Tin-cured silicone rubber is a commonly used RTV-2 silicone material in industrial silicone mold making. It is typically composed of a Part A base and Part B curing agent. By properly adjusting the ratio between the silicone and curing agent, one can have better control over working time and curing time to meet the requirements of different mold-making processes. In this article, we will analyze the results of different adjustments made to the silicone and curing agent ratio.
silicone and curing agent
The Importance of Mixing Ratio
Apart from the influence of temperature and thickness, one of the most significant factors affecting the working time and curing time of tin-cured silicone is the amount of curing agent used. Currently, most tin-cured silicone available in the market have recommended mixing ratios ranging from 100:2 to 100:5, base silicone to curing agent.
- If the amount of curing agent is less than 100:1.5, it may result in difficulties in curing the silicone or failure to achieve the expected hardness.
- If the amount of curing agent exceeds 100:5, the silicone may contain excessive crosslinking agent, leading to problems such as increased hardness, decreased demolding performance, weakened elasticity, and brittleness.
Therefore, it is advisable to use the curing agent within the manufacturer's recommended ratio range, typically between 100:2 and 100:5. Staying within this range ensures that the silicone cures to the desired properties and quality. Deviating too far from the recommended ratios can cause curing and performance issues, so it is essential to follow the manufacturer's guidelines for optimal results.
The Ratio of Silicone to Curing Agent
Taking a typical 100A:3B ratio of tin cure silicone as an example, the working time at 25°C (77°F) conditions can range from 30 to 40 minutes. By adjusting the ratio of silicone to curing agent, the working time can vary between 10 and 80 minutes. The table below presents data on working and curing times for different ratios:
| Silicone to Curing Agent Ratio | Working Time (Minute) | Curing Time (Hour) |
|---|---|---|
| 100A:1B | 60-80 | ≥24 |
| 100A:1.5B | 50-60 | 16±2 |
| 100A:2B | 40-50 | 14±2 |
| 100A:2.5B | 35-45 | 12±2 |
| 100A:3B (Typical Ratio) | 30-40 | 10±2 |
| 100A:3.5B | 25-35 | 8±2 |
| 100A:4B | 20-30 | 6±2 |
| 100A:4.5B | 15-20 | 5±2 |
| 100A:5B | 10-15 | 4±2 |
Please note that these times are approximate and can vary based on factors such as temperature, humidity, and specific silicone formulations. It's essential to refer to the manufacturer's instructions and conduct small-scale tests to determine the optimal ratio and curing time for your specific application and working conditions.
Operational Suggestions
The characteristic of liquid silicone materials is that their viscosity increases during curing, leading to reduced flowability. Therefore, when using tin cure silicone, it's essential to pay attention to the ratio of silicone to curing agent to meet your specific needs. Thoroughly mixing, stirring, and vacuum degassing during the working time are crucial steps to ensure success. Thus, it's advisable to allocate a working time that is no less than 10 minutes. By properly controlling the ratio of silicone to curing agent, you can precisely meet the requirements of various mold-making processes and obtain high-quality silicone molds.
