Calendering grain

Describes a material that has different physical properties in different directions. See Calender Grain. 

Difference in physical properties along and across a section of rubber compound resulting from the passage of the rubber through a mill nip, a calender nip or through an extruder die. See Calender Grain. 

In manufacture, the abrasive grain is mixed with cmde mbber, sulfur, and other ingredients for curing, then passed through calender roUs to produce a sheet of desired thickness. The wheels are stamped from this sheet and heated under pressure to vulcanise the mbber. 

Grain - The unidirectional orientation of rubber or filler particles occurring during processing (extrusion, milling, calendering) resulting in anisotropy of a rubber vulcanizate. 

On any calender line there are several possible sources of contamination, the first being the raw materials used. In most resins there will be a small number of discoloured grains, which are accepted up to a specified level. On occasions a manufacturer s equipment fails and produces resin with more than normal contamination of this kind. Some particles may not be discoloured but may fail to disperse and so cause small lumps in the film (known in clear films as fish eyes ). On the other hand, lumps may not necessarily be attributable to faults in the resin—they can arise also from poor dispersion of plasticizer, or from degradation taking place at some stage in the process. 

Calendered TPO skin laminated to polyolefin foam core for lower instrument panels are produced by PolyOne Engineered Film for assembly to the i.p. substrate. The instrument panels are assembled by Delphi Automotive Interior Systems from Mytex TPO thermoformed skin/foam laminates. TPO provides resistance to heat, UV, scratch, ductility, low gloss grain, soft touch, and minimal fogging. 

Thermoformed calendered sheeting requires the use of pol5mer alloys in order to maintain the embossed surface grain under the thermoforming process used for IP fabrication. These products are typically about 75/25 blends of flexible PVC/ABS (acrylonitrile-butadiene-styrene terpolymer). The plasticizer systems are similar to those used in the slush-molding process, except for occasional use of DIDP and other low-volatility phthalates as a partial component in the plasticizer blend for the primary purpose of cost reduction. 

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