2.Structural Introduction
2.1 furnace body
The bogie hearth furnace body steel structure is made from 8# -12# channel
steel and 4-14mm steel plates. The side pillar and back pillars are made from
sectional steel, and are reinforced with sectional steel bracings. The external
wall of the furnace is painted with 2 layers of primers, and 2 layers of coating
paint. The key part of the furnace is painted with heat resistant paint.
2.2 lining
The main material of the furnace lining is made of high temperature refractory
fiber folding block at the long-term service temperature of 1000℃. This refractory
lining structure has the advantages of low heat conductivity, strong anti-shock capacity,
and anti-erosion. Aluminum silicate fiber compression block with thickness of 300mm
is designed as the high temperature refractory layer.
2.3 bogie
The bogie is comprised of heat preservation material, bogie frame and moving
mechanism. The refractory layer is divided into 3 sub-layers, i.e., 1st top high-alumina
brick layer, and 2nd and 3rd layer with both light clay bricks.
The bogie framework is made of 12# channel steel. The bogie has enough rigidity
to ensure no deformation under full load operation. The gap between the two sides
of the furnace bogie and the frame of the fire-resistant trolley should be fixed.
The bogie surface plate is made of 6 mm high quality steel plate. The function is to
disperse the bogie load (make the load distributed evenly) and enhance the frame
rigidity.
The bogie is self moving type. There are 4 wheels with the diameter of 240mm. Two
wheels are driving wheels, and the other two are driven wheels.
The bogie traction mechanism: the trolley traveling mechanism is driven by AC motor
reducer, and the driving mode is reducer sprocket structure. The trolley goes in and
out of the furnace through the reducer sprocket in the transmission device and the
traveling wheel under the trolley to drive the trolley traveling sprocket to mesh and
drive the trolley traveling, which is stable and reliable.
2.4 furnace door
The bogie hearth furnace supplier door is comprised of all-fiber lining and steel
structure shell. The door is built with silicate aluminum compressed fiber blocks
same as that for the furnace body. The shell is a welding structure from sectional
steel and steel plates. The furnace door has the feature of simple, practical, reliable
and convenient maintenance.
Driving mode of furnace door: electric hoist is used to move up and down vertically.
furnace door lifting is completed by a set of pulley block and electric hoist. The pulley
block is installed on the upper gantry of the furnace door. The furnace door is connected
with the steel wire rope through the ring chain, and the electric hoist is installed on the
gantry of the furnace door.
The structural features of furnace door: the main material of furnace door is welded with
steel plate and section steel, and the intersection is reinforced with hexagon reinforcing
plate, which can not only ensure the overall rigidity and strength of furnace door, but
also make the furnace door light and reduce the weight of furnace door. The fiber lining
adopts the hanging riveting method, which can effectively ensure the firmness of the
fiber due to the frequent opening and closing of the furnace door, and increase the
service life of the furnace door.
The upper and lower safety mechanisms are set on the furnace door and interlocked
with the trolley. In order to prevent the trolley from running out of control and hitting
the rear wall of the furnace, a mechanical elastic limiting device is installed on
the trolley
2.5 burning system
The burning system is comprised of Krom high speed burners, proportional
combustion control system, gas valve, solenoid valve, burner control box, etc.
The burner has the functions of automatic ignition, flame detection, and flame out
alarm. The burner controller receives the control signal of the temperature controller
and controls the large/small fire status of the burner based on the heat load
requirement so that adjustment of the temperature is realized.
A) The burner has adjustment function and the adjustment rate is 1:10 and the air
efficient is 1-5. The burner could meet the temperature uniformity of the heat treatment
process and effectively control the air-gas ratio so that the fuel consumption is reduced.
B) When the furnace is working, the burning system could automatically cut off the
electrical gas valve and general safety valve in the case of power failure detected by
the alarm system. When the power supply is resumed, the worker needs to open
the safety valve and restart the ignition program after purging function is confirmed.
The burner is set with a proportional control unit which enables alternative burning
of large and small fire, fire out alarm, and re-ignition. The burner control box has both
manual and self-run modes available. The worker could operate in front of the furnace
or in the control cabinet.
C) The pipe before the burner is equipped with solenoid valve, and manual gas
adjustment valve. The valve system could realize an ideal gas/air supply ratio so
that the air excess efficient is lower than 1.1.
2.5.1 air system
The air piping system is comprised of high pressure centrifugal fan, automatic regulation
valve, pressure gauge and pipes. The air volume is to match the gas volume, and the
air excess rate is lower than 1.20.
2.5.2 gas supply system
The general gas supply pipe is equipped with a pressure regulation device
(equipped with a filter), a low pressure switch and a pressure gauge. For the sake
of safety there is one fast cut-off valve on the general gas pipe.
2.5.3 discharge system
The heat treatment furnace trolley takes direct fume discharge method. The fume is
directly vented out through the flue pipe to the atmosphere. The fume conducts heat
exchange with the heat exchange before emission to the atmosphere.
2.5.4 Furnace pressure control system
The pressure on the working table in the furnace is kept at (+15 Pa), which is very
beneficial to the uniformity of temperature and the thermal efficiency of the furnace.
When the pressure in the furnace is too high, the hot air in the furnace will escape from
the furnace mouth and other unsealed places, resulting in the heat loss caused by the
escape of the flue gas; because the high temperature flue gas in the furnace escapes to
the outside of the furnace, it will affect the door, the side seal and burner of the furnace
directly, which is related to the overall service life of the furnace; when the pressure in the
furnace is too low, a large number of cold air outside the furnace will be absorbed into the
furnace, as well. The heat loss of off-furnace flue gas is increased. The low pressure of the
furnace causes the diffusion of cold air outside the furnace into the furnace, and secondary
combustion is formed due to the entry of oxygen-containing cold air, which has adverse
effects on the uniformity of furnace temperature, oxidation of workpiece and thermal
efficiency of the furnace. Therefore, effective technical measures must be taken to control the
furnace pressure with full automatic control. Our method is to control the furnace pressure
effectively by using a system consisting of pressure taking device, pressure transmitter,
intelligent instrument and so on. The furnace pressure is controlled in the optimum state
(the surface of the trolley is in a slightly positive pressure). At this time, the exhaust gas is
in a dynamic equilibrium state, which can not only ensure that the furnace gas does not
overflow, but also ensure that the cold air outside the furnace is not sucked into the furnace,
so as to save energy and maximize the efficiency of the furnace.
2.5.5 Heat exchange and flue system
A flue is set at the back of the furnace, and it is carried out with the heat exchanger
(according to the national standard GB3486-83). The flue leads to the outside of the
factory building. The cold air is exchanged with the heat exchanger to preheat the
combustion-supporting air before entering the burner, so as to improve the heat efficiency
of the furnace.
Heat exchangers and flue gas exhaust pipes are insulated by internal insulation (using
fiber castables) to ensure the service life of heat exchangers and flues.
2.5.6 fault detection and alarm system
The tempering bogie hearth furnace has a complete fault detection, alarm, diagnosis,
and safety protection system. On the control cabinet there is an alarm lamp.
2.6 control system
control system has the following parts: Ⅰ. Burning control system; Ⅱ. Electrical power
control system; Ⅲ.temperature control system .
Measures taken for burning control system:
K type thermal couple gets mV signal and sends it to temperature PID controller
(SHIMADEN brand). The temperature controller calculates the signal and outputs
4-20mADC control signal to the electrical actuator. The actuator further sends a signal
to the burner controller after calculation.
The burner controller is mainly responsible for ignition and flame detection. When the
terminal receives the ignition signal, the burner controller carries out flame simulation
and self testing stage. If during this simulation and self-test stage the burner couldn’t
detect the flame signal. The burner controller would open the gas solenoid valve and
convert the voltage 220VAC to 5KV for ignition (ignition time about 3S). If the burner
detects the flame signal in the safe time period (about 8S), the yellow indication light of
the burner would be on (ignition successful). If the burner couldn’t detect the flame signal,
the red light would be on (ignition failed). The burner controller is locked and the gas solenoid
valve is cut off.
B) electrical power control system: The electrical power control system mainly controls
ON/OFF of the fan, and IN/OUT of the bogie.
C) temperature control and record system
The system has the functions of temperature setup, control and digital display. And also
there is an audible and visual alarm at over-temperature situations.
Temperature control zone arrangement
A:temperature control system
The furnace is equipped with 1 thermal couple and an intelligent temperature controller.
The furnace is controlled by 1 zone.
B: instrument temperature control
The temperature controller allows setup of heating time, holding time, and cooling time.
It has self-tuning and self-adjustment function, and displays SV and PV.
