Question

Tire manufacturing process, emphasizing the importance of pitch sequencing

Answer 1

TIRE MANUFACTURING

A passenger car tire is manufactured by wrapping multiple layers of specially formulated rubber around a metal drum in a tire-forming machine. The different components of the tire are carried to the forming machine, where a skilled assembler cuts and positions the strips to form the different parts of the tire, called a "green tire" at this point. When a green tire is finished, the metal drum collapses, allowing the tire assembler to remove the tire. The green tire is then taken to a mold for curing.

• (1) The first step in the tire manufacturing process is the mixing of raw materials to form the rubber compound. Railcars deliver large quantities of natural and synthetic rubber, carbon black, sulfur, and other chemicals and oils, all of which are stored until needed. Computer control systems contain various recipes and can automatically measure out specific batches of rubber and chemicals for mixing. Gigantic mixers, hanging like vertical cement mixers, stir the rubber and chemicals together in batches weighing up to 1,100 pounds.
• (2) Each mix is then remilled with additional heating to soften the batch and mix the chemicals. In a third step, the batch goes through a mixer again, where additional chemicals are added to form what is known as the final mix. During all three steps of mixing, heat and friction are applied to the batch to soften the rubber and evenly distribute the chemicals. The chemical composition of each batch depends on the tire part—certain rubber formulations are used for the body, other formulas for the beads, and others for the tread.

• (3) Once a batch of rubber has been mixed, it goes through powerful rolling mills that squeeze the batch into thick sheets. These sheets are then used to make the specific parts of the tire. The tire body, for instance, consists of strips of cloth-like fabric that are covered with rubber. Each strip of rubberized fabric is used to form a layer called a ply in the tire body. A passenger car tire may have as many as four plies in the body.
• (4) For the beads of a tire, wire bundles are formed on a wire wrapping machine. The bundles are then formed into rings, and the rings are covered with rubber.
• (5) The rubber for the tire tread and sidewalls travels from the batch mixer to another type of processing machine called an extruder. In the extruder, the batch is further mixed and heated and is then forced out through a die—a shaped orifice—to form a layer of rubber. Sidewall rubber is covered with a protective plastic sheet and rolled. Tread rubber is sliced into strips and loaded into large, flat metal cases called books

• (6) The rolls of sidewall rubber, the books containing tread rubber, and the racks of

• beads are all delivered to a skilled assembler at a tire-building machine. At the center of the machine is a collapsible rotating drum that holds the tire parts. The tire assembler starts building a tire by wrapping the rubber-covered fabric plies of the body around the machine drum. After the ends of these plies are joined with glue, the beads are added and locked into place with additional tire body plies laid over the beads. Next, the assembler uses special power tools to shape the edges of the tire plies. Finally, the extruded rubber layers for the sidewalls and tread are glued into place, and the assembled tire—the green tire—is removed from the tire-building machine.

Curing

• 7 A green tire is placed inside a large mold for the curing process. A tire mold is shaped like a monstrous metal clam which opens to reveal a large, flexible balloon called a bladder. The green tire is placed over the bladder and, as the clamshell mold closes, the bladder fills with steam and expands to shape the tire and force the blank tread rubber against the raised interior of the mold. During this curing process, the steam heats the green tire up to 280 degrees. Time in the mold depends on the characteristics desired in the tire.
• 8 After curing is complete, the tire is removed from the mold for cooling and then testing. Each tire is thoroughly inspected for flaws such as bubbles or voids in the rubber of the tread, sidewall, and interior of the tire. Then, the tire is placed on a test wheel, inflated, and spun. Sensors in the test wheel measure the balance of the tire and determine if the tire runs in a straight line. Because of the design and assembly of a modern tire, rarely is one rejected. Once the tire has been inspected and run on the test wheel, it is moved to a warehouse for distribution.

IMPORTANCE OF PITCH SEQUENCING

Pitch sequencing of tire during tire designing process is very vital in order to reduce friction noise between tire and road surfaces which leads to noise pollution and low life of tire threads .

A tire tread having design cycles or pitches in which the circumferential lengths of repeated arep randomly modulated in certain selected sequences  to reduce the amount of noise generated by the tread tire thread when the tire rolls on a road surface.