Research on Construction and Application of Intelligent Coating Production Line for Steel Bridges

At this stage, China has become the world's largest in terms of total bridge construction, but there is still a certain gap from the bridge-building power.

1 The overall design plan of the intelligent coating production line

1.

Wenzhou Oujiang Beikou Bridge is the world’s first three-tower four-span double-layer highway steel truss suspension bridge.

Considering the overall size characteristics of the large section of steel truss girder, a "graded and step-by-step" manufacturing and coating process was developed.

Figure 1 Large-segment structure and block diagram of steel truss girder

The maximum net size of the main truss truss is 20.

1.

According to the structural characteristics of steel truss beam products, after analysis and research, it is planned to transform the existing No.

According to the site survey, the existing sandblasting room has an internal length of about 52m, an inner cavity width of 23.

Figure 2 Layout of smart sandblasting workshop

1.

According to the structural characteristics of the steel truss beam product, through the intelligent research on the equipment and system of the paint shop, it is proposed to add 2 intelligent cantilever spraying robots in the existing paint shop No.

Figure 3 Layout of the smart paint shop

2 Research on intelligent coating equipment technology

2.

2.

The top crane robot sandblasting system adopts a gantry double-beam design, equipped with a spraying robot arm, and the end of the robot arm carries a sandblasting gun head

Table 1 Parameters of the top gantry eight-axis robot

Figure 4 The top gantry eight-axis robot

Before the top crane robot runs, according to the structural characteristics of the bridge deck blocks and steel trusses, the running trajectory is edited and a special program is generated, as shown in Figure 5

Figure 5 Sandblasting trajectory of the top crane robot

When the spray gun pressure is selected as 8kgf/cm2, the experiment is carried out according to the distance from the workpiece 200mm, 300mm, 400mm, 500mm, 600mm, 700mm, 800mm, 900mm, 1000mm, 1200mm, and the following conclusions are drawn: (1) When the distance is less than 700mm, the sand The speed has not been accelerated to the maximum, the blasting force is small, and the blasting efficiency is low.
When the distance is more than 1200mm, the flying speed of sand particles will attenuate more severely, and the blasting effect will be relatively poor
.
(2) In the range of 700~1200mm, the closer the distance is, the greater the striking power; but the sprayed sand covers a small area.
In order to achieve a uniform sandblasting effect, a faster swing speed and more frequent posture changes are required
.
The distance between the spray gun and the workpiece is 800~1000mm
.

In addition, the relationship between nozzle flow rate, nozzle diameter and nozzle working pressure (multiple test data and analog calculation) is shown in Table 2
.

Table 2 The relationship between nozzle flow rate, nozzle diameter and nozzle working pressure

Through process test comparison, the best process parameters are selected: nozzle diameter 17mm, sandblasting pressure 8.
4kgf/cm2, flow rate 40m³/min, spray distance 800～1000mm, spray gun swing angle 70°, spray width S=2* L*tan(70/2)=1120mm, moving speed 1.
5～3m/min, overlap width 8～10cm, sandblasting efficiency S=1*1.
5*60～1*3*60=90～180
.

2.
1.
2 Bottom wheeled robot

The bottom wheeled robot sandblasting system adopts the structure of a movable trolley equipped with a robotic arm.
The end of the robotic arm carries a sandblasting gun head.
The trolley is equipped with an observation room.
The construction staff can observe the spraying operation in time and stay in the observation room.
It can control the movement, steering, start and stop of the trolley and the movement of the mechanical arm
.
The robot is also equipped with 8 degrees of freedom, which can take into account the automatic sandblasting of the bottom of the steel truss and the bottom of the bridge deck
.

The technical parameters of the bottom sandblasting robot are shown in Table 3 and Figure 6 (the 8 axes in the figure are the same as the 8 axes in Table 1)
.

Table 3 Bottom sandblasting robot parameters

Figure 6 Bottom sandblasting robot

Before the bottom sandblasting robot runs, according to the structural characteristics of the bridge deck block and the main truss, the running track is edited and a special program is generated, as shown in Figure 7
.
Starting from the starting point, the robot cooperates with the 8-axis linkage to complete the spraying work of the steel deck and truss of the entire bridge deck
.

Figure 7 Sandblasting track of bottom sandblasting robot

Through the process test comparison, the bottom blasting robot process parameters are basically the same as the top blasting robot parameters, that is, the blasting pressure is 8.
4kgf/cm2, the flow rate is 40m³/min, the spraying distance is 800～1000mm, and the spray gun swing angle is 70°.
Spray width S=2*l*tan(70/2)=1120mm, moving speed 1.
5～3m/min, overlap width 8～10cm, sandblasting efficiency S=1*1.
5*60～1*3*60= 90～180
.

2.
2 R&D and application of intelligent spray paint system

The intelligent paint spraying system consists of 2 cantilevered robots.
The cantilever spraying robot is equipped with a total of 8 axes to control the movement of the spray gun
.
The technical parameters of the painting robot are shown in Table 4 and Figure 8
.

Table 4 Parameters of cantilever painting robot

Figure 8 Cantilever painting robot

The entire system performs corresponding spraying work from the starting point of spraying, and the direction of the working path is shown in Figure 9
.
Cooperate with 8-axis linkage to complete the spraying work of the entire bridge deck steel deck and inclined top surface
.

Figure 9 Painting running path of cantilever painting robot

After many actual painting experiments, when the spray gun is too close to the workpiece, the atomization effect of the paint mist is poor, which affects the quality of the coating film
.
When the spray gun is too far away from the workpiece, the painting rate is low and the paint waste is serious.
After comprehensive consideration, the best process parameters are selected: nozzle diameter 0.
055in, nozzle model 855, spraying width 0.
5～0.
8m, overlap width 3～ 5cm, moving speed 150～300mm/s, painting pressure 0.
6MPa, flow rate 3m³/min, spray distance 500mm, angle between spray gun and working surface is 90° visual spraying efficiency: S=0.
377*(120～250) *3600/1000=163～340m2/h
.

The actual work of the cantilever painting robot is shown in Figure 10
.

Figure 10 Working status of cantilever painting robot

3 Intelligent monitoring system technology

According to the requirements of intelligent painting operations, develop a real-time refined production data management system.
According to the principle of distributed control (combination of centralized control and decentralized control), an editable logic controller (PLC) is used to fully control the main equipment and valves.
The running status of will be reflected on the display
.
With the display screen and touch screen as the system's operation and monitoring platform, the entire system is divided into three levels: equipment layer, control layer, and monitoring layer
.
The equipment layer uses PLC to remotely connect each I/O controlled device, the control layer uses PLC as the control host of the system, and the monitoring layer uses display and color touch screen as the system's monitoring platform to dynamically display the operating status of each I/O device
.
Provide a user-friendly operating environment for operators to keep abreast of on-site equipment status (centralized control room), as shown in Figure 11
.

Figure 11 Intelligent monitoring large screen

In addition, the system integration control is equipped with a management software system.
The management system includes the following contents: dynamic display of the operating status of each I/O device, control of the operation/stop of field equipment; video monitoring of the operation of the on-site intelligent coating system, And archive it as a construction video; in addition, it can also check the time and related problems of the alarm information generated by the equipment (due to the modular design of the equipment, the alarm information for fault location is very accurate), equipment operation status, equipment maintenance records, historical operation records, Operating time (including the corresponding sprayed beam section number), operators and other data are statistically recorded.
The above information can be transmitted to the building information modeling (BIM) system through the industrial 5G network, so that the overall process of intelligent construction operations can be traced Sex
.

At the same time, the painting room is equipped with temperature and humidity sensors, dust concentration sensors, paint mist detectors and other sensor alarm devices.
The feeding system is equipped with pressure sensors that can monitor the sandblasting pressure, spraying pressure and other data to ensure coating.
The installation and construction environment and equipment status meet the requirements
.

4 Advantages of intelligent coating production

4.
1 Efficacy improvement

Take the standard large section of the Wenzhou Oujiang Northkou Bridge as an example for the efficacy analysis, as shown in Table 5
.

Table 5 Power analysis

It can be seen from Table 5 that the overall efficiency of sandblasting is increased by 500%, and the efficiency of painting is increased by 114%.
The overall improvement effect is obvious.
The process parameters will be further optimized in the future to improve the efficiency
.

4.
2 Quality improvement

The intelligent sandblasting robot system is controlled by the system to ensure the uniformity of the sandblasting quality on the surface of the steel beam, uniform spraying, stable quality, safe and efficient
.
Replace manual operations with mechanical equipment to realize intelligent automated operations, online intelligent monitoring, real-time monitoring of the production process, and reduce the occurrence of quality defects caused by labor due to personal habits and work experience.
The system has the optimization and online monitoring of production process data and process parameters.
And fault diagnosis and treatment, full tracking of manufacturing information, product quality traceability, lean production management and other functions, intelligently coordinate work under the unified management of the central computer
.
According to statistics, the coating thickness of the first round steel truss girder section of Wenzhou Oujiang Beikou Bridge is uniform, the thickness deviation is controlled within ±30μm, the minimum coating adhesion is 6.
8MPa, and the average is 8.
5MPa, all exceeding the specification requirements
.

4.
3 Safety improvement

Replace manual operations with mechanical equipment to achieve intelligent automated operations, online intelligent monitoring, real-time monitoring of the production process, equipment fault diagnosis and early warning, the system has visual processes and offline programming trajectory planning functions, which greatly reduces the time and space of manual operations, and improves Intrinsically safe
.
The spray painting system adopts explosion-proof design, and uses explosion-proof motors and electrical components.
The main electronic control components are arranged in the explosion-proof electric control box to ensure the safe operation of the spraying system
.
In view of the dangerous factors generated in the process of sandblasting and painting, it has established pre-judgment and early warning of potential safety hazards and intelligent operation of the system to ensure safe production
.

5 Conclusion

As one of the research results of intelligent steel bridge manufacturing, the intelligent coating production line has been successfully applied in the coating construction of the steel truss girder of the Beikou Bridge on the Oujiang River in Wenzhou, greatly improving the production efficiency and quality of the steel truss girder bridge coating and achieving good economic benefits.
And social benefits, it has extensive promotion value in the industry
.

Intelligent bridge coating is the future industry development trend, and it will be more popularized
.
In order to better promote the development of the coating industry, upstream and downstream companies must continue to optimize and improve the performance of intelligent coating equipment, and continue to optimize the application performance of intelligent coating equipment in complex spaces, such as some blind corners and edges of steel bridges.
Intensify and other positions, continue to improve the stability of the equipment, and continue to deepen the development and application of intelligent coating quality inspection equipment
.