The girth gear is the primary drive component that transmits rotational power to rotary kilns and ball mills. Mounted around the kiln or mill shell and driven by the pinion, it must deliver reliable torque transmission under enormous loads. LIMING manufactures precision girth gears ≥5T with superior cast steel metallurgy.
A girth gear (also called a gear ring or ring gear) is a large-diameter gear that encircles the cylindrical shell of a rotary kiln or ball mill. It meshes with a smaller driving pinion gear connected to the motor and gearbox, converting the rotational force into the slow-speed rotation of the kiln or mill. Because the girth gear carries the entire drive torque of the equipment, it is one of the most critical and expensive spare parts in a cement plant.
Girth gears operate under demanding conditions: heavy cyclic loads, shock torque from startup, thermal expansion of the kiln shell, and continuous exposure to dust and vibration. A failed girth gear can shut down an entire production line for weeks. LIMING's girth gears are engineered with precise tooth geometry, high-quality cast steel, and controlled heat treatment to ensure smooth meshing, quiet operation, and long service life.
We produce both ball mill girth gears and rotary kiln girth gears in single-piece or split (two-half) designs. Split gears are easier to install and replace on operating equipment without removing the shell, while single-piece gears offer superior rigidity for new installations.
LIMING manufactures girth gears from two primary cast steel grades, selected based on the application, gear diameter, and torque requirements:
| Material Grade | Tensile Strength (MPa) | Yield Strength (MPa) | Hardness (HB) | Typical Application |
|---|---|---|---|---|
| ZG310-570 | ≥570 | ≥310 | 163-229 | Ball mills, rotary dryers, medium-duty kiln drives |
| ZG35CrMo | ≥590 | ≥390 | 180-240 | Large rotary kilns, heavy-load continuous duty |
ZG310-570 is a high-strength carbon cast steel suitable for most ball mill and rotary dryer applications. For large rotary kilns operating continuously at high torque, ZG35CrMo offers superior hardenability, fatigue resistance, and tooth surface durability due to its chrome-molybdenum alloying. Both materials are normalized and tempered to achieve uniform hardness throughout the gear section.
Precision manufacturing, superior metallurgy, and decades of experience in large gear production.
In-house foundry handles gears weighing 5 to 50+ tons. Wood mold patterns ensure dimensional accuracy for large diameters.
CNC gear hobbing machines achieve tooth profile accuracy to GB/DIN standards for smooth, quiet meshing with minimal wear.
Girth gears can be supplied with matching pinions — inspected together to ensure proper tooth contact and backlash.
Technical assistance for installation, alignment, and commissioning. On-site measurement and reverse engineering available.
| Parameter | Specification |
|---|---|
| Product Type | Girth Gear / Gear Ring (single-piece or split) |
| Material Options | ZG310-570, ZG35CrMo (cast steel) |
| Processing Weight | ≥5 tons (up to 50+ tons) |
| Outer Diameter | 3,000 mm – 12,000+ mm (custom) |
| Face Width | 300 mm – 800 mm (per design) |
| Module | 16 – 50+ (per gear specification) |
| Number of Teeth | Custom per design requirements |
| Pressure Angle | 20° standard (other angles available) |
| Gear Accuracy | GB 10095-88 Class 9-10 / DIN 3962 Class 9-10 |
| Heat Treatment | Normalized + tempered, tooth surface hardening available |
| Tooth Surface Hardness | 180-240 HB (up to HRC 50+ with surface hardening) |
| Inspection | UT, MT, hardness testing, tooth contact pattern check |
| Lead Time | 60-120 days (depending on size and complexity) |
A multi-stage process that ensures dimensional accuracy, material integrity, and precise tooth geometry.
Full-size wooden pattern constructed to exact gear dimensions including shrinkage allowance and machining stock.
Molten cast steel poured into sand molds formed from the wood pattern. Controlled solidification prevents defects.
Normalizing and tempering relieves casting stress and achieves target hardness and toughness throughout.
CNC turning of OD, bore, and faces followed by precision gear hobbing to exact tooth profile and module.
Tooth contact pattern testing, UT/MT inspection, hardness verification, and dimensional CMM report.