Liquid Silicone Rubber (LSR) has increasingly gained popularity across a wide range of industries, thanks to its non-toxic, transparent, and tear-resistant properties. It has become a preferred material for applications in sectors such as baby products, kitchenware, medical devices, automotive, and bathroom fixtures. As a company committed to providing high-quality silicone products, Silkeypad understands the importance of precision in the manufacturing process, especially when it comes to customization. One common question we encounter in the industry is whether Shore hardness and color can be adjusted in the LSR injection molding process.

In this blog, we will explore the challenges and considerations associated with altering Shore hardness and color in LSR injection molding, and why these adjustments may not always be practical for every production scenario.

Can Shore Hardness and Color Be Adjusted in the LSR Injection Molding Process?

The short answer is yes—both Shore hardness and color can be altered in the LSR injection molding process. However, the process is not without its challenges, and there are several factors to consider before making such changes. While the potential for customization exists, it can often come at the cost of time, material waste, and additional cleaning requirements, especially when switching between different hardness levels or colors during production.

When it comes to Shore hardness, LSR material typically comes in a range of hardness levels, with Shore A hardness being the most commonly used for many applications. However, changing the Shore hardness of the material during the injection molding process is a time-consuming and inefficient task. In scenarios where small production runs are involved, testing different Shore hardness levels may not be practical due to the high amount of waste material that is generated. For example, when altering the Shore hardness, the material that is purged from the system before achieving the desired hardness can be substantial, and the cleaning process required can take up to an entire day. This makes Shore hardness changes more complicated and resource-intensive compared to other molding methods, such as compression molding, where adjustments can be made more easily.

Likewise, changing the color of the LSR during the injection molding process presents its own challenges. In compression molding, changing the color is relatively straightforward—simply adding pigment to the mix and milling the material suffices. However, in the case of LSR injection molding, the color change process is much more involved. Similar to Shore hardness changes, switching colors during injection molding requires significant time and effort, particularly in cleaning the feeding systems, nozzles, and needle valves. Ensuring that the mold produces parts with the correct color after a change involves thoroughly cleaning the system to prevent cross-contamination between different color formulations.

While both Shore hardness and color modifications are possible, it is important to understand the constraints that come with them. At Silkeypad, we are committed to delivering high-quality LSR products, but we also emphasize the need for efficient production. In most cases, altering hardness or color is not recommended for small production runs, as the material waste and extended lead times can reduce the overall efficiency of the project. For larger production volumes, however, such changes may be more feasible.

Why Is It So Difficult to Clean the Cold Runner in LSR Injection Molding?

One of the primary reasons why altering Shore hardness and color is difficult in LSR injection molding is the complexity of the process, especially when it comes to cleaning the cold runner system. Unlike compression molding, where the setup is more straightforward, LSR injection molding systems feature intricate feeding systems, nozzles, and needle valves that need to be thoroughly cleaned after each production cycle.

The cold runner system, which carries the LSR material from the injection machine to the mold, is often a source of contamination when switching between different materials or colors. Any residual silicone material left in the system can impact the quality of the next production cycle, resulting in unwanted variations in Shore hardness or color. This is why it is crucial to properly clean the entire system between different runs. Cleaning the cold runner, needle valves, and feeding systems is an extensive process that requires attention to detail and can take up to half a day to complete.

Even a small amount of leftover material can lead to issues with the final product. This is a critical factor to consider when determining whether changing Shore hardness or color is worth the effort for your specific production needs. If the system is not properly cleaned, the results can be subpar, leading to discrepancies in the final product, as seen in the following example.

Real-World Example: A Case of Improper Cleaning

To illustrate the challenges involved in LSR injection molding, let’s examine a real-world scenario that occurred at Silkeypad. One of our customers requested 10 Shore A liquid cannula samples made from medical-grade LSR. Our team used 10 Shore A material to produce the samples, but when the samples were tested, we found that their hardness was higher than expected—approximately 20 Shore A rather than 10 Shore A.

After a thorough investigation, our production team discovered that the cause of the discrepancy was an incomplete cleaning process. The previous batch of material used in the system was 30 Shore A, and despite the switch to 10 Shore A material, traces of the harder material remained in the feeding system. As a result, the new samples exhibited higher hardness than intended. This example highlights the importance of proper cleaning and how even small amounts of residual material can affect the final product. At Silkeypad, we always ensure that our cleaning processes are meticulously followed to avoid such issues and deliver products that meet the highest standards of quality.

Best Practices for Shore Hardness and Color Changes in LSR Injection Molding

While altering Shore hardness and color during LSR injection molding is possible, it is essential to approach these changes with caution. Here are a few best practices to consider:

1. Minimize Material Waste: For small production runs, it may not be worth the time and resources required to alter Shore hardness or color. If adjustments are necessary, ensure that you are working with larger production volumes to make the changes more feasible and cost-effective.
2. Implement Thorough Cleaning Procedures: To ensure that Shore hardness and color adjustments are successful, it is crucial to implement rigorous cleaning protocols. This includes purging the system of any residual material and thoroughly cleaning the feeding system, needle valves, and nozzles.
3. Plan for Extended Lead Times: When making Shore hardness or color changes, be prepared for longer lead times. The time required to clean the system, set up the new material, and test the results can add significant delays to the production process.
4. Work with Experienced Professionals: Working with an experienced silicone molding company, like Silkeypad, can help streamline the process. Our team has the expertise and equipment to handle even the most complex LSR injection molding projects, ensuring high-quality results and minimal waste.

In conclusion, while it is possible to modify Shore hardness and color in LSR injection molding, the process is not without its challenges. By working with a reliable partner like Silkeypad, you can ensure that your production runs are efficient and that your silicone products meet your exact specifications. Contact us today to discuss how we can assist with your next LSR injection molding project and help you achieve the best possible results.