Shore Hardness is the resistance a material has to indentation. Determining a materials Shore Hardness requires the use of a durometer, which is a device that measures the depth of an indentation in the material by creating force through a presser foot.
In order for people to have a point of reference on how hard a material is different shore hardness scales have been created. There are 12 different Shore Hardness scales depending on the type of material that is being measured.
When dealing with rubbers and plastics two scales are used. The A Shore Hardness scale is used to measure flexible rubbers commonly used in molds. Hard rubbers, semi-rigid plastics and hard plastics are measured using the D Shore Hardness Scale.
Both of these scales have ranges from 0-100. The lower the Shore Hardness is on the scale the softer and more flexible the material will be. As you increase upwards on the scale materials become stiffer and less flexible.
When selecting a rubber or plastic to use for your mold making needs there are a couple of things that should be taken into consideration.
How delicate is the item that you’re molding.
If you’re making a mold of an item that has sharp undercuts, thin parts or protrusions it is recommended to use a material that provides greater flexibility and stretches easily. This will insure that you’re able to extract your model from the mold without it breaking.
How much detail is needed for your project.
When using rubbers and plastics detail is directly related to the hardness of the material that you’re using. The harder a material is the greater casting detail it will provide. For example, if you were making a mold for a stone back splash you would want to use a harder material to pick up textural detail within the rocks.
Abrasion resistance refers to a materials ability to withstand any method of wearing down or rubbing away by means of friction. This point should be taken into consideration if you are planning to use a rubber or plastic mold for construction applications. Some of these application would include architectural precast concrete, cast veneer and flexible form liners. In construction applications you want your material to provide enough flexibility, while being durable and insuring a long useful life.
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