Method "A/B" Run
General Description
In a Method A/B test both a Method A test and Method B test are performed on
the same charge of material. The melt flow rate, derived from Method A, is
equated to the Method B flow equation and solved for apparent melt density. The
value in doing this test is obtaining a valid apparent melt density which can later
be used in a sole Method B test (no manual cuts of extrudate nor weighing) to
achieve results equivalent to Method A (operator must make manual cuts and
weigh sample).
Calculations: Method A/B
Method B MFR =
R L
600
2
T
B
Method A MFR
=
M600
T
A
=
MT
B
LR
2
T
Where R= radius piston (cm), TB is time to traverse the Method B distance L
(sec), L = Method A length of flag (cm), M is the mass in grams of material
collected over the time TA in seconds. MFR has units of g/10 min. (grams/10
minutes).
is called the apparent melt density and is defined by equating the
methods, the Method B flow rate must equal Method A.
This apparent melt density definition forces the two test methods to
agree. DYNISCO POLYMER TEST recommends taking an average of
apparent melt densities from at least five separate A/B tests on representative
samples of polymer. This average apparent melt density can then be used for
Method B tests to get Method A values without having to make cuts! It is called
an "apparent melt density" because it is actually a correlation coefficient that
forces Method A and Method B to agree. If there were no leakage past the
plunger tip and the extrudate were bubble free and few other minor factors were
taken into consideration then a true melt density could be assessed. All lengths
are in mm.
Series 4000 Melt Indexer Operation Manual Method "A/B" Run
27
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