The centralized paint transfer system is a pipeline network composed of various components and conveying pipelines. It can not only ensure that the paint is conveyed at an appropriate pressure and flow rate, but also control the temperature and other characteristics of the paint. Its main components include: paint tank, circulation tank, conveying pump, voltage regulator, filter, pressure regulator and temperature control system. Generally, a centralized paint transfer device composed of these components and pipelines is called a module in engineering, and each module can have several paint supply outlets. When the system is running, usually a transfer pump pumps paint and thinner into the paint mixing tank for adjustment. The adjusted paint is pumped into the circulating tank by the same transfer pump, and then the transfer pump passes the paint in the circulating tank. The pressure regulator and filter are pumped into the main pipeline and sent to each gun station for spraying, and the remaining paint is returned to the circulating tank through the pipeline network. Since the paint is circulated in a closed system, the pollution of the paint by external impurities is avoided, thereby ensuring the cleanliness of the transported paint. The design of the centralized paint distribution system is described in detail below.
Design requirements for paint mixing rooms
As the installation space of the centralized paint transfer system, the paint mixing room is also the source of paint transportation. It has certain requirements for the location, cleanliness, supply and exhaust air, temperature and humidity, and antistatic of the paint mixing room. Here is a brief introduction to the design requirements of the paint booth.
First of all, in the preliminary planning, the paint adjustment room should be relatively close to the paint line, in order to reduce the length of the conveying pipe network, reduce investment costs, and reduce the amount of paint circulation, which is also convenient for color change cleaning.
Secondly, the paint room has high requirements for cleanliness. Generally, a new air supply air conditioner is used, and the temperature and humidity can be controlled to ensure that the paint is allocated and transported in the temperature and humidity environment required by the process, and reduced by adjusting the humidity Generation of static electricity.
Third, there will be a certain amount of solvent volatilization in the process of paint preparation and transportation. To discharge these volatile solvents to the outside, a good air supply and exhaust system is required. For air supply and exhaust mode, the number of air changes is generally required to reach 15-30 times / h.
Finally, the anti-static of the paint room is very important. Generally, epoxy resin or terrazzo conductive floor is used, which is selected according to the investment cost of the owner. At least one lead wire (galvanized flat steel or copper bar) is reserved in the paint mixing room as the main electrostatic discharge access point for the centralized paint distribution system. The plane layout of the paint booth in the painting workshop is shown in Figure 1.
The basic definition of the paint cycle is: it consists of multiple supply pipelines and is designed into a corresponding pipeline network, which is not only used to provide paint to the gun station, but also maintains and controls the characteristics of the paint's process requirements. The working mode of supplying paint and pipeline to each gun station. There are three types of paint circulation methods: dead-end (supervisor) circulation system, two-line circulation system and three-line circulation system.
1. Dead-end (supervisor) circulation system
The dead-end cycle (see Figure 2) system is the simplest system. It supplies paint from a central source to each gun station, and each pipe to the gun station is a single tube. The main loop sends paint to each gun. Stand and then return to the paint booth. Its advantages: simple design, easy operation, less investment, and only a small amount of paint filling system; its disadvantages: not suitable for automotive metal paint, difficult to control the paint temperature, difficult to change colors, because each outlet All are cleaned separately.
2.Two-wire circulation system
The two-line circulation system (see Figure 3) is used to effectively control the pressure of the paint gun station through the change of the supervisor. The paint is supplied to each gun station from a central source. Each exit to the gun station can be circulated. Go to each gun station, and then cycle back to the paint booth. Its advantages: the supervisor is divided into a paint supply pipe and a return pipe, and the paint can be recycled to the gun station to ensure a good circulation of the paint. Because the two-line circulation pipeline can eliminate the gun station paint pressure regulator, the system is relatively simple, easy to change colors, and save energy at the same time, so it is the mainstream model in the current world automotive industry; Add gun exits at will.
3.Three-line circulation system
The three-wire circulation system (see Figure 4) is a more complicated system. The main director is divided into a paint supply pipe and a return pipe. The paint can be recycled to the gun. Each gun station is equipped with a separate regulator to adjust the outlet pressure. Its advantages: the outlet pressure of each gun station is controlled separately. If the spraying station is increased, the gun station outlet can be added. Its disadvantages: the design is complicated, the cost investment is large, and the paint is filled more.
Composition of centralized paint distribution system
The centralized paint transmission system adjusts the paint for mixing, filtering, voltage stabilization and parameter adjustment. After pressurization, it is sent to the paint supply system of each spraying station through the pipeline. It has the advantages of consistent station parameters, small color difference, convenient operation, high coating utilization rate, high efficiency, safety and convenient management. It is particularly suitable for continuous production of multiple paint types, multiple stations and large output, and is widely used in automobiles, etc. The production area is adopted by modernization and large-scale production. A paint transfer system generally consists of the following 4 parts.
1.Pump module and paint control element
Pump modules and paint control elements are the heart of a centralized paint supply system. It mainly includes:
(1) Agitators, filters, pressure regulators, pressure regulators and back pressure regulators for fluid handling elements
(2) Paint delivery pump;
(3) Paint buckets for paint supply components (circulating buckets, paint buckets), level controllers, automatic paint replenishment systems, and feed pumps, etc.
(4) Hydraulic components of power components, air filters, pressure regulators, oil misters and runaway protectors.
2.Paint pipeline network system
The paint pipe network system is different according to the requirements of different coating performance and the distance, material and specifications of the gun station. The design of the pipe network system will be described in detail below.
3. Gun Station
The gun station is composed of multiple channels of paint, solvent and air interface, and contains various quick-change connectors, valves, pressure regulators and hoses. When the spray gun is connected to the corresponding exit of the gun station, it can get the supply of paint, air, etc. for spraying operations.
It can adjust and monitor the temperature, flow and pressure of paint through the touch screen or the man-machine interface of the industrial computer. It has the functions of setting, controlling, displaying, alarming and recording, and can upload the data to the central control room via the network. . The function of the control system is selected according to the actual needs of customers.
Design of centralized paint distribution system
The above describes the installation conditions, circulation methods, and system configuration of the centralized paint transfer system. At present, the mainstream two-line paint circulation system is widely used. The following is a detailed introduction to the design of a complete solvent-based two-line paint transfer system.
Before designing the system, the customer's process input data must be clear (see Table 1). According to the input basis provided by the customer, the design of the centralized paint delivery system can be completed. The input data mainly includes:
(1) Public power water (cold water, hot water or steam), electricity and compressed air;
(2) Coating parameters: coating density, viscosity, solid content and coating type (solvent-based or water-based paint);
(3) Maximum spraying flow rate and pressure for manual section, automatic section and make-up section;
(4) the number of gun stations and the distance between each gun station;
(5) Trend of workshop public power and HVAC;
(6) The floor plan of paint mixing room and spray booth.
2.Selection of paint conveying pump
According to the relevant input of the design input in Table 1, determine the selection of the paint delivery pump.
(1) The influence of flow factors on selection Q = Q1 + Q2, where Q is the working flow of the main pump; Q1 is the circulating flow, that is, the flow rate when the paint maintains a flow rate of 60 FT / min in the main pipe; Q2 is all guns Station spray flow.
(2) The influence of pressure factors on the selection p> pG + Δp + p other, p is the outlet pressure of the main pump, pG is the working pressure of the spray gun, Δp is the pressure loss, and p is the other pressure in the pipeline. Loss, so you must consider this factor when selecting a model. Based on the calculated flow rate and main pump output pressure, a suitable main pump can be selected.
3.Design of conveying pipe network
The entire paint conveying pipe network is the main artery of paint conveying. Excellent pipe selection and design is to ensure the high quality of paint spraying. The manufacturing process, material, connection method and reducing diameter of the pipeline directly affect the paint spraying quality of the paint cycle machine.
(1) Pipeline manufacturing process and material selection are based on different paint types. In general, water-based paints are sst316 and solvent-based paints are sst304. Be sure to choose products from large first-tier manufacturers and companies that have passed the quality management system certification, so as to fully ensure the quality of the pipeline. Generally, cold drawn seamless stainless steel pipes are selected and passivated. The working pressure is at least 300 pis (1 psi = 6.895 KPa).
(2) Linkage of pipelines The main circulation loops generally use card sleeves or automatic argon arc welding links, or card sleeves and automatic argon arc welding methods, that is, 6 m section card sleeve links and 6 m section automatic argon arc welding links. Select according to customer requirements.
(3) Reduction design of the pipeline According to the design input in Table 1, we designed the two-line centralized paint transfer system delivery pipe network. Determine the size of the paint pipeline, including the supply and return pipes, the supply and return pipes, and the supply and return hoses in the manual section and the automatic section, as shown in Table 2.
From the analysis in Table 2, it is concluded that except for changes in the supply pipe diameter and return pipe diameter, the other inputs do not need to be changed, that is, they must be determined before the design begins. By using the pipeline design software developed by the world's largest fluid equipment company, the United States Graco Corporation, to enter the pipeline diameter, the relevant data such as flow rate, gun station pressure, and pressure loss can be obtained, as shown in Table 3.
It can be seen from Table 3 that the velocity and pressure of each gun station meet the design requirements. In actual design, if the pressure or flow rate of some gun stations does not meet the requirements, we adjust the diameter of the pipeline until it is adjusted to meet the corresponding flow rate and pressure. The total system flow and module outlet pressure are also calculated at the same time, which determines the selection of the paint delivery pump.
4.Paint temperature control and hydraulic power system
(1) Paint temperature control system High-quality paint delivery must ensure a constant paint temperature, especially the construction of water-based paint, which requires higher temperature and humidity of the spraying environment and constant paint temperature. Under normal circumstances, the spray booth greenhouse is controlled at (23 ± 1) ℃ / 65 ～ 75%, and the paint temperature is (23 ± 1) ℃. The control of paint temperature is usually controlled by a pipe-in-pipe system. Its principle is: heat and heat are exchanged with the paint through the circulation of cold and hot water (cold water temperature 7-12 ° C, hot water temperature 35-45 ° C). The flow of hot water is controlled by the proportional valve controlled by the PLC to control the opening of the proportional valve to achieve the purpose of controlling the temperature of the paint.
(2) The hydraulic power system is gradually eliminated due to the large noise, high pulse and easy to condense water of the air plunger pump, and replaced by the hydraulic plunger pump with large flow, low noise, small pulse and stable operation. Since the hydraulic motor is used as the driving device of the lower cylinder of the pump, as a power source of the hydraulic motor, a hydraulic power system must be configured. The main considerations in terms of design are:
① The main pump should be a constant pressure variable pump, which can ensure a stable flow and pressure and make the hydraulic motor run stably. In addition, when several sets of paint transmission and adjustment systems are closed for maintenance, there is no need to adjust the parameters of the hydraulic station. The excess flow and pressure are discharged through the relief valve and the relief valve, which protects the hydraulic control unit of the hydraulic motor and will not cause Over-voltage operation.
② The 15% margin of the entire hydraulic power system should be considered to facilitate the increase in the use of paint transmission systems in the future. Q = Q1 + Q1 × 15%, where Q is the total flow of hydraulic oil and Q1 is the flow of hydraulic oil required for the paint delivery system.
③ After the hydraulic oil is cooled, the temperature is 30-40 ° C, and the cooling source is 7-12 ° C. The chilled water is cooled by a plate or shell heat exchanger, and the cold water flow is controlled by a proportional valve.
④Hydraulic oil circulation pipeline adopts dead-end circulation (single-line type). Because of high pressure transmission (hydraulic oil outlet pressure is usually around 10MPa), high pressure seamless steel pipes must be used. High pressure flanges are used for main pipe connection. Connection, inlet and outlet are equipped with high pressure ball valves for maintenance.
⑤ The main road should not be laid on the top of the paint tank as far as possible. It should not be on the same level as the paint tank to prevent the hydraulic oil from dripping on the paint tank during maintenance or pipeline leakage, causing paint pollution (see Figure 5).
The centralized paint transfer system has been widely used in major automobile painting workshops, and it has fully demonstrated its advantages in terms of high cycle, frequent color change and high quality. An excellent centralized paint distribution system brings together the ingenuity and experience of experienced designers and plays an inestimable role in modern automobile production.