Great Manchester Run 2015

Great Manchester Run 2015

It’s a rare occurrence that the sun shines in Manchester but it certainly did for this year’s Great Manchester Run.

Our very own Accounts Administrator, Andy Rosthorn decided to get on his running shoes in aid of raising money for a great cause, Leukemia and Lymphoma Research.

An estimated 40,000 people took part in the 10km race which is Europe’s largest 10km event, set up as a legacy event after the 2002 Commonwealth Games. Famous marathon runner Haile Gebrselassie was competing in the elite men’s race along with numerous celebrities taking part.

The race followed routes around various landmarks in Manchester including the famous Old Trafford football stadium and MediaCity in Salford Quays, before heading back towards the finish line along Deansgate in the city centre.

Andy finished the race in 51:32, a personal best and a time he was proud of. In total he raised an impressive £320 with Silicone Engineering adding a generous contribution to the final amount.

Andy said “The atmosphere and camaraderie on the day was amazing and I was really pleased with the amount raised for such a great charity which is close to my heart”

Although finding the race challenging, Andy is now thinking of competing in this year’s Salford 10km in September so we look forward to more pictures of the budding athlete in his stride!

Well done from all at Silicone Engineering!

Andy from Silicone runs Great Manchester Run 2015

 

Andy (left) and his friend Gary Rawnsley

 

Great Manchester Run

 

40,000 people set off on Deansgate, Manchester.

Silicone Engineering at the Races!

Silicone Engineering at the Races!

Once again the world famous TT road race returned to the Isle of Man for another year of high speed, adrenaline fuelled, road racing.

After last year’s successful debut TT, the Silicone Engineering Race Team were busy preparing for this year’s event where they were looking to improve in both the bike and sidecar classifications. Over 60,000 people descended on the island to watch the very best riders tackle the 37.7 mile winding course that sees an elevation change of up to 1300ft*.

Lead rider Russ Mountford had a successful festival beating his previous average lap speed by 2 seconds, averaging a staggering 126.8mph around the course. Russ competed in the Superbike, Superstock and Classic TT classifications, finishing 14th, 16th and 16th.

Russ also competed in the 600cc classification where he was 5th in practise however, unfortunately an electrical problem on the bike caused him to pull out of both races whilst running in the top ten.

John Holden came 2nd and 3rd in the sidecar classifications achieving two podium finishes which was great news for the team.

Team manager, Paul Iddon said “We really upped the level in all aspects, both on and off the track in comparison to last year. Silicone Engineering’s sponsorship and branding was really impressive this year with a bigger brand presence in the paddock, which we were all proud of. Russ and John exceeded expectations to really push the team on for the year ahead.

Both riders now look forward to the Southern 100 road race back on the Isle of Man in July.

We’d like to say a big congratulations to all the Silicone Engineering Racing team on another successful TT and good luck for the up and coming races, we’ll look out for the Silicone Engineering logo zooming past!

Facts from Dunlop

*Facts from Dunlop

Silicone Saddles Up for Charity Bike Ride!

Another member of the Silicone Engineering team was busy doing their bit for charity this month. Ulrike Landherr, Senior Commercial Coordinator saddled up for the annual Trinity Hospice bike ride to raise money for the hospice.

Over 800 riders took part in the 30-year-old event which followed a 45 mile (72km) route through the Lancashire countryside. Starting in Lytham, the ride passed through Kirkham and Poulton le Fylde before finishing back in Lytham.

We asked Ulrike a few questions about the ride to get her thoughts on the event:

What prompted you do the bike ride?

I enjoy cycling and keeping fit anyway, but raising money for charity whilst cycling is even better.

Who took part in the ride with you?

My step-sister and a couple of friends

What were the highlights of the ride?

Completing the ride and receiving my medal. I also enjoyed the lunch break in a beautiful rural spot with lovely weather and getting the chance to chat to other participants.

Would you do it again and have you any plans for future rides this year?

This was my third year of doing this ride and I am aiming to participate every year as long as possible. There is one next month also organised by Trinity Hospice which goes from Manchester to Blackpool (60 miles) – I am thinking about partaking as long as my legs will let me!

 

Ulrike completed the ride in 5h 30m and managed to raise £103 for the hospice which was a great effort.

A big congratulations from all at Silicone Engineering!

Difference between platinum and peroxide curing?

When we talk about platinum or peroxide curing in the silicone world, curing is when the silicone rubber is chemically cross-linked by means of the addition of a peroxide or platinum curing agent. The curing agents differ chemically to give the end product, in this case silicone, different properties. Here we look at the positives and negatives of each system to make it clearer when deciding on what silicone material you require for your application.

 

Peroxide Cured Silicone

Positives

  • Easier to process – needs less temperature to cure the silicone
  • Once mixed, a peroxide cured silicone compound has a vastly superior shelf life so can be stored and used for longer
  • Generally cheaper to buy the raw ingredients so more competitive prices
  • Tried and tested systems and the industry standard

Negatives

  • Sheets and tubing not as clear as platinum cured silicone. Peroxide is more translucent in appearance rather than transparent
  • Needs talc or an introduction of a liner to prevent the silicone sticking to itself especially when manufacturing silicone sheeting

 

Platinum Cured Silicone

Positives

  • Sheets and tubes are clearer so more visibility through the material
  • Can be run talc free
  • Generally physical properties are better especially tensile strength and tear strength
  • Viewed as being the cleaner silicone out of the two which is why it is favoured in the Food, Beverage and Medical sectors

Negatives

  • More expensive than peroxide which can be prohibitive if cost is an issue
  • Harder to process – needs relatively high temperatures to cure
  • Short shelf life – once mixed the compound has a very short shelf life and so this usually leads to waste such as head set ups being scrapped etc

At Silicone Engineering we offer both peroxide and platinum grades of silicone. The majority of silicone we make is peroxide cured silicone however for applications within the Food, Beverage and Medical sectors, we also offer platinum grades which are favoured in these sectors.

Overall, both curing systems produce quality silicone materials if manufactured to high standards and specifications. Both have positives and negatives and which one you choose should be in relation to the application and where the silicone will end up.

Open and closed cell silicone sponge differences?

It is important when choosing any form of silicone sponge to understand the difference between open and closed cell. Confusing the two could lead to failure of a seal or gasket in application.

Open Cell Sponge

Open cell basically means that each cell, or if you like bubble, is openly connected to the next cell. These cells are not complete closures therefore water, moisture and dust can very readily make their way into the cell structure.

A good example of an open cell sponge is the type of sponge that is used to wash a car or wash the dishes at home. If you place the sponge in a bucket of water, you see the sponge soaking up lots of water which is then squeezed out again onto the car. The water is allowed to pass through each cell and therefore gets absorbed and held within the sponge.

Closed Cell Sponge

Closed cell sponge has a much different cell structure to open cell. Each cell in a closed cell silicone sponge is a complete closed sphere trapping air within each cell. Unlike open cell, water, moisture and dust cannot readily enter the cell structure due to the lack of connectivity between the cells. Closed cell sponge is great for sealing when water and dust need to be kept out of an application as it has very low water absorption. Our silicone sponge can achieve IP65 and IP66 ratings for sealing performance.

closed cell sponge

What is Water Absorption?

At Silicone Engineering we produce closed cell silicone sponge. This is a big selling point as many applications require protection from water and dust ingress.

We’ll use the example of what would happen if an open cell sponge was used in an airplane assembly; If the sponge seal absorbed moisture on the ground, once in flight at 32,000 ft the moisture would then freeze causing the assembly to expand, crack and fail, potentially causing a disaster.

Due to very low water absorption in closed cell sponges this would not happen and is why they are used as seals and gaskets in the Aerospace industry.

plane2

Closed cell sponges also tend to be a lot firmer because when you press the sponge, as well as compressing the rubber you are also compressing the air inside the cells. With open cell sponges this air can escape when compressed therefore the only resistance is from the rubber itself.

So when choosing silicone sponge for a certain application, make sure you understand the difference between open and closed cell.

Discover more about Silicone Engineering’s closed cell sponge grades, both sponge sheeting and sponge extrusions

 

What Makes Rubber Stretchy?

There is one thing that all rubbers, natural and synthetic, have in common – they are all stretchy. In essence that’s what makes rubber, rubber!

But what exactly makes it stretchy. The answer to this is entropy.

Entropy is a state of disorder. There is an important law of physics called the Second Law of Thermodynamics which says that a system will move from a state of order to disorder. We have all seen this in everyday life. For example a room is easy to make messy but hard to make clean again. It is easy to crash a new car but hard to repair it afterwards.

Entropy is often inconvenient but it is also the thing that makes rubber stretchy. Remember that rubber molecules are polymers and are shaped like very long chains. When a piece of rubber is just sitting there without any strain, the molecules are just tangled up in a random mess, similar to the diagram below:

entropy 1

When molecules are like this we say they have a high degree of entropy. However, when the rubber is stretched, the chains become aligned in one direction, like the diagram below:

entropy 2

When the chains are aligned they are in a state of order. They don’t have as much entropy as they did before the rubber was stretched. Once you let go of the rubber the chains go back to their relaxed state of high entropy and disorder. This is what makes rubber go back to its original shape and size.

You can observe this happening yourself by taking an rubber band with your two hands and stretch it. While it is stretched hold it to your face and you should feel the band become hot. This is because the chains can line up into extremely ordered arrangements called crystals. This is how the rubber molecules are arranged in a crystal:

entropy 3

When molecules form crystals they give off heat hence the reason the rubber band gets hot when stretched. When you let go of the rubber band the polymer molecules break out of the crystals. Whenever molecules break out of crystals they absorb heat hence the reason the rubber band now goes cold.

Cross-linking

There is something else that makes rubber stretchy and that is called cross-linking. Most rubber objects are made of some kind of cross-linked rubber. Cross-linking is a way of chemically joining all the polymer chains of a piece of rubber into one giant molecule. Take a look at the picture below and you can see the difference between a polymer that is cross-linked and one that isn’t.

polymer

In a piece of cross-linked rubber, the cross-links (shown in red) tie the polymer chains into one specific shape. This means the rubber will hold its shape better. Without cross-links, the rubber might deform after being stretched over and over again.

How much does silicone rubber stretch?

Some Silicone rubbers can stretch up to 1000%! (That’s about 100x its original length!)

Typically the softer the silicone the more it stretches, 20 shore will stretch a lot more than an 80 shore grade. In addition, Silicone Engineering has specially designed specific silicone grades that can outperform a regular silicone, grades such as our high tear or platinum cured silicone have a much-improved elongation than a general purpose silicone.

Typical general purpose silicone elongation range can be from 300 to 500% maximum elongation, with higher hardness grades of silicone tending to the lower end, and lower hardness grades tending towards the higher end.

Got another question about silicone or want to find out more? Speak to one of our silicone experts by clicking here or view our products.

What is the shelf life of a silicone product?

Standards that give shelf lives for elastomers, group different types into categories. BSI SO2230 puts silicone into Group C which has the lowest sensitivity to ageing effects and gives silicone an initial ten years shelf life.

After this it needs to be tested in some way to prove that it is still “fit for purpose”. Fit for purpose usually means that the material still meets the manufacturers original specification although it can be very difficult to test an extruded or moulded part to original specification nevertheless things can be done. Thereafter it needs testing every 5 years.

Another British Standard Aerospace Series BS 4F 68 puts silicone into group X, shelf life for Group X and none specified. Both of these standards are quoted on the Silicone Engineering delivery notes.

Silicone Shelf Life
Silicone Shelf Life

Silicone Rubber – Life in Service (LIS):

Once again and as is often the case with these questions it all depends on many factors. When we get asked about shelf life of silicone it often relates to the environment of where it is being kept. If the product is packaged and delivered and placed on a shelf in perfect cool conditions then shelf life would be an awful long time.

In our laboratory, we can perform heat age testing where we prematurely age the product by exposing it to elevated temperatures, this has the effect of increasing the chemical reaction. This is what decomposition is, a chemical reaction, this is why the product needs to be kept in cool conditions. At intervals during the aging period, Silicone Engineering removes a sample and performs various tests to determine how much it has degraded. After each time period the product becomes worse. As a general rule, when a product’s physical properties degrade to approximately 50% of its original values then the stuff is getting to the end of its useful life and is probably no longer fit for purpose.

Why would any designer specify 400% elongation and keep the part in service when the elongation was now much lower at say 100%?

You will notice words are commonly used like probably, general rule and approximately, this is because with these discussions nothing falls off the edge of a cliff, it is a gradual thing that is happening as the silicone degrades and someone needs to “make a call”. This general rule is not the same for every customer or application, indeed the silicone may still work well down to as far as 10% of its original properties but realistically they would want that percentage to be a bit higher. Consideration needs to be given to the various stages within the life of the silicone.

– Used brand new = standard life in service (whatever that is for the application and conditions)

– Been on the shelf for 10 years = standard life in service, minus some

– Been on the shelf for 20 years = standard life in service, minus some more

How do Silicone Engineering quantify the “minus some” and the “minus some more” because the rubber has aged. There is another rule of thumb that is generally accepted in regard to performing ageing testing to try to predict the life of an elastomer. An increase in temperature of 10°C will effectively halve the life in service. Therefore, if a seal operating at 50°C would last 6 years in service, then an increase of service temperature to 60°C would halve the life in service to 3 years.

This is of course a rough estimate and should not be taken too literally but it gives a broad answer.

Of course the opposite works too in regard to shelf life, keep it cool and it will last longer however, this does not mean in freezing temperatures as this could also have a negative effect on shelf life.

Silicone Base Rubber
Silicone Engineering’s Mill Room

Life in Service example;

They test a silicone sheet as found (new) and record the results. In service the sheet will operate at 150°C. Silicone Engineering then heat age a similar sheet in a lab oven at a higher temperature say 200°C (but it could be higher or lower) until the physical properties are approximately 50% of the original values. For this particular application and for purposes of this example, we can say that product has reached the end of a useful life in service. Using the above ‘ready reckoner’ formula, and using it in reverse, we can then work out an approximate life in service at 150°C.

LIS Continuous @ 200°C = 6 weeks

LIS Continuous @ 190°C = 12 weeks

LIS Continuous @ 180°C = 24 weeks and so on

I have worked out that LIS Continuous @ 150°C would be around 190 weeks.

If the product was seeing 150°C for only 8 hours a day then the LIS would be approximately three times this.

This is a hypothetical example to show you how operating temperature can affect the life in service.

Silicone Sponge
Silicone Sponge Extrusions

To conclude, storage, packaging, temperature, humidity, mechanical/abrasion, pressure from stacked items are all important factors that can affect the shelf life of silicone rubber. Under ideal conditions silicone even after a considerable time will arguably still be in the same condition it was on the day of manufacture and will be fit for the purpose for which it was made. If stored in hot conditions with other adverse influences then the shelf life can be reduced somewhat. Shelf life and life in service are linked as one will affect the other. During adverse storage the shelf life and so the life in service is potentially eroded however, it is important to remember it is a gradual process of degradation which happens naturally.

After a period of 10 years, parts need to be inspected to ensure the physical properties are not reduced. The truth is though, that it is when the parts are in service that significant degradation will take place and it is then that Silicone Engineering cannot legislate for the uncertainty of, and the variation in, the service conditions. Life in service will be very different to any ageing conditions undertaken in the lab, so they cannot say how long a product will last in service, only try to back up and support other information that may suggest a LIS estimate. Silicone Engineering would also guess that in the days of Just In Time etc. there will be few cases of companies buying silicone then stock piling them for 10 or 20 years.

To find out more about our Silicone Products visit our Products page or to find out how silicone compares to EDPM, view our comparison.

How easily does silicone stick to different surfaces?

Silicone Adhesion

We often get asked a number of questions relating to silicone sticking to other surfaces and substrates. As simple as it may seem, the answer is often more difficult depending on the types of materials involved in the adhesion process. Here we will try to explain the basics of silicone and its adhesive properties to other surfaces.

Once cured, silicone can be extremely difficult to stick to surfaces. Silicone rubber will almost always need some form of adhesive to enable them to fix to a surface and in many ways can be related to Teflon by the way it repels things sticking to it, hence the reason Teflon® is use for frying pan coatings.

713

There are many different adhesives that can be used from double sided tape all the way to uncured silicone. Different surfaces such as glass, wood, metal and plastic do possess different adhesion properties i.e. good or bad or somewhere in between.

Many customers are puzzled why they experience problems when trying to glue silicone to some other substrate. Here we try to explain some fundamentals that need to be understood if you need silicone to stick to another substrate.

Firstly you need to understand that silicone does not stick to anything other than the adhesive system or the PSA (pressure sensitive adhesive). This means silicone does not interface directly with wood or metal or any other material, instead it interfaces with the PSA itself. The diagram below explains this.

Silicone rubber adhesive diagram

PSA

Pressure Sensitive Adhesive is what it says it is – an adhesive which is sensitive to pressure. If the adhesive strip/sheet is applied to a surface and pressure is applied to it, it will stick. The trouble is that as stated before, different substrates will stick better than others.

Surface Energy

This is the problem! There is a numerical value and unit that depicts how readily or not any particular substance will accept glue or PSA. There are many different types of glue/adhesive systems some of which utilise a chemical reaction to create a bond, PSA relies purely on “mechanical bonding”. Surface energy or interface energy, can be measured and if a surface has a low value then it will be difficult to adhere to. It will be no surprise that silicone has a low surface energy value therefore creating a non stick surface.

For example: If you take a sheet of silicone and pour on some water, the water will just run off and will not “wet out” as they say.

Looking at the chart; silicone lies around the same vicinity as Teflon® (PTFE) which as mentioned earlier is what they coat onto non-stick frying pans. Surface energy is measured in dynes per centimeter. The dyne level is the actual reading of the critical surface tension. The chart below compares the relative surface energy of commonly used substrates. Silicone comes right at the bottom with a value of 24 along with Teflon®.

Relative surface energy table

 

Although a problem, the Alchemists have been at work to help out as usual. By means of the addition of various chemicals to the materials surface, the surface energy of Silicone Engineering’s silicone can be increased somewhat in order to allow at least adequate adhesion. It is difficult for just anyone to achieve this level of adhesion as these chemicals are not too readily available and they need to be used within strict application and operational guide lines.

So to answer the original question, silicone is not any more difficult to adhere to one surface than it is to another, it is the ability or not, due to surface energy, of any material to adhere to the PSA.

If they take silicone and try to stick it to two different materials say EVA and Nylon, one would get the impression that silicone sticks to Nylon better than EVA however, it is the Nylon’s ability to adhere to the PSA that is better than EVA’s ability to adhere to the PSA.

What does silicone not adhere/stick to? What does stick to silicone rubber?

Due to the low surface energy of cured silicones, it is almost impossible to get anything to easily stick to silicone. Because of this special glues and surface preparations are needed to bond cured silicones to another material.

What glues work with silicone?

Once cured Silicones can be notoriously difficult to adhere, here are a few tried and tested methods below.

  • RTV’s (Room-Temperature-Vulcanization silicone)
  • Special acrylics/PSA (Pressure sensitive adhesives)
  • Heat vulcanized silicone glue

If a customer has an adhesion problem with our silicone, Silicone Engineering first ask is the silicone coming away from the adhesive or is the silicone along with adhesive coming away from the other surface. As with silicone, other surfaces can be difficult to adhere to, look at the list in the Low Surface Energy column above. Trying to stick PSA backed silicone sheet to aluminium would produce a good bond, but using the same sheet and trying to stick it to Teflon, the bond would not be very good at all.

Silicone does not have a problem with sticking to other materials but it is the PSA that might!

Silicone Engineering have the capabilities to adhesive back both sheeting and extrusions. To find out more about our silicone products, ask one of our experts.

What is compression set?

‘Set’ is a term that is used to describe something that has been deformed by a force and when released does not return fully or at all to its original shape – it is said to have “set” in this position. Caravan tyres are a good example. When the owner lays up the caravan for the winter, he needs to ensure the tyres are properly inflated. If this is not done and the tyres are left underinflated, due to the weight of the caravan the bottom of the tyre that is in contact with the road will squash flatter than it should. After being left in this position for 5 months the tyres develops a “set”. Even when subsequently properly inflated, the tyre will retain a set and will be misshapen and useless. When a customer closes a door onto a Silicone Engineering sponge gasket, they want to know that it will spring back when they open the door so that on closing again, the seal is maintained. Good compression set properties are mostly to do with good rubber choice and fully chemically cross linked and post cured products. The compression set test is a common test in our laboratory.

A standard test specimen is measured then compressed in a jig to a certain percentage of its original thickness. The jig is placed in an oven at high temperature for a specified time then released and left to recover whereupon it is then re-measured. A calculation is done and a compression set value is derived.

Note: It is important to be aware that there are two ways to represent compression set.

As an expression of the amount compressed.

% = ((t0 – t1) / (t0 – ts)) x 100

As an expression of the overall thickness of the test specimen.

% = (t0 – t1) / t0 x 100

Where,

t0 = original thickness

t1 = thickness of specimen after recovery

ts = thickness of the spacer bar used

The difference is that the “Numbers” will be different, people just look at numbers without necessarily understanding the significance. At 1 above, the percentage set is a percent of the thickness compressed whereas at 2 above, the percentage set is a percent of the overall thickness of the test piece. Let’s give an example;

A 20mm specimen is compressed by 50%

(20mm – 15mm) / (20mm – 10mm) x 100 = 50% compression set.

(20mm – 15mm) / 20mm x 100 = 25% compression set

Silicone Engineering can see from the above that if the customer considers the number only i.e. 25% or 50%, then they think that number 2 is better yet both of these are the same, they are only representing them as different functions, number 1 as a function of the amount compressed and 2 as a function of the overall thickness of the specimen. It is therefore, important to know which standard is being used when looking at compression set values. This is because also, the pass/fail criteria is different for each of methods 1 & 2. Take a look at the table below.

Standard Maximum Compression Set %  Calculation (from above)
SAE AMS 3195/6 60 1
ASTMD 1056 60 1
EN ISO 1856 15 *** 2

*** EN ISO 1856 (or its predecessor) is the standard that Silicone Engineering have used throughout its 55+ year history. The standard tells you how to conduct the test and how to calculate the results, unlike the other example of ASTMD 1056 where this is both a standard and specification, EN ISO 1856 being only a standard does not stipulate a maximum compression set value, this is left to the individual to decide. In this example, SE decided to use this standard and to specify its own value at 15% maximum compression set.

Compression set in Silicone Sponge – Open and Closed cell:

It is also important that the customer knows whether the cell structure is open or closed as this has a bearing on the test itself and can make a huge difference to the value. Here are all the parameters that are needed to perform the test.

– How much to compress the sample

– How long to go in the oven

– Temperature of the test

– Recovery time before re-measuring

– Calculation to use.

Compression set more than virtually any other rubber test, needs to be qualified by reporting all the above parameters. It is useless to quote a number without the accompanying data which shows how it was performed and under what conditions. This is because all of these items will and do affect the values quoted. Squash it more – the result will be worse, leave it longer, turn up the heat – the result will be worse. When the compression jig is opened and the samples released, it takes time for the sponge to return to normal. ASTMD 1056 points out that open cell sponges require 30 minutes recovery before re-measuring whereas closed cell varieties require 24 hours recovery before re-measuring.

Why is this? When open cell sponges are compressed, the air within is immediately expelled and depending on the amount of compression, the rubber content is compressed some. On releasing from this compression, the air immediately fills the cells returning the sponge very quickly to near normal. Closed cell sponge works a bit different.

When the sponge is compressed, the air inside each cell is compressed and depending on the amount of compression the rubber content is compressed some. With the open cell sponge the air has gone straight away but with the closed cell sponge the air cannot escape but is compressed. As the temperature increases within the ageing oven the air will become even more pressurised. Silicone rubber is a permeable elastomer. This means that gases including air will penetrate then permeate the very thin membrane like walls of the sponge cells. Over the next 24 hours – the duration of the test – some air will escape due to the high temperature and pressure exerted by the test jig. On releasing from this compression, the partially airless cells want to hold the sponge in the compressed state – a bit like sucking it in! The rubber portion of the sponge (the other portion is air) will try to exert pressure through its natural “memory” however it is initially fighting against the fact that each partially evacuated balloon is resisting. Atmospheric pressure and silicone’s inherent permeability will, over time, recover the sponge to “near” normal.

Rather a lengthy explanation hopefully by now you can see that there is a vital difference between the two types of sponge that needs to be recognised and acknowledged. Herein potentially there is a problem. Customers who have historically dealt with open cell sponges and so are used to very fast recovery times, expect the same from our closed cell sponge.

To recap: ASTMD 1056 points out that open cell sponges require 30 minutes recovery before re-measuring whereas closed cell varieties require 24 hours recovery before re-measuring.

There is good reason for this as explained above, and those who have written the standards have done so from a point of knowledge on the subject however, even after having had this explained and pointed out, some can be adamant that they need 30 minute recovery.

To find out more, check out our silicone products page!

Why is silicone classed as a premium rubber?

Silicone seems to be more expensive than other rubbers, why is this?

Silicon is the second most abundant element in the Earth’s crust (about 28% by mass) so if it is so abundant we ask the question – why is it so expensive? Here we try to explain why silicone rubber is classed as a more premium rubber compared to more conventional rubbers on the market.

There are many factors dictating the cost of any particular product, supply and demand, rarity, desirability. Cost is determined by availability, degree of difficulty in harvesting it, the kind and amount of processing required, the versatility of the product and market prices

Essentially silicone costs more due to the high energy costs associated with its manufacture (conversion of sand to high purity silica, then further refinement of silica before the chemical reactions that polymerise it), there are also a number of expensive components needed during the manufacture of silicone (copper metal, hydrogen fluoride). Also, silicone only makes up a small part of the global chemical industry – there is a significant economy of scale in the petrochemical industry at raw material production that silicone just doesn’t/can’t match.

In the end though, silicone is a product that is noted and universally accepted as being the best in class elastomer for extreme temperature environments which offers a unique combination of performance that justifies its cost in comparison to other elastomeric materials.

Difference between ‘curing’ and ‘vulcanisation’? – Silicone

In practical terms, there is no difference between curing and vulcanisation. The name for the process by which any elastomer material becomes cross linked is curing. Vulcanisation is the name used for curing when a system uses sulphur.

What does HTV mean?

High Temperature Vulcanisation

Why are some silicone rubbers specified as ‘addition cure’?

Addition cure silicone is what we call Platinum cured. Addition Cure refers to the method by which the cross links form in the rubber. In a traditional peroxide cure silicone rubber, thermal breakdown of the peroxide creates the chemical that forms the cross links between the polymer chain. In an addition cure system certain side branches on the chains themselves link together to form the cross links. In many common compounds this reaction needs platinum to be present in the formulation to act as a catalyst.

What does thermoset (cross linked) mean?

Silicone rubber used at Silicone Engineering is mainly of the HCR variety. In this world of abbreviations people sometimes understandably get mixed up. HCR is often referred to as Heat Cured Rubber however, High Consistency Rubber is the correct abbreviation.

HCR uses a heat-activated peroxide cure catalyst system to chemically cure the rubber. This converts the material from compound to rubber form.

A cross link is a chemical bond that links one polymer chain to another. Thermoset simply means the silicone compound has been “Set” by means of “Temperature” (Thermo).

The most basic answer is that a Thermoset is a material that has been irreversibly cured, normally by the use of temperature. Cross Links are the chemical bonds that form between the individual polymer strands during the curing process. When something has been “Cross Linked” this means that it has been cured.

What is the UL94-V0 safety standard?

Here we look at the UL standard 94-V0 which is used as a safety standard across a number of sectors relating to material’s flammability.

UL stands for Underwriters Laboratories, an American Company similar to BSI, the British Standards Institute, in the UK. UL write safety standards that cover almost everything imaginable, and issue approvals for products that their auditing and counter testing says meets the requirements of a specified standard.

UL94 is a standard set by UL for testing for flammability of plastics however, the standard is widely used and accepted within the rubber industry. For UL94-V0 there are many different tests within UL94 including vertical, horizontal and 45° flame tests which all are given different classification designations. This particular one (V0) is a vertical flame test which depending on results, V-0, V-1, or V-2 classification can be achieved, V-0 is the most difficult to achieve and is what most customers require.

Where do UL94-V0 products get used?

Generally, UL standards are used as a safety rating in a wide range of applications, from telephone receivers and computer screens to domestic ovens and hot water boilers. Whenever people are concerned about the hazards as a result of their product burning, then UL94 is becoming the most commonly referenced standard where there is no pre-existing industry norm.

Naturally UL parts are used where it is important that in the event of a fire, silicone would play its part in keeping the fire at bay. Silicone is usually laminated onto or becomes a part in a “composite” and it is this composite that needs to ultimately meet the UL standard for flammability. Applications are too many to mention suffice to say that to enter into the American market, all household and domestic products such washing machines, televisions, vacuum cleaners as well as automotive and electrical/electronic wiring and components need to comply with UL at some point.

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