible oil, beverage water, cola drinks and other products often requires the use of wire wound filters. Industries such as pure water, organic solvents, printed circuit boards, electroplating, and the medical and health fields all have a high dependence on wire wound filters.   

Wire wound filter can effectively remove suspended solids, particles, etc. from liquids. High flow rate with minimal pressure loss. High filter residue load and long service life. Can withstand high filtration pressure. According to the properties of the filtered liquid, there are various materials available for the filter element to choose from, ensuring good compatibility between the filter element and the filtrate.

6、 The filtration principle of wire wound filter element

In addition to the interception effect of the aperture grid formed by the overlapping of filter fibers, the wire wound filter also includes the hooking effect of fibers on the channel wall and the sedimentation effect of particles in the channel.   

1. The hooking effect of fibers on the filter channel wall

The liquid flows from the outer layer of the filter element through a narrow, long, and curved channel into the inner layer. The walls of the filter element channel are covered with curled fiber fluff, which can hook particles in the liquid and trap them in the channel.

2. The sedimentation of particles in the filter channel

The channel of the filter element is narrow, long, and curved. When the liquid passes through at a certain flow rate, it repeatedly collides with the channel wall, and the particles in the liquid gradually deposit in the channel, just like the sludge deposited when river water flows through the bend of a river channel.

3. Filtering principle

The liquid to be filtered is pressurized through the inlet of the filter, passes through the filter layer from the outside to the inside through the filter element, and is filtered into a clear liquid, which is then discharged through the outlet. Impurities are trapped in the deep and surface layers of the filter element, thereby achieving the purpose of filtering the liquid.

The liquid first enters the lower part of the filter housing through the inlet pipe, and then flows through the filter element from the outside to the inside. At this time, coarser particles will immediately settle down and be discharged through the drain valve, while smaller particles will be intercepted by the filter element. **After the clean liquid is collected by the filter tray, it flows out through the outlet pipe. The liquid to be filtered flows into the wire wound filter element, and then splits inside the filter element. After filtration, emulsification, water molecule growth, and aggregation, the filtered liquid flows out from the outlet, impurities are trapped in the filter element, and the aggregated water droplets settle in the sedimentation tank and are discharged through the drain valve.

4. Maintenance of wire wound filter element

A、 When using dust removal filters (PP filters, wire wound filters), it is necessary to prevent particulate matter from entering the interior of the filter, blocking or jamming the system.   

B、 After using for a period of time, it is necessary to maintain and upkeep the filter element.    

C、 It also needs to be cleaned regularly. After prolonged use, the filter element will accumulate a large amount of impurities or other pollutants in the system, and needs to be cleaned to fully utilize its function.   

D、 To ensure that the filter paper is always in a moist state and cannot dry out, thereby extending its usage time and ensuring filtration accuracy.   

E、 Through fiber filtration, dust easily enters the dust storage device in the dust removal filter element, and then undergoes back blowing to remove the viscous substances on the filter cartridge. This does not affect the filtering effect of the filter cartridge and can better protect the environment, greatly extending its service life.