The paint and coatings industry relies on filtration technologies to enhance product quality and production efficiency. In an environment where established manufacturing processes may become stagnant, innovative filtration solutions can revitalize efficiency and elevate quality.

Removing solid particles from liquids is often handled by filter bag systems, valued for their simplicity, ease of use and versatility. This technology finds widespread application across industries.

“A range of filter lines is available to meet specific application needs and achieve the best balance between cost and performance,” said Wim Callaert, product manager at Eaton’s filtration division.

Understanding Needlefelts

Needlefelts are among the most common materials used in liquid bag filtration. They are made from staple fibers, typically polypropylene and polyester, which are entangled by needling to form a robust structure. This design creates depth filtration media with nominal efficiency, capable of trapping dirt particles within its matrix. Needlefelt filter media can be sewn or welded with a metal or plastic ring, with each method offering unique benefits.

“Needlefelt media has been around for decades. It’s strong, it works well, and it’s used in a lot of applications because it does most of the jobs needed,” said Callaert. “But there’s always room for improvement, whether by making the media thicker or increasing the surface area in the filters.”

One way to improve needlefelt filtration is by increasing the media thickness, which creates more void space for trapping dirt particles. Thicker media can hold more dirt, extending the filter's life. For instance, thicker versions of standard needlefelts provide similar retention efficiency but can hold two to three times as many dirt particles due to their increased thickness, potentially reducing the frequency of filter changes and associated costs.

Another method to enhance filtration efficiency is by increasing the surface area of the filters. This can be achieved by adding more filters to expand capacity, though this requires additional investment and floor space.

Innovative product designs can also increase surface area within existing housings without significant extra costs or space requirements. For example, filter bags with an inverted core in the center of the basket can provide 65% to 70% more surface area. This design also reduces internal dead volume by at least 75%, minimizing waste when full drainage is not possible.

Increasing surface area within the same housing also decreases the velocity of liquid passing through the filter media. Lower velocity improves the loading pattern of contaminants into the filter depth, allowing for more efficient particle capture and extending the life of the filter.

The filter element inverted core incorporates an additional internal structure made of the same extended-life needlefelt filter material, positioned within the main filter bag. This improves the contaminant loading pattern and reduces fluid velocity through the media without requiring a larger housing.

Cost Analysis of Filtration Processes

Filtration costs extend beyond the initial price of filters, encompassing factors such as maintenance cycles, process downtime, labor, product loss, and disposal costs. The initial investment in higher-capacity filters, although seemingly expensive, can reduce the number of filters needed over time and enable existing filter housings to handle larger volumes, leading to significant long-term savings.

Frequent replacements increase downtime and labor costs, impacting overall efficiency. During maintenance cycles, halting production to change filters reduces productivity, and the associated labor costs can be substantial. The procedure involves stopping the operation, isolating and draining the filter, opening and closing the housing, replacing the bag, cleaning, restarting the system, and managing logistics for both new and used filter bags.

Filtration processes often result in liquid product loss, as filters retain some processed liquid. While this loss may be negligible for inexpensive liquids, it can become significant for high-value substances such as paints, chemicals and pharmaceuticals. Disposal of used filter bags and their contents can also be costly, particularly when dealing with chemical waste requiring special handling and disposal procedures. These comprehensive cost factors highlight the importance of understanding and managing the total cost of filtration processes to optimize operations, achieve greater efficiency and realize substantial savings.

More to Consider

Environmental Hazards
In many plants, system operators must wear protective gear, including masks, to change dirty consumable filter media. Minimizing maintenance intervals is crucial, as volatile organic compounds (VOCs) can be released when opening filtration units for consumable changes.

Maintenance requirements largely depend on the type and capacity of the selected filtration solution. Systems must be designed and adequately sized to operate for extended intervals between changeouts, often targeting weeks or even months.

Batch vs. Continuous Filtration
In batch filtration, optimizing filter capacity to handle entire batches without mid-process changes is essential to prevent interruptions and time losses. On the other hand, continuous filtration benefits from extending intervals between filter changes to improve efficiency. Fixed intervals, such as at the end of shifts or days, are often preferred, with the optimal filter choice varying by customer and application. Both methods aim to balance operational efficiency and safety, ensuring seamless production processes.

Matching Filter Bags to Paint and Coatings Filtration Needs

The market offers a wide array of filter bag options from various manufacturers, each designed to optimize filtration processes for improved performance and cost efficiency.

Entry-Level Solutions
For manufacturers seeking a straightforward and cost-effective option, sewn needlefelt filter bags provide an ideal solution. These bags are suited for basic applications and everyday filtration tasks where the goal is to remove relatively low volumes of contaminants effectively, and where high capacity and extended life are not critical considerations.

Constructed from a dense network of interlocking fibers, standard needlefelt in a sewn format achieves reliable filtration performance by capturing particles on both the surface and within the depth of the material. Additionally, the manufacturing process allows for customization in dimensions, materials and configurations to meet specific operational requirements.

Enhanced Performance
For more rigorous filtration tasks, welded filter bags offer enhanced durability and contaminant retention. The welding process eliminates the potential for leakage through needle holes and creates a strong bond at the seams. A matching plastic ring is welded on instead of the metal ring, providing a complete, bypass-free seal. The plastic ring can also be fully incinerated with the used bag during disposal.

Higher Capacity
For applications demanding higher capacity and longer filter life, extended life needlefelt filter bags present a significant upgrade. These bags feature enhanced media thickness, delivering two to three times the dirt-holding capacity of standard options. Their design incorporates a larger void volume that optimizes the filtration process, capturing a wide range of particle sizes throughout the entire depth of the media.

Extended-life filter bags, often characterized by double-thick needlefelt media, are well suited to environments with high contamination loads or fine particulates. These bags can also be constructed with a fully welded design and a matching plastic ring for enhanced performance.

Advanced Solutions
Advancements in filtration technology combine increased surface area with extended life media to deliver improvements in capacity and efficiency. These types of filters are particularly suited for high volumes and continuous filtration processes.

One example is the HAYFLOW™ filter bag concept, which features a unique inner core that acts as an additional filtration surface, enlarging the outer layer and enhancing overall filtration capacity. The reduced internal volume of the filter bag also minimizes the amount of product retained after processing, decreasing product loss. This feature is especially beneficial in applications involving high-value liquids.

Standard filter bags for #2 size bag filter vessels feature a 7-inch diameter opening and a 32-inch length, resulting in a total surface area of 4 square feet. With a maximum flow rate of roughly 176 gallons per minute, operating at half this rate is recommended to ensure a decent lifespan. A filter bag with an additional cylindrical protrusion extending upward from the bottom center increases surface area by 65% to 7.5 square feet. This allows a #2 size bag filter housing to handle higher flow rates more easily and extends the lifespan of the filter bags by three to five times on average.

Maximum Capacity
For the most demanding filtration tasks, pleated filter bags provide an effective solution. Pleating involves folding the filter material into a series of ridges and valleys, significantly increasing the surface area without requiring a larger filter housing. This expanded surface area allows for higher contaminant loading and longer filtration cycles, increasing capacity levels by up to 10 times compared with standard needlefelt bags. Various pleated filters are available for bag housings, offering standard and high-efficiency filtration levels or standard and high-capacity media. 

Oil Absorption
In some applications, an additional process step is required to absorb oil. Traditional filtration systems may require separate stages for particle filtration and oil absorption, leading to more complex setups, additional equipment and higher operational costs. Filters with an extra internal core made of open-matrix melt-blown media can combine particle retention and oil absorption into a single streamlined step.

“Their dual functionality means that a single filter bag can handle both particulate and oil contamination, streamlining the filtration process and reducing the need for separate oil-absorbing filters,” Callaert said.

Optimal Outcomes
Selecting the right filter bag for specific paint and coatings applications is critical to optimizing processes, reducing costs and ensuring high-quality output. The filtration industry offers diverse solutions to meet various needs, including comprehensive filter bag lines that support consistent operations.

Starting a conversation with a filtration expert is the best way to identify the ideal solution tailored to specific requirements.

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*All images courtesy of Eaton.