Pipe Extrusion Line

Second presentation of course work in Tallinn University of Technology.

1. Pipe Extrusion Line TALLINN UNIVERSITY OF TECHNOLOGY PRESENTATION POLYMER TECHNOLOGY-1 BY: WALI KHAN

2. Pipe Extrusion and its variants are used to produce pipe, hose, and tubing as illustrated in figure above. Extruder pumps molten material through annular die Die shape the molten material into tube (Pipe) Calibration unit finalize the dimensions of extrudate Cooling tank is used to quench the pipe Haul off draws the cooled pipe for next operation Cutter is use to cut the pipe in required lengths Pipe Extrusion Line

3. PVC-U Pipe Extrusion System

4. Extruder screw transport materials from hopper to metering zone Barrel heaters and friction inside barrel produces heat to melt materials Mix additives with primary material in molten state Produce homogeneous mixing Pump molten material though die Extrusion Section

5. There two types of dies using mostly for pipe extrusion given below Spider-arm Die Cross-head Die Die Types Spider-arm Die In this die, melt is fed from the base of die and surrounds a mandrel which is supported by up-to 24 spider arms. The spider arms are streamlined to minimize the disturbances of the flow, and the channel cross section is reduced in the next section of the die to assist fusion and prevent weld lines. The final land length is 10 to 30 times the pipe wall thickness and has a uniform diameter. Dies for polyolefins have a longer distance between spider and land sections to permit compression and decompression of the melt before it reaches the land.

6. There two types of dies using mostly for pipe extrusion given below Spider-arm Die Cross-head Die Die Types Cross-head Die A cross-head die is transition piece that usually alters the direction of melt flow in by 90° to coat the wire. Design of the cross-head should be streamlined with minimum melt residence time. The most common type of die for thermoplastic extrusion is tube die (A) that extrudes thin wall tube around wire. The tube is drawn by vacuum onto the wire after it leave the die. The vacuum is pulled the clearance between the conductor and its passageway through cross-head. Type (B) is pressure die in which the melt comes in contact with the wire prior to leaving the die while the melt is under pressure. 1 5 6 7 11 10 4 9 8 12 13 2 3

7. Screen pack or breaker plate die: In this type of die, the mandrel is supported by a metal screen containing 1-mm diameter holes that fits onto the back of the mandrel. This design does not require a compression zone due to the lack of spider arms and used mainly for large-diameter polyolefin pipe. Spiral mandrel die: A better solution, particularly for larger pipe die to avoid weld lines is spiral mandrel die. Here the mandrel is rigidly supported, and the melt flow is directed around it in an initially helical pattern, which is converted to axial flow by the geometry of the flow channels and lands. Weld lines are eliminated but difficulty is to ensure an even flow rate at all points of the die outlet. As melt exits die, it swells slightly. Therefore, it requires size adjustment, namely calibration. Die Types

8. For the extrusion of pipes, profiles, and similar semi-finished products, the calibration and cooling sections are connected to the die that has shaped the melt. The goal is to solidify the melt by contact with calibration (Sizing) die in the calibration section to a thickness sufficient for transferring the take-off forces and still maintaining the desired dimensions. The calibration practically always means that the extrudate is pulled through one or more so-called calibrators, made predominantly from metal (brass, steel, aluminum). Pipe Calibration Systems There are many kinds of advance calibration systems available now a days but here, only three will be discussed in detail Extended water-cooled mandrels Vacuum calibration Pressure calibration Friction calibration Internal calibration Precision extrusion pull forming Moveable calibrators

9. When extrudate is drawn along an extended water-cooled mandrel, the diameter of the mandrel fixes the internal diameter of the pipe or tubing. This mandrel is tapered to compensate for shrinkage of the plastic and the pipe thickness is controlled by the die gap and pull-off rate. Although this system is difficult to control, it is used in products where internal diameter is critical. Pipe Calibration Systems Water-cooled mandrel

10. In calibration with vacuum, the contact between the calibrator system and the extruded profile necessary for its cooling and sizing is achieved by applying vacuum to the calibration equipment. In this process, the equipment can surround the profile completely (closed external sizing), the vacuum being applied through fine boreholes or slits in the surrounding wall as shown in figure. The profile is pulled through plates, between which vacuum is applied The main advantage of this process is that there is no floating plug in the interior of the profile. It is only necessary to maintain atmospheric pressure inside the profile. For this purpose, boreholes for equalizing the air pressure are arranged in the mandrel or cores of the profile die. Pipe Calibration Systems Vacuum Calibration

11. In contrast to vacuum, during pressure forming or calibration through pressure, the air inside the pipe is pressurized while the air out-side is the pipe is at atmospheric pressure. The change in pressure still forces the exterior of the pipe against calibration rings, but a plug at the end of the pipe prevents the air from escaping. Puller speed and die gap again control the wall thickness. Pipes and tubes are usually cooled in a water bath that is part of the calibration unit and many lines require a second water bath for high throughputs or for profiling of the bath temperature. Large diameter pipes dimensions are controlled by pressure or vacuum calibration, and water is spray system cools the pipe. Pipe Calibration Systems Pressure Calibration

12. Haul-off units are part of pipe extrusion line, their main purpose is to pull pipe through calibration unit, cooling tanks. The wall thickness is determined by haul-off unit too. Haul-off Systems

13. There are many kinds of plastic pipe cutters like conventional ones but plasma ray cutter and laser cutter using as a advance technology in pipe cutting techniques. Pipe Cutters

14. Handbook of thermoplastic elastomers (Second Edition) by Drobny, Jiri Extrusion – The definitive processing guide and handbook by Giles, Harold Extrusion Dies for Plastics and Rubber - Design and Engineering Computations (3rd Edition) by Michaeli, Walter Modern Plastics Handbook by Charles A. Harper References