Open Gears for the Mining Industry: Material and Manufacturing Process Selection

One of the characteristics of the mining industry is the need to deal with large and heavy-section components. The concept of heavy-section is relative and, in the case of this paper, the authors will cover both the material selection criteria and two new manufacturing solutions available for large open gearing. Open gears for the mining industry drive grinding mills up to 10,000 HP with a single pinion and daily throughputs of approximately 30,000 metric tons (∼ 66,600 pounds). They are further characterized by some unique numbers such as weights in excess of 100 metric-tons (∼ 222,000 pounds), diameters up to 13.6 meters (45 ft.), face widths up to 1,143 mm (45 inches), tooth sizes up to 40 module (5/8 diametric pitch), rim thickness up to 250 mm (10 inches), and hardness up to 350 Brinell, with machining tolerances to AGMA Q10 in accordance with AGMA 2001-B88 [1]. The most demanding challenges in the advancement of this technology and the manufacturing of these components are achieving AGMA GRADE 2 material requirements in heavy-section gear rims and overcoming the many obstacles associated with welding high-strength low-alloy (HSLA) materials of extraordinary size and mass. This paper demonstrates how these challenges have been overcome by providing a thorough description of the manufacturing process. Beginning with steel making, the topics are melting, special refinements, forging, rolling, specialized heat treatment, metallurgical enhancements for improved weldability and material testing. Topics relating to the fabricating and general manufacturing process are: cold forming of heavy-section high-strength, low-alloy rim plates, the application of both nontraditional and traditional welding processes, nondestructive testing, machining and tooth cutting.