First, the development trend of bearing heat treatment technology
Bearing
heat treatment is directly related to the quality of the subsequent
processing, which eventually affect the use of agricultural machinery
parts lining the performance and life expectancy, bearing heat treatment
is bearing manufacturing in the large energy consumption and large
pollution. Bearing
heat treatment equipment directly affects the quality of bearing heat
treatment, as well as energy consumption and pollution. In recent years, with the progress of science and technology, the
development trend of heat treatment technology is mainly reflected in
the following aspects:
(1)
Cleaning Heat treatment Wastewater, exhaust gas, waste salt, waste oil,
and electromagnetic radiation generated by the FB090 bronze rolling
bushings will all cause pollution to the environment. Solve
the problem of environmental pollution heat treatment, the
implementation of clean heat treatment (or green environmental
protection heat treatment) is the development of heat treatment
technology one of the directions. This places high demands on the atmosphere of heat treatment, quenching oils and cleaning equipment.
(2)
Precision heat treatment Precise heat treatment is to fully ensure the
stability of the optimization process, to achieve the quality of the
product quality bushing sliding bearing dispersion is small (or zero),
heat distortion to zero, reducing the amount of grinding to improve
production efficiency, saving materials . To
achieve precision heat treatment must have good uniformity of
temperature, temperature control accuracy, and quenching agent good
cooling and stability. Bearing precision heat treatment can take the overall quenching and induction hardening two roads.
(3)
Energy-saving heat treatment Select a new type of insulation materials
to improve energy efficiency of heat treatment equipment; optimize the
heat treatment process, improve process output, give full play to the
equipment capacity. Bearing
manufacturers at this stage are doing experiments in this area, for
example, make full use of waste heat, waste heat, some manufacturers
have used forging heat treatment of bearing parts ball annealing; the
use of low energy consumption, short cycle replacement process longer
cycle, energy consumption Of the process; lower bainite quenching process to a certain
extent, within a certain range, with a shorter bainite quenching process
instead of a long cycle, large energy carburizing process.
(4)
Less non-oxidative heat treatment is controlled by heating the
atmosphere instead of the oxidizing atmosphere to a controlled
atmosphere with precise control of the carbon potential and nitrogen
potential. The performance of the parts after heat treatment is
improved. Defects in heat treatment such as oxidation, decarburization
and cracks are greatly reduced , After finishing heat treatment to reduce the amount of retention, improve material utilization and machining efficiency. Vacuum heating gas quenching, vacuum or low pressure carburizing,
nitriding, nitrocarburizing and boronizing can significantly improve the
quality of the workpiece, reduce distortion and improve life
expectancy.
Second, bearing heat treatment equipment
1. Annealing equipment
At
this stage, the annealing equipment in our country is the coexistence
of oxidation furnace and protective atmosphere furnace. The oxidation
furnace is more than the protective atmosphere furnace. The periodic
furnace and continuous furnace coexist, and the periodic furnace is more
than the continuous furnace. As
early as the 1960s and 1970s, the United States, Britain, Japan and
other countries have fully popularized the push rod and roller hearth
isothermal nodular annealing furnaces, shorten the annealing cycle, save
energy and improve the annealing quality. With
the development of bearing parts machining technology, as well as the
use of precision forging and precision rolling (cold rolling) process,
parts blanks machining accuracy is getting higher and higher, resulting
in the need for annealing annealing atmosphere. Bearing industry should promptly promote the protection of the
atmosphere of ball annealing, to reduce the oxidation and
decarburization after annealing, improve processing efficiency,
energy-saving materials, reduce costs.
2. Conventional martensite hardening tooling equipment
China's
bearing industry at this stage conventional martensite hardening
tooling equipment varies from the protection medium can be divided into
non-protective media oxidation furnace, controlled atmosphere furnace
and vacuum furnace. Unprotected
medium oxidation furnace accounts for about 25% of the bearing heat
treatment equipment, a protective medium less non-oxide furnace bearing
heat treatment equipment accounted for about 50% of the controllable
atmosphere furnace bearing heat treatment equipment accounted for about
20% of the vacuum furnace bearing heat treatment About 5% of equipment From the production cycle can be divided into cycle furnace and continuous furnace.
In recent decades, martensite hardening tooling equipment development mainly in the following areas:
(1)
Automated production line At present, the automatic production line
adopted in China can be divided according to its structure (or workpiece
movement in the furnace): a muffle mesh belt furnace, a muffle mesh
belt furnace, a cast chain furnace, a roller hearth furnace ,
Roller furnace with furnace and rotary hearth series production line,
the material, the pre-cleaning, protective atmosphere (or controlled
atmosphere) heating, quenching, cleaning after (sometimes secondary deep
cold roller hearth furnace for second cryogenic ) And tempering are done automatically. Production
line automation and control of high precision, after processing the
quality of the workpiece uniform, the entire heat treatment production
line can be used as part of the bearing automatic production line. Different
heat treatment lines are suitable for the heat treatment of bearing
components of different types and sizes, depending on their structural
characteristics. For example, the belt furnace is suitable for small and
medium sized bearing rings. The rotary hearth furnace is suitable for
small batch bearing rings. The roller hearth furnace is equipped with
automatic lifting Quenching device, suitable for larger wall bearing parts; roller furnace for rolling and small ferrules.
(2)
multi-purpose furnace carburizing or carbonitriding in a controlled
atmosphere, but also quenching in a protective atmosphere to complete
the workpiece without oxidation quenching process. It is a cycle furnace, mainly for small batch, multi-species bearing parts heat treatment.
(3)
Induction heating quenching, tempering induction heating equipment with
heating speed, energy saving and small deformation, etc., after
treatment of the workpiece has some conventional heating does not have
the performance. China's current application of bearing heat treatment is mainly
concentrated in the turntable bearing and car wheel bearings, and GCr15
steel basically no application.
(4)
Vacuum furnace heating under vacuum can reduce or avoid the oxidation
of the workpiece, with high-pressure gas quenching can control the
cooling and deformation of the workpiece to avoid the environmental
pollution caused by oil quenching to achieve clean heat treatment. In
addition, the vacuum heat treatment, the workpiece microstructure more
uniform, the same surface and heart tissue, uniform hardness, is
conducive to the improvement of bearing fatigue life. Vacuum
furnace is mainly used in special steel heat treatment (heating
temperature above 1 000 ℃) and some demanding GCr15 steel bearing parts
on the quenching, bearing heat treatment in China is widely used. The development trend of vacuum furnace is quenching by
hyper-pressure gas quenching instead of oil, and the application of
vacuum carburizing furnace to solve the application of new steel in
bearing field.
(5)
Quenching cooling medium and equipment Quenching medium can be divided
into three categories: oil-based, water-based and gas quenching medium. Oil-based quenching medium is the most commonly used quenching medium. Ordinary
quenching oil is N32 or N22 system-wide loss of oil, in order to
improve its cooling performance, anti-aging properties, light
performance and high temperature performance were added refrigerant,
cleaning agents, brighteners and antioxidants, forming a rapid oil, Fast
bright oil and high temperature graded isothermal oil series of
quenching oil, used in different sizes and requirements of the bearing
parts of the quenching; In addition, there are low volatile vacuum
quenching oil. The disadvantage of oil-based quenchant media is the air pollution
caused by soot during the quenching process, which causes water
contamination during the subsequent cleaning process.
Water-based quenching media is an aqueous solution of organic polymers, anti-corrosion agents and other additives. Different
cooling characteristics can be obtained by changing the type and
concentration of the organic polymer to suit the quench cooling
requirements of different bearing components. In the quenching and cooling process, the organic matter attached
to the surface of parts, can reduce the risk of quenching and cracking
parts, and does not produce fumes, easy to clean, non-polluting, is the
development of quenching medium.
Gas
quenching is the use of inert gas as a medium (commonly used nitrogen),
the compressed gas through the specially designed nozzle is sprayed
onto the workpiece surface, in order to achieve quenching and cooling of
the workpiece. Cooling characteristics and deformation can be controlled by adjusting the pressure of the gas and the structure of the nozzle. Gas quenching than water-based quenching cleaner, and lower cost, the key technology is the nozzle structure design. China's gas quenching in the field of bearings is still in its
infancy, the structure of the nozzle design technology there is a
certain gap.
Quenching cooling equipment is quenching medium in addition to quenching effect of another major factor. Quenching
cooling equipment control parameters at this stage less, generally only
the oil temperature and oil circulation control. Foreign
commonly used quenching tank multi-parameter control, such as oil
temperature, oil cooling characteristics, the direction of oil
circulation and mixing, as well as the speed, the way the workpiece into
the oil, etc., in order to get the best quench organization and
performance, at the same time Deformation to a minimum. Some bearing manufacturers in China are also trying
multi-parameter control, especially through the conical bearing on the
way to control the oil into the workpiece to solve the angle of
quenching changes in the process.
Multi-station automatic quenching press has been applied in our
country, but the degree of automation can not keep up with foreign
countries.
(6) cleaning equipment cleaning is usually necessary after oil quenching process. The
cleaning equipment used in the continuous production line generally
completes the process of hot soapy water immersion, water spray and hot
air drying, with oil-water separation device. In
the advanced cleaning equipment, there is a secondary cooling device
(equipped with refrigeration equipment, adjustable temperature between 5
~ 10 ℃) before drying to reduce the content of retained austenite and
improve the dimensional stability. At this stage of our country, the cleaning equipment mainly adopts
high-pressure cleaning liquid to clean. This cleaning is ineffective on
the non-through hole and the small oil ditch, often resulting in more
tempering, more pollution and sometimes fire.
Vacuum cleaning is the development of cleaning equipment in recent years. The
advantages of this kind of cleaning equipment are as follows: the
cleaning effect is good, especially for cleaning parts with complex
structure, and the surface of the workpiece is bright after cleaning;
the safety, cleaning and cleaning fluid are clean water, and do not add
the chlorides and petroleum which are harmful to the environment Class
solvent; high degree of automation, and can be used instead of
low-temperature cleaning cleaning tempering, tempering save the cost. In recent years, ultrasonic cleaning, eddy current cleaning in the heat treatment effect is also very good.
Bainite isothermal quenching equipment
According to the characteristics of bearing processing, the
equipment used are mainly two categories: automatic production line and
cycle furnace.
(1)
small number of automatic production lines, large quantities of
bearings suitable for automated production, such as the production of
railway bearings and more use of automated production lines. Automatic
production line mainly by the protective atmosphere of the furnace and
the isothermal quenching tank composition, which is part of the
equipment used in isothermal quenching according to the movement of the
workpiece can be divided into three categories: Rotary, push disc and
conveyor belt. Developed
by the love Hsien Lin rotary type, push plate isothermal quenching
equipment is transferred to the end or push plate mechanism isothermal
salt bath, the workpiece according to a certain beat out, the memory
control sequence of materials, the action by the PLC program control . This type of equipment is highly automated but heavily invested.
(2)
periodic isothermal quenching equipment rolling mill bearings due to
the variety, small quantities, small and medium-sized mill bearing
manufacturer to use more box furnace or pit furnace + quenching cooling
tank + isothermal tank + cleaning tank, there are also used + Isothermal tank. The configuration less investment, applicability, but labor-intensive, poor security. At present, the bainite isothermal quenching to promote the
occasion, the bainite isothermal quenching instead of carburizing steel
used in the load of the smaller mill bearings in our country has been
successfully applied.
4. Protect the atmosphere and control
As
surface quality requirements increase after quenching of workpieces,
heating of the (controlled) atmosphere is gaining in popularity and heat
treatments including annealing are heated in a protected (or
controllable) atmosphere. 1970s, the main use of endothermic atmosphere. The
endothermic atmosphere is a mixed gas of feed gas and air partially
reacted under the action of a catalyst to form a protective atmosphere
containing 18% -23% of CO, 37% -42% of H2, and the balance of N2, This atmosphere in the field of bearing heat treatment there are applications. Nitrogen
propane atmosphere in the field of China's bearing heat treatment
quenching the most widely used, nitrogen and methanol components of the
atmosphere similar to the endothermic atmosphere, nitrogen-methanol as
the representative of the nitrogen-based atmosphere in the furnace with
more applications. In
the 1990s, there was a process of gas generation that introduced air
and hydrocarbons directly into the furnace at temperatures above 800 °
C, a stratified atmosphere. Through
the study found that the atmosphere containing high CH4 composition,
although the gas reaction does not reach a similar endothermic
equilibrium, but its carbon transfer ability or by the atmosphere of CO
and H2 content to control the use of oxygen Carbon dioxide potential can be achieved by combining the probe with the CO2 analyzer. Straightforward
atmosphere has the main advantage of saving a lot of raw material gas
consumption, according to statistics, this atmosphere, whether used in a
periodic atmosphere furnace or continuous atmosphere furnace, the feed
gas consumption savings of up to about 70%. Today,
there are about 300 sets of atmospheric furnaces around the world that
use this atmosphere for various heat treatments such as carburizing,
carbonitriding and protective atmosphere quenching. Straight-born atmosphere in the field of bearing more applications in the field of carburizing.
The
practical application in recent years shows that the service life of
the oxygen probe is not well defined, and the difference between the
carbon potential measured by the oxygen probe and the actual value is
also unpredictable. Therefore,
the controlled atmosphere is sometimes uncontrollable due to the
failure of the oxygen probe, resulting in defects such as
decarburization and oxidation. Our country at this stage often used to regularly verify the
measurement accuracy is not conducive to full automation stove, and
sometimes even affect the normal production.
In
view of the above reasons, a dual measurement system has been developed
abroad. One of them has a standard oxygen probe for normal control of
carbon potential and another independent measurement system for
detecting the working condition of the oxygen probe. That is, the two
systems respectively measure the atmosphere Carbon potential, when the results show a great deviation, it will alarm. The second measuring system working element can be a CO2 infrared analyzer or a miniature oxygen probe (λ-probe). To date, many atmospheric furnaces have been installed with this dual measurement system.
Looking
at the whole, the domestic bearing heat treatment technology and
equipment, there are still far more developed countries, especially in
the gap between the larger annealing equipment. Bearing
heat treatment technology and equipment than other industries also have
a certain distance, improve bearing quality related to the
revitalization of China's equipment manufacturing industry.
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