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IMUTHANE Processing

IMUTHANE Processing. Mobile liquids (2 or more parts) Accurate ratio control needed (ratios range from 1:1 to 3:100) Good mixing Accurate temperature control at all stages Moisture exclusion Good degassing Proper molds and filling techniques Finishing techniques.

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IMUTHANE Processing

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  1. IMUTHANE Processing

  2. Mobile liquids (2 or more parts) Accurate ratio control needed (ratios range from 1:1 to 3:100) Good mixing Accurate temperature control at all stages Moisture exclusion Good degassing Proper molds and filling techniques Finishing techniques Processing of Castable Polyurethane Elastomers – Basic Considerations

  3. Do’s and Don’t’s of Urethane Processing III

  4. Processing – Degassing • Degassing removes dissolved and absorbed gases, from manufacture and those generated through natural aging • Viscosity and surface tension of the prepolymer entrap air and other gases • Degassing of the prepolymer is carried out at the processing temperature: 80 – 100°C • Degassing of the prepolymer is carried out in a vacuum of 28.5” Hg

  5. Processing – Degassing • Degassing is complete when vigorous foaming stops – the time required is dependent on: • the amount of prepolymer • the temperature of the prepolymer • the size and shape of the vessel • the degree of vacuum • the amount of entrapped gases • Use a container that is twice the volume of prepolymer to be degassed to allow for foam rise • It may be necessary to re-heat the prepolymer after degassing because of heat loss

  6. Do’s and Don’t’s of Urethane Processing IV

  7. Processing – Prepolymer Preparation • Refer to Technical Datasheet for specific processing requirements • Heat only the required amount of prepolymer to the processing temperature • Add pigment, anti-foam, other additives • Degas at the processing temperature, usually 80 – 100°C • Reheat to processing temperature if required

  8. Processing – Curative Preparation • Refer to Technical Datasheet for specific processing requirements • Weigh the appropriate amount to cure the prepolymer, allow for residual • Heat to the required processing temperature, if required (e.g. MBCA) • Curative is always added in liquid form to hot prepolymer

  9. Mix Ratio / Stoichiometry • What is Stoichiometry? • It is the ratio of reactive groups in the curative to reactive groups in the prepolymer • It is represented by % Theory • The best mix of properties is found between 95 and 100% Theory • Outside of this range there can be significant impact on the physical properties

  10. Mix Ratio Calculation • %NCO is the weight per cent of reactive isocyanate groups in the prepolymer. It can be found on the drum label or CoA for each batch. • EW is the equivalent weight of the curative. It can be found in the Technical Datasheet. • For GR133.5, EW = 133.5 • For GR107, EW = 107 • Calculation:

  11. Mix Ratio Calculation – Example 1 • IMUTHANE 22-90A cured with GR107 • 22-90A: %NCO = 4.15%. • GR107: EW = 107 • Desired %Theory: 95% • Calculation:

  12. Mix Ratio – Effect on Tensile Strength & Elongation

  13. Mix Ratio – Effect on Tear Strength

  14. Mix Ratio – Effect on Compression Set

  15. Do’s and Don’t’s of Urethane Processing V

  16. Processing – Mixing • Check to ensure correct temperatures before mixing • Mixing can be achieved: • Using a plastic container & spatula • Using a drill with attachment • By machine • Thorough mixing by hand is achieved by scraping the sides and the bottom of the container and using a figure-8 stirring pattern • Mix quickly and thoroughly and avoid entraining bubbles • Pour mixing can cause poor physical properties • Degas after mixing if time permits (hand mixing) • Remember – safety – ventilation, gloves, eye wear, protective clothing

  17. Mixing Issues – Curatives • Curatives like IMUCURE GR107 are Liquid and very easily mixed into prepolymers.

  18. Do’s and Don’t’s of Urethane Processing VI

  19. Processing – Pouring • When the prepolymer and curative are mixed, the mixture is poured into the hot mold for curing • Pouring should be carried out in a way that minimises turbulence and stops bubble entrapment in the mold • Pour evenly and avoid splashing • Other molding techniques include: • Injection • Rotational • Centrifugal • Vacuum

  20. Processing – Temperatures • Material temperature – what does it affect? • Demold hardness and toughness • Cure consistency • Efficiency of production • Efficiency of mixing • Ratio – temperature effects viscosity which can change back pressure in machines, and cause mixing difficulties if hand mixing

  21. Processing – Temperatures • Mold temperature – what does it affect? • Demold hardness and toughness • Cure consistency – incorrect mold temperature causes • Shrinkage • Voids, cracks • Sink marks, “christmas tree effect” • Efficiency of production • Bonding for to metal.

  22. Processing – Molds • Mold temperature – refer to Technical Datasheet for material • Molds should be coated with a release agent to ensure easy removal of cast parts • Take care in handling molds – any damage to surfaces will be reproduced in the polyurethane part • Wide material choice for making molds – steel, aluminium, polyurethane, silicone rubber, … • Mold material must be dimensionally stable, heat resistant and inert to the chemical reaction

  23. Processing – Cure & Post-Cure • Material in the mold must be allowed to cure before demolding – the time required depends on the material and varies from 10 minutes to several hours. • Material is then post-cured, generally for 16 hours at the specified temperature. Time and temperature will depend on the material. • Post-cure is necessary to develop physical properties. • Full property development occurs over the next 7 days at ambient conditions.

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