Measure what you see.
Mandrel Set
A member of
Operating Instructions
Additives & Instruments
Mandrel Set
Operating Instructions
English
PF-1412
BYK - Gardner USA
9104 Guilford Road
Columbia, MD 21046
USA
Phone 800-343-7721
301-483-6500
Fax 800-394-8215
301-483-6555
www.byk.com/instruments
BYK-Gardner GmbH
Lausitzer Str. 8
D-82538 Geretsried
Germany
Tel. 0-800-gardner
(0-800-4273637)
+49-8171-3493-0
Fax +49-8171-3493-140
Description
Description
When a coated panel is bent tightly around a
cylinder of known diameter, the damage caused
by distending the coating may be evaluated.
Panels of a variety of fl exible materials, including
steel to 1/32“ thick, may be used with the BYKGardner Mandrel Set.
After bending the coated panel, the fl exibility
of the coating is indicated by the nature and
extent of cracking and fl aking and the radius
of curvature required to produce these fl aws.
Similarly, the fi lm‘s adhesion may be rated by the
extent to which the loosened fl akes or chips of the
damaged fi lm have adhered to the substrate, or
separated from it, during or after the bending. It
may also be desired to bend uncoated panels of
certain materials and then examine their surfaces
for signs of damage.
2
General Information
General Information
The BYK-Gardner Mandrel Set is described in
ASTM D522 „Test Methods for Mandrel Bend Test
of Attached Organic Coatings“. The BYK-Gardner
Mandrel Set has nine stainless steel rods of the
following diameters: 1“, 3/4“, 1/2“, 7/16“, 3/8“,
5/16“, 1/4“, 3/16“, 1/8“. The rigid black anodized
aluminum frame has slots in its base for holding
rods not in use and „V“ shaped cuts at its top for
supporting a mandrel in use.
3
Operation
Operation
A mandrel rod is simply placed in position in cuts
at the top of the frame and then the test panel is
folded tightly around the rod, coated face upward
and outward. The coating may be examined
for cracking, fl aking and other types of damage
caused by elongation. Various samples may be
bent on one specifi ed rod as a standard „pass or
fail“ test or rods of decreasing diameter may be
used with one type of test coating to learn what
degree of elongation fi rst produces failures in the
coating. Whatever approach is used, the Mandrel
Set will continue to yield useful and accurate data
as long as the rods are not bent by attempting to
fold heavier gage panels around them.
4
Theory
Theory
When a test panel of known uniform thickness is
bent closely around a mandrel of known diameter,
the THEORETICAL change in length of the faces
of the panel may be calculated. After bending,
the outer curved surface will have been stretched
a certain amount, the inner surface compressed
an equal amount, and a plane midway between
these faces will have remained the same length.
Based on this theory, the percent elongation of the
outer (usually coated) surface is simply 100 t/(D+t)
where „t‘‘ is the thickness of the panel and „D“ is
the diameter of the cylindrical mandrel. For a 1/32“
panel bent over a 1/8“ mandrel, the percent
elongation would be 100 x 1/32 (4/32 + 1/32) =
100 x 1/5 = 20%.
The ACTUAL change in length of the surfaces
will vary from the theoretical changes by a small
difference in percentage that is a factor of the material being used, the panel thickness and mandrel
diameter. This discrepancy between the calculated
and true percent elongations is seen in the following table describing a cold-rolled steel panel
1/32“ thick.
Diameter of Mandrel 1-1/2” 1” 3/4” 1/2” 1/4” 1/8”
Theoretical % Elongation 2.0 3.0 4.0 5.9 11.1 20.0
Actual % Elongation - 3.3 - 6.7 13.8 28.0
The discrepancy occurs because the plane at
which no stress or compression is experienced is
not found exactly halfway between the two faces
of the panel. In the above example, the level of
no change in length is encountered closer to the
bottom surface than the top and gets closer to
5
Theory
the surface against the mandrel as the diameter
decreases. The material seems to be more readily
stretched than compressed, therefore, the outer
surface is extended a little more than would be
theoretically anticipated.
6
253 017 659 EDFIS 0408 Europe
Loading...