Weibold! Academy: Rubber Granulates, Rubber Powder, Tire Derived Steel and Tire Derived Fiber

Dear Readers,

Weiboold Academy LogoThis is the third article from our monthly blog series, called “Weibold! Academy”.

The idea behind these articles is to provide our readers and our newsletter subscribers with valuable knowledge about the tire recycling industry.

We started our educational series with the basics and month by month we will together dwell deeper into the world of tires and the ways of recycling them.

We believe that a good knowledge foundation might be beneficial for everyone involved in the industry and each month we will cover different topics, thus providing you with important know-how for the tire recycling industry.

In the second article from our series we started explaining about the recycled rubber output spectrum and we also started covering the topic about Rubber Granulates.

In this part we will continue with it – we will explain to you about coated rubber granulates from tire or technical rubber input material and about rubber granulates from technical rubber scrap recycling. We will continue then with rubber powder, tire derived steel and we will finish this article with helpful information about tire derived fiber.

Coated rubber granulates from tire or technical rubber input material

Coated rubber granulates have been offered to the market since end of season 2003, where regular tire and/or technical rubber granulate is coated with paint. The idea was to have a greater variety of colors and to reduce the risk of leaching of any substances not conforming to the existing environmental standards. The latter is no issue anymore as rubber granulates from tire input material have been widely proven to conform to all environmental standards.

The greater variety in colors is clearly a major advantage but must be offset with much higher costs and the uncertainty how long the coating will last. Rubber, of course, is an elastic material and during different temperatures and also the exposure to football players continuously expands and shortens. The coating may become brittle sooner or later. Due to regulative reasons there is a very strong market for colored granulates in Italy. The hype in other markets is over and demand became recently rather low.

Should one plan to color granulates it is recommended to organize a test certificate for abrasion resistance tested with the Hard grove tester (ISO 5074).

Rubber granulates from technical rubber scrap recycling

When talking about granulates made of technical rubber, EPDM (Ethylene Propylene Diene Monomer) is in everybody’s mind. It must be clearly stated that in only few cases one can call such a product EPDM rubber. Other typical technical rubbers are called NR, SBR, NRSBR, HR, Butyl, etc.

Some recycling companies do not only shred tires, but also technical rubber scrap. Many (but not all) technical rubbers are classified as EPDM. But even among rubber products classified as EPDM the components vary greatly. Products made of EPDM rubber are used in many different applications which all require very distinctive properties. E.g. EPDM rubber hoses in car engines need to be oil and heat resistant. EPDM products used in the interior of a car contain anti-fogging agents.

Shredding and milling technical rubber scrap is worthwhile considering for rubber powder producers operating suitable equipment. There are numerous producers of rubber parts (e.g. automotive industry) which collect a substantial amount of punching waste during their production process. This production waste can easily be correctly sorted and custom grinded. This closed loop recycling process usually allows for excellent margins. One must be very careful about a proper cleaning of the plant before switching to another input material for custom grinding purposes.

Rubber Powder

In general rubber powder is differentiated from rubber granulate by the grain size. Fractions below 1 mm (1000 microns) are commonly called rubber powders. Rubber powders can range down to as small as 50 microns with mean particle sizes of 800 microns from wet grinding processes, 600 microns from ambient processes, and 400 microns from cryogenic processes. As rubber granulates is a relatively common product, powder has become a valuable raw material whose price attains high values depending on its input material, production process, quality and availability.

Rubber powders can be used in a wide variety of applications ranging from new tire manufacturing, sealants, coatings, molded, injection or extruded goods, belts, rubber compounds to modifying asphalt cements for improved road life.

The most important application for rubber powders can be found in the compounding industry. If the processing method and input material is properly chosen, the compounder will be able to achieve substantial savings in material costs. Improved mixing and curing properties are sometimes said to be additional benefits. Not only compounding of various rubbers for rubber goods production is an interesting market for rubber powders but most and for all the production of TPE granulates; i.e. Thermoplastic Elastomers originating from recycling rubber powder and recycled plastic (PP, HDPE, or LDPE).

Rubber powders must be differentiated by its way of production:

  • Normal Temperature (Ambient) Process
  • Cold Temperature (Cryogenic) Process
  • Waterjet Milling Process

Rubber powders are showing high growth potential.

The users are not yet easily recognizable and it is therefore very difficult to find relevant customers for quick sales. Unfortunately poor quality sampling from existing tire recyclers to compounders and other potential users of rubber powders destroyed the believe of such users in the availability of high quality and consistent material. It is therefore very important to leave an extremely professional first impression with customers. Samples need to be properly marked and 100% of comparable quality. Samples should never be sent to a customer after removing it from one single big bag. It is advised to take one small sample each day of a week and collect the average material over a full week. The samples from each day should be properly mixed. This simple process guarantees a representative average quality which minimizes complaints by the client in the future.

Tire Derived Steel

Most modern vehicular tires contain steel as reinforcement, as belts in the sidewalls of the tires and as bead wire (which anchors the tire to the wheel rim). Steel used for tire beads is usually high-tensile bronze-coated wire; high-tensile brass-coated steel cord is used in the construction of tire steel belts. These coatings are important because both obviously contain copper, which is a potential contaminant when it comes to recycling the steel. It should be noted that this copper is an important constituent in helping to develop CuS (copper sulphide) links between the rubber and the steel, thereby facilitating the bonding of the rubber to the steel reinforcement.

Tire Derived Fiber

‘Fiber’ is the generic term used to categorize fiberglass; cellulose; nylons; polyester and cotton materials used in tires. These are also loosely referred to as ‘textiles’. Confusingly, the term ‘fiber’ is often used in the literature to refer to steel strands recovered from processing scrap tires. However, in this report the term ‘fiber’ is used to refer to the textile content of a tire. The term ‘steel fiber’ refers specifically to steel used in reinforced concrete.

When striving for high-quality rubber powders, first-class fiber separation is a must. Generally, the more lucrative the market the more stringent the quality requirements for fiber.

Click here to read the first article and here for the second article from the Weibold! Academy series!

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