Category Archives: Rubber

All our blog posts that are to do with rubber

Allcocks at the IRC Rubber Convention 2014 – Manchester

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As we blogged at the time, we attended and manned a stand at the IOM3’s Rubber Convention this year in Manchester. We enjoyed meeting many people from the rubber industry as well as those researching the next big developments for rubber.

Andy Rushton and our stand at the IRC Rubber Convention 2014

Over the two days of the convention (14th and 15th May) we gave out two copies of a history of Manchester in photographs. The first was won by Ms Karin Janet Stein Brito (see picture below) of the Polymer Technology Centre – SENAI in Brazil, whilst the second was won by Mr Bill Adam of Adam Polymer in the UK.

We look forward to the next conference and hope to spread the word of Rubber Reclaim and Rubber Crumb such as their benefits in formulation and myriad uses.

The Cake Analogy – Fillers

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Fillers

When it comes to the rubber industry, there is one metaphor that seems to explain all the necessities and intricacies of rubber. “Making rubber is a lot like making a cake”. Since starting at J Allcock & Sons, I’ve heard it over a dozen times, and it still surprises me how apt a saying it is!

I’ve tried punching holes in the saying, and thought I’d finally done it when it came to this subject. If virgin rubber is the flour, release agents the butter on the tin and accelerators the yeast, what would fillers be in the cake analogy?

Calcium Carbonates – CaCO3­

Calcium Carbonate is a classic filler for the rubber industry. A cheap and fine grade filler suitable for almost all rubber compounds. If you want to reduce the cost per kilo of a rubber compound (and have already tried reclaim/rubber crumb, we hope!) CaCO3 can stiffen up a compound as well as significantly decrease the total cost of a compound, but it will decrease the compound’s physical properties (another point Reclaim and Crumb can beat CaCO3 on)

J Allcock & Sons provide 2 main types of Carbonate, Trucarb and V/40S Whiting. Trucarb is affectionately known as ‘Ground-up Derbyshire’ as it is simply naturally occurring limestone ground into a fine powder. If you are looking for a cheap filler, Trucarb is the way to go. V/40S Whiting is exactly the same chemically as Trucarb, but acquired from evaporating river water in Italy, and is therefore purer. This produces extremely fine powder of bright white, which is perfect for decreasing the weighted cost of a white compound, without dulling the brightness.

Here is the first hurdle for the cake analogy. Calcium Carbonate is, ironically, a lot like Sodium Bicarbonate in cakes, reducing the total amount of flour needed to produce the same amount of cake batter.

Taken From: http://www.glogster.com/marianchemistry5/calcium-carbonate-sophia/g-6mfbv68tglod14n058a6ja0

Barytes

Barytes is a powder of Barium Sulphate, and is at least twice as dense as CaCO3. Barytes is extremely good at adding weight to your compound, such as a use in moulding rubber weights. Barytes is also very resistant to acid corrosion, as well as x-rays, infrared and radar. It can provide a ‘deadening’ quality to the rubber compound too.

We provide a single grade of Barytes, Barytes Supreme, which may not provide stealth-grade material, but will bring weight and deadening to a rubber compound.

Barytes could be considered as the fruit and raisins of a cake, any rubber compound made with Barytes will come out like a fruit cake; hard, heavy and resistant to almost anything.

 

Taken from: http://www.barytes.org/barytes.html

‘Talc’/Magsil – Magnesium Silicate

Talc is another speciality filler for the rubber industry (as well as plastics, paints and paper). Thanks to it’s microscopic disc shape, Talc is able to add slip to a compound (see below for an excellent diagram). Very little talc is needed to help a compound through extrusion and calendaring, as well as adding some mild reinforcement to your compound. Talc has an extremely ‘active’ surface, again due to the flat disc shape of the particles, and thus can absorb sulphur and slow a compound’s cure rate. This can be rectified with the use of glycol.

Taken From: http://en.wikipedia.org/wiki/File:Talc.GIF

Talc is also often used externally on a compound as a dusting agent (or anti-tack agent) , allowing the stacking of uncured compound sheets without the risk of them sticking together (exactly like the cosmetic use for Talcum powder).

Talc can also be partnered with Silanes, a molecule designed to chemically bond fillers with compounds such as rubbers and plastics, allowing a much larger amount of filler to be used without the degradation of properties normally associated with the use of fillers en-masse. (this will be expanded upon in the next blog post)

Two grades of Talc are available from J Allcock & Sons; Magsil Topaz 350 (or T350) which is our standard Talc, or Magsil Diamond which is a finer powder and thus is able to add greater slippage.

With its brilliant white colour, this fine powder has to be the icing on the cake, literally. Though icing sugar may not add slip to the top of a cake, it is a final addition that completes the baking of a cake in much the same way as powdering with talc signifies the completion of a rubber compound’s mix.

Thanks to Norman for helping with the technical details and editing. As always, if you have any questions please don’t hesitate to contact me by e-mail at matt@allcocks.co.uk or by telephone on +44 (0)161 223 7181

Rubber Reclaim Part 2

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Although we’ve blogged about Rubber Reclaim in two previous posts (31/08/12 & 13/09/12), we thought another blog would reinforce Rubber Reclaim as a viable rubber hydrocarbon source, carbon black source and process aid.

In the 31/08/12 blog, which is still available to read, we wrote about how it is made, its basic properties and why a compounder should use it. In this post we hope to expand on these slightly and talk about ourselves, as UK and European suppliers of Reclaim.

How Rubber Reclaim is made:

Step 1) Collection and Selection of suitable materials

This is probably the most important step. In order to get a uniform and consistent product you have to use the correct materials. This is a part of the process that for many years has been overlooked hence producing inconsistent materials.

Step 2) Reduction in size and removal of contaminants.

In Tyre Reclaim this consists of removing the bead wire, cutting out the side wall then granulating the remaining materials to 2-4mm removing textile and metals.

In Butyl Reclaim Tubes are de-valved  and patches removed before being granulated.

Step 3) Blending

The rubbers are mixed with the chemicals required and the oils needed for the reclaiming process to take place.

All the chemicals and oils used today are REACH registered and compliant on PAH’s

Step 4) Cooking

This is where the materials are heated up. There are 2 main ways this is done either using an extruder to produce mechanical heat. Alternatively the materials are cooked in a digester using steam pressure to give 160° C

Step 5 ) Mastication

Either in the extruder or on a 2 roll mill the rubber is worked which breaks the polymer chain, also refining and blending the reclaim

Step 6) Filtering

The better quality producers at this point extrude the materials through a 60’s mesh (250 µm) filter to remove any undigested materials (nibs)

Step 7) Finishing

The filtered material is either extruded into blocks or is put back on a mill where a paper thin sheet is built up to 15mm thickness before being cut into blocks, coated in anti-tack agent and weighed off into the desired bundle weight (normally 25 kilos, but any bundle size is possible on request)

So why should you use Rubber Reclaim?

3 Reasons; RHC Source, Carbon Black Source and Processing Aid.

1) Rubber Hydrocarbon Source

Reclaim is a more cost effective source of rubber hydrocarbon than virgin rubber.

  • Attractive Price – Reclaim generally contains 50%+ RHC . For every 1% Reclaim you add you save 0.6% on Compound Cost*
  • Price Stability – Prices are not affected by NR and SBR prices.

* Based on an average compound cost of £1-70/kg

NR Prices versus Reclaim Prices

NR Prices versus Reclaim Prices

2) Carbon Black Source

  • Tyre reclaim contains approximately 27% of reinforcing Carbon Black
  • Easy to use as a Black Masterbatch
  • Much cleaner and easier to handle

3) Processing Aid

  • Improved Processing
  • Uniformity
  • Low Heat Development
  • Low Thermoplasticity
  • Minimum Reversion
  • Low Swelling and Shrinkage
  • High Rate of Cure
  • Good Aging
  • Good Shape Retention
  • Improved Tack

Other Savings include reduced mixing times and power consumption

Markets

There are 3 main types of rubber reclaim; tyre, butyl and EPDM. These reclaim serve a number of markets:

1) Tyre Reclaim

  •  Tyres- New
  • Retreading
  • General Moulding
  • Belting
  • Adhesives
  • Footwear
  • Sheeting/Matting

2) Butyl Reclaim

  • Inner Tubes
  • Tyre Lining
  • Tyre Repair
  • Cable Bedding Compound
  • Sound Reduction
  • Sheeting & Belting
  • Mastics and Adhesives

3) EPDM Reclaim

  • Automotive Extrusions
  • Hoses
  • Civil Engineering Extrusions
  • General Moulding
  • Roofing Membrane

Where do J. Allcock & Sons fit in?

J. Allcock & Sons are UK distributors of  Rubber Reclaim for GRP Limited, who are based in India and have a maximum capacity of 89,000MT’s per year.

We have been supplying reclaim from GRP Limited for many years and have proven it to be a successful partnership and have expanded our customer base overseas.

Although GRP Limited have distributors all over the world, any enquiries are welcome and if we cannot supply GRP Products to your location ourselves, we would happily point you in the right direction!

 

To conclude this post. Please do not hesitate in emailing ja@allcocks.co.uk  or phoning on +44 (0)161 223 7181 for any enquiries or information on reclaim. We firmly believe reclaim has a place in todays rubber compounding market.

 

Red/Brown & Green FKM Crumb Available

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Red/Brown and Green FKM Crumb

Red/Brown and Green FKM Crumb

J. Allcock & Sons’ now have the ability to provide an extra 11 tonnes of Red/Brown FKM Crumb and 4 tonnes of Green FKM crumb per month.

Cured FKM scrap is sent to our facilities on a monthly basis and we granulate and “crumb” this FKM scrap to  72′s and 120′s mesh particle size. These particle sizes are not averages, so when we say 120′s Green FKM Crumb, we mean the biggest particle you will find will be 120′s mesh!

We always ask the customers we visit: What’s the cost of testing FKM Crumb in your compound? Compare that amount, to the amount you will be saving if tests came back positive and you started using it…

If you are interested in trialling some of the above crumb, please contact us at ja@allcocks.co.uk or +44 (0) 1612237181.

Alternatively, if you are unsure about using a different FKM compounded crumb in your own FKM compound, why not speak to us about “crumbing” some of your scrap and J. Allcock & Sons’ sending it back to you?

Carnauba Wax

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I haven’t written a technical blog recently, so I have decided that I should write one regarding Carnauba wax. We have high stocks of Type 3 Carnauba wax, in powder form, so perhaps it might bring us some new sales!

With the help of Norman Challinor, here is some information on Carnauba wax!

Carnuaba wax is also known as Brazil wax and Palm wax. It is a hard wax obtained from the leaves of the palm copernicia prunifera - a plant native to and only grown in north eastern Brazil.

It is usually in the form of hard yellow / brown flakes that can also be ground down to a fine powder and often offered in that alternative form.

Due to its fantastic properties compared to other waxes, most people believe it is one of the best waxes in the world; hence it is sometimes referred to as the “queen of waxes.”

It has a melting point of 80 – 86 oc and a density of about 0.97

The main components are:-

Aliphatic esters                                                   (40% by wt.)
Di-esters of 4 – hydroxycinnamic acid                (21% by wt.)
ω – hydroxycarboxylic acids                               (13% by wt.)
Fatty acid alcohols                                              (12% by wt.)

Predominantly derived from acids and alcohols in the c26 – c30  range.

Carnauba wax, can come in Type 1, Type 3 and Type 4. These “types” relate to the purifity level, with Type 1 being most pure and Type 4 being least.

It has a very wide range of uses, including …..

  • Polishes (Usually Type 4 used)
  • Food (chewing gum, gravy, sauces, sweets etc) (Usually Type 1 used)
  • Pharmaceutical (tablet coating agent)  (Usually Type 1 used)
  • Cosmetic (Usually Type 1 used)
  • And of course, as a process aid and mill / mould release agent in rubber compounds, particularly the harder to process specialist materials. (Usually Type 3 used)

For rubber compounders:

In rubbers, the hard nature of the material will not act as a softener but will behave as an internal lubricant, facilitating the incorporation and dispersion of the non-rubber ingredients.

Its relatively low melting point means that it will migrate to the surface of the rubber and form an extra, very thin, layer between the rubber surface and the metal it is in contact with – - i.e. The mill bowls or the mould surface.  The hardness of the wax means that it will not act as a sticky softener, but will form a release layer, overcoming the tendency for the rubber to stick to the metal.

Allcocks mostly sell, Type 3 Powder, and we really focus on selling to the high specification rubber compounding industry, such as FKM compounds.

Here is some technical information on our T3 Carnauba Wax Powder:

Solubility                                      Insoluble in water; partially soluble in Alcohol.
.                                                   Soluble on warming in Ethyl Acetate & Xylene.
Melting Point                               80-86°C
Acid Value                                   2-7 mg KOH/g
Sponification Value                     78-95 mg KOH/g
Ester Value                                 71-93 mg KOH/g
Sulphated ash                             No more than 0.25% w/w
Unsaponifiable matter                 50-55 μm
Particle Size                                100%  passing 600 μm
.                                                   94.8% passing 300 μm
.                                                   88.1% passing 250 μm
.                                                   40.6% passing 125 μm

If you have any questions regarding carnauba wax, please feel free to email ja@allcocks.co.uk! Despite only selling T3 Carnauba Wax powder, please feel free to get in touch regarding other types, we may be able to help.

ISO 9001:2008

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J. Allcock & Sons have been certified ISO 9001:2008 since 14th of January 1997. This month we had our re certification audit and have now gained certification up until 9th March 2016.

We are proud to be certified ISO 9001:2008 and believe this shows our commitment to keeping high standards and customer satisfaction throughout our organisation. We also believe we are probably the only rubber recycler in the UK to attain this certification.

ISO 9001:2008 Certificate

 

 

Butyl Reclaim (GRP BRI 75R) Now Stocked

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J. Allcock & Son’s will now be STOCKING GRP BRI 75R Butyl Reclaim (Formerly BT.999.)

We have decided to take this important step forward in butyl reclaim supply, as there has been a huge increase in demand over the past year and we expect this to continue throughout 2013.

J. Allcock & Son’s, where possible will always try to be your most flexible supplier. We understand the need to deliver a high quality service. After all, what is the point of using a high quality product, if you do not know that you are going to receive it when you need it?

  • GRP BRI 75R is manufactured by Gujarat Reclaim & Rubber Products Ltd., India.
  • GRP BRI 75R is a reclaimed rubber made from Butyl inner tubes, together with reclaiming aids.
  • GRP BRI 75R is PBN free and PAH conformant.

Product Description

  • Colour: Black
  • Form:   “Blanket”

Composition

  • Carbon Black:            32 ± 4%
  • RHC (by difference):  50% min
  • Ash Content:              4 ± 2%
  • Acetone Extract:        9 ± 3%

Properties

  • Specific gravity:                                1.14 ± 0.02
  • Mooney Viscosity at 100°C:             30-45 ML 1+4
  • Hardness Shore A:                           51 ± 3
  • Tensile Strength:                              75 kg cm^-3 min
  • Elongation @ Break:                        480 % min
  • State of refining:                               Superfine

Data sheets for GRP BRI 75R can be found online, in our data sheet library or on the butyl reclaim product page.

J. Allcock & Sons Ltd. also stock GRP NRM 35R (formerly GR.444 Tyre Reclaim) and GRP NRC 25R (formerly RT-SLAB Tyre Reclaim)

J. Allcock & Sons Ltd. are the official UK distributors for Gujarat Reclaim & Rubber Products Ltd.

For any further technical questions on GRP BRI 75R, please feel free to phone or email, and ask for Norman or Luke.

Differences between Size Reduction, Reclaiming and Devulcanisation, in the recycling of rubber.

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Differences between Size Reduction, Reclaiming and Devulcanisation in the recycling of rubber.

We have consistently found that the rubber industry confuses itself when discussing recycled rubber. Information has started to become lost and miss-translated; people have stopped collaborating and sharing their knowledge. The purpose of this blog post is to hopefully clear up the difference between the three types; size reduction, reclaiming and devulcanisation. I have already written about both size reduction and reclaiming processes and their advantages, but feel a post about the differences between all three at once,  is worth my time.

First of all, let’s quickly discuss each process:

Size Reduction

Recycled rubber has now become the term most associated with size reduction recycling. This is due to the fact that there has been no chemical process involved in the recycling process. It has been, exactly as named, “Reduced in size”.

There are 3 main types of size reduction recycling; Ambient Grinding, Cryogenic and Wet Paste.

  1. Ambient grinding is grinding/tearing the rubber to the small sizes at room temperature. This is our preferred recycling technique as we firmly believe it gives not only the most economical sized reduced rubber but also the most reusable (due to its shape giving the largest surface area).
  2. Cryogenic is the freezing of scrap rubber using liquid Nitrogen and reducing the size literally by smashing it to pieces. This is less economical due to the amount of liquid nitrogen used per kilo of scrap rubber (1:1 Ratio). The final shape also gives a much smaller surface area as it has flat surfaces, this means less rubber can lock/bond into the rubber compound.
  3. Wet Paste is another grinding technique. This is where the rubber is ground while in water. This can produce finer particles than ambient grinding due to the rubber being in cooled down by the water. Unfortunately this technique is not very economical because the ground rubber almost has an affinity to the water and drying the recycled rubber is extremely hard and costly.

Rubber Reclaim

This is where people start to get confused. Reclaim, Rubber Reclaim, Reclaimed Rubber, as stated is a much more complicated form of recycled rubber, it has been put under a chemical process. In fact, it has been put under a complex thermochemical and mechanical process.

Rubber is first reduced in size and then mixed with oils/reclaiming agents and heat. Without getting into too much detail, this process shortens the polymer chain.

Notes:

  • During the reclaim process small amounts of sulphur cross links may be broken – but not enough to claim it as devulcanisation.
  • For rubbers, such as Nitrile (NBR) which has high chemical and heat resistance, reclaim is not yet possible.

Devulcanisation

Devulcanisation is the rarest of rubber recycling, but probably has the biggest potential. It is the breaking of the sulphur cross links. Breaking these sulphur cross links means that the resulting recycled rubber is almost exactly like the starting rubber compound. The recycled rubber will contain up to 90% of the original properties. This would make it the easiest recycled rubber to reuse.

Unfortunately breaking the sulphur cross links is extremely difficult and not many devulcanisation techniques are available due to economical issues at present. Although Remould.org.uk are getting close.

Differences between Size Reduction, Reclaiming and Devulcanisation:

From the explanations above, the differences are clear.

Chemical Structures:

  • Size reduction has no effect on the chemical structure of the rubber.
  • Reclaiming rubber breaks bonds within the polymer chain (and a small amount of sulphur cross-links) and therefore has an effect on the polymer chain length.
  • Devulcanisation has a small amount of effect on polymer chain length but mostly gives large polymer chains which have no sulphur cross links.

Uses:

  • Size reduction is an additive/cheapener rather than a material for replacing rubber polymer in the rubber compound. The ratio of the original materials in the rubber compound would be the same. Larger, size reduced, rubber (rubber granules) can be used in horse arenas and playground surfaces.
  • Reclaim, unlike size reduction can be used to replace some rubber polymer being added in the rubber compound. In fact, if you really wanted, reclaim could make rubber compound by adding curatives/accelerators, although the quality would be poor.
  • Devulcanisation, similar to reclaim would be able to replace the rubber polymer. In fact, it would probably be able to replace nearly the entire rubber polymer and most of the compound!

Visual:

  • Size reduction of rubber produces, shred (for tyres only), granules and crumb.
  • Reclaim is extruded into blankets on a mill.
  • The best devulcanised rubber would be extruded and would be available like reclaim.

 

I hope this post will shed some light on the confusion between the two different types. If you have any questions feel free to leave a comment and I will get back to you ASAP.

 

Rubber Reclaim

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All kinds of recycled rubber materials are often referred to as “Reclaim”. So much so that you would think it had become a generic term. This is not true. Rubber reclaim, Reclaimed Rubber, or just Reclaim, is a very specific type of material.

It refers to vulcanised (cured) waste or scrap that has been rendered fit for re-use by a complicated thermochemical process.

The waste rubber is granulated quite small to release and facilitate the removal of any metal and fabric that may be present. It is then subject to a combination of heat, pressure and chemical softening / plasticising  agents  for a period of time in a large retort. After discharge, the treated waste is refined to remove any nibs or hard bits of unprocessed material. This is done by extruder sieving and/or a refining mill. The later is like a normal rubber processing mill, but with short, stubby rolls with a pronounced camber and high friction ratio. The material passes repeatedly through the mill and the coarse “bits” are pushed out to the sides of the mill nip (the wider part, due to the camber) and fall out into catchment trays at each side. The good, refined material is taken off the mill as a paper thin sheet and wound up on itself to make thick slab. The material from the sides can be used to make lower grade, coarser “tailings” reclaim.

Basic properties

The reclaim still contains the same amount of rubber hydrocarbon, carbon black, fillers and process aids that were in the original rubber compound, plus the extra softeners that were added. The process has NOT broken the sulphur cross-links, but has broken the polymer chains down into shorter lengths, radiating out from the cross-links. In effect looking like a “star fish” shape.

This produces a new raw material that has the same basic chemical make up as the original, but is :-

  • Softer
  • More pliable
  • Easier to process
  • Will act as a process aid in new compounds
  • “Shape retaining” due to the new 3D structure
  • Capable of being re-vulcanised (requires the addition of sulphur / accelerators or similar). With no further additions it will produce a cured sheet and this is used as one of the basic quality control tests to check hardness, tensile strength, etc of the reclaim itself.

Why should you use it?

For the compounder:-

From a purely technical point of view, it is a raw material that should not be ignored. If you need to formulate a good quality NR or SBR black compound, the addition of tyre reclaim will not add anything that is probably not already there i.e. there will be no compatibility problems.

If you are going to make a cheap, low quality commercial black compound, the sky’s the limit. You can add as much reclaim as you want. (as mentioned above – reclaim alone, plus sulphur and accelerator can be cured just like a full compound. The physical properties are not very high, but they are there, unlike a cheap filler which can only reduce the properties).

If you need to improve the processability, the addition of extra oil or softeners will often leave the uncured compound “limp” and sticky. Reclaim will overcome the problem – it has already been softened and it really will help processing – particularly extrusion and calendering – its 3D structure makes the resultant compound almost thixotropic, retaining its shape when static, but immediately softening when worked (processed).

For the accountant:-

If the original costing has been done correctly, an allowance will have been made for any legitimate waste that the process will generate (trimmings, flash, moulding sprue and runners, short ends etc) and this will have been included in the raw material cost.  However, the use of a proportion of reclaim may enable some of that cost to be recovered.

The improved processing and flow rate may well shorten mixing cycles, extrusion and calendar times, moulding blank preparation, etc.  All with attendant cost savings.

Remember – the higher the current raw polymer costs – the more economical is the use of reclaim.

How do you use it?

A good quality tyre reclaim will have approximately :-

Rubber Content             50%

Ash Content                    7%                 (mainly as zinc oxide + mineral filler)

Carbon Black                27%

Oil + process aids         16%

  • SG will be about 1.14
  • It will cure fully and bond into the compound (it cannot separate at a later date)

So ….. don’t just simply add some reclaim. Take out some of the rubber and replace it with double the quantity of reclaim. Overall, the rubber hydrocarbon content will stay the same. Cure properties will not be noticeably different, physical properties will reduce very slightly (in proportion to the amount of reclaim added), processability and flow rate will improve.

Rubber Crumb / Granules

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The process of making rubber goods produces a certain amount of waste. Some of this will be legitimate, such as flash, sprue, runners, etc, and some (almost inevitably) will be due to rejects and other problems. As long as the waste is cured (vulcanised) it can usually be recycled by size reduction into usable materials again. The ideal situation is when the producer segregates and saves the waste and it is then recycled and used back into their product.

The incoming waste is identified and checked and is then progressively broken down in size by passing it through very high energy cutters and granulators. The granulators have a removable, perforated “basket” as the base and this can be changed as required. The full range of sizes runs from 2.5 to 30mm. The common, usual sizes would be 4 or 6mm, and larger chunks would “whirl” around inside, passing through the cutters again and again, until they were small enough to fall through the basket. Vibrating sieve units separate or grade the output. High strength magnets are used at every possible flow point to ensure that any residual metal particles are removed. The product may need multiple passes and will then be bagged (25kg or “big bags”).

At this stage the material is known as “granules” and has a ready outlet in safety surfacing and the like.  It is used in the same way as the stone “chips” in tarmac. A typical specification would be 6 – 2 mm rubber granules – that means that no particle will be larger than 6mm and anything smaller than 2mm will have been removed (i.e. no dust) – that would be used as Base Layer for a surface. Another grade would be 4 – 1mm (on a similar basis) and would be used for the Top Coat  i.e. the visible surface. The sizes can be varied as required and the material used could be Tyre Rubber, EPDM, Nitrile etc. This type of material has a relatively low added value.

Rubber Crumb

This is where the real value of this type of recycling can be found.

The waste rubber is first granulated to about 4mm and then passed to a series of rotary grinding machines. Again, magnets are used at every possible place to remove any particles of residual metal (mainly from the original tyre construction). Once started, the process continues automatically – the powder is fed to sealed sieve units where the only exits are:

  • Correct sized material to the bagging units
  • Oversize material, which has not passed through the sieve, is automatically returned to the system and is reground until it is the correct size.

The actual sieves can readily be changed to make a wide range of particle sizes, and unlike some processes, our stated sieve size means the largest possible size the crumb can be – not the average.

Basic properties

In essence, the true basic properties of the material are the same as the properties of the waste material used to make the crumb or granules. However, the real properties that we are interested in are as follows:-

  1. A relatively inert material of known and controlled particle size (no oversize or dust)
  2. A material that is compatible with the type of rubber compound it is going back into.
  3. A material with a jagged, partially activated, very high surface area that will chemically bond into the rubber article when it is cured (vulcanised)  -   (crumb particles cannot be seen on the surface of the cured article, nor can they be “prised out” – crumb is used as an anti-tack dusted onto the surface of tyre sidewall veneer compound, that disappears completely when the tyre is cured).
  4. A material that is very cost effective, environmentally sound and technically viable

(Note: For very high tech applications (FKM etc) the compounder / producer can have peace of mind knowing that the only chemical materials in the crumb are exactly the same as in the product they are making – no compatibility or contamination issues.  That is of course, as long as they make use of our bespoke service, where they supply THEIR waste material, and we use it (and nothing else) to make THEIR own crumb.)

Why should you use it?

For the compounder:-

a)     The low initial cost and the possible value recovery aspects will make you popular

b)     The technical aspects can be extremely useful –

In small additions of 5 to 10 phr (parts per hundred of rubber)

  • It can reduce air trapping
  • It can reduce “laking” on the surface of “flat” mouldings
  • It can improve hot tear strength
  • It can reduce flow, or excessive “creep” in the uncured rubber

In larger additions – above 10 phr, to as much as you like – see i.

  • Physical properties will fall in relation to the amount of crumb added. If there are no physical requirements – cheap ladder feet, wheel barrow tyres, sleeping policemen  etc, over 50% of the total weight can easily be added.
  • As a cheap filler it is a low S.G., readily compatible blend of hydrocarbons and mineral material.  In very high additions it may be necessary to increase the amount of sulphur / accelerators slightly.

For the accountant:-

a)     It is low price material in the first place.  The word “cheap” conjurers up the wrong idea.

b)     Taken in conjunction with a robust system of internal waste collection and segregation – which is then passed onwards to the recycler – hopefully to be returned as “house” crumb – the economic advantage is completely maximised :-

  •  A useful, low cost raw material put back in stock
  •  Value recovery of internal waste and scrap
  •  Elimination of waste rubber disposal costs

How do you use it ?

Just like any other rubber filler.  If large amounts are used it will be better to add it after the addition of any oils, plasticisers or process aids.  It can have a tendency to absorb the oils resulting in slightly higher hardness than expected.