Practical Tips for Using Purging Compounds in Just-In-Time Low-Volume Production with Different Materials or Colors

Managing frequent material or color changes in low-volume production can be a daunting challenge for plastics processors. Just-in-Time (JIT) manufacturing, with its focus on minimal inventory and custom molding, requires precision, speed, and efficiency. Frequent mold and material changes leave no margin for error, making every decision critical to maintaining profitability.

In this high-stakes environment, purging compounds can significantly reduce downtime, prevent waste, and keep operations running smoothly. While exact results will vary depending on the customer and their specific process, the principles remain universally beneficial.

The Challenge: Quick Material and Color Changes

Transitioning between different colors or materials in short production runs is particularly vulnerable to contamination. For example, switching from a dark, filled material to a clear cosmetic-grade resin can lead to contamination issues, wasting time and resources. In extreme cases, production could be delayed by an entire day.

Without the proper tools, scrap rates can skyrocket as machines waste material attempting to meet quality standards. Homemade purging methods, such as using detergents, sawdust, or regrinds, often fail to fully clear contaminants and can delay production even further.

Real-World Example: Switching from Black PP to Clear PC

Let’s explore a scenario to illustrate these challenges and how purging compounds make a difference.

Scenario Details:

• The job requires transitioning from black, 5% talc-filled polypropylene (PP) to clear, unfilled polycarbonate (PC) on a 450-ton machine.
• The total PC required is 100 lbs., with an additional 20% startup allowance (120 lbs. total) to account for scrap and purging.
• The machine cannot be taken offline to pull the screw without causing schedule disruptions.
• Each hour of machine downtime costs $150.

Using a homemade purge, this changeover could take up to 6 hours. In contrast, a commercial purge completes the switch in just 1 hour. Here’s what this means in real terms:

Homemade Purge:

• Extended downtime adds $750 in pre-production costs (5 additional hours x $150/hour).
• Increased risk of contamination, leading to more scrap and delays.

Commercial Purge:

• Rapid changeover minimizes downtime, saving $750 and preserving material quality.
• The process ensures a seamless transition, reducing waste and maximizing production time.

While the numbers in this example are specific to the described scenario, the takeaway is clear: purging compounds provide a more reliable, cost-effective solution for JIT low-volume production.

The Bottom Line

Every production environment is unique, and results will vary depending on the materials, machine size, and production goals. However, the consistent benefits of purging compounds—faster changeovers, reduced contamination, and minimized waste—make them an essential tool for meeting the demands of JIT manufacturing.

When time and material are at a premium, investing in the right purging solution can safeguard your schedule, profitability, and customer satisfaction.