Focusing on the design, manufacturing processes, heat treatment techniques, and key quality control points for all types of standard and non-standard gears.
| Parameter | Full Available Range |
| Module / DP Range | M1 ~ M25 / DP 1 ~ DP 25 |
| Number of Teeth (Z) Range | Z18 ~ Z250 |
| Max. Outer Diameter | ≤ 1000mm |
| Accuracy Grade | GB/T 10095 Grade 4~8, equivalent to AGMA Grade 10~14 / ISO Grade 4~8 |
| Tooth Surface Roughness | Ra 0.8 ~ 6.3μm |
The full name of spur internal gear is spur internal-mesh cylindrical gear. It is a core category of spur cylindrical gears adapted to compact transmission and heavy-duty reduction scenarios. Its gear teeth are evenly distributed on the inner circumferential surface of the hollow circular ring, and the tooth trace direction is completely parallel to the gear axis. When used in pairs, it meshes internally with an external pinion to realize power and motion transmission between two parallel shafts, and the two shafts rotate in the same direction after meshing.
In daily industry contexts, the term “internal gear ring” mostly refers to spur internal gears by default. It is a basic transmission component featuring high structural compactness, strong load-bearing capacity and high contact ratio, widely used in planetary reduction mechanisms and slewing drive systems.
It adopts a concave involute tooth profile, which mates with the convex tooth profile of the external gear, delivering a constant transmission ratio and good tolerance for center distance deviation. The tooth trace is parallel to the gear axis, and no axial thrust is generated throughout the meshing process, which simplifies the design of bearings and housing structures. Limited by the internal annular structure, the conventional hobbing process cannot be applied; the gear is formed by gear shaping and gear skiving, and high-precision products require a matching internal gear grinding operation. The supporting cutting tools feature high standardization, ensuring strong interchangeability of finished products. The standard specification for pressure angle is 20°, while many imported older pieces of equipment adopt the non-standard specification of 14.5°.
It adopts an internal mesh transmission configuration, where the external pinion is nested inside and meshes tangentially. The transmission center distance equals the difference between the pitch circle radii of the two gears, and the two shafts rotate in the same direction — this is the core difference from external mesh transmission. In internal mesh, more teeth engage simultaneously with a higher contact ratio, resulting in lower tooth surface contact stress and stronger load-bearing capacity. The nested layout greatly reduces the transmission volume, but its internal heat dissipation performance is inferior to that of external mesh, making it more suitable for gearbox applications with closed oil bath lubrication.
The transmission efficiency of a precision-grade spur internal mesh system can reach 98%–99%, ranking among the top tier of gear transmissions. The relative sliding speed between the concave and convex tooth surfaces is low, so the friction loss is lower than that of external mesh pairs of the same specification. Combined with the characteristic that spur gears generate no additional axial friction, its overall torque transmission capacity per unit volume significantly outperforms external spur gear solutions.
The spur gear structure retains the feature of full-face-width simultaneous meshing. During high-speed operation, it is prone to shock, vibration and noise, and long-term high-frequency impact will aggravate tooth root fatigue. Meanwhile, the machining difficulty and cost of internal gears are higher than those of external gears of the same precision; large-size thin-walled parts are prone to deformation, and improper design is likely to cause tooth profile interference. It is more suitable for heavy-duty reduction scenarios in compact spaces with medium and low speeds and steady loads. For high-speed heavy-duty scenarios with low-noise requirements, helical internal gear solutions are preferred.
| Parameter | Standard Mass Production (General Service) | High Precision Custom (Precision Transmission) |
| Core Dimensional Specifications | ||
| Module / DP Range | M1 ~ M25 / DP 1 ~ DP 25 | M1.5 ~ M12 / DP 2 ~ DP 16 |
| Number of Teeth (Z) Range | Z18 ~ Z250 | Z20 ~ Z150 |
| Max. Outer Diameter | ≤ 1000mm | ≤ 800mm |
| Face Width Range | ≤ 300mm | ≤ 250mm |
| Internal Tip Diameter Range | φ20mm ~ φ900mm | φ30mm ~ φ700mm |
| Secondary Machining Options | Outer diameter locating spigots, mounting flanges, end-face threaded holes and outer diameter keyways available in production | Full-process single-setup machining, strictly ensuring inner-outer concentricity and gear ring runout accuracy |
| Tooth Profile & Accuracy Specifications | ||
| Tooth Profile Standard | Involute profile, available in both metric and inch standards | Involute profile, custom non-standard profiles and profile shift coefficients available |
| Standard Pressure Angle | 20° (default), 14.5°/15° customizable | 20°, 14.5°/15°/22.5° and other non-standard angles customizable |
| Accuracy Grade | GB/T 10095 Grade 7~8 Equivalent to AGMA Grade 10~11 / ISO Grade 7~8 |
GB/T 10095 Grade 4~6 Equivalent to AGMA Grade 12~14 / ISO Grade 4~6 |
| Profile Modification | Standard profile | Tip relief and lead crowning available |
| Tooth Surface Roughness | Ra 3.2 ~ 6.3μm | Ra 0.8 ~ 1.6μm |
| Remarks | The above are the standard machining parameter ranges of our spur internal gears (internal gear rings). Special specifications, non-standard structures and custom profile shift designs can be manufactured based on your drawings. | |
High-quality blanks are forged and normalized to eliminate internal stress and stabilize material structure.
Turning, milling and hobbing/shaping are applied to form the target tooth profile with strict accuracy control.
Carburizing quenching or tempering processes to improve tooth surface hardness and core toughness.
Grinding of tooth flanks, bores and datum faces to correct deformation and enhance meshing precision.
Full-dimensional verification by gear measuring center and CMM to qualify products before release.
Professional anti-rust and protective packaging to keep products intact during storage and transit.
High-precision gear grinding delivers tooth surface roughness as low as Ra 0.4, with tight meshing, low vibration and noise for smoother equipment operation.
Premium materials matched with precise heat treatment ensure wear-resistant tooth surfaces and impact-resistant core, cutting maintenance and replacement costs.
Custom solutions for high-speed heavy load, corrosion resistance and food-grade scenarios, eliminating trial-and-error costs in product selection.
Scaled production supports tiered pricing for bulk orders with consistent quality; full-process control guarantees stable lead time and complete after-sales support.
Representative: Grade 45 Steel
Represented by Grade 45 steel, high-quality carbon structural steel features balanced comprehensive mechanical properties, moderate strength and toughness after quenching and tempering, excellent machinability and high cost-effectiveness. Its tooth surface hardness can be improved via high-frequency quenching, but the internal tooth surface is prone to deformation during quenching. It is suitable for conventional light-to-medium load internal gear rings, with poor hardenability, low resistance to heavy load impact and no rust resistance.
Representatives: 42CrMo, 20CrMnTi, 20CrMnMo
Alloy structural steel has far better hardenability than carbon steel. Through heat treatment, it can achieve both wear resistance on the tooth surface and impact resistance at the core, with controllable deformation, making it the dominant material for internal gear rings. It is applicable to high-precision transmission scenarios with medium-heavy to heavy impact loads, and has relatively higher material cost and longer production cycle.
Representatives: 304 & 316 Stainless Steel
Stainless steel boasts excellent corrosion and rust resistance, which can meet the requirements of clean production, and is suitable for humid and highly corrosive acid-alkali working conditions. However, its mechanical strength and wear resistance are inferior to those of alloy structural steel, the machining of internal teeth is significantly more difficult, and its load-bearing capacity is limited. It is only applicable to light-load and low-speed transmission scenarios, with relatively high cost.
Representative: Tin Bronze
Copper alloy has excellent antifriction and wear resistance, low transmission noise, as well as corrosion resistance and non-magnetic properties. The machining accuracy of small-size internal teeth is easy to guarantee. However, its overall strength is much lower than that of steel, so it is only suitable for precision transmission scenarios with extremely small modules, light loads and low speeds, and fits working conditions requiring quiet operation, magnetic shielding and high-frequency small loads.
Representatives: QT450, QT600
Ductile iron has good castability and low cost, with better vibration and noise reduction performance than steel. Its strength and toughness are superior to gray cast iron but inferior to alloy structural steel. It is mostly used for large-diameter, low-speed internal gear rings with stable loads, has relatively weak impact resistance, and is not suitable for high-speed and heavy-load working conditions.
Representatives: POM, PA66, PEEK
Engineering plastics can be molded into complete internal gear rings in one injection molding process, featuring high mass production efficiency and remarkable cost advantages. They are inherently self-lubricating, quiet, vibration-damping, lightweight and corrosion-resistant. POM, with balanced rigidity and wear resistance, is the first choice for general applications; PA66 has better toughness; high-end PEEK is suitable for high-temperature and highly corrosive working conditions. They are fit for light-load and low-speed scenarios, with obvious performance degradation under heavy loads and high temperatures.
In this most core application scenario, the spur internal gear ring is one of the three core components of a planetary reduction mechanism. It mostly serves as a fixed ring gear nested inside the reducer housing, and works with the sun gear and planet gears to achieve transmission with a large reduction ratio. The transmission generates no axial force, the housing features a compact structure, and its torque output capacity per unit volume far exceeds that of parallel-axis external-mesh reducers. It is widely used for low-speed stage reduction in industrial gear motors and heavy-duty gearboxes.
It is a standard component in electric drive reducers, automatic transmissions and differentials of new energy vehicles. The nested layout can greatly reduce the volume of the powertrain and adapt to the limited installation space in vehicles. Large-module spur internal gear rings are also widely adopted in the slewing mechanisms and hoist transmissions of equipment such as excavators and rotary drilling rigs. With multi-tooth meshing, they deliver strong load-bearing capacity and adapt to heavy-load and impact operating conditions.
The core internal gear rings in servo planetary reducers and RV reducers mostly use high-precision spur internal gears. Featuring compact size and high transmission accuracy, they can achieve high-torque reduction in narrow spaces, and are widely applied in scenarios with dual requirements for precision and space, such as industrial robot joints, rotary worktables and automatic indexing mechanisms.
In wind turbine speed-increasing gearboxes, slewing drives for photovoltaic tracking brackets and solar tracking systems, large-diameter spur internal gear rings are core transmission components. They operate stably under low-speed and heavy-load conditions. Their annular structure can be integrally integrated with support bearings, greatly simplifying the overall structure of the slewing system and reducing equipment weight and installation cost.
Large-module alloy steel spur internal gear rings are widely used in the planetary reduction mechanisms of heavy machine tool spindles, main transmission gearboxes of rolling mills, and lifting mechanisms of metallurgical equipment. Internal mesh transmission boasts a high contact ratio and low tooth surface contact stress, can withstand low-speed and high-torque loads, and meets the demand for heavy-load continuous operation in metallurgy and heavy processing industries.
High-strength carburized and quenched spur internal gear rings are commonly used in the closed reduction systems of roadheader traveling mechanisms, mine hoists and heavy hoisting equipment. Compared with external mesh transmission, the internal mesh structure has stronger impact resistance and overload resistance. The fully enclosed layout isolates dust and oil contamination, adapting to the harsh operating environment in mines.
Inner VCI vacuum anti-rust process fully seals tooth flanks and critical machined surfaces, effectively resisting salt spray and moisture during ocean and air freight to keep precision gears corrosion-free throughout long-distance transit.
We select cost-effective logistics channels with stable transit time and controlled costs. Full logistics tracking is available with real-time status updates to ensure reliable and punctual delivery.
All products are covered by a 1-year warranty. Quality defects caused by non-human factors are fully guaranteed, removing your procurement concerns.
Our professional technical and after-sales team is always available to respond quickly to inquiries and after-sales needs, and efficiently resolve issues during installation and operation.
We support full-parameter OEM/ODM customization based on 2D/3D drawings or physical samples, including module, tooth profile, material and heat treatment specifications. You only need to provide core gear parameters, detailed drawings or physical samples to start the customization process.
You can send physical samples to us via international courier. Upon receipt, we will complete full-dimensional measurement and parameter verification, then arrange sample production after confirming the solution, ensuring the finished product fully matches the original in installation dimensions and transmission performance.
Prototype orders usually ship within 15–25 days, subject to heat treatment and grinding scheduling. Lead time for bulk orders will be confirmed after process finalization, with stable and well-managed production schedules.
We adopt a tiered pricing policy — the larger the order quantity, the more favorable the unit price. All orders follow the same production and quality inspection standards with strict accuracy control. Quality will never be compromised for larger order volumes.
We can include dimensional inspection reports, hardness test records and material certificates with each shipment. For high-precision key projects, professional inspection data from CMM and gear measuring centers is also available.
All products come with a 1-year warranty covering material defects and manufacturing quality issues under normal use. We also have a professional technical team to provide full-process consultation and selection support.
Spur gears feature a simple structure and no axial load, ideal for medium-low speed general transmission with higher cost-effectiveness. Helical gears run smoother with lower noise and higher load capacity, suitable for high-speed heavy-duty applications. We can recommend the optimal solution based on your actual requirements.
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info@destinytrans.com 
