Advances in Filtration Using Sintered Metal Filters

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Key takeaways:

• Sintered metal filters offer high efficiency in particulate removal, with capabilities for backwashing and long service life.

• These filters are suitable for high-temperature applications and various industrial uses, including chemical and power generation sectors.

• The design and selection of sintered metal filters depend on their particulate holding capacity and the characteristics of the particles being filtered.

• They are advantageous for processes requiring high filtration efficiency, durability, and resistance to corrosive environments.

Abstract

Filtration technology utilizing sintered metal media provides excellent performance for separation of particulate matter from either liquid or gas process streams (i.e., liquid/solids and gas/solid separation) in numerous industrial liquid and gas filtration applications. Sintered metal filter media, fabricated from either metal fibers or metal powders into filtration elements, are widely used the in the chemical process, petrochemical and power generation industries. Applications require particulate removal to protect downstream equipment, for product separation, or to meet environmental regulations.

Sintered metal media provide a positive barrier to downstream processes. Sintered metal media have demonstrated high particle efficiency removal, reliable filtration performance, effective backwash capability, and long on-stream service. These filters can provide particulate capture efficiencies of 99.9% or better using either surface or depth media. Operating temperature can be as high as °C, depending on the selection of metal alloy. Along with the filtration efficiency consideration, equally important criteria include corrosion resistance, mechanical strength at service temperature, cake release (blowback cleanability), and long on-stream service life. These issues are critical to achieving successful, cost effective operations.

The life of such filter media (filter operating life) will depend on its particulate holding capacity and corresponding pressure drop. This accumulating cake can be periodically removed using a blowback cycle. The effectiveness of the blowback cycle and filter pressure drop recovery is a critical function of the properties of the accumulating particles in the cake and the filter media. Depth filtration media configured in a polishing filter may be utilized in those applications with light particle loading.

In addition to providing superior filtration in a single pass, clean-in-place backwashable media reducesoperator exposure to process materials and volatile emissions. While applications include high temperature and corrosive environments, any pressure driven filtration process with high operating costs has the potential for improvement using sintered metal filtration technology.

This paper will discuss filter-operating parameters of sintered porous metal media and filtration system design criteria for optimizing performance in a number of chemical process streams.

Introduction

The 21st century brings many economic and environmental challenges to the chemical industry. Major drivers for change include market globalization, demand for improved environmental performance, profitability, productivity and changing workforce requirements. Future competitive advantage in the chemical processing industry will come from patented technology and technical know-how. New economical high yield and high quality processes will characterize much of the industry's production capacity with improved environmental impact and energy efficiency.

A high percentage of the chemical industry's products and processes involve solids (particulate) handling. Filtration technology offers a means of reducing solids through mechanical separation via patented filter design and unique systems operation. Filtration can improve product purity, increase throughput capacity, eliminate effluent contamination (minimizing or preventing air and water pollution) and provide protection to valuable equipment downstream of the filter. Advances in filtration technology include the development of continuous processes to replace old batch process technology. Cost savings include less hazardous waste for disposal and labor savings from new technology. Fully automated filter systems can be integrated into plant process controls.

Solids reduction includes the removal of suspended solids from process effluent waste streams and cleaning solvents. The liquid product recovered is valuable for recycle to another chemical feed stream. Waste minimization includes the reduction of hazardous solids materials for recovery or recycle and solids reduction of non-hazardous materials to landfill. Filtration can reduce wastewater feed stream BOD (Biological Oxygen Demand), COD (Chemical Oxygen Demand), TSS (Total Suspended Solids), and TOC (Total Organic Carbon). These are the main parameters for which current emissions are measured with regard to local and international standards.

Filtration Fundamentals

Knowledge of filtration fundamentals is essential to ensure appropriate design of filter media and the optimum selection of appropriate media and filter design for each filtration application. Two main filtration modes can be considered, i.e., depth filtration and surface filtration. In the case of depth filtration, the particles are captured inside the media; while in surface filtration they are retained, as the term explains, at the surface where subsequently a cake of particles is formed.

Surface filtration is primarily a straining (sieving) mechanism where particles larger than the pore size of the filter media are separated at the upstream surface of the filter; their size prevents them from entering or passing through the pore openings. Subsequent particles accumulate as a cake that increases in thickness as more particle-laden fluid is forced into the filter medium. The cake, due to its potentially finer pore structure, may aid in the separation of finer particles than can be achieved by the filter media. However, the cake must exhibit sufficient porosity to permit continued flow through it as filtration proceeds. Processes can be run under constant flow/increasing pressure or constant pressure/decreasing flow. Because most surface filters are not perfectly smooth or have perfectly uniform pore structure, some depth filtration can take place that will affect the life of the filter.

Depth filtration is mainly used in applications where small particle levels have to be separated such as in the protection of downstream equipment against fouling or erosion, protection of catalysts from poisoning and in product purification. The particles penetrate into the media and are subsequently captured within its multiple layer structure. This multiple layer structure prevents premature blocking of the media and increases the capacity to hold dirt and on-stream lifetime. Because the particles are captured within the depth of the media, off-line cleaning will be required. This off-line cleaning can be accomplished with solvents, ultrasonic vibration, pyrolysis, steam cleaning or water back flushing. In addition, the media may be pleated, a configuration that minimizes housing size and cost.

Understanding of the ability of a filter to remove particles from a gas stream passing through it is key to successful filter design and operation. For fluids with low levels of particulate contamination, filtration by capturing the particles within the depth of a porous media is key to achieving high levels of particle efficiency. The structure of sintered metal provides a tortuous path in which particles are captured. Particles capture continues as a cake of deposited particles is formed on the media surface; however, particles are now captured on previously deposited particles. The life of such filters will depend on its dirt holding capacity and corresponding pressure drop. For fluids with high particle loading, the operative filtration mechanism becomes cake filtration. A particle cake is developed over the filter element, which becomes the filtration layer and causes additional pressure drop. The pressure drop increases as the particle loading increases. Once a terminal pressure is reached during the filtration cycle, the filter element is blown back with clean gas and/or washed to dislodge the filter cake. If the pore size in the filter media is chosen correctly, the pressure drop of the media can be recovered to the initial pressure drop. However, if particles become lodged within the porous media during forward flow, and progressively load the media, the pressure drop may not be completely recovered after the cleaning cycle.

Filtration rates are influenced by the properties of the feed particle concentration, viscosity and temperature. The filter operating mode can be constant pressure, constant flow rate, or both with pressure rising and flow rate dropping while filtering. Filtration cycle will be constrained if solids are fast blinding and allowable pressure has been reached, or for cake filtration, if the volume for cake buildup has been filled, even if the allowable pressure drop has not been reached. Permeability is expressed as flow rate against pressure drop. Permeability is influenced by filter type, fluid temperature and solids loading.

Sintered Powder Metal Media

Sintered metal media are manufactured by pressing metal powder into porous sheet or tubes, followed by high temperature sintering. A scanning electron photomicrograph of a typical sintered powder metal media is shown in Figure 1. The combination of powder size, pressing and sintering operation defines the pore size and distribution, strength and permeability of the porous element. Pore size of sintered metal media is determined using ASTM E-128. The media grade designation is equivalent to the mean flow pore, or average pore size of the filter. Sintered metal media are offered in grades 0.1, 0.2, 0.5, 1, 2, 5, 10, 20, 40 and 100. The filtration rating in liquid for media grades 0.2 to 20 is between 1.4 and 35 µm absolute. The filtration rating in gas ranges from 0.1 to 100 µm absolute.

Filter cartridges fabricated from sheet or tubes have an all welded construction. The filter media is designed and engineered with a stable porous matrix, precise bubble point specifications, close thickness tolerances, and uniformity of permeability, which assure reliable filtration performance, effective backwash cleaning and long on-stream service life.

Sintered Metal Fiber Media

Metal fiber filter media consists of very thin (1.5 to 80 μm) metal filaments uniformly laid to form a three-dimensional non-woven structure sintered at the contact points. A scanning electron photomicrograph of a typical sintered metal filter media is shown in Figure 2. These media are explicitly designed for either surface or depth filters. Either single or multi-layered construction are utilized with each layer comprised of potentially different diameter fibers to achieve optimal performance, e.g., pressure drop, filtration efficiency, particle loading capacity, and media strength. The multi-layered material has a graduated design, so the dirt holding capacity is much higher and consequently the life expectancy is longer. The final filter rating is determined by the weight per used layer, the fiber composition of the layer and the combination of several layers. The availability of a high porous structure (up to 85%) offers a very higher permeability and hence a low pressure drop.

The properties of metal fiber filters, fabricated from various metal alloys, for gas filtration applications allow the use in extreme conditions: high temperature, high pressure and corrosive atmospheres. The primary benefits of sintered metal filters are: strength and fracture toughness, high pressure and temperature capabilities, high thermal shock resistance, corrosion resistance, cleanability, all-welded assembly, and long service life.

Fiber metal media have a higher porosity than the powder metal media, thereby resulting in lower pressure drop. For high temperature or corrosive applications, Bekaert has developed fibres in other alloys besides AISI 316L. Inconel® 601 and Fecralloy® are used for high temperatures (up to 560°C and °C respectively) whereas Alloy HR can withstand temperatures up to 600°C and wet corrosive environments.

The inherent toughness of the metal filters provides for continuous, back pulsed operation for extended periods. For high temperature applications, additional criteria such as creep-fatigue interactions, and high temperature corrosion mechanisms need to be addressed. Filters with semi-permanent media are cost effective, since such units lend themselves to minimal downtime, closed and automatic operation with minimal operator intervention, and infrequent maintenance.

The proper selection of filter media with appropriate pore size, strength and corrosion resistance enables long-term filter operation with high efficiency particle retention. The filtration rating in liquid is between 2 and 35 µm absolute. The filtration rating in gas ranges from 0.1 to 10 µm absolute.

Filter Design

The filter design for liquid/solids separation is selected which produces the required filtrate, minimizes backwash or blowdown and maximizes throughput. Three types of filter configurations are described as follows:

1.) Outside-in filtration

Traditional liquid/solids barrier separation occurs on the outer perimeter of a closed-end tubular filter element (LSP). A gas assisted pneumatic hydro-pulse backwash has proven to be the most effective cleaning method for sintered porous metal filters.

2.) Inside-out filtration

Liquid/solid barrier separation occurs on the inside of a closed-end tubular filter element (LSI). LSI backwash modes include: a.) Full shell slurry backwash, b.) Empty shell slurry backwash, c.) Empty shell and empty element wet cake backwash and d.) Empty housing wet cake discharge.

3.) Inside-out Multimode filtration:

Liquid/solids (barrier or crossflow) separation occurs on the inside of open-ended tubular filter element (LSM and LSX). Elements are sealed within two tube sheets, thereby allowing for either top or bottom feed inlet. The LSM filter, with a feed recirculation feature, has proven itself in several continuous loop reactor systems. The downward velocity controls the cake thickness of the catalyst with the lower the velocity resulting in a thicker cake. Filter backwash modes are similar to LSI backwash modes and also includes a bump-and-settle type backwash that allows concentration of solids without draining the filter element or housing. Continuous loop reactor system may not require backwashing.

Scale-ability of the filtration systems allows for accommodating high flow rates and increased solids capacity. Filtration units are suitable for batch or continuous processes. Single housing filter systems are recommended where flow rates allow and flow can be stopped for a few minutes prior to backwash, or if off line periods can be tolerated for maintenance. Two filter dual systems are recommended where continuous flow is required and short periods of off line can be tolerated for maintenance. Three filter systems are recommended for continuous operation even during maintenance periods.

Benchscale and Pilot Testing 

A valid method of evaluating filter performance is through bench scale and pilot testing. Filter testing typically begins with a simple disc feasibility test to qualify media and obtain critical filtration characteristics. Successful feasibility studies usually progresses to more involved testing of pilot equipment. Pilot testing helps develop successful commercial separation practices. While bench scale tests produce reliable indication of filter performance, data obtained in pilot scale testing on a process line will show filter operating parameters with normal process variations. Development programs require direct access to suitable equipment over an extended period. Pilot testing of sintered metal backwashable filters can provide the following information:

• Verification of filtrate quality;
• Filter thruput per cycle at various flux rates;
• Rate of rise in pressure drop vs. thruput;
• Backwash volume and resulting solids concentration;
• Scale up data for full scale sizing;
• Accurate cost estimates;
• Demonstrate high product value;
• Reliable operation with high on-line time and low maintenance;
• Demonstrate new technology at a commercial scale.

In addition to verifying filter performance, pilot testing provides the opportunity for the operating engineer to learn to use the equipment and conduct experiments that optimize filter operation for their particular process. Pilot test trials address significant technical questions and problems prior to full-scale commercialization. The outcome of pilot plant operations verify:

• Filtration/reaction studies verified at laboratory and pilot plant scale;
• New technology demonstrated;
• High volume product consistently recovered;
• Product separation and recovery optimized;
• Capacity testing completed;
• Overall operating efficiency.

Media Selection 

Feasibility Case Study: Catalyst Solids Removal

A typical approach for feasibility testing and media selection is illustrated in the following test case. The objective was to evaluate the filtering characteristics of a new catalyst to support an existing LSI commercial filter installation. Filtration studies were conducted with a 70-mm disc test filter using both Grades 5 and 10 media to compare filter performance. Catalyst particle size distribution (PSD) was measured using a Horiba LA-910 Laser Scattering Particle Size Distribution Analyzer. The size range (based on volume %) was 0.51 to 60 µm with a mean size of 13.4 µm. SEM microscopy at - X magnification verified particle size distribution as shown in Figure 3. Catalyst slurry was filtered once through at a constant rate using Grades 5 and 10 media housed in the 70-mm disc filter housing shown in Figure 4. A particle size distribution comparison of feed and filtrates (Grade 5) sample is shown in Figure 5. Test results indicate that filtration using Grade 5 media resulted with a lower rate of rise pressure than Grade 10 media as indicated in Figure 6. Filtrate turbidity samples were similar. Filtrate from the Grade 5 media measured 2.9 NTU, while filtrate from Grade 10 media measured 2.3 NTU. The 1/8 inch thick filter cake backwashed effectively from the Grade 5 media surface. Some catalyst remained in the porous structure of the Grade 10 media, indicating that catalyst had blocked some of the surface pores.

Test results indicate that Grade 5 media is better suited for filtration of new catalyst sample using the HyPulse LSI filter configuration. Pilot testing at the commercial facility verified results of feasibility study and resulted in purchase of replacement cartridges for an existing filter vessel.

Commercial Applications 

Application 1:

Laboratory disc tests conducted in April indicate suitability of sintered metal filter for catalyst recovery application. Bench scale pilot filter tests were conducted at the customer's lab facility to verify filter performance and filtrate quality. In November pilot testing with continuous catalyst filtration using 2% slurry demonstrated consistent flux rates of 0.2 gpm/ft2. A comparison of filter performance from disc testing through pilot testing is listed in Table 1. Axial velocity through the filter controlled cake thickness. The rate or velocity through the filter was optimized in bench scale testing. Optimal filter performance indicated that the filter could operate at pressures < 10 PSI without backwashing. Tests were conducted over about hours with no significant change in operating performance. The project gained approval to move to the final stage.

The objective of pilot test development program was to convert isomerization process from batch to continuous. The first commercial plant was scheduled for operation in . The process was started up in July in accordance with parameters established during the pilot testing. System dynamics experienced during start-up and initial operation exhibited performance similar to the pilot test studies. The filter operated successfully to recover and recycle precious metal catalyst after solvent wash and removal of 10% of the catalyst from the process after each batch. Process liquid is hazardous, however, because the filter system is completely enclosed, solvent could be used to wash and re-slurry catalyst back to the reactor.

The primary (larger) LSM catalyst filter is designed for bulk catalyst filtration and recycle. The filter design offers completely enclosed automated operation with minimal filter cleaning/regeneration. Fresh catalyst is added to each batch. The smaller LSP filter is designed for catalyst removal from the system. After 7 years of operation the filter bundle was replaced during a preventive maintenance schedule. The filtration system continues to operate since its initial installation in .

Application 2:

This catalyst filtration concept was proved in laboratory testing to confirm filter operating parameters and media selection. A development program utilizing pilot testing used a reactor equipped with filtration apparatus capable of separating product from catalyst, whereby the product can be removed from the

reactor while the catalyst is retained, thus permitting the reaction to be run semi-continuously or continuously. Testing utilized the HyPulse® LSM filter design.

By equipping a reactor with a means of maintaining catalyst in the vessel, the reactant can be pumped and the catalyst free product continuously removed. The hydrogenation process stops when the catalyst charge deactivates. The preferred method of filtration was to install a re-circulation loop onto the reactor,

as shown in Figure 7. For an extended batch or continuous process, a larger charge of catalyst is used to ensure sufficiently large commercially viable production quantities. This process allows up to a 50% reduction in total cycle time and an increase in over 65% in the amount of product run as indicated in Table 2.

Application 3:

The first use of sintered metal filters using inside-out (LSI) HyPulse® filtration technology for continuous slurry oil filtration was in . The installation demonstrated the suitability of sintered metal media for high temperature filtration of slurry oil for a carbon fiber development process. The filter operated reliably for many years producing clean oil with solids content of less than 20 ppm and was eventually shut down because of low product demand. Since then, refineries around the world have become aware of the benefits of filtration using sintered metal media for catalyst fines removal in slurry oil service.

Throughout the 's numerous LSI filtration systems have been installed for FCC slurry oil filtration. The largest continuous filtration systems utilizes (3) 66' LSI filters as shown in the schematic in Figure 8. Filtration cycle time ranges from 2 to 16 hours operating at 30 & 60 PSI, respectively in the filtration of ppm slurry oil. Extended cycle times were obtained by running two filters simultaneously, but staggered in cycle time, with the third being on stand-by for utilization when one of the other filter units is backwashed. The filter design uses a full shell backwash. Efficiency of the recovered product using two filters on line exceeds 99.8%.

Since there have been many refineries in China have installed LSI filtration systems for catalyst removal in resid fluid catalytic cracking (RFCC) units. A filtration system with (2) 24' LSI filters was installed in a RFCC unit with 1.4 million metric tons (mt) per year capacity and an output of slurry oil of 180 mt/day. The slurry oil has an average 3,000 to 5,000 ppm solids concentration. Cycle time varies from 2 to 8 hours. The filtrate solids content is under 50 ppm. The filter is controlled by local PLC that communicates with refineries distributed control system (DCS) to enable the operator monitor the filtration in the control room. The system is running continuously since then supplying a local company with clean filtrate to produce carbon black.

Application 4:

A process for producing Uranium Dioxide utilizes a HyPulse® gas/solids venturi pulse (GSV) blowback sintered metal filters, as shown in Figure 9, for the recovery of Uranium oxide fines from a process kiln. The sintered metal filters must withstand kiln off-gas stream temperatures of 300°F and be chemically resistant to the gaseous components. The primary risks associated with this conversion are chemical and radiological. The conversion process uses strong acids and alkalis that involve turning uranium oxide into soluble forms, leading to possible inhalation of uranium. In addition, the corrosive chemicals can cause fire or explosion hazards.

Successful field applications and laboratory support provided performance data that resulted in the first commercial filter installation put in service in . The completely enclosed GSV filter operates with 99.999% efficiency with a very low solids load to the filter and infrequent backpulsing. Key operating parameters include controlled approach velocity to the filter, high efficiency, and use of venturi for blowback for continuous operation. Today, one uranium conversion plant continues to operate in the United States using this patented process.

 

 

Application 5:

Cleanable sintered metal fibre filters offer an economical solution to processes with increased demand for higher particulate removal efficiency in extreme conditions. The development of metal fiber filter media such as Bekipor® contributed to an increased quality level through higher filter efficiency and a longer onstream

lifetime. Traditional separation systems such as cyclones, ElectroStatic Precipitators (ESP) and disposable filters are losing their appeal. Figure 10 compares emissions efficiency and relative cost of fiber metal compared to ESP and cyclones.

A highly porous structure, which is a characteristic of a sintered metal fibre medium, offers a high permeability and hence low pressure drop, even at high filtration velocities. This results in a low capital expenditure and low running costs. The cleanability for both on line cleaned surface filtration as for off line cleaned depth filtration is excellent.

This application used Bekiflow® HG for removal of alumina and alumina hydroxide dust having a particle size of 50% < 15 μm. Gas temperatures measured 842 °F. Dust concentration before the filter measured 250-800 mg/Nm³. Gas concentration after filtration was less than 30 mg/Nm³. Maximum pressure drop was 15 mbar. Total surface area of the filter was 830 m2. Fiber metal filters offers limited pressure drop and was tested for guaranteed lifetime of 27,000 operating hours. Customer benefits include less filter surface required, smaller bag house therefore less installation place required.

Summary 

Sintered metal media provides an effective means of filtering to remove particulate whether they are impurities or valuable by-product of a chemical process stream. These media are ideally suited for more demanding applications involving high temperatures, high pressures, and/or corrosive fluids. Chemical

companies are utilizing filtration to minimize waste products at the source rather than at the end of the line of the production process. Filtration improves product quality and protects downstream equipment in the production of chemical based products. Advances in filtration technology include the development of continuous processes to replace old batch process technology. Liquid/solids filtration using conventional leaf filters is messy and hazardous to clean and require extended re-circulation time to obtain clean product. Traditional gas/solids separation systems such as cyclones, ElectroStatic Precipitators (ESP) and disposable filters are being replaced by sintered fiber metal filtration systems.

Sintered metal filters should be operated within the design parameters to prevent premature blinding of the media due to fluctuations in process operations. Use of flow control assures the filter will not be impacted with a high flow excursion. Filter efficiency increases as the filter cake forms. The cake becomes the filter media and the porous media acts as a septum to retain the filter cake. Filter cakes can be effectively washed in-situ and backwashed from the filter housing. A gas assisted pneumatic hydropulse backwash has proven to be the most effective cleaning method for sintered porous metal filters. Sintered metal filters can be fully automated to eliminate operator exposure and lower labor costs while providing reliable, efficient operation.

 

Bekiflow and Bekipor are registered trademarks of Bekaert.

Hypulse is a registered trademark of Mott Corporation.

 

 

FAQs: Sintered Metal Technology

Q: What is sintered metal?

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A: Sintered metal refers to a specialized material made by compacting and forming metal powder under heat and pressure, creating a solid, porous structure ideal for filtration and various industrial applications.

Q: How are sintered metal filters manufactured?

A: Sintered metal filters are produced by compacting metal powder in a mold and then heating it to a temperature below the metal's melting point, causing the particles to bond without liquefying.

Q: What are the main advantages of using sintered metal filters?

A: Sintered metal filters offer high durability, excellent temperature and corrosion resistance, and the ability to withstand harsh environments, making them suitable for challenging industrial applications.

Q: In what industries are sintered metal filters commonly used?

A: Sintered metal filters are widely used across various industries, including pharmaceuticals, food and beverage, chemical processing, and aerospace, for their efficiency in removing particulates from gases and liquids.

 

A sintered filter is a type of filter that is made from powder materials, using pressure and heat to make them bond together while keeping a porous structure.

If you want to learn more about sinter filters, this blog has these parts you may like to read:

• Characteristics of Different Sintered Materials
• Main Features of Sintered Filters
• Steps of Producing Sinter Filters
• Advantages of Sintered Materials
• Potential Disadvantages of Sintered Parts
• How the Porous Filters Work?
• Industry Applications of Sintered Porous Filters
• Maintenance of Sintered Filter Elements
• Frequently Asked Questions

Characteristics of Different Sintered Materials

The sign is used to represent different degrees.

Sintered Material Cost Corrosion Resistance Durability Heat Resistance Other Features Sintered Bronze Filter ** ** ** ** Good Thermal Conductivity Sintered Plastic Filter * *** * * Lightweight' Easy Production Sintered Stainless Steel Filter *** *** **** **** Heavyweight Sintered Titanium Filter ***** ***** **** **** Best Performance in Harsh Environments Sintered Glass Filter (Fritted Glass Filter) ** **** ** ** Brittle Sintered Ceramic Filter **** **** *** **** Brittle

Main Features of Sintered Filters

Filtration Ratings

The filtration rating is also called filtration accuracy, which refers to the ability to remove specific particles from the fluid. It can be measured by the size of particles that the sintered porous filter trapped.

The filtration rating can be expressed in terms of microns (µm), which represents the particle sizes. Typically, the general filtration rating of sintered metal filters ranges from 0.5 to 100 microns (µm).

Among those sintered filters mentioned above, those used in special environments could offer filtration ratings of a higher level. For instance, the filtration rating of sintered plastic filters can reach 0.2 micron when used in pharmaceutical, biotech, or microelectronics.

Working Temperature

Each sintered material has a specific working temperature range.

Some could be hard to stand at high temperatures like sintered plastic filters could work at 150°C approximately at most, or thermal degradation may occur.

Some have better heat resistance as sintered ceramic elements' working temperature can be up to °C.

If the operating temperature is too high that filters can't withstand, the pores gap will change, affecting the filtration efficiency. On the contrary, when the operating temperature goes too low, the whole structure may be brittle, and easy to be damaged.

You may want to know the recommended temperatures of each sintered material:

Types of Sintered Filter Recommended Temperature Sintered Bronze -50°C to +150°C Sintered Plastic -20°C to +80°C Sintered Stainless Steel Lower than 600°C Sintered Titanium Lower than 300°C Sintered Glass (Fritted Glass) Lower than 100°C Sintered Ceramic Lower than 800°C

You need to consider the operating temperature range and the specific requirements of your application. Only in this way can you ensure consistent performance.

Steps of Producing Sinter Filters

Then, how to make sintered parts? Just follow these 4 steps.

Mixing and Blending in Powder Metallurgy (PM)

Depending on your application, you can choose common types of powder materials such as metal powders or polymer powders.

In addition, you can also mix the powders to achieve specific properties.

Powder Stamping

With intense pressure, powder materials are compacted in molds that have variable shapes (sintered disc, sintered plate, sintered tube, etc.). However, the whole porous structure remains relatively loose.

Sintering Process in Powder Metallurgy

The key step of manufacturing is the sintering process in powder metallurgy, which determines the properties of sintered parts.

Filter materials will be heated to a temperature lower than its melting point, bonding the powders together, while keeping physical properties.

Secondary Operations in PM

After the filter elements cool down to room temperature, check the quality according to your requirements.

If there are some deviations, then reprocess (cutting, polishing, or machining). Finally, clean the sinter filters to remove contaminants.

Advantages of Sintered Materials

Why choose sinter filters? Here are some advantages that ensure their reliable filtration performance.

• Corrosion Resistance

Most of the sintered metals have a natural resistance to corrosive chemicals so they can still maintain a good state under chemical reactions.

Sintered glass and sintered ceramic also have excellent performance in corrosion environments.

• Enhanced Purification

You can choose sintered filters of specific filtration accuracy to keep the filtration efficiency at a high level.

In HVAC (Heating, Ventilation, and Air Conditioning) systems, sintered metal filters with filtration ratings ranging from 5 to 20 microns are commonly chosen to protect HVAC equipment from contaminants. These filters can effectively capture various particles in the air.

What's more, the material that does not react chemically with the fluid can avoid the entry of new substances. In all, the filtered results will be more accurate.

• Pressure Sustaining

If there are pressure fluctuations during the filtration, the entire system will be affected to some degree.

Due to their mechanical strength, sintered metal filters are good at maintaining fluid pressure to ensure stable system operation.

• Robust Durability

Sintered filters have better durability and longer service life in extreme temperatures. With proper maintenance, these sintered parts can be used for many years, often ranging from 3 to 10 years or even longer in some cases, which can reduce the number of replacements, thereby saving costs.

Potential Disadvantages of Sintered Parts

Though many advantages are provided, they still have some potential drawbacks that you need to notice:

• Cost

The choice of materials mainly determined the cost of sinter filters. High-performance materials can be more expensive.

Also, the complexion of the manufacturing process adds to the cost.

In March , the price of stainless steel mixed powder (SS-303L) with a diameter of 100 microns in China is about $590,000 /ton.

• Clogging:

As time goes by, small pores may become clogged with particles, reducing the filtration efficiency. In other words, they need regular cleaning and maintenance.

Cleaning may require specialized equipment and procedures. Some sintered elements used in chemical environments can be more challenging to clean thoroughly. This means it costs not only money but also extra time.

• Material Limitations

Raw materials for making sintered filter elements are not of a wide range.

What's more, one material cannot be applied to all situations. So for special environments, the choice will always be limited.

• Production Time

Compared to other filters, the manufacturing time of sintered filters is long. For different sintered materials, the production time of some sintered metals may be longer.

For example, if the production time of a batch of sintered bronze filters is 1 day, the same number of sintered stainless steel filters could take a week or more.

So if buyers need a great amount of sintered filters, it's better to place the order in advance.

How the Porous Filters Work

For Oil or Water Treatment

Sintered porous filters are widely used in fluid filtration or liquid filtration, allowing fluid (liquid) to pass through the pores.

When flowing through the filter, particles larger than the pore sizes are trapped, thus the fluid is purified.

For Noise Reduction and Soundproofing

When the sound waves go into the filter, they will cause the air in the filter to vibrate. This movement creates friction and resistance, which turns the energy of sound into heat, reducing the amplitude of the sound waves.

Industry Applications of Porous Filters

Due to plenty of distinct advantages, sintered filters have a wide range of applications.

• Food and Beverage Industry

For beverage production, you can use filter layers to filter pulp and suspended solids to ensure the clarity of the liquid.

Meanwhile, purified water for food processing can also be obtained by water treatment.

• Chemical Industry 

In chemical processing industries, these sintered filters can be used in corrosive environments, like sintered glass filters used in laboratories.

Some chemical waste may be harmful to the environment, which requires some filtration of these substances.

• Electric Industry

You can also use sintered filter elements to remove impurities in the operating conditions. It can maintain the normal operation of the machine and extend the service life.

(For instance, sintered bronze filter discs are used in vents of electric motors to prevent the entry of dust, moisture, and other contaminants while allowing air exchange. This helps to maintain the internal environment of the motor.)

• Petroleum Industry

Porous metal filters are used to remove contaminants from fuels and lubricants, ensuring smooth operation and prolonging the life of machinery.

(Sintered stainless steel filter tubes are used to remove contaminants from crude oil during production and transportation processes. These metal filters help to keep product quality, protect equipment, and prevent pipeline fouling.)

Maintenance of Sintered Filter Elements

Regular Inspection

Visual inspection is to check for signs of damage and decide whether it needs replacement.

Then perform a short filtering action, and test the filtered fluid to see whether the filter layer is clogged.

Sintered Parts Cleaning

After a period of use, there may be some residual dirt on the filter layers, which will cause blockage if not cleaned in time.

• A common method is ultrasonic cleaning, which can effectively remove fine particulates and contaminants.
• If an element's surface has some chemicals that are difficult to wash off, using chemical solutions that can dissolve the contaminants is the easiest way to clean up.

FAQ

After a basic introduction, you may still have some of these questions:

What affects the filtration ratings?

The uniform pore size is the key point to the precision, which affects the final filtration efficiency. What's more, the sintered powder sizes could make a difference.

Why Sintering is Important?

As said above, the numbers and sizes of pores distributed on the filters directly determine the filtration efficiency. It is the temperature and time of sintering that control these factors, that's why sintering does matter.

As delineated by Wikipedia, this method is integral to the fabrication processes employed across various substances, including metals, ceramics, plastics, and more.

Can sintered metal filters be used for sterile filtration in pharmaceutical applications?

Yes, of course they can.

Filtration in the pharmaceutical industry usually involves liquid filtration and gas filtration, which stays in line with the scope of the application of sintered metal filters.

(For example, you can use sintered metal filters in the final filtration, removing residual particles or microorganisms before packaging.)

What filtration rating is a paper coffee filter'

Generally, paper coffee filters have average pore sizes ranging from 10 to 20 microns, which vary depending on the material type and brand of the coffee filter.

If you are referring to the espresso puck screens, especially those made from sintered stainless steel, the filtration rating is around 150 microns.

Can porous metal filters be customized?

Yes.

According to your application and requirements, you can customize specific characteristics (pore sizes, powder sizes, sintered materials, shapes, and flow rate) of your porous metal filters.

In addition, the operating environment needs to be considered as well.