1 Preface

Coating device cattle production is often inseparable from the measurement and weighing of materials, where new projects, design institutes and owners to jointly explore the entire production process and layout, but also must be involved in measuring and weighing because of metering control and weighing control program often also causes coating production process and equipment layout of the larger changes in the determination of the investment costs, the owners are often willing to tilt to the measurement and weighing system can be said that the measurement and weighing of coating production has attracted more and more attention. Coating production measurement and weighing has increasingly attracted attention, this paper will discuss this topic from the following several.

2 classification

(1) according to the production process, coating device often includes two major workshops; resin workshop and paint selection workshop.

Resin workshop solvent metering, raw material metering, resin metering, etc.; Selection of paint workshop solvent metering and finished paint metering.

(2) According to the nature of the medium points; paint production in the measurement and weighing is often liquid and solid (powder) for more.

3 measurement and dosing control system composition

Solvent metering system as an example flowmeter fixed value control instrument, the solvent metering dosage system, the optional flowmeter has; elliptic gear flowmeter, turbine flowmeter and so on. This type of flowmeter can be directly installed in the main pipeline, and can be selected with in situ pointer or digital meter head, with in situ accumulation device and return to zero device, high-grade and in situ setting device. Transmission devices generally choose the integration of good. Control valves are often selected after the position of the switching valve, optional cylinder type ball or solenoid valve, the installation position is often set according to the needs of the process in the tank (tank) of the inlet pipeline or outlet pipeline.

The core of the system is a fixed-value control instrument, it is the solvent flow measurement and fixed-value control of special instruments, IDD-300-type fixed-value control instrument, for example, its output is a pulse volume, the control output for the relay contacts, pulse volume output has two kinds of output buffer and conversion output, the instrument has a total amount of total, batch, cumulative amount of a variety of display functions, the instrument with an 8031 microprocessor with a power failure protection The instrument is equipped with 8031 microprocessor with power failure protection function. Its working principle is; flowmeter incoming counting input pulse through the input protection "circuit," by the "input threshold" circuit to determine its high and low levels (0 ~ 1V low, 3 ~ 30V high) and then to the central processing part of the corresponding flow operation, cumulative operation, fixed-value control judgments and so on; Central processing part of the calculation results sent to the display unit for display, while the judgment results sent to the "output interface" circuit, in order to read the door for control, digital display and the keyboard are scanning method of the instrument's control relay output capacity is large, for the double-knife double-throw, ~ 220V/3A. in the production of coatings, in addition to solvents, there are raw materials in the viscosity is not high, but also the viscosity of the raw materials. There are raw materials in the viscosity is not high relatively clean liquid can constitute such measurement control system.

4 weighing and dosage system composition

4.1 weighing structure

Coating production, raw materials in the powder and some of the media should not be measured in the pipeline, the use of weighing devices to measure and control.

Weighing module weight transmitter (weighing terminal) - PLC - control valves (variable frequency motors, etc.)

Take a typical kettle weighing as an example; three weighing modules installed at the bottom of the reaction sign will transmit the weight signal of the kettle to the junction box, which will connect the output weight signal of the weighing module in parallel to the weighing terminal or weight transmitter, which will process the weight signal into the corresponding weight data. The weighing terminal generally provides certain input/output control functions to the field actuator, while the weight transmitter generally provides the weight data and other information to the upper system, such as PICDCS, through a specific form.

4.2 Classification of weighing and control

In production practice, there are often batching weighing, feeding weighing finished product weighing and so on.

Batching can be distinguished as sequential batching and continuous batching. Sequential dosage is more commonly used, a variety of materials in accordance with the set formula order to join the weighing meter (measuring tank), at any time only allowed - a kind of material added. Weighing control equipment to detect changes in the weight of the weighed material, and control the corresponding material silo discharge door and weighing material out of the door, this dosage is characterized by only a set of weighing device, simple structure, high precision. Continuous dosage; for some occasions that do not allow intermittent sequential dosage work, or require continuous work, continuous dosage can be used, all kinds of materials are weighed separately, and at the same time in accordance with the set flow rate added to the mixing meter (tank) in the mixing can be realized in the PIC to the PDD adjustment of the feed flow rate of this dosage is characterized by continuous feeding or proportional feeding, high precision, fast speed. Constant flow feeding; in some production processes that require constant flow feeding often take this more accurate weighing and control methods, when the weight of the weighing meter is between the lower and upper limit, the upper feeding port is closed, the weighing terminal calculates the current flow and the flow rate with the

Gross weight type quantitative control: gross weight type quantitative control process is relatively simple, the container or package is placed directly on the weighing platform, through the control of the discharge port switch to achieve quantitative control process, the liquid fixed-value loading is more often used in this form, which is characterized by a simple structure, high precision.

Net weight type quantitative control: net weight type quantitative control process is through an intermediate metering bucket to complete the quantitative discharge process, the beginning of the metering meter discharge door closed, open the upper feeding port for fixed-value charging, to reach the target value of closing the feeding port, and open the opening of the mouth of the material will be put into containers or packages, and then enter into the next cycle of control, in order to improve the efficiency of the work, a variety of charging speeds can be taken, generally for the double-speed, i.e., fast and slow addition, but also the opening of the mouth will be put in containers or packaging, and then into the next control cycle. That is, fast and slow addition, can also be used to double weighing wheel for high-speed fixed-value control, which is characterized by integrated structure, high precision and speed.

Reduced-weight quantitative control: Reduced-weight quantitative control device is a weighing module directly installed in the storage of materials, through the weighing terminal to weigh the storage silo, and at the same time control the storage silo discharge port, so as to control the silo each time the weight of the reduction of the material can be achieved by the purpose of quantitative discharge. Reduced weight quantitative control method can be used in the factory's existing storage material can be directly modified, the implementation of the project is relatively easy, in the weight of the storage silo is not very large, or the requirements of the discharge precision is not high in the case can be used in this way, which is characterized by a simple structure, medium precision.

5 Conclusion

From the above discussion can be seen, coating production in the measurement and weighing, although there are many common things, but practical often according to the characteristics of specific media and production process requirements, can not be generalized.