Method for optimizing a water cooling channel structure of a central impression cylinder of a flexographic printing machine

Abstract

The application discloses a kind of optimization methods of soft printing machine center impression cylinder water cooling flow channel structure, step one, according to the actual structure parameter of cylinder, define the boundary condition of model, material attribute, initial condition, select fluid model and convergence algorithm, establish the finite element model of cylinder in combination with actual working condition, the geometric model is established;Step two, calculate the temperature distribution of cylinder section and the maximum temperature difference of cylinder surface axial, with the minimum temperature difference as the optimization goal, the inlet flow rate is optimized by single factor method;Under the optimal inlet flow rate, the flow channel structure is optimized by Taguchi method, and the flow channel structure parameters that minimize the axial temperature difference of the cylinder surface are selected as the optimization result;The application is based on finite element simulation method, considers the double action of oven heating and cooling water cooling on cylinder body, reduces the axial temperature difference of cylinder body surface as optimization index, optimizes the structure parameters of center impression cylinder cooling water flow channel, improves the uniformity of cylinder surface temperature.

Description

Technical Field

[0001] This invention relates to the field of printing equipment technology, specifically to an optimization method for the water-cooled flow channel structure of the central impression cylinder of a flexographic printing press. Background Technology

[0002] Flexographic printing, characterized by its green, environmentally friendly, energy-efficient, and high-performance characteristics, is a core technology in my country's printing and packaging industry. Satellite flexographic printing presses, as representative equipment, are widely used in carton pre-printing, flexible packaging printing, and paper printing due to their high printing speed, high registration accuracy, and stable structural performance. The working principle of a satellite flexographic printing press involves arranging the printing colors evenly and symmetrically around a central impression cylinder. The printing material adheres closely to the surface of the central cylinder, and each color cylinder rotates at the same surface linear velocity as the central cylinder, thus achieving multi-color printing.

[0003] During the printing process, as the hot air nozzles (heated air temperature reaches 70-80℃) of the drying devices between each color group dry the surface of the printed film, the dissipated heat heats the surface of the central impression cylinder. Furthermore, the friction between the printed film and the central impression cylinder causes the continuously heated surface of the cylinder to expand and deform, leading to a decrease in registration accuracy. Therefore, to address thermal expansion, a built-in circulating water cooling method is often used for temperature control. However, existing cooling systems often fail to achieve optimal control results due to a lack of overall and local coordination in their flow channel design. Moreover, since there are many models of central impression cylinders, each requiring different cooling structures, optimizing the flow channel structure using trial and error is time-consuming and labor-intensive. Therefore, proposing an efficient, low-cost, and precise optimization design method is an effective measure to shorten the cylinder development cycle, reduce development costs, and improve the temperature control accuracy of the cylinder surface. Summary of the Invention

[0004] This paper presents an optimized method for the water-cooled flow channel structure of the central impression cylinder in a flexographic printing press. This method ensures a constant and uniform temperature on the surface of the impression cylinder during printing, preventing the expansion of the cylinder surface from affecting registration accuracy and thus avoiding phenomena such as missed printing, smearing, and dirty printing. Regulating the surface temperature of the central impression cylinder through circulating cooling water effectively prevents printing problems caused by cylinder thermal deformation, thereby improving the printing quality of satellite flexographic printing presses.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is: an optimization method for the water-cooled flow channel structure of the central impression cylinder of a flexographic printing machine;

[0006] Step 1: Establish a geometric model based on the actual structural parameters of the drum. Combined with the actual working conditions, define the boundary conditions, material properties, and initial conditions of the model. Select the fluid model and convergence algorithm to establish the finite element model of the drum.

[0007] S101: Establish a three-dimensional geometric model of the drum. The structure of the drum includes an outer drum, an inner drum, a spiral flow channel between the outer drum and the inner drum, a central shaft, water inlet pipes and water outlet pipes coaxially mounted at both ends of the central shaft, a connecting water pipe connecting the water inlet and outlet pipes and the spiral flow channel, and end caps on both sides.

[0008] S102: Define the drum heat exchange model; the multi-stage heat exchange between the drum and the oven hot air and cooling water includes convection and thermal radiation between the drum and the oven hot air, and the calculation expression is:

[0009]

[0010] In equation (1): q is the heat transferred from the hot air in the oven to the drum; T sa Indicates the temperature of the drum body; T air Indicates the air temperature near the drum; T air∞ The temperature of the air furthest from the drum is represented by σ, which is the Boltzmann constant; ε represents the temperature of the air furthest from the drum. pol ε represents the thermal radiation coefficient of the drum body. air The coefficient of thermal radiation of air is represented by α; α is the convective thermal conductivity.

[0011] The formula for calculating the convective heat transfer at the solid-liquid interface formed between the cooling water and the inner wall of the drum in the spiral flow channel is as follows:

[0012] q s =h s (t w -t s (2);

[0013] In equation (2): q s h is the heat transferred from the drum to the cooling water. s t is the convective heat transfer coefficient between the cooling water and the inner wall of the drum. s Water temperature; t w The surface temperature of the flow channel;

[0014] S103: Define the simulation boundary conditions; the boundary conditions include the oven heat source temperature and wind speed, the drum rotation speed and initial temperature, and the cooling water flow rate and temperature at the inlet; the expression for calculating the inlet water velocity v based on the cooling water flow rate is:

[0015]

[0016] Equation (3); where: Q is the flow rate, and A is the cross-sectional area of ​​the inlet pipe of the central impression roller;

[0017] S104: Defines the material properties of the cooling water, drum, and air zone; each material property includes density, specific heat capacity, and thermal conductivity.

[0018] S105: Select the turbulence model of the cooling water in the spiral flow channel and the convergence algorithm of the finite element simulation;

[0019] The Reynolds number of the cooling water boundary inside the spiral flow channel is calculated based on the cross-sectional shape. The flow state of the cooling water inside the spiral flow channel is analyzed, and the calculation expression is as follows:

[0020]

[0021] In equation (4): l is the width of the flow channel cross section, and R is the nominal radius of the spiral flow channel;

[0022] Reynolds number R in a spiral tube e The calculation expression is:

[0023]

[0024] In equation (5): v, ρ, and μ are the flow velocity, density, and viscosity coefficient of the cooling water, respectively, and d is the characteristic length of the spiral flow channel cross section;

[0025] Determine the fluid state within the helical flow channel, by Re > Re bd The fluid state inside the spiral flow channel is determined to be turbulent; further, a turbulence model for the cooling water inside the spiral flow channel is selected.

[0026] Step 2: Calculate the temperature distribution of the drum cross section and the maximum axial temperature difference on the drum surface. With the minimum temperature difference as the optimization objective, the inlet flow velocity is optimized using the single-factor method. Under the optimal inlet flow velocity, the Taguchi method is used to optimize the flow channel structure, and the flow channel structure parameters that minimize the axial temperature difference on the drum surface are selected as the optimization result.

[0027] S201: Obtain the surface temperature distribution curve and maximum axial temperature difference of the drum through finite element simulation; with the goal of reducing the maximum axial temperature difference, optimize the inlet flow rate using the single-factor method and select the optimal cooling water inlet flow rate;

[0028] S202: Under the optimal cooling water inlet flow rate, the Taguchi experimental design method was used to optimize the spiral flow channel structure parameters and select the flow channel structure that minimizes the axial temperature difference on the drum surface.

[0029] Preferably, in step S102: an air zone with n-1 hot air inlets is established, assuming the number of printing color groups is n, and the blowing speed and temperature of the oven outlet of the air zone are defined as the heat load of the roller.

[0030] Preferably, the flow channel structure parameters include the spiral flow channel pitch, the flow channel cross-sectional height, and the flow channel cross-sectional width.

[0031] Preferably, the turbulence model uses the shear stress transport k-omega (SSTk-ω) model for numerical simulation; the convergence algorithm uses a coupled solver to solve the computational object in a steady state.

[0032] Preferably, the inlet flow velocity is selected as 0.8m / s, 1.5m / s, 2m / s, 3m / s, or 5m / s.

[0033] Preferably, during the establishment of the finite element model, the coupling surface between the air domain and the roller is defined as a moving wall, the movement type is rotation, and the rotation speed is the same as the roller rotation speed.

[0034] Preferably, the spiral channel pitch is selected as 1500mm, 1000mm, 800mm, or 500mm; the channel cross-sectional height is selected as 15mm, 25mm, 30mm, or 35mm; and the channel cross-sectional width is selected as 100mm, 150mm, 200mm, or 300mm.

[0035] The beneficial effects of this invention are:

[0036] This invention, based on the finite element method, considers the dual effects of oven heating and cooling water cooling on the roller body. It uses reducing the axial temperature difference on the roller surface as an optimization index to optimize the structural parameters of the cooling water flow channel in the central imprinting roller, thereby improving the uniformity of the roller surface temperature. This optimized design method can effectively shorten the roller development cycle, reduce development costs, and improve the accuracy of roller surface temperature control. Attached Figure Description

[0037] Figure 1 This is a flowchart of the present invention;

[0038] Figure 2 This is a schematic diagram of the satellite-type flexographic printing press structure of the present invention;

[0039] Figure 3 This is a schematic diagram of the central impression cylinder structure of the present invention;

[0040] Figure 4 This is a schematic diagram of the finite element model of the central impression cylinder of the present invention;

[0041] Figure 5 This is a schematic diagram of the drum spiral flow channel structure of the present invention;

[0042] Figure 6 This is a simulated temperature cloud diagram of the drum cross-section of the present invention;

[0043] Figure 7 This is a graph showing the axial temperature difference on the surface of the drum according to the present invention;

[0044] Figure 8This is a bar chart showing the axial temperature difference on the surface of the roller at different inlet flow rates according to the present invention;

[0045] Figure 9 This is a bar chart showing the axial temperature difference on the surface of the roller with different flow channel structures according to the present invention.

[0046] In the diagram: 1. Unwinding device; 2. Ink cartridge; 3. Plate cylinder; 4. Anilox roller; 5. Ink unit drying oven; 6. Central impression cylinder; 7. Drying device; 8. Rewinding device; 9. Outer cylinder; 10. Spiral guide plate; 11. Inner cylinder; 12. End cap; 13. Bolt; 14. Central shaft; 15. Sealing ring; 16. External water pipe; 17. Water pipe. Detailed Implementation

[0047] The technical solutions of the present invention will now be clearly and completely described in conjunction with the accompanying drawings.

[0048] The present invention will be described in detail with reference to the accompanying drawings, and the specific steps are as follows:

[0049] like Figure 1 As shown, the technical solution provided by this invention, a design method for a circulating water cooling channel of the central impression cylinder in a satellite-type flexographic printing press, includes: establishing a geometric model based on the actual structural parameters of the cylinder; determining the boundary conditions of the model, defining material properties and initial conditions based on actual working conditions; selecting a fluid model and convergence algorithm; establishing a finite element model of the central impression cylinder; calculating the temperature distribution of the cylinder cross-section and the maximum axial temperature difference on the cylinder surface; optimizing the inlet flow velocity using a single-factor method with the minimum temperature difference as the optimization objective; and optimizing the channel structure using the Taguchi method under the optimal inlet flow velocity. The channel structure parameters that minimize the axial temperature difference on the cylinder surface are selected as the optimization result.

[0050] like Figure 2 The diagram shows the structure of a satellite flexographic printing press. The overall printing structure consists of an unwinding unit, a printing unit, a drying unit, and a rewinding unit. The printing unit consists of a central impression cylinder, an oven, a printing plate cylinder, an anilox roller, and an ink cartridge.

[0051] This printing press is an eight-color printing press, with each color group arranged evenly and symmetrically around the central impression cylinder. Each color group is equipped with an oven to dry the substrate. The printing material moves in close contact with the surface of the central large cylinder, and the cylinder surface is continuously heated by the heat dissipated from the oven.

[0052] Furthermore, the drum heat transfer model is analyzed. Drum heat conduction is a multi-stage heat exchange process between the oven hot air, the drum body, and the cooling water. The gradient order of system temperature change is convection and thermal radiation between the outer drum and the oven hot air, and its calculation expression is:

[0053]

[0054] In the formula: q represents the heat transferred from the hot air in the oven to the drum; T sa Indicates the temperature of the drum body; T air This indicates the air temperature near the drum (oven outlet temperature); T air∞ The temperature of the air furthest from the drum is represented by σ, which is the Boltzmann constant; ε represents the temperature of the air furthest from the drum. pol ε represents the thermal radiation coefficient of the drum body. air α represents the thermal radiation coefficient of air; α is the convective thermal conductivity.

[0055] The formula for calculating the convective heat transfer at the solid-liquid interface formed by the cooling water and the inner wall of the outer drum is as follows:

[0056] q s =h s (t w -t s )

[0057] In the formula: q s h is the heat transferred from the drum to the cooling water. s t is the convective heat transfer coefficient between the cooling water and the inner wall of the drum. s Water temperature; t w This refers to the surface temperature of the flow channel.

[0058] like Figure 3 As shown, the roller structure includes an outer roller 9, an inner roller 11, two end caps 12, and a central shaft 14. Four spiral guide plates 10, welded to the inner roller and extending axially, are located between the inner and outer rollers. A rotary joint is connected to one end of the central shaft, and a chiller is connected to the outside of the rotary joint to supply cooling water to the entire cooling roller system in a metered manner. The spiral guide plates are welded to the inner roller, and the end caps are welded to the rollers and the central shaft. The inner and outer rollers are assembled using a heat-fitting method.

[0059] The outer and inner rollers are made of Q275 carbon steel with high thermal conductivity, effectively improving the heat exchange efficiency between the cooling water and the rollers. Simultaneously, several Q275 spiral water channel baffles are welded to the outer surface of the inner roller to form an axially rotating spiral water channel, further enhancing heat conduction. To prevent corrosion of the spiral pipes and inner and outer rollers during long-term use, the materials are polished and chrome-plated. The inlet and outlet channels are coaxially fitted, and the central shaft is made of Q345 structural steel to improve roller strength and ensure the concentricity of the central shaft and the roller body.

[0060] This invention achieves boundary condition loading for oven heating of the drum by establishing an air zone with 7 hot air inlets. The oven outlet blowing velocity of this air zone is defined as 30 m / s, and the temperature is 70°C.

[0061] Figure 4The finite element model of the central impression cylinder is used, and the rotational speed n of the cylinder is assigned as 1.33 rad / s based on the actual printing speed.

[0062] The formula for calculating the drum rotation speed is:

[0063]

[0064] Where v is the printing speed and r is the roller radius.

[0065] The model roller and cooling water are rotating, and the air zone slides relative to the outer wall of the roller. The coupling surface between the air zone and the roller is set as a moving surface, the movement type is rotation, and the rotation speed is the same as the roller's rotation speed.

[0066] The initial temperature of the drum is set to 20℃. Considering the influence of materials on heat transfer, various material parameters are added during the construction of the drum finite element model, mainly including the density, specific heat capacity, and thermal conductivity of cooling water, outer drum, and air domain.

[0067] The cooling water has a density of 998.2 kg / m³, a specific heat capacity of 4182 J / (kg·K), and a thermal conductivity of 0.6 W / (m·K).

[0068] The outer roller is made of Q275, which has a density of 7850 kg / m3, a specific heat capacity of 480 J / (kg·K), and a thermal conductivity of 48.9 W / (m·K).

[0069] The air density is 1.225 kg / m³, the specific heat capacity is 1006 J / (kg·K), and the thermal conductivity is 0.024 W / (m·K).

[0070] The cooling water inside the flow channel undergoes heat conduction with the outer roller, resulting in a cooling water temperature of 4℃ and a flow velocity of 0.88 m / s at the inlet. The expression for calculating the inlet water velocity based on the cooling water flow rate is:

[0071]

[0072] In the formula: Q is the flow rate, and A is the cross-sectional area of ​​the inlet pipe of the central impression roller.

[0073] Furthermore, based on the cross-sectional shape, the boundary Reynolds number of the cooling water inside the spiral pipe is calculated, and the flow state of the cooling water inside the channel is analyzed. The calculation expression is as follows:

[0074]

[0075] In the formula: l is the width of the flow channel cross section, and R is the nominal radius of the spiral flow channel.

[0076] The expression for calculating the Reynolds number inside a spiral tube is:

[0077]

[0078] In the formula: v, ρ, and μ are the flow velocity, density, and viscosity coefficient of the cooling water, respectively, and d is the characteristic length of the spiral flow channel cross section.

[0079] Determine the fluid state within the flow channel, from Re > Re bd The fluid state inside the flow channel is determined to be turbulent.

[0080] Considering the flow state of cooling water in spiral pipes and the application range of fluid models, this invention selects the SST k-ω model, which combines the k-ε model in free flow and the k-ω model near the wall, as the turbulence model for cooling water in the flow channel. It is a low Reynolds number model that corrects some shortcomings of the k-ε and k-ω model formulas. The Coupled solver is selected to perform steady-state solutions for the computational object.

[0081] Furthermore, the temperature distribution curve of the drum surface and the maximum axial temperature difference were obtained through finite element simulation. With the goal of reducing the maximum axial temperature difference, the inlet flow velocity was optimized using a single-factor method to select the optimal cooling water inlet flow velocity. Under the optimal cooling water inlet flow velocity condition, the Taguchi experimental design method was used to optimize the spiral flow channel structure parameters, selecting the flow channel structure that minimizes the axial temperature difference on the drum surface. For example... Figure 5 This is a schematic diagram of the spiral channel pitch p, channel cross-sectional height h, and channel cross-sectional width b.

[0082] Furthermore, the inlet flow velocity is selected as 0.8m / s, 1.5m / s, 2m / s, 3m / s, or 5m / s.

[0083] Furthermore, the spiral channel pitch p, channel cross-sectional width b, channel cross-sectional height h, and number of channels n should satisfy the following relationship:

[0084] n*b <p

[0085] Remove structures that do not meet the requirements. The Taguchi method parameter table is as follows:

[0086] Table 1. Taguchi Orthogonal Experiment Table

[0087] 1 1500 100 15 2 1500 150 25 3 1500 200 30 4 1500 300 35 5 1000 100 25 6 1000 150 15 7 1000 200 35 9 800 100 30 10 800 150 35 13 500 100 35

[0088] like Figure 6 and Figure 7 The figures shown are the finite element simulation cloud map and the axial temperature curve of the drum surface, respectively.

[0089] like Figure 8The figure shows a bar graph illustrating the axial temperature difference on the drum surface at different inlet flow velocities. As the inlet flow velocity increases, the axial temperature difference on the drum surface gradually decreases. When the inlet water flow velocity exceeds 2 m / s, the decreasing trend of the axial temperature difference on the drum surface gradually diminishes. Considering both the drum cooling effect and energy loss, an inlet flow velocity of 2 m / s was selected for the following study.

[0090] like Figure 9 The bar chart shows the axial temperature difference on the roller surface for flow channel dimensions designed using the Taguchi method. Flow channel structure No. 7 exhibits the smallest axial temperature difference on the roller surface.

[0091] The present invention provides an optimization method for the water-cooled flow channel structure of the central impression cylinder of a flexographic printing machine, which can effectively shorten the cylinder development cycle, reduce development costs, improve the temperature control accuracy of the cylinder surface, ensure uniform temperature of the impression cylinder surface during the printing process, and improve printing accuracy.

[0092] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An optimization method for the water-cooled flow channel structure of the central impression cylinder of a flexographic printing machine, characterized in that, Step 1: Establish a geometric model based on the actual structural parameters of the drum. Combined with the actual working conditions, define the boundary conditions, material properties, and initial conditions of the model. Select the fluid model and convergence algorithm to establish the finite element model of the drum. S101: Establish a three-dimensional geometric model of the drum. The structure of the drum includes an outer drum, an inner drum, a spiral flow channel between the outer drum and the inner drum, a central shaft, water inlet pipes and water outlet pipes coaxially mounted at both ends of the central shaft, a connecting water pipe connecting the water inlet and outlet pipes and the spiral flow channel, and end caps on both sides. S102: Define the drum heat exchange model; the multi-stage heat exchange between the drum and the oven hot air and cooling water includes convection and thermal radiation between the drum and the oven hot air, and the calculation expression is: In equation (1): q is the heat transferred from the hot air in the oven to the drum; T sa Indicates the temperature of the drum body; T air Indicates the air temperature near the drum; T air∞ The temperature of the air furthest from the drum is represented by σ, which is the Boltzmann constant; ε represents the temperature of the air furthest from the drum. pol ε represents the thermal radiation coefficient of the drum body. air The coefficient of thermal radiation of air is represented by α; α is the convective thermal conductivity. The formula for calculating the convective heat transfer at the solid-liquid interface formed between the cooling water and the inner wall of the drum in the spiral flow channel is as follows: q s =h s (t w -t s ) (2); In equation (2): q s h is the heat transferred from the drum to the cooling water. s t is the convective heat transfer coefficient between the cooling water and the inner wall of the drum. s Water temperature; t w The surface temperature of the flow channel; S103: Define the simulation boundary conditions; the boundary conditions include the oven heat source temperature and wind speed, the drum rotation speed and initial temperature, and the cooling water flow rate and temperature at the inlet; the expression for calculating the inlet water velocity v based on the cooling water flow rate is: Equation (3); In the diagram: Q represents the flow rate, and A represents the cross-sectional area of ​​the inlet pipe of the central impression cylinder. S104: Defines the material properties of the cooling water, drum, and air zone; each material property includes density, specific heat capacity, and thermal conductivity. S105: Select the turbulence model of the cooling water in the spiral flow channel and the convergence algorithm of the finite element simulation; The Reynolds number of the cooling water boundary inside the spiral flow channel is calculated based on the cross-sectional shape. The flow state of the cooling water inside the spiral flow channel is analyzed, and the calculation expression is as follows: In equation (4): l is the width of the flow channel cross section, and R is the nominal radius of the spiral flow channel; Reynolds number R in a spiral tube e The calculation expression is: In equation (5): v, ρ, and μ are the flow velocity, density, and viscosity coefficient of the cooling water, respectively, and d is the characteristic length of the spiral flow channel cross section; Determine the fluid state within the spiral flow channel, by R e >Re bd The fluid state inside the spiral flow channel is determined to be turbulent; further, a turbulence model for the cooling water inside the spiral flow channel is selected. Step 2: Calculate the temperature distribution of the drum cross section and the maximum axial temperature difference on the drum surface. With the minimum temperature difference as the optimization objective, the inlet flow velocity is optimized using the single-factor method. Under the optimal inlet flow velocity, the Taguchi method is used to optimize the flow channel structure, and the flow channel structure parameters that minimize the axial temperature difference on the drum surface are selected as the optimization result. S201: Obtain the surface temperature distribution curve and maximum axial temperature difference of the drum through finite element simulation; with the goal of reducing the maximum axial temperature difference, optimize the inlet flow rate using the single-factor method and select the optimal cooling water inlet flow rate; S202: Under the optimal cooling water inlet flow rate, the Taguchi experimental design method was used to optimize the spiral flow channel structure parameters and select the flow channel structure that minimizes the axial temperature difference on the drum surface.

2. The method for optimizing the water-cooled flow channel structure of the central impression cylinder of a flexographic printing machine according to claim 1, characterized in that, In step S102: an air zone with n-1 hot air inlets is established. Assuming the number of printing color groups is n, the blowing speed and temperature at the oven outlet of this air zone are defined as the heat load of the roller.

3. The method for optimizing the water-cooled flow channel structure of the central impression cylinder of a flexographic printing machine according to claim 1, characterized in that, The flow channel structure parameters include the spiral flow channel pitch, flow channel cross-sectional height, and flow channel cross-sectional width.

4. The method for optimizing the water-cooled flow channel structure of the central impression cylinder of a flexographic printing machine according to claim 1, characterized in that, The turbulence model uses the k-omega model of shear stress transport for numerical simulation; the convergence algorithm uses a coupled algorithm solver to solve the computational object in steady state.

5. The method for optimizing the water-cooled flow channel structure of the central impression cylinder of a flexographic printing machine according to claim 1, characterized in that, The inlet flow velocities were selected as 0.8 m / s, 1.5 m / s, 2 m / s, 3 m / s, and 5 m / s.

6. The method for optimizing the water-cooled flow channel structure of the central impression cylinder of a flexographic printing machine according to claim 2, characterized in that, In the process of establishing the finite element model, the coupling surface between the air domain and the roller is defined as a moving wall, the movement type is rotation, and the rotation speed is the same as the roller rotation speed.

7. The method for optimizing the water-cooled flow channel structure of the central impression cylinder of a flexographic printing machine according to claim 3, characterized in that, The spiral channel pitch is selected as 1500mm, 1000mm, 800mm, and 500mm; the channel cross-sectional height is selected as 15mm, 25mm, 30mm, and 35mm; and the channel cross-sectional width is selected as 100mm, 150mm, 200mm, and 300mm.

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