business
FIRESTONE'S TIRE PROBLEM Company admits tire design, manufacture combined to produce tire failures Marc S. Reisch C&EN Northeast News Bureau
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irestone has admitted that design and manufacturing problems contributed to tire failures resulting in 148 U.S. traffic deaths. But some industry experts go further and suggest that the manufacturing problems led to poor chemical bonds between the rubber components and steel belts, which led to the tread separation problems those tires have experienced. The tires—the Firestone ATX, ATXII, and Wilderness AT—were primarily used as original equipment on Ford's sport-utility vehicle, the Explorer. Firestone says the tires were made at the company's Decatur, 111., plant. Initial reports of the Firestone problem surfaced in May when Ford recalled Firestone tires used on the Explorer in Venezuela, Colombia, Ecuador, and Saudi Arabia. In early August, Firestone, with prompting from the government watchdog National Highway Traffic Safety Administration (NHTSA), recalled 14.4 million tires in the U.S. 'Tire making is a complicated process," one observer tells C&EN. "Lots of variables lead to anomalies, and the public is exposed to them." With 325 million tires produced annually in the U.S., even a 0.1% failure rate means a large number of potential tire problems. The August Firestone recall was the second largest tire recall on record. The largest was in 1978, when Firestone recalled 14.5 million steel-belted radial tires that, according to NHTSA, could "fail in service without prior warning," leading to "a loss of vehicle control and an accident." At the time of the ATX, ATXII, and Wilderness AT recalls in August, the company said 6.5 million of those tires were still on the road. To date, it says it has replaced 5.6 million of the tires. Parent company Bridgestone estimates the 12
JANUARY 1, 2001 C&EN
cost both to recall the tires and to settle the inevitable product liability lawsuits will come to $750 million. It figures about $450 million alone will go to settle lawsuits. Firestone claims that the recalled
the same tires produced at different plants. However, Firestone contends that certain other factors that have led to tire failures have not been under its control. Lampe continues to point out—as the company has from the start—that Ford's recommended tire pressure of 26 psi is too low. The low pressure led to increased running tire temperature and a consequent decrease in belt adhesion. Ford has recently recommended an increase to 30 psi for tires mounted on the Explorer. In addition, Lampe contends that consumers have put more weight in the vehicle than the tires were designed to carry, "which led to a decreased margin of safety for tire performance." Lampe was also quick to note that "tire industry experience demonstrates that many tread separations can be caused by various forms of tire damage encountered in daily use, such as punctures, improper repairs, severe impacts, or being misapplied. Many of the reported incidents are attributable to these factors, and not those identified in the company's root cause investigation." Tire industry critics say it is always easy for tire manufacturers to point to other factors affecting tire wear—such as environmental conditions and the vehicles themselves—and that it is a reason why manufacturers are slow to initiate a recall. Still, Firestone pledged to change manufacturing practices at its Decatur plant. Unlike its other plants, the Decatur facility processes rubber and antioxidants to make lubricant-coated rubber pellets to place between the steel belts
tires experienced belt separation when a complex combination of factors all came into play. Some of those factors were apparently under Firestone's control. According to John Lampe, president, chairman, and chief executive offi— — — cer of the Nashville, What's inside a tire? Tenn.-based Bridgestone/Firestone unit of Japan's Bridgestone Corp., a design flaw in the ATX tires could lead to cracking in the tire shoulder, making it easier for belts to detach under specific conditions. ATX and Wilderness AT tires produced at Decatur "exhibited different belt adhesion characteristics, including lower initial adheSource: Rubber Manufacturers Association sion," than those of
Sidewall
in its tires. Some in the industry think the pellets pick up too much lubricant, making for a poor bonding material. Other Firestone plants extrude thicker rubber slabs and place them between the belts, effecting a better chemical and mechanical bond with the belts. Firestone pledges to adapt that practice now in Decatur. Firestone has come a long way from its original contention that nothing was amiss with its tires or its manufacturing methods and that the problems with the tires were due to Ford's lowfillpressure recommendation. The lower pressure recommendation was meant to increase the Explorer's stability and soften the ride. However, the lower pressure also reduces the vehicle's ability to carry weight without tire overheating. Still, Firestone awaits the report of an independent investigator, Sanjay Govindjee, hired by the company in mid-September to assess the cause of tire failure on the Explorer. Govindjee is a professor in the department of civil and environmental engineering at the University of California, Berkeley. He specializes in studying the strength of various materials, including the elastomers and metals used in tires. He has degrees in mechanical engineering from Massachusetts Institute of Technology and Stanford University. Govindjee's final report is expected soon. In a memo to Firestone in mid-October, Govindjee pointed the way to Firestone's own findings: "The issue involves a complex interaction of ATX and Wilderness AT tire design, manufacturability, and loading conditions by the Explorer." He also said he was focusing his inquiry on the interbelt materials— the rubber used between steel belts to help bond the belts with the tire. "All evidence to date points to a slowly developing fatigue crack that propagates through the belt wedge material and then subsequently into the belt skim between the steel belts," he wrote. A belt wedge is material placed around the circumference of the tire sidewalls between the steel belts to stiffen and strengthen the tire. "At some stage, the cracks reach a critical size and the tires subsequently fail." Tires are very sophisticated composites with hundreds of parts and materials, one expert notes. They contain man-made and natural rubber, steel belts and beads, and polyester and nylon reinforcing materials. They also contain numerous chemical additives
used to control rubber cure and bonding to components and to help protect the tire from premature breakdown due to heat, stress, and exposure to the environment. The Firestone tires failed because of a faulty design, the expert agrees. 'The material Firestone used was probably marginal," he says. In some cases, the company still has not mastered the art of adhering steel and rubber, he continues. That same inability to make sure the steel properly bonded to the rubber
was behind the recall of 14.5 million Firestone 500 tires in 1978, he points out. The expert also suggested that labor problems at the Decatur plant in recent years exacerbated the problems of a bad tire design. While the expert did not suggest employees sabotaged the tire building process, he did suggest that new employees brought into the plant may have contributed to manufacturing problems through inexperience. Tire builders make tires one at a time and control the assembly and cure of a
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business tire—a difficult task even for an experienced tire builder. Tire design and labor prob lems likely contributed to the Firestone tire tread separa tions. But the expert attributes the rollovers of Ford Explor ers when treads separate to the Explorer's high center of gravity. The high center of gravity and potential instabili ty of the vehicle when acci dents occur at high speeds is typical of other sport-utility ve hicles as well. And while underinflated tires do tend to break down more rapidly, the expert thought the contribution of low inflation accounts for only a fraction of a percent of the problems Ford and Firestone have had with the tires for the Explorer. "People tend to run tires underinflated. It's hu man nature," he adds. "And a good tire can withstand some temperature build up. But with a marginal design, you add to the problem with underinflation." According to one mechanical engi neer who has followed Firestone over the years, and who is also a consultant for plaintiff attorneys, Firestone has a systemic problem when it comes to ad hering rubber and steel. Because steel and rubber do not adhere to one anoth er, steel wire for use in tires is coated with brass. The brass reacts with the rubber, forming a chemical and me chanical bond, the engineer explains. However, when the steel mesh is cut to form a belt, there will always be a weak spot where rubber and exposed steel do not bond. Good tire design minimizes the po tential for belt adhesion failures, the en gineer says. There is an art, the engi neer says, to the mixture of sulfur used both to vulcanize rubber and to bond the brass-coated steel belts to the rub ber. For instance, a high sulfur content along with adhesion promoters allows a good bond of brass-coated steel with rubber, but a sulfur content that is too high can prematurely cure the rubber, trapping air and preventing a good bond to rubber. Tire builders must add retarders to slow rubber curing until ad hesion with the steel belts takes place, and then they must add accelerators to speed the cure. Despite their expected long service life, radial tires can and do fail prema turely when the steel separates from the 14 JANUARY 1, 2001 C&EN
The wreckage of a sport-utility vehicle involved in a two-car accident in Arizona, the cause of which is believed to be tread separation of Firestone Wilderness AT tires, is shown in this Arizona Department of Public Safety handout photo.
rubber. Some tire makers add a nylon ply or two to help resist mechanical forc es during tire use that could cause the steel to separate. "Firestone was told to
put nylon into its tires but chose not to do it," the engi neer says. "It's really impossible to make a tire that doesn't fail," the engineer explains. In de signing tires, manufacturers try to keep their costs down while still providing a tire that can safely convey pas sengers for 40,000 to 80,000 miles without incident. And in the case of Firestone, and Ford's Explorer, both the car design and the tire design represented com promises that may have had fatal consequences.^
Rhodia ChiRex Steps Out On Pharmaceutical Chemicals Stage
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hodia's acquisition of ChiRex, an nounced in July, looked to all the world like the French company's entry into the advanced pharmaceutical chemicals business. To Rhodia execu tives, however, the purchase is an inte gration move that makes both firms stronger suppliers to the drug industry. The acquisition was completed on Sept. 1, and Rhodia ChiRex had its first board meeting later that month—a "very, very fast integration," according to Jean-Claude Bravard, president of Rhodia's fine organics division and chairman of Rhodia ChiRex. In contrast, he notes, DSM's acquisition of Catalytica—another of last summer's pharma ceutical chemical mergers—was an nounced just days after Rhodia's deal but didn't close until Dec. 18. Rhodia ChiRex will have sales of about $170 million this year, mostly from ChiRex; only $30 million will come from Rhodia operations in high-end pharmaceutical chemicals. Likewise, 85% of the combined drug synthesis ca pacity of the new company, which is al most 1,000 m3, comes from ChiRex. But Bravard and Marc-Antoine Mal let, Rhodia ChiRex's chief executive offi cer, see synergies between the two op
erations that run deeper than just capac ity and sales. They say the acquisition unites two firms—neither of which was perfect in the eyes of customers—into a cohesive unit combining big-company security and small-company speed. Mallet notes that the more entrepre neurial ChiRex had a reputation for quick customer response—for example, promising a 10-day turnaround on in quiries about pharmaceutical active in-
Rhodia ChiRex is one of three Rhodia pharmaceutical units Pharmaceutical intermediates 15% \ ^ — - * • η
Bulk analgesics 45%
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Rhodia ChiRex 40% 2000 pharmaceutical sales : $385 million
