PHYSICO-MECHANICAL CHARACTERISTICS OF ELASTOMER CUTTING
For designing a shredder cutting apparatus, it is essential to understand the physics of destroying vulcanized rubber reinforced with steel. Rubber is a hyperelastic material whose stress-strain state is described by nonlinear models such as the Mooney-Rivlin model. The empirical Mooney-Rivlin constants for an OTR tire tread are approximately C10 = 0.8061 MPa and C01 = 1.8050 MPa, while for the sidewall C10 = 0.1718 MPa.
The rubber shredding process in a shredder involves a combination of compressive, tensile, and shear forces. The shear strength, measured per ASTM D732 standards, for industrial vulcanized rubbers ranges from 15 to 25 MPa (N/mm2). The cutting resistance comprises four main components: (1) cohesive strength (fracture toughness) of the elastomer, (2) tangential Coulomb friction stress between the steel blade and rubber, (3) adhesive peel stress, and (4) shear stress associated with surface deformation.
Engineering calculations show that the force at the blade edge must create contact stress significantly exceeding 25 MPa to ensure not just indentation (elastic pressing) but full rupture of the rubber macromolecular network and destruction of high-strength steel cord. High-torque shredders (e.g., EDGE VS420) deliver up to 240,000 Nm (177,000 lb-ft) of shaft torque, converting hydraulic pressure into extreme shear force.
SHAFT WRAPPING PREVENTION
One of the primary operational problems in tire shredding is the tendency of long rubber strips, bonded by flexible steel cord, to wrap around the rotors. Elastomer belts can withstand significant tensile deformation (up to 300-500% elongation) before rupture. Wrapping blocks the gaps between blades, sharply reduces throughput, and causes hydraulic pressure spikes that overload the pumps.
To prevent this phenomenon, advanced systems (such as Arjes Impaktor and EDGE Slayer) use asynchronous or synchronized counter-rotating dual shafts combined with an intelligent overload protection system (SCU). When the system detects a pressure spike indicating the onset of wrapping or the entry of non-shreddable metal (tramp metal), the shafts automatically stop and perform a reverse stroke, ejecting the wrapped material back into the loading hopper, after which the cutting cycle resumes. The presence of mechanically adjustable side combs also minimizes gaps, forcing material to pass through the cutting zone without being able to wrap around the axis.
FINANCIAL ECONOMICS OF METAL CORD EXTRACTION
The mass fraction of high-strength steel wire in mining OTR tires ranges from 18% to 25%. Thus, from a single tire weighing 10,000 lbs, approximately 2,000-2,500 lbs (about 1 metric ton) of steel can be extracted. The most massive component is the tyre bead — bundles of high-strength wire holding the tire to the rim. While a passenger car tire bead weighs 0.5-1.5 kg, in OTR tires it reaches 5-50+ kg.
Integrating a hydraulically adjustable overband magnetic separator into the shredder design automates steel cord extraction during primary and secondary shredding. On the scrap market, cleaned high-strength steel cord qualifies as valuable scrap, with market prices varying from GBP 80 to GBP 200 per ton (approximately USD 100-250) depending on purity. At the scale of a mining enterprise disposing of thousands of tons of tires annually, metal extraction can generate hundreds of thousands of dollars in additional revenue, radically reducing the payback period (TCO) of the shredding complex and covering a significant portion of fuel and maintenance costs.
