Gravimetric Melt Flow Rate Analyzer

What is the Gravimetric Melt Flow Rate Analyzer?

A gravimetric analyzer cuts extrudate at timed intervals and weighs it to obtain the melt mass-flow rate directly, exactly as the reference method prescribes. It is the most straightforward way to demonstrate compliance with ISO 1133 or ASTM D1238.

Overview

The instrument comprises a temperature-controlled barrel, a piston with defined mass, certified weights, a hardened die and a cutting guide. The operator loads and compacts the plastic, waits for the preheat time specified by the condition, then cuts extrudate at fixed intervals once steady flow is established, and weighs the segments on a balance. Because the result depends only on mass and time, traceability is simple and the calculation is transparent, which is why certificates of analysis are usually based on this method. Repeatability depends on cutting consistency, so a timer with clear signalling and a fixed manual technique are important. A balance with 0.1 mg resolution is normally recommended, and automated cutter models reduce timing scatter while still delivering segments for weighing.

How does it work?

The method heats a plastic sample in a barrel of defined bore, compacts it with a piston and extrudes it through a die of defined diameter and length under a controlled load. Mass-flow rate is obtained by weighing extrudate cut over a known time, and volume-flow rate by recording piston displacement with an encoder. Dividing mass flow by volume flow gives melt density at the test temperature, which is a useful check on filler loading and on batch consistency. Temperature, load, die geometry and preheat time are fixed by the standard condition applicable to the plastic, so results from different laboratories are comparable only when the same condition letter is used. Comparative testing, where a reference material is run on the same instrument, is often the most practical way to confirm instrument condition.

What are the key features?

• Timed cutting with audible or visual interval signal
• Certified weights covering standard load conditions
• Hardened steel die to the standard bore and length
• Digital temperature controller with stability display
• Levelling feet and reference spirit level
• Balance interface and result calculation software

What are the technical specifications?

A typical gravimetric melt flow rate analyzer configuration offers temperature range of 50–400 °C, temperature accuracy of ±0.2 °C, load weights of 0.325 / 1.2 / 2.16 / 5 / 10 / 21.6 kg, die dimensions of Ø 2.095 mm × 8.000 mm, barrel bore of 9.55 mm and cut interval of 10–60 s, operator controlled. Values are indicative of the product class; the exact figures for each configuration are confirmed on the quotation and the calibration documents supplied with the instrument.

Which applications is it used for?

The Gravimetric Melt Flow Rate Analyzer is used in certificate of analysis testing for resin lots, dispute resolution between supplier and converter, reference measurements for instrument checks and inspection of single production samples. Across the wider Melt Flow Analysis class, laboratories also deploy it for lot release of polyethylene and polypropylene grades, verification of recycled plastic melt flow consistency and effect of filler and reinforcement on flow behaviour.

Which standards and certifications apply?

Relevant standards and methods include ISO 1133-1, ASTM D1238, ASTM D3364, GB/T 3682.1, GB/T 3682.2 and IEC 61010-1. Certification candidates for this model are CE and ISO 9001 manufacturing; each is to be confirmed for the specific configuration before shipment, and certificates are supplied only where they have been issued.

Level the instrument and allow full thermal equilibration before the first measurement, then verify barrel temperature with an external probe. Check die bore and length against the standard tolerance and replace worn dies, because an enlarged bore lowers the measured value. Use only dried material for hygroscopic plastics stated in the method, and discard any extrudate containing bubbles or voids. Clean the barrel between materials with purging compound, not with metal tools. Keep weights traceable and record the standard condition, sample mass, preheat time and any melt density value with every result so that a reviewer can reconstruct the test.

How do I select the right Gravimetric Melt Flow Rate Analyzer?

Choose the gravimetric method when the result must be directly traceable to the standard and when sample numbers are moderate. Confirm that the weight set matches the condition letters you use, and that the temperature range covers your highest test temperature. Order a spare die and a certified thermometer, because periodic verification depends on being able to check geometry and temperature independently.

How does it compare with other Melt Flow Analysis variants?

Define the output you need first. For routine lot release, a gravimetric instrument that weighs timed cuts is adequate and easiest to defend against the standard. When results must be traceable in a digital system or the material is difficult to cut, an instrument with piston displacement measurement is preferable. Where throughput dominates, choose a multi-position analyzer or a robotic loading configuration. Add a melt density capability when filler content or batch-to-batch density variation is a quality concern. For filled, reinforced or very high molecular weight plastics, specify the load set and a corrosion- or abrasion-resistant barrel and die, because standard hardware may not reach the required condition or may wear quickly.