Sintering Process in Powder Metallurgy

What is a Sintered Filter?

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 MaterialCost  Corrosion Resistance  Durability  Heat ResistanceOther 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 1000°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 FilterRecommended Temperature
Sintered Bronze-50°C to +150°C
Sintered Plastic-20°C to +80°C
Sintered Stainless SteelLower than 600°C
Sintered TitaniumLower than 300°C
Sintered Glass (Fritted Glass)Lower than 100°C
Sintered CeramicLower 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 2024, 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

2 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

1 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.

Frequently Asked Questions

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.

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