Page 93 - Intro Predictive Maintenance

84 An Introduction to Predictive Maintenance

Table 5–1 Belt-Drive Failure: Symptoms, Causes, and Corrective Actions

Symptom Cause Corrective Action
High 1X rotational frequency in Unbalanced or eccentric Balance or replace sheave.
radial direction. sheave.
High 1X belt frequency with Defects in belt. Replace belt.
harmonics. Impacting at belt
frequency in waveform.
High 1X belt frequency. Unbalanced belt. Replace belt.
Sinusoidal waveform with period
of belt frequency.
High 1X rotational frequency in Loose, misaligned, or Align sheaves, retension or
axial plane. 1X and possibly 2X mismatched belts. replace belts as needed.
radial.
Source: Integrated Systems, Inc.

belt elasticity tends to accelerate wear and the failure rate of both the driver and
driven unit.

Fault Frequencies

Belt-drive fault frequencies are the frequencies of the driver, the driven unit, and the
belt. In particular, frequencies at one times the respective shaft speeds indicate faults
with the balance, concentricity, and alignment of the sheaves. The belt frequency and
its harmonics indicate problems with the belt. Table 5–1 summarizes the symptoms
and causes of belt-drive failures, as well as corrective actions.

Running Speeds

Belt-drive ratios may be calculated if the pitch diameters (see Figure 5–5) of the
sheaves are known. This coefficient, which is used to determine the driven speed given
the drive speed, is obtained by dividing the pitch diameter of the drive sheave by the
pitch diameter of the driven sheave. These relationships are expressed by the follow-
ing equations:

Drive Sheave Diameter
Drive Reduction =
Driven Sheave Diameter

Ê Driven Sheave Diameter ˆ
Drive Speed, rpm = Driven Speed, rpm ¥
Ë Drive Sheave Diameter ¯
Using these relationships, the sheave rotational speeds can be determined; however,
obtaining the other component speeds requires a bit more effort. The rotational speed
of the belt cannot directly be determined using the information presented so far. To