Industrial seal self study guide - SKF.com

Seal Selection (cont.)
l
A
B
Seal Selection Criteria
Factors to consider when selecting a seal for a particular application
(fig. 5c) include:
H
F
A variety of factors determine
proper seal selection (fig. 5c).
E
G
D
C
• Basic seal function
• Shaft surface finish (A)
• Shaft speed and direction (G)
• Shaft and bore conditions (B)
• Shaft eccentricity (E)
• Seal material/lubricant compatibility
• Underlip temperature (F)
• Contaminants (abrasiveness) (C)
• Pressure (internal/external) (I)
PERCENT FAILURE
100
90
80
70
60
50
40
30
20
10
(fig. 5d)
DUAL LIP
SEAL
SINGLE LIP
SEAL
RELATIVE TIME TO FAILURE
In many applications, seal life can be extended simply by substituting
the same size seal (O.D. and I.D.), but of slightly different design or with
a different lip material. A narrower seal width can usually be used (see
following “Seal Width vs. Seal Performance” section). The seal selected
must be able to meet the application’s requirements for operating
temperature, pressure, and other factors listed above.
Single Lip vs. Double Lip Seals Test Results
In its development of new seal designs, SKF has conducted extensive
testing. One series of tests has compared single lip with double lip
seals (fig. 5d). Test objectives were to determine:
• Does the double lip seal’s secondary (dust) lip help or hinder
the primary lip?
• How does the double lip seal’s overall performance compare
with that of the single lip seal?
During testing, these measurements were taken:
Test results:
• Temperature vs. shaft speed.
• Dust ingestion vs. time.
• Peak performance vs. temperature rise.
• The double lip seal failed at 270 hours.
• The single lip seal, tested under identical conditions, was still
running at 1254 hours.
• The single lip seal was proven to run four times longer than
the double lip seal.
48
• The single lip seal runs cooler.