When you are able recognise these signs of
glazed diamond segments on the job your peers will
regard you as a Master of Diamonds
The first signs of
glazed segments on a concrete grinder
cupwheel are:
● The speed of grinding
(wearing away the concrete) has slowed down
to a crawl
●
The cupwheel is very hot when you
inspect it
●
The diamonds appear as shiny
black dots
in the segments (see pic below)
● You have to apply much more effort to achieve the same
grinding speed as when you began and it
is still slower
● You think you need more weight on the disc
to grind faster
● The disc becomes unstable and begins to
jump around uncontrollably
The white spots in the above picture
indicate flattened, shiny diamonds which
normally appear dark to the human eye,
but white to the camera. These are
partly glazed diamond segments.
Why this happens
The sands from the concrete have not
worn away the bond of the segments and
the diamonds have become worn and are
nearly flat.
This results in less cutting action
which causes the operator to apply more
pressure because the diamonds are no
longer protruding out of the segment
bond.
The glazed surface of the segment
rubs on the concrete instead of cutting
it away causing extreme heat which
buckles the disc and makes it jump
around.
There are visual signs
too
- Rocket trails
(see picture below)
- Shiny black spots
- white ones in the picture
(see picture above)
The first thing you notice is the
absence of rocket trails on the parts of
the
segments that were cutting.
These are the tapering lines
of metal behind a diamond when the
segment is right for the floor hardness
and the cupwheel cuts happily.
When these rocket trails are diminished or
completely gone the segment is glazed.
...however, they do not have to be missing
completely for you to have glazed
segments for the following two reasons
1. If the rocket
trails are only 20% as big as they normally
are then the segment is partially
glazed.
2. If the wear
area of the diamond segments (the
highest points) are glazed, but the
lower parts of the segments have deep
rocket trails
.. you must ignore the lower
sections because they occurred some time
earlier on softer concrete. Just look at
the high spots.
Shiny dark spots are diamonds
that have been worn flat.
You rarely see
these shiny, dark spots on a disc that
is cutting normally, you only see them
on glazed segments or partially
glazed segments so they are a sure
sign that the matrix is too hard for the
hardness of the concrete.
The above picture shows good rocket
trails behind exposed diamonds and no
shiny flat spots.
Sometimes there are clear rocket trails
on the inside of the segments closest to
the centre of the cupwheel with shiny flattened diamonds
on the outside area of the segments which indicates that the
outside area was
in contact with the hard floor but the
inside area was previously worn a little
below that and did not quite touch the hard
concrete floor and so they did not polish.
This means that the floor is too hard
and will continue to glaze the segments
even though you can see rocket trails.
How to tell if your
disc bond is too soft
The easiest way is when the disc cuts
in too aggressively and deeply with only
light pressure applied.
If it is difficult to
control the depth of cut or if you have
to move the disc too quickly then the
segment bond will most likely be too
soft.
This can also occur when a coarse
disc is used on very soft concrete which
does not necessarily reflect on the
bond.
When the bond is too soft for the
concrete the cupwheel will cut deeply
and aggressively and the bond will wear
away quickly.
Diamond cupwheel
selection
Remember, you need more than one
cupwheel for your concrete grinder
and probably 3 or 4 to be able to grind
all your jobs at the speeds you expect.
Choose Very Coarse for heavy coatings
removal and for good bond key for heavy
coatings you apply later.
Purchase all
the bonds available in that range so you
will never get stuck on a job.
Choose Coarse for fast removal of the
surface, for coatings removal and
general preparation without the deeper
score marks of Very Coarse.
Again
purchase all the bonds available.
Choose Fine for a smooth finish, for
softer concrete and for removal of
grinding shoulders and take all the
bonds.
Choose Very Fine for dry grinding to
a fine finish suitable to coat with a
clear coating later for a polished
concrete look, or as the final finish
before using resin bond pads to polish a
floor.
Very fine can also help remove
grinding marks.
Choose PCD scrapers (see the next
page) for rapid removal
of coatings, especially when they are
heavier than 500 microns thick.
Floors
should be finished with a diamond
grinding disc after using the
PCD scraper disc to remove the coating.
Next page
"Coating Removal"
