| TYPE l | MANUAL LUBRICATION. Oil applied periodically with brush or spout can. | The limiting RPM for each lubrication |
| TYPE ll | DRIP LUBRICATION. Oil applied between link plate edges from a drip lubricator. | type is read from the column to the |
| TYPE lll | OIL BATH or OIL SLINGER. Oil level maintained in casing at predetermined height. | right of the boundary lines shown. |
| TYPE lV | OIL STREAM. Oil supplied by circulating pump inside chain | loop on lower span. |
3.3 Sprocket Selection
Recommendations
Where smooth performance and
long service life are desired, sprockets with 17 or more teeth, but less than
67, should be used.
On slow speed and special
purpose installations or where space limitations are a factor, sprockets with
less than 17 teeth can be used.
Use of sprockets with more than
67 teeth tends to reduce the normal service-life of the chain.
Hardening the smaller sprocket
teeth tends to equalize the rate of wear with the large sprocket in the drive.
Sprockets should have hardened teeth when any of the following conditions
prevail.
| 1. | Sprocket has less than 24 teeth and the rotative speed exceeds 600 R.P.M., or 1/8 of the maximum speed recommended for sprockets with that number of teeth, whichever is smaller. (See horsepower rating, Table 15). | |
| 2. |
The chain speed is approximately 100 feet per minute or less and the chain loading is about 1/7 of the average tensile strength or greater. |
3.4 Selection of Center
Distances
Quite often the center distance
for a roller chain drive is determined within limitations by other machine
components or considerations. Although it is not essential that the smaller
sprocket have 1200 chain wrap for satisfactory operation and performance, it is
recommended as good practice when conditions permit.
Chain wrap on the smaller
sprocket of a two-sprocket drive with ratio 3.5 to 1 or less, will always be
1200 or more. Chain wrap increases as center distance is increased.
For an average application, a
center distance of 30 to 50 pitches of chain represents good practice. For
pulsating loads, shaft centers as short as 20 pitches of chain may be preferable
when sprocket sizes permit. Close attention should be given to proper center
distance for the chain length (preferably an "even" number of
pitches).
3.5 Chain Drive Selections for
Very Slow Speeds
Where the linear speed of the
chain is to be under 100 feet per minute and the installed chain length exceeds
about 50 pitches, roller chains may be selected on the basis of their
"endurance limit" and without regard for the customary horsepower
ratings. Roller chains selected on this basis are considered primarily as
"tension members."
The "endurance limit"
of a chain is the tensile load which it can accept for an infinite number of
cycles without introduction of metal fatigue (failure). Although it is not
directly related to the tensile strength, a reasonable approximation of
linkplate "endurance limit" (allowable working load is 1/7 of the
chain's average tensile strength.) The recommended "endurance limit"
of chains with offset links and/or connecting links with slip-fit coverplates is
1/2 of the chain's average tensile strength. Because of their lower capacity,
offset links and slip-fit coverplates should be avoided in high load
applications, and connecting links with press-fit coverplates should be used.
The tensile strength for the chains is given in the product pages as:
#25 Hardened Steel--925
lbs
#25 Hardened Steel--700 lbs
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