Cast Steel Large and Half/Segments Gear Ring
The ball mill girth gear (also called ring gear, gear wheel, or large gear) is the largest and most important transmission component in the ball mill drive system. It is a large ring gear bolted around the outside of the mill cylinder. Together with the pinion, it forms the main drive train that rotates the entire ball mill.
The girth gear is driven by the motor through the pinion. When the pinion rotates, it turns the large girth gear, which then rotates the entire ball mill cylinder for grinding operations. It is one of the most expensive spare parts in a ball mill, so its quality directly affects the reliability and operating cost of the whole grinding system.
Types of Girth Gear Structure
AGICO offers both integral and segmented girth gears based on customer requirements and mill specifications
Integral Girth Gear (One-Piece Structure)
The entire gear ring is cast as one complete piece. This form is simple in structure and offers high overall strength. However, due to its large size, an integral girth gear is better suited to small and medium-sized ball mills with smaller diameters.
Segmented Girth Gear (Split Structure)
For large‑diameter ball mills, the girth gear is usually divided into two or more segments (e.g., two halves, 4 piece or more segments). The segments are cast separately and then assembled on‑site using bolts. The segmented structure offers several advantages:
- Simplified maintenance: Worn segments can be replaced individually without replacing the entire gear
- Reduced transportation costs: Segmented design can reduce transportation costs
- Easier installation: Segments are easier to handle and install on-site
Girth Gear Technical Specifications
- Outer diameter: 0.8 – 16 meters (800 – 16,000 mm)
- Weight: 1 – 150 tons (customizable)
- Module: 10 – 60 (hobbing), up to 120 (milling)
- Material types: Cast steel ZG45, ZG310-570, ZG42CrMo, ZG35CrMo, ZG40CrNiMo, 38CrMoAl, ductile iron, hardened gear steels (20CrMnTi, etc.)
- Gear types: Spur gear, helical gear, double helical gear
- Structure: Integral (one-piece) or segmented (2 or more segments)
- Heat treatment: Normalizing, quenching + tempering, carburizing + quenching, tooth surface induction hardening
- Accuracy grade: DIN 3962 Class 6 (standard), Class 4-5 (ground), AGMA Q9-Q10
- Hardness: 320-360 BHN (gear ring), 57-62 HRC (pinion)
- NDT methods: UT, MT, PT
- Application: Ball mill, rotary kiln, rotary dryer, SAG mill, rod mill
Advantages of AGICO Ball Mill Girth Gear
High‑Strength Cast Steel Material
AGICO girth gears are made of high‑quality alloy steel and carbon steel, such as ZG42CrMo, ZG35CrMo, and ZG310‑570. These materials provide excellent strength, wear resistance, and impact resistance, ensuring a long service life under heavy loads.
Smooth Transmission, Low Noise
We use CAE simulation software before casting to optimize the design and prevent defects. We also carefully control machining accuracy to ISO 1328 grade 6-8. This ensures the girth gear meshes smoothly with the pinion—less vibration, less noise, and less wear.
Anti-Deformation Technology
Large girth gears easily bend or warp during manufacturing. AGICO uses special anti-deformation methods. We do heat treatment to remove internal stress, slow cutting to prevent bending, and stress analysis before machining. This ensures your girth gear stays straight and round, so it transmits power smoothly for many years.
Strict Quality Control
AGICO has a large production capacity with heat treatment furnaces up to 16×20×6 meters. Every girth gear undergoes non-destructive testing (UT, MT, PT), chemical analysis, and tooth accuracy inspection. AGICO is ISO9001 certified.
Custom & Engineering Support
We accept custom orders based on customer drawings, including any diameter, tooth type (spur, helical, or double helical), and material. Our engineers provide full technical support from design to installation.
Long Life, Easy Maintenance, Fast Delivery
With proper lubrication and maintenance, AGICO girth gears can last 15 years or more. Our segmented design allows worn segments to be replaced individually, reducing downtime. Standard lead time is 30–45 days, with global logistics support.
Manufacturing Process of Ball Mill Girth Gear
1. Casting simulation (CAE) → 2. Wood pattern making → 3. Sand mold making → 4. Smelting → 5. Molten steel testing → 6. Pouring → 7. Sand cleaning → 8. Heat preservation → 9. Secondary cleaning → 10. Heat treatment → 11. CNC machining (hobbing, grinding) → 12. Non-destructive testing & tooth inspection → 13. Packaging & delivery
Applications
Our ball mill girth gear is suitable for:
- Cement plants (cement mills, raw mills, coal mills)
- Mining industry (SAG mills, AG mills, rod mills)
- Rotary kilns and dryers
- Power stations and steel plants
- Metallurgical and chemical industries
Installation and Transportation
Installation Tips
- Inspect the girth gear for damage before installation.
- Clean all mating surfaces.
- Carefully align the gear with the mill shell.
- Tighten bolts in a cross sequence using a torque wrench. Re-torque after 24 hours of operation.
- Lubricate the gear and run the mill empty for 2–4 hours before full load.
Packaging and Transport
- Packaging: Seaworthy plywood crates or steel pallets, rust-proof oil, plastic wrapping.
- Segmented gears: Each segment is packed separately with labels.
- Handling: Use designated lifting points. Store on flat, dry ground.
- Support: AGICO provides installation drawings, torque specifications, and optional on-site guidance.
AGICO Factory
Girth Gear and Pinion – The Drive Pair
The girth gear and pinion form the heart of the ball mill drive system. The pinion is a smaller gear that engages directly with the girth gear. The motor rotates the pinion, and the pinion turns the girth gear, which then rotates the entire mill cylinder. Proper matching of the girth gear and pinion is essential for efficient power transmission, low noise, and long equipment life.
AGICO supplies complete girth gear and pinion sets that are designed as a matched pair. We ensure:
- Correct tooth profile and backlash: Prevents excessive wear and vibration
- Same material grade and heat treatment: Ensures uniform wear rates between the two gears
- Precision alignment: Our machining guarantees proper center distance and contact pattern
We also supply replacement pinions for existing girth gears. Our pinions are made of high-strength alloy steel with hardened tooth surfaces (57-62 HRC), offering excellent wear resistance and a service life that matches or exceeds the girth gear.
Whether you need a new girth gear and pinion set or a replacement pinion, AGICO provides custom‑engineered solutions based on your mill specifications and original drawings.
Frequently Asked Questions (FAQ)
Q1: What is the difference between girth gear and ring gear?
A: They are the same part.
Q2: What is the service life of AGICO girth gear?
A: 10–15 years or more with proper maintenance.
Q3: Can AGICO produce girth gears according to my drawings?
A: Yes. We accept custom orders based on customer drawings.
Q4: What is the lead time?
A: Standard lead time is 30–45 days.
Q5: How to maintain a ball mill girth gear?
A: Maintain proper lubrication, check tooth contact, monitor alignment, and inspect for vibration or noise.
Q6: Do you sell other ball mill spare parts?
A: Yes. Pinions, trunnions, liners, diaphragms, bearings, and complete mill systems.
Q7: What certifications does AGICO have?
A: ISO9001 certified with independent import/export rights. Products meet ASTM, DIN, BS, and ISO standards.
