Self-lubricating
bearings have a wide range of operating temperatures, adequate solid
lubricant content, uniform release, good self-lubricating properties,
and good seizure resistance, which can effectively protect journals and
achieve long-term use. Suitable
for operation in high temperature, low speed, heavy load, large dust,
water shower, and shock and vibration environment. It can be widely used
in the rolling of machinery and equipment such as mining machinery,
metallurgy, petroleum, chemical industry, food, textile, papermaking,
printing and dyeing. And sliding bearing parts.
The
aluminum liquid produced in the aluminum electrolytic cell is poured
into the mixing furnace after being sucked and sucked by a vacuum. After
passing over the ratio of the liner sliding bearing and removing the
slag, it flows into the aluminum ingot casting machine and is casted.
The formed solid is called aluminum. Ingots, produced aluminum ingots are stacked by stackers. In order to increase production efficiency, the dry bearing must be
cooled with a large amount of cooling water before the aluminum ingot is
formed. During the cooling process, the huge thermal energy of the
aluminum liquid is released into the cooling water to generate hot water
vapor.
Casting
machine bearing is in the high temperature and steam environment, many
bearings are grease lubrication, the added grease will melt away due to
high temperature and slip composite bearing flow removed, maintenance is
difficult, the equipment surface is also difficult to clean wipe. In addition, steel bearings are susceptible to corrosion and rust in
hot and humid environments. The failure rate is very high and equipment
maintenance costs are high. Equipment operations are often plagued by
the following two problems.
It
is difficult to achieve high-temperature continuous operation of the
oil supply operation. The casting machine's puller, transfer, ingot, and
inverting devices are all installed in the unit housing. Each rotating
bearing is designed with a nozzle device that periodically injects
grease and must be stopped when oil is injected. Remove the shell and press the grease with a grease gun. And
the whole machine has more than 30 oil injection points, long-term
operation and maintenance can not achieve this cumbersome oil injection
operation, had to carry the thin oil cans pouring in the running outside
the bearing sleeve, the lubricant is difficult to enter the friction
between the bearing, large Some bearings are in friction.
High
ambient temperature, grease lubrication is not suitable for the current
molybdenum disulfide grease used in the casting machine rolling
bearings are considered to be resistant to high temperature grease, we
know that its base oil is a petroleum product, plus a small amount of
high temperature resistant molybdenum disulfide additive, its
temperature limit That is 120 °C. It is measured that the working temperature of the bearing of the
casting machine can reach 200°C, which is far beyond the limit of the
temperature resistance of the grease.
Under
such high temperature conditions, the base oil in the grease will be
thinned and gradually evaporated. The remaining carbon slag, molybdenum
disulfide, and dust will be mixed into a solid block and solidified on
the cage of the rolling bearing, not only losing its lubrication effect. It also hinders the normal operation of the rolling bearing and
wears quickly. It can stop for up to 2 weeks and remove the bearings to
clean the oil.
First, the wear condition
The
abnormal wear of the bearings caused by the two major problems in the
operation of aluminum ingot casting equipment bearings is more serious. Taking an aluminum enterprise's pulling spindle mechanism as an
example, the average service life of the bearing is 2 months. When the
wear is serious, the 5MM inner ring is worn out, causing the equipment
to continue to operate.
Wear is uneven. The
reason is that the original design to oil can not be achieved, had to
be outside the bearing in the operation of burning thin oil, a small
amount can be burned into the bearing, the wear is small, can also be
seen from the table more than 50% of the shaft and sleeve does not It is lubricated, but it produces strong adhesive wear under dry friction. This wear quickly increases the clearance between the shaft and
the sleeve, so that the dust can easily enter and cause a vicious cycle.
Second, the selection of oil-free self-lubricating bearings
In order to solve the problems of high temperature, low speed, heavy
load, large dust, water showering, and shock and vibration in mechanical
equipment, oil-free self-lubricating bearings are selected.
1.
The structure of the bearing The self-lubricating bearing is developed
on the metal friction surface of the bearing base with an ordered and
sized hole, and embedded in a metal sheath made of molybdenum disulfide,
graphite, etc. Bearings, solid lubricant friction area of 25-65%. The solid self-lubricating block can work normally at a high temperature of 280°C. However, due to its low mechanical strength, weak carrying capacity,
and easy deformation, it can inhibit this shortcoming by inserting it in
a metal hole, forming a metal part to support the load, and a
self-lubricating block to act as a lubricant.
The
lubrication mechanism of this self-lubricating bearing is that during
the sliding friction between the shaft and the sleeve, a part of the
self-lubricating material molecules is transferred to the metal surface
of the shaft, filling the small non-planar surface, and forming a layer
of relatively stable solid lubricant film. Causes the wear between the solid lubricant films to prevent sticking and abrasion of the shaft and the sleeve. This
combination of plausibility combines the complementary advantages of
copper alloys and non-metallic wear-reducing materials, and is
particularly suitable for the movement of oil-free, high-temperature,
high-load, low-speed, anti-fouling, corrosion-resistant, and strong
radiation environments. It can be used under special working conditions where it is wetted
with water or other solutions and no lubricating grease can be added at
all.
2.
The self-lubricating block accounts for the ratio of the surface area
occupied by the self-lubricating block and the operating speed and
bearing strength. The operating speed is low; the bearing pressure is
high, and the area occupied by the metal should be larger. For example, the area occupied by the self-lubricating block of the
walking roller bearing for grasping the trolley is about 25%, the
lubrication of the spindle bearing of the pulling spindle mechanism is
sufficient, and the bearing strength is not large, and the area occupied
by the self-lubricating block is about 65%.
3, the technical requirements of the bushing material Bushing should
be made of alloyed copper, the bushing must have high hardness,
generally must be heat treated, its hardness is not lower than HRC45.
4, the self-lubricating block geometry and inlay requirements. The
shape of the self-lubricating block is cylindrical and rectangular.
Self-lubricating can use columnar shape according to the occupied area,
and vice versa. No matter what shape it must be inlaid firmly to prevent it from falling off during operation.
5.
The clearance gap between the bush and the shaft The coefficient of
linear expansion of the self-lubricating block is approximately 10 times
that of steel. In
order to adapt to bearing temperature changes, the gap between the
shaft and the bushing is adjusted from the original four-piece metal
fitting (D4/DC4) to 0.032 to 0.15mm to 0.45 to 0.5mm. The self-lubricating block protrudes the bushing metal 0.2 to 0.4 MM on the side of the friction pair. This will be fully lubricated during the initial running-in period of
the bearing operation, reducing the power consumption of power driving.
6, the advantages of oil-free self-lubricating bearings
A, no oil lubrication or less oil lubrication, suitable for places
that can not be refueled or difficult to refuel, can be used without
maintenance or less maintenance;
B, good wear resistance, low friction coefficient, long service life;
C. There is a proper amount of elasticity and plasticity, which can
distribute the stress on a wide contact surface and increase the bearing
capacity of the bearing;
D, static and dynamic friction coefficient is similar, can eliminate
the crawling at low speed, so as to guarantee the working precision of
the machine;
E. Can reduce vibration, reduce noise, prevent pollution, and improve working conditions;
F. A transfer film can be formed during operation to protect the grinding shaft without biting axis.
G. The hardness requirement of the grinding shaft is low, and the
unconditioned shaft can be used, thereby reducing the processing
difficulty of the relevant parts;
H, thin-walled structure, light weight, can reduce the mechanical volume;
I. The bushing is made of brass and can be used in corrosive media.
Through
the practice of an aluminum company, casting machine bearings have been
replaced with oil-free self-lubricating bearings, which have been used
continuously for 15 months and are still in operation. The clearance
between shafts and bushings is generally not more than 1 mm. It is
expected that it can be used for another 12 months. More than the original service life (2 months).
Oil-free
self-lubricating bearings can be used not only in aluminum ingot
casting machines, but also in oil-free, high-temperature, high-load,
low-speed, anti-fouling, anti-corrosion, and high-radiation
environments, as well as in water. Or other solutions infiltrate and can not add lubricating grease at
all under the special working conditions of the equipment, this type of
bearing has a wider promotion value.
At
present, most of the bearings used in various mechanical industries are
balls, needles and the like, but a small number of them have adopted
self-lubricating bearings. It is believed that in the near future,
bearings from lubricating will become the dominant bearing. The following are the application features and advantages of some self-lubricating bearings:
1, no oil lubrication or less oil lubrication, suitable for places can
not refuel or difficult to refuel, can be used without maintenance or
less maintenance;
2, good wear resistance, low friction coefficient, long service life;
3, there is a proper amount of elastoplasticity, which can distribute
the stress on a wider contact surface and increase the bearing capacity
of the bearing;
4, static and dynamic friction coefficient is similar, can eliminate
the creep at low speed, thus guarantee the working precision of the
machinery;
5. It can make machinery reduce vibration, reduce noise, prevent pollution and improve working conditions;
6, in the course of operation can form a transfer film, play a role in
the protection of the grinding shaft, no bite axis phenomenon;
7. For the low hardness requirement of the grinding shaft, the shaft
without the quenching and tempering treatment can be used, thereby
reducing the processing difficulty of the relevant parts;
8, thin-walled structure, light weight, can reduce the mechanical volume;
9,
the back of the steel can be plated with a variety of metals, can be
used in corrosive media; has been widely used in various mechanical
sliding parts, such as: printing presses, textile machines, tobacco
machinery, micro-motors, automobiles, motorcycles and agricultural and
forestry machinery and many more.
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