What is the definition of "preload"?
The tension created in a fastener when it is first tightened. Preload must be greater than the external forces applied to the assembly to prevent joint failure.

Learn more about preload in the class Understanding Torque 210 below.


Fasteners Training


Class Information
Fasteners Training Tooling U-SME classes are offered at the beginner, intermediate, and advanced levels. The typical class consists of 12 to 25 lessons and will take approximately one hour to complete.
Class Name:Understanding Torque 210
Description:This class explains the importance of torque as well as how torque is derived and applied to bolted joints. Includes an Interactive Lab.
Prerequisites: 700117  700120  700125 
Difficulty:Intermediate
Number of Lessons:15
Language:English, Spanish
 
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Class Outline
  • Objectives
  • What Is Torque?
  • What Is Preload?
  • What Is Clamping Force?
  • The Importance of Torque
  • The Effects of Overtightening and Undertightening
  • Factors Affecting Torque
  • Determining Torque
  • How Torque Is Derived
  • Applying Torque
  • Proper Torque: An Example
  • How Torque Is Measured
  • Inspecting Bolted Joints
  • Inspecting Torque Tools
  • Summary
  
Class Objectives
  • Define torque.
  • Explain the importance of preload.
  • Explain the importance of clamping force.
  • Explain the importance of torque.
  • Describe the effects of overtightening.
  • Describe the effects of undertightening.
  • Describe factors that can affect torque accuracy.
  • Describe factors to consider when determining torque.
  • Explain how torque is derived.
  • Describe methods for applying torque.
  • Solve for the torque value.
  • Describe methods for measuring torque.
  • Describe methods for inspecting bolted joints.
  • Explain the importance of inspecting torque tools.

Class Vocabulary

Vocabulary TermDefinition
bolt A cylindrically shaped, threaded device used for fastening parts. Bolts usually have blunt ends and mate with a nut.
breakaway torque The torque value that registers when the fastener is first turned.
calibration The act of adjusting a measuring instrument against a standard to ensure its accuracy.
clamping force The compressive force that a fastener exerts on a joint.
click wrench A type of wrench that measures the amount of torque applied to a fastener. A click wrench indicates the torque value with the use of a digital display.
clutch A coupling found inside a motorized device that connects or disconnects parts to drive the mechanism.
compression A pushing or pressing force that is directed toward the center of an object.
dial wrench A type of wrench that measures the amount of torque applied to a fastener and displays the torque value on a dial.
distance The amount of space between two points. Torque is determined by multiplying force times distance.
embedding To be enveloped by or surrounded by another material or object. A fastener is embedded into the base component. Embedding can cause changes in torque.
English system A standard system of measurements based on the inch, second, pound, and Fahrenheit degrees. English measurements are primarily used in the United States and England.
fatigue strength The maximum stress a fastener can withstand for a specific number of repeated applications prior to its failure.
force The push or pull that gives energy to an object. Torque is determined by multiplying force times distance.
friction A force that resists motion between two components that are in contact with each other. Friction is an obstacle to overcome when accounting for torque.
friction stabilizer A device used in bolted joints that regulates the amount of friction in the joint. Friction stabilizers help engineers to maintain the proper torque.
hard joint A joint in which it takes the fastener less than a 30° turn to get the fastener from fitting snugly to reaching torque.
impact wrench A screwdriving tool that uses a discontinuous drive clutch and compressed air to achieve torque. Impact wrenches are often used to tighten lug nuts on cars when changing a tire.
inspection torque The amount of preload in a fastened joint.
load The overall force that is applied to a material or structure. A fastener that supports the weight of an object is withstanding a load.
metric system A standard system of measurements based on the meter, second, kilogram, and Celsius degrees. The metric system is internationally recognized.
preload The tension created in a fastener when it is first tightened. Preload must be greater than the external forces applied to the assembly to prevent joint failure.
repeatability The ability of an object to deliver accurate and dependable results over a long period of time.
residual torque The amount of tension that remains in a joint after fastening a threaded fastener.
screw A threaded device used for fastening parts or transferring motion. Screws usually have pointed ends.
screwdriving tool A tool that assembles a screw into a joint. Screwdriving tools can be manual or powered by compressed air, electricity, or batteries.
shearing force The cutting and separating of material through its cross section.
soft joint A joint in which it takes the fastener more than a 720° turn, or two full rotations, to get from fitting snugly to reaching torque.
strain gauge A device used to measure the amount of strain within an object. Strain gauges are used when inspecting bolted joints.
stress The applied force over a certain area that tends to deform an object or structure.
tension A pulling force that is directed away from the object and attempts to stretch or elongate the object.
test crib A designated area in which engineers can test and calibrate tools. Oftentimes, the environmental conditions that exist in the test crib cannot mimic the conditions that exist on the shop floor.
thread stripping A type of fastener failure that occurs when a fastener is over-tightened. Thread stripping causes deformed fastener threads.
threaded fastener A type of fastener that contains threads. Bolts, screws, and nuts are examples of threaded fasteners.
torque The amount of force applied to tighten a threaded fastener.
torque audit A process by which an inspector checks a fastened joint to ensure that the correct torque has been obtained.
torque tool A type of tool that is programmed to achieve specific torque results as it drives down a threaded fastener. Torque tools are essential to ensure that a finished product is safe.
ultrasonic device A device that uses acoustic frequencies well above those heard by the human ear. Ultrasonic devices are used when inspecting bolted joints.
vibration Rapid linear motion between components. Vibration can negatively affect torqued joints.