Spur gear pair

A gear pair can be rated on its own, without shafts. This tutorial rebuilds the Spur gear pair example, then changes the load and the face width and reads how the safeties respond.

The numbers are those of this version of Axomek. To compare: open the Spur gear pair example. It starts a new project from the example in place of yours, so save yours first (the app asks) and come back to it with Switch project (Ctrl+P).

Step 1: add the pair

1. Start a Blank project. Open Gears in the navigation.
2. Choose Add a gear pair. Pair G1 appears.
3. Set Name to Input stage.
4. Under Load, set Face load factor KHβ to 1.2.

Leave the other inputs at their starting values:

Step 2: read the rating

The results column on the right shows the pair's Safety factors and its checks: All 4 checks pass.

Ft is 2·T/d1 = 2 × 150 000 N·mm / 60 mm = 5000 N, with the pinion's reference diameter d1 = z1·mn = 60 mm.

Pitting governs this pair: SH uses 73 % of its minimum of 1.0, SF only 33 % of its 1.4. That is typical for case-hardened gears with standard proportions. The root safeties are high because a module of 3 mm is generous for this torque.

Look at the views in the centre: Mesh draws the teeth in engagement, Tooth contact the loaded tooth contact (transmission error, mesh stiffness, line load across the face), Sliding and life the specific sliding and the safeties over life, and Root FE the tooth root stress by finite elements next to the rating's.

Step 3: load it harder

Set Pinion torque to 250 N·m.

The contact stress grows with the square root of the load: $1082\times \sqrt{250/150}\approx 1397\mathrm{MPa}$, close to the 1391 MPa the rating gives (some factors change with the load). The root stress grows in proportion to the load, so SF falls by about 250/150.

All checks still pass, but the pinion's pitting safety now uses 93 % of its minimum. Its row shows the warning mark.

Step 4: widen the face

Set Face width b to 45 mm.

A wider face spreads the load. It works as long as the face load stays even: on a real shaft a wide face is more sensitive to misalignment. Here KHβ is the fixed 1.2 you entered. To compute it from the pinion shaft instead, use Face load (method C) with the bearing span and the pinion's offset.

Step 5: check scuffing

Fast, heavily loaded gears can scuff: the oil film breaks down and the flanks weld locally.

1. Open Scuffing in the inspector and choose Check scuffing. It starts with an oil temperature of 70 °C and an oil that fails at FZG load stage 10.
2. Two checks join the list:

A Scuffing view now appears among the views, with the temperatures along the path of contact. Try FZG failure load stage 7 for a plain oil, or a higher Oil temperature, and watch the safeties fall.

The mesh loss at 250 N·m and 45 mm face width is 282.5 W of 39.27 kW: 99.28 % efficiency.

Step 6: export the gears

Open the command palette (Ctrl+K) and run Export the gear pair as STEP. Choose the pinion or the wheel and a Bore diameter (0 = solid). The gear is written as a STEP solid, its flanks and root fillets generated by the basic rack, for your CAD model.

What you learned

• Pitting usually governs case-hardened pairs; the root safety has margin.
• σH scales with the square root of the load, σF in proportion to it.
• Face width is the simplest lever for pitting, within the limits of the face load distribution.
• Scuffing is a separate check, switched on per pair.

Related

• Gear pairs
• Gear rating (ISO 6336)
• Gear scuffing
• Tutorial: single-stage gearbox
• Reading checks and safeties