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Great Video: How to make 2-Part Silicone Mold | Part 1
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Great Video: How to make 2-Part Silicone Mold | Part 1

Understanding Platinum Silicones

This section provides an overview of platinum silicones, their properties, and differences compared to tin silicones.

Properties of Platinum Silicones

  • Platinum silicones have low viscosity, making them easy to mix, pour, and evacuate air bubbles.
  • They cure well against a wide variety of materials.
  • They come in a range of hardness options, from extremely soft to very firm.

Curing Issues with Platinum Silicones

  • Platinum silicones can have issues when poured against certain surfaces such as clays containing sulfur, natural rubbers, enamel and latex paints, some resins used in 3D printing, and tin-catalyzed silicones.
  • It is recommended to run a small test on an unknown surface before using platinum silicone.
  • Applying an acrylic sealer coat can help prevent curing issues on questionable surfaces.

Advantages of Platinum Silicones

  • Platinum silicones have higher temperature resistance and are more dimensionally stable over time.
  • They can accommodate a wider variety of polyurethane chemistries for casting purposes.

Choosing the Right Silicone for the Project

  • For the project discussed in the transcript (making a mold for a helmet), TC 5041 platinum silicone with a 45 shore hardness and excellent tear strength was chosen.
  • The silicone has relatively low viscosity for easy pouring and produces a firm yet flexible end product.

Mixing and Pouring Silicone

This section covers the process of mixing and pouring platinum silicone for mold-making.

Calculating Silicone Quantity

  • The inside volume of the mold box is measured and subtracted from the master's volume to determine the required amount of silicone.
  • A minimum of 3.38 pounds of silicone is needed based on density values provided in the datasheet.

Mixing Ratio and Preparation

  • The TC 5041 platinum silicone has a mixed ratio of 100 parts A to 10 parts B.
  • It is recommended to mix an extra 15-20% of material to account for variations in calculations and residue.

Mixing Process

  • The double mix method, as described in the video "How to Properly Mix Two-Part Resin Systems," is used.
  • Sufficient room above the liquid is left in the mixing container to allow for expansion during vacuuming.

Vacuum De-Airing

  • Vacuum de-airing the silicone before casting helps achieve better mold quality and longevity.
  • An ideal vacuum de-airing system requires a pump capable of pulling high levels of vacuum (28-29 inches of mercury) with a minimum rating of 5-6 CFM.

Pouring the Silicone

  • The first half of the mold is poured by slowly streaming silicone on the flange, not directly on the master, to prevent air entrapment.
  • The silicone is filled until it reaches the top level of the box.

Demolding and Applying Mold Release

This section explains demolding techniques and applying mold release before pouring the second half of the mold.

Demolding Process

  • The splitter board is removed from the bottom of the mold box after an overnight cure.
  • A thinner piece of plastic supported by thicker MDF wood is used as a flexible splitter board for easy removal.
  • Styrene sheet alignment keys are removed, and any silicone flashing is trimmed with a sharp hobby knife.

Applying Mold Release

  • Before pouring the second half of the mold, motor lease (aerosol spray designed for silicon-to-silicon applications) is applied to exposed silicone surfaces.
  • To avoid surface texture and overspray on details like alignment keys, a styrene cutout is used to shield them while applying aerosol spray or manually applying mold release with a small acid brush.

The transcript is already in English, so there is no need to respond in a different language.

Adding Discussion New Section

This section discusses the need to discuss adding something at a certain point in the transcript.

Adding Discussion

  • At 0:15:23 , it is mentioned that there is a need to discuss adding something.
Video description

Link to PART 2 - Casting the Urethane Part: https://youtu.be/tnY86LIHf_I Making a 2-Part silicone mold is an essential skill to learn for casting polyurethanes. Using simple methods developed over several decades in Rapid Prototyping, learn how to make a silicone mold that produces high quality parts. For 40 years, BJB Enterprises, Inc., an ISO 9001:2008 Company, has been in the business of formulating and supplying quality liquid resin systems to a vast array of industries and with a myriad of applications in mind! BJB offers a complete line-up of Castable Polyurethanes, Epoxy Systems, Silicone Casting Rubbers, Polyurethane Foam Systems, Aliphatic Water Clear Urethanes, Sprayable Polyurethanes, Pigments and Release. Be sure to visit our website: www.BJBEnterprises.com 0:00 Introduction 0:47 Rigid Plastics 0:52 Rigid & Flexible Foams 1:08 Two Part Silicone Mold 1:55 Primed and painted with clear auto paint. 3:25 Double-Sided Tape 4:28 Cut Thin Strips of Tape 4:33 Apply Thin Perimeter 4:39 Measure & Mark Master 4:49 Peel Off Backing & Place On Splitter 5:10 Fill with Modeling Clay & trim with Shaping Tool 5:46 Feathered Edge 6:04 Demold clean part simulating an injection molded part 6:17 Styrene Sheet 6:32 Fasten with glue or tape 6:51 Pre-Molded Keys 7:57 Building Blocks 8:02 Large Diameter Pipe 8:14 Silicone can form a mechanical lock on rough surfaces 8:22 ABS Plastic Sheet 8:50 Making walls too thin can cause distortion 9:02 Mold box with clamps incorporated 9:11 Hot Glue to Splitter Board 9:37 Tin Catalyzed (condensation cured) 10:12 Sulphur Containing Clays 10:27 Run Small Test on Unknown Surfaces 12:25 Use a mixing container with plenty of room for expansion. 13:14 Continue pulling vacuum for several minutes. 14:39 Aerosol Spray creates a texture 15:38 Plastic Rod 15:53 Provide Make-Up material from shrinkage. 16:24 Vent Risers 16:51 Risers decrease wear on the mold 17:14 Equipment Injection 17:32 Placement of fill port & vents is a critical detail.