GRINDING GUIDE
Diamonds
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Pressure.
Hardness of bond.
Diamond grit size.
Number of segments under the machine.
Adding an additional abrasive (e.g. sand, silicone carbide)
on the floor will increase wear.
Background
Diamond abrasives usually consist of 2 components:
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Diamond powder (also known as diamond crystals or grit).
By changing the size of the diamond powder or grit, we
can change how coarse or fine the scratches will be that
are left behind from the grinding process.
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A binding agent (metal or resin). Diamond powder is
mixed and suspended in either a metal or resin binding
agent. When suspended in a metal binding agent, the
finished product is referred to as a Metal Bond or Sintered
diamond segment. When suspended in a resin binding
agent, the finished product is referred to as a Resin Bond
diamond segment or pad. By changing the hardness of
the binding agent, we can change how fast or slow the
diamond abrasive will wear.
Generally, the faster a diamond segment wears, the faster the
productivity will be. By varying the above factors, changes
can also be made to effect the following:
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Scratch pattern.
Current draw of machine.
Flatness of floor (see next section).
Ease of operation.
Determining the hardness of
concrete
All concretes are measured by their compressive strength
and depending on which part of the world you are from,
different compressive strength indices (e.g. PSi & MPa) are
used. Generally, the higher the compressive strength rating,
the harder the concrete and therefore, the harder it will be to
grind.
However, other factors beside compressive strength ratings
determine how hard the floor will be, and therefore, the
correct diamond selection. Since grinding normally only deals
with the surface of the concrete (top 5mm or 1/4 inch), often
the way the concrete floor has been finished or the condition
of the surface will have a greater bearing on what type of
diamond to select, rather than the compressive strength
rating of the concrete.
Surface factors to consider when making a diamond
selection
Generally, if a concrete surface is very smooth (i.e. Most likely
it has been heavily trowelled/helicopted), the concrete will
behave as if it has a high compressive strength and therefore,
require a soft bond segment.
Accordingly, if a concrete surface is coarse/aggressive (e.g.
rain-damaged, shot blasted, scarified, exposed aggregate
e.t.c.), the concrete will behave as if it has a low compressive
strength and therefore, require a hard bond segment.
Surface coatings/contaminants (e.g. Epoxy coatings, ceramic
tile adhesives, levelling compounds/screeds) will often have a
larger bearing on what diamond to select, than will the
compressive strength of the concrete.
As a general rule, when grinding a concrete slab for the first
time and you are unsure about its hardness, always begin
with harder bond diamonds under the machine. This will
ensure the least amount of wear on the diamond segments. If
a hard diamond segment is not suited to the application, all it
has cost is a little amount of time without wearing out the
diamonds.
If performed the other way around (i.e. a soft segment is used
to begin with) and the concrete is soft or possesses an
abrasive surface or surface contaminant, it is quite possible to
wear-out a considerable amount of diamond in very short
period of time.
General Principles
The following are general rules regarding diamond segments
in grinding applications. As with all general rules there are
exceptions or cases when it is not the case.
Diamond grit size
Changing the size of the diamond grit to a smaller particle/grit
size will effect the performance of the diamond tool in the
following ways:
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Create a finer scratch pattern.
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Increase life of diamond tool.
The opposite will occur when changing to a larger particle/grit
size.
Binding agent
Increasing hardness of bond will:
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Create a finer scratch pattern.
Increase life of diamond tool.
Decrease production rate.
The opposite will occur when making the metal or resin bond
softer.
Number of diamond segments/pads under the
machine
Increasing the number of segments under the machine will:
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Reduce pressure on each individual diamond segment -
reduce wear rate on diamond segments.
Reduce load on the machine and cause the grinder to
draw less current.
Create a smoother scratch pattern (particularly on soft
floors).
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The opposite will occur when decreasing the number of
segments under the machine.
Summary of diamond principles
Diamond segments need to wear in order to achieve
productivity. Diamond segment wear can be influenced by the
following factors:
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