Effective process for precuring tire components. (Process Machinery).

A precure process for tire components to improve green strength and stabilize fabric cord, steel wire or gum rubber components has proven to be very advantageous in the extremely competitive tire business. In particular, if the precure treatment is done correctly and in-line with other processes, it can be very cost-effective.

The cost reductions and advantages are primarily produced by the reductions in material or the tire component's weight. These reductions in some cases can he as high as 20% in the overall thickness of the rubber material used in the tire component.

The pretreatment or precure process can be achieved with a variety of treatment methods. However, any technique used must be very precise to achieve the desired tack, green strength and product quality. Specifically, the issue of precure is very important, since it affects green strength and percent recovery. Many precure techniques find it difficult to precisely control tack and cure in the same process. In addition, any precure technique must be effective and precise at line speeds of up to 100 m/min., in order to be considered for an in-line process.

The use of high energy electrons can and does provide a very controlled and high-speed precure technique. The cure can be precisely maintained to insure good tack and improved green strength at production speeds in-line with the calender and/or extrusion process. Early work by Hunt and Alliger using electron beam technology indicates the relative improvement in green strength in relation to the dose or treatment.

One of the unique characteristics of high energy electrons is that a substantial portion of the curing process occurs in the body of the material, not on the surface. This may explain why the tack is less affected than by other surface treatment processes.

Discussion

In the past several years, significant changes in the high-energy electron beam equipment used to precure tire components have occurred. Most of these changes were linked to the tire manufacturers' need to reduce the size of the e-beam equipment and improve its practicality as an in-line system. Although tire manufacturers in the U.S. pioneered the use of EB equipment to process tire components, it was the Japanese manufacturers that adapted the equipment for the in-line processing of tire components.

The original e-beam equipment designs usually were based on experience gathered from research and development programs. The manufacturer of the e-beam equipment usually supplied input on the construction and basically dictated how to use these systems. The EB vendors also set the installation requirements, all of which were not necessarily what the tire manufacturer/user wanted.

A typical system used in an offline senti-research environment might have measured 70 to 80 feet long, 35 to 40 feet high and 16 to 20 feet wide. The concrete wall thickness in the treatment area would average four to six feet. Outside of these structures, pay-off and take-up equipment added another 60 to 80 feet to the system's length. All of this equipment had to be placed off-line or perhaps in a separate building because of its size. In addition, no manufacturer felt the e-beam system would be reliable enough to be an in-line process.

The overall complexity of operating these systems usually required a graduate electrical engineer or someone with very similar specialized training, able to solve numerous problems. Despite these drawbacks, the technology continued to move forward and e-beam equipment eventually became more accepted as a production process with only minor changes in the overall size of these systems.

A push by U.S. manufacturers to reduce the size of these facilities was initially accomplished by using the directional characteristics of accelerated electron beams and their tendency to produce radiation in a forward direction. In other words, most of the environment needed to protect personnel from the hazardous effects of these radiations was required in the forward beam direction.

The solution was to put the treatment area below ground level. Therefore, the factory floor became part of the vault, with the natural environment of the ground providing the bulk of the radiation shielding.

This solution was quite popular with U.S. manufacturers of tire products that incorporated either cord or fabric to stabilize the green rubber. Precuring these ply materials required a pay-off and take-up system with idler pulleys to direct the product under the e-beam system. The use of idler pulleys also allowed the product to run through a maze designed to protect personnel against the scattered electrons and x-rays produced in the treatment area.

In addition to this innovation, e-beam equipment manufacturers began to work closely with tire manufacturers to design automation systems that met industry demands. The use of programmable controllers or computers, plus improved software options, added to user-friendly operation.

In the early 1980s, a number of changes was occurring in Asia, particularly true in the Japanese market where the cost of production could no longer be dependent on low-cost labor. Automation and in-line processing were seen as the keys to increasing production and reducing labor costs. The major advantage of the in-line process was that it eliminated the need and cost involved with the off-line pay-off and take-up product handling equipment.

Moving the EB precure operation from off-line to an on-line process allowed the manufacturer to use existing handling equipment available on the calender or extrusion line. This was another key to improved productivity. The in-line process required that the size and reliability of the e-beam system be similar to the equipment on the rest of the line. Tire manufacturers demanded that the EB vendors provide up-time and predictability so managers could plan their production and maintenance activities without fear of unscheduled downs. The definition used for a reliable system was one preventive maintenance per year.

Along with the improved reliability, manufacturers insisted on more production-friendly equipment with improved automation to ensure consistent product quality. Product transport needed to control the EB precure unit so that start-up, shutdown and reel-to-reel product change could be done with little or no product loss.

Typical of all controls in tire line applications was that they were designed to be reliable under the most extreme conditions of heat, dust and humidity. It was therefore necessary for the e-beam operation to be simplified so that inexperienced operators could run the system. The precure process needed to track the line speed in order to provide a constant cure level. The control also had to be capable of supplying a periodic update on the operation and all aspects of the process.

The next major problem to be solved concerned the size of the EB precure systems. In order to install an e-beam system on-line, production managers needed flexibility in locating the unit. To do this, space requirement had to be reduced.

The answer was to utilize a combination of lead and steel to replace the traditional concrete vault. These systems, when combined with the latest advances in automation, provide the flexibility, reliability and size necessary to meet the tire production line demands.

These new self-shielded e-beam units also considered equipment maintenance. To do this, openings were provided to allow access to the treatment area. All components in the treatment room were removable. Special tools were provided to ensure quick and easy maintenance.

The result provided the tire manufacturer with an e-beam system capable of precuring web type ply materials in an on-line situation.

The precuring of ply materials was and still is the most irradiated tire component in use today. However, manufacturers continued to look at other tire components that might offer even more savings with a precure process. One of the obvious candidates was the precuring of gum rubber materials or non-reinforced tire components, particularly for larger tires. The use of e-beam processing for green rubber or squeegee materials for truck and bus tires presented a new set of problems to be resolved.

Tire components such as squeegee or other low-tension materials can be processed by electron beams, but their composition was considered too difficult to handle in an in-line situation. Typically, these tire components have low green strengths and do not have the benefit of fabric or cord material to add strength during the irradiation process.

Generally, these are not suitable for unsupported handling systems like those used for ply materials. Typically, e-beam systems used to precure squeegee materials were placed in an off-line position, mostly because of the complex under beam handling equipment and conveyor systems needed to transport the material under the beam. A cooperative effort between tire manufacturers and e-beam equipment makers provided a dramatic improvement in this equipment. The result of these efforts is equipment designed specifically for processing low-tension or gum rubber materials.

This new generation of shielded EB processing equipment provides the tire maker with many options in the design and layout of the production line. Systems can be installed in almost any environment and location. This new generation of EB equipment contains the necessary features required to handle low tension materials in a production environment.

The advantage the new equipment has over its off-line predecessor is that new models are relatively small enough to be installed in existing tire production facilities. These production upgrades provide the manufacturers with an improved final product, prolonging the life of an existing production line by reducing tire component weight and cost, while improving overall tire quality.

Conclusion

Tire manufacturers considering a new production line or upgrading an existing line now have a wide selection of EB precure equipment from which to choose. Each version is designed to meet specific production demands. Layout of the production line can be accomplished with generally only minor considerations for the precure process. Small compact systems are available to precure essentially all types of tire components.

In the future, as manufacturing requirements change, equipment vendors must be ready, willing and able to work with their customers in solving process problems. Management committed to a teamwork solution provides the incentive for both the equipment vendor and manufacturer to meet future challenges, the goals being to improve the product quality, to add value and reduce cost.