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

Hex Chrome – Uses in Defense/Aerospace Applications

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• Primers • Sealants • Bond primers (structural adhesive primers) • Conversion coatings

Source: TURI Summary of Policy Analysis

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.

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.

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TUR of Hexavalent Chromium (HC)

Aluminum Substrate

HC Conv. Coating

HC Sealant

Topcoat

HC Primer

Aluminum Substrate

HC Conv. Coating

Non-HC Sealant

Topcoat

Non-HC Primer

Aluminum Substrate

Non-HC Conv. Coating

Non-HC Sealant

Topcoat

Non-HC Primer

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Current State DFARS Compliant Hex Chrome Free

Bond (Structural Adhesive) Primers

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Aluminum Substrate

Adhesive

HC Bond Primer

Aluminum Substrate

HC Bond Primer

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Current State DFARS Compliant

Aluminum Substrate

Adhesive

Non-HC Bond Primer

Aluminum Substrate

Non-HC Bond Primer

Hex Chrome Free Evaluation Contributors to One or More Phases

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Government

Academia Industry

Research Overview

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Research Focus

Time- frame

Purpose Materials Evaluated

Primers/ Sealants

2012 - 2013

Screening level research of the key factors for sealant performance

4 sealants, 2 primers 2 conversion coatings 2 aluminum alloys 2 fastener types

Sealants 2013 - 2014

• DFARs compliance for sealants • Sealant removal evaluation

6 sealants

Bond Primers (structural adhesive primers)

2014 - 2015

• DFARs compliance for bond primers

6 bond primers 2 adhesives 2 aluminum alloys 3 surface preparations

Conversion Coatings

2015 - Totally hex chrome free stack-up: conversion coating, sealant, primer, & topcoat

TBD

Sealants

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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.

Sealant Applications

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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)

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.

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Sealant Selection

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Vendor Vendor PN

Specification Purpose Chemical Class Corrosion Inhibitor

PPG Aerospace

PS-870 MIL-PRF-81733 Type II Class 1 Grade A

Baseline Polysulfide Hexavalent chromium

3M AC-735 MIL-PRF-81733 Type II Class 1 Grade B and AMS 3265 Class B

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-6040-71 )

MIL-PRF-81733 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

Test Vehicle Assembly Drawing

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8 stainless steel fasteners with 100 degree countersunk heads

Three aluminum plates: 2” x 4.5” x 0.25” (alloy 7075 only)

1 bottom plate

2 top plates

Areas of Inspection: 1) Butt Joint & Faying Surface

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Faying surface area of two top plates

Faying surface of bottom plate (not including the bottom of the butt joint

Butt joint area (2 sides and bottom area with scribe)

Areas of Inspection: 2) Fastener Hole Areas

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Countersink hole area (for 8 holes per TV)

Hole barrel area on top and bottom plates (for 8 holes per TV)

Sealant Research Process

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Test plan development All participants

Test vehicle mechanical stress analysis

Northrop Grumman Test vehicle CAD design

Raytheon

Aluminum plate machining NASA

Sealant Research Process

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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.

Sealant Research Process

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Accelerated Corrosion Test 1,000 hours

SO2 Salt Fog, ASTM G85 Annex 4 (24 Test Vehicles) Lockheed Martin

Long-term Corrosion Test 1 year duration (6 Test Vehicles)

NASA

Sealant Research Process

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Statistical Analysis & Write Paper

TURI, UMass Lowell

Sealant Removal TURI, UMass Lowell

Corrosion Inspection & Analysis

Lockheed Martin

Primer Research Results

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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

Sealant Research Results

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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)

Sealant Remover Project Background

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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.

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).

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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?

Sealant Remover Project Results

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• 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)

Upcoming Research Results

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• Evaluation still in process.

• Anticipate results to be available around summer 2015.

Bond Primer Hex Chrome Free Research:

Conversion Coating Hex Chrome Free Research:

• Anticipate research to be initiated during late 2015.

For Further Information

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Greg Morose 978-934-2954 Gregory_Morose@uml.edu Toxics Use Reduction Institute University of Massachusetts Lowell

http://www.turi.org/Our_Work/Business/Industry_Sectors/Aerospace_Defense/Aerospace_Defense_Industry_Collaborative_Research