Bag filter selection is a critical element of a successful dust control system. Factors such as operating Liquid Filter Bag temperature, dust loading and physical characteristics of the particulates are important in selecting a fabric material that will provide optimal performance.

Typical materials include standard and acid resistant aramid fabrics (Nomex), felt, PTFE, and P84. P-84 works well in high pH applications and resists acid attacks and flex abrasion.
Needle Felt

Needle felt filter bags are a critical part of industrial filtration systems. They are made from densely packed fibers that create a permeable barrier through which liquids can flow while trapping particles. They are used in a variety of industries, including pharmaceutical processing, chemicals, and coal-fired power plants. Needle felts are durable and highly effective in removing abrasive, coarse materials. They can also be customized to meet specific application requirements. They are available in different material constructions and micron ratings, as well as with welded or sewn seams.

Needler felts are woven from standard synthetic fibers or specialty high-temperature fibers such as Nomex and Aramid. They offer high dirt holding capacity, strong corrosion resistance, large flow and convenient operation. Moreover, they are easy to install and have a long service life. Besides, they are characterized by excellent thermal stability and good chemical resistance.

The three-dimensional structure of the needled felt enables deep filtration, which separates coarse particles on the surface from fine ones in the depth of the fibers. This leads to a higher solids capture efficiency. Felts have a unique manufacturing advantage over woven fabrics in that they can be developed by altering efficiency, permeability, basis weight, scrim design and finish to customize media for specific end-use applications. This capability allows smaller, specialized lots of felt to be produced more economically than a conventional woven fabric that requires larger minimum runs, adding cost and inventory risk to the process.

Felts can be treated with various methods to improve performance and durability, such as glazing or chemical treatments. During the glazing process, felts are smoothed by mechanically rubbing them against each other. The resulting smooth surface facilitates cake release, a key factor in efficient filtration. Durable chemical treatments, such as PTFE and fluorocarbons, are often used to coat the surface of the felt and improve its ability to resist abrasion and corrosion.

Needle felts should be cleaned and maintained regularly to keep them in optimal condition. This maintenance should be done with caution as the bags may contain hazardous substances that can cause injury or illness. Cleaning and maintenance of the bags should be conducted according to the manufacturer’s instructions. They should be kept away from direct sunlight or heat, and they should be regularly washed to remove any contaminants. Lastly, they should be kept in a cool and dry place to ensure their long lifespan.
Nonwovens

Nonwovens are the new kid on the block, a relatively recent technology that has opened doors for everyday convenience that were unthinkable not too long ago. From disposable wipes that clean machine tools and oil-covered hands to specialized air filtration in automobiles and helicopter cabins, nonwovens are making products possible that were only dreams or wild imagination not so long ago.

Nonwoven fabrics offer a huge spectrum of achievable characteristics through fabric selection, web formation and bonding techniques and are used in a wide variety of markets including medical, apparel, automotive, construction, filtration and geotextiles. The versatility of nonwovens also allows them to be reverse engineered based on specific functional requirements.

Spun-laid nonwovens, which are manufactured from polymer granules through extrusion into filaments that are then heat and quenched to form a continuous web, are the most common type of nonwoven. These can be made from either natural or manmade fibers with options for co-extrusion that lead to bico filaments which allow the addition of more properties to the web such as strength, water resistance, tensile strength and softness. The most common raw material is PP.

Hydroentangled nonwovens use a similar process to spun-laid nonwovens but the polymer granules are pre-formed into bundles that are entangled together by an electrostatic charge. This creates a mat of individual fibers that are very dense and have a high porosity. This mat of individual fibers provides excellent mechanical and acoustic properties for filter medias and also offers low pressure drop.

Needlepunched and meltblown nonwovens are also available in a number of different configurations to meet a range of filtration needs. For example, Vliesstoffwerk Sandler GmbH, Schwarzenbach/Sale, Germany, offers traditional thermal bonded and needlepunched media as well as brand new meltblown media designed for a variety of applications. The company's products are designed for self-supporting dry, dust and HVAC filtration as well as liquid and automotive filtration.

The newest of the company's offerings is a multi-layered, high-efficiency meltblown product that was developed specifically for air filtration in helicopter cabins. This product, named CombiFil, uses a combination of ultra-fine and coarse polyester filaments that provide depth filtration. This results in lower pressure drop, a long service life and energy savings.
Polypropylene

Polypropylene is a durable, flexible thermoplastic material that has numerous uses. It’s used in a wide variety of industries, including manufacturing, textiles and packaging. It can be recycled many times, without degrading significantly in quality. It also has excellent fatigue and chemical resistance, as well as a good softening point. Polypropylene is easy to work with, making it a popular choice for things like bottle closures and hinges that attach lids to bottles.

During production, raw polypropylene goes through a process called extrusion. This involves heating and shearing it, which creates long, narrow filaments that resemble silk. These filaments can then be rolled into yarns or used as an input for non-woven bags. Some manufacturers use a special process that allows them to make extra-fine filaments. This creates a filter medium with an extremely fine, consistent structure that has better filtration efficiency.

It’s possible to get a broad range of finishes and treatments on these filter bags, which can increase their useful life. For example, a hydro-oleophobic coating can help resist water and oil. This can reduce cleaning frequency, lower maintenance costs and improve fluid handling. Other treatments include singed, glazed and calendered finishes. These processes reduce fiber migration and provide other benefits, such as dimensional stability and improved dust cake release.

Depending on the application, you can choose from different thicknesses of these bags. Thicker bags can offer more flow resistance, while thinner bags are better suited for liquids that aren’t thick enough to cause damage to the bag or equipment. It’s important to find the right thickness for your specific application, as it will impact your total operating cost.

Polypropylene is often combined with other materials to boost their strength and performance. For example, it can be laminated to BOPP film to make stronger, more flexible woven bags. This is especially helpful for applications where the bags are handled or transported frequently. It’s also possible to use block or random polypropylene copolymers. Block copolymers have ethylene and propylene monomer units arranged in a regular pattern, which gives them more strength and stiffness than random copolymers.
Polyester

Polyester is a type of synthetic fiber that was developed by DuPont in the 1940s. It is used in a wide range of industrial applications, including air and water filtration. It is available in many micron ratings and can be made into different shapes to fit a variety of filter bag styles.

Polyester can be a good choice for industrial liquid filtration because it is inexpensive and works well in most conditions. It is also highly durable and can be reused for a long time. It is non-flammable, ozone and acid resistant, and can hold up to high temperatures. It is also resistant to abrasion and can resist flexing.

In addition to being affordable and versatile, polyester is also eco-friendly. It is produced from fossil fuels, such as coal and petroleum. These are limited resources that must be protected from overuse and waste. Using fossil fuels to produce polyester harms the environment because it releases carbon dioxide, a greenhouse gas that traps heat in the atmosphere and causes global warming. The good news is that newer polyesters are being created from plant-based materials, which could be a step in the right direction for this harmful material.

Whether you choose a standard or custom-made filter bag, it is important to make sure that the fabric matches the application. Filter bags made from the wrong type of material can cause problems that will affect filtration performance and efficiency. This may result in clogged filters, increased maintenance costs, or a higher energy bill.

Liquid process slurries can be extremely dirty, so you need to ensure that the filter bags are able to handle these harsh substances. For example, if you are working with a highly corrosive substance that can damage the mesh of your bag, it is important to use a thicker bag.

You can find a large selection of liquid filter bag sizes and types online. However, it is usually best to work with a distributor or supplier who can provide expert advice on the best solutions for your specific needs. They can also work with you to design and manufacture custom bags within a set time frame.