Manitowoc National Crane NBT40 Series, Service Manual

Page: 17 / 220

National Crane
Published 8-01-2017 Control # 287-11
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NBT40 SERVICE MANUAL INTRODUCTION
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10
Fatigue Of Welded Structures
Highly stressed welded structures are subject to cracking
(fatigue) when repeatedly subjected to varying stresses
caused by twisting, shock, bending, and overloads. Inspect
equipment periodically for weld fatigue. The frequency of
inspections depends on the age of the equipment, the
severity of the application, and the experience of the
operators and the maintenance personnel. The following are
known high stress areas and should be inspected as part of
a preventive maintenance program:
• Hydraulic cylinder and boom pivot attaching points.
• Outrigger pads, beams, boxes and attachment
structures.
• On the frame in the area of doubler plates and
crossmembers.
• Turntable bearing connection (where bearing is welded
to the crane turret).
• Counterweight support structures (were applicable).
• Hydraulic cylinder end connections.
The above is provided only as a guide and your inspection
plan should not be limited to the areas listed. A visual
inspection of all weldments is good practice.
Loctite
Follow the directions on the Loctite container. There are
different Loctite types for different applications. The following
types of Loctite brand adhesives are available from the parts
department of the local National distributor.
Application of Medium Strength Loctite
NOTE: The fastener can be re-used and the adhesive can
be re-applied over cured adhesive residue.
The following procedure covers the proper application and
curing method for medium strength Loctite adhesive/sealant
(Loctite #243). Clean dirt and oil from the threaded surfaces,
both male and female.
Adhesive/Sealant Application
1. Apply a bead several threads wide in the approximate
area of threaded contact (Figure 1-3).
2. In a blind hole application, apply several drops of
adhesive in the bottom of the hole so that the adhesive is
forced up when the bolt is installed.
3. After installation, fixturing occurs within five (5) minutes.
The time required to achieve full strength is 24 hours.
Fasteners And Torque Values
Use bolts of the correct length. A bolt which is too long may
bottom before the head is tight against the part it is to hold. If
a bolt is too short, there may not be enough threads engaged
to hold the part securely. Threads can be damaged. Inspect
them and replace fasteners, as necessary.
Torque values should correspond to the type bolts, studs,
and nuts being used.
The torque tables are provided by Manitowoc for reference
when performing maintenance.
Use of proper torque values is extremely important. Improper
torquing can seriously affect performance and reliability.
Identification of fastener grade is always necessary. When
marked as a high strength bolt (grade 5, 8, etc.), the
mechanic must be aware that he/she is working with a highly
stressed component and the fastener should be torqued
accordingly.
NOTE: Some special applications require variation from
standard torque values. Reference should always
be made to component overhaul procedures for
recommendations.
Special attention should be given to the existence of
lubricant, plating, or other factors that might require variation
from standard torque values.
The use of lubricants on zinc-flake coated parts shall be
prohibited since this will change the required torque value.
When maximum recommended torque values have been
exceeded, the fastener should be replaced.
Previously installed bolts and nuts of Grade 8 or Class 10.9
and higher may not be reused.
When referring to the applicable torque charts, use values as
close as possible to the torque values shown to allow for
wrench calibration tolerance.
DANGER
Loctite type adhesives contain chemicals that may be
harmful if misused. Read and follow the instructions on
the container.
!
Bead Application
FIGURE 1-3
Reference Only