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Fire resistance, thermal degradation and heat stabilisers – what do all of these mean?

Silicone rubber has an outstanding reputation for being a reliable, durable construction material with a higher melting point and ignition point than other common polymers such as PP and PVC. These properties make silicone an excellent choice of material for use in high temperature applications. A handful of silicone manufacturers, including here at Jehbco, can enhance the high temperature performance of silicone rubber by including fire resistant additives or heat stabilisers in the silicone manufacturing process. But how do these additives affect the final silicone product, and in which applications should they be used?

When silicone rubber is exposed to high temperature environments for extended periods, as expected in automotive, refrigeration and certain electrical applications, they will lose their elasticity and flexibility, becoming brittle before ultimately tearing. In industry, this is measured by the high temperature exposure time required for the rubber to lose one half of its standard elongation at room temperature. Typically, general silicone rubber can be used indefinitely at temperatures below 150oC, for 1000 hours at temperatures around 200oC and for short periods of time at 350oC and above before breaking. Traditional heat stabilisers such as cerium oxide or titanium dioxide inhibit silicone oxidation, which slows the degradation process by over 100 orders of magnitude. This helps preserve the elasticity and elongation and increase the lifetime of the silicone product.

 

Fire resistance, thermal degradation and heat stabilisers

Fire resistance, thermal degradation and heat stabilisers

 

When exposure to fire or temperatures around silicone’s autoignition point (>450oC) becomes a possibility, then the products’ resistance to thermal degradation and fire resistance need to be considered.  Resistance to thermal degradation refers to the initial ignition point of the material and describes how the rubber will behave when exposed to radiated heat. This is best pictured by thinking of a piece of silicone in a room with a very high temperature. The ability of silicone to withstand igniting at this elevated temperature is its resistance to thermal degradation, and can be quantified under standards such as the AS 1530.3 and EN 45545 standards. These standards measure the temperature and time taken to ignite, the smoke released from the material, time taken to extinguish and amount of heat released during combustion. Which of these measurements is most relevant will vary depending on application. Flame or fire resistance typically refers to the behavior of silicone when directly exposed to a flame. This is frequently standardised using the UL 94 test which measures how long the sample will take to ignite, and how long it takes to extinguished after being immersed in a hot flame. Additives can be used to influence the way silicone combusts in extreme temperatures or in contact with flame, including a variety metal hydroxides which release water vapour upon combustion to cool the subsequent flame, and other additives being developed and tested at Jehbco.

With all this in mind, deciding which blend of additives to use for any application can be difficult. Jehbco offers a unique range of fire additives and expertise in manufacturing fire resistant silicones that are can be custom engineered to suit most specific applications. Many of Jehbco’s existing products are already certified under various international fire safety standards to ensure peace of mind.  For more information about heat stabilisers and fire additives, please visit our website and contact us with any questions.

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Silicone Hardness and Shore Durometer

Jehbco’s silicone extrusions are used in a wide range of applications, from aircraft seals to medical grade tubing.  To make sure you have the right silicone for your application, the application requirements have to be closely matched to the silicone properties.  There are many material properties that may affect our silicone’s performance in your application.  One of the most important properties is hardness or “durometer”.

The hardness of a material refers to how easily the material resists deformation under compression.  Put more simply, if something is pressed against the surface of a material, hardness tells us how easily the material is deformed or marked.   Depending on the material, there are several standard tests that can be used to determine hardness.  Metals are often tested using the Vickers or Rockwell procedures – these press a small tool into the surface of the metal under a standard load and measure the size of the resulting mark.

For elastomers such as silicone, hardness is measured using the Shore Durometer test.  This test measures the depth that a small cone can be pressed into the surface of the silicone.  The depth that the cone sinks into the silicone is converted to a value on the Shore Durometer scale.  The cone sinks deeper into soft silicones and these have a low value on the scale.  If the silicone is hard, the cone doesn’t sink very far and the value on the Shore scale is high.

 

Silicone hardness and the Durometer Scale with Jehbco Silicones

Silicone hardness and the Durometer Scale with Jehbco Silicones

 

There are several variations of the Shore Durometer test for different types of elastomers.  The most common are Shore Durometer A for soft elastomers and Shore Durometer D for hard elastomers.  Each test gives a hardness value from 0 to 100.  The Shore A test is generally used to measure the hardness of Jehbco silicones – most of our silicones fall between 25 and 80 Duro Shore A.  Jehbco has equipment to test Shore hardness to the ASTM D2240 standard.

To get an idea of what the different hardness scales mean, 25 Duro silicone can be easily compressed with your fingers – think of the rubber that rubber bands are made of.  80 Duro silicone is much harder to compress, more like the rubber in a shoe sole.

To ensure that the silicone you choose for your application performs as required, it must have the right durometer.  For applications such as vacuum sheeting, a low durometer might be just right, while gaskets may require a medium to high durometer.  Jehbco can tailor a silicone material to the durometer required for your application.

For any further questions about how durometer will affect your application please contact our sales team.

 

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Silicone Tear Strength

Silicone Tear Strength

Jehbco’s extruded silicone products are used in a multitude of application areas, and we have a range of silicone grades to suit every application.

When selecting a silicone grade for your application, it is essential to determine the tear strength required.  Tear strength measures a material’s ability to resist failure by tearing.  For polymers such as silicone, this is determined by measuring the speed of growth of existing cracks when the material is placed under tension.  This is measured in Newtons of tensile force per millimetre of product thickness.  Tear strength not only measures how easily a material will fail by tearing when placed under load, but provides an indication of the abrasion and wear resistance of the material.

If the tear strength is lower than required, silicone can suffer from wear and form cracks and tears.  Applications such as piping in the food and beverage industries, gaskets, seals and vacuum blankets require silicone free from wear and cracks.  In the best case, cracks and tears will reduce the product longevity.  In the worst case, these cracks and tears can cause product failure, leakage and damage to other parts of the system.

 

Figure 1: Jehbco high tear silicone sheeting for vacuum blankets.

Figure 1: Jehbco high tear silicone sheeting for vacuum blankets.

 

By selecting a silicone with sufficient tear strength, the danger of product failure can be avoided.  A good first step in determining the tear strength required for your application is to look at similar applications and the tear strength of the materials used, measured in N/mm.  Jehbco produce a range of silicones with different tear strengths to suit many applications.

Tear strength is an important material property and Jehbco can tailor a silicone product to the tear strength requirements of your application.  For any help with your application please review the Jehbco website www.Jehbco.com.au, and contact us with any questions.

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Coefficient of Friction of Silicone Extrusions

Friction is the force opposing movement when two materials make contact.  Knowledge of friction is essential for many of our customers’ applications:

  • it determines forces in moving systems such as O’Rings seals,
  • it describes the ability of a seal to remain in place without adhesive
  • it affects the compression of a gasket when pressed between two metal surfaces.
Figure 1: Friction force on a block

Figure 1: Friction force on a block

Figure illustrates the frictional force on a block resting on an incline.  Gravity pushes the block down the incline, and friction opposes this force.  Friction is a phenomenon that is still not understood completely, and frictional force cannot be calculated using any theoretical equation – it must be measured directly for the system of interest.  A surprising and useful empirical result is that frictional force depends only on the force pushing materials together and not on their area of contact.  This is because friction is due to atomic contact between surfaces. The area of atomic contact is very small and depends above all upon the force between surfaces, not their areas.

The coefficient of friction is the ratio of friction force to normal force.  Most material combinations show two types of friction – a strong frictional force when the materials are not sliding (static friction), and a weaker force when they are sliding (kinetic friction).  Different methods are used to measure each type of friction.

To measure the static coefficient of friction, the two materials can be tilted (as in Figure 1) until one of the materials begins to slide.  The static coefficient of friction is the tangent of the angle of tilt when the materials start sliding.

Measuring the kinetic coefficient of friction is more involved, and requires careful measurement of the force required to keep two materials sliding at a constant speed.  Many test rigs have been designed for this.  The most important factor is that the test conditions match application conditions as closely as possible to ensure results are relevant to the application.

Jehbco have developed in-house testing procedures and facilities to measure the coefficient of friction in customer applications.  If friction is important in your application, we can tailor a test to your application conditions and give detailed information on the performance of our products.

For any help with your application please review the Jehbco website www.Jehbco.com.au, and contact us with any questions.

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Cured Silicone Extrusion for Expansion Joint Sealing

Waterproofing is fundamental in construction.  Buildings are designed to give shelter – this means keeping wind and water out.  The most difficult and important job of cladding and roofing is to prevent water entering the building.  Jehbco produce sealing products that make waterproofing of claddings simple.

One of the difficulties in cladding large buildings is thermal expansion.  Temperature variations cause cladding panels to expand and contract.  If the panels are too large or their movement is restricted, this will cause the panels to warp and buckle.  This issue is generally solved by using small gaps which give the structure the freedom to expand and contract.  These gaps between panels are termed expansion joints.  To ensure the cladding system is waterproof, these expansions joints must be filled with a seal that is able to absorb the expansion and contraction of the joint whilst preventing water from entering.

 

Cured Silicone Extrusion for Expansion Joint Sealing

Cured Silicone Extrusion for Expansion Joint Sealing

 

In Australia, the Australian Building Codes Board (ABCB) requires building cladding systems to adhere to AS4284: Testing of building façades.  This ensures that buildings in Australia meet minimum requirements for strength and waterproofing.

Leaks in building façades are a serious issue.  If water enters the building’s outer layer, it can cause damage to insulation, electrical and ventilation systems, wall linings and belongings.  This damage can cost millions of dollars and be very difficult to repair.

Compliance with AS4284 ensures building façades will not leak and expensive damage and repair is avoided.  Expansion joints are one of the most difficult areas to seal and make AS4284 compliant.  At an expansion joint, there is a natural gap for water to enter.  The gap expands and contracts, meaning any seal has to be flexible enough to seal a range of gap widths.

Jehbco silicone extrusion profiles, designed for façade waterproofing, have passed AS4284 certification for use in building façades.  These profiles are pre-cured silicone products, able to expand and contract to seal expansion joints through a range of gap widths.  They are easy-to-install, aesthetically pleasing expansion joint seals which eliminate the hassle and mess of wet seals whilst ensuring AS4284 compliant waterproofing to protect your building.

Jehbco can tailor a facade sealing solution to your construction application. For any help with your application please review the Jehbco website www.Jehbco.com.au, and contact us with any questions.

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Jehbco’s Carbon Footprint

Jehbco is committed to reduce our carbon footprint and making our products more sustainable. This is achieved by ensuring that there is minimal waste in the production process as well as ensuring that are products are made to last. Silicone is made of readily made resources and is a more environmentally friendly and sustainable option than more damaging products to the environment.

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Silicone Extrusions in Aviation

Silicone’s excellent properties and versatile nature make it a valuable material in aviation.  Silicone is able to operate under a wide range of conditions and Jehbco produces customised mixes of 100% silicone materials to meet varied specialised design requirements.

Jehbco’s silicone design and manufacturing capabilities provide light weight, easy to use silicone extrusion products which are an ideal choice for aircraft interior applications such as cabin floor and ceiling panels, baggage compartments and galleys. Silicone materials can conform to national and international standards for aircraft fire safety due to silicone’s fire retardant nature.

Jehbco’s silicone extrusions are able to provide a strong seal over a large pressure differential, making then a good choice for aircraft door and window seals.  In addition, silicone has an extremely wide range of operating temperatures, from -50 ℃ to 230 ℃, and is UV and ozone resistant, making it suitable for sealing applications on external surfaces and for gaskets in engine and power plant systems. Silicone’s high dielectric strength (typically ⩾ 200 MV/m) makes it suitable for flexible electrical insulation. Additionally, Jehbco’s extrusions can be made to meet higher or lower temperature resistance and conductivity requirements that exceed the industry standards for general silicone extrusions.

 

Silicone Extrusions for Aviation and Aircraft Applications with Jehbco Silicones

Silicone Extrusions for Aviation and Aircraft Applications with Jehbco Silicones

 

For applications in confined spaces requiring minimal outgassing, Jehbco is able to produce Controlled Volatility (CV) silicone extrusions. These products are engineered to meet industry standards for low VOC.

The strength of adhesion between silicone and fibreglass resins such as polyester and epoxy is low making Jehbco extrusions an ideal product for fiberglass moulding.

Fluorosilicones for Fuel Applications

Traditional silicone materials exhibit low resistance to hydrocarbon fuels.  However, with the addition of fluoro groups, our silicone’s excellent mechanical properties are combined with high hydrocarbon resistance.  Jehbco’s fluoro silicones have the same high range of operating temperatures, insulation and fire retardant properties as regular silicone.  In addition, fluoro silicones are resistant to damage from common aviation fuels.  This combination of properties has made fluoro silicone a very popular material choice for gasket and O-rings applications in aircraft fuel systems and systems using fire-resistant hydrocarbon hydraulic fluids.

To learn more about Jehbco’s custom engineered silicone extrusions, Contact Our Sales Team.

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Application of Silicone Adhesives

It’s normally not that hard to stick different material together, but when sticking silicone extrusions to different substrates, the only thing that can stick to silicone is almost always silicone.

This is where we often find non-silicone based adhesives fail. They generally lack this property unique to silicone and when failure occurs it can lead in-field leakage, warranty claims and not so happy customers.

We often get asked exactly why Silicone materials are resistant to glues and adhesives. It comes down to the fact of it having a ‘Low Surface Energy” in contrast to other materials.

Brick wall crack which can be repaired by Jehbco Silicones, manufactured in Australia

Brick wall crack which can be repaired by Jehbco Silicones

This means that in short those molecules on a surface of Silicone say compared to standard wood glue are energetically less favourable than other materials. This means Silicone is quite resistant in its own right, making it a great sealing material for a range of applications.

The best adhesives to glue silicone to metal or plastic substrates are silicone-based adhesives. Silicone adhesive works by providing a strong, flexible bond between silicone parts along with high elongation.

Silicone rarely fails in application and in the instances it does, it’s quite often due to contamination of the adhesive. So before installing the silicone seals, it’s necessary to clean the application substrates with clean fabric and detergent.

A variety of detergents could achieve this including detergent with isopropyl alcohol. Use of detergents with lotions, waxes, fragrances, oils or creams is not advisable as then can often leave an invisible residue on the surface.

For example. interior grove walls with grease and/or oil present will need special attention for removal of contaminants. Quite often this will require cleaning with a solution of isopropyl alcohol with warm water and a ‘lint-free’ cloth.

Usage of primers is also another way of adding strength to the adhesion. By priming the surface of a silicone rubber, one can enhance the bond ability potential by changing the surface chemistry. Combined with certain adhesives the user of primers can be very effective.

It is noteworthy that primers normally expire within 18 months from the manufacture date, and if not stored as per manufacturer instruction (i.e. exposed to air/moisture), they can expire prematurely and this is noted by the liquid becoming milky.

 

Dow Corning 1200 OS Primer Clear - Bearing Distributors

Dow Corning 1200 OS Primer Clear – Bearing Distributors

 

A common primer is Dow Corning 1200 OS Primer Clear which can be purchased from Bearing Distributors (61 2 9822 5806). It works well with common silicone-based adhesives such as Silastic 747. It’s important to follow the standard process listed below to prime and apply adhesives to achieve a strong adhesion:

1. Selection
Before you commence the job, it’s critical to work out exactly the materials you need. This may include the cleaning fluid, primer, the wet liquid silicone and of course the solid silicone profile piece.

2. Cleaning
Clean both surfaces, silicone extrusion as well as the frame. Isopropyl alcohol-based detergents works well for cleaning. The premier itself is also a good cleaner!

3. Priming
When both surfaces are cleaned, prime both surfaces (by wiping or spraying). It’s important to let the primer to dry (aka flash) before applying the adhesive.

4. Adhesion
Apply silicone adhesive onto the supporting surface and lay the silicone extrusion onto the adhesive and press it so the adhesive gets evenly distributed in between.

5. Clamping
Clamp the two substrates together for minimum 2 days so the adhesive cures. It’s important not to put too much clamping force; otherwise the sealant would walk away from between substrates. 0.5mm adhesive is the minimum thickness to achieve a strong adhesion.

6. Testing

Once you have removed the clamps, it’s critical to test the strength of the adhesive bond. We recommend the ‘Pull Test’ which is simply pulling the silicone with reasonable strength to see that it holds up. If it comes off there may have been problems with the cleaning or product – if it remains, chances are you have a safe and stable seal.

To learn more about Jehbco’s silicone rubber and suitable adhesives, Contact Us right here.

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Importance of Heat Stabilizing Additives to Silicone

Stabilizers are used to maintain the polymer’s appearance, strength, toughness and flexibility, so as in keeping the performance of the polymer’s existing attributes. Whereas for construction products made of polyvinyl chloride, heat stabilizers are commonly used as window profiles, cable ducts and pipes. But due to heavy metal content, the effects of stabilizers for polymers in the environmental are indeed very disturbing.

Heat is the common weakness of plastics despite its versatility and usefulness as compounds. PVC famous polymer benefitting from the heat stabilizer additives, generally used in many applications such as a construction material, in medical devices, children’s toys, as housing protection for delicate cables and wires, and even in credit cards. However, PVC is also susceptible to heat damage. Several functions must be satisfied by heat stabilizers in PVC that include neutralizing hydrogen chloride, to replace frail carbon-chlorine bonds, and preventing oxidation.

Jehbco Silicones Heater Hose, custom engineered and manufactured in Sydney, Australia

Jehbco Silicones Heater Hose

Ultimately brittleness, hardness and glassiness happen to non-stabilized material while the stabilized material keeps its flexibility and extendable attributes. Although both stabilized and non-stabilized silicone rubber loss physical properties with undisrupted high temperature aging time, but the rate and degree of wearing down was far greater for the non-stabilized samples as compared to the stabilized specimens. Accordingly, blends of stabilizers are used to protect the polymer at various stages throughout the polymer lifecycle.

For many years thermal stabilizers such as cerium oxide, titanium dioxide and iron oxide are being used in silicone rubber compounds in order to prevent the loss of elasticity of such compounds as they age at heightened temperatures.

A principle that is often applied to estimate the practical life of silicone and other elastomeric material is the maturity required to cause the material to lose one-half of its initial elongation. Consequently, a more effective thermal antioxidant for silicone rubber materials has been found, like for instance what has been added to Jehbco silicone rubber would create a large positive effect on their maturity life under elevated temperature.

Indeed, the silicone elastomer additives not only slow down the degradation process of its physical property but they also reduce the generation of environmentally unwanted sewage discharge, which are harmful to the long-term memory of elastomer properties.

For more information about Jehbco silicone rubber heat stabilizers, visit the website and Contact Us right here.

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Silicone Material Resistance to Low-Temperature

Low temperature applications are common in industries like: pharmaceutical, food production, brewing, chemical, refrigeration, automotive, petroleum, textile, electronics and aerospace. Low temperature performance is one of the most overlooked properties in seal performance. Exposure to low temperature can contract elastomeric materials, resulting in decreased compression and possible leakage and when lower than their design limit, seals become less flexible and brittle.

Jehbco Silicones JHS clear tubing, FDA approved, manufactured and extruded in Australia, designed by engineers

Jehbco Silicones JHS clear tubing, FDA approved

A cryogenic seal or otherwise called mechanical seal having a temperature below 0 degrees Celsius. There are series of issues occur for conventional mechanical seals using low temperature products that include being less likely corroded cryogenic fluids but are toxic and are enumerated under the section on “safety and environmental issues”. Almost always low temperature application will be too low for conventional seals. Unless otherwise, an alternate sealing method will be chosen to design a seal which in most cases elastomer take the top spot.

Most of the time cryogenic fluids are poor lubricators, in which mechanical seals successfully rely on the fluid film creation that will now precede issues with conventional mechanical sealing. This can lead to “slip stick” vibration problems where common resolution ended up getting the right materials to use. Consequently during extreme cases cryogenic seals and components needed to be dried first prior to seal installation due to the presence of a lubricant or moisture. This can lead to seal faces shearing or shattering during start-up of machinery.

Furthermore, cold applications freeze any moisture in the surrounding area hence mechanical seals connect the sealed fluid and atmosphere. Which obviously anything within the seal not immersed in the fluid freezes, this happen on mechanical seals with springs outside of the sealed product. Another tendency will occur where the rotating and stationary components are intact, for instance the clamp ring and the gland. On such cases immediate attention is required on face design and / or holder materials of construction to prevent loose or holder distortion.

Due to the earlier mentioned failure applications, study and research continues and it come across the discovery of silicone rubber being able to resist high and low temperatures way better than organic rubbers. Without noticeable change in its properties, silicone rubber can be used with no limit and can excellently withstand cold temperatures. When comparing silicone rubber from organic rubbers, the earlier stay elastic at lowest temperatures when organic rubbers become brittle.

Moreover with silicone rubbers water absorption to roughly 1% only, it can be immersed in water (cold water, boiling water, warm water) for a long time but without significant change on its electrical properties or mechanical strength. Solid silicone sheet rubber’s low temperature flexibility still tops any other elastomer as it remains functional even at lowest temperature. Gaskets and cushioning pads are readily fabricated from solid silicone rubber sheet material. Elastomeric fabrication capabilities counterpart: adhesive lamination, die cutting, water jet cutting of prototypes, slitting to width and production components.

Accordingly, the operating temperature ranges of silicone elastomers are wider than most organic elastomers. Solid silicone rubbers are proven to be more resistant to degradation, do not become soft and irreversibly deform when subjected to low temperatures, naturally flexible at low temperatures which organic elastomers cannot and lastly, can withstand compression set.

For more information on how Jehbco solid silicone rubber reacts to low temperature, browse the website and Contact Us right here.

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