What defines an unacceptable part?

Transcription

1 Process and Raw Material Control for Optimizing Castable Polyurethane Production Stan K. Kulikowski, Jr. Product Development Manager Fenner Precision What defines an unacceptable part? The part still feels sticky after curing Voids Sinks or excessive shrinkage Soft or flimsy parts Little green strength Low tear strength: parts crumble when they are removed from the mold Possible Root Causes Cure process Mixing methodology Mix ratio Raw Material Degradation Prepolymer Curative 1

2 Root Cause Analysis All of the root causes are often interconnected! Mold Temps Cure Times Mix Ratio Curative Condition Mixing method Calibration Heat History Water content Cure process Potential Defects Parts are sticky after curing Parts have sinks or excessive shrinkage Soft or flimsy parts Poor Green Strength Low tear strength Cure Process Preventative Measures Mold temperatures Contact measurement of mold Should be close to the manufacturer s recommended cure schedule Cure time Times that are too long can be as bad as times that are too short 2

3 Mixing Methodology Potential Defects Parts are sticky after curing Parts have voids Soft or flimsy parts Poor Green Strength Low tear strength Mixing Methodology Preventative Measures Hand batching Stirring is not usually sufficient Consider using a mechanical mixer Addition of materials Always measure prepolymer first Mix all additives to the prepolymer, without catalyst or curative Add the catalyst and curative as the last step Adding the curative too quickly can cause it to crash out of the prepolymer Great temperature differentials could also cause the curative to crash out Mixing Methodology Preventative Measures Machine Mixing Review mix motor speeds Mixing too fast can introduce air to the mixture Review material flow rates Differentials in flow rates can cause the mixture to be off ratio Material temperatures Degassing of raw materials 3

4 Mix Ratios Potential Defects Parts are sticky after curing Soft or flimsy parts Poor Green Strength Low tear strength Mix Ratios Common causes of ratio problems Machine calibration Incorrect stoichiometry calculation used Component weights Use of degraded raw materials Preventative measures Daily machine calibrations Scale calibrations and resolution Verification of ratios and calculations Raw Materials Prepolymer condition Curative condition Catalyst Additives 4

5 Curatives Potential issues Thermal exposure MBOCA MCDEA Accelerates oxidation Reduces the amount of amine available to react with isocyanates Liquid will turn dark brown as it oxidizes Moisture contamination Ethacure Polyols Curatives Preventative Actions Thermal exposure Only melt the material as you need it Perform a visual inspection of the liquid. Use a nitrogen blanket on the material to reduce the possibility of oxidation Moisture contamination Use desiccant canisters open containers Apply nitrogen blankets to materials before sealing for storage Keep containers sealed when not in use Curatives Potential issues Adiprene K One shot system with a blocked curative Blocked curatives tend to have a salt complex Salt is hydroscopic: Water can destabilize the matrix Exothermic reaction between water, amine and NCO can be self-sustaining 5

6 Curatives Preventative Actions Adiprene K Keep desiccant cartridges on open containers Keep containers sealed when not in use Only tap what is required from containers Use nitrogen for long term storage Prepolymers Potential Issues Heat history Moisture contamination Prepolymers Potential Issues Heat history Melting time Melting temperature 6

7 Prepolymers Potential issues Prepolymers Preventative Actions Moisture contamination Use nitrogen when drums are opened Limit the number of times that containers are opened Keep containers sealed until just before use Heat history Develop a procedure for recording oven time Do not exceed 200 hours of elevated temperature Heat the prepolymer only to the level required for melting Prepolymers Preventative Tasks NCO Titrations Use Isopropanol as a solvent to dissolve prepolymer Use 1M HCl and DBA as titrants Autotitrate or use a color change indicator Use titrated value for mix ratio calculations rather than container value 7

8 Questions 8