Calendered Sheets

AppHcatioas of dibasic lead phthalate, coated grade, iaclude 90 and 105°C rated PVC electrical iasulation, plastisols, profile extmsions, calendered sheet, and molded products. The recommended range of usage ia viayl electrical iasulatioa is 5—7 parts pet huadred resia, depending oa the particular iasulatioa classiftcatioa to be met. Ia geaeral-purpose extmded and molded PVC stocks, approximately 3—6 phr of coated dibasic lead phthalate is suggested. 

The main applications for CPVC arise from the fact that the material has a softening point of about 100% and very good chemical resistance. Particular interest has been shown in waste and soil systems which may pass hot water effluents. Calendered sheet may be vacuum formed for uses where hot filling techniques are employed, for example in jam packing. 

By crossing the axes of both rolls in the surface of the calendered sheet the effect of roll deflection can be compensated partially. If Co represents the cross axes setting displacement the resulting clearance Yca(z) is given by... 

Beside roll deflection and therefore thickness gradients in the product high pressure in the calender nip may cause varying positions of the cords in the calendered sheet in case of cord coating. 

Arrow-shaped markings on the surface of calendered sheet mbber due either to the use of insufficiently warmed stock or to too low temperature of the calender rolls. 

The degree to which a raw elastomer or unvulcanised compound returns to its original dimensions on the removal of an applied stress which has caused deformation. Die swell in extrusions and increase of thickness of calendered sheet are examples of recovery. 

Change in dimensions of an unvulcanised rubber (calendered sheet or extruded section) on cooling from the processing temperature. Also the volume contraction of a moulded rubber product on cooling from vulcanising temperature. See Coefficient of Thermal Expansion (Volumej. Shrinking... 

The process of controlled, gentle warming of unvulcanised calendered sheet rubber to reduce its anisotropy and prevent subsequent distortion of articles made from the sheet and cured by embedding in chalk in open steam. 

In order to minimise air entrapment and blistering, the thickness of each sheet is generally limited. To build up the required thickness of the final sheet, two or more plies of calendered sheet are usually laminated on the bottom bowl of a three-bowl calender. 

Sulfonated EPDMs are formulated to form a number of rubbery products including adhesives for footwear, garden hoses, and in the formation of calendered sheets. Perfluori-nated ionomers marketed as Nation (DuPont) are used for membrane applications including chemical-processing separations, spent-acid regeneration, electrochemical fuel cells, ion-selective separations, electrodialysis, and in the production of chlorine. It is also employed as a solid -state catalyst in chemical synthesis and processing. lonomers are also used in blends with other polymers. 

Thick walled tubes are built-up to the required thickness of say 25 to 50mm from calendered sheets of about 1 mm thickness and the same is wrapped with wet cloth which gives additional pressure when shrunk, thus giving better consolidation. The tubes are built up on mandrels. The preferred method of curing is by using hot water. 

This system involves the use of some form of heating by air or steam in a chamber in a manner such that the vulcanization occurs immediately after the rubber is formed in an extruder or calender. This is a suitable process for extruded profiles and calendered sheets and conveyor belts. Liquid curing method (LCM) is also a continuous process which involves the use of suitable hot liquid baths in which extruded profiles can be passed through and vulcanized continuously. Items can be cured rapidly at temperatures from 200°C to 300°C however the compounds must be suitably designed to prevent porosity as this is a common problem with any extrudate. Suitable materials for curing medium includes bismuth-tin alloys, an eutectic mixture of potassium nitrate and... 

Calendering sheets for chemical plant construction and lining are usually required to be 4 to 5 mm thick. To obtain a satisfactory surface, the thickness is to be built up in plies of 1 mm or 0.8 mm thick sheets. The plying up at the calender is usually done by means of a rubber covered breast roll working against the bottom roll as shown in the above figure 13.4. 

Fish eye - A thin elongated void in a calendered sheet. A surface imperfection. Not detrimental to service life. 

The results of the work are shown in the tables and curves. As shown in Figures 3 and 3A and Table III (paper at pH 4.8), there was an increase in folding endurance from 1470 to 2010 on spraying the sheet with 0.0314% Cu [(CH3 COO)2-H20]. Such an increase is usual when a calendered sheet is wetted and relaxed. The expected rapid loss of folding endurance for a sheet of this pH showed up in both dry and humid ovens. 

Calendered sheet is usually less glossy than extruded material. Calendering may be preferable for certain applications requiring its higher tensile properties, product uniformity, and unusually close gauge... 

The type of sheet most frequently used today is still natural rubber. It may be compounded with a number of different modifiers or fillers, depending on the service for which it is intended, varying from soft to hard, and from a uniformly calendered sheet to laminates of soft and hard or laminates including fabric-reinforcing. 

With the war years, polyvinyl chloride (PVC) resins came under study, and plasticized PVC compounds, based on these resins, became available as calendered sheet lining materials-the material of choice for stainless steel pickling and for chrome plating and other exposure employing mixtures of chemicals including such strong oxidants as nitric and chromic acid which rapidly attack natural rubber. (A higher temperature limit modification now seldom seen is PVDC, for which the continuous temperature limit is said to be 170°-180°F.)... 

Use Calendered sheet and film extruded and molded items electrical wire insulation coatings for wood, metal, fabrics, and paper. 

The most widely plasticized polymer is polyvinyl chloride (PVC) due to its excellent plasticizer compatibility characteristics. Only by incorporation of a plasticizer a degree of flexibility is achieved, which makes PVC suitable for applications such as cable insulation or sheathing, calendered sheets, floor covering, flexible profile or synthetic leather. However, plasticizers have also been used and remain in use with other polymer types. 

Surface profiles of both sides of a calendered and an uncalendered sheet were recorded with a Talysurf 5 instrument (Rank Taylor Hobson, England), and are reported in Fig. 13. The surface is different in each case, but the bulk conductivity is not significantly altered. The pressure applied to the electrodes within the cell has not changed the surface profile of the sheet for the calendered sample. Although a difference is observed for the uncalendered sample, the surface is not as smooth as that of the calendered sheet after pressure is applied. 

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