DRAGON INNOVATION, INC.

COURSE 13BASICS OF WATERPROOFING

DECEMBER 10, 2014

WILLIAM DRISLANE | VP ENGINEERING & MANUFACTURING | @DRAGONINNOVATE | WWW.DRAGONINNOVATION.COM

Waterproofing standards

What is being done?

• Water proof container? Like a tank, or bottle…• Do you need to be able to open it?• Does it have fittings? How are you handling air in the tank?• Are you protecting electronics?• Is it permanent or replaceable?• Do you have to clean it?• Is it strong and thick enough to handle clamping loads (Space

for screws)• Space constraints force a face seal?• Can you use hoop stress?

TYPES OF SEALS

O-Ring (Removable)

O-Ring, Continued

• Types of O-ring seals• Face Seals

• Removeable• Single-use (crushed)

• Circumferential (Gland) Seals• Dynamic• Static

• Groove design• Rectangular• Half-dovetail• Dovetail

O-Ring, Continued• Factors that affect O-ring sealing performance

• Dimensions• % Compression of O-ring• Surface finish of groove• Direction (lay) of the grain of surface finish in groove• Chemical compatibility - O-ring and groove material• Entrapment of fluid behind O-ring - ‘burping’ and ‘virtual

leaks’.• For dynamic seals

• Speed, friction, and heating of O-ring• Thermal runaway driven by negative CTE.

• Proper lubricant• Contamination• Temperature

• —> Use Parker or Apple Rubber O-ring handbooks

Permanent Joints (Welding)

• Ultrasonic Welding: High frequency, low amplitude. Good for smaller parts. Joint design is important, can also use specific textures.

• Vibration welding: Good for larger parts. Lots of flash, needs special joint to control the flash. Melts lots of plastic.

• Spin Welding. Circular joint. Heat parts by mechanical friction• Laser welding. Send IR laser through translucent part to

opaque part. Laser heats weld interface. Must have strong contact between parts. Part size does not matter.

• Solvent Bond: Generally MEK based solvents. Must control temp and humidity, can be messy and hard to control. Not best for hermetic seals.

• RF Welding. Good for thin sheets like a bladder design.• Hot Plate welding. Good for butt joints and large parts. A bit

messy.

Permanent Joints (Welding)

Permanent Joints (Welding)

Permanent Joints (Welding)

Protecting Electronics

• Conformal Coating. Generally a silicone coating used to protect electronics in an enclosure from humidity and incidental contact with fluids. Main advantage is it allows parts to be inspected and re-worked. Disadvantage is not an absolute seal.

• Potting: Generally Epoxies or Urethanes. Completely encapsulates the electronics. If Surface mount components used needs to remain flexible

LPMS

• Low Pressure Molding

• Generally a Nylon base material

• Basically hot melt glue

• Can also get Polyester based systems

• Can get in different colors, durometers, adhesive properties

F$%#@!& Wires!

• If have wire bundles, there are small gaps between them. Creates capillary action that pulls water into your electronics.

• Need to try to separate them to eliminate gaps.

• Strain Relief beyond seal point. If wires are flexing back and forth, seal will be effected.

• Select a sealing agent that bonds well to the wires

• Try to match expansion rates, or ensure sealant is flexible (RTV)

• If Using RTV make sure there are no motors effected by silicone oxides from off-gasing.

dragon@dragoninnovation.com