Sinter filtration is an effective filtration method where the residue, filtrate or both contained the desired compound(s). The glassware for these setups is available in a range of sizes for filtration volumes between ~10 mL and 25 L.
For more information, please visit JINTAI.
Sinter funnels consist of a glass funnel containing a sintered disc or frit, which is made of a fine mesh of glass fibres. The frit comes in several different porosities, which is a measure of the size of the holes in the frit, and thus, how fine a material can be filtered. These are generally referred to using a scale of 0-5, where 0 is a very coarse filter and 5 a very fine filter. The most commonly used frit is a 3, which is suitable for the isolation of most common laboratory precipitates and crystals from recrystallisations.
Sinter funnels are often used in active filtrations particularly with Celite and Silica.
Sinter filtrations are generally carried out using a sinter funnel fitted into a Buchner flask setup, although filter adapters fitted into a round bottomed flask can also be utilised. The step by step instructions below apply to the former setup.
Fit vacuum tubing to the vacuum outlet of the Buchner flask and seurely clamp the flask in place around the neck. Take care when clamping to ensure that the clamp is not above the top of the flask neck, especially when using a Buchner ring, as this may reduce the effectiveness of the filtration
Attach the vacuum tube to the vacuum connector, but keep the vacuum turned off at this stage.
Place a Buchner ring or cone into the top of the Buchner flask.
Insert the sinter funnel through the cone or ring into the flask.
Slowly open the vacuum and check that the setup is working. The sinter will be 'sucked' towards the flask and become secured, due to the reduced pressure inside the flask. Turn the vacuum off before starting filtration.
You may wish to check the sinter is clean and not blocked by running solvent thorugh the sinter. Generally, you should use the same solvent system that your material is suspended in. You don't want to introduce other solvents which may cause issues with your reaction, eg the introduction of water into an otherwise dry organic layer. If you do 'test' or clean the sinter, you should empty the flask before starting filtration. Carefully remove the sinter funnel and place somewhere safe where it will not be knocked / fall over, before removing the Buchner flask. The notes under 'drying material under vacuum' contains an appropriate step by step method for carrying this out.
These instructions assume a conical flask containing a suspension of material to be filtered. The instructions may need to be adapted for other setups.
Carefully pour in some of your suspension into the sinter funnel and carefully open the vacuum. Check that the filtration is proceeeding.
Continue to top up the funnel with remaining material. It is a good idea to swirl the flask before pouring to try and get any solid material into the suspension so that it transfers into the funnel.
Once all the liquid has been transferred into the funnel, it is likely that some residual solid remains in the flask. Ideally the flask is 'rinsed out' using small volumes of additional solvent. The choice of solvent (and volumes used), often needs careful consideration (see notes below).
The isolated product is also often 'washed' in the solvent at this stage. Details on this procedure are listed separately.
Allow the vacuum to pull through all the solvent in the sinter to be left with a reside in sinter.
At this stage, the filtration is usually followed by a brief 'drying over vaccuum' in order to remove residual solvent in the material.
Where the filtrate is desired, the time over active vacuum should be minimised. This is to minimise the evaporation of solvent from the filtrate.
Often when collecting a product via vacuum filtration, it is desirable to wash the collected material using a solvent. Washing the residue allows the removal of unwanted material, such as small amounts of the filtrate to be removed from the residue. Careful choice of the solvent is important to ensure that product is not lost through dissolving portions of the residue (see notes below).
In order to effectively wash a residue:
Turn off the vacuum and release the vacuum pressure. The easiest way to release the vacuum is to carefully disconnect the rubber tubing from the vacuum pump connection, which will allow air to enter the previously evacuated system.
If using a different solvent, it may be sensible to empty the collection flask of the filtrate. This is especially important where the material would go into different waste streams.
Add some of the washing solvent into the sinter to form a suspension with the residue. Use a spatula to stir up the residue to ensure that the residue is thoroughly washed in the solvent. Make sure the sinter is supported during this process, as the release of the vacuum means that the sinter is no longer being secured into the flask.
Slowly turn the vacuum back on, allowing the washing solvent to be pulled through into the flask below.
Repeat the above steps as nescessary.
In order to effectively dry material over vacuum, it is nescessary to empty the collection flask of any solvent. As many of the solvents used in the lab are volatile, prolonged vacuum filtration would cause the flask contents to evaporate. This reduces the effectiveness of any attempts to dry the residue over vacuum.
Turn off and carefully release the vacuum to the setup. The easiest way to release the vacuum is to carefully disconnect the rubber tubing from the vacuum pump connection, which will allow air to enter the previously evacuated system.
Remove the sinter and place this somewhere secure, where it isn't going to be knocked over or broken.
Empty the collection flask of the filtrate.
Reclamp the flask back in place and reconnect the vacuum tubing to the pump.
Return the sinter to the setup.
Open up the vacuum and allow the residue to begin to be sucked dry for a few moments.
When the material looks visibly dry, break up the residue using a spatula whilst still over vacuum.
Periodically stir the residue with a spatula to allow the solid to fully dry over vacuum.
Once the residue is dry, turn off the vacuum and carefully release the vacuum.
Isolate the material.
When isolating the residue, consideration needs to be given as to where the residue wants to be for the next steps. For example, this might be to place the material into a watch glass or sample vial for characterisation, or it might be placed into a conical flask for further steps, such as recrystallisation.
The isolation of material will be carried out using a spatula to transfer the contents of the sinter into another vessel. Note that it is usually a good idea to record the mass of the empty vessel prior to transfer, so that you can determine how much material has been isolated following transfer.
When removing residue from the sinter, care should be taken to not 'scratch' at the sinter surface too much, as it is possible to break up the surface of the sintered frit, which results in fragments of glass fibre being isolated.
Where the filtrate is desired, the vacuum should be turned off as soon as possible after filtration in order to avoid evaporation of the solvent.
Turn off and carefully release the vacuum to the setup. The easiest way to release the vacuum is to carefully disconnect the rubber tubing from the vacuum pump connection, which will allow air to enter the previously evacuated system.
Remove the sinter and place this somewhere secure, where it isn't going to be knocked over or broken.
Disconnect the vacuum tubing from the Buchner flask.
Pour out the solvent from the neck of the flask into the desired vessel for the next step. Be aware of the flask side arm, and ensure that the flask is poured with the side arm remaining uppermost, so that solution is not lost via this arm. It is good practice to use a funnel when pouring to ensure the material isn't spilled.
Rinse the flask out with addtional small volumes of solvent to ensure that all of the filtrate is transferred.
Sinter funnels have particular challenges with cleaning, as material may be present inside the sintered frit, as well as in the funnel and stem. For general cleaning, the procedure listed below should be appropriate, however it is sometimes nescessary to follow cleaning procedures specific to the materials or procedure which have been used. the procedure assumes that the residue has been collected following filtration.
Rinse out any residual precipitate with small volumes of solvent into an appropriate waste stream. Ideally use a solvent the residue is known to be soluble in. In most cases, this is likely to be acetone.
Return the sinter to an empty Buchner flask setup. Add acetone into the funnel, then turn on the vacuum to draw the acetone through the sintered frit which allows this to be cleaned.
Empty the solvent flask into the appropriate waste stream.
Return the funnel into the flask and next draw water through the sinter.
Re-empty the flask, and repeat the steps to draw through a further portion of acetone.
The sinter should now be clean. The remaining glassware (Buchner flask) can be cleaned in a conventional manner.
Where material is known not to be soluble in the solvent forming the supsension, then volumes of solvent can be used without worrying about solubility issues. In other situations, such as following a recrystallisation, the precipitate could potentially be redissolved if lots of solvent was used to wash out the precipitate, or the solvent makup could be affected in a multi-solvent system recruystallisaiton which could cause problems. In general, to avoid redissolving material which is trying to be isolated, small volumes of ice-cold solvent of the recrsyallisation system (in the same proportions used) would be the most appropriate choice here.
Sometimes it is also nescessary to empty the flask between washing stages of the precipitate where different solvents are used. This is often driven by the need to consider the waste disposal routes for solvents. For example, a precipitate might be intitially isolated from water, before being washed with a water miscible solvent, and finally an organic solvent. It would be usual to empty the Buchner flask between each washing to ensure appropriate disposal of the filtrate in these cases.
When filtering, it is possible that the receiving flask could become filled, and would need emptying before continuing. With a Buchner flask, you should not let the solvent level go above the stem of the sinter funnel, or let the solvent level approach the side arm of the Buchner flask. If you are approaching either of these situations, stop the filtration, and transfer the filtrate contents before resuming the filtration
Sometimes sinter funnels become blocked with material, leading to slow or a stoppage in filtration. A blocked filter can be diagnosed by the sinter still being held in place by vacuum (ie the issue is not caused through poor vacuum), but no material is being drawn through.
Blocked filtrations can arise for a number of reasons:
The solid being isolated includes very small particles which are resulting in the sinter pores becoming blocked.
The filtration conditions are leading to precipitation in the sinter funnel. E.g. the use of an antisolvent to collect crystals from a recrystallisation is resulting in material being precipitated during the filtration in the sintered frit.
The solution to slow filtration depends on the precise cause. For very fine particulates, consider filtration using a filter agent, or an alternative filtration method (e.g. gravity). Note filter agents generally limit the filtration to processes where the filtrate is the desired product.
When collecting products, the solvent choices in washing are very important. When collecting products from recrystallisation, it is important to not affect the solvent composition to avoid causing precipitation. See the notes on solvent choices.
This is generally not an issue from material passing through the sinter, but from the evaporative losses due to the vacuum nature of the filtration. This is especially common in recrystallisation where the filtrate (known as the 'mother liquour') will contain material in solution. Under vacuum, the solvent is liable to evaporate, which results in precipitation occurring. This material is likely to be of significantly lower purity than the crystals already isolated.
Scratching of the sintered glass surface can result in fragments of glass fibre being broken off the sinter. Take care when isolating product to avoid scratching at the surface.
Porous sintered bronze elements FAQ, applications beyond filtration plus references
Read Part 1 to find out more about sintered porous bronze filter elements and their use in small plastic inline fuel filters >>
Read Part 2 to find out more details about how to make sintered porous bronze filter elements and how they work >>
An FAQ section about sintering, porous sintered bronze fuel filter elements and depth filters
How does depth filtration work?
Fine particles suspended in a fluid passing through a depth filter may impact or run into the filter material and stick or adhere to it. This particle impact and capture is called adsorption.
Depth filters have complex, meandering and irregular interconnecting pores (tortuosity). This tortuosity increases the likelihood that depth filters can capture suspended particles in one or more ways (particle capture mechanisms).
Particle capture mechanisms are also called principles of filtration, mechanisms of filtration and mechanisms of particle capture.
The ways depth filters capture fine particles are (see the illustration)
Diffusion interception
Tiny particles suspended in liquids are bounced around by the molecules of the liquid. This random bouncing (Brownian Motion) increases the odds that particles bounce out of the fluid stream and bump into the filter material where they may stick.
Direct interception
Depth filter materials have tiny, winding, interconnecting passages or pores (tortuosity). Many of these pores or passages taper or interconnect with smaller passages.
Fluid can easily flow through narrower passages, but particles that are too large cannot pass through. When this happens, filter material directly captures these particles.
Inertial impaction
As the liquid passes through filter material (filter media), the flow follows the path with the lowest resistance to flow. Particles carried along in the fluid have mass and velocity. These combine to give moving particles momentum.
Momentum is the tendency for a moving object to keep moving in a straight line. Unless another force interacts with it, the particle does not change direction. Inertia is this resistance to changing direction.
The winding passages (tortuosity) inside depth filters cause liquids passing through it to change direction repeatedly. When this happens, the momentum and inertia of particles in the fluid cause them to try to keep going on in a straight line. This straight-line motion causes them to strike the filter material where they likely stick.
The technical aspects of depth filtration can be quite tricky. If you are interested in learning more about the mechanisms of particle capture by depth filters, check out this downloadable PDF reference resource:
Principles of Filtration from the Pall Corporation >>
What are filter elements?
Filter elements are the components inside a filter that do the actual filtering. Plastic inline fuel filters direct fuel flow through the filter element, capturing debris and particle contaminants.
Fuel filter elements for small inline filters tend to have a slightly conical or drum shape. These element shapes maximize the element surface areas and flow rate through the filters.
Flow direction matters for small inline filters, usually indicated by flow direction arrows molded into the filter body.
Filter elements are added to the fuel filter during their assembly because the elements arrive as separate parts. This interchangeability allows for variations in filter element material and design. Filter element design variations provide more options for micron rating and flow rate.
Types of fuel filter elements typically used in small plastic inline filters
How do you clean a sintered bronze filter?A combination of ultrasonic cleaning and appropriate solvents can clean porous sintered bronze filter elements. This approach works best if the solvents flow in reverse through the filter (backflushing or backwashing).
Cleaning the sintered metal fuel elements inside small plastic inline fuel filters is not practical because
Backwashing can extend the life of a sintered bronze fuel filter but, over time, fine particles build up and cause the filter to become plugged. Even before flow stops, restricted flow can make a filter unusable. The relatively low cost of plastic inline fuel filters means replacing them as needed is usually the best option.
Find out more about cleaning porous sintered filters at the CTG Technical Blog >>
What is a sintered filter?
Manufacturers use a powder metallurgy process to produce porous metal parts like sintered filter elements. In this process, metal powders are sintered or heated to a temperature that causes the powder particles to bond together.
Controlled sintering leaves interconnecting, winding passages or pores throughout the filter body.
The pores allow air or liquid to flow through the filter. They capture particles at the pore openings on the surface as well as down inside the pore passages.
How are sintered filters made?
For porous bronze filter elements, the manufacturing process used is called pressureless sintering or gravity sintering.
Pressureless sintering begins with pre-alloyed, spherical bronze powders poured into appropriately shaped dies or molds.
Metal powders pour freely, much like a liquid. Vibrating powder-filled dies ensure that metal powders fill the dies but do not leave any voids.
Dies filled with bronze powder are moved to a controlled-atmosphere, multi-stage furnace. The furnace heats the dies to the bronze's sintering temperature. Sintering temperatures are always lower than the melting point of the alloy and its primary metal.
Sintering heat causes the metal to diffuse between the powder particles where they touch. This diffusing metal creates narrow metal necks where the powder particles bond together to make mechanically strong parts.
For filter elements, applying sintering heat just long enough achieves the desired filter porosity.
The sintering temperature and die material are also chosen so that the bronze powder does not bond with or stick to the die surfaces. The dies are then allowed to cool.
After cooling, the final step is to remove the new filter elements from the dies.
Plastic fuel filter assembly combines the porous sintered filter element and filter's plastic body components. Ultrasonically welding the body components together holds the filter element tightly inside the finished fuel filter.
Precision and good manufacturing quality control ensure both leakproof welds and proper filter element placement.
Learn more about plastic fuel filter bodies at the ISM blog >>
What is sintering?
Sintering is a powder metallurgy process where metal powders are fused to create mechanically strong parts. The heat used to sinter a metal powder is less than the metal's melting point. But this heat is still high enough to cause the metal to flow together and bond powder particles together where they touch.
Sintering requires controlled-atmosphere, multi-stage furnaces.
What is the sintering process?
Sintering begins with filling a part die or mold with metal powder.
Pressing or compacting the powder into the die is the next step when making solid parts and porous self-lubricating bearings. The pressure causes the metal powder particles to stick together. While not strong, these "green" parts hold their shape after being released from the die.
For fuel filter elements, the sintering process begins a little differently.
Similar to making solid parts, the process for filter elements begins with pouring metal powder into dies. Vibrating the dies removes any voids or empty spaces. The metal powder remains loose in the dies until sintering.
Are you interested in learning more about sinter filter? Contact us today to secure an expert consultation!
After being shaped in dies, "green" metal parts or powder-filled dies are exposed to a precise sintering heat. Sintering requires controlled-atmosphere, multi-stage furnaces.
This heat is enough to cause the metal to diffuse between the particles (diffusion bonding). This diffusing metal creates narrow necks of metal that bond the particles together. Additional sintering causes these necks of metal to grow.
This "Sinter neck formation" micrograph (photograph taken through a microscope) shows the metal necks that form between spherical sintered metal powder particles.
Sinter neck formation
Enough additional sintering can produce solid parts. Additional heating causes more and more metal to diffuse between the metal particles. Space between particles shrinks to the point where the parts become almost completely solid (densification).
For porous parts, the right amount of diffusion bonding leaves a pattern of holes on the surface. The holes or pores on the surface connect to a complex winding matrix of interconnecting passages throughout the finished part.
Carefully controlled sintering time and temperature create the required porosity of finished filter elements.
Producing porous metal parts requires careful control of these variables:
Metal powders used for making sintered porous fuel filter elements also need to be
Carefully controlled sintering creates fuel filter elements with just the right amount of particle fusion. The result is a highly porous metal with controlled pore size and good depth filtration.
Learn more about sintering and sintering theory in this slide deck from Peter M. Derlet at the Paul Sherrer Institut >>
What is particle size distribution?
Particle-size distribution (PSD) is a way of describing the relative amounts of different-sized particles contained in batches of powder or other granular material. PSD provides particle analysis as a relative percentage or fraction of the total batch of material.
Usually, this information comes in a chart that graphically illustrates both percentages and particle sizes. Special measurement tools and techniques provide the data for these charts.
Sorting batches of powder for very consistent particle distribution is possible using sieving and other techniques.
The particle size data generated from analyzing these powder batches create bell-curved particle-size distribution graphs (see the illustration). The more carefully the powder is sieved and sorted, the narrower the bell curve is.
Manufacturers use highly spherical bronze powders with narrow particle size distributions to make sintered filter elements. The ready availability of uniform bronze powders makes it economical to produce sintered filter elements with specific porosity and micron ratings.
These special bronze powders also make it economical to manufacture sintered bronze filter elements small enough for small plastic inline fuel filters.
Shimadzu, an analytical and measuring instruments company, has a great series of articles on particle size distribution >>
What is diffusion bonding?
Diffusion bonding, also called solid-state diffusion bonding, is a metal bonding process that resembles welding. When exposed to sintering heat, metal diffuses between powder particles where they touch.
The heat of sintering dramatically speeds up a tendency for the metal in each particle to migrate towards and intermix with metal from other particles.
Metal blending and fusion bind the particles together by causing metal "necks" to form and grow where the particles touch. These necks link the metal powder particles together.
Over time, exposure to the sintering temperature causes metal necks to grow larger and become stronger. The formerly loose particles become solidly locked together to make a mechanically strong part.
Find out more about diffusion bonding at Wikipedia >>
What is the difference between sintering and melting?
Pressure sintering, solid-state sintering and pressureless sintering (gravity sintering) all use temperatures below the metal's melting point. This temperature is called the sintering temperature. Even though it is less than the metal's melting point, it is high enough to cause the metal to quickly diffuse between each particle (mass transport). This metal diffusion bonds the particles together (diffusion bonding).
At the metal's sintering temperature, heat bonds the powder particles together, creating mechanically strong parts.
Solid parts and densification
Pressure sintering and solid-state sintering techniques produce solid parts starting with metal powders.
These powder metallurgy processes use a combination of heat and pressure to cause the metal to diffuse between the metal powder particles where they touch. This bonds the particles together. The parts are then kept at the sintering temperature long enough (dwell time) to eliminate the empty spaces between the particles (densification or consolidation).
Pressureless sintering and porosity
Pressureless sintering is the specific type of sintering used to make porous fuel filter elements. Filter elements produced using pressureless sintering have a uniform porosity that runs throughout the metal. Pressureless sintering is a relatively economical and useful way to make metal filter elements.
All sintered parts require special furnaces
All sintering requires controlled-atmosphere, multi-stage furnaces. The controlled atmosphere protects metals from exposure to oxygen-rich air. Exposure to oxygen during sintering creates metal oxide films that inhibit particle fusion.
Controlling the atmosphere or gases inside sintering furnaces also provides better, more uniform heat transfer inside the different furnace stages.
What is the sintering temperature?
In powder metallurgy, sintering is the heat treatment used to fuse metal powder particles to make solid parts. Sintering temperatures are less than the melting point of both the alloy and its primary metal.
Sintering temperatures are lower than melting temperatures because sintering does not use melting to bond the particles together. Instead, the heat of sintering is enough to cause the metal to diffuse between the powder particles. Diffusing metal causes interconnecting metal necks to form, grow and bond the particles together where they make contact.
Porous sintered bronze filter elements used in small plastic inline filters are tin bronze, usually about 89-91% copper and 9-11% tin.
Find out more about sintering temperatures and the difference between it and molten metal casting at Marlin Steel Wire Products >>
Why is sintering done?
Sintered parts made using suitable materials and sintering techniques can be mechanically strong while still being filled with tiny winding, interconnecting passages. Parts produced this way can be used for filtering, sound dampening, sparging, flame and spark arresting, self-lubricating bearings and more.
Sintering causes metal "necks" to form and grow between the tiny bronze spheres. Metal diffuses or flows together at the particle contact points to create solid metal bonds.
The controlled sintering of porous sintered parts provides parts with metal necks that are narrower than the sphere diameters. The result is tortuous or sinuous winding passages that run through the depth of the porous metal walls.
Because porous bronze filter elements start as highly spherical particles, sintering produces filter elements with controlled porosity and specific micron ratings.
For both porous and solid parts, sintering has advantages:
What are powder metallurgy's disadvantages?
Making porous sintered filter elements requires the use of powder metallurgy techniques. They have distinct advantages over other manufacturing techniques for making solid parts.
It is important to note the disadvantages of powder metallurgy processes:
Horizon Technology has a helpful article outlining some of the significant advantages and disadvantages of using powder metallurgy instead of machining to produce metal parts >>
What is pressureless sintering?
Sintering is a powder metallurgy manufacturing technique. Pressureless sintering (gravity sintering) is just one of many types of sintering.
Steps in the pressureless sintering process
Sintering temperatures vary by alloy and are lower than the melting point of the primary metal in the alloy.
During sintering, the metal powder does not melt. The temperature is high enough to cause narrow, metal-to-metal bonds or necks to form where the metal powder particles touch.
The result is a fully hardened, mechanically strong part that has excellent porosity. Porosity is the intricate pattern of winding, interconnecting passages throughout the walls of the finished part.
Pressureless sintering is especially useful for producing filter elements, but the process requires careful control of
A careful, precise manufacturing process provides filter elements with good porosity, which makes them very efficient.
Efficiency means porous sintered bronze filter elements are very good at capturing small particles without creating too much restriction or reduced flow through the filter.
What's unique about the bronze powders used to make fuel filter elements?
It is necessary to control both the filter walls' porosity and the filter element's micron rating when making porous sintered bronze filters. This kind of control requires bronze powder with specific qualities.
Bronze powder requirements for making filter elements
Deoxidizing gives these bronze metal powders a light gloss. Because of this, better-quality sintered bronze filter elements tend to be shiny.
How are spherical bronze powders made?
Gas atomization is the process most widely used to produce highly spherical metal powders.
It involves pouring the molten bronze through inert gas jets. The pressurized gas coming out of the jets breaks the molten metal into fine metal droplets. These molten droplets cool down and harden as they fall.
Metal powders made by gas-atomization tend to have a perfectly spherical shape and are very clean.
What about ethanol, methanol and E85 gasohol materials compatibility?
In general, material compatibility with methanol is more challenging than gasoline-ethanol blends, including E85 flex-fuel. Unless used as a racing fuel, most fuel filter exposure to methanol comes from fuel additives. Additives for treating water contamination or for preventing fuel line freezing sometimes contain methanol as an ingredient. Any filter that is methanol compatible is also E85 compatible.
Find out more about gasohol (gasoline-ethanol) blends and outdoor power equipment from OPEI, the Outdoor Power Equipment Institute >>
Low-quality materials and fuel compatibility
Low-quality paper filter element filters may not hold up well when exposed to gasohol (E10, E15 and E85). Lower-quality filters frequently use adhesives to attach the filter paper to the paper filter element's cap or end. These adhesives usually are not compatible with ethanol. The adhesive bonds weaken over time, and adhesive failure allows fuel flow to bypass the filter paper altogether.
Filter body plastics also matter when it comes to compatibility with ethanol, methanol and gasohol blends. High-quality OE and OEM aftermarket fuel filters have plastic bodies made with materials with very good resistance to ethanol and gasohol blends and limited exposure to methanol.
A good maintenance rule of thumb for plastic inline fuel filters is to use high-quality OE replacement and OEM aftermarket plastic inline fuel filters made by reputable manufacturers like ITW Fastex Filtration and ITW Powertrain Components.
For both Powersports and Outdoor Power Equipment (OPE) applications, recommended best practice is to replace fuel filters at least once every year.
Find out more about ANSI-OPEI B71.10- compliant inline plastic fuel filters and shut-off valves from ITW Fastex Filtration and ITW Powertrain Components >>
What are the effects of ethanol on gasoline?
Ethanol or ethyl alcohol is the alcohol added to gasoline to make gasohol blends like E10, E15 and E85. Ethanol absorbs water more quickly than straight gasoline does. When a small engine with only a partially full tank of a gasoline-ethanol blended fuel sits around for a while, moisture can build up in the fuel system and may separate.
Find out more about standard ethanol fuel mixtures at Wikipedia >>
Ethanol, gasohol and absorbed water
If water does settle out, it settles out at the bottom of the tank. This settling happens because water is heavier than both gasoline and ethanol. This settling can also occur in fuel lines and carburetor bowls.
Fuel containing water can create problems for plastic inline fuel filters that use paper filter elements if they are not compatible with gasohol. Water absorption can cause low-quality filter paper to swell and lose strength.
The paper filter elements used in low-quality filters are also more likely to be degraded by exposure to ethanol. This ethanol also causes low-quality filter papers to lose strength.
Filter elements like porous sintered bronze are not affected by water or ethanol in the fuel.
Make sure that the plastic used for the filter housing is ethanol compatible also. Most lower quality plastic inline fuel filters use plastics that are less able to stand up to prolonged exposure to gasohol.
Low-quality filters are also more likely to be assembled using adhesives that may not withstand gasohol.
High-quality OEM fuel filter manufacturers use filter elements, body materials and assembly techniques not degraded by water and ethanol.
Find out more about materials and chemical compatibility with the ISM Chemical Compatibility Chart >>
Besides fuel and oil filtration, what other applications use porous sintered bronze elements?
Porous sintered bronze is mechanically strong and made with very controlled levels of porosity. These features make porous bronze parts and elements useful for a variety of applications:
Breathers
Breathers filter exhaust gases or incoming air. In this way, they serve as oil reservoir vents, air exhaust vents, air intakes and vacuum pressure equalization ports. Breathers can help reduce the exhaust of tiny, suspended oil droplets, although they are not as efficient as dedicated oil mist filters.
Get more information about the BV series breather vents in the ISM catalog >>
Liquid aeration
Pressurized gas passed through porous sintered bronze elements comes out as fine bubbles when suspended in liquids. The gas in these tiny bubbles is absorbed or dissolved into the liquid. Used this way, porous bronze elements can gasify or aerate liquids (sparging).
Find out more about the use of sparging (chemistry) or gas flushing (metallurgy) at Wikipedia >>
Exhaust mufflers
Mufflers or exhaust mufflers dissipate the velocity and dampen the noise level of compressed air coming out of pneumatic valve exhaust ports, air cylinders, air tools and similar applications.
MS series speed control muffler cross-section
showing the porous sintered bronze element
Get more information about the MS series speed control mufflers in the ISM catalog >>
Condensation traps
The porosity of sintered porous bronze allows it to retain water vapor by causing water to condense inside the porous bronze. In this way, porous sintered bronze elements are used both for drying exhaust and for protecting devices from corrosion caused by moisture entering the system.
Flame suppressors
Flame suppressors or arrestors prevent a flame from entering or leaving equipment while also providing precise gas flow control.
Porous sintered bronze elements have both high thermal conductivity and porosity. These features allow the flow of combustible gasses while preventing ignition. The porous bronze element absorbs and dissipates the heat from a flame front or combustion wave and stops combustion.
Powder fluidization
Sintered bronze can also fluidize fine powder solids. Fluidization is provided by passing pressurized gas through porous bronze elements.
Fluidization makes it easier to manipulate powder solids by causing them to behave more like a liquid. It does this by increasing the solids-to-air ratio. The increased solids-to-air ratio reduces the density of the gas and powder mix. This change in density allows the particles to become suspended and flow more easily.
Pressurized fluid flow control
The porosity of sintered bronze elements can provide a very precise, constant and controlled pressure drop for pressurized fluid processes.
Snubbers or pressure snubbers
Snubbers protect gauges and pressure instruments from damaging shocks caused by sudden pressure surges and fluctuations in fluid or gas flows. As a beneficial side effect, they also help ensure gauge accuracy by smoothing out pressure transients (spikes).
SNUB series pressure snubber
Get more information about the SNUB series pressure snubbers in the ISM catalog >>
Some additional reference resources about porous sintered bronze filters, powder metallurgy and sintering
Advances in Filtration Technology Using Sintered Metal Filters at the Mott website >>
Characteristics and Properties of Copper and Copper Alloy P/M Materials at the Copper Development Association website >>
How Modern Powder Metallurgy Stacks Up Today: A Comparison of Conventional Powder Metallurgy Versus Competing Methods at the Horizon Technology >>
Metal Powder Atomisation Methods for Modern Manufacturing by John J. Dunkley via the Johnson Matthey Technology Review >>
Porous Metal Design Guidebook PDF from SpinTek >>
Sintering Theory by Peter M. Derlet at the Paul Scherrer Institut. It is a lecture slide deck PDF >>
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, sintered porous 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-Filter fuel filters
ITW Fastex Filtration and ITW Powertrain Components Visu-Filter fuel filters are compliant with ANSI/OPEI B71.10-.
The ISM catalog includes
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