Solid OTR tires are designed for the harshest worksites. Scrap, recycling, waste transfer stations, demolition, CDE material recycling, and foundry all experience extreme conditions.
For this reason, solid OTR tires are engineered and manufactured with special compounds to resist chunking, cutting and heat, all features of the kind of challenging environments in these industries. In this article, we discuss what compounds typically go into a solid OTR tire, what purpose they serve and why these compounds matter.
What’s in a Tire Compound?
In essence, a tire compound is a vulcanized rubber recipe composed of multiple materials. Natural rubber is harvested from latex rubber trees and then undergoes a complex process to make it usable in manufacturing a tire. It all depends on the base rubbers for a particular tire, but natural rubber could be used for applications that require a lot of heat resistance.
Sometimes, a more cut-resistant or wear-resistant type of tire may be required based on the application, this is when manufacturers incorporate some synthetic rubbers such as SBR or BR, derived from petroleum products. In addition, additive materials are then introduced, such as carbon black or silica, to further reinforce the tire compound.
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Applications for Solid OTR Tires
Solid OTR tires must have high heat-resistance in their compounds as applications that utilize solid OTR tires are typically in waste, recycling, or scrap. Applications in waste and recycling stations and scrap metal typically generate a lot of heat through constant use and harsh working environments. Because there is no air in solid tires, they are far more resistant to chunking, chipping, and blowouts.
The Importance of Solid OTR Tire Construction
While the types of compounds remain essential to the durability and performance of solid OTR tires, how the tires are built and engineered plays a pivotal role as well. For example, one must consider how hard (measured in durometer) the rubber is within a solid OTR tire. A typical solid OTR contains tread rubber that is about 65-75D in hardness. The base tread underneath the top tread is about 90D in hardness. Below illustrates what a typical, “2-stage” (meaning they are two stages of construction inside the tire) solid OTR contains.
In addition to the high durometer in the rubber within a solid OTR tire, manufacturers also incorporate sidewall apertures that appear as holes around the tire’s sidewall. These apertures are usually defined by each manufacturer on what purpose they serve depending on the design. Traditionally, they are used for cooling and stability.
3-Stage Solid Tire Construction
While a traditional 2-stage solid OTR tire contains high durometer rubber to combat severe environmental challenges in scrap yards and waste stations, tires are more than just their tread. A 3-stage solid OTR tire contains a three-stage construction with a specialized cut-resistant top tread, a cushion center with heat-dissipating cushion compound, and a base natural rubber layer. Below is an illustration that shows a 3-stage solid OTR tire:
When comparing against a traditional 2-stage tire, the top tread of a 3-stage tire takes up about 50% of the tire, with a 65-70 durometer in hardness. It contains a center layer that has 65D and takes up about 25% of rubber. Lastly, the base layer, with 90D, makes up another 25%. However, the big difference maker in this 3-stage build is the center cushion where the sidewall apertures sit.
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Each manufacturer defines its solid OTR apertures differently in terms of purpose. In MAXAM’s solid OTR tires, the patented “double-D” shaped apertures are positioned within the 65D center cushion rather than b within the 90D base. By having the apertures sit in a lower durometer center compound, this will significantly absorb shock better than having apertures placed at the base compound.
In essence, rubber compounds within solid OTR tires are built to withstand heat, cut and chunking. While these rubber compounds make up the durometer, or hardness, that’s required for solid OTR tires, it’s always important to consider how these tires are designed and manufactured.
