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Carbon Resistance Strip: Carbon and Phenolic Resin in Ethyl Acetate, Cured on Semi-Cured Phenolic Sheet
Podolsky (Wirt Company, US 2,060,114, 1936) bonded the carbon film into its base: the phenolic sheet is only half cured, the coating carries the same kind of resin, and its solvent (ethyl acetate) softens the sheet's surface. Heated calender rolls then finish the cure of sheet and coating together, so the track is hard, does not rub off and lasts. Cut across, the sheet gives resistance strips for a variable resistor.
The picture: our diagram.
Intermediate
1 day
Instructions
1
1
Mix 21 carbon, 26 resin, 53 solvent
Mix 21 carbon, 26 resin, 53 solvent
Make a solution of 21 % carbon, 26 % phenol-formaldehyde resin and 53 % ethyl acetate. The patent says the exact proportions are not essential; this is its example.
Materials for this step:
Carbon21 parts
Liquid Bakelite (Phenol-Formaldehyde Condensation Product)26 partsTools needed:
Ethyl Acetate
Balance Scale
Glass Beaker
Stirrer
Full-Face Respirator
Rubber Gloves2
2
Coat the semi-cured sheet
Coat the semi-cured sheet
Use a phenolic sheet whose cure was stopped before it fully hardened. A roller turning in a pan of the solution coats its underside.
Materials for this step:
Semi-Cured Phenolic Sheet1 pieceTools needed:
Dip Coating Roller PairFull-Face RespiratorRubber Gloves3
3
Cure between calender rolls at 350 °F
Cure between calender rolls at 350 °F
Pass the coated sheet between calender rolls heated to about 350 °F (177 °C). This finishes the cure and bonds the coating to the sheet. The patent sometimes calenders it again to burnish the surface.
Tools needed:
Heated Calender Rolls
Heat-Resistant Gloves4
4
Cut into strips
Cut into strips
Cut the sheet across into strips of the width wanted. Ours: tin snips.
Tools needed:
Tin SnipsRubber GlovesMaterials
3- 21 partsPlaceholder
- Placeholder
- 1 piecePlaceholder
Tools Required
10- Placeholder
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