HMD TRUCKING

Truck tires are one of the most complex engineered products in the world because tires have no moving parts!

So a truck tire is mostly rubber?

Yes. By weight, roughly 40 percent rubber. Although this can vary, depending on the type of tire, the rubber is about three-quarters natural and one-quarter synthetic material.

Why so much natural rubber?

Trees make great natural rubber. Natural rubber last a long time and tends to run cool. It is an important component in treads and any other of the tire that must flex a great deal. One type of natural rubber is called smoked sheet, because the latex from the tree is  coagulated by smoke which acts as a preservative.

Why not make tires 100 percent out of natural rubber?

With natural rubber, you have to take what you get. When you make synthetic rubber, you can engineer it to create rubber with particular performance characteristics.

What kind of characteristics?

Synthetic rubber can be engineered to have built-in cut resistance, for example. That can be very valuable in treads and side-walls. Synthetic rubber is formulated for irregular wear resistance and for excellent wet traction. The ratio of natural to synthetic rubber depends on the particular component of the tire.

What is “carbon black” and why so much of it?

Carbon black is very finely powdered pure carbon – a bit like the soot that forms on the inside of an oil lamp. Carbon black is a filler that makes up about 30 percent of tire, which is a lot when you consider how light weight carbon black is.

What doe’s a “filler” do?

It adds enormous strength. One way to think of rubber is to compare it to the concrete in a modern building. Often, steel bars are embedded in the concrete, adding strength. Rubber reinforced with carbon black in more abrasion-resistant than rubber alone, is stronger, wears more slowly, and is easier to process. Carbon black also helps protect rubber against ultraviolet (UV) light from the sun.

Why is that important?

You might say that tires are like our skin. They can get a sort of “sunburn” which can cause rubber molecules to break down and become brittle. That can make tires wear faster and cause surface cracks. Carbon black tends to shield rubber molecules from UV light, like a sunscreen.

There’s plenty of steel, isn’t  there?

At about one-fifth of the tire by weight, steel is a major component, especially for the “three b’s”, beads, belts, and body. Just as the carbon black acts as a sort of “rebar” for the “concrete” of the rubber, the steel cord in a radial tire acts like the steel frame in modern building. Different kinds of steel, diameters of steel wire, and types of cable are engineered for specific purposes. Some steel cords consist of a large number of stands wound together.

Why is the cable a golden color?

There’s a special coating on each individual strand to help it adhere to the rubber in the tire. Normally, rubber and steel don’t stick together very well, but that’s essential in a radial tire. The coating is tightly bonded to the wire, and in turn bonds tightly to the rubber during precessing.

It doesn’t take much sulfur, does it?

A little bit goes a long way. Sulfur is one of the most important vulcanizing agents. During curing, sulfer atoms actually connect different rubber molecules together, effectively making several smaller molecules into one big one. When rubber is cured with sulfer, the sulfer links the strands to each other.

What’s the problem with oxidation?

Oxygen, like UV light, can breakdown rubber molecules, making rubber brittle, causing cracks, and rapid wear. Oxygen in the air can cause this, and zone, a special type of oxygen molecule, is especially hard on tires. Adding antioxidants and antiozonants helps prevent those tiny cracks you see in the side-walls of tires. So here’s a tip: Avoid washing tires to much, and especially avoid putting compounds on the sidewalls to make them shine. The waxes, antioxidants and antiozonants are designed to protect the surface of the tire. By cleaning them off, you’re removing that protection, causing tires to age prematurely.

What does the “accelerator” do?

There are lots of different kinds of rubber in a tire. They all have to be cured together, in the same amount of time. Accelerators help control the speed of thecure, so everything ends up fully  cured, without having to spend excessive tire in the mold.