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Bushing fit
Bushing fit
Assembly method
Clearance Fit
- There is a gap when two objects are combined or combined, and the movement is smooth.
- Other terms: gap fit, loose match, this fit is often called loose match.
Interference Fit
- There is no gap when the two objects are combined or matched, and they are tightly connected and kept together by friction, which is not easy to cause displacement. This is most commonly used in conjunction.
- Other terms: interference fit, tightening fit, pressure fit, friction fit, tight fit, this fit is often called only fitting.
Overfit, Transition Fit
- When two objects are combined or combined, they are in a good match, between the gap between the seeming and non-existent.
- Other nouns: adaptation, fit, QQ, this is expressed by QQ.
The above statement may not be formal, I hope it can help readers understand better, and for a more professional statement, please refer to the following link.http://www.taiwan921.lib.ntu.edu.tw/mypdf/drawing13.pdf
What does QQ mean?
QQ is not a Martian emoji, but a common saying in the industry, which means that the tightness of the two objects after matching is between tight and loose, a little tight and not too tight, a little loose, and not too loose, which is just right.
Q stands for Flexible, Bound, from the association of Taiwanese “Q Da Da”, Q is a long sound, Da Da is a short sound, the first expression is to be flexible to food, and now it has evolved to this field, expressing that the two objects are a little resistant and can work freely, QQ, so do you understand?
How it is applied
Installed in the hole
The outer diameter of the bushing is closely matched with the base hole, and the two become one. The outer diameter of the shaft liner is larger than the inner diameter of the hole.
The shaft is operated on the inner diameter of the bushing, and can be loose, tight or QQ according to customer needs.
Mounted on the shaft
The inner diameter of the bushing and the shaft are closely matched, and the two become one, and the inner diameter of the bushing is larger than the outer diameter of the shaft.
It operates on the inner diameter of the base hole, and can be loose, tight or QQ according to customer needs.
Interference
For example: the outer diameter of the bushing is 8.10 mm into the inner diameter of the metal hole 8.00, the size overlaps by 0.10 mm, but the bearing lining can be pressed into the metal hole, because of the elasticity of the material, and the interference is a noun extended from the interference fit, representing the numerical size, the larger the value, the more the size of the two objects overlaps, if the shaft lining is assembled into the hole, the greater the interference, the greater the interference. The greater the assembly force, also known as the compression force.
The amount of interference has a limit, which varies according to different materials, and when the value is too large, the object may be permanently deformed, damaged, scraped and thinned, etc., so you need to pay attention when using it.
Calculate the interference
When installed in the hole
Interference = outer diameter of the bushing – inner diameter of the metal hole
When installed on the axis
Interference = outer diameter of the metal shaft – inner diameter of the bushing
Interference force
Interference force, such as the spring being compressed, the greater the deformation, the greater the force, the compression force is equal to the rebound force, so the interference is directly proportional to the interference force, the greater the interference force, the greater the assembly force, and the less easy it is to fall off.
See Similar Words<Compression force>、<Pull it out>Explanation.
Installation method:
- manpower
- When the interference force is small, it can be installed by manpower.
- Auxiliary tools or machines
- When installation is not possible by human power, tools such as rubber hammers or lever arms must be used, and if that is not enough, mechanical press-in must be used, such as hydraulic machines.
- Grease
- Apply grease to the contact area during installation to reduce the friction coefficient and wear, which can reduce the assembly force.
- Chamfering
- Chamfer the edge of the base hole shaft and the shaft lining, bevel 30 degrees, during installation, the force is evenly distributed on the circumference, the force is gradually and slowly changed, not an instantaneous change, which will help to be more stable and less damaged during installation.
- Thermal expansion and contraction
- Using the material properties, the heating part expands, assembles it on the shaft while it is hot, and shrinks back to its original size after cooling.
- Moisture absorption
- Ditto, using the material characteristics, the plastic shaft lining is forced to absorb water and expand, so as to complete the assembly on the shaft, and then the water will slowly volatilize and gradually shrink in size until it reaches equilibrium with atmospheric moisture.
Above, the fifth and sixth points need to pay attention to size changes.
The benefits of interference cooperation
- Eliminate gaps
- When the shaft lining is closely matched to the hole or on the axis, it creates a pressure around it, which in turn eliminates the backside clearance and can be more closely attached to the circumference. According to Hertz theory, plastics have elastic changes, and even a little particle or impurity in the pores may be able to cover and absorb under surface pressure.
- Stable position
- Bearing the above, when the interference of the bearing is matched in the hole or on the shaft, a pressure and friction pressure (resistance) are generated, so that the bushing is not easy to produce displacement due to external force and vibration, so the greater the interference force, the more stable the position. For more information, please refer to Pull Force.
- Stable environment
- The greater the interference, the more stable it can be in some harsh environments, as shown in the figure below.
- In this emphasis, the interference is the confrontation environment, very simply they are just the subtraction between the inner and outer diameters, not the interference force, because there are many factors of interference force, such as friction coefficient, even if the friction coefficient is 0.7, as long as the interference is equal to zero, the interference force is equal to zero.
- In addition, the material absorbs water and moisture in a similar way. For related articles, see Moisture Absorption, Thermal Expansion and Contraction.
Low interference and at low temperatures, shedding occurs
The interference is high and can still be maintained at low temperatures
- Dimensionally stable
- As mentioned above, it has the ability to resist environmental changes, as long as there is an interference, the inner diameter of the bushing almost does not change.See image for details [high interference and can still be maintained at low temperatures].
![See image for details [high interference and can still be maintained at low temperatures].](https://unionmaterial.com/wp-content/uploads/2022/05/%E5%B9%B2%E6%B6%89%E9%87%8F%E8%BC%83%E9%AB%98%E6%99%82-%E4%BF%9D%E6%8C%81.jpg){kind=link}
- Stable operation
- When the plastic shaft lining is installed in the hole, it is exaggerated to change from a large diameter to a small diameter, so that the material is in a state of pressure, its rigidity is improved, the amount of deformation when subjected to external force will be reduced, the positioning accuracy will be improved, and the shaft will work stably.
