SITIS Archives - Topic Details
Program:  SBIR
Topic Num:  AF071-107 (AirForce)
Title:  Rapid Cure, Environmentally Acceptable Liquid Shim
Research & Technical Areas:  Materials/Processes

  Objective:  Develop an environmentally acceptable rapid cure liquid shim for aircraft application.
  Description:  A liquid shim material is used in abundance on modern aerospace structures to control outer mold line (OML) surfaces to specified design tolerances. The currently qualified liquid shim material is a two part epoxy resin which requires an 8 hour cure. Unfortunately, the long cure time results in a bottle neck in the military aircraft assembly sequence. The liquid shim material also contains crystalline silica, a known human carcinogen, to enhance both the physical properties of the material and flow characteristics. Crystalline silica exposure limits are regulated by the Occupational Safety and Health Organization. Potential international partners are also concerned with the presence of crystalline silica since US regulations are not as stringent as those established by the European Union. Test data collected to date has shown that the permissible exposure limits can be exceeded during normal production operations such as sanding and drilling. An environmentally acceptable liquid shim material must have the following attributes: environmentally acceptable (zero VOC, no HAPS/HAZMAT), cure time <1 hour, sandable in <4 hours, 25 percent flexibility (-65 to 250 F), and be resistant to standard aircraft fluids

  PHASE I: The contractor shall select commercially available resins, additives, and extender pigments to meet the above attributes. The contractor shall formulate trial batches of shim materials and characterize cure time and flexibility. The contractor shall identify a final shim material formulation.
  
  PHASE II: Develop, test and demonstrate characteristics of the proposed material system to meet or exceed requirements of aircraft manufacturers. The contractor shall identify a representative structural component for demonstration of the shim material in an operational environment. The contractor shall produce enough liquid shim material for characterization of material properties.

  DUAL USE COMMERCIALIZATION: Military application: Potential transition to the fleet via specification modifications and revisions to Aircraft Weapons Systems technical manuals. Any logistical constraints will be resolved during this phase. Commercial application: Similar requirements are needed for commercial aircraft.

  References:  1. Mollie, J.-P. Paquet, R.L., "Performance of new silicone adhesives and encapsulants at high and low temperatures", Automotive Electronics, 1991, Eighth International Conference on Automotive Electronics, 28-31 Oct 1991, pp 174-177 2. 29 CFR 1926.55, 1910.1000 (OSHA PEL for Crystalline Silica) 3. J. D. Donaldson, S. M. Grimes, A. D. Houlson, S. Behn, "Curing of a polysulfide sealant with sodium birnessite", Journal of Applied Polymer Science, Vol. 77, No: 6, pp 1177-1181

Keywords:  liquid shim, crystalline silica, silica, rapid cure

Questions and Answers:
Q: 1. Is the substrate that we are shimming composite or steel?

2. Are we shimming between two substrates or is this applied to the surface?
A: 1. Composite and some aluminum.

2. Both.
Q: 1) What type of thickness are you looking for?
2) Is this a new project or are you already working with someone else on it?
3) Has anything been tried in the past?
A: 1) Up to 0.1 inch.

2) This is a new SBIR topic.

3) Not to replace the silica.
Q: 1. Is the substrate that we are shimming composite or steel?

2. Are we shimming between two substrates or is this applied to the surface?
A: 1. Composite and some aluminum.

2. Both.
Q: 1) What type of thickness are you looking for?
2) Is this a new project or are you already working with someone else on it?
3) Has anything been tried in the past?
A: 1) Up to 0.1 inch.

2) This is a new SBIR topic.

3) Not to replace the silica.

Record: of