The construction of a tire is a precise, expensive, and time-consuming process. Smaller tire manufacturing plants have traditionally used a single-stage, tire-building machine to construct the various components of a tire. The advantage is precision, but the glaring disadvantage is time. Larger tire manufacturing plants have converted the process to utilize a muti-stage tire-building machine. Despite the added expense, multi-stage machines can produce 1,000-1,200 tires a day compared with the 400 per day produced by the single-stage building machine.
It’s difficult to say which component is most important to a tire’s construction, but it’s difficult to argue it is not the rubber. Tire manufacturers ship in raw rubber, either natural or synthetic. The rubber bails are received, weighed and stored until ready for use. Through a mixer, the raw rubber is combined with carbon black and oil. Through a mill and tread extruder, the beginning of the tread begins to take shape. The run of rubber compound is sent through a linear foot scale, then cooled. After the tread cuts are made, the tread is weighed.
In a separate process, wires are sent through a calendaring process that combines the single wires into the specified combination of wires. These twisted wires are combined into compound and cut into belts. A tire is constructed with an inner liner, body plies, steel belts, the sidewalls and the tread. The resulting construction is called the green tire, or an uncured tire. After construction, the tire in placed into a curing press.
A single-stage tire-building machine utilizes separate drums for the different components. An incorporated drum used to construct the steel belts and tread affords the benefit of precision through the transfer of the belt/tread package. This simplified construction technique allows for better quality control, because any problem can be traced to one machine. Also, the bead of the tire is held in place during the entire building process. Lastly, training is enhanced because a tire builder can be trained on one machine. On the downside, tire stitching causes a slow-down in production, because no other construction can occur, while the stitching is performed.
A multi-stage tire-building machine is much larger and much more expensive. However, what is lost in plant space and investment is easily recouped by vastly increased efficiency. However, what is gained in efficiency is potentially lost in quality control. With a multi-stage building machine, quality control must be more acute, because problems can no longer be isolated to one machine. Of particular concern is storage after the first phase of construction. Temperature and humidity levels are vitally important to ensure the integrity of the first stage tire build. If there is a problem with storage, the entire process is compromised.
Tire-building continues to evolve with ever-increasing technology. But, at its root, tires are still constructed by hand under the watchful eye of an experienced tire builder. Human mistakes occur occasionally, eventually resulting in scraped tires or roadway failures.
Written by:
Guy L. Watts, II
Watts Guerra LLP
4 Dominion Drive, Bldg 3, Suite 100
San Antonio, Texas 78257
Phone (210) 447-0500
© Watts Guerra LLP 2015
