Xinxiang Hexie Feed Machinery Manufacturing Co.Ltd
Control and operation of extrusion process
The control and operation of extruder is the most difficult in feed processing equipment. Because there are many factors affecting the quality of extruded products, they affect each other. And the effect of the results can`t be reflected immediately, but with a certain lag. If the operation is slightly improper and there is no timely adjustment, the production will not be able to proceed normally. Therefore, extruder operators must be trained. They must master the working principle and production theory of extruder. Operators need to be able to directly control and adjust the variables such as raw material composition, feed quantity, water content, temperature and pressure of the extrusion chamber and screw speed according to the changes through practical operation training, so as to ensure that the products can meet the requirements of quality standards.
First. The variables in the extrusion process
There are two main types of variables in the extrusion process:
1. The independent variables
They are given by the operator and do not change due to changes in other parameters. The independent variables that have a direct impact on the product during the extrusion process are:
(1) Composition of raw materials
This is the key variable of the product characteristics, and the required parameters and operation control mode are different for materials of different components in the extruder. Therefore, it is very important to carefully determine and precisely control the proportion of each component. Even a small change in the amount of some components can cause a great change in the extrusion process. If the fat content has a great influence on the extrusion effect, for example, the sugar content can easily lead to browning of the product. Therefore, once the formula and process for production is determined, the operator must operate in accordance with the formula ratio and requirements.
As one of the raw material components, water plays a special role in the extrusion process. A lot of material is added to the moisture in either the conditioning or the extrusion of the extrusion prior to extrusion, the friction to increase moisture is reduced, so it is controlled individually as a separate variable. Adding water to the material can be either a gas or a liquid. The amount of water added and the position of water added can change. The change of water will greatly affect the pressure and temperature in the extrusion chamber during the extrusion.
(3) The screw rotation speed
Some Extruder Screw speed in the design has been determined, can`t be changed at will. But some extruders, especially twin-screw extruders, are equipped with speed regulating devices. The operator can adjust and control the screw speed according to the need, which brings great convenience to the operation.
(4) Feed Quantity
This is an independent variable that must be controlled. The operator should strictly control the feeding amount in accordance with the process requirements, quality and output.
(5) Cutting speed
Adjusting the cutting speed is used to meet and ensure the shape of the product.
2. The dependent variable
It is the amount of change caused by the change of the independent variable in the process of operation. The dependent variables in the extrusion process are:
The temperature of materials in the extruder is affected by not only the heating conditions, but also the components of materials, moisture, unconsumed quantity, friction of materials in the extruder, the amount of mechanical energy converted into heat energy and external cooling conditions. Temperature is the most important monitoring value, which can be adjusted by changing other independent variables. The operator must strictly control the change of extrusion temperature, can`t exceed a certain range, or the quality of production may occur qualitative changes.
During extrusion, the internal pressure is affected by screw characteristics, rotating speed, material composition, moisture content, feeding amount and material flow characteristics, as well as the geometry of the template and the porosity. Pressure is also a monitoring value, to be adjusted by changes in other independent variables. It has something to do with temperature. If the temperature is high, the greater the pressure would be.
The fluidity of extruded material in molten state is complex. Its viscosity varies with material composition, moisture, temperature and shear rate. The change of viscosity affects the fluidity of materials, as well as the friction, which will cause the change of temperature and pressure.
(4) Residence time
By the screw geometry size and speed and other factors decided.
In operation, we should master the independent variable to control the dependent variable. In particular, control the extrusion process of constant temperature and pressure. The change of dependent variable has a lagging process, so we should not be too hasty in adjusting and changing independent variable, but gradually and slowly.
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