Electron beam tire processing equipment.

In the last 10 years there have been some significant changes in the high energy electron beam equipment used to precure tire components. Most of these changes were brought about by the tire manufacturer's need to:

* reduce cost;

* improve quality;

* automate the line;

* increase line speed;

* have a reliable continuous process;

* reduce floor space.

The manufacturers of electron beam processing equipment were being challenged and in some situations the process was replaced by other manufacturing techniques.

To the tire manufacturer, electron beam equipment meant that a sizable area of the plant had to be taken out of production for a large ugly concrete radiation vault. Factory personnel would usually compare these structures to fall out shelters, better suited for use during a nuclear attack than for processing tire components.

The first vault designs put into production were usually based on experience gathered from research and development programs. Input for the construction of these systems was most often supplied by the manufacturer of the electron beam equipment with the tire manufacturer at the mercy of the vendor's specifications.

A typical vault might be 70 to 80 feet long, 35 to 40 feet high and have a width of 16 to 20 feet. The wall thickness in the treatment area could be four to six feet thick. Outside of these structures pay off and take up equipment would add another 60 to 80 feet to the overall length of the system. All of this equipment had to be put off line simply because no one felt that the electron beam system was reliable enough to be on line. Added to the problem was the complexity of operating the system, which usually required a graduate electrical engineer or someone with very similar specialized training.

In spite of all these drawbacks, technology continued to move forward and in time the electron beam equipment became more accepted as a production process although there was little change in the overall size of these systems.

As tire manufacturers became accustomed to electron beam technology they began to insist on more production friendly equipment with improved automation to ensure consistent product quality. Conveyor systems needed to be controlled by the electron beam unit so that startup, shutdown, reel change and product change could be done with little or no product loss.

In addition to the trend toward automation, there was a push to reduce the overall size of these facilities. Initially this was accomplished by using the unique 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 and side directions. The solution seemed obvious, why not put the vault below ground level. In this way the concrete floor became part of the vault with natural environment providing the bulk of the radiation shielding.

This solution was certainly adequate for tire products that incorporated either cord or fabric to stabilize the green rubber. Precuring these body ply products used a pay off and take-up system with idler pulleys to direct the product under the electron beam system. The use of idler pulleys also allowed the product to be run through a maze designed to protect personnel against the scattered electrons and x-rays produced in the treatment area.

Clearly the overall size of the shield vault had been reduced, although the product handling equipment remained high due to the separate facilities required for the off-line process. The penalty of having an off-line process is that product handling equipment has to be provided for a single process separate from the line.

Unfortunately, reliability of this equipment was still not good enough for it to be considered as an on-line production tool. Added to this problem the issue of maintainability, working in the treatment area was hot, cramped and a dirty job. In many cases, the product handling equipment had to be removed in order to work on the electron beam unit.

In spite of these problems many of these units were built and are still operating successfully today. Over the years improvements have been made and upgrades installed to reduce the downtime and increase power levels. However, the push by the tire manufacturers for automation on the line continued.

Electron beam equipment manufacturers began to work closely with tire manufacturers to design automation systems that met industry demands. This was particularly true in the Asian market, where the cost of production could no longer be dependent on cheap labor. Automation was seen as the key to increasing production and reducing labor cost. Another key to improved productivity was to move the precure operation from off line to on line process. This would require that the reliability of the electron beam system be the same as the equipment on the rest of the line. The definition used for a reliable system in this situation was one preventive maintenance per year. Tire manufacturers demanded that uptime be predictable so that managers could plan their production and maintenance activities without fear of unscheduled down times.

To achieve these goals not only did the mechanical equipment have to be rugged and reliable, but so did the electronic control system.

Typically, controls on the line were designed to be reliable under the most extreme conditions of heat, dust and humidity. In addition to this, it was necessary that the operation be simplified so that inexperienced operators be able to run the system. The control system also had to be capable of supplying a periodic up-date on the operation of all aspects of the system. This information was usually sent to a host computer system, where production managers could evaluate each and every run to ensure it met quality standards.

The next major problem to be solved concerned the size of the electron beam systems. In order to install a system on-line, production managers needed flexibility in locating the unit and in reducing the space requirements.

The obvious answer was to utilize a combination of lead and steel, to replace the traditional concrete vault. These systems, combined with the latest advances in automation, provided the flexibility, reliability and size necessary. The tire manufacturer now had an electron beam system capable of precuring web type body ply product in an on-line situation.

In addition, these units took into consideration the problem of maintaining the equipment. Large openings were provided for treatment area access. All components in the treatment room are easily removable. Special tools were provided to ensure quick and easy maintenance.

Equipment features that included compact size, reliability, automation and easy maintenance now provided the tire manufacturer with the process flexibility necessary for integration into the production line. Electron beam processing equipment for web type body ply tire components was now a production reality.

Other tire components were being processed by electron beams but because of their composition were considered too difficult to handle in an on-line situation. The most abundant production tire component in this category was tire inner-liners. Typically these components have green strengths of three lbs. or less (table 1).

Table 1 - innerliner stock composition
Innerliner                    Parts by weight
Butyl rubber                        20
SBR 1502                          33.5
Natural rubber                      45
Whole tire reclaim                  20
GPF black                           50
Whiting                             45
Tackifying resin                    10
Medium process oil                6.25
Stearic acid                         1
Zinc oxide                           5
Accelerator (sulfenamide type)       2
Phenol polysulfide                   1
Sulfur                             0.3
Precure - innerliner stock        0      5     10     15     20
                                Mrad   Mrad   Mrad   Mrad   Mrad
(1) Peak lbs., green strength    3.0   15.3   20.0   22.0   33.8
(2) Percent recovery             8.0   31.5   42.5   80.0   not
                                                           tested

Generally these are unsuitable for an unsupported conveyor system of the type used for body ply product. In the case of green rubber tire components, it was necessary to use a full support conveyor system, requiring a rather complex underbeam system.

Typically electron beam systems used to precure innerliners were very complex and were always placed in an off-line position. The same old problems of reliability and maintainability plagued this equipment, particularly where the product handling equipment was concerned.

The drive to automate and integrate this equipment into the production line was again pushed in the Asian market. To solve the problems of product handling required a very dynamic working relationship between the tire manufacturer and the equipment vendor. The development of new production equipment is best solved by the combined expertise of both the vendor and the manufacturer working together in a team effort. The result of these efforts is usually equipment worthy of the process.

Comparing this equipment to the original concept for this product gives the impression of what it would be like to compare the original Model A to the streamlined vehicles of the 1990s.

The result of this joint effort between the vendor and the manufacturer is a processing precure system that is reliable, repeatable and serviceable.

The following key factors were design goals established in the beginning of the development program.

* Reliability - meant that only schedule maintenance was acceptable preferably one preventive maintenance per year.

* Repeatability - if you do not have process repeatability there is no process.

* Automation - the system must be capable of running and monitoring the process with little or no human intervention.

* Redundancy - the equipment should be capable of continued operation, with no effect on process, even after a component failure.

* On-line capability - the preferred mode of operation is the equipment be installed in the process line with the ability to run product faster than the feed process.

* Maintainability - the system must be easy to maintain with maintenance turn around time in hours not days.

* Product tracking - the equipment must be capable of interfacing with any production line host computer and/or product tracking system.

* Operator friendly - this was an absolute requirement that the entire system be operated by a single code entry and that it also have remote control capability.

This new generation of self shielded advanced electron beam processing equipment provides the tire manufacturer with many options in the design and layout of the production line. Systems can be installed in almost any environment and location. Today electron beam equipment is available that has the necessary features required in all production worthy equipment.

The advantage the new advance designed equipment has over its predecessor is that it is small enough, relatively speaking, 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 cost and improving tire quality - a two-fold benefit from a single piece of equipment.

The development program teaming manufacturer and vendor was carried out even though the tire market is a relatively small segment of the overall electron beam market.

Conclusion

Tire manufacturers considering a new production line, or upgrading an existing line now have a wide selection of electron beam equipment to choose from, designed to meet specific production demands. Layout of the production line can be accomplished without special consideration, for the precure process.

In the future as manufacturing requirements change vendors must be ready, willing and able to work with their customers in solving process problems. Management committed to a team work solution, provides the incentive for both vendor and manufacturer to meet the challenges of tomorrow.

References

[1.] J.D. Hunt and G. Alliger (1979) Rubber - application of radiation to the tire industry - Radiation Physics and Chemistry - Volume 14. [2.] R. Fernald and D. Grant (1980) High Voltage Engineering Corp. - Publishers. [3.] B. Thorburn and D. Shah (1981) Environmental management using electrons - proceedings of Environmental Engineering Conference - A.S.C.E. Publishers. [4.] I. Sakamoto, K. Mizusawa, Y. Kubota and Y. Hoshi 1990) The recent status of E.B. processing accelerators in Asia - Radiation Physics and Chemistry Volume 35. [5.] Y. Hoshi and K. Mizusawa (1991) 5MV-30mA industrial electron processing system - Nuclear Instruments and Methods in Physics Research, North-Holland Publishers.

Acknowledgements

"Electron beam tire processing equipment" is based on a paper presented at the October 1991 meeting of the Rubber Division, ACS.

"Advanced extrusion control technology" is based on a paper presented at the October 1991 meeting of the Rubber Division, ACS.

"Powdered rubber technology - an equipment concept" is based on a paper presented at the May 1991 meeting of the Rubber Division, ACS.

"Mixer with variable intermeshing clearance" is based on a paper presented at the October 1991 meeting of the Rubber Division, ACS.