Basic Extruder Line Lay-out in Cable Industry
A basic extrusion line either for coating or jacketing is consist of 5 different units. In order from starting point ; Pay-off , Extruder , cooling/curing shaft, capstan ( pulling ) and take-up units are synchronized. Eventhough a simple lay-out as above is enough and capable of coating desired wire with plastic, additional auxiliary units will be added in order to maintain good quality and higher output volume. Preheater, feeding accumulator, dancer, powdering unit, in-line diameter gauge, spark tester, take-up accumulator, co-extruder are common auxiliary units. Some of these units such as spark tester and diameter gauge would be ensuring the quality of final product while others increasing output per minute.
Pay-Off : Starting point of extrusion line. Loaded with either wire or cable core to be coated. It feeds the Extrusion line. It can be as simple as a flyer or a motor driven with accumulator for high speed extrusion. Bobbin size also determines the type of the pay-off unit. Selection of pay-off unit based on final product type and estimated line speed. Bobin size is very important since bigger payload means less downtime which results increased output. On the other hand, smaller bobbin size mean less weight and less tension on wire.
Extruder : Main Unit of Extrusion where plastic is formed and coated over bare conductor or cable core. Thermoplastic material would be melted to be formed while thermoset plastics would be formed cold to be cured later on.
Screw & Barrel couple is the hear of extruder machine. By means of rotating screw in the barrel; plastic is pushed to extrusion head where it would be coated and formed. There are many variations of screw and barrel. Common aim is to produce screw and barrel according to physical aspects of extruded plastic. The angle of flyers , diameter over length ratio and zones of screw determined by extruded plastic , expected outcome, line speed, minimum and maximum diameter of final product.
Cooling Shaft : Thermoplastic coated cable should be cooled after extrusion process. A cooling shaft is full of water where extruded cable will go through. Water in cooling shaft is would be warmed up. In order to maintain a stable temperature; water needs to be cooled. Dimensions of cooling shaft would be determined by minimum and maximum cable size, line speed , ambient tempeature and water tank capacity.
Curing Shaft: Thermoset plastics extruded as cold forming. After extrusion process, plastic needs to be cured to be finished product. Curing heat and using of gases vary according to the type of plastic extruded. Cross linked therrmoplastics - XLPE for example- also cured and vulcanized as thermoset plastics. Dimensions of the curing unit would be determined by line- speed , desired temperature and Physical characteristics of the plastic material.
Capstan : Pulling extrudate through extrusion process and feeding take-up unit. Final dimensions of the product would be determined by adjusting capstan speed and extruder speed. Capstan's pulling speed and pulling force determines the line speed. A capstan is simply accoupled pulleys. Pulleys can be positioned vertical , horizontal. A caterpillar machine can be used as a capstan.
Take-UP: It is at the end of an extrusion line. Various types possible with various names attached. Starting from a single bobbin/reel fork type. It can be double with manual or automatic change. For Bigger size reels it can be self traversing tower type. Size of the reel which is also defined by the size of the cable extruded and the line speed would determine the type and size of the unit. Traverse unit is a must. A dancer or accumulator unit may be required in front of Take-up unit as line speed increases.