Sintered Porous Bronze Fuel Filters – Part 1

Benefits of porous sintered bronze filter elements and how they are made

8419-01-9909 porous sintered bronze element fuel filter made by ITW Fastex®. Click on this image to find out more about these plastic inline filters.
8419 ITW Fastex® Visu-Filter

Filter elements and plastic inline fuel filtersLight duty carbureted vehicles, Outdoor Power Equipment (OPE) and Powersports are heavy users of plastic inline fuel filters. Inline fuel filters are easy and fast to replace and provide filtration protection from debris, fine particles and other contaminants.

These fuel filters are also widely marketed as OE original equipment parts and OEM aftermarket add-ons.

Design engineers have a significant impact on which fuel filters are used on original equipment and what replacement filters should be recommended. They base these decisions on required fuel flow rates, filter physical space requirements and the particle sizes the filter needs to stop (micron rating).

Get more information more about the 8419 ITW Fastex® Visu-Filter in the ISM catalog>>

Plastic inline fuel filters have two primary components:

  • Filter bodies that hold the filter elements and provide molded-in hose barbed connections
  • Filter elements that do the work of capturing and retaining the debris, particles and contaminants

Learn more about the plastics used to make high quality inline fuel filters at the ISM blog >>


Types of fuel filter elements
Filter elements used in small plastic inline fuel filters
Here is a list of the filter element types most commonly used in plastic inline fuel filters. Each one has its own distinct advantages. Most OEM filter manufacturers usually produce an array of plastic inline fuel filters that includes all of these filter element types.

  • Polyester mesh screen
  • Porous sintered bronze
  • Stainless steel mesh screen
  • Polymer treated cellulose (paper)

This article focuses on porous sintered bronze filter elements, sometimes called "stone" or "rock" filters by end users. I look at what makes sintered porous bronze an excellent filter element choice. I also provide an overview of how porous bronze filter elements are formed.

Read Part 2 of this article to find out more details about bronze, depth filtration and how sintered porous bronze filter elements are made >>
 

Porous bronze and inline fuel filters

Porous sintered bronze filter element.
Sintered bronze filter element

Mechanically strong but porous
Porous bronze is an intriguing material. Generally, we expect solids, especially metals, to be, well, solid. Porous bronze filter elements use a specialized metalworking process called pressureless sintering. The results are mechanically strong but porous metal parts.

The production process for porous metal filters makes useful components that are relatively economical, highly customizable, efficient and mechanically strong.

Plastic inline fuel filters with sintered bronze filter elements have a very distinctive look. They also offer a unique blend of performance capabilities that make them a useful option for filtering fuels.

Porous sintered bronze filter element advantagesPorous sintered bronze filter elements are

  • Relatively lightweight
  • Very strong and durable
  • Easily formed into precise shapes
  • Efficient at capturing and holding onto contaminants
  • Highly compatible and corrosion resistant to hydrocarbon fuels and oils
  • Able to have their service lives extended by backwashing or backflushing

Find out more about the corrosion resistance and chemical compatibility of bronze >>
*Check out our information about chemical compatibility and get a copy of our Chemical Compatibility Chart. It includes brass, bronze and copper, plus other metals, plastics and elastomers.

Sintered bronze filter elements are relative lightweight
Weight matters because inline fuel filters connect to flexible fuel lines exposed to significant vibration and impact stresses.


Sintered bronze filter elements are strong and durable
Outdoor Power Equipment (OPE) and Powersports require inline fuel filters that are tough and durable. The selected filter elements and body materials in these filters must also handle gasoline and the wide range of gasoline-alcohol blends available in the marketplace.
 

Sintered bronze filter elements are efficient
Sintered bronze filters have a relatively large surface area plus good filter depth. The tiny winding and interconnecting passages that saturate the full thickness of the filter element walls (interconnected porosity or tortuosity) provide filter depth.

Depth filtration can retain particles smaller than the filter element's rated pore size. They can do this while also allowing good fuel flow even as contaminants build up inside the filter.

The ability to capture debris on the filter element's surface, plus capturing fine particles inside the element walls, makes sintered bronze filter elements very efficient.
 

Methanol molecule 3D model. Click the image to  find out more about the chemical compatibility of materials.
Methanol molecule 3D model

Sintered bronze filter elements have excellent fuel compatibility
Bronzes are copper alloys, and they have excellent corrosion resistance to a wide variety of chemicals. The bronze used to make sintered bronze filter elements is called tin bronze, an alloy of tin and copper.

Each type of bronze has unique resistance qualities to various chemicals. Tin bronze is an ideal material for fuel filter elements. It is exceptionally resistant to oils and hydrocarbon fuels, including diesel, gasoline, gasoline-alcohol (ethanol) blends and methanol.

Find out more about gasohol (gasoline-ethanol) blends and outdoor power equipment from OPEI, the Outdoor Power Equipment Institute >>


What about sintered bronze filter elements and backwashing?
Porous sintered metal filters provide a combination of strength, heat resistance and corrosion resistance. Because plastic inline fuel filters have plastic housings, they cannot benefit from the ultrasonic cleaning techniques used for industrial sintered filter elements.

Backwashing or backflushing, with or without solvents, can extend the life of small sintered bronze fuel filters, but a thorough cleaning is not a long-term option. Fortunately, this type of inline filter is economical enough that it's practical to replace during regular maintenance cycles or whenever a filter becomes clogged.

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Manufacturers produce porous bronze filter elements using the sintering process
Sintering and powder metallurgy
Sintering is a type of powder metallurgy. This type of metallurgy makes mechanically strong metal items from metal powders. The powders are shaped and may or may not be compacted. After being shaped, they are then sintered or heated to produce the finished parts.

Making porous tin bronze filters requires a particular type of powder metallurgy called pressureless sintering. While most sintering uses a combination of compression and heat, pressureless sintering uses heat only. It is only the heat of sintering that fuses the powder particles.

Learn more about pressureless sintering at the OpenLearn website >>


Sintering begins with metal powder
Porous sintered bronze filter elements like those used in ITW Fastex Visu-Filters, begin as highly spherical metal powders.

Careful control of the size of these tiny bronze spheres is required. It involves special sieving techniques and the choice of a narrow enough particle size range (particle size distribution). The goal is to make sure the particles are consistent enough to produce filters with the desired filter rating.

Learn more about spherical bronze powders are made at the Copper Development Association website >>


Bronze sintering powder is poured into molds or dies
When making bronze filter elements, the process begins by pouring pre-alloyed spherical bronze powder into molds or dies. Fortunately, metal sintering powders behave almost like a liquid when they are poured.

The process of filling empty filter element dies with metal powder includes vibration. Vibrating the dies settle the powders in the dies and ensures the powder fills the dies without leaving any voids.

 

Sintering furnace interior.
Sintering furnace interior

Sintering furnaces heat the dies to the correct sintering temperature
The heat of specialized sintering furnaces bonds the bronze particles together. Parts are kept in the furnace just long enough, leaving pores or passages that run through the finished pieces.

Sintering temperatures are lower than the melting point of the bronze alloy. It is usually about two-thirds of the alloy's melting temperature. Sintering temperatures are also lower than the melting point of the primary metal in the alloy.

The sintering temperature of tin bronze, a copper and tin alloy, is less than the melting point of both the tin bronze alloy (copper and tin) and the copper.

A look at how sintering temperatures are calculated from PMD, PM Distributors >>


Sintering furnaces are highly specialized
The sintering furnaces are multi-stage furnaces with controlled atmospheres. Controlling the type of gas or gas mixture surrounding the parts prevents problems from oxidation. It also provides more consistent heat transfer at each of the heating and cooling stages.

Oxidation is a problem during sintering because it creates an oxide layer on the particles. Unless prevented from forming, the oxide layer acts as a barrier and inhibits or prevents the powder particles from bonding.


Filter elements inside plastic inline fuel filters

Choosing good value over a low price
What matters most for design engineers and reputable aftermarket and replacement parts distributors is not a low price. Instead, they want to choose good value plastic inline fuel filters made by high quality OEM manufacturers. They need to be sure they are getting the reliability and greater end-user satisfaction they need.

For durability, reliability and end-user satisfaction, plastic inline fuel filters need

  • Strength and durability
  • Materials that can withstand exposure to a variety of fuels
  • Materials and construction able to withstand exposure to harsh operating conditions

Find out more about the plastics used to make fuel filter bodies at the ISM blog >>

Examples of outdoor power equipment and powersports applications. Clockwise from top left: riding lawnmowers, small outboard engines, snowmobiles and motocross bikes.


Why does the strength and durability of filter elements matter?Small plastic inline fuel filters need to be tough and durable, especially for small transportable internal combustion-powered machines, Powersports machines and Outdoor Power Equipment (OPE).

Exposure to heat, impact, vibration and other mechanical stresses can cause inadequate or inappropriate materials and construction to fail unexpectedly.

Learn more about our products for the Small Engine and Automotive OEM marketplace >>


Of course, inline filter element performance matters too
The build quality of filter elements can vary just as much as the quality of the filter bodies. Bronze is the right material choice for hydrocarbon fuels and oils.

Precisely made quality porous bronze filter elements can be held flush against their mating surface inside the filter housing. This tight fit prevents fuel from bypassing the filter element.

These filter elements also provide an appropriate level of particle protection without overly restricting flow.


Fuel options and why filter element materials matter
Transportable machines powered by internal combustion engines and power sports equipment also need to be compatible with the types of gasoline and gasoline-ethanol blends that end users are likely to use. Filter elements need to be just as compatible with fuels as the filter body materials.

Find out more about standard ethanol fuel mixtures at Wikipedia >>

8423-01-9909 porous sintered bronze element plastic elbow fuel filter made by ITW Fastex®. Click this image to find out more about these plastic inline filters.

 

8423 ITW Fastex® Visu-Filter

Compatibility with gasoline and gasoline-alcohol blends is critically important
Besides gasoline and diesel, modern plastic inline fuel filters need to be compatible with gasoline-ethanol fuel blends ranging from E10 to E85. Broad compatibility is vital because finding pure gasoline fuel has become increasingly difficult.

Get more information about the 8423 ITW Fastex® Visu-Filter in the ISM catalog >>

There is also likely to be occasional exposure to methanol. Methanol is used as a specialty racing fuel and an ingredient in some gasoline additives. Additives marketed for removing water in gas tanks and preventing fuel lines from freezing are the most likely to contain some methanol.

Find out more about gasohol (gasoline-ethanol) blends and outdoor power equipment from OPEI, the Outdoor Power Equipment Institute >>

High-quality OEM plastic inline fuel filters use materials that can stand up to this wide variety of fuels, fuel blends and other chemicals. Using the right materials is essential, but the parts made from them also need to be manufactured and assembled following good manufacturing and quality control best practices.

Good manufacturing best practices and tight quality control are why OEMs frequently include "precision" in their product descriptions.


What does "precision fuel filters" mean, and why does it matter?
Plastic injection molding can be a very cost-effective way of producing large numbers of very consistent plastic parts. Uses include the components made for assembly into plastic inline fuel filter bodies or housings.

The difference between typical injection molded plastic parts and precision molded plastic parts is the allowed tolerances or acceptable range of variation in a part's dimensions. A good rule of thumb is dimensional tolerances for precision molded parts are significantly tighter than for general-purpose injection molded parts.

Producing intricately shaped and consistent body components require precise control of variations in the injection production process.

Controlled, precision-made plastic parts require

  • Molding machine accuracy for dimensional consistency
  • Carefully controlled mold temperatures for predictable material shrinkage
  • Raw materials free of absorbed moisture for predictable behavior when melted

Learn more about the importance of temperature control when working with thermoplastics at the International Polymer Engineering website >>

High-quality plastic filters use body components made of engineering plastics. The plastic filter bodies are assembled from the body components using ultrasonic welding.

The ultrasonic welding process for engineering plastics is exacting. It requires consistent, relatively intricate plastic shapes at the component joints or bonding surfaces. It also requires a careful and complex production setup with equally rigorous quality control.

The results of properly controlled ultrasonically welded and precision molded engineering plastics are plastic inline filters with strong, durable and leakproof joints.

Find out more about the plastics used to make fuel filter bodies at the ISM blog >>

Why do filter flow rates matter?

Micron rating affects the flow rate
Small inline fuel filter flow rates matter because a filter that restricts flow too much can cause an engine to surge or lose power. Internal combustion engines need a steady fuel flow to run smoothly and provide additional power when needed.

Users who buy aftermarket plastic inline fuel filters often consider replacing an original equipment filter with a similar filter with a lower micron rating. But, if they replace an 80-micron filter with a 10-micron filter, the reduced fuel flow rate has a good chance of creating performance issues.

The best internal combustion-powered machine designs use fuel filters with the fuel flow rates necessary for trouble-free engine performance.

Machine designers help out the end user by taking the machine's expected exposure to contamination into account. Specifying correctly-specified, easy-to-replace, high-quality plastic inline filters is an easy way to increase user satisfaction and extend a machine's useful life.

It's important to know where filter flow rates come from
Flow rates are based on idealized laboratory testing conditions, i.e., standard fluids, temperatures and pressures. Because of this, most machine designers and design engineers request sample filters and confirm fuel flow rates against their machines' real-world operating conditions.

A widely used rule of thumb is that fuel filters with micron ratings below 40 to 70 microns work best for small engines with fuel pumps.

Generally, machine designs using small plastic inline filters with low micron ratings locate them between the fuel pump and the carburetor. A careful evaluation of fuel filter options may also need to include gravity feed flow rates.

Gravity flow or feed versus fuel pumps

8426-01-9909 polyester mesh screen element plastic fuel filter made by ITW Fastex®. Click this image to find out more about these plastic inline filters.
8426 ITW Fastex® Visu-Filter

Some engines don't need a fuel pump
Small internal combustion engines (chainsaws, weed trimmers, edgers, and similar machines) require relatively low fuel flow rates. For these engines, fuel pumps are unnecessary.

These smaller engines often use in-tank inline filters or screens because of space limitations.

Get more information about the 8426 ITW Fastex® Visu-Filter in the ISM catalog >>

Carbureted engines without fuel pumps usually perform best with filters using metal or polymer (plastic) mesh screen filter elements. Still, it is not uncommon to find filters with porous sintered bronze filter elements used on gravity-fed engines.

Bronze filters work well as long as their gravity flow rates are high enough. Design engineers are aware of this and make their filter selections accordingly.


Bronze vs. Paper - filter micron ratings, fuel filter elements and flow rates
Screen filter elements can only capture larger particles that might clog carburetor fuel passages. Engines using screen filters do not provide the same protection from fine particles as porous bronze and paper filters. The fuel going into these engine gas tanks needs to be clean and kept clean because of this.

End users often refer back to this rule-of-thumb: "suck through screen, push through paper" when choosing an add-on or aftermarket filter. This type of approach is useful when no manufacturer's original equipment (OE) genuine part or OEM aftermarket replacement part is available.

Marketplace demand generally tends to be for courser (higher micron rating) filters upstream of fuel pumps and lower micron rated filters on the downstream side.

Find out more about filter mesh screen, microns and particle sizes at the ISM Mesh and Micron Sizes page >>

Porous bronze filters have performance advantages
Porous sintered bronze fuel filters have a performance advantage because their flow rates tend to be higher even while they are efficient at capturing fine particles.

Plastic inline fuel filters with porous sintered bronze filter elements tend to have micron ratings in about the middle of the range between mesh screen and paper filters. Because of this, flow rates are a critical specification for sintered bronze filter elements. They matter for both original equipment (OE) and OEM aftermarket replacements.


About this three-part series on sintered porous bronze fuel filters

Sintered Porous Bronze Fuel Filters - Part 1: Benefits of porous sintered bronze filter elements and how they are made  >>
An overview of porous bronze filter elements, why they are so effective in small plastic inline fuel filters and what it takes to produce high-quality sintered porous bronze fuel filters.

Sintered Porous Bronze Fuel Filters - Part 2: About depth filtration and the porous filter elements used in fuel filters >>
More detail about bronze, porous sintered bronze filter elements as depth filtration, how to make them, and their installation and use.

Sintered Porous Bronze Fuel Filters - Part 3: Porous sintered bronze elements FAQ, applications beyond filtration plus references >>
An FAQ about sintering, porous sintered bronze fuel filter elements and depth filters. It also includes an overview of other applications that use porous bronze filter elements, plus a list of references.

 

 

Selected ITW Fastex Filtration Visu-Filters  with a variety of filter elements. Click the image to image to find out more  about these plastic inline filters.

Selected ITW Fastex Filtration Visu-Filter fuel filters

ITW Fastex Filtration and ITW Powertrain Components Visu-Filter fuel filters are compliant with ANSI/OPEI B71.10-2018.

Visit our catalog

 

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Sintered Porous Bronze Fuel Filters - Part 2 >>
Part 2 of this article contains an FAQ covering sintering, porous sintered bronze fuel filter elements and depth filters. It also includes an overview of other applications that use porous bronze filter elements, plus a list of references.
 

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Steven C. Williams headshot March, 2018.About the author

Steven C. Williams my LinkedIn profile link button.Steven C. Williams, BS, is the technical writer and an inbound marketing specialist at Industrial Specialties Manufacturing (ISM), an ISO 9001-2015 supplier of miniature pneumatic, vacuum and fluid circuitry components to OEM's and distributors all over the world. He writes on technical topics related to miniature pneumatic and fluidic components as well as topics of general interest at ISM.       


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