Doosan D50S-5 Operation & Maintenance Manual page 135

tip. tip.
Bent or Twisted Forks Bent or Twisted Forks
Forks can be bent out of shape by extreme Forks can be bent out of shape by extreme
overloading, glancing blows against walls or other overloading, glancing blows against walls or other
solid objects or using the fork tip as a pry solid objects or using the fork tip as a pry bar.
Bent or twisted forks are much more likely to break Bent or twisted forks are much more likely to break
and cause damage or injury. They should be and cause damage or injury. They should be
removed from service immediately. removed from service immediately.
Fatigue Fatigue
Parts which are subjected to repeated or fluctuating Parts which are subjected to repeated or fluctuating
loads can fail after a large number of loading cycles loads can fail after a large number of loading cycles
even though the maximum stress was below the even though the maximum stress was below the
static strength of the part. static strength of the part.
The first sign of a fatigue failure is usually a crack The first sign of a fatigue failure is usually a crack
which starts in an area of high stress concentration which starts in an area of high stress concentration
This is usually in the heel section or on the fork This is usually in the heel section or on the fork
mounting. mounting.
As the crack progresses under repetitive load As the crack progresses under repetitive load
cycling, the load bearing cross section of the cycling, the load bearing cross section of the
remaining metal is decreased in size until it remaining metal is decreased in size until it
becomes insufficient to support the load and becomes insufficient to support the load and
complete failure occurs. complete failure occurs.
Fatigue failure is the most common mode of fork Fatigue failure is the most common mode of fork
failure. It is also one which can be anticipated and failure. It is also one which can be anticipated and
prevented by recognizing the conditions which lead prevented by recognizing the conditions which lead
up to the failure and by removing the fork service up to the failure and by removing the fork service
prior to failing. prior to failing.
Repetitive Overloading Repetitive Overloading
 
Repetitive cycling of loads which exceeds the Repetitive cycling of loads which exceeds the
fatigue strength of the material can lead to fatigue strength of the material can lead to
fatigue failure. The overload could be caused by fatigue failure. The overload could be caused by
loads in excess of the rated fork capacity and loads in excess of the rated fork capacity and
by use of the forks tips as pry bars. Also, by by use of the forks tips as pry bars. Also, by
handling loads in a manner which causes the handling loads in a manner which causes the
fork tips to spread and the forks to twist laterally fork tips to spread and the forks to twist laterally
about their mountings. about their mountings.
Fork Inspection Fork Inspection
Overloading Overloading
Extreme overloading can cause permanent bending Extreme overloading can cause permanent bending
or immediate failure of the forks. Using forks of less or immediate failure of the forks. Using forks of less
capacity than the load or lift truck when lifting loads capacity than the load or lift truck when lifting loads
bar.
and using forks in a manner for which they were not and using forks in a manner for which they were not
designed are some common causes of overloading. designed are some common causes of overloading.
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First Installation First Installation
1. 1. Inspect forks to ensure they are the correct size Inspect forks to ensure they are the correct size
for the truck on which they will be used. Make for the truck on which they will be used. Make
sure they are the correct length and type for the sure they are the correct length and type for the
loads to be handled. loads to be handled.
If the forks have been previously used, perform If the forks have been previously used, perform
the "12 Month Inspection". the "12 Month Inspection".
If the forks are rusted, see "Maintenance and If the forks are rusted, see "Maintenance and
Repair". Repair".
2. 2. Make sure fork blades are level to each other Make sure fork blades are level to each other
within acceptable tolerances. See "Forks, Step within acceptable tolerances. See "Forks, Step
Maintenance Section Maintenance Section