Premium solution for grinding large gears

A manufacturer of grinding wheels for gear grinding has introduced new premium grinding wheels for the series production of large gears for wind turbines in a process-safe manner. A precision-molded abrasive grain ensures maximum stock removal volume.

The series production of large gears requires a high level of quality, excellence and continuity in production. Particular emphasis is placed here on maximum synergy between the grinding machine, the grinding process and the grinding wheel. After several successful trials on various Klingelnberg Höfler Rapid grinding machines carried out with customers in their production facilities, Krebs & Riedel has received several large orders for grinding large gears from abroad and has introduced the new premium grinding wheels with process reliability. Krebs & Riedel is one of the world's leading manufacturers of grinding wheels for gear grinding in the automotive and EV sectors. The family-owned company is also expanding into other sectors where large gears are manufactured with the new Blue Moon TZ premium product range.

In recent years, wind power has been instrumental in saving CO2 emissions. Wind turbines are becoming larger and more powerful, while production costs must be reduced. This requires production methods that can manufacture gears cost-effectively and with high quality, even with complex flank modifications. Gear sizes in wind power typically range from 800 to 4000 mm. Some gears can even reach 8000 mm in diameter and weigh up to 100 tons. The most common size in the field of external gears is 1200 mm in diameter and ranges from module 12 to module 52. Profile grinding wheels typically have a diameter of 100 - 450 mm.

Only perfectly ground gear geometry ensures optimum power transmission for high wind turbine efficiency and smooth running. Grinding burn must not occur under any circumstances, because the forces acting on the gear are very high and tooth breakage is very costly. High-precision gear quality is a matter of course at Klingelnberg and Krebs & Riedel. It increases the service life of the individual gear components and thus makes a significant contribution to reducing maintenance and production costs. To achieve maximum synergy between the grinding machine and the grinding wheel, Krebs & Riedel optimizes the process with application engineering support at customers' sites around the world and offers the Blue Moon TZ, a new premium grinding wheel with a precision-molded abrasive grain.

Blue Moon TZ is characterized by a very high cutting performance and a very high removal volume. "In some trials, the stock removal rate (Q'w) was more than 30 mm³/mms," says Sigurd De Ridder, senior application engineer at Krebs & Riedel, who conducts trials and process optimization for customers worldwide. He says, "Precision-molded abrasive grains are state of the art today. Blue Moon TZ is comparable in performance to other precision-molded abrasive grits on the market. It is self-sharpening, very sharp-edged, microcrystalline and has an elongated trapezoidal bar shape." The homogeneous pore structure of Blue Moon TZ contributes to an extreme improvement of the entire cooling system during the grinding process. Due to the open structure, the entire grinding wheel is immediately flooded by the cooling fluid. Even at extreme stock removal rates, the chip is transported away from the contact surface. This avoids heat input, which could lead to thermal damage to the gear.

On average of all tests on Klingelnberg Höfler Rapid 2500 machines, Sigurd De Ridder had the following grinding results: A cooler grind and longer tool life, combined with up to 20% faster grinding time compared to standard grinding wheels. The longer tool life and higher grinding performance help to reduce costs while achieving the same, or even better, quality from the gear. On average of all dressing tests, Sigurd De Ridder achieved the following results: 20% longer dressing intervals, 30% less infeed, which also results in a longer dressing wheel life. Another side effect is that the machines have lower power consumption after optimization.

The profile grinding machines of the Rapid series for large workpiece sizes are designed for component diameters up to 8,000 mm. Depending on individual requirements, they are equipped with an extended stroke range (L variant) and are also available in two variants. In addition to the standard configuration, the machine is also available with a small grinding head to accommodate very small grinding wheel diameters of 300-20 mm (K variant). In all configurations, machines of the Rapid series can be converted from external to internal gears in a very short time by means of optional internal gear grinding arms. In addition, the special arrangement of the machine axes, a thermally stable and virtually vibration-free machine bed made of mineral casting, as well as wear-free torque drives in the machine table and the grinding head for 5-axis grinding contribute to the proven precision, consistent quality and enormous flexibility. Thanks to the highly flexible grinding head with integrated 3D probe and adjustment of the helix angle during the grinding process, gears can be topologically modified in 1-flank grinding or 2-flank grinding, depending on the permissible deviations. In the process, the measurements with the optionally available testing devices already ensure a controlled grinding result during the grinding process.

Series production of large gears requires many hours of workpiece setup, programming, grinding, dressing and testing. It is important to use a premium grinding wheel with precision-molded abrasive grain. The dressing and grinding processes should be optimally set on the grinding machine and optimized by application engineering support. Blue Moon TZ premium grinding wheels have proven themselves not only in the grinding of planetary gears, spur gears and IR outer and inner rings. They have also helped reduce production costs when grinding drive shafts, automotive gears and screw conveyors. (OM-07/23)