Composite construction notes

EPOXY NOTES

Paste (thin) THV-500 epoxy

(10.02.2013) – This is like thick paint / yogurt. Still cascades, flows , drips from the wooden stirring stick

  • 67% – base
  • 33% – harder
  • 15% – glass bubbles
  • 3% – aerosil

Example:

  • 21gr epoxy
  • 3,1gr glass bubbles
  • 0,6gr aerosil

Paste (thick) THV-500 epoxy (firm no dripping)

(10.02.2013) – This is like whipped cream remains firm on wood stirring stick. Used it on a 4″ Phenolic tube for fin fillet with radius = 5. Fillet is light weight and finishing with alocohol is good. However strength & adhesion could be upgraded when epoxy paste like THV-700 or polymix paste is used. 21gram epoxy + 4,6gr fillers is enough for a 4 fin HPR rocket with radius 5mm.

  • 67% – base
  • 33% – harder
  • 19% – glass bubbles
  • 3% – aerosil

Example:

  • 21gr epoxy
  • 4,0gr glass bubbles
  • 0,6gr aerosil

Paste (firm) THV-500 epoxy (polyservice-style)

(05.08.2009) – This is more a dry putty like play-doo / chewing gum (but lighter) consistincy with a very fine texture. Does not stick well. Can be rolled in you hand into a ball. Because it is dry, finishing can be tricky. When filliting with a dowel I saw some rimples in the finishing due to friction. For obtaining a nice shiny paste I would propose to use only halve of the suggested glass bubbles and aerosil

  • 67% – base
  • 33% – harder
  • 30% – glass bubbles
  • 6% – aerosil

Example:

  • 4gr – base
  • 2gr – harder
  • 2gr glass bubbles (4 teaspoons)
  • 0,36gr aerosil (1 teaspoon)

Final sand coat Jurriaan (27.02.2008)

  • 4gr – base
  • 2gr – harder
  • 0,5gr glass bubbles (1 teaspoon)
  • 0,18gr aerosil (1/2 a teaspoon)

Paste by volume THV-500 epoxy (compositerockets-style)

  • 1ml epoxy
  • 3ml glass bubbles

Example:

  • 6ml epoxy (4 + 2 gr) – 100%
  • 18ml glass bubbles / 3,5 teaspoons (1,35gr) – 22%

Fillers

Glass Bubbles.

100ml = 9gr = 20 teaspoons’

  • 1 teaspoon = 0,45gr by weight
  • 1 teaspoon = 5,00ml by volume

These bubbles are actually hollow glass spheres. Because this high-quality glass is very crush resistant, the foam is much stronger, stiffer and water-resistant than any foam made by chemical foaming. These foams displace 4-6 times their weight in most resins and improve the handling characteristics of the base resin. They have a low bulk density and are nontoxic. Mix resin and hardener as directed, then fold in the glass bubbles. Upon cure, a strong, low-density product results which is easy to sand and file. May be shaped to form compound angles and curves. The term “micro” was applied to the mixture of microspheres and epoxy early in the development of composite structures. Although microspheres have been replaced by glass bubbles the word “micro” is still commonly used to reference the mixture. “Micro is used to fill voids and low areas, to glue foam blocks together and as a bond between foams and glass cloth. Micro is used in three consistencies – (1) a “slurry” which is a one-to-one by volume mix of epoxy and glass bubbles, (2) “wet micro” which is about two to four parts glass bubbles by volume to one part epoxy, and (3) “dry micro” which is a mix of epoxy with enough glass bubbles to obtain a paste which will not sag or run (about five parts to one by volume). In all instances, glass bubbles are added to completely mixed epoxy resin and hardener. Wet micro is used to join foam blocks and is much thicker than slurry (it has the consistency of honey) but can be brushed. Dry micro is used to fill low spots and voids and is mixed so that it is a dry paste and will not sag. Apply with a putty knife. Never use micro between glass layers. CAUTION – When mixing epoxy and glass bubbles, wear a dust mask and keep your face away from the balloons that may float up into the air. Although glass balloons are inert, they can lodge in your eyes or in your lungs and cause problems. Handle with care.

Cab-O-Sil / AEROSIL

  • 100ml = 5,5gr = 20 teaspoons
    • 1 teaspoon = 0,24gr by weight
    • 1 teaspoon = 5,00ml by volume

is a fumed lightweight silica thickener used to reduce the flow of epoxies on vertical surfaces, as well as filling pinholes with its smooth texture.

Cotton Flox a structural resin filler. The mixture of cotton fiber and epoxy is referred to as “flox”. The mixture is used in structural joints and in areas where a very hard, durable buildup is required. Flox is mixed in much the same way as dry micro but only about two parts flock to one part epoxy is required. Mix in just enough flock to make the mixture stand up. If “wet flox” is called out, mix it so it will sag or run. Flox is often used to reinforce a sharp corner. Paint a light coat of pure epoxy inside the corner, trowel flox in to make a triangular support. The flox corner is done just before one glass surface is applied for a wet bond to one surface.

Milled Glass as the name implies, this material is made by milling fiberglass into a very thin consistency. This material is used in preparing a structural filler. This material is used in fillets that require structural integrity. Milled fiber fillers have higher strength than cotton flock but have fine particles of fiberglass that can penetrate the skin.

Source: Aircraft Spruce and Specialty – http://www.aircraftspruce.com/menus/cm/thickening.html