Corrosion-Resistant Melt Flow Index Tester

What is the Corrosion-Resistant Melt Flow Index Tester?

A corrosion-resistant melt flow index tester uses an alloy barrel and die, and usually inert gas purging, to test polymers that release aggressive vapours when melted. It is the appropriate instrument for vinyl chloride polymers, halogenated flame-retardant compounds and fluoropolymers.

Overview

Vinyl chloride polymers and halogenated compounds release hydrogen chloride or hydrogen fluoride at melt temperature, and these gases attack the steel and hardened plating of standard barrels and dies. A corrosion-resistant tester addresses this by making the barrel, die and piston from a nickel-chromium-molybdenum alloy such as C-276 or from a stainless grade with equivalent resistance, and by adding a gas purge so that acidic vapours are carried away from the melt surface. Temperature control and die geometry are the same as for standard units so results remain comparable with the usual standards. Cleaning practice matters more than with other polymers, because residues left in the barrel continue to corrode it and to affect subsequent tests, so purging compound and prompt disassembly are part of the operating procedure.

How does it work?

A melt flow tester consists of a heated vertical barrel with a defined bore, a hardened steel die at the bottom, a piston and a set of certified weights. Polymer granules are loaded, compacted and held at the test temperature, then extruded through the die under a specified load. In method A, timed portions of extrudate are cut and weighed, and the result is expressed in grams per ten minutes. In method B, an encoder records piston displacement against time and the melt volume-flow rate is calculated in cubic centimetres per ten minutes, which can be converted to mass flow using the melt density. Temperature, load, die geometry and thermal equilibration time are all fixed by the method, because melt viscosity depends steeply on temperature and shear rate.

What are the key features?

• Barrel, die and piston in corrosion-resistant alloy
• Gas purge connection for acidic vapours
• Standard die geometry for comparable results
• Removable barrel liner for inspection and replacement
• Temperature range suited to vinyl and fluoropolymers
• Cleaning accessories and purging compound guidance

What are the technical specifications?

A typical corrosion-resistant melt flow index tester configuration offers wetted alloy of Nickel-chromium-molybdenum alloy (C-276 type), temperature range of 50–400 °C, temperature accuracy of ±0.2 °C, die dimensions of Ø 2.095 mm × 8.0 mm, purge gas of Nitrogen, 0.1–0.5 L/min and load weights of 0.325 / 1.2 / 2.16 / 5 / 10 / 21.6 kg. 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 Corrosion-Resistant Melt Flow Index Tester is used in melt flow testing of polyvinyl chloride compounds, fluoropolymer and halogenated resin inspection, flame-retardant masterbatch quality control and testing of chlorinated and brominated polymer grades. Across the wider Melt Flow Testers class, laboratories also deploy it for polyolefin resin production and grade certification, incoming inspection of polyethylene and polypropylene and recycled plastics quality screening.

Which standards and certifications apply?

Relevant standards and methods include ISO 1133-1, ISO 1133-2, ASTM D1238, 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.

Install the tester on a level, vibration-free bench away from draughts, and allow the barrel to reach thermal equilibrium before the first test, which usually takes 15 to 30 minutes. Clean the barrel and die after every test or every material change, using purging compound for degraded polymer; never scrape the barrel bore with hardened tools. Verify temperature with an external thermometer in the bore at defined intervals, check die dimensions against the method tolerance, and keep weights traceable. Dry hygroscopic polymers before testing, discard any extrudate containing bubbles or voids, and repeat the test when a single cut deviates strongly from the others.

How do I select the right Corrosion-Resistant Melt Flow Index Tester?

Specify a corrosion-resistant instrument whenever the material list contains polyvinyl chloride, chlorinated polyethylene, halogenated flame retardants or fluoropolymers. Confirm that barrel, die and piston are all made from the corrosion-resistant alloy, because plating a standard steel barrel is not equivalent. Ask for a replaceable liner, since alloy parts are costly and the liner is the part that degrades, and agree on purge gas supply and a cleaning procedure in writing.

How does it compare with other Melt Flow Testers variants?

Start from the standard your customer or specification cites, because ISO 1133 and ASTM D1238 fix different loads and procedures. Method A is sufficient for routine resin grading, while method B is preferable when the laboratory needs a fast result or the material is difficult to cut cleanly. Choose a high-temperature barrel when the scope includes engineering polymers such as polyamide, polysulfone or polyether ether ketone, and a corrosion-resistant barrel for PVC and fluoropolymers. Automatic units pay back where more than about ten tests per day are run, and multi-station units suit polyolefin plants that compare several production lines in one shift. Specify the load set, temperature range, data export format and cleaning accessories.