Injection Molding Foam Guidelines

SAFOAM USER’S GUIDE This ‘SAFOAM User’s guide’ was prepared as a service to the customers using Reedy International Corporation’s SAFOAM family of endothermic foaming agents. Reproduction or distribution of this brochure, in whole or in part, is prohibited without the permission of Reedy International Corporation. TABLE OF CONTENTS 1. Introduction ........................................................................................................1 SAFOAM - Its Use in Thermoplastics ........................................................2 2. Structural Plastics and Polymer Selection .........................................................3 Properties of Amorphous Polymers .............................................................3 Properties of Crystalline Polymers ..............................................................4 Properties of Thermoplastic Elastomers ......................................................4 3. Foaming Agent Selection ...................................................................................6 Physical Foaming Agents ............................................................................7 Chemical Foaming Agents ...........................................................................7 Exothermic Chemical Foaming Agents Azodicarbonamide .................................................................................8 Endothermic Chemical Foaming Agents Sodium Borohydride ..............................................................................9 Traditional Acid/Carbonate Systems ...................................................10 SAFOAM Endothermic Chemical Foaming Agents .................................10 Gas Evolution and Rate .............................................................................12 4. SAFOAM in Injection Molding ......................................................................16 Introduction to Structural Foam .................................................................16 Thermal Conductivity ..........................................................................17 Acoustical Properties ...........................................................................17 Benefits of Foaming ...................................................................................18 Structural Design Flexibility ................................................................18 Density ...........................................................................................18 Weld Lines .....................................................................................18 Knit Lines ......................................................................................19 Improvements in Processing ................................................................19 Lower Internal Stresses ........................................................................19 Large Complex Parts............................................................................19 Lower Costs .........................................................................................20 Resin Usage ...................................................................................20 Tooling Expenses ...........................................................................20 Processing Charges ........................................................................21 Flexibility in Part Production ...............................................................21 Part Design .................................................................................................21 Load Considerations ............................................................................21 Stress-Strain Curves .............................................................................21 Apparent Modulus and Creep ..............................................................22 Fatigue Properties ................................................................................22 Recommended Maximum Working Stress ..........................................23 Thermal Stress/Co-efficient of Thermal Expansion ............................23 Structural Designs ................................................................................23 TABLE OF CONTENTS Bending ................................................................................................26 Tension .................................................................................................27 Compression ........................................................................................27 Injection Molding Processes Using SAFOAM .........................................29 Processing Methods ...................................................................................29 Conventional Injection Molding Machines .........................................29 Specialized Low Pressure SFM Machines ...........................................30 Low Pressure Process with Chemical Blowing Agents .......................30 Co-Injection (Sandwich) SFM Machines ............................................31 Gas Counter-Pressure SFM .................................................................31 Direct-Gassed Nitrogen SFM ..............................................................33 High Pressure SFM ..............................................................................34 Gas Co-Injection ............................................................................34 Gas Assist Molding ........................................................................34 Chemical Gas Assist Molding .......................................................34 CoralFoam®....................................................................................34 Over Molding .................................................................................35 Processing Equipment Standard Injection Machines ...............................................................35 Chemical Structural Foam Machines ...................................................35 Physical or Inert Gas Machines ...........................................................35 Molding Machine Settings ..................................................................................36 Clamping Force ....................................................................................36 Melt Temperatures ...............................................................................36 Mold Temperatures ..............................................................................37 Cooling .................................................................................................37 Mold Cooling .......................................................................................37 Pressure Settings ..................................................................................37 Injection Pressure ...........................................................................37 Hold Pressure .................................................................................37 Injection Speed ....................................................................................38 Functional Design ................................................................................38 Wall Thickness and Material Flow Lengths ........................................38 Transition Sections ..............................................................................39 Fillets and Radii ...................................................................................40 Tolerances/Warpage Control ...............................................................40 Draft Angles .........................................................................................41 Snap-Fits ..............................................................................................42 Hinges ..................................................................................................43 Bosses ..................................................................................................46 Ribs ......................................................................................................46 Guides ..................................................................................................47 Louvers ................................................................................................48 Nozzle Design ......................................................................................48 TABLE OF CONTENTS Tooling Molds ...................................................................................................49 Corrosion Resistance .....................................................................50 Thermal Conductivity ....................................................................50 Heat Treatment...............................................................................50 Sprues, Runners, Gates and Gate Locations ........................................50 Sprues .............................................................................................50 Runners ..........................................................................................50 Gates ..............................................................................................51 Gate Locations ...............................................................................51 Vents ....................................................................................................51 Secondary Operations Painting ................................................................................................53

Load more