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IEEE-PSES Presentation: Don't Get Burned By Plastics


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The use of Plastics in electrical products continues to grow. What started with circuit boards and transformer bobbins, now includes most enclosures and component bodies. New applications for plastics appear every day. Yet most engineers know little more than to ask for the UL flame rating.

To prevent getting “burned” during your compliance evaluations due to improperly specified plastics, it is important to know how to incorporate plastics into electrical products. We will discuss the core plastics requirements, material verification, differences between North American & International plastics standards, and the plastics tests. Perhaps even more importantly, we will discuss application specific plastics tests, how to avoid them, and how to prepare for them when they cannot be avoided.

This is a presentation intended for engineers and technicians who are involved with the design and/or compliance verification of products that incorporate plastics.

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IEEE-PSES Presentation: Don't Get Burned By Plastics

  1. 1. Don’t Get Burned By Plastics © 2008 Educated Design & Development, Inc.
  2. 2. Presented by Bill Bisenius – President, NCE/NCT Educated Design & Development, Inc. 901 Sheldon Dr., Cary, NC Tel: 919 -469-9434; Fax: 919 -469-5743 919-469- 919-469- Product Safety Consulting, Test Equipment & Training Services from People Who Know Product Safety
  3. 3. Part A Plastics General Compliance Issues
  4. 4. General Compliance Goals AVOID Non-compliance problems that n require re-design & material changes, Additional, unanticipated tests n PLASTICS = TERRIBLE SURPRISES
  5. 5. Plastics & Compliance It’s all about the PREPARATION
  6. 6. Plastics & Compliance Plastics is one part of your product safety compliance work that can be done almost entirely on paper before making a costly mistake
  7. 7. “Polymeric Materials” Thermoplastics: can be resoftened by n heating Thermosets: cures by chemical reaction n and cannot be resoftened Elastomerics: stretches to 2x+ length @ n room temp; returns to original length
  8. 8. Plastics - Key Issues “Bar Samples” vs. End Product n Plastic Mfg vs. Product Mfg n Flammability vs. Other Properties n Flammability – using rated plastics n Other properties – end product tests n are frequent
  9. 9. Plastics & Compliance Properly selected plastics for each application will help you avoid the need for “plastics” testing
  10. 10. Flame Rating System HB or HBF = Most Flammable V-2 = V-1 = V-0 = 5VA/VB = Least Flammable
  11. 11. Part B Plastics The Standards
  12. 12. Identifying Standards In what countries will your product n be marketed? What is your end product standard? n • Does it contain plastics requirements? • Does it reference other plastics standards?
  13. 13. U.S. Plastics Standards UL94: Flammability of Plastic n • Target = plastics manufacturers • Testing bar samples for flame rating : Horizontal & Vertical flame tests
  14. 14. U.S. Plastics Standards UL746 Series: Polymeric Materials n • UL746A: Short Term Property Evaluations • UL746B: Long Term Property Evaluations • UL746C: Use in Electrical Equip. Evaluations • UL746D: Fabricated Parts • UL746E: Laminates, Fibre, PWB Materials
  15. 15. U.S. Plastics Standards UL746A: Short Term Property Evaluations n • Physical Properties: Tensile, Impact, Material Distortion Under Load • Electrical Properties: High Voltage Dielectric, CTI, High Voltage Arc Tracking, • Resistance to Ignition from Electrical Sources: Hot Wire Ignition, High Current Arc Ignition, High Voltage Arc Ignition, Glow Wire Test, • Tests for Polymer identification
  16. 16. U.S. Plastics Standards UL746B: Long Term Property Evaluations n • Long-Term thermal aging programs - Temperature Index rating • Target = Plastics manufacturers • NOT something end product manufacturers want to mess with
  17. 17. U.S. Plastics Standards UL746C: Use in Electrical Equip. Evaluations n • Target = End product manufacturers • Includes flame and “other” property tests • Flame: 12 mm, 20 mm, 127 mm • Electrical: CTI, Dielectric, HAI, HWI, GWEPT • Mechanical: Impact, Crush Resistance, Mold Stress, Strain Relief, Conduit Connections
  18. 18. Inter. Plastics Standards IEC60695-11 Series: Flame Tests n • IEC60695-11-2: 1 KW Flame Test • IEC60695-11-3: 500 W Flame Test • IEC60695-11-4: 50 W Flame Test • IEC60695-11-5: Needle Flame Test
  19. 19. Inter. Plastics Standards IEC60695 Series: Other Properties n • IEC60695-2-10/11/12/13: Glow Wire Test • IEC60695-10-2: Ball Pressure Test • IEC60695-10-3: Mold Stress Test • IEC60695-9-1: Flame Spread Test IEC60112: Tracking Test: CTI, PTI n
  20. 20. Part C Plastics Tests U.S. & International
  21. 21. Flame Tests - General Use the proper equipment = many 1) burner variations for IEC tests, Use the proper gas supply = critical for 2) proper flame temperature, Flame calibration requirements, 3) Colors and thickness affect results, 4) Be Safe – don’t underestimate the 5) potential for disaster
  22. 22. Flame Test Set-Up Flame hood with gas 1) controls, Burners, 2) Gas supply, 3) Test stand, 4) Wire gauze, burner 5) mounts, cotton, Flame calibration 6) equipment,
  23. 23. Horizontal Burn Testing HB/HBF Ratings per UL94 20 mm flame height, n 45° angle flame angle, n One, 30 second flame n application, Permitted to burn for n limited rate (100 mm)
  24. 24. Vertical Burn Testing V-0, V-1, V-2 per UL94 20 mm flame height, n Vertical flame angle, n Two, 10 second flame n applications, Very brief period n between flame applications, Must not drip burning n particles that ignite cotton 300 mm below
  25. 25. Vertical Burn Testing 5VA, 5VB per UL94 125 mm flame height, 40 n mm inner blue cone, 20° flame angle, n Five, 5 second flame n applications, 5 seconds between flame n applications, Must not drip burning n particles that ignite cotton or make hole in plastic.
  26. 26. 12 mm Flame Test per UL746C & IEC60695-11-5 Needle Flame Test, n 12 mm flame height, n Butane vs. Methane, n End product test, n Two, 10 second flame n applications, One minute between flame n applications, Sample must not be n consumed.
  27. 27. 20 mm Flame Test per UL746C 20 mm flame height, n Vertical flame angle, n Two, 30 second flame n applications, One minute between n flame applications, Sample must not be n consumed.
  28. 28. 127 mm Flame Test per UL746C 127 mm flame height, n End product test, 20° flame n angle, Five, 5 second flame n applications, 5 seconds between flame n applications, Must not drip burning n particles that ignite cotton or, burn for more than 1 minute after last flame, or make hole in plastic.
  29. 29. Flame Tests - Tips Air inlet adjustment changes the color of the n flame, Gas pressure adjustment changes the height n of the flame, Air holes closed 1) Air holes half open 2) Air holes nearly fully 3) open Air holes fully open 4)
  30. 30. Flame Tests - Tips Some plastics will pass higher ratings in 1) the end product = oxygen limitations, especially with small products, Timing is “everything ” = use a helper to 2) run the stop watch, Have a GREAT test stand with enough 3) sturdy clamps to insure nothing moves, Don’t light your clothes on fire, 4)
  31. 31. Dielectric Test Plastic used as an n insulator must be tested to insure overvoltage transients will not damage the insulation, Insulation tested n between precision probe tips at 100 g, Foil wrap enclosures n for hipot testing
  32. 32. Ball Pressure Test Ball Pressure Tester n evaluates mold deformation under elevated temperature, Performed in oven, n Some standards n require the Ball Pressure Test Stand, UL indicates equivalent n to Vicat Softening Test
  33. 33. Mold Stress Release Test Plastic Enclosures n tested to insure no mold stresses will reflow, Sample put in oven at n 10°C over max. temperature on the material during temperature testing, No openings may form n that will allow probes to enter.
  34. 34. Glow Wire Test Glow wire test is an n alternative “flame” test, 550 - 960°C element n pressed against sample with 1N force for 30 seconds, Flame must extinguish n within 30 seconds and, must not ignite tissue paper below.
  35. 35. Tracking Test Determines the n material’s resistance to surface tracking, CTI & PTI ratings, n Surface tracking can n lead to ignition of the material Voltage applied with n conductive drops
  36. 36. Hot Wire Ignition Test Resistance to ignition n from electrically heated wire, Intended for insulating n materials in contact with electrically heated live parts
  37. 37. Part D Designing For Compliance Using Plastics
  38. 38. KEY Question #1 What does your end product standard require for plastic enclosures, internal plastics, & circuit boards? • Does it contain plastics requirements? • Does it reference other plastics standards?
  39. 39. KEY Question #2 Are each of the plastics used in your product properly flame rated? • Enclosure Plastics? • Internal Plastics? • Printed Circuit Boards? • At the thickness & color used?
  40. 40. KEY Question #3A Does your application require any additional properties in any of your plastics? • Plastic close to arcing parts? • Plastic supporting live parts? • Live parts near plastic enclosure? • CTI rating needed for traces? • Outdoor = UV, cold, weather
  41. 41. KEY Question #3B If your application requires additional properties in some of your plastics, do you have certified ratings? • HWI, CTI, HVTR, HAI No ratings? Time for Special Testing!
  42. 42. Plastics – Product Design Enclosures n Decorative Parts n Foam Parts n Internal Plastics n Printed Circuit Boards n Insulated Wiring n
  43. 43. Selecting Plastic Materials Is the material certified? n What is the flammability rating at the n thickness & color used? Within temperature ratings of material? n Any conductive coatings? Certified for n application to this specific material? Are other physical properties needed? n (i.e. HWI, HAI, CTI, etc.)
  44. 44. Flammability of Materials Decorative Parts min. HB n Foam Parts min. HBF n PWB’s min. V-1 n Wiring V W-1 n Internal Plastics min. V-2 n Plastic Enclosure n : products up to 40 lbs min. V-2 : products over 40 lbs min. 5V
  45. 45. Design Comments UL flame ratings are generally accepted 1) for CSA, IEC, EN (CE), etc. End product tests can leave you in the 2) lurch = what if you fail, do you control the plastic composition? BEWARE of components that have 3) plastic bodies and serve as part of the enclosure.
  46. 46. Don’t Get Burned By Plastics CONCLUSION
  47. 47. William S. Bisenius (Bill) 24+ years of Product Safety experience n NCE/NCT n BSEE from SJSU (IEEE student chapter President) n President/Co-Founder of E.D.& D. n Former Engineering Group Leader for UL n = ITE, Lab, Lasers, Appliances, Seminars Develops Product Safety Test Equipment n Consultant/Seminar Leader in ITE, Lab, n Medical, Lasers, IP Codes, Appliances