﻿GET_GEVOMechL2_01_01_01_38 - ANIMATION Screen
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You have reached the end of this module!

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In this module, you learned to:

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Identify the different types of bolts based on thread profile, strength, and size.

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Bolts are classified by shape, material and finish, which are specified by industry standards, such as the American Society for Testing Materials (ASTM) and the International Standards Organization (ISO).

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Inch standards are set by ASTM and metric standards by ISO.

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Both the Inch and Metric standards use a symmetrical V-shaped thread profile.

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The Inch standard identifies pitch as the number of threads per inch and the Metric standard identifies pitch as the distance between corresponding points on adjacent threads.

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For inch-size fasteners, the material strength is specified by the "grade".

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For metric fasteners, the term "property class" is used.

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Identify the forces that operate on a bolted joint.

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Threaded fasteners are tightened for clamping parts together and transmitting loads.

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A screw or bolt thread is an extension of an inclined plane.

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This inclined plane has been wrapped around a shaft.

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When the thread is turned, it moves the mating part or nut up the inclined plane.

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When more turning force, or torque is applied to the shaft, the more force is exerted on the nut.

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This force creates a tension in the bolt, which clamps the mating parts together.

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Generating sufficient preload force is the key to strong and reliable bolted joints that will not loosen or break under load.

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Rotating the bolt or nut, which in turn stretches the spring, generates the preload force.

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The more the bolt or nut is rotated, the more the bolt stretches and generates more preload.

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When there is no tension load (Ft) applied to the joint, the clamping force (Fc) equals the preload force (Fp).

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If the tension load is equal to the preload, there is no clamping force.

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If the tension load is increased beyond the initial preload force, the joint will separate.

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Joints are loaded with shear forces (Fs), tension forces (Ft) or a combination of both.

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In general, the preload force determines the strength of the joint.

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The mating parts act like a spring, but a much stiffer spring.

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In the ideal case, the mating parts are much, much stiffer than the fastener.

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To ensure satisfactory performance of mechanical equipment and to avoid costly failures, it is important to tighten all nuts on vital bolts and studs according to values given in the appropriate maintenance instructions.

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Describe the different tightening methods used for locomotive maintenance.

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Insufficient preload, caused by an inaccurate tightening method, is a frequent cause of bolted joint failure.

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There are four main methods that our engineering group utilizes to control the preload of a threaded fastener:

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Torque control

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Angle control (also known as turn-of-the-nut)

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Bolt stretch or elongation measurement

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Tensioning

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In torque control method, a rotary force is applied to the nut as it moves down the threads of the bolt.

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Once the nut contacts a surface, it begins to act like a screw jack, forcing the bolt to stretch.

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Angle control is also known as the “turn-of-the-nut” method.

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The nut or bolt is turned a predetermined number of degrees after all play has been removed from the joint.

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Bolt elongation measurement is a tightening method that still depends on torque to stretch a bolt, but it does allow for improved measurement of the actual clamping force that is being produced.

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A method which solves most of the stated problems with torque control and bolt elongation measurement tools is the tensioning method.

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Describe special tools commonly used for different tightening methods.

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Some of the special tools commonly used include:

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Torque wrenches

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Adapters

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Tensioning tools

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The clicker torque wrench, sometimes called a digital wrench, works by preloading a "snap" mechanism with a spring to release at a specified torque.

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It is often necessary to use adapters with a torque wrench to reach inaccessible bolts or nuts.

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When adapters are used, the reading of the torque wrench dial is not the actual torque exerted.

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The additional torque exerted on the nut or bolt depends on:

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Length of the adapter.

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Angle at which the adapter is positioned on the wrench.

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Each tensioner is designed for a specific application.

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The basic elements of a tensioner are:

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A base that rests on the component, providing an anchor for the pulling force.

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A hydraulic cylinder that will thread onto the bolt, then stretch it to its recommended tension.

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A cap that mates with the nut and allows the operator to turn it on or off.

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Define the recommended tightening sequences on the GEVO diesel engine.

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The tightening sequences used are:

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Criss-cross tightening sequence for circular bolt patterns.

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Spiral tightening sequence starting in the middle for non-circular bolt patterns.

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Tightening sequences result in minimizing bolt preload variations due to elastic interactions.

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In some instances a pre-torque/final torque sequence is used.

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With this sequence, each bolt is tightened to a pre-torque value for the first pass and then the second pass at the final torque value.

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This will reduce the preload reduction caused by the tightening of the other bolts in the joint.

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Identify the sources of documentation for standard bolt torque values.

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It is essential when maintaining the locomotive to apply the correct torque values to all fasteners.

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The standard bolt torque value tables should be used when a specified value is not listed in the maintenance manual instructions for the particular application.

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Each Running Maintenance and Backshop Manual publication that contains maintenance procedures has a Data or Torque Values section located at the back of the publication.

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Also, the torque value for a given application is listed as part of the procedural step.

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Some fasteners have a pre-torque and a final torque value.

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The reason for this is to minimize the variations caused by friction between fasteners.

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This means that all fasteners are first torqued to the pre-torque value and then to the final torque value.

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One way our engineering group indicates a pre-torque and final torque is by separating the two values by a "/”.

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There are two ways that our engineering group indicates a range for the torque: For example, in 50 to 60 lb.-ft (commonly read as ft-lb), any torque value of 50 through 60 lb.-ft is valid.

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For 90 plus or minus 9 lb.-ft, a valid torque is 81 through 99 lb.-ft.

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Convert torque values from U.S. Customary to Metric and vice versa.

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Most torque wrenches have both units of measurement, Pound-Foot (or Foot-Pounds) and Newton-Meters.

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If a conversion has to be made, 1 lb.-ft. = 1.3558 Nm.

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The metric equivalent uses a comma instead of a decimal point in some documentation.

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When doing conversions, use a decimal point in place of a comma.
