The Evolution of Liquid Silicone Rubber (LSR) Injection Molding: A Journey Through Time
In the world of injection molding, hot runner systems have come a long way. From once being considered a high-end option reserved for specialty applications, they’ve evolved into a mainstream choice for many molders looking to reduce waste, improve efficiency, and streamline production.
But with hot runners becoming the new norm in many sectors, one question remains: Are cold runners still relevant?
Let’s break it down.
A Quick Look Back: The Rise of Hot Runners
Hot runner systems were developed to eliminate the waste associated with cold runners—plastic that solidifies in the runner channels and must be ejected, reground, or discarded. These systems use heated components to keep the plastic in a molten state within the manifold and nozzles, delivering it directly to the mold cavities.
Over the past couple of decades, the technology has improved dramatically:
- Temperature control has become more precise
- Startup times are faster
- Maintenance has become easier
- Design options are broader, including valve gates, sequential gating, and more
For many processors, hot runners offer:
- Material savings (especially with expensive or engineering-grade resins)
- Shorter cycle times
- Less scrap
- Better part quality and consistency
So, Why Do Cold Runners Still Exist?
Despite the appeal of hot runners, cold runners haven’t gone away—and for good reason.
Here’s when and why cold runners still make sense:
1. Lower Initial Tooling Cost
Hot runner systems can add significant upfront cost to a mold—sometimes tens of thousands of dollars. For short production runs or prototype tools, a cold runner system is often more economical.
2. Simple Part Designs
For basic parts where the material is cheap and scrap can be reground, the advantages of hot runners may not justify the investment.
3. Frequent Material Changes
Hot runners can be tricky when switching between resins, especially if there’s risk of degradation. Cold runners allow faster changeovers with less risk of contamination.
4. Certain Medical or Regulatory Applications
Some applications require a cold runner approach due to validation processes, cleanroom requirements, or traceability of regrind use (or non-use).
Making the Right Choice
Like most things in manufacturing, it’s all about the trade-offs. Consider:
|
Factor |
Hot Runner | Cold Runner |
| Tooling Cost | Higher | Lower |
| Material Waste | Lower | Higher |
| Cycle Time | Shorter | Slightly Longer |
| Maintenance | More Complex | Simpler |
| Best For | High-volume, high-cost resin, complex gating | Low-volume, simple parts, frequent material changes |
If you’re producing millions of parts a year, hot runners can save you a fortune over time. But for smaller runs or less critical parts, cold runners still offer reliability, simplicity, and cost-effectiveness.
Hybrid Systems Are a Thing
Some processors now use semi-hot or hot-to-cold runner systems—where a hot manifold feeds into a cold runner section. These hybrid setups can offer a balance of cost and performance, especially in multi-cavity tools.
New Integration Capabilities: OPC UA and Hot Runner Systems
Modern injection molding machines are increasingly adopting OPC UA (Open Platform Communications Unified Architecture) to enable seamless communication between machine controls and auxiliary systems. This includes direct integration of hot runner controllers, allowing for centralized monitoring, real-time diagnostics, and improved process control—all from the injection molding machine’s interface.
Need Help?
For molders who are weighing these choices or looking to optimize their existing runner systems, outside expertise can be invaluable. Partnering with Kruse Analysis provides access to deep technical know-how and decades of experience in injection molding troubleshooting and simulation. Whether you’re evaluating hot vs. cold runner trade-offs, refining part and mold design, or seeking data-driven consultation to improve cycle times and quality, Kruse Analysis offers practical insights that help processors make smarter, more profitable decisions. At the same time, Kruse Training equips mold designers and engineers with the education they need to understand the full impact of runner selection, part geometry, and processing parameters—building a foundation of knowledge that pays dividends in every project.
Final Thoughts: It’s Not Either/Or
The evolution of hot runner technology has reshaped the injection molding landscape, but cold runners remain a smart choice in the right context. The key is to assess your production volume, material costs, tooling budget, and maintenance capabilities—and choose what makes the most sense for your specific application. And if you want confidence in your decision-making, consider leveraging Kruse Analysis for expert consultation and Kruse Training to strengthen your team’s capabilities—so you can get it right the first time and every time.
To find more information:
Training for Injection Molding Professionals – Kruse Training