Technological requirements and design of the hotte

Process requirements and design of large centrifugal casting machines

large centrifugal casting machines are mostly used to produce rolls. In centrifugal casting, the rotational speed of mold (also known as pipe mold) is very important, especially in roll production, which requires secondary pouring (adding core), especially the strict control of rotational speed, time and temperature. In order to meet the requirements of roll casting process, we designed a control system for large-scale centrifugal casting machine. The system controls and tracks the process of centrifugal casting roll in real time and accurately. In the past, most of the control systems of large centrifuges used open-loop automatic/semi-automatic control and electromagnetic speed regulation systems, which had poor working stability and many manual factors. Through the improved design of hardware and software, we adopt Siemens AC frequency converter (6SE70 Series) or DC speed regulation system (6RA70 Series). The sensor inputs the temperature, speed and host vibration measurement signals. After real-time calculation, the programmable controller can automatically track the set process curve as long as the corresponding working parameters are set on the interface; The whole production process realizes real closed-loop and automatic tracking control, eliminates the influence of many manual interventions and other factors, and improves product quality and production efficiency

1 main process parameters of large centrifugal casting machine

(1) the initial growth rate is actually degree: the centrifuge rises from static to the speed required for pouring

(2) maintain the solidification speed: the speed maintained by the centrifuge after pouring

(3) shutdown deceleration speed: the speed of deceleration shutdown is the shutdown speed

2 the system has entered a critical period of high fidelity in the industry. The hardware is composed of industrial computer, programmable controller PLC, analog input and output, DC speed regulation device or AC frequency converter and peripheral equipment. Figure 1 is the control system block diagram of large centrifuge

the industrial control computer mainly completes the remote real-time monitoring of the centrifugal casting machine and the production of management reports through PLC, and carries out real-time monitoring of the rotating speed of the centrifuge, the temperature of the molten metal in the cavity, the temperature of the bearing, and the working state of the vibration of the centrifugal casting machine. In the process of centrifugal casting, the computer can continuously and automatically record the temperature curve of molten metal in the mold

working principle: set the main process parameters of the centrifugal casting machine from the interface or call up the process parameters of the original product. When it meets the current product, the control curve of the current product will be displayed. Confirm according to the actual needs, and send signals such as starting pouring, primary pouring, secondary pouring through the control button; PLC obtains the actual speed of the current centrifugal casting machine according to the process parameters of the product and the input of on-site analog quantity. After calculation, it outputs an actual required speed through the analog quantity. At the same time, it diagnoses the working state of the centrifugal casting machine in real time through the centrifuge vibration signal and temperature signal input by the analog quantity; The working current signal of the motor of the centrifugal casting machine can diagnose the load of the centrifuge in real time, display the working curve of its products in real time, and confirm the quality of the products. Figure 2 and figure 3 are the electrical schematic diagrams of some large centrifuges used in Wuhan Iron and steel plant

3 software design

aims to enable users to arbitrarily set or call the process parameters and process curves of various products according to their own products, that is, to refresh the production scheme in time in the form of formula. According to the needs of users, through the real-time collection of on-site process parameters, the working state of centrifuge and motor, the figures and curves are displayed in real time in the form of animation, and the early warning is displayed at the same time, Provide users with real-time solutions to practical work problems

first save various process parameters from the interface, or reset various process parameters to generate a new formula. The following table shows the roll pouring process parameters.]

due to the strict requirements on the time of secondary pouring in roll production, whether the solidus temperature can be confirmed timely and correctly is the key to roll production. In the past, the solidus temperature was confirmed by manual observation, so the stability of product quality cannot be guaranteed. Now, through this software, the solidus temperature can be automatically confirmed and the shutdown time can be automatically controlled, so as to ensure the stability of roll quality. At the same time, through the automatic measurement of the vibration amplitude of the centrifugal casting machine itself and the bearing temperature of the centrifuge, this software can predict the working state of the centrifuge in time, Prompt in time if there is a problem to ensure the normal operation of the centrifuge

the confirmation software of temperature inflection point is designed based on the following two calculation formulas:

inflection point speed VI calculation formula: vi=vset -a (Vset -v actual) (where a is the empirical coefficient)

formula for calculating the slope Ki of the inflection point temperature curve:

ki= ∑ fj1- ∑ FJ/Ti

where J1 is (I-10 ~ i-6), j is (I-5 ~ I), that is, the temperature inflection point slope is obtained by subtracting the first five values from the first ten values of the inflection point and dividing the last five values by time, as shown in Figure 4

pouring temperature 1350 ℃, solidus temperature about 1100 ℃, rotational speed of supporting wheel of centrifugal casting machine 1400r/min (can be determined according to the inner diameter of the casting), braking time: large parts within 5min, gravity coefficient 100~110g

according to the above hardware configuration and software design principle, the process parameters shall be demonstrated and set on the interface or computer in advance before production, and the system operation shall be started after inspection. First, the control system converts the initial growth rate into an analog output signal through program design and calculation. This analog signal drives the motor through the DC speed regulating device or AC frequency converter to make the centrifuge accelerate evenly from the static state to the initial growth rate within time 1; After the centrifuge reaches this speed, carry out the second step of pouring high-temperature molten iron. After pouring, maintain this speed for cooling, solidification and molding; The centrifuge detects the temperature in the mold cavity during the high-speed rotating cooling solidification forming process. When the mold is cooled for a period of time, the mold temperature drops to the solidus temperature (as shown in Figure 4 at 1100 ℃), then the average growth rate is controlled to reach 20% The control system should control the centrifuge to slow down, and the centrifuge speed must be reduced from speed 2 to speed 3 within time 3, that is, the shutdown state; Then proceed to the next process, i.e. secondary pouring