Sheet Extrusion: Sheet is produced by forcing molten thermoplastic through a long horizontal slit die. The extruded hot web passes around metal cooling rolls and is then cut up or rolled up. The sheet leaving from the slit die is picked up by vertical stack of three rolls. The polishing rolls are usually chrome-plated and provided with temperature control by circulating oil. The polishing rolls impart a good surface to the product without warpage. The temperature of the top rolls should be as high as possible without sticking, while the bottom roll should be just cool enough to prevent distortion.
Material used: HIPS is the most important sheet material. HDPE, PVC, ABS are also used. Sheet grades usually have high melt viscosity.
Process line: The sheet leaving from the slit die is picked up by vertical stack of three rolls. The polishing rolls are usually chrome-plated and provided with temperature control by circulating oil. The polishing rolls imparts a good surface to the product without warpage. The temperature of the top rolls should be as high as possible without sticking, while the bottom roll should be just cool enough to prevent distortion. From the polishing rolls the sheet passes along a conveyor, which consists of free running rollers. The sheet is pulled by the pulling rolls are covered with elastomers. Their speed is adjusted to be slightly less than that of the polishing rolls to allow for shrinkage that takes place as the sheet cools. The sheet is cut into desired dimensions by means of razor blades (thin sheets), shear cutting device (Standard sheets), or circular saws (thick sheets).
Extrusion coating:
1. The plastic is coated over a substrate like paper, by extruding through a slot die downward between two rolls.
2. Substrate is fed between the molten plastic and the roll and is joined with the plastic by pressure between rolls without the use of an adhesive.
3. Material used LDPE & PVC, PP, HDPE, Monomer etc. are also used.
4. Equipment compresses of Pre treatment unit Coating unit Take off & winding.
Wire Coating/Cable Covering: Unit comprises of
1. Un wind unit (For conductor)
2. Pre treatment unit
3. Wire coating unit
Steps Involved:
1. Wire/conductor is unwound & straightened by Tension
2. Control Unit.
3. Pre treated to promote adhesion of molten plastic
4. Then passed through the Cross head die of the coating unit
5. Coated wire is then cooled by passing through cooling trough
6. Wound on the winder
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