CALENDERING PROCESSCORPORATE TRAINING AND PLANNING CALENDERING PROCESS BASIC PRINCIPLE • Calendaring is the process of squeezing a plastic melt between two or more counter rotating cylinders or rolls to form a continuous film and sheet. • The art of forming a plastic sheet has been adopted from the technique of making paper, metal and rubber in industries CORPORATE TRAINING AND PLANNING and it needs blending. • Other then PVC resin ABS. mixing and compounding by addition of suitable chemicals called as additives and fillers to make compound before processing in the calendering plant.Plastic material and its Compound • The PVC resin is generally processed in calendaring plant. PE. CORPORATE TRAINING AND PLANNING . PP and Styrene are also used for calendering process. • Fluxed material delivered to the first calendar nip is regulated to form a rolling bank. at the final nip. the desired thickness is obtained from the smallest bank possible to minimize stress in the sheet.Calendering process with plant details • The rolls are heated either by steam or hot oil and roll temperature ranges from 150° to 180°C. CORPORATE TRAINING AND PLANNING . The sheet passing the first nip forms another bank between the second and third rolls. CORPORATE TRAINING AND PLANNING . Take off roll CORPORATE TRAINING AND PLANNING Sheet . the hot sheet coming from the stripper rolls is passed between a steel roll nipped by a rubber roll that forces the PVC into the grain. it may be nipped against the sheet on the last calendar roll or a laminating station may be installed in place of the embossing rolls. • To laminate another sheet or a fabric to the calendared sheet. CORPORATE TRAINING AND PLANNING .Embossing and laminating • To create leather like grain or other surface structure. • Melt is maintained and delivered to the calender at around 140-160°C. CORPORATE TRAINING AND PLANNING . • The calender roll squeezes a plastic melt into a flat sheet.Calendering process with plant details • After fluxing and gelation. either a two roll mill or an extruder is used to form strands or any acceptable forms. CORPORATE TRAINING AND PLANNING .Cooling and winding of the sheet • The sheet is cooled by passing it over cooling rolls then through a thickness gauge prior to being wound-up. • The sheet is then trimmed to required width and wound on a tube or cut to length and stacked as sheets. • The trimmed edges of the sheet can be recycled. • Other considerations include whether the plastic is laminated to a fabric on the calender.Precautions to be taken during processing • Preparation of stock for calendering. the take off. conditions on the calender. thickness measurements. and control to wind up. CORPORATE TRAINING AND PLANNING . Types of calenders • Superimposed calenders (I –Type) • Offset calenders (L or Inverted L Type) • Z type of Calenders The ‘ I ‘ type calender rolls has the advantage of taking up a minimum of floor space and offers the designer a more simple problem for the strength of the side frames CORPORATE TRAINING AND PLANNING . The inverted ‘L’ offers a good compromise. since the first pair of horizontal rolls hold the input material easily succeeding two nips can be arranged to give good control CORPORATE TRAINING AND PLANNING .Types of calenders Z’ type calender has the advantage that bending of the rolls caused by pressure of material in the nip has no effect on the succeeding nip and therefore tends to improve thickness accuracy. .Type CORPORATE TRAINING AND PLANNING . CORPORATE TRAINING AND PLANNING . • High pressure hot water (H. • The hot oil can be circulated through the rolls to achieve the high operating temperature.P. through each roll.W.W. Processing Parameters The processing parameter needs to be set and control are temperature. pressure and the nip gap.).H. CORPORATE TRAINING AND PLANNING .H. speed.P.This is effective method to heat the calender rolls by circulating H. 2nd High 2nd -3rd 3rd -4th Medium Low CORPORATE TRAINING AND PLANNING . Nip Gap 1st .(°C) Speed( m/min. Roll Temp.) 1st 165 80 2nd 168 82 3rd 171 85 4th 174 88 Nip gap between rollers: Roll No.Examples: Roll No. TABLE 1 • • • • • Roll No. Roll Temp. (°C) 1st 145-150 75-80 2nd 150-155 80-82 3rd 155-160 83-85 4th 160-165 85-90 Speed ( m/min.) • Nip gap high Roll 1 Roll 3 Nip gap low • Roll 2 •Nip gap medium Roll 4 CORPORATE TRAINING AND PLANNING Nip gap between rolls Roll No 1-2 2-3 3-4 Nip Gap High Medium Low . thus increasing the nip of opening at either end of the rolls. • High forces can bend the rolls. can be avoided by extra second bearing on roll CORPORATE TRAINING AND PLANNING . • Crossing the rolls slightly.Mechanism against Roll bending • The calender lines during operation generate very high forces exerted on the rolls to squeeze the plastic melt into a thin web or sheet. • Roll bending. Troubleshooting in calendaring process Faults Causes Compound formulation The use of wrong ingredients or wrong quantities Poor gauges Improper temperature Improper compound Improper flow Streaks Poor compounding Improper temperature Contamination Thickness variation Bent / deflection in rolls Mis alignmentt Film curling or side bending Wrong roll design Non uniform roll temperature Discoloration Regrind material Poor compound Quality of Pigment CORPORATE TRAINING AND PLANNING . • Increase in maximum width of film / sheet. • Versatile in product design and pattern and permits lamination & embossing without additional equipment. it is safer by calendering process than extrusion process. • PVC being heat sensitive material. • Better control of film / sheet thickness.Advantages of Calendaring Process • Delivery/ output of a calender is high. • Better optical properties due to cooling chilled rolls. CORPORATE TRAINING AND PLANNING . swimming pool liners.Applications • The applications include sheets in hospitals. flooring. Printer blankets. automobiles applications. rain coats. counter tops. heat shrunk for blister packaging or used plain as wrapping materials. thermoform sheets. • They may be heat-sealed. water tank liners. medical applications. reservoir films. folders. luggage bag applications. table cloths. files. upholstery. mulches. vapor barriers. and Toys. wall covers. draperies. CORPORATE TRAINING AND PLANNING . packaging applications. stationery items.