Issue link: http://read.dmtmag.com/i/34501
Results of bead heat: 1. Immediate failure: In some cases, after periods of hard braking where brake drums reach very high temperature (in excess of 600° F), immediate failure can occur. This normally occurs when a truck is brought to a stop for a period of time with very high brake temperatures. Often this occurs when an over the road truck stops at a truck ramp at the bottom of a long descent. As the heat rises from the brake drum, there is excessive heat buildup in the portion of the tire bead directly above the brake drum (inner bead of inside dual). The high temperature can cause a breakdown of the rubber products in the bead area and allow the steel body cables to unwrap from the bead. This could result in a rapid air loss occurrence. This phenomenon is also common in urban and refuse fleets when the driver stops for a break after a period of hard braking. 2. Premature aging of the casing:Heat is a tire’s worst enemy! A tire subjected to high heat conditions over an extended period of time will experience accelerated aging of the rubber products. The accelerated aging may result in a blowout during operation, or it may render the casing unsuitable for retread. The graph on the previous page demonstrates how operating with bead temperatures in excess of 200°F will significantly reduce your casing life. Bead damage as a result of brake heat is recognizable in 3 stages of severity. In the first stage, the bead starts to turn inward. This can be visibly identified on the tire when it is dismounted. A straight edge placed across the beads from one bead to the other no longer rests on the bead point, but now rests closer to the bead bearing area. 3rd Stage – Partial Unwrapping of the Casing Ply The second stage occurs when the rubber in the bead area starts to split or crack, indicating that the steel casing plies are starting to unwrap. 2nd Stage – Bead Splitting From Heat The third stage is when the casing ply fully unwraps from the bead. In extreme cases the casing ply unwraps from the bead all the way around the tire. At this point the tire completely separates from the bead wire. The bead wire can entangle itself around the axle if this type of separation occurs. 1st Stage – Turning of the Bead 58 Section Three: Extending Tire Life 3rd Stage – Complete Unwrapping of the Casing Ply