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2344 E. Speedway Blvd.
Tucson, AZ 85719


Facts About Tire Manufacturing Defects

Manufacturing defects contributing to tread/belt separations are common place. During the manufacturing process, it is not uncommon for contaminants, such as moisture, grease, oil, dirt and water to accumulate on the surfaces of the components, including the steel belts. If a tire is manufactured with an area of contamination on the belt surface, the proper chemical reactions will not occur during the vulcanization process and tire will leave the plant with an area of poor or non-adhesion.

It is essential that a tire be manufactured so that areas of trapped air do not exist within the tire. Trapped air is considered a contaminant that interferes with the adhesion between the adjacent rubber components, including the two steel belts.

While there are cases where wood chips or plastic are present in the tire, in the vast majority of cases, due to the manner in which the tire is vulcanized in a curing press at high temperatures, one will usually be unable to identify the contaminants.

After the steel belts are calendared by coating the steel belt cables with rubber known as belt skim stock, the belts are rolled and taken to an area of the plant where they cool. The steel belts are rolled around a cotton or plastic liner that leaves impressions in the rubber coating of the steel belts. If the steel belts (and other rubber components) are used before they become overaged and no contaminants are present on the belt surface when the tire is vulcanized, the adjacent rubber surfaces will flow together eliminating any the “pattern marks” or “liner imprints” from the rubber surfaces.

If, however, the steel belts or other rubber components are overaged (have lost their “tack”) or contaminated, it is not uncommon to see pattern marks on the failure surface of the accident tire. Occasionally these pattern marks will appear as diamond shaped as illustrated in the photograph below (see Figure 3). More commonly, these pattern marks will appear as dimple shaped as shown in the photograph below (see Figure 4).

Figure 3

Diamond Shaped Patterns Evidencing Tire Failure Defect

Figure 4

More Common Dimple Shaped Patterns Evidencing Tire Failure Defect

Snaked, Wavy or Off Centered Steel Belts

Tire companies design and manufacture steel belted radial passenger and light truck tires with two steel belts. The lower, or number one, steel belt is wider than the top, or number two, steel belt. This creates a step off at the belt edges, and is known as a stepped or pyramid belt construction. The step off reduces the stresses at the belt edges. Unfortunately, it is not uncommon for the tire builder to improperly position the top belts so that at various locations there is no step off. This is a clear manufacturing defect that increases the stresses at the belt edge and the development of separations. An illustration of snaked or wavy belts appears below (see Figure 5).

Figure 5

Tire Manufacturing Defects: Snaked, Wavy or Off Centered Steel Belts

Bare Cable

Because steel does not adhere well to rubber, the thin wires forming the steel cables used in the steel belts are coated with brass. Spools of these cables are stored in a humidity controlled area of the plant known as the creel room. Cables from these spools are fed through a small opening in the creel room to the calendars where the cables are coated with belt skim stock rubber to form the steel belts. If a tire manufacturer does not follow proper quality control procedures, during this process contaminants, including moisture, can attach to the belt cables. These contaminants can and do prevent adequate adhesion between the cables and the rubber in the belt skim rubber (poor wire to rubber adhesion). As a result, certain tread/belt separations occur because of the lack of adhesion between the belt skim stock rubber and the belt cables. This appears in an accident tire in the form of bare cables. These cables may or may not be yellow or brassy in color.

2344 E. Speedway Blvd. Tucson, AZ 85719 Phone: (520) 884-4301 Fax: (520) 884-4802