Bearing Design Guide: Chapters Eight through Eleven: REVISITED
Graphite Plugged & Grooved Bearings
Bearing Design Guide: Chapter Eight: Grooves for Grease and Graphite Filled Bearings
The groove width (W) for grease lubricated bearings should be increased
by 1/32" of that of oil grooves with depth (D) remaining the same or
slightly deeper by 1/64".
The wider grooves permit the
shaft a longer contact period with the less mobile grease supply and
permit a greater surface coverage of graphite filled grooves.
The suggested groove width (W) and depth (D) as shown below:
Bearing ID Groove Width (W) Groove Depth (D)
0.5 3/32 0.094 3/64 0.046
1 5/32 0.156 5/64 0.078
2 3/16 0.188 3/32 0.094
3 1/4 0.25 1/8 0.125
4 9/32 0.281 9/64 0.14
5 5/16 0.312 5/32 0.156
6 13/32 0.406 13/64 0.205
7 15/32 0.469 15/64 0.234
8 17/32 0.531 17/64 0.265
9 19/32 0.593 19/64 0.296
10 21/32 0.656 21/64 0.328
11 23/32 0.719 23/64 0.36
12-20 25/32 0.781 25/64 0.39
Since these grooves are not as critical as oil grooves, they can be
toleranced looser to plus-or-minus 1/64 to plus-or-minus 1/32.
In grease lubricated bearings where exposed to contaminants such as
dirt, ash or other debris, it is advisable to provide an annular or
circular groove near the end of the bearing within 1/8" to 1/411 to
create a dam effect. Such an effect will act as a reasonable seal,
preventing contaminants from entering the bearing surface.
Bearing Design Guide: Chapter Nine: Graphited and Solid Lubricated Bearings
Solid lubricated bearings such as graphite or molybdenum disulfides are
used in severe environmental situations where normal fluid or grease
lubricants cannot be used because of abnormal temperatures which would
tend to carbonize or freeze the lubricant to brittle solids.
They find usage constantly in chemically-reactive environments, in
nuclear radiation and vacuum environments and where normal lubricants
cannot be tolerated. They also are used where there is limited access to
resupplying the lubricant or where it can be neglected.
These solid lubricants can be used in form of colloidal powders in
suspension of a grease carrier or held and bonded by various binders.
Graphite itself, although one of the most popular solid lubricants,
requires some absorbable gases, moisture or hydrocarbon vapors to
develop low-shear strength.
The gases and water vapor in the normal atmosphere are usually
sufficient to ensure an adequate supply of absorbable medium but a brief
immersion in a heated oil eliminates chance.
Graphite in excellent through temperatures ranges through 1000 degrees F but are generally not
satisfactory in high altitudes nor in a vacuum conditions since desorption occurs.
Molybdenum disulfide is an excellent solid lubricant below 750 degrees
For in a vacuum since it does not require presence of adsorbable vapors.
However, above 750 degrees Fin the presence of air or oxygen, it
deteriorates and becomes an abrasive. It is also more expensive than
graphite so it has limited usage.
As with graphite, molybdenum disulfide and the other solid lubricants
require a binder to make it adhere to the bearing surface. There are
various binders available that can be formulated.
The thermoplastic resins such as cellulesic or acrylic resins are
easily sprayed, fast drying, requiring no baking but are limited to 150
degrees F.
The thermosetting phenolics have a service temperature of 400 degrees F with good adherence.
The epoxy resins adhere well and are safer than phenolics being stable through 600 degrees F but requiring heat-curing.
Some inorganic binders such as sodium silicate would exceed the 750
degrees F and would be suitable for graphite but limited to a lower
temperature for molybdenum disulfide.
For an economical solid lubricant containing bearings, the standard
available sintered powdered metal bearing with 18% porosity offers an
excellent surface for retaining graphite or molybdenum disulfide
formulation that would require a burnish operation of the lubricant into
the surface.
 |
| Molybdenum Disulfide-Natural State |
 |
| Molybdenum Disulfide Powder |
 |
| Molybdenum Disulfide Grease |
Bearing Design Guide: Chapter Ten: Graphited Wall Thickness Calculation
 |
| Graphite Plugged Bearing |
Since
the solid lubricant must be held in form of grooved configurations,
plugs or sticks in a series of drilled holes, they require a substantial
depth to be retained properly.
The minimum wall thickness of groove-filled solid lubricated bearings
can follow the width (Y'/) and depth (D) described in Chapter VIII. Plug
lubricated bearings with a .5 diameter should be held to 3/16" minimum
wall thickness and then increased 1/32" for each nominal half-size
above. That is, for a 1" ID bearing, a wall thickness of 7/32" should be
considered for plug graphited bearings.
 |
| Graphite Plugs |
A general rule of thumb: wall thickness= .08D + 1/8'' (where Dis the bearing ID.)
The overall length on solid lubricated sleeve bearings can range in
various lengths depending on the load, speed, and type of the
application. The normal recommended LID ratio is 1. 5. This is to
minimize possible shaft deflection and to offer greater stability and
surface area. The maximum LID ratio recommended should rarely exceed a
ratio of 3 since misalignment edge-loading and frictional heat can be
appreciably increased.
The
accepted standard solid lubricant coverage should average 30 to 3 5% of
the surface area. However, the calculation of plug size and lubricant
coverage is shown below. The plug diameter and drill size should be no
larger than the wall thickness but no less than half.
 |
| Graphite Sticks |
CALCULATION OE LUBRICANT COVERAGE AND PLUG SIZE:
Percentage of Graphite or Solid Lube Coverage
Drill Size 10% 15% 20% 25% 30% 35% 40% 45% 50%
3/16 8.95 13.43 17.9 22.38
26.85 31.33 36.81 40.28 44.5
1/4 5.03 7.54 10.05 12.57 15.08 17.6 20.11 22.62 25
5/16 3.22 4.83 6.44 8.05 9.66 11.27 12.88 14.49 16.1
3/8 2.23 3.35 4.47 5.59
6.7 7.82 8.94 10.06 11.1
7/16 1.64 2.46 3.28 4.1 4.92 5.75 6.57 7.39 8.2
1/2 1.26 1.89 2.51 3.14
3.77 4.4 5.03 5.66 6.28
1. Choose the appropriate drill or plug size.
2. Locate the desired solid lubricant coverage
Use factor number opposite drill or plug size
3. Multiply bushing ID x bushing length.
Multiply factor number to obtain the number of holes or plugs.
Example: 2" ID x 2 112 OD x 2" length
1. 1/4 plug diameter
2. 35% coverage from chart 17.6
3. 2 x 2" length x 17.6 = 70 drilled holes or plugs.
Bearing Design Guide: Chapter Ten: Graphited Wall Thickness Calculation
The
running clearances for solid lubricated bearings must be substantially
greater than in oil and grease lubricated bearings because the
frictional heat generated is not dissipated.
An allowance of .002 minimum per inch of diameter should be considered.
Further, since solid lubricated bearings are not generally machined or
bored after assembly 11close in11 of the ID must be allowed for. This
allowance must be increased further if the bearing is to be used in
abnormal temperature service to allow for expansion or contraction of
the shaft.
For more specific clearance allowances, use the attached calculation
sheet either for normal temperatures or for abnormal temperature
service. (Reference Chapter 6.)
Surfaces Finishes:
Solid lubricated sleeve bearings do not require the high degree of
surface finishes of oil lubricated bearings. The slightly rougher
bearing ID finish is desirable to permit the solid lubricant to coat its
surface. Therefore, a bearing surface ID finish of 63 RMS to 125 RMS
should be satisfactory. The shaft finish, however, should be ground or
polished smooth to approximately 32 RMS.
Upon installation of the solid lubricated bearing, there will be
instant wear until the shaft and bearing become coated with the solid
lubricant. It would be advisable to submerge the graphited bearing in an
oil bath of slightly heated oil to penetrate the plugs or filled
graphite grooves to enhance its initial "running in" or "bedding in" to
reduce this initial wear to an acceptable minimum.
Note that the drilled and plugged holes do reduce the strength and structure of the bearing while adding to the cost.
Many times it would be more economical to utilize filled groove
configurations since they do not weaken the bearing to any noticeable
degree.
Although a solid lubricant can be retained in a serrated ID which can
be broached for economy, tests have shown that such a structure weakens
the lands in the bearing ID and limits the load and speed capabilities
to less than 50 PSI and 30 fms.
General Information:
Some commercially available solid lubricants containing compounds of
graphite and molybdenum disulphide are sold by Lubriplate and Emhart
Companies as Never-Seize and Dri-Slide.
The coefficient of friction for solid lubricated bearings are
appreciably higher than those for oil and grease ranging from .15 to .35
initially then reduced to a lower acceptable level.
Ok...I'm
done. I know that was a lot of information all at once, but I thought
they should go together. I have watched the plugging process a few
times here in our warehouse and I gotta say it was pretty cool. From
sticking them in, to watching them get ground down to become one with
the bearing or wear plate is a neat thing to watch.
I hope you find this as interesting as I do, that's it for now. Until next time my metal loving friends...
Sand
casting is probably the oldest method in practice. In this process the
mold is prepared using sand or silica and the molten liquid metal is
poured into it. The mold is made of two parts, the cope and the drag. A
wooden pattern is placed between these two parts, called the mold
cavity. The liquid metal enters here and casts itself. The shape of the
mold cavity is similar to the final object after the refining 
The
Centrifugal casting process uses a mold which is fixed to a motor on an
axis to rotate it at high speeds. The speed of rotation depends on the
metal to be cast and the shape required. This method is mainly used for
the production of cylindrical components like pipes. As the motor
rotates, the metal gets pushed towards the outer walls of the cast and
solidifies. The centrifugal process is unsuitable for making
linear-shaped and dense 
Continuous
casting, as the name implies, converts molten metal into a continuous
moving ingot shape with a rectangular or round cross section. Time,
energy, and labor are saved. Generally, a water-cooled mold is employed,
receiving molten metal in one end and delivering a continuous
solidified product out the other. The molds can be vibrating or moving,
slow or fast.
Drawing is the pulling of a metal piece through a die by means of a
tensile force applied to the exit side. A reduction in cross-sectional
area results, with a corresponding increase in length. A complete
drawing apparatus may include up to twelve dies in a series sequence,
each with a hole a little smaller than the preceding one. 
Rolling is the most widely used deformation process. It consists of
passing metal between two rollers, which exert compressive stresses,
reducing the metal thickness. Where simple shapes are to be made in
large quantity, rolling is the most economical process. Rolled products
include sheets, structural shapes and rails as well as intermediate
shapes for wire drawing or forging. Circular shapes, ‘I’ beams and
railway tracks are manufactured using grooved rolls.
