Issue link: https://read.dmtmag.com/i/34500
HEAT STUDY BRAKE HEAT OVERVIEW Truck brake often reach very high temperatures. Brake drums can reach temperatures of 600° F or more and are in very close proximity to the wheels. This heat can be easily transferred to the wheels and tires. Brake drum heat is transferred to the wheel primarily through radiation and convection. The hot brake drum radiates heat in all directions to the wheel. In addition, the drum heats the air between the drum and the wheel. The heated air rises and transfers additional heat energy to the wheel through convection. Much of the heat is transferred to the wheel in the bead mounting area due to its close proximity to the brake drum. The wheel then directly conducts heat to the tire bead resulting in elevated temperatures in the tire bead area. Excessive bead heat can affect tire life in many truck tire applications. Vehicles in urban and refuse service are most commonly associated with bead heat issues, but any application that experiences hard braking can be affected. Results of bead heat: 1. Immediate Failure: In some cases, after periods of hard braking where brake drums reach very high temperatures (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 stop 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 process results in a tire rapid air loss. 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 carcass: 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 below demonstrates how operating with bead temperatures in excess of 200°F will significantly reduce your casing life. Duals – Close to Brake Drum CASING LIFE vs BEAD TEMPERATURE 400 350 300 250 200 150 1 64 Operation and Handling 10 100 Casing Life (hr) 1,000 10,000 Bead Temperature (F)