The design of the cooling section of the curing furnace in the powder coating of construction machinery has been improved!

With the continuous development of the construction machinery coating industry and the continuous improvement of the country's environmental protection requirements, the environmental protection and energy saving advantages of powder coating technology in the construction machinery industry have gradually emerged, and various construction machinery manufacturers have established powder coating production lines

1 Design points of cooling section of powder solidification furnace

1.

Powder coating has gradually developed from thin plate parts and small structural parts to large structural parts in the field of construction machinery, and now there are more and more applications of large structural parts

1.

The design of the cooling section after drying generally requires that it reaches room temperature after cooling

The forced cooling section is composed of a chamber body, an air supply and exhaust device, an air supply and exhaust pipe, and a blower hood

The strong cooling chamber (cooling section) is generally composed of a steel frame and a 50mm-thick composite sandwich rock wool board.

The blowing hood of the strong cooling room adopts an adjustable high-speed air blowing nozzle.

The air supply and exhaust device is the core component of the strong cooling chamber, which is generally customized by professional manufacturers

2.

The effect of the cooling section is closely related to the design of the cooling section.

2.

The design of the strong cooling chamber is generally to directly use the external air for cooling.

For some retrofitted equipment, the fan pulley can be replaced, the speed of the fan impeller can be increased, and the design margin of the fan in the cooling section can be used to increase the air volume, so as to achieve the effect of increasing the wind speed of the blowing nozzle [4]
.

2.
2 Rational use of cache area

Due to the characteristics of thick plate thickness and complex structure of large-scale structural parts in the construction machinery industry, the phenomenon of recuperation is common, which seriously affects the production
.
Therefore, in terms of process design, a longer buffer area is usually designed after cooling, so that the workpiece can continue to dissipate the remaining heat after reheating, so that it does not affect subsequent operations
.
Usually, the way to use the buffer area to solve the problem of heat recovery is to let the workpiece dissipate naturally, and the heat will be dissipated into the workshop
.
Such a method will increase the temperature in the relevant area of ​​the workshop, thereby reducing the working environment of the workshop, and at the same time, due to the lack of effective heat dissipation means, the heat dissipation efficiency of the workpiece is low
.

In view of the above shortcomings, now more closed buffer areas are used in the use of buffer areas, with exhaust fans (negative pressure fans or axial fans) to continue to maintain the air flow rate on the surface of the workpiece, and at the same time, so that the heat dissipated will not be Affect the work production environment
.

2.
2.
1 General composition of closed buffers

The design of the closed buffer area is generally composed of three parts: the chamber body, the blowing system and the exhaust system
.

1) Chamber body design: The chamber body design is generally consistent with the strong cooling chamber, and the structure, appearance and form remain the same
.

2) Design of air blowing system: The air blowing system generally adopts negative pressure blower, and the air intake adopts the form of passive air intake.
The negative pressure blower is used to maintain a certain air flow rate on the surface of the workpiece to speed up the heat dissipation of the workpiece
.

3) Design of exhaust system: The exhaust system is usually divided into two types: active exhaust and passive exhaust
.
Passive exhaust usually means that the chamber body does not have a top, and is exhausted from the top of the chamber body to the workshop through the principle of upward flow of heat
.
The active exhaust system uses a centrifugal fan or an axial fan to dissipate the heat from the workpiece into the chamber and discharge it to the outside, thereby reducing the ambient temperature inside the chamber, thereby accelerating the heat exchange between the workpiece and the air to improve the heat dissipation efficiency
.

2.
2.
2 Optimization and improvement of closed buffer design

For the construction of the coating line, under the condition of a certain overall investment, the investment amount that can be given to the cooling section is very limited.
Therefore, the cost issue needs to be considered when designing the closed buffer area.
On the premise of ensuring the effect, the best Potentially reduce investment
.
The general design has the following optimization directions:

1) Design optimization of the air blowing system: The negative pressure fan is a commonly used fan for exhaust air in the factory.
It is characterized by low air pressure, high air volume, low cost and low energy consumption.
A negative pressure fan
.
Due to the characteristics of hot air flowing upward, the negative pressure fan can be placed at the lower part of the workpiece and blow air from bottom to top
.
The air inlet should be equipped with expanded metal mesh or shutters to prevent foreign objects from entering
.
The specific method is shown in Figure 2
.

2) Design optimization of the exhaust system: the exhaust fan can be an axial flow fan or a centrifugal fan.
The selection of the exhaust fan does not have to be completely matched with the blower.
The room temperature is too high
.
This reduces the size of the fan, thereby reducing energy consumption
.
Since the heat in the buffer zone is lower than that in the strong cooling chamber, the exhaust air can be exhausted to the outside of the workshop or to a high point in the workshop (usually more than 2000mm above the chamber body)
.

2.
3 Improve the performance of heat exchange medium

The design concept of the cooling section is usually to blow air to the surface of the workpiece to take away the heat of the workpiece for cooling purposes
.
In such a process, the air velocity on the surface of the workpiece increases, taking out heat.
Due to the low specific heat capacity of the air, the heat taken away by the air per unit volume is very limited.
At the same time, due to the increase in the air temperature, the ability of the air to take away heat is further reduced.
[5]
.
Therefore, the heat exchange medium is replaced and the specific heat capacity is increased, so that the heat that can be taken away by the medium per unit volume is increased, thereby improving the effect of the cooling section
.

Water is an economical medium with high specific heat capacity, so an atomizing device can be added to the air supply and exhaust device.
After the water is atomized, the mixed medium of air and water mist is evenly blown onto the surface of the workpiece with the air blower to cool the workpiece
.
The evaporation of water mist takes away a lot of heat, so as to achieve better cooling effect
.

This method generally increases the cost of construction and also increases the cost of use.
It is rarely used in the construction machinery industry.
It is usually used in the case where there is no buffer area after cooling, and the parts need to be unloaded in a short time
.

3 Practical cases

Taking the newly built powder coating line of a construction machinery enterprise in Changsha as an example, the design of its cooling section is analyzed
.

3.
1 Introduction to the project

The powder coating line of this project adopts the process of shot blasting - pretreatment cleaning - drying - powder spraying - powder solidification - cooling
.
The workpiece to be coated is a large structural part, the maximum size is 7 500mm×1500mm×2000mm, the thickness of the workpiece is 8~25mm, the production cycle is 20min/station, the ambient temperature range is -5~35℃, and the conveying method is the accumulation and release chain
.

The cooling section is designed as a 2-station forced cooling chamber and a 3-station closed buffer area.
The forced cooling time is 40 minutes, plus the cooling time of the buffer area is 60 minutes, and the total cooling time is 100 minutes
.

3.
2 Design of cooling section

The two parts of the strong cold room and the closed compartment body design are consistent with other equipment of the coating line.
The length of the strong cold room is 16000mm, and the length of the closed buffer area is 24000mm
.
The outer wall is made of 50mm composite rock wool sandwich panel, and both ends are open without opening and closing doors
.

3.
2.
1 Design of Air Supply and Exhaust in Strong Cooling Room

The supply air volume is calculated according to 6 times of ventilation/min, and the supply air volume is 61000m3/h
.
The blowing nozzles of the blowing hood are arranged in a staggered manner.
The horizontal spacing of the nozzles is 400mm, and the vertical spacing is 500mm.
The total number of nozzles is 350.
The calculated blower outlet wind speed is 14.
8m/s, which basically meets the design requirements
.
The exhaust air volume remains the same as the supply air
.

The air supply and exhaust system adopts an integrated air supply and exhaust machine, which is placed on the side of the chamber body.
The air supply and exhaust pipes are folded by galvanized steel plates in sections, and each section is connected by flanges
.
The air supply directly adopts the workshop air, and the exhaust air is discharged to the outside of the workshop
.

3.
2.
2 Air supply and exhaust design of closed buffer area

The air supply adopts a negative pressure fan.
The fan bracket is made of angle steel and placed on the lower part of the workpiece.
The fan is placed on the fan bracket and blows air from bottom to top.
The lower part of the chamber body is evenly arranged with passive air inlets and blinds
.
The air supply volume of a single negative pressure fan is 30,000m3/h, and a total of 7 fans are used, which are evenly distributed in the room
.

3.
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