What effect does temperature have on the mold making and casting processes?
Posted on 7/24/2014
Mold making and casting materials are affected by temperature in different ways and under different circumstances depending on the base chemistry.
• Latex mold making rubber, latex foam and acrylic latex polymer products (such as Matrix G, C and Neo).
For best results, store and use latex products at room temperature (72°F / 23°C). Important: if latex is allowed to freeze, it is unusable and should be discarded.
Cold – Any material containing latex is susceptible to cold temperatures. Using latex in cold environments will prolong the evaporation process, especially if humidity is high.
Heat – higher temperatures will accelerate the cure of latex. If making
a mold with latex rubber, higher temperatures in dry conditions (low humidity) will accelerate evaporation of the rubber.
Humidity – humid environments will slow the evaporation process thereby slowing the cure of latex rubber.
• Urethane Rubbers, Plastics and Foams
For best results, store and use urethane products at room temperature
(72°F / 23°C). If material freezes, it can be used after being brought back to room temperature. Thoroughly pre-mix Parts A & B before dispensing.
Cold – Colder environmental temperatures will increase working time (pot life) and delay cure time of urethane rubbers and plastics. If urethane rubber or urethane plastics that take overnight to cure are applied in too cold of an environment, they may not cure at all.
Heat – Elevated temperatures will reduce the pot life and cure time of urethane rubbers and plastics.
Humidity – Urethanes are easily affected and should be used in a low humidity environment. Humidity will react with urethanes and may cause bubbles or foaming in the material.
• Silicone Rubber
For best results, store and use silicone products at room temperature
(72°F / 23°C). If material freezes, silicone base will become very thick. It can be used after being brought back to room temperature.
Important: storing silicone in elevated temperatures can significantly reduce the shelf life of unused product.
Cold – Tin-Cure Silicones – Colder temperatures do not have as dramatic an effect as they do on other materials. Accelerated silicones can even be used to make molds over frozen models.
Platinum-Cure Silicones – Colder environmental temperatures will increase working time (pot life) and delay cure time of platinum silicones. If applied in too cold of an environment, they may not cure at all.
Tin-Cure Silicones – warmer temperatures do not have as dramatic an effect as they do on other materials. You cannot “heat cure” tin-catalyzed silicones.
Platinum-Cure Silicones – Elevated temperatures will reduce the pot
life and cure time of platinum catalyzed silicone rubber. Many mold makers will use heat to accelerate the cure time (demold) of platinum silicone molds.
Tin-Cure Silicones – Will cure faster in humid environments.
Platinum-Cure Silicones – Humidity generally does not affect platinum silicones.
In addition to environmental temperatures, you need to monitor :
1. Temperature of material in containers – You may be using material in an environment that is at room temperature, but the temperature of material in the containers will dictate how the material behaves. Example, if you store urethane plastic in a hot garage and bring it inside to a 72°F / 23°C environment to use it, the pot life might be half of what you would normally expect.
2. Temperature of original model or mold – Mold Making – if the model to which you are applying rubber is too cold, mold rubber will take longer to cure or may not cure at all. Make sure your original model is exposed to at least room temperature several days before applying mold rubber. What If My Model Is Frozen? There are applications calling for making a mold over a frozen model. It is best to use an accelerated silicone rubber (such as Mold Max 30 with Fast Cat curative). The model will begin to condense as soon as it is exposed to warm temperatures, and the moisture coming off of the model will not affect accelerated silicone.
Casting – if you are casting a fast cure urethane plastic that has a high exotherm into a cold mold, you may experience what is known as “thermal shock”. Thermal shock may cause surface imperfections in the casting.
Post Curing At Elevated Temperatures – See “Heat Curing & Post Curing”
The FAQ list is offered as a guideline and offers possible solutions to problems encountered during mold making and casting. No warranty is implied and it is up to the end user to determine suitability for any specific application. Always refer to the provided Technical Bulletins (TB) & Material Safety Data Sheets (MSDS) before using any material. A small scale test is suggested to determine suitability of any recommendation before trying on a larger scale for any application.