Application of Digital Communication Techniques to Plastic Extrusion Process

Abstract –Extrusion of molten plastic onto wire and other metal shapes requires very close control of numerous variables to ensure consistent product quality at maximum production rates。 To accomplish a higher extruder performance, the hardware structure and software design of a plastic extruder control system based on digital communication technique is presented。 The system is constituted of an integrated control mode with Personal Computer (PC) and programmable logic controller (PLC)。 The working principle, hardware and software are described in detail。 The virtual produce results indicate that the designed control system ensures a good plastic extruder control。83507

Keywords –PLC, extruder, digital communication, control system

I  INTRODUCTION

Extrusion machine (also known as extruder) has been used in the wire and cable industry for the production of wire and cable insulation sheath。 The theme for the production of wire and cable insulation sheath is the core technology in the whole of wire and cable generating process。 Therefore, the generation accuracy, reliability and degree of automation of the extrusion machine play a very important role in the wire and cable industry。 Because of the advantages of PLC such as conveniently programming and combining, reliable and working fast and in the industrial local direct input and output signals, it is currently used by many wire and cable manufacturers    in

our country。 However, most of the extrusion machines whit PLC controllers equipped are based on the PID regulator using analog control。 Analog control is one kind of control technique with many faults, such as, low accuracy, low reliability, and low stability, and hard to repair。 And some others defects of the extrusion machine, such as delay factors of itself and nonlinear retardation factors, which can cause bad effects to the machine, ordinary PID regulator can not control the process perfectly。 After analyzing the actual design and the process of construction, this paper presents the fuzzy control system for extrusion machine using the digital communication as the main control method。 This new control system overcomes the defects of ordinary PID control, and is fitted for using DCS in a whole workshop, even in a whole factory。

II  PROCESS FLOW AND SYSTEM COMPOSITION

AProcess flow

Fig。1 shows the Process flow chart of extrusion machine, in which the line between the pay-off rack and the take-up rack indicates the process of mental core wire。 The pay-off rack releases the thread with a permanent speed under the effect of the traction motor。 When core wire passes through the main

Fig。 1。  Process flow chart

motor head, the main engine will drive the head in order to let the heated rubber be extruded, so the rubber can be evenly attached on the surface of metal wire core, which

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then form the cable insulation sheath。The diameter gauge between the main motor head and traction motor is used for measuring the diameter of the cable with insulation sheath attached on。The control system mainly use this parameter to regulate the speed ratio between the host and the traction motor, constructing the double-loop, so as   to

keep the thickness of insulation sheath in a desired value。 The cable with insulation sheath attached on will be tested through the traction followed by spark machine and concave-convex detecting instrument, and then the resistance,degree of surface smoothness and uniformity will be examined respectively。 These parameters will be used to adjust the temperature of different heating zones from the main motor head。 At take-up rack, the axis can switch one from another automatically under control system 。it also can start automatically when the line is disconnected or the take-up rack can not switch the line。 So these can make sure that pay-off rack will work normally despite some common breakdowns arise during the course of axis switching between the accumulator rack and the take-up rack 。