If you work with moulding materials, you already know how frustrating it is when materials don’t perform as expected. Warping, curing issues, contamination, or reduced strength often come down to one simple issue:
They weren’t stored or handled properly.
The good news? Protecting your materials doesn’t require complicated systems just consistent best practice. Here’s how you can protect your moulding materials, reduce waste, and get more reliable results every time.
Silicone Moulds: Faster Curing, Less Working Time
As room temperature increases, the chemical reaction between the A and B components of your silicone rubber increases in speed. An increase of just 7°C can cut your working time almost in half. This leaves you much less time for bubbles to escape or any vacuum degassing you would do. The faster thickening can also potentially cause larger packets of air to form and leave voids in your mould, or even solidify before you’re able to even finish your pour.
If your materials are stored near machinery, heaters, or in direct sunlight, their properties can start to change long before you use them. That can lead to:
- Premature curing
- Warping
- Reduced performance
- Shortened shelf life
What you can do:
- Store materials in a temperature-controlled area
- Keep them out of direct sunlight
- Avoid storing near hot equipment
- A stable environment means consistent performance.
Resins: Flash Curing and Internal Stress
Room temperature has a similar - if slightly milder - effect on two-part resins, with a reduction of working time by 50% or more per 10°C increase. Resins create an exothermic reaction when mixed, meaning the resin will heat itself during curing, risking ‘thermal runaway’ where the increased temperature speeds up the reaction, which in turn increases the temperature further. At the extreme end of this process you can suffer from flash curing, in which your entire batch may cure before you’re able to even pour. In thicker pours the heat of your cast can also cause internal stress within your cast, potentially leading to a brittle cast or cracking.
Polyurethane Foams: Rapid Expansion and Cell Collapse
Polyurethane foams are particularly susceptible to temperature increases, with both the cream and rise times being noticeably decreased. A system with a normally 30 second cream time can lower to as fast as 10 seconds with a 10°C increase, which leaves very little time to accurately pour. Rapid expansion within your mould could also prevent the foam from properly expanding into all parts and details of your mould. This leads to forming irregular cells within the foam that are a higher risk of collapse. Polyurethane foams in particular can release increased amounts of volatile emissions that can put your health at risk.
Now this might all seem like a nightmare and you may feel you should wait until later in the year, but you’ll be pleased to know that there some very simple proactive steps you can take to avoid losing or damaging your work.
General Hot Weather Tips:
The biggest action you can take to counteract these issues is obviously to reduce the working temperature. Setting up portable fans or an air conditioning unit can help keep your workspace cool, with even a few degrees being able to restore valuable working time. Storing your materials in a temperature-controlled environment or a cool area will also help extend working time, try to avoid sun-exposed storage as even in a cool room if your materials are hot you can face the same issues. You can also pre-cool your mixing containers, but make sure to avoid condensation buildup. Another easy change can be to work in cooler hours of the day, avoiding midday where temperatures are generally highest.
Material Specific tips:
There are also some precautions you can take that are specific to each process: Silicone can sometimes have slower catalyst versions available if you’re unable to cool your workspace or materials. For Resin casts, slow-cure hardeners or ‘low-exotherm’ (sometimes labelled as ‘deep pour’) formulations can be used to lessen the heat increase. Mixing smaller batches can prevent heat buildup, and pouring those smaller batches in thinner layers allows the heat to dissipate faster and more evenly. Finally for Polyurethane foams preparation will be key. With such short working times you’ll want to make sure your mould and any tools you need are ready and in position before you mix your foam, and that you’re ready to pour immediately after dispensing the two parts.
These proactive steps towards protecting your materials from higher temperatures not only help make your working life easier, but also ensures your products maintain their reliability and performance for longer.
Please get in touch for any product, process or storage enquiries regarding the above topic.
info@mouldlife.co.uk / 01638 750 679 / live chat
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