The tire industry's never-ending search for a smoother rolling, more uniform tire has led engineers to focus on eliminating the splice-or more accurately, the effects of the splice.
The splice-the joint where two ends of a tire's many component layers are joined in traditional manufacturing-can be the source of a tire's ``disuniformities,'' things like weight imbalance, dynamic stability etc.
Technically it's impossible to eliminate the splice in a product made up of layers of fabric, rubber and steel wire. But engineers have discovered that by building a tire out of smaller component sections laid directly onto a toroidal building core and employing strip winding, the negative effects of the splice are effectively eliminated.
The development in the past decade of a number of automated tire-manufacturing systems has changed the definition of a splice, yielding a number of advantages, including:
* Greatly enhanced symmetry and uniformity;
* Improved quality constancy;
* Lower scrap rates in production;
* Less probability of premature failure; and
* Increased durability.
What does it mean in layman's terms?
Consumers will enjoy a smoother ride and more uniform wear. Tire dealers should notice the difference in the reduced need for wheel weights for balancing, and a resultant drop in time needed to balance a set of tires.
Some of the factors driving the development of new manufacturing systems, according to David Van Emburg, director of product marketing for Michelin Americas Small Tires, include:
* Increased sensitivity of newer-generation vehicles to noise/vibration/harmonics (due to lighter weight construction);
* The need to satisfy consumers used to the smooth ride of higher-profile 14- and 15-inch tires as they migrate up to larger sport-utility vehicles with lower profile 17- and 18-inch and even larger-sized tires;
* Larger tires that use more materials (more mass), and contain larger splices; and
* Smaller production runs of larger, more vehicle-specific tires, meaning more frequent changes in the manufacturing equipment tooling and semi-finished components.
``It all comes down to consumer expectations and consumer satisfaction,'' Mr. Van Emburg said.
The most significant change in tire manufacturing in the past decade has been the advent of automated systems that build tires on toroidal cores-roughly speaking, hollow doughnut-shaped cores (mimicking the shape of a tire). These systems are replacing the decades-old process of building tires on flat drums and then inflating them to their desired shape.
Group Michelin, with its C3M process, was the first company to offer tires commercially made using the toroidal-building concepts, rolling out C3M-produced tires in Europe in the early 1990s. Since then, Michelin has made more than 20 million tires using the C3M process at six plants worldwide-four in Europe and two in the U.S.
Michelin officials said C3M-actually CMMM, for ``Confection'' (French for manufacture), Mandrin (the solid core), Mono-filament (single cords) and Michelin-is well suited to the production of tires with distinctive performance characteristics. Michelin demonstrated the system's ability to place components with precision with the design-your-own BFGoodrich Scorcher tire featuring colored stripes in the tread.
C3M accounts for 20 percent of Michelin's high-performance tire production. In addition, Michelin has demonstrated to customers in Europe that C3M manufacturing cells are so mobile that plants can be moved and made operable at different locations within days.
Pirelli S.p.A. also has now developed its own automated process-dubbed MIRS, for Modular Integrated Roboticized System-that manufactures tires in small, self-contained cells with no manual handling of the tire's components other than to load them into automated servers that supply the materials on-demand to the robotic builders.
Building the tire on a toroidal drum, in essentially the inflated profile, means the tire's casing and belt components do not undergo any change in shape or stress in either the manufacturing or curing processes, according to Andrew Kearton, director of manufacturing at Pirelli Tire North America (PTNA) Inc.
Robotic building means great accuracy and repeatability, according to J. Steven Carpino, director of research and development at PTNA, factoring out even minute variances that occur with traditional building processes.
The core-building process also means beads are done differently, spiral wound in three separate windings with the casing material interwoven, Mr. Kearton said. This greatly reduces the chance of bead area separations, he noted.
Additionally, the software controlling the robotic manufacturing adjusts all the component feeders with each size change to the optimum length/width/volume for that particular sized tire, Mr. Kearton said. Developments in this area also mean the company can make ``on-the-fly'' changes to a tire's construction in order to incorporate a design tweak or an individual OE customer's particular specifications.
Oddly enough, toroidal core-based building takes the industry back to its roots. In the early days of tire manufacturing, each tire was built individually on a wooden core that was wrapped and cured in an autoclave.
Reducing the splice to a barely perceptible thing is a key target of Goodyear's Impact (Integrated Manufacturing/Precision Assembled/Cellular Technology) system, which takes a significantly different approach to achieve the same result.
``Precision manufacturing will yield a lighter, thinner tire that will run cooler-and therefore with less rolling resistance-longer and smoother,'' said Rick V. Vannan, former director of advanced process and product technology for Goodyear.
``We expect tires built with the full complement of Impact technologies to be so uniform as to require no wheel weights for balancing,..and that would apply to any tire, built anywhere in the world,'' Mr. Vannan said in an earlier interview. He retired from Goodyear in late 2002.
Goodyear minimizes the splice by using something it calls the hot-former. This invention is a series of computer-controlled, extruder-fed, contoured-roll calenders linked by a conveyor belt that pre-assembles tire casing components into what is called a ``composite laminate.''
Goodyear maintains that laminating these various components together while they're still warm achieves several improvements: increased uniformity; greater precision in terms of component thickness and placement; and reduced use of or even elimination of processing chemicals designed to retard the vulcanization process until the cure cycle.
An Impact-built tire still has a splice, but Goodyear has increased the angle at which the sonic knife cuts through the composite laminate, increasing the surface area of the ends to be spliced and thereby reducing its effect.
All of the firms' new systems promise reductions in space needed, energy used and staffing. Michelin has stated a C3M module needs only about 10 percent of the space required by conventional manufacturing. And each module of Pirelli's MIRS manufacturing system only requires two employees to operate.
Still in development or on the drawing board are ideas such as: filament or ribbon-winding of belts, which would be made of short fiber composites for shear stiffness; injection molding of bead packages or partial pre-curing of tread packages to shorten cure times in the press; and the use of organic fibers in place of steel wire to create jointless belts without cut edges.
These new manufacturing systems are a step in the right direction, said Jacques Bajer, founder and owner of Tire Systems Engineer Inc., but they still don't address fully the question of improving structural integrity.
As long as the vehicle industry continues to increase the number of models it offers and continues to demand distinct tire fitments for each, the tire industry will be hard pressed to truly revolutionize itself, Mr. Bajer contends.
Instead, he campaigns for the industry to ``demassify'' itself, or seek ways to take layers of complexity out of the manufacturing process in order to solidify the structural integrity of the product itself.