Application of gas catalyst infrared in powder solidification of hydraulic support

Text/Xie Bo, Wu Chengfeng, Xu Kai, Zhao Jingjing, Liu Xingya

(Yankuang Donghua Heavy Industry Co.

Abstract: The application of gas-catalyst infrared in the powder coating line of hydraulic support is studied, the principle and characteristics of the gas-catalyst infrared heating system are introduced, and the technical solution for powder curing of the hydraulic support is proposed, and the new powder coating line To verify

Keywords: hydraulic support; powder; solidification; gas catalyst infrared

0 Preface

As a green paint with high solid content and low VOC, powder coating has a wider application range.

Yankuang Donghua Heavy Industry Co.

1 Principles and characteristics of gas catalyst infrared

1.

The natural gas is catalyzed by a platinum catalyst to produce a flameless reaction, forming an infrared radiation source, and generating diffusely reflected light waves, which can be reflected to the grooves and dead corners of the workpiece except the inside of the cavity

The gas catalytic infrared radiator uses a special platinum catalyst to convert natural gas or propane gas into medium and long wave infrared radiation

1.

Gas catalyst infrared is used in the field of powder coating curing, which has its natural advantages

The infrared radiation wavelength of the infrared wave system produced by it is between 3.

2 Overall plan

2.

The maximum size of the hydraulic support product: 5200mm×2000mm×1900mm; the maximum mass: 13,500kg; the production cycle: 15min/piece; the workpiece conveying method: accumulation conveyor chain
.

2.
2 Scheme design

Hydraulic support products have complex structure, large quality, different sizes, and large disparity in wall thickness; the thickness of the steel plate is about 100mm, and the average thickness is about 40mm
.

According to the characteristics of the hydraulic support product, this project adopts the gas catalyst infrared heating heating + hot air circulation heat preservation curing process
.
The first is 30 minutes of catalyst infrared heating to increase the temperature of the workpiece to 130~150 ℃; then 60 minutes of hot air circulation insulation; a door is set between the infrared curing oven and the hot air curing oven to ensure the safety of the system while saving energy and reducing consumption
.
The infrared furnace uses a 96-board design
.
The infrared stop position is 2 stations, the maximum length of the workpiece is 5.
2m, and 48 catalytic plates are arranged on the left and right sides respectively, which is a wrapped structure
.
Each board is equipped with a manual ball valve separately.
When a heating board fails, the solenoid valve automatically responds, temporarily closes the board in the area group where the failed board is located, and sends an alarm
.
The operator can manually check and close the fault board after the corresponding ball valve, so that the system can continue to run to ensure regional safety
.

3 Infrared heating system design

The furnace body adopts a modular design and is composed of a feeding zone, an effective heating zone and a discharge zone.
The furnace body is made of galvanized sheet
.
The surface of the external panel of the effective heating zone and the inner panel for installing the catalytic plate inside the furnace body are made of 304 stainless steel
.
The effective heating area is composed of independent modules, and the modules are connected by bolts, which is convenient for installation and maintenance, and is conducive to the adjustment of the length of the later production line
.
Each module adopts a symmetrical design.
The two sides are connected by the top cover and the base.
The sheet metal parts are connected by bolts or rivets to ensure sufficient stability.
The outer panel can be disassembled separately to facilitate installation and maintenance
.
The base is close to the ground with an air inlet to replenish fresh air
.

The catalytic furnace body adopts profiling design (see Figure 1) to ensure that the workpiece is within the optimal radiation distance as much as possible; at the same time, considering the different product specifications, the catalytic plate power is adjusted in proportion to maximize the personalized heating of products of different specifications Scheme
.
The technical parameters of the gas catalytic infrared heating plate: the surface temperature is 175~480℃, the maximum output power is about 25kW/m², and the maximum gas consumption of natural gas: 0.
9m³/h (1.
8kg/h)
.

The gas catalytic infrared heating system adopts GPS gas pulse control
.
High and low pressure crossover operation and stable output.
Through the battery valve and pressure reducing valve, the gas flow through the catalytic plate is adjusted to realize the energy transmission size.
The maximum 1:1 configuration can flexibly control the temperature of different areas
.

4 Equipment operation process

(1) Start the heating process
.
First, the forced exhaust operation is performed for 5 minutes, then the catalytic heating plate is electrically preheated for 15 minutes, and then the natural gas is passed through high fire operation for 3 minutes, and the electric heating is turned off
.

(2) Turn off the heating process
.
When heating is stopped, all gas valves are turned off, and the exhaust air is closed with a delay of 5 minutes to prevent gas or heat in the furnace from being exhausted
.

(3) In the emergency stop mode, all outputs are disconnected, and the fan still needs to be turned off after a delay of 5 minutes to prevent gas or heat in the furnace from being exhausted
.
 

5 Effect verification

In order to verify the effect of the workpiece after being sprayed with pink and externally cured, a verification test of the entire process of the hydraulic support product was carried out on the new powder coating coating line
.

5.
1 Selection of powder coatings

The hydraulic support is composed of castings, forgings, hot-rolled steel plate welded parts and other types of parts.
The structure of the structural parts and the oil cylinder are very different, and there are differences in the surface roughness grades of newly-made workpieces and over-repaired workpieces
.
Therefore, the powder coating formulation design needs to take into account the coating requirements of various parts
.

Currently in the machinery industry, most powder coatings use epoxy primer + polyester flour or a coating system of pure polyester powder coating
.
With reference to the mature experience in the field of heavy anti-corrosion coating, combined with the characteristics of the product of this project, after researching and analyzing the special environment of coal mines, referring to the definition of ISO12944-2017 coating durability, the durability of 7~15a under C5 environment is considered, and the durability is considered at the same time.
Economical, this project finally chooses the epoxy + polyester double coating process
.

5.
2 Test workpiece and process flow

A total of 3 different types of products were selected for this test, as shown in Figure 2
.

The test process is as follows: test piece shot blasting → test piece anti-rust → test piece online → degreasing → water washing → silane → pure water washing → drying → powder spraying → powder spraying → infrared curing → hot air circulation curing → forced cooling → test piece Offline → storage and inspection of test pieces
.

5.
3 Test process

5.
3.
1 Shot blasting of test piece

The test piece was shot blasted first, and the shot blasting time was about 15 minutes.
The telescopic jack and the side push jack were the overhauled workpieces.
To remove the original coating, shot blasting was performed twice
.
Because the powder test spraying time is the next day, in order to prevent the workpiece from returning to rust and affecting the spraying quality, the workpiece is sprayed with a water-based rust inhibitor for rust prevention after shot blasting
.

5.
3.
2 Pre-processing

After the test piece was put on the line, it was degreased (9min), washed with water (9min), silane (1min), washed with pure water (9min), and then entered into the drying room.
The test piece was rusted before and after drying
.
The powder coating manufacturer carried out sandpaper cleaning and rust removal treatment on the workpiece
.

5.
3.
3 Powder spraying

The experiment adopts the powder + flour dry-to-dry spraying process, and sprays with a manual electrostatic spray gun (Nuoxin)
.
The effect after spraying is shown in Figure 3 .

5.
3.
4 Powder curing and forced cooling

The test set cycle time is 9min, the catalyst infrared curing time is 9min, the hot air circulation curing time is 45min, and the forced cooling time is 45min
.
The test workpiece enters the solidification furnace and forced cooling chamber according to the order of the upper parts to complete the powder solidification and the cooling of the workpiece
.

In order to verify the temperature rise characteristics of the catalyst infrared, four sampling points of the test piece and air temperature were selected and the external surface temperature was tracked to verify the actual temperature.
The results are shown in Figure 4
.

The temperature rise curve of the three sampling points of the workpiece in Figure 4 proves that the gas catalyst infrared can quickly heat up; the powder coating part can quickly heat up to 100°C within 2 to 5 minutes; most of the radiant energy is concentrated and directly transmitted To the coating, the melting and flattening speed of the powder is greatly increased, the powder coating quickly reaches the melting temperature, the quality of the coating is improved, and the production efficiency is improved; compared with the traditional hot air circulation process, the drying time is reduced 30%, the equipment area has been reduced by 50%
.

5.
4 General inspection of test pieces

After the completion of the coating process of the test piece, the quality inspection was carried out immediately.
The inspection items include appearance inspection, film thickness inspection, and adhesion test.
For adhesion test, refer to GB/T9286-1998 "Cross-cut test of paint and varnish film" "
.
The finished test piece is shown in Figure 5, and the inspection results are shown in Table 1
.

It can be seen from Table 1 that the film thickness and adhesion of the test piece using the infrared curing method meet the relevant standards and technical requirements, and the infrared heating has a significant effect in improving the curing efficiency and quality of the workpiece
.

5.
5 Salt spray test

After the completion of the coating process of the test piece, the side push jack cylinder and the test plate of the test piece were selected to test the salt spray resistance of the coating
.
The salt spray test is based on GB/T10125—2012 "Artificial Atmosphere Corrosion Test Salt Spray Test" (same as ISO9227: 2006 "Corrosion Test Salt Spray Test in Artificial Environment").
The test pieces were subjected to 720h, 840h and 1440h destructive neutral salt spray tests, and the test results are shown in Table 2
.

It can be seen from Table 2 that after the 720h salt spray test of the test plate, there is no abnormal phenomenon such as blistering or rust in the test area.
The two sides of the scratch are slightly corroded, and the average unilateral delamination width is 0.
1mm; the test piece is subjected to 840h salt spray.
After the fog test, no obvious corrosion was seen on both sides of the scratches.
After the 1440h destructive salt spray test, the unilateral corrosion width of the test piece was less than 2mm, and no bubbles, rust, cracks, or peeling appeared in other areas
.
After the rust was cleaned, there was no obvious corrosion on both sides of the scratch
.

Figure 5 After the salt spray test of the finished test piece, the test piece and the test panel were evaluated according to the ISO4628-2016 "Assessment of Paint and Varnish Coating Aging" standard.
The evaluation results are: blistering level 0, corrosion Ri0 level, cracking ( 0) S0 level, spalling (0) S0 level, maximum unilateral delamination width ≤ 3mm, maximum unilateral corrosion width ≤ 2mm
.

Analyzing the test process and the test results, it can be seen that the film thickness and adhesion test of all sprayed test parts meet the technical requirements of Yankuang Donghua Heavy Industry Co.
, Ltd.
hydraulic support product protective coating, and the salt spray test performance far exceeds the product technical requirements.
The surface of the layer is smooth and uniform, the coating film is plump, the color is consistent, there are local shrinkage defects, and the appearance quality basically meets the requirements
.

6 Conclusion

The gas catalyst infrared + hot air circulation process is used in the field of powder curing of hydraulic supports; the preheating section uses infrared radiation heating to quickly heat the surface of the workpiece to the required curing temperature, with fast heating and high thermal efficiency, which greatly reduces the process time of powder curing, and The powder can be melted as quickly as possible, and the film quality is good; the heat preservation section uses hot air circulation to dry the dead corners and inner cavities of the workpiece that cannot be radiated by infrared, so as to avoid the problem of incomplete drying
.

This is also the first application of gas catalyst infrared in the powder line of hydraulic supports, and there are some shortcomings
.
For example, how to improve the flexibility of gas catalyst infrared to suit different types of products, and how to balance the relationship between the energy consumption cost and efficiency of thick plate curing? It needs to be further studied in the future production practice
.

references

[1] Wang Minglei.
Discussion on Coating Process Design of Coal Mine Machinery Hydraulic Support [J].
Modern Paint and Coating, 2010 (9): 63-65.

[2] Li Longyu, Wang Minglei, Li Haibo, etc.
Discussion on the green painting workshop of coal mining machinery[J].
Modern Paint and Painting, 2016 (2): 65-65.

[3] Wang Shuai, Zhu Ming.
The application of gas catalyst infrared in the powder curing of climbing car structural parts [J].
Modern Paint and Painting, 2019 (9): 32-34.