All Tecnoflon® PFR are peroxide curable materials; thanks to Solvay Specialty Polymers proprietary polymerization technology, this translates into very easy process ability, from compound mixing, to preforming, molding and post-curing.
- Easy compounding with two-roll mills; no exotic chemicals are needed
- Very simple preforming, preferably by screw extruders
- Short curing cycles at relatively low temperatures (from 150 to 180°C)
- Relatively short post-curing cycles in air circulating oven (max 24 h)
Tecnoflon® PFR behave similarly to peroxide cured fluoroelastomers, in terms of ingredients used for compounding, processing conditions as well as shrinking rates. This means that standard process equipment (open mills, presses, tools and ovens) for FKMs is suitable to Tecnoflon® PFR seals manufacturing too.
Tecnoflon® PFR perfluoroelastomers are best suited for two-roll mills mixing. The elastomer must be at first pre-heated by loading it onto the open mill with a wide enough gap between the rollers and progressively reducing the gap. Once the rubber has covered most of the roller width, sticking on the fast cylinder, the ingredients, previously mixed, are progressively added, taking care to distribute them along the whole length of the rollers.
After the incorporation and the preliminary dispersion of the ingredients, the compound is completed by working with a reduced gap aiming at dispersing completely and homogenizing the ingredients. In this phase, the technician operates 6 cuts of the compound in diagonal up to ¾ of the length of the cylinder, alternatively from the left to right and vice versa. After that, the compound is discharged.
Tecnoflon® PFR compounds can be readily processed by means of conventional elastomer processing methods such as compression, transfer and injection molding. Alternatively they can be extruded into hoses or profiles and subsequently cured in an autoclave.
Preforming (by extrusion)
When processing Tecnoflon® PFR by means of compression molding into seals, pre-forming (i.e. the shaping of the uncured compound in the form of a cord) is recommended. This optimizes the manufacturing process as well as enhances the seal performance. Additionally accurate compound pre-forming reduces the amount of flash, resulting in less process waste and improved efficiency. It is recommended to carry out the pre-forming by means of conventional elastomer screw extruders with L/D ratio falling in the range between 6 and 12. Ram extruders can be used for the same purpose but, due to their different layout, they’re less efficient than screw extruders in keeping a smooth and constant size extrudate.
Extrusion parameters must be fine tuned according to the compound properties and the apparatus design; as starting point, 50°C for the barrel and 70°C for the die are recommended. The operating conditions, when set properly, will results in a smooth and constant profile. Particular care must be taken to prevent excessive heat buildup in the compound which will result in scorching.
Vulcanization of the compounds is most commonly carried out in compression moulding presses. The process conditions depend on the compound, the press and the tool design as well as on the item geometry. However PFR 94 and PFR 06HC based compounds can be effectively moulded at 160°C, while 175 °C is the optimal curing temperature for PFR 95, PFR 95HT, PFR 5910M and PFR 5920M compounds. The curing time depends mainly on the items size and geometry, for instance the larger the cross-section, the longer the curing time.
Post cure step is needed for all FFKMs in order to complete the cure, eliminate impurities and strengthen filler-polymer interactions. Post cure parameters are related to the oven type. Therefore optimal conditions must be tuned to the system in use. As starting point for the optimization, the following are recommended when ovens with 7 to 14 complete air changes per hour are used:
- PFR 94 and PFR 06HC: 4 h @ 230°C
- PFR 95 and white PFR 95HT: 8 hours rise from RT to 250°C followed by 16 hours at 250°C
- Black PFR 95HT: 8 hours rise from RT to 290°C followed by 16 hours at 290°C
- Translucent PFR 5910M and PFR 5920M: 8 h @ 230°C
For higher number of air changes (i.e. > 50 per hour), milder conditions (i.e. lower temperatures and/or shorter times) are advisable.