Rocas - Abrasividad 1
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Transcript of Rocas - Abrasividad 1
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8/20/2019 Rocas - Abrasividad 1
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All rocks a nd s oils
cons ist o f minerals that
have a distinctive
sc ratc h hardness . To
define this hardness, the Moh’s
hardness scale is the standard
reference used . The s ca le is
divided into 10 increments ,
ranging from talc (with a hardness
of 1) as the softest, up to
diamond (hardness 10) as the
ha rdest. The sc ale is natura lly
linear from a hardness of 1 to 9,
with each mineral being able to
sc ratch the one b elow it in the
scale.
Among the mos t common
minerals, mica and ca lcite are
very s oft (hardness 2.5 and 3,
respectively), while feldspar,
pyroxene and amphibole ma y be
cha racterised a s medium hard
(hardness 6). Quartz and garnet
are very hard (hardness 7 and 7-
7.5, respectively), and to a great
extent, determine the degree of
TB M cutter we ar.
Cutter life can be estimated from the
rela tive pe rcentag e o f minera ls of different
Moh’s hardness classes (>7, 6-7, 4-5 and
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Thes e method s no rmally g ive a fa irly reliable
estimation of the abras iveness . The greates t
challenge in most cases is to collect
represe ntative samp les.
Vickers hardness defines the micro-
indentation hardness of a mineral, a nd
provides a Vickers hardness number (VHN).
The ha rdness number is defined a s the ratio
of the load ap plied to the indentor (gram or
kilogram force) divided by the conta ct a rea
of the impression (mm2). The Vickers
indentor is a square based diamond pyramid
with a 130˚ included ang le betw een oppo site
faces, so that a perfect indentation is seen
as a sq uare with equa l diag ona ls. A virtually
linear relation has been found b etwee n
Moh’s hardness and VHN (in log-scale), as
shown in Figure 1.
As with Moh’s hardness, the use of VHN is
primarily for the purpose of preliminary
estimates of abrasivity and the expected
cutter wea r.
The Cerchar tes t is performed b y
sc ratching a freshly broken rock surfac e w ith
a sharp pin of heat-treated alloy steel (figure2). The C ercha r Abra sivity Index (CAI) is the n
calculated as the average diameter of the
ab raded tip of the s teel pin in tenths of mm
after 10mm of travel ac ros s the rock surface.
The ad vanta ge o f this tes t is tha t it ca n be
performed o n irregular roc k sa mples. The
CAI value is related directly to cutter life in
the field. C AI values va ry betwee n less tha n
0.5 for soft rocks (such a s s hale and
limestone) to more than 5.0 for hard rocks
(such as quartzite).
The LCP C Abrasimeter Tes t involves the
taking of s amples o f rock, s oil or
synthetically created material a nd tes tingusing the 4mm-6.3mm frac tion. C oa rse
grained material has to be crushed and
sieved and fine gra ined ma teria l (
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of a pprox. 2kg is us ed for preparation of
abras ion po wder.
• Crushing is d one g ently in several crusher
steps to avoid excessive production of
fines . The initial crushing is pe rformed in a
jaw crusher with the outlet opening
adjusted to 10mm. Further crushing is
performed using a sma ller lab oratory
crushe r in minimum 2 s teps . The outlet
opening is a djusted to approx 3mm-4mm
prior to the first crusher step.
• The c rushed ma terial is sieved o n a 1mm
qua dratic mes h. The fraction < 1mm is
transferred to a suitable pan and the
frac tion > 1mm is c rushed ag ain after
ad justment of the o utlet ope ning to
app rox. 1mm. This proce ss is repea ted
until the g rain size d istribution is 99%