Industrial seal self study guide - SKF.com

Testing for the Presence of Machine Lead
Testing the shaft surface for machine lead can be done simply and with
a minimum of tools. The most effective method requires a 36 inch
(914.4mm) length of cotton quilting thread, a one ounce weight and
silicone oil.
Mount the shaft in a chuck so the shaft surface is level. Lightly coat the
shaft with oil. Suspend the weight on the thread as shown here.
Rotate the shaft at approximately 60 rpm. If the thread moves along
the shaft, machine lead is present (fig. 7g).
Bore Requirements
The lead corner, or entering edge, of the bore should be chamfered
with a 15/30 degree angle and free of burrs. The inside corner of the
bore should have a maximum radius of .031 (.79mm). This will help
prevent seal damage during installation. Chamfer length should be
.060” to .090” (1.50 to 2.29mm); see fig. 7h.
Bore Tolerance
Similar to shafts, the inch (RMA) system for seal bores also uses
a “floating” range based on the nominal diameter plus or minus
some value depending on the base size. With the metric (ISO)
standard however, the tolerances for bores (typically ISO H8) are
applied as a plus value/minus zero. Unlike shafts and seal lips, the
bore fit for seals can be significantly affected by the tolerance applied
to the hardware. For the best results, the correct bore diameter
for the tolerance system used should always be observed.
Refer to the SKF Handbook of Seals for tolerance data and further
information on housing bores.
Bore Hardness
No specific Rockwell hardness is recommended. Bore hardness need
only be high enough to maintain interference with the seal’s outside
diameter.
Bore Material
Ferrous and other commonly used metallic materials (like aluminum)
are acceptable for the bore. Bore material must be compatible with the
seal type used; if an aluminum bore is used, thermal expansion may
have to be considered.
Testing the shaft surface for machine
lead is a simple process requiring a
minimum of tools (fig. 7g).
(fig. 7h)
FINISH 100 microinch
OR LESS
Ra
(2.5 micrometer)
R .031
(0.79 mm)
.060 - .090
(1.52 - 2.229 mm)
15-30
7
63