Common terms for mechanical properties of fasteners

Torque

Torque is a force that produces rotation. Here are some of the most common examples of torque:

1. String the watch 2. Unscrew the cap 3. Turn the door handle 4. Screw in the screw

Torque needs to be considered in most applications

There are slight differences in the following four torques

1. Driving torque

2. Locking torque

3. Break away torque

4. Preset torque

All these torques are encountered in practical application, but their importance is different in different service conditions

1. Driving torque - the rotational force required to combine the parts

2. Locking torque - the force required to make the combination of parts reach the preset tightness

3. Loosening torque - the rotational force required to separate the combined parts

4. Preset torque - a characteristic set on the fastener that causes the fastener to produce resistance due to the friction force to achieve the purpose of preventing loosening once the fastener is locked into the mating thread workpiece. The driving rotating torque required to overcome the friction torque is called preset torque

Driving torque: driving torque is the main consideration in screw cutting, screw rolling and self-locking parts application. As the maximum force required for rotating parts, requirements are necessary. Too high driving torque will cause rotation failure and rotation failure, all of which will increase the cost of fasteners, so it is necessary to reduce the driving torque as much as possible. This demand leads to another one Engineering requirements "drive pull ratio". It is the relationship between the torque value required by the drive fastener and the torque value required by the internal thread matched by the anti pull or damage. The larger the range of this value, the more conducive to reducing the poor assembly, repeated assembly and reducing the corresponding cost, the more applicable the fastener

For thread rolling self tapping screws, the required drive to strip ratio is 1:3, that is to say, if there is one unit of driving torque, there are three units of tensile strength matching thread strength

Locking torque: the locking torque is the force to screw the fastener to the required tightness or torque tension value. It is expressed as a maximum value. This means that the specified tightness or clamping force should be obtained when the torque is less than the specified maximum torque, which is important in any case. Because the fastener should be able to properly lock to ensure normal assembly, but this should not This excessive increase in torque. Excessive torque requirements will cause failure of the drive system, increased labor intensity, failure of the fit, all of which will cause an increase in fastener costs

Loosening torque: the loosening torque refers to the rotating force when the fastener is loosened from the locking state. It has the most practical significance when the fastener is easy to loosen. Generally, the loosening torque is related to the self-locking fastener (not only the self-locking fastener, but also the anti loosening fastener). It is expressed by a minimum value, that is, the fastener cannot be separated from the assembly by the torque less than the loosening torque

Preset torque: technically speaking, the preset torque is a kind of resistance to rotation. It usually refers to the torque when the fastener that is locked but not locked is screwed out. Like the loosening torque, the preset torque is used in the situation that is easy to loosen, and its specified value is the minimum value. Under the action of less than the specified torque, the fastener must be locked (but not one Each fastener requires a certain torque to drive, which is the "driving torque" of the preset torque, and each preset torque fastener requires a larger torque to lock to ensure the proper locking state, which is the "locking torque". Each fastener needs a certain torque to loosen it from the locking state, which is the "loosening torque" ”Each fastener shall be taken out with a certain torque when it is not locked but still locked, which is the preset torque. The test unit of torque is pound inches or pound feet. One pound inch is the force produced by one pound acting at a distance of 1 inch perpendicular to the rotation center. Two pound inches is the force produced by two pounds acting at a distance of 1 inch perpendicular to the rotation axis The force produced by a force of two inches apart or one pound. From this, it can be concluded that

Moment = vertical distance x force from axis to torsion

If you divide pound inch by 12, you get pound foot. If you multiply pound inch by 12, you get pound foot. The choice of units depends on the value. For example, we usually use 100 pound foot instead of 1200 pound inch

Note: pound inch and pound foot are technically correct units. But we often write them as inch pound and foot pound. Torque is the force necessary to produce rotation. It is the force acting on the end of the arm to produce rotation

Answer the questions (don't look at the previous content):

1. What is torque?

2. What are the four different torques?

3. What is the unit of torque?

Check the above materials to check your answers. If there is any omission, write down the correct answers

Tensile strength

Tensile strength refers to the material's ability to resist breaking under external tension. Have you ever pulled the rubber strip? If so, you are testing the tensile strength of the rubber strip. The tensile strength of fasteners is the same, which is the tensile value that the fastener can bear without breaking

Tensile strength is the most common physical property of fasteners. It is the ultimate strength of fasteners. It is also the load bearing capacity (load BEA) of fasteners considered in application