What is a good friction coefficient?
60 — Excellent friction. Equal to or greater than . 50 — Adequate. Equal to or less than .
What is coefficient of friction in bolts?
The coefficient of friction can vary from 0.04 to 1.10, depending on the materials and the lubricants being used between mating materials.
How do you calculate frictional thread?
The thread friction torque is then calculated by subtracting the pitch torque from the thread torque. Graphically, this makes the input torque definition look like Figure 6. The amount of thread torque and underhead torque present in a given tightening can be described using friction coefficients.
What is the range of friction coefficient?
The coefficients of friction ranges from near 0 to greater than 1. Under good conditions, a tire on concrete may have a coefficient of friction of 1.7.
What coefficient of friction is slippery?
The coefficient of friction (COF) is the measurement of a surface’s frictional resistance. Essentially, this number tells you how slippery a surface is. A COF of 0 (zero) means that there is no friction between the two surfaces.
What is K on a torque chart?
The K Factor is an experimentally determined constant that relates the torque applied to the load induced in the fastener. This factor is affected by the condition of the fastener, the lubricant used and the condition of the flange.
What is considered a low coefficient of friction?
Coefficient of friction (COF) is a dimensionless number that is defined as the ratio between friction force and normal force (Eqn (2.1)). Materials with COF smaller than 0.1 are considered lubricous materials.
Is a lower coefficient of friction better?
For example, ice on steel has a low coefficient of friction, while rubber on pavement (i.e. car tires on the road) has a comparatively high one. In short, rougher surfaces tend to have higher effective values whereas smoother surfaces have lower due to the friction they generate when pressed together.
What does a friction coefficient of 1 mean?
If materials have a coefficient value of one, it means the friction force is the same as the normal force. In other words, the force required to move the object is equal to that object’s weight. Objects can also have a friction value higher than one.
What is K value in tightening torque?
The K factor is used to account for the energy lost to friction and other factors during the tightening process. The generally accepted K factors for this calculation are: 0.20 for assemblies with dry threads (no lubrication) 0.15 for assemblies with lubricated threads.
How is nut torque calculated?
The basic formula T = K x D x P stated earlier takes these factors into account and provides users with a starting point for establishing an initial target tightening torque.
What is a high friction coefficient?
A higher coefficient of friction means that more friction force is present relative to the normal force. There are two types of coefficients of friction. One is kinetic, which means the object or objects are already in motion; the other is static, which means the objects are at rest.
Can coefficient of friction exceed 1?
The coefficient of friction can never be more than 1.
Do the friction coefficients for thread and underhead regions of fasteners duplicate?
The friction coefficients for the thread and underhead regions of the fastener will most likely not duplicate the conditions on the normal production parts. This should be recognized as not a major problem as long as we are focusing on obtaining the tension-angle coefficient.
How do you calculate underhead friction torque?
Once contact is made with the underhead area, the underhead friction torque is measured as the difference between the total input torque and the thread torque. Figure 12. Determining Frictional Forces As clamp force is developed, the pitch torque is calculated and subtracted from the thread torque to compute the thread friction torque.
What is the coefficient of friction?
Coefficient of Friction Friction force develops between contacting surfaces of two bodies and acts to resist relative motion between the bodies. The friction force, F, is proportional to the normal force, N, and the coefficient of friction, μ : where μ s is the coefficient of static friction and μ k is the coefficient of kinetic friction.
What happens to thread friction when underhead friction is overcome?
After the underhead friction is overcome and the shank of the fastener absorbs a slight additional torsional wind-up, the thread friction is over come permitting added elongation and tensioning to occur. Figure 46. Torque-Time Signature with Good Lubrication