ASTM D1238

Introducing ASTM D1238 - Industrial Physics
ASTM D1238 is a global ASTM international standard method to determine the rate of extrusion of molten thermoplastic resins using an extrusion plastometer.

At a prescribed temperature, this ASTM standard provides the means to measure the flow of a melted material. The information from the ASTM D1084 test will help you to differentiate grades of plastic, such as polyethylene, or understand the degradation effects on the plastic as a result of molding.

Melt density is the density of the material in a molten state, not to be confused with the standard density value of the material. With reduced molecular weight, you find that degraded materials typically flow more and can exhibit reduced physical properties.

In some ways this test is similar to the process for ISO 1133 which you can learn about by clicking here.
The ASTM D1238 testing process
ASTM D1238 features four extrusion testing procedures - from A to D.
ASTM D1238 procedure A
ASTM D1238 procedure A is used to determine the melt flow rate (MFR) of a thermoplastic material, measured in grams of material/10 minutes (g/10 min). You simply measure the mass of material that extrudes from the die over a given period of time.

This ASTM approach is typically used for materials with melt flow rates that fall between 0.15 and 50 g/10 min.
ASTM D1238 procedure B
ASTM D1238 procedure B is an automatically timed extrusion testing measurement used to determine both the melt flow rate (MFR) and the melt volume rate (MVR) of thermoplastic materials. Measurements in this ASTM test are based on the determination of the volume of material extruded from the die over a given period of time.

MFR measurements made with ASTM D1238 procedure B are reported in g/10 minutes. MVR measurements are reported in cubic centimeters / ten minutes (cm3/10 min).

The volume is converted to a mass measurement by multiplying the result by the melt density value for the material.

Procedure B of this ASTM standard is generally used on materials with melt flow rates from 0.50 to 1500 g/10 min.
ASTM D1238 procedure C
ASTM D1238 procedure C is an automatically timed measurement used to determine the melt flow rate (MFR) of polyolefin materials. It’s generally used as an alternative to procedure B for samples with melt flow rates greater than 75 g/10 min.

Procedure C of this ASTM standard involves the use of a modified die. It’s commonly referred to as a “half-die” as it has half the height and half the internal diameter of the standard die used with procedures A and B. So it keeps the same length to diameter ratio. The test procedure is similar to B, but the results obtained with C shouldn’t be assumed to be half of those results produced with B.
ASTM D1238 procedure D
ASTM D1238 procedure D is a multi-weight test, known as a ‘flow rate ratio’ (FRR) test. This ASTM standard approach allows you to determine the MFR using two or three different test loads: either increasing or decreasing the load during the test on one charge of material.

The FRR is a dimensionless number derived through this ASTM standard by dividing the MFR at the higher test load by the MFR at the lower test load. The results you get from  multi-weight tests can’t be compared directly with results derived from procedure A or B.

Test Procedure:

Through the ASTM D1238 process you load approximately seven grams of the sample into the barrel of the pre-heated melt flow apparatus.

A material-specific weight is applied to a plunger and the molten material is forced through the die. A timed extrudate is collected and weighed, with MFR values calculated in g/10 min.

After working out the flow rate of the sample itself, and the resin it’s molded from, you can work out a percentage difference with this method of extrusion testing.
ASTM D1238 testing equipment
So, how can Industrial Physics improve your ASTM D1238 testing?

MFR300 microprocessor melt flow system

A perfect partner for your ASTM D1238 quality assurance, quality control and R&D requirements - the MFR300 verifies and validates sample materials…fast!  It’s highly accurate and easy to use with sophisticated touch screen electronics and the latest in on-board microprocessor technology.

With insightful Windows based Techni-Test™ software included as standard and multi datapoint capture - for accurate flow curve analysis.

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6MPCA advanced melt flow system

The 6MPCA is our most advanced microprocessor controlled melt flow indexer. It’s built with the latest Techni-Test software and can accurately determine MFR, MVR and density readings at test temperatures.

The liquid crystal display (LCD) provides simple on-screen instructions, and the ASTM test parameters are easy to type in. To conduct a test, molten polymer is extruded through a closely controlled orifice. The melt flow indexer uses set test temperature and pressure parameters, produced by a dead weight system.

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Your global test and inspection partner for ASTM D1238