Aerospace/Defense Supply Chain: Collaborative Research Results for Hex Chrome Free Materials

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1 Aerospace/Defense Supply Chain: Collaborative Research Results for Hex Chrome Free Materials Greg Morose Toxics Use Reduction Institute University of Massachusetts Lowell November 20, 2014

2 Hex Chrome Uses in Defense/Aerospace Applications Primers Sealants Bond primers (structural adhesive primers) Conversion coatings Conversion coatings inhibit corrosion on metal parts, and are important in military, nautical and aerospace applications. Conversion coatings account for the most significant ongoing use of hexavalent chromium in Massachusetts. Source: TURI Summary of Policy Analysis 2

3 Hex Chrome: Driver for Change Defense Federal Acquisition Regulation Supplement (DFARS), May 2011 No Department of Defense contract may include a specification or standard that results in a deliverable containing more than 0.1% hexavalent chromium or requires use or removal during subsequent phases of the deliverable, unless an exception or approval applies. Several exceptions include conversion coatings; hard chrome plating; chromic acid anodizing; most chromate metallic ceramics; and chromate washes, etches, pickling, etc. 3

4 TUR of Hexavalent Chromium (HC) Current State DFARS Compliant Hex Chrome Free Topcoat HC Primer HC Sealant HC Conv. Coating Topcoat Non-HC Primer Non-HC Sealant HC Conv. Coating Topcoat Non-HC Primer Non-HC Sealant Non-HC Conv. Coating Aluminum Substrate Aluminum Substrate Aluminum Substrate 4

5 Bond (Structural Adhesive) Primers Current State DFARS Compliant Aluminum Substrate Aluminum Substrate HC Bond Primer Non-HC Bond Primer Adhesive Adhesive HC Bond Primer Non-HC Bond Primer Aluminum Substrate Aluminum Substrate 5

6 Hex Chrome Free Evaluation Contributors to One or More Phases Government Academia Industry 6

7 Research Overview Research Focus Timeframe Purpose Materials Evaluated Primers/ Sealants Screening level research of the key factors for sealant performance 4 sealants, 2 primers 2 conversion coatings 2 aluminum alloys 2 fastener types Sealants DFARs compliance for sealants Sealant removal evaluation 6 sealants Bond Primers (structural adhesive primers) DFARs compliance for bond primers 6 bond primers 2 adhesives 2 aluminum alloys 3 surface preparations Conversion Coatings Totally hex chrome free stackup: conversion coating, sealant, primer, & topcoat 7 TBD

8 Sealants Sealants containing soluble hexavalent chromium compounds are used in aerospace/defense manufacturing primarily for the filling of gaps and recesses to prevent water intrusion in an attempt to prevent corrosion of the base metal. 8

9 Sealant Applications 1. Sealant applied to the threads of a fastener (wet installation) 2. Sealant applied to the ends of a fastener 3. Sealant applied to butt joint (for example a ¼ inch gap between materials) 4. Sealant applied to faying surfaces (the surfaces of materials in contact with each other and joined together) 9

10 Sealant Research Project Objectives Conduct technical performance testing to evaluate the corrosion resistance of six types of sealants for four different types of sealant applications. The research results should provide significant statistical data to justify the use of DFARS-compliant assembly including hex chrome free sealants. Continue the working relationship with research participants as a basis for continued collaborative research. 10

11 Sealant Selection Vendor PPG Aerospace Vendor PN PS-870 Specification Purpose Chemical Class Corrosion Inhibitor MIL-PRF Type II Class 1 Grade A 3M AC-735 MIL-PRF Type II Class 1 Grade B and AMS 3265 Class B Baseline Polysulfide Hexavalent chromium Alternative Sealant Polysulfide Zinc phosphate PPG Aerospace PR-1775 AMS 3265 Class B Alternative Sealant Polysulfide Phosphite salt, other materials PPG Aerospace PR-2870 (RW ) MIL-PRF Type II Class 2 Grade B Alternative Sealant Polythioether Proprietary Flame Master CS 5500N CI Not yet qualified Alternative Sealant Polysulfide Molybdates PPG Aerospace PR-1440 AMS-S-8802 Type 2 Class B Negative Control Polysulfide None 11

12 Test Vehicle Assembly Drawing Three aluminum plates: 2 x 4.5 x 0.25 (alloy 7075 only) 2 top plates 8 stainless steel fasteners with 100 degree countersunk heads 1 bottom plate 12

13 Areas of Inspection: 1) Butt Joint & Faying Surface Butt joint area (2 sides and bottom area with scribe) Faying surface area of two top plates 13 Faying surface of bottom plate (not including the bottom of the butt joint

14 Areas of Inspection: 2) Fastener Hole Areas Countersink hole area (for 8 holes per TV) Hole barrel area on top and bottom plates (for 8 holes per TV) 14

15 Sealant Research Process Test plan development All participants Test vehicle mechanical stress analysis Northrop Grumman Test vehicle CAD design Raytheon 15 Aluminum plate machining NASA

16 Sealant Research Process Conversion Coating (MacDermid Iridite 14-2) Northrop Grumman Test Vehicle Assembly* Raytheon Test Vehicle Preconditioning U.S. Navy *Fasteners for the test vehicle provided by Bombardier. 16

17 Sealant Research Process Accelerated Corrosion Test 1,000 hours SO 2 Salt Fog, ASTM G85 Annex 4 (24 Test Vehicles) Lockheed Martin Long-term Corrosion Test 1 year duration (6 Test Vehicles) NASA 17

18 Sealant Research Process Sealant Removal TURI, UMass Lowell Corrosion Inspection & Analysis Lockheed Martin Statistical Analysis & Write Paper TURI, UMass Lowell 18

19 Primer Research Results In general there was no significant difference in corrosion resistance observed between Hex Chrome containing primer or Hex Chrome-free primer regardless of aluminum alloy or conversion coating used. Metal Finishing Magazine May/June 2013 edition 19

20 Sealant Research Results For the faying surface/butt joint areas, several alternative sealants containing non-hex chrome corrosion inhibitors (AC-735, CS 5500N CI, PR-1775, and PR-2870) provided equivalent corrosion prevention performance to the baseline sealant PS-870. For the fastener holes and ring around the fastener areas, several alternative sealants containing non-hex chrome corrosion inhibitors (AC-735, PR-1775, and PR-2870) provided equivalent corrosion prevention performance to the baseline sealant PS-870. Hex Chromium-Free Sealants for Defense and Aerospace August 2014 (print and on-line versions) 20

21 Sealant Remover Project Background Polysulfide and polythioether based sealants are widely used in the aerospace/defense industry to seal and protect components of aircraft, missiles, and other products. Maintenance, repair, and overhaul (MRO) operations require the removal of sealant from coated surfaces, mostly with the aid of sealant removal chemicals. In the aerospace/defense industry, commonly used sealant removers include hazardous chemicals such as toluene, methylene chloride, and N-propyl bromide. 21

22 Sealant Remover Project Approach This assessment identifies and evaluates potentially safer alternatives for sealant removal applications. The sealant removal performance of the alternatives was evaluated using a designed experiment. The environmental, health, and safety impacts of the alternative removal products were evaluated using the Pharos Chemical and Material Library chemical hazard assessment tool and the Toxics Use Reduction Institute s Pollution Prevention Options Assessment System (P2OASys). A complete description of the research approach, methods, and results will be provided during Session D: Cleaners, Strippers, and Solvents: What s What and Who s Who? 22

23 Sealant Remover Project Results For the technical performance of the sealant removers, the Polygone 310 AG product had the best results for all the sealant removers evaluated. The Diestone DLS, SkyKleen 1000, and Soy Safe Graffiti Remover products exhibited sealant removal performance comparable to that of toluene. For environmental, health, and safety considerations, the SkyKleen 1000, Polygone 310 AG, and Diestone DLS products had safer chemical profiles than toluene, npb, and methylene chloride. The Soy Safe Graffiti Remover could not be fully evaluated because of limited information on the MSDS and the non-disclosure of the actual ingredients of the product. Assessment of Safer Polysulfide and Polythioether Sealant Removers for Aerospace/Defense Industry Applications October 2014 (on-line version) 23

24 Upcoming Research Results Bond Primer Hex Chrome Free Research: Evaluation still in process. Anticipate results to be available around summer Conversion Coating Hex Chrome Free Research: Anticipate research to be initiated during late

25 For Further Information Greg Morose Toxics Use Reduction Institute University of Massachusetts Lowell _Defense_Industry_Collaborative_Research 25