- Stage 1 – Tire Shredding – Common Terms
- Stage 2 – Steel Removal – Common Terms
- Stage 3 – Granulation & Fiber Removal Common Terms
- Stage 4 – Final Milling & Screening – Common Terms
Stage 1 – Tire Shredding – Common Terms
BTU (British Thermal Unit)
Tires contain an energy value when used as fuel. This value is measured in BTU. As an example: Wood incinerates at 4,375 BTU Bituminus coal incinerates at 12,750 BTU Tire chips incinerate at 15,500 BTU
Processed tires that are cleanly cut into fairly uniform pieces or chips that satisfy end user specifications
Civil Engineering Applications
A form of reusing scrap tires, either whole or shredded, in place of naturally occurring materials in construction. Some examples are; an aggregate replacement in leachate collection systems, lightweight fill material, crash barriers and reef construction.
Clean Cut Chip
A term that is defined as the least amount of exposed wire extending beyond the rubber particle. Clean cut chips, is a term commonly used to describe the cut that is made by a CM Tire Shredder. CM owns the patented Holman Knife technology that achieves the closest knife tolerances and produces the cleanest cut and most consistently sized chip in the industry. The #1 choice for TDF users globally.
Nominal Chip Size
A term commonly used to refer to the average size product (chip) that comprises 50% or more of the throughput in a scrap tire processing operation. It should be noted that any scrap tire processing operation also would generate products (chips) above and below the nominal range.
Primary or Single Pass Shred
A term used to define a whole tires first cut through a Primary Shredder. This first cut leaves the tire in large randomly cut pieces.
A size reduced scrap tire. The reduction in size was accomplished by a mechanical processing device, commonly referred to as a shredder.
Tire Derived Aggregate (TDA)
Tire Derived Aggregate (TDA) has physical characteristics that make it well suited for many civil engineering applications. It has vibration damping properties which can be used in highway and light rail projects to minimize vibrations; as well as road beds, and supporting highway embankments. It also has good drainage properties for septic and leachate systems.
Tire Derived Fuel (TDF)
A fuel derived from scrap tires of all kinds. This may include whole tires or tire processed into fairly uniform clean cut pieces which satisfy the specifications of the end user for fuel. One of the first, and still the largest, markets TDF has become a popular source of clean alternative energy, with a higher BTU value than coal, is stable, readily available and requiring little preparation to burn. In a coal-burning plant, a pound of TDF may displace as much as 2 pounds of coal. Clean cut, consistently sized chips are essential for this application.
Tire Derived Material (TDM)
Any rubber, steel or fabric material derived from processing tires. These materials are found in a variety of sizes, shapes and forms.
A mechanical device used to reduce whole or rough shredded tires into smaller pieces, known as chips.
Stage 2 – Steel Removal – Common Terms
An amorphous form of carbon produced commercially by thermal or oxidative decomposition of hydrocarbons. It is used for manufacturing tires and other products such as; pigment in inks, paints and toners, as active carbon and for fabrication electrodes and cell battery cores. Carbon Black is also used in the manufacture of off road tires.
One of the primary products, resulting from the tire pyrolysis process. The other primary products are pyrolytic gas and oil.
The extraction of the fuel or heat value from whole or processed tires through incineration.
Gasification is a process that converts organic or fossil fuel based carbonaceous materials into carbon monoxide, hydrogen and carbon dioxide. This is achieved by reacting the material at high temperatures (>700°C), without combustion, with a controlled amount of oxygen and/or steam. Tire chips or crumb rubber is often used in a gasification process.
A term used to describe Stage 2 tire processing where the steel is removed from the tire rubber, (Steel Liberation). This process is typically accomplished through the use of a primary granulator such as a CM2R or CM4R Liberator, which is designed to process pre-shredded tires through a ripping and tearing process that cleanly removes the steel from the rubber fraction, producing clean high grade steel and wire-free coarse ground rubber readily usable as mulch for landscapes or for loose playground or equestrian ground cover.
Pyrolysis is the thermal decomposition of an organic substance such as crumb rubber from tires in the absence of Oxygen. In pyrolysis large hydrocarbon molecules of the substance break down into smaller molecules. Generally three products form as a result of pyrolysis: a fuel gas, liquid (pyrolytic oil)- up to 60% and solid residue (char)- 35-40%. The solid char is composed of carbon black, which may be used for manufacturing tires and other rubber products, as a pigment in inks, paints and toners, as active carbon and for fabrication electrodes and cell batteries cores. The liquid fraction consists of a mixture of oils, which may serve as a fuel or a raw material in oil refinery process. The combustion heat of the liquid fraction is 18,000 BTU/lb (42,000 kJ/kg). The gaseous product is composed of the gases: CO, CO2, H2, CnHm. The typical temperature range of pyrolysis is 750-1800°F (399-982°C).
Waste to Energy
Todays waste-to-energy plants are highly efficient power plants that utilize municipal solid waste (MSW) and TDF as their fuel in combination with coal, oil or natural gas. Instead of the cost to transport fossil fuel from some distant source, waste-to-energy plants find value in what others consider waste. Waste-to-energy plants recover the thermal energy contained in the trash in highly efficient boilers that generate steam that can then be sold directly to industrial customers, or used on-site to drive turbines for electricity production.
A processing goal that is ethical, economical, and efficient to guide people in changing their practices to emulate sustainable natural cycles, where all discarded materials are designed to become resources for others to use. Zero Waste means designing and managing products and processes to systematically avoid and eliminate the volume and toxicity of waste and materials, conserve and recover all resources, and not bury them. Implementing Zero Waste eliminates or greatly reduces waste to landfills which create a threat to planetary, human, animal or plant sustainability.
Stage 3 – Granulation & Fiber Removal Common Terms
Ambient Ground Rubber
Rubber that results from the process used to recycle scrap tires at or above room temperature, (ambient temperature) by granulation and / or milling.
Material derived by reducing scrap tire or other rubber into uniform granules with the inherent reinforcing materials such as steel and fiber removed along with any other type of inert contaminants such as dust, glass or rocks.
Cryogenically Ground Rubber
Rubber that results from the process of freezing scrap tire or other rubber and crushing the rubber to the particle size desired.
A technology for processing materials at very low temperatures. In processing rubber, liquid nitrogen or commercial refrigeration methods are commonly used to embritle rubber. The embrittled rubber is then processed in a hammermill or granulator to a desired product size.
Dust Collection and Air Quality Control Systems
Industrial air systems that are designed specifically to remove dust and fiber associated with tire processing from the equipment line. It also functions as an air cleaning system to filter and clean the contaminated air and return it to the environment as clean breathable air.
Fines aka: Rubber Fines
Rubber material that is below the desired market size.
Fines aka: Rubber Fines
The textile or reinforcing materials liberated from scrap tires or other rubber reinforced products during processing for crumb rubber.
Fluff aka: Nylon or Fiber
A machine that shears apart scrap tire rubber, cutting the rubber with revolving steel plates that pass at close tolerance, reducing the rubber to smaller sizes, commonly known as crumb rubber.
Stage 4 – Final Milling & Screening – Common Terms
A blend of crumb rubber modifier (CRM) (finely processed to a No. 16 to No. 30 mesh gradation) and asphalt cement, which is utilized as the binder in various types of pavement rehabilitation and construction procedures. The CRM percentage can range from 15 to 26 percent CRM by weight of the asphalt cement depending on the specified application. The CRM and asphalt cement are blended at elevated temperatures to promote the chemical and physical bonding of the two constituents. Various petroleum distillates or extender oils may be added to the blend to reduce viscosity, increase spray-ability and promote workability. The blend can be used as the binder in chip seals, cape seal applications, pond linings, or gap and open graded hot mix. When used as a binder in hot mix applications, the aggregate gradations and the quality of the aggregate need to conform to industry approved specifications.
A machine that tears apart scrap tire rubber by passing the material between rotating corrugated steel rolls, thereby cracking the rubber and reducing it into various sizes.
Rubber comprised of finely dispersed particles, less than 40 mesh in size, that are generally characterized as light, dry and having very high surface areas. ASTM defines powdered rubber as being composed mainly of non-spherical particles that have a maximum particle dimension equal of below 40 mesh (425 microns).
Rubber-Modified Hot-Mix Asphalt
A hot-mix asphalt mixture that incorporates crumb rubber modifier (CRM) in order to modify the asphalt mix.
A method that blends the crumb rubber modifier with the asphalt cement before the modified binder is added to the heated aggregate.
A method where the crumb rubber modifier is mixed with the aggregate before the asphalt cement/binder is added.
Magnets Such as: Cross Belt Magnet, In Line Magnet or Drum Magnet
Powerful magnets are installed throughout the tire recycling process to remove the steel fraction from the rubber.
Steel aka: Tire Wire, Bead Steel, Bead Bundle, Tread Steel
The steel fraction found in all passenger car, light truck, SUV and heavy duty truck tires, OTRs and mining tires.
Crumb Rubber Sizing Specifications
Inch: 1/36th of a yard, 25.4 millimeters Millimeter: 1/1000th of a meter, .0394 inch
The opening between the wires of a screen – term commonly used to describe or measure the size of crumb rubber. Crumb rubber is sized by the screen or mesh through which it passes in the production process. The finer the screen/mesh the more openings it will have per linear inch, i.e. 30 mesh means there are 30 holes or openings per linear inch. The greater number of openings, the smaller the material must be to pass through the screen. A minus “-” symbol refers to material that has passed through the screen, i.e. -30. Technically crumb rubber sizes are expressed in two numbers. The second number is preceded by a plus (+) symbol and indicates the size particle that has been retained on the screen.
Screens or Multi Deck Screens
A large sieve of suitably mounted wire cloth, grate bars, or perforated sheet iron used to separate materials by size. The screens are a part of the production line of equipment to separate the desired size of crumb from the other sizes, and recycle the other for the purpose of further size reduction.
A process for classifying rubber particles. Gradations are usually expressed in terms of total percent passing or retained. The percent passing indicates the total percent of rubber that will pass each given sieve size. The total percent retained is the opposite of percent passing or the total percent passing each given sieve.
Crumb Mesh Size Range in Each Market Category
|Molded and Extruded Products||4 – 100 mesh|
|Asphalt Modification 16 – 40 mesh||16 – 40 mesh|
|Sport Surfacing||1/4″ – 40 mesh|
|Automotive Products||10 – 40 mesh|
|Tires||80 – 100 mesh|
|Rubber and Plastic Blends||10 – 40 mesh|
|Construction||10 – 40 mesh|