NORD Drivesystems B1000 - Manual (Page 66)

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INTRODUCTION
G1000 – Subject to Change Without Notice
Engineering
AGMA
Service Classes
AGMA Selection Method
Gearmotors
Before a gearmotor is selected, an application class
number must be determined. Since application clas-
sifi cation represents the normal relationship between
gear design power rating and the maximum potential
transmitted power, it is suggested that the applica-
tion class number be applied to the nameplate rating
of the electric motor. The application class numbers
are l, ll, and lll.
Their relationship to service factor is:
Class Numbers f
B
I 1.0 - 1.39
II 1.4 - 1.99
III ≥ 2.0
Application class numbers may be selected from the
table. Some operational characteristics that affect an
application’s classifi cation are:
• Starting conditions: Starting conditions where peak
loads exceed 200 percent of rated load, applications
with frequent starts and stops and reversing applica-
tions require special analysis. Rated load is defi ned as
the unit rating with an application class number of I
(1.0 - 1.39 service factor).
• Overloads: Loads in excess of the rated load are
con-sidered overloads. Overload can be of momen-
tary duration, periodic, quasi-steady state, or
vibratory in nature. The magnitude and the
number of stress cycles require special analysis to
prevent low cycle fatigue or yield stress failure.
Applications with high torque motors, motors for
intermittent operation and applications where
extreme repetitive shock occurs or where high-
energy loads must be absorbed as when stalling
require special consideration.
• Brake equipped applications: When a gear drive is
equipped with a brake that is used to decelerate
the motion of the system, select the drive based on
the brake rating or the equivalent power, which
ever is greater. If the brake is located on the output
shaft of the gear drive, special analysis is required.
• Reliability and life requirement: Applications
requiring a high degree of reliability or unusually
long life should be given careful consideration by
the user and NORD GEAR before assigning an
application class number. High reliability and life
should be addressed by using an increased safety
factor agreed to between NORD and the purchaser.
Synchronous motors, certain types of high torque
induction motors and generator drives require spe-
cial analysis. Synchronous motors have high transient
torque during starting and restarting after they trip
out momentarily.
Induction motors of special high slip design can pro-
duce extremely high starting torque. High torque
loads are produced when the motor trips out for a
very short time and then the trip re-closes.
Generators have extremely high loads when they are
out of phase with the main system and when there
are across the line short circuits.
Adjustments to the gear drive selection may be
necessary when one or more of the following
conditions exist:
• Ambient conditions. Extremes of temperature and
environment.
• Lubrication. Any lubricant not in accordance with
NORD’s
recommendations.
• Misalignment and distortions due to inadequate
foundations.
• Reversing applications.
• High-risk applications involving human safety.
The purpose of this table is to provide a guide in the
selection and application of gear drives designed and
rated in accordance with AGMA Standard 6009.
The service factor table has been developed from the
experience of manufacturers and users of gear drives
for use in common applications and has been found
to be generally satisfactory for the listed industries
when gears are applied using AGMA standards. It is
recommended that the user and NORD Gear agree
upon class numbers for special applications when
variations of the table may be required.