When molding, should choose silicone or polyurethane?
One method of replicating a sculpture is to cast it into a mold taken from the product.
How to choose materials for making elastic molds for castings made of plaster, concrete, polymer concrete, polymer (polyester and epoxy) resins?
Let's consider the advantages and disadvantages of some of the compound types available.
Flexible ("rubber") matrix forms allow you to copy and replicate complex textures and surfaces. They are used to produce artificial stone, decorative tiles, gypsum plaster moldings, small architectural moldings, statues and art products, patterned candles, fiberglass products, etc.
There are four materials used to make elastic molds: PVC (formoplast), silicone, polyurethane and thiokol materials.
When molding, should you choose silicone or polyurethane?
What about silicone for molds?
Organosilicon compounds can be single-component, two-component and multi-component.
One-component compounds are primarily construction sealants used to seal joints. They harden only in small layer thicknesses and are not used in molds.
The mold is manufactured using two-component materials: organosilicon compound (main component) + catalyst.
When mixed with a catalyst, mold silicone hardens at room temperature. This material is easy to mix and allows for variations in component dosage. No toxic substances are released when mixed. It is easily removed from the model material, exhibits virtually no shrinkage, requires no additional lubricant, and allows casting over a wide temperature range.
Advantages: The salient features of silicone casting materials are heat resistance (up to 200°C and higher), resistance to a variety of aggressive environments, ease of use and non-toxicity (silica gel is widely used in medicine), and high impression accuracy. The disadvantage is that the strength is moderate, equivalent to the strength of Formoplast, but not as strong as polyurethane.
What about polyurethane for molds?
The most expensive and durable component is cast polyurethane.
These are two-component or multi-component materials.
The price of polyurethane for molds is quite high because there are only American and European polyurethane products on the CIS market.
In Ukraine and Russia, the production of polyurethane castables for making molds has not yet been mastered.
Just like silicone compounds, molded polyurethane hardens at room temperature when all the ingredients in the kit are mixed.
The pouring instructions must be strictly followed when mixing: the proportions of all components when mixing must be observed. If the proportions are incorrect, strength and durability will be reduced because unreacted ingredients can cause shape destruction.
When opening a certain amount of packaging, the entire raw material must be used at once, i.e. it cannot be divided into different parts, since the polyurethane component begins to interact with air and moisture and deteriorate - changing its properties.
The difficulty of this job is also that polyurethane adheres strongly to any material that is released from the mold. A large amount of lubricant is required and the model must be carefully lubricated.
The ingredients of polyurethane are toxic, please do not let it come into contact with air and moisture. Major brands of polyurethane are not resistant to materials such as plaster, cement, polymer resins, etc., so you need to pay attention to the manufacturer's recommendations.
For each material, you need to choose a specific brand of polyurethane. Polyurethane molds are mainly used for materials with pouring temperatures up to 70 °C.
Advantages: high strength properties, high flexibility, low shrinkage.
Disadvantages: high price, toxic, difficult to operate, requires increased and thorough lubrication, thicker viscous materials and difficult to fill.