Flexible mold

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A mold is a hollow shape which exactly encloses the shape of a desired object. The object is usually created by pouring a liquid into the mold and allowing it to solidify: typical liquids include molten metal or plastic, plaster of Paris, epoxy resin.

Molds generally divide into two classes: solid or flexible.

There are five different types of flexible mold compounds in significant use today.

Contents

[edit] Hot-Melt

polyvinyl chloride

  • inexpensive, worn molds can be melted and recast.
  • hazardous to handle due to high temperatures required for melting.
  • use limited to model and pattern materials that are heat resistant.

[edit] Latex

  • produces a very elastic, thin-walled, strong mold
  • shrinkage is high
  • molds must be supported to prevent distortion.
  • 10 to 20 brush coats must be applied for adequate thickness, with time allowed to "dry" in between each coat, making the mold is slow and time consuming.

[edit] Silicone rubbers

  • excellent molds for casting resins and foams
  • material cost is extremely high.

[edit] Polysulfide rubbers

  • versatile and are especially useful for casting plaster, Hydrocal, and other water mixed cements.
  • can be used for casting wax candles and some limited use for resin casting.
  • easy to handle, non-adhesive and can be poured over clay or practically any type of model or pattern, using very simple release agents such as soap or Vaseline.
  • can be used to take impressions directly from a waterclay or plastelene model, so that permanent master models can then be cast in plaster or Hydrocal.

[edit] Polyurethane flexible mold compounds

  • limited shelf stability
  • "moisture conscious"
  • easy to handle with simple mixing ratios and good fluidity.
  • can be used for pouring practically any type of cementitious material, casting resin or foam formulation.
  • Cost of material is far below that of the silicones and appreciably lower than polysulfides.

From the standpoint of general utility and economy, the polyurethanes surpass all other types.

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