SOP: Internal Slosh-Coating for 3D-Printed Manifolds
Objective: Create a continuous, pinhole-free internal barrier resistant to Jet A-1 and hydraulic fluids. Material:Caswell Phenol Novolac Epoxy (or equivalent fuel-tank grade).
1
Internal Surface Prep
20 min + drying time
Thoroughly degrease the internal bore using Isopropyl Alcohol (99%). 3D prints can harbor oils from handling or manufacturing. Blow out with compressed air to ensure no loose carbon fiber dust or support fragments remain. The interior must be bone dry.
2
Port Masking
10 min
Seal all but one opening of the manifold using silicone plugs or heavy-duty painters tape. For threaded ports, use sacrificial plastic bolts to ensure the epoxy doesn’t foul the threads.
3
Precise Mixing
5 min (Critical Step)
Mix the Caswell epoxy in a clean container using a 2:1 ratio by volume. Stir slowly for 2 full minutes to avoid introducing air bubbles. Do not whip the mixture; micro-bubbles create leak paths in the cured coating.
4
The Slosh Cycle
15 min
Pour the mixed epoxy into the open port until the manifold is ~25% full. Seal the final port. Rotate the manifold slowly in all axes—think of a rotomolding motion—ensuring the fluid coats every internal “ceiling” and corner.
5
Drainage & Clearing
20 min
Open the ports and drain the excess epoxy back into a container. Crucial: Use a low-pressure air line (5 PSI) to gently blow through the manifold for 5 minutes. This prevents “pooling” in deep pockets which could restrict flow or alter the manifold’s internal volume.
Curing Schedule
Novolac epoxies are high-performance and require patience to achieve full chemical cross-linking.
- Initial Set: 8–12 hours at room temperature (75°F / 24°C). The part is safe to handle but not chemically resistant yet.
- Functional Cure: 24–48 hours. The coating is hard and can be pressure tested with water.
- Full Chemical Resistance: 7 days. Do not expose to Jet A-1 or Skydrol before this point.
Pro Tip: To accelerate the process for industrial deadlines, you can “force cure” the part after the initial 12-hour set. Place it in a curing oven at 140°F (60°C) for 4 hours. This ensures maximum cross-link density and immediate fuel readiness.
Post-Coating Inspection
Before putting the part into service, perform a visual check using a borescope if possible. Look for:
- Uniformity: A glossy, “wet-look” finish across all visible internal surfaces.
- No Pooling: Ensure no thick “slugs” of epoxy have hardened in narrow channels.
- Adhesion: Ensure no visible peeling at the port entries.
Which O-ring materials and sealants are best specifically for Skydrol exposure vs. standard mineral-based hydraulic oils?