Sleeve bearing is a precision mechanical foundation piece. As
the rapid development of scientific and technological progress, the
quality of customer requirements for bearing products is getting higher
and higher. It
is important for the manufacturer to provide high quality products that
meet the standards and meet the performance of the host, but it is more
important to use bearings properly. I
in recent years engaged in motorcycle special bearing technical work,
often encountered such a problem, that is, the bearing is qualified by
the test, but after the installation of the bearing stuck or the use of
early stop when the failure. The
main performance of the rotation card stagnation, a serious exfoliation
of the face, the cage serious wear and tear and even broken. Failure
analysis results show that the quality of the bearing itself is not
much, mostly due to improper installation and use caused. To this end, I think it is necessary to bearing the common failure
mode and mechanism for some superficial review, with a view to play a
role in attracting people.
First, the bearing failure mechanism
1. Contact fatigue failure
Contact fatigue failure refers to the bearing surface by the role of alternating stress and failure. Exposure
to fatigue The peeling occurs on the bearing working surface and is
often accompanied by fatigue cracks, which are first generated from the
maximum alternating shear stress below the contact surface and then
extended to the surface to form different flaking shapes such as pitting
or pitting, Peeling off into small pieces called shallow peeling. Due
to the gradual expansion of the stripping surface, and often to the
deep expansion, {TodayHot} the formation of deep peeling. Deep peeling is the source of fatigue that is in contact with fatigue.
2. Wear failure
Wear
failure refers to the relative sliding friction between the surface of
the work surface of the metal caused by continuous wear and tear
failure. Continued
wear and tear will cause damage to the bearing parts and eventually
lead to loss of bearing dimensional accuracy and other related problems. Wear
may affect the shape of the change, with the gap increases and the
surface morphology changes, may affect the lubricant or make it a
certain degree of pollution caused by complete loss of lubrication
function, so that the loss of rotation accuracy of bearings can not even
normal operation. Wear failure is one of the common failure modes for all types of
bearings, which can usually be divided into the most common abrasive
wear and adhesive wear.
Abrasive
wear refers to the bearing working surface squeeze between the external
hard particles or hard foreign body or metal surface grinding and
contact with the relative movement of the surface caused by wear and
tear, often in the bearing surface caused by plow-like scratches. Hard
particles or foreign matter may come from inside the host or from the
host system other adjacent parts from the lubrication medium into the
bearing inside. Adhesive
wear refers to the friction surface due to the micro-protrusion or
foreign body friction surface uneven force, serious deterioration in the
lubrication conditions, due to local friction heat, easy to cause local
friction and friction micro-welding phenomenon, serious When
the surface metal may be partially melted, the contact surface forces
the local friction welding point from the substrate to tear and increase
the plastic deformation. This adhesive-tear-adhesive cycle process constitutes an adhesive
wear, and in general, slight adhesion wear is called abrasion, and
severe adhesive wear is called bite.
3. Fracture failure
Bearing failure is mainly due to defects and overload two factors. When the external load exceeds the material strength limit caused by part fracture known as overload fracture. The cause of the overload is that the host is faulty or improperly installed. Bearing
parts of the micro-cracks, shrinkage, bubbles, large foreign debris,
overheating tissue and local burns and other defects in the impact of
overload or severe vibration will also cause damage in the defect, known
as defective fracture. It
should be noted that {HotTag} bearings in the manufacturing process,
the raw materials into the factory re-inspection, forging and heat
treatment quality control, processing process control can be correctly
analyzed by the instrument whether the existence of defects in the
future must still strengthen control. But in general, the failure of the bearing failure usually occurs mostly for overload failure.
4. Clearance change failure
Bear
in the work, due to external or internal factors, so that the original
with the gap change, reduce the accuracy, and even cause "killed" called
the clearance change failure. External factors such as excessive amount of interference, the
installation is not in place, the temperature rise caused by the
expansion, transient overload, etc., internal factors such as residual
austenite and residual stress in the unstable state are caused by the
main reason for the failure of clearance.
Second, the common failure mode and countermeasures
1. Unidirectional position of the channel flaking
The
unilateral displacement of the channel is mainly manifested in the
serious flaking zone at the junction of the channel and the barrier. The cause is that the bearing is not in place or during operation. Take the countermeasure is to ensure that the bearing installed in
place or free side bearing outer ring with the gap to match, so that
when the bearing overload bearing compensation.
2. The channel flakes in a symmetrical position in the circumferential direction
Symmetrical
position peeling occurs in the inner ring for the surrounding ring
peeling, while the outer ring was symmetrical position of the spalling
(that is, the short axis of the ellipse direction), the main reason is
because the shell hole oval is too large or half split shell structure , Which in the motorcycle camshaft bearings in the performance is particularly evident. When
the bearing into the elliptical shell hole or half of the separation of
the shell tight, the bearing outer ring to produce an oval, in the
short axis of the clearance significantly reduced or even negative
clearance. Bearing
under the action of the load, the inner ring rotation produces a
circumferential peeling traces, the outer ring only in the short axis of
the symmetrical position of peeling marks. This
is the main reason for the early failure of the bearing, the bearing
failure test showed that the bearing diameter roundness from the
original process control of 0.8μm to 27μm. This value is much larger than the radial clearance value. Therefore,
it can be sure that the bearing is working under severe deformation and
negative clearance, the work surface is easy to form early abnormal
wear and tear off. The countermeasure is to improve the accuracy of the shell hole
machining or as far as possible without using the shell hole half of the
separation structure.
3. Roller tilted off
In
the bearing face was peeling off the belt, indicating that the bearing
is working in the inclined state, when the tilt angle reaches or exceeds
the critical state, easy to form early abnormal wear and tear off. The main reason is due to poor installation, shaft deflection, journal
and shell hole low precision, to take measures to ensure that the
bearing installation quality and improve the shoulder, hole shoulder
axial runout accuracy.
4. Ferrule rupture
Fracture failure is generally rare, often caused by sudden overload. (Forbidden),
forging defects (overheating), processing defects (local burns or
surface microcracks), host defects (poor installation, poor lubrication, Instantaneous overload), etc., once the overload load or severe vibration are likely to break the ring. Take measures to avoid overload shock loads, select the appropriate
amount of interference, improve installation accuracy, improve the use
of conditions and strengthen the bearing manufacturing process of
quality control.
5. Cage is broken
Cage failure is an occasional abnormal failure mode. The main causes are the following five aspects:
A. Cage abnormal load. Such
as the installation is not in place, tilt, excessive interference and
other easy to cause clearance reduction, increased friction and heat,
the surface softening, premature abnormal peeling, with the expansion of
peeling, peeling foreign body into the cage hole, The movement of the block and the additional load, increased the wear
of the cage, so the deterioration of the cycle, it may cause damage to
the cage.
B. Poor lubrication mainly refers to the operation of the bearing in a
lean state, easy to form adhesive wear, the working surface of the state
deteriorated, adhesive wear tear objects easy to enter the cage, the
cage to produce abnormal load, may cause the cage fracture.
C. Invasion of foreign matter is a common pattern of failure of the cage. Due to the intrusion of foreign hard foreign body, increased the wear
of the cage and produce abnormal additional load, may also lead to cage
fracture.
D. Creep phenomenon is also one of the reasons causing the cage to break. The
so-called creep multi-finger ringing phenomenon, the mating surface in
the case of insufficient amount of interference, due to sliding the load
point to move around the direction of the collar relative to the shaft
or shell to the circumferential direction of the phenomenon of
deviation. Once the creep is generated, the mating surface is significantly worn,
and the weary powder may enter the interior of the bearing, creating an
abnormal wear - roller off - the process of wear and additional load on
the cage, as well as possibly causing the cage to break.
E. Cage
defects (such as cracks, large pieces of different metal inclusions,
shrinkage, bubbles) and riveting defects (lack of nails, pad or half
cage cage surface gap, serious riveting) and so may cause damage to the
cage The To take countermeasures in the manufacturing process to be strictly controlled.
Third, the conclusion
In
summary, from the bearing failure mechanism and failure mode, we can
see that, although the rolling bearing is a sophisticated and reliable
body base, but the use of improper also cause early failure. Under normal circumstances, if the correct use of bearings, can be used to fatigue life. The
early failure of the bearing is mainly due to the manufacturing
precision, installation quality, conditions of use, lubrication effect,
external foreign body intrusion, heat influence and sudden failure of
the host. Therefore,
the proper and reasonable use of bearings is a systematic project, in
the bearing structure design, manufacture and installation process, for
the early failure of the link, take appropriate measures to effectively
improve the bearing and the host life, which is manufactured The plant and the customer should have shared responsibility.
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