Break-Away Force For LM76 Self Lubricating Linear Bearing Slides:
get a system in motion you must overcome the static weight
of the system as it sits. It is important to
know this value when you are
designing a drive system. Design for the breakaway force not the dynamic force. Many of our competitors fudge the numbers by using the Dynamic Value in their
For a Self Lubricating Linear Bearing Slide,
we calculate the
a linear slide employing 2 rails and 4 Self Lubricating PTFE pillow block bearing
assemblies and supporting
horizontal, centered load of 250lbs.
Static Self Lubricating Linear Bearings 30% of System Load to get the system
250lbs Load x .30 = 75 Lbs.
Dynamic Self-Lubricating Linear Bearings ( In Motion ) 10% of system load
250lbs Load x .10 = 25 lbs.
Breakaway Force Requirements - Static
Self Lube PTFE
30% of Load - Static
10% of Load - Static
Pressure Velocity )
PV is determined by 2 factors:
Pressure ( PSI )
and Velocity (SFM)
W=Static Load on a single bearing
d= Bearing Inside Diameter
b= Bearing Length
225 pound load applied to a 1" inside diameter bearing that is 2.25" long
Note: Determining PSI: ID x Length
P=225/(1" x 2.25" ) or P = 100 PSI Velocity = 50 Feet per
PV=100 (PSI) x 50 FPM
LOAD CAPACITY EXAMPLES
Example 2 LOAD: LM76
Self Lube Bearing vs. Linear ball
bearing. How does a 1" ID ( inside diameter ) LM76 Minuteman ( L1625-18SL )
against a comparable 1" ID Ball Bushing?
1" linear ball bearing is rated @ 1050 pounds
A direct drop-in replacement MINUTEMAN bearing is rated at:
1" ID x
2.25" ( length ) = 2.25 x *5000 PSI = 11,250 pounds
Example 3 LOAD: FDA/USDA
Compliant Self Lube Bearing vs. Ball Bearing
Once again, we will use a standard 1" Ball Bearing with a Published Load Capacity
of 1050 pounds:
ID Ball Bearing = 1050 Pounds
A direct drop-in replacement 1" ID LM76 FDA/USDA Bearing
with our white
FDA compliant PTFE liner = 2250
1" ID x 2.25" ( length ) = 2.25 x 1000 PSI = 2250 pounds static load
EDGE LOADING: Sleeve-type linear
motion bearings, more so than ball bearings ( rolling element ),
parallel shafting to be aligned as closely as possible to avoid edge loading.
Edge loading can cause higher-than-acceptable friction, binding and subsequent wear.
One answer for
situations where shaft alignment is not true, is LM76's self aligning
bearings have a slight radius on the OD
( outside diameter ) which allows the bearing
to rock in the housing and allows
for .009 per linear linear inch misalignment. Another
option is a "full float"
bearing which is suspended in the housing bore with o-rings.
Note: this remedy
does change the shaft-to-bore alignment.
When you have a cantilevered load:
MUST OBSERVE THE 2:1 RATIO RULE!Because moment loading can
result in edge loading of sleeve-type linear bearings, correct spacing between
bearings on a single shaft ( vertical or Z axes):
and spacing between shafting
on horizontal applications ( X,Y axes ):
must meet the 2:1 ratio rule.
If this rule is violated, friction will increase, the system will
the bearings will fail.
OPEN BEARING LOAD CAPACITY
hanging upside down ) open style sleeve bearings is not an optimal
design configuration. System load is forced into the bearing slot - the weakest
part of the bearing. Depending on load and possible moments, point loading on
of the slot can result in hot spots, liner cold flow and excessive wear.
LM76 if you are employing this configuration in your design.
Coefficient of Friction Graph
The graph illustrates the
coefficient of friction values for:
Ceramic Coated ( lubricated )
Self Lubricating Linear Motion Bearings
Note 1: That the LM76 Ceramic
Coated bearing offers a very low coefficient of friction as opposed to
the Self Lube Bearings. If you can
lubricate, the LM76 Ceramic Coated bearing will ensure
low friction, long life,
low cost and unlimited velocity.
Note 2: all LM76 self lubricating linear bearings cannot exceed 400SFM.