HT2C High Temperature Tooling Compound
HT2C is a strong, lightweight, fiber reinforced paste epoxy system designed for preparing tools and fixtures that will be exposed to elevated service temperatures. HT2C is a high temperature epoxy novolac system that has excellent heat resistance. The cured material exhibits very good toughness for stable, durable tools. When used in the sandwich panel construction method described here, HT2C provides lightweight, strong, stable tools that will give long service in a variety of high temp applications. HT2C is a syntactic paste that has lightweight micro spheres incorporated to give the cured product lighter weight for easier handling. The resin and hardener components have very smooth consistencies. They combine easily to a creamy, workable paste that is easy to handle and apply. The system is color coded to insure a uniform, consistent mix. The curing exotherm of HT2C is very low, so shrinkage is negligible. HT2C is a non-toxic product, for improved safety in the work place. Clean-up is easily accomplished with soap and water. Tools fabricated with HT2C are easy to handle, have a very high strength-to-weight ratio, are very stable, and easily machined.
|HT2C Resin||HT2C Hardener||ASTM Method|
|Viscosity||Smooth Paste||Smooth Paste||D2392|
|Specific Gravity, gms./cc||.7||.7||D1475|
|Mix Ratio, by Weight||100 : 33||PTM&W|
|Pot Life, 4 fl oz Mass @ 77°F||45 – 60 min.||D2471|
DIRECTIONS FOR USE
For general tooling applications, a sandwich construction method is
recommended as follows: Apply 2 layers of PT1935 A/B epoxy surface coat
to a properly prepared pattern using standard techniques. If desired,
PT1995 graphite filled surface coat can be used. Follow with 2 or 3
layers of Style 7500 type glass cloth impregnated with high temperature
laminating resin. A ¼ to ½ inch thick layer of HT2C is then applied to the back of the high temp laminate. The HT2C
layer is allowed to stand until it is firm enough to proceed. Finally,
an additional 2 or 3 ply layer of cloth and high temp laminating resin
is applied to the back of the HT2C.
(1.) Mixing – HT2C resin and hardener are color coded to give a visual indication of a uniform, thorough mix. Small quantities of HT2C can be mixed by hand, but mechanical mixing is much more efficient for larger batches. Either a dough mixer or a stationary paddle 5-gallon pail mixer will do a good job of mixing HT2C. A uniform gray color, free of light or dark streaks indicates complete mixing.
(2.) Roll Out The HT2C – A constant and uniform thickness is always desirable in a composite tool, no matter what the construction method. This approach yields the most consistent performance as well as the most efficient use of materials. The best way to achieve this with HT2C is to utilize a “roll-out” board. This is a board 1 to 1.5 feet wide, about 3 feet long. Thickness spacers are attached to the surface so that HT2C can be rolled out like bread dough to a uniform thickness. First, a layer of waxed kraft paper or plastic film is placed on the board. Then a quantity of mixed HT2C is placed onto the waxed kraft paper or plastic film, and a second layer of paper or film is placed on top of the HT2C. A large diameter PVC pipe is then used to roll the HT2C to a uniform thickness, as determined by the thickness of the spacers.
(3.) Transfer to the Tool – After the HT2C is rolled out, cut it into manageable pieces of approximately 1 square foot. Then transfer the HT2C to the tool and lay it onto the wet top layer of the laminating resin. The mixed HT2C has good cohesive properties, and is not crumbly, so the transfer is easy to do. In placing the pieces of HT2C, be sure to butt the adjoining edges together properly so that there are no voids in the tool, which would cause weak spots. Also, press the HT2C firmly into the wet resin layer, so that there are no voids just behind the tool surface. A “tie coat” is sometimes used between the laminate and HT2C layer to provide better adhesion to the laminate and minimize trapped air between the layers. A quantity of mixed HT2C is diluted with mixed high temperature laminating resin to yield a thick, paintable consistency, and brushed onto the laminate before the HT2C pieces are applied. This “tie coat” provides a good bond, and fills any small gaps between the layers, for better cured performance.
(4.) The Backing Laminate – When completing the tool, the HT2C must be allowed to firm up somewhat before the laminate is applied. Thirty to forty minutes is usually sufficient, but the actual time required will depend upon the ambient temperature in the shop. After the HT2C is firm enough, the top layers of epoxy and fiberglass are applied, and the tool is ready for curing. A “tie coat” is not needed with the backing laminate, as the laminating resin will naturally soak into the HT2C a little, bonding well.
(5.) Curing The Tool – HT2C will gel at room temperature, but requires an oven post cure before service. Always allow the HT2C tools to gel completely at room temperature before post curing – 18 to 24 hours is usually sufficient. After the room temp. cure, HT2C tools can be post cured either supported on the pattern, or free standing. Whenever possible, a supported post cure is always recommended for that extra margin of insurance against distortion. In either case, post cure the tool as follows:
a. Place the tool in a cold oven and slowly raise the temperature to 150°F, and hold for 3 to 4 hours.**
b. Then, slowly raise the temperature to 250°F, and hold for 3 to 4 hours.
c. Then, raise the temperature to 350°F, and hold for 4 hours.
d. Allow the oven to cool to room temperature. Then the tool can be removed, cleaned up and put into service.
** It should be noted that the post cure temperature stages refer to the temperature of the tool. Thermocouples are typically used to insure that the tool has reached the required temperature at each stage, before the specified time at temperature is begun.
TYPICAL MECHANICAL PROPERTIES
|HT2C A/B||ASTM Method|
|Mix Ratio, by Weight||100 : 33||PTM&W|
|Mixed Viscosity, @77°F, centipoise||Smooth Cohesive Paste||D2393|
|Pot Life, 4 fl.oz. Mass, @77°F||45 – 60 min.||D2471|
|Cured Hardness, Shore D, @77°F, @300°F*||58 – 60 Shore D||D2240|
|Specific Gravity, grams, cc||.67||D1475|
|Density, lb./cu. in.||.024||D792|
|Specific Volume, cu. in./lb.||41.5||D792|
|28 lb. Pail Kit Coverage @ 1/2″ thickness||16.2 Square Feet||PTM&W|
|Ultimate Flexural Strength, (Panel), psi||9100 psi||D790|
|Flexural Modulus, (Panel), psi||635,000 psi||D790|
|Compressive Strength, (Panel), psi||6800 psi||D695|
|Glass Transistion Temperature, Tg (Peak)||331°F||D648|
|Coefficient of Thermal Expansion, Range 200-300°F:||1.414 x 10-5 in./in./°F|