Blog

Melt Flow Indexers: How to Ensure a Refurbished Plastometer Meets ASTM D1238

Why Melt Flow Index (MFI/MFR) remains essential

Melt flow rate (MFR) / melt index (MI) is one of the most common QC tests in plastics because it’s:

• fast
• standardized
• strongly correlated with molecular weight changes
• useful for detecting degradation and lot variation

That’s why many polymer buyers and processors still require ASTM D1238 melt flow data.

If you’re buying a refurbished plastometer (melt flow indexer), the critical question is:
Will it produce results that are comparable to our current method and customers’ specs?

What ASTM D1238 compliance depends on (the big 5)

1) Temperature accuracy and stability

Melt flow is extremely temperature-sensitive. A small deviation can shift results enough to fail a spec.

What you want:

• accurate setpoint control at your method temperatures
• stable equilibrium with minimal overshoot
• verified measurement capability (calibration checks)

2) Die condition and geometry

The die must be:

• clean and undamaged
• dimensionally correct
• free of scoring, wear, and polymer buildup

A worn die can change flow resistance, altering measured melt flow rate.

3) Piston condition and barrel integrity

Inspect:

• piston fit (smooth movement without binding)
• barrel wear, scoring, and cleanliness

Friction and leakage affect results.

4) Weight set completeness and verification

D1238 methods require specific loads.
Ensure:

• correct weights are included
• weights are verified (and labeled)
• the load combinations required by your materials are supported

Missing or incorrect weights can limit the methods you can run.

5) Timing, cut-off, and procedure discipline

MFI methods depend on:

• preheat time
• timing accuracy
• consistent cut-off technique (manual or automatic)

If your lab runs high volume, automatic cutting/extrusion timing can improve repeatability across operators.

Refurbished melt flow indexer: acceptance test plan (practical)

Before finalizing a purchase or putting a unit into production:

1. Run a known reference material (or your internal control resin).
2. Compare results against:
• your current instrument
• historical control chart ranges
3. Repeat across multiple runs to check repeatability.
4. Confirm temperature equilibrium timing and stability.

This ensures the refurbished unit aligns with your lab’s real-world method.

Common reasons results don’t match (and how to fix)

• temperature probe drift → verify calibration and stability
• worn die/barrel → replace or recondition
• inconsistent preheat time → standardize SOP
• operator technique variation → consider automatic features and training

Buying checklist (what to confirm from the seller)

• ASTM D1238 capability for your required methods/conditions
• included die(s), weights, piston and barrel condition
• maintenance history and calibration records (if available)
• manuals and SOP guidance
• whether the unit is manual vs semi-automatic vs automatic

Explore our inventory.

Bottom line

A refurbished plastometer can be a high-ROI purchase if it:

• holds temperature accurately
• has a clean, correct die and barrel/piston system
• includes verified weights
• supports repeatable timing and method discipline

Talk with us
Tell HiTechTrader your resins (PP, PE, ABS, nylon, etc.), required D1238 conditions (temp/load), and throughput. We can help you choose a refurbished melt flow indexer configuration that matches your QC needs and avoids hidden compliance gaps. Click here to contact HiTechTrader.