Page 286 - Gear Technology Solutions

19.8 Manufacturing and Operation

Either straight bevel gears or spiral bevel gears are recommended as speed
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increasers. For straight bevel gears, the Coniflex Pro design software and the
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Coniflex cutting process provides the optimal geometry and optimization fea-
tures, like conjugate flanks with kinematic tip relief. For spiral bevel gears, the
Gleason face milling completing design offers kinematic flank optimizations
(UMC) for conjugate profiles and end relief.

It is recommended to case carburize pinion and gear and heat and quench the
pinions to a surface hardness of 62 HRC and the gears to 59 HRC. The differ-
ence in surface hardness reduces the metallurgic affinity of the contacting sur-
faces and therefore reduces the risk of scuffing.

After heat treatment, the speed increaser gears should be ground with a low
surface roughness, preferably below 0.5mm Ra. If a controlled break-in with
moderate loads and speeds which increase from low to high is not possible,
then a superfinishing or phosphate coating of the flank surfaces is recom-
mended.

Hypoid gears which are used as speed increasers should receive a small root
relief of 10 to 15 microns in the grinding process. This will prevent load con-
centration peaks, leading to scoring. After heat treatment a phosphate coating
of the flank surfaces will reduce or prevent flank surface damage.

All speed increasers should be lubricated with fully synthetic high-pressure oil,
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for example Castrol SAF-XO. A speed increasing bevel gear transmission
should be filled with 40% to 50% of its inside volume with oil. The fast-running
pinion has to be placed above the oil level, or just slightly dipping into the oil. If
the gearbox is used unidirectional, then an orientation like in Figure 3, with a
counterclockwise rotating gear will transport the oil from the sump directly to
the pinion teeth. The arrangement described will reduce oil churning. Exces-
sive oil churning reduces the cooling effect the oil should provide, and it reduc-
es the ability for a hydrodynamic oil film between the meshing flanks because
the churned oil foam delivers mostly air between the meshing flank surfaces.

If the described ideal condition for an oil sump is not given for a certain design,
then a piping system for forced lubrication which pumps low quantities of oil
into the meshing zone must be considered. The oil must be supplied before
the mesh which means, referring to Figure 3 (gear rotates counterclockwise),
the oil supply comes from below. In the case of a bidirectional speed increaser,
the oil supply must come from both directions into the meshing zone (above
and below in Figure 3).

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