Hardness
http://en.wikipedia.org/wiki/Hardness
HardnessFrom Wikipedia, the free encyclopediaThis article is
about mechanical properties of materials. For other uses, seehard
(disambiguation)."Durezza" redirects here. For the French wine
grape, seeDurezza (grape).Hardnessis a measure of how
resistantsolidmatteris to various kinds of permanent shape change
when a compressiveforceis applied. Some materials, such as metal,
are harder than others. Macroscopic hardness is generally
characterized by strongintermolecular bonds, but the behavior of
solid materials under force is complex; therefore, there are
different measurements of hardness:scratch hardness,indentation
hardness, andrebound hardness.Hardness is dependent
onductility,elasticstiffness,plasticity,strain,strength,toughness,viscoelasticity,
andviscosity.Common examples ofhard matterareceramics,concrete,
certainmetals, andsuperhard materials, which can be contrasted
withsoft matter.Contents[hide] 1Measuring hardness 1.1Scratch
hardness 1.2Indentation hardness 1.3Rebound hardness 2Hardening
3Physics 3.1Mechanisms and theory 4See also 4.1Other strengthening
mechanisms 5References 6Further reading 7External linksMeasuring
hardness[edit]
A Vickers hardness testerThere are three main types of hardness
measurements:scratch,indentation, andrebound. Within each of these
classes of measurement there are individual measurement scales. For
practical reasonsconversion tablesare used to convert between one
scale and another.Scratch hardness[edit]Main article:Scratch
hardnessScratch hardness is the measure of how resistant a sample
is tofractureor permanentplastic deformationdue to friction from a
sharp object.[1]The principle is that an object made of a harder
material will scratch an object made of a softer material. When
testing coatings, scratch hardness refers to the force necessary to
cut through the film to the substrate. The most common test isMohs
scale, which is used inmineralogy. One tool to make this
measurement is thesclerometer.Another tool used to make these tests
is the pocket hardness tester. This tool consists of a scale arm
with graduated markings attached to a four wheeled carriage. A
scratch tool with a sharp rim is mounted at a predetermined angle
to the testing surface. In order to use it a weight of known mass
is added to the scale arm at one of the graduated markings, the
tool is then drawn across the test surface. The use of the weight
and markings allows a known pressure to be applied without the need
for complicated machinery.[2]Indentation hardness[edit]Main
article:Indentation hardnessIndentation hardness measures the
resistance of a sample to material deformation due to a constant
compression load from a sharp object; they are primarily used
inengineeringandmetallurgyfields. The tests work on the basic
premise of measuring the critical dimensions of an indentation left
by a specifically dimensioned and loaded indenter.Common
indentation hardness scales areRockwell,Vickers,Shore,
andBrinell.Rebound hardness[edit]Rebound hardness, also known
asdynamic hardness, measures the height of the "bounce" of a
diamond-tipped hammer dropped from a fixed height onto a material.
This type of hardness is related toelasticity. The device used to
take this measurement is known as ascleroscope.[3]Two scales that
measures rebound hardness are theLeeb rebound hardness
testandBennett hardness scale.Hardening[edit]Main article:Hardening
(metallurgy)There are five hardening processes:Hall-Petch
strengthening,work hardening,solid solution
strengthening,precipitation hardening, andmartensitic
transformation.Physics[edit]
Diagram of astress-strain curve, showing the relationship
betweenstress(force applied per unit area) andstrainordeformationof
a ductile metal.Insolid mechanics, solids generally have three
responses toforce, depending on the amount of force and the type of
material: They exhibitelasticitythe ability to temporarily change
shape, but return to the original shape when the pressure is
removed. "Hardness" in the elastic rangea small temporary change in
shape for a given forceis known asstiffnessin the case of a given
object, or a highelastic modulusin the case of a material. They
exhibitplasticitythe ability to permanently change shape in
response to the force, but remain in one piece. Theyield strengthis
the point at which elastic deformation gives way to plastic
deformation. Deformation in the plastic range is non-linear, and is
described by thestress-strain curve. This response produces the
observed properties of scratch and indentation hardness, as
described and measured in materials science. Some materials exhibit
bothelasticityandviscositywhen undergoing plastic deformation; this
is calledviscoelasticity. Theyfracturesplit into two or more
pieces.Strengthis a measure of the extent of a material's elastic
range, or elastic and plastic ranges together. This is quantified
ascompressive strength,shear strength,tensile strengthdepending on
the direction of the forces involved.Ultimate strengthis an
engineering measure of the maximum load a part of a specific
material and geometry can withstand.Brittleness, in technical
usage, is the tendency of a material to fracture with very little
or no detectable plastic deformation beforehand. Thus in technical
terms, a material can be both brittle and strong. In everyday usage
"brittleness" usually refers to the tendency to fracture under a
small amount of force, which exhibits both brittleness and a lack
of strength (in the technical sense). For perfectly brittle
materials, yield strength and ultimate strength are the same,
because they do not experience detectable plastic deformation. The
opposite of brittleness isductility.Thetoughnessof a material is
the maximum amount ofenergyit can absorb before fracturing, which
is different from the amount offorcethat can be applied. Toughness
tends to be small for brittle materials, because elastic and
plastic deformations allow materials to absorb large amounts of
energy.Hardness increases with decreasingparticle size. This is
known as theHall-Petch relationship. However, below a critical
grain-size, hardness decreases with decreasing grain size. This is
known as the inverse Hall-Petch effect.Hardness of a material to
deformation is dependent on its microdurability or small-scaleshear
modulusin any direction, not to anyrigidityorstiffnessproperties
such as itsbulk modulusorYoung's modulus. Stiffness is often
confused for hardness.[4][5]Some materials are stiffer than diamond
(e.g. osmium) but are not harder, and are prone tospallingand
flaking in squamose or acicular habits.Mechanisms and
theory[edit]
A representation of the crystal lattice showing the planes of
atoms.The key to understanding the mechanism behind hardness is
understanding the metallicmicrostructure, or the structure and
arrangement of the atoms at the atomic level. In fact, most
important metallic properties critical to the manufacturing of
todays goods are determined by the microstructure of a
material.[6]At the atomic level, the atoms in a metal are arranged
in an orderly three-dimensional array called acrystal lattice. In
reality, however, a given specimen of a metal likely never contains
a consistent single crystal lattice. A given sample of metal will
contain many grains, with each grain having a fairly consistent
array pattern. At an even smaller scale, each grain contains
irregularities.There are two types of irregularities at the grain
level of the microstructure that are responsible for the hardness
of the material. These irregularities are point defects and line
defects. A point defect is an irregularity located at a single
lattice site inside of the overall three-dimensional lattice of the
grain. There are three main point defects. If there is an atom
missing from the array, avacancy defectis formed. If there is a
different type of atom at the lattice site that should normally be
occupied by a metal atom, a substitutional defect is formed. If
there exists an atom in a site where there should normally not be,
aninterstitial defectis formed. This is possible because space
exists between atoms in a crystal lattice. While point defects are
irregularities at a single site in the crystal lattice, line
defects are irregularities on a plane of atoms.Dislocationsare a
type of line defect involving the misalignment of these planes. In
the case of an edge dislocation, a half plane of atoms is wedged
between two planes of atoms. In the case of a screw dislocation two
planes of atoms are offset with a helical array running between
them.[7]In glasses, hardness seems to depend linearly on the number
of topological constraints acting between the atoms of the
network.[8]Hence, therigidity theoryhas allowed predicting hardness
values with respect to composition.
Planes of atoms split by an edge dislocation.Dislocations
provide a mechanism for planes of atoms to slip and thus a method
for plastic or permanent deformation.[6]Planes of atoms can flip
from one side of the dislocation to the other effectively allowing
the dislocation to traverse through the material and the material
to deform permanently. The movement allowed by these dislocations
causes a decrease in the material's hardness.The way to inhibit the
movement of planes of atoms, and thus make them harder, involves
the interaction of dislocations with each other and interstitial
atoms. When a dislocation intersects with a second dislocation, it
can no longer traverse through the crystal lattice. The
intersection of dislocations creates an anchor point and does not
allow the planes of atoms to continue to slip over one another[9]A
dislocation can also be anchored by the interaction with
interstitial atoms. If a dislocation comes in contact with two or
more interstitial atoms, the slip of the planes will again be
disrupted. The interstitial atoms create anchor points, or pinning
points, in the same manner as intersecting dislocations.By varying
the presence of interstitial atoms and the density of dislocations,
a particular metal's hardness can be controlled. Although seemingly
counter-intuitive, as the density of dislocations increases, there
are more intersections created and consequently more anchor points.
Similarly, as more interstitial atoms are added, more pinning
points that impede the movements of dislocations are formed. As a
result, the more anchor points added, the harder the material will
become.See also[edit] Hardness comparison Vickers hardness test
Brinell hardness test Hardness of ceramics Toughness Schmidt hammer
Roll hardness tester Tablet hardness testing Persoz pendulumOther
strengthening mechanisms[edit] Grain boundary strengthening
Precipitation hardening Solid solution strengthening Work
hardeningReferences[edit]1. Jump up^Wredenberg, Fredrik; PL Larsson
(2009). "Scratch testing of metals and polymers: Experiments and
numerics".Wear266(12): 76.doi:10.1016/j.wear.2008.05.014.2. Jump
up^Hoffman Scratch Hardness Tester. byk.com3. Jump up^Allen, Robert
(2006-12-10)."A guide to rebound hardness and scleroscope test".
Retrieved2008-09-08.4. Jump up^Jeandron, Michelle
(2005-08-25)."Diamonds are not forever".Physics World.5. Jump
up^San-Miguel, A.; Blase, X.; Mlinon, P.; Perez, A.; Iti, J.;
Polian, A.; Reny, E. et al. (1999-05-19). "High Pressure Behavior
of Silicon Clathrates: A New Class of Low Compressibility
Materials".Physical Review83(25):
5290.Bibcode:1999PhRvL..83.5290S.doi:10.1103/PhysRevLett.83.5290.6.
^Jump up to:abHaasen, P. (1978). Physical metallurgy. Cambridge
[Eng.]; New York: Cambridge University Press.7. Jump up^Samuel, J.
(2009). Introduction to materials science course manual. Madison,
Wisconsin: University of Wisconsin-Madison.8. Jump up^Smedskjaer,
Morten M.; John C. Mauro; Yuanzheng Yue (2010). "Prediction of
Glass Hardness Using Temperature-Dependent Constraint Theory".Phys.
Rev. Lett.105(11): 2010.doi:10.1103/PhysRevLett.105.115503.9. Jump
up^Leslie, W. C. (1981). The physical metallurgy of steels.
Washington: Hempisphere Pub. Corp., New York: McGraw-Hill,ISBN
0070377804.Further reading[edit] Chinn, R. L. (2009). "Hardness,
bearings, and the Rockwells".Advanced Materials & Processes,
167 (10), 2931. Davis, J. R. (Ed.). (2002).Surface hardening of
steels: Understanding the basics.Materials Park, OH: ASM
International. Dieter, George E. (1989).Mechanical Metallurgy.SI
Metric Adaptation. Maidenhead, UK: McGraw-Hill Education.
0-07-100406-8 Malzbender, J. (2003). "Comment on hardness
definitions."Journal of the European Ceramics Society.23 (9). DOI
10.1016/S0955-2219(02)00354-0 Revankar, G. (2003). "Introduction to
hardness testing."Mechanical testing and evaluation, ASM Online
Vol. 8.External links[edit] An introduction to materials hardness
Guidelines to hardness testing Testing the Hardness of
MetalsCategories: Condensed matter physics Matter Solid mechanics
Materials science Hardness tests
Hardness comparisonFrom Wikipedia, the free encyclopediaThere
are a large number ofhardnesstesting methods available
(e.g.Vickers,Brinell,Rockwell,MeyerandLeeb). Although it is
impossible in many cases to give an exact conversion, it is
possible to give an approximate material-specific comparison table
e.g. forsteels.Hardness comparison table[edit]
BrinellHB(10mm Ball, 3000kg load)VickersHV(1kg)RockwellC HRC(120
degree cone 150kg)Rockwell B HRB(1/16" ball 100kg)LeebHLD[1]
800-72-856
780122071-850
760117070-843
745111468-837
725106067-829
712102166-824
68294065-812
66890564-806
65286763-799
62680362-787
61477561-782
60174660-776
59072759-770
57669457-763
55264956-751
54563955-748
52960654-739
51458753120731
50256552119724
49555151119719
47753449118709
46150248117699
45148947117693
44447446116688
42746045115677
41543544115669
40142343114660
38840142114650
37539041113640
37038540112635
36238039111630
35136138111621
34635237110617
34134437110613
33133536109605
32332035109599
31131234108588
30130533107579
29329132106572
28528531105565
27627830105557
26927229104550
26126128103542
25825827102539
24925025101530
24524624100526
2402402399521
2372352399518
2292262298510
2242212197505
2172172096497
2112131995491
2062091894485
2032011794482
2001991693478
1961971592474
1911901492468
1871861391463
1851841291461
1831831190459
1801771089455
175174988449
170171787443
167168687439
165165586437
163162485434
160159384430
156154283425
154152182423
152150-82420
150149-81417
147147-80413
145146-79411
143144-79408
141142-78405
140141-77404
135135-75397
130130-72390
114120-67365
105110-62350
95100-56331
9095-52321
8185-41300
7680-37287
References[edit]1. Jump up^H.Pollok, Umwertung der Skalen
(Conversion of Scales), Qualitt und Zuverlssigkeit, Ausgabe
4/2008.External links[edit] Hardness Conversion Table Brinell,
Rockwell,Vickers Various steels Rockwell to Brinell conversion
chart(Brinell, Rockwell A,B,C) Struers hardness conversion
table(Vickers, Brinell, Rockwell B,C,D) Brinell Hardness HB
conversion chart(N/mm2, Brinell, Vickers, Rockwell C)
Schmidt hammerFrom Wikipedia, the free encyclopediaASchmidt
hammer, also known as aSwiss hammeror a rebound hammer, is a device
to measure theelasticproperties or strength ofconcreteorrock,
mainly surface hardness and penetration resistance.
Original Schmidt Concrete Test Hammer
Testing the compressive strength of a concrete cube using
Schmidt hammerIt was invented by Ernst Schmidt, a Swiss engineer.
The Schmidt hammer is distributed byProceqand TQC worldwide.[1]The
hammer measures the rebound of a spring-loaded mass impacting
against the surface of the sample. The test hammer will hit the
concrete at a defined energy. Its rebound is dependent on the
hardness of the concrete and is measured by the test equipment. By
reference to the conversion chart, the rebound value can be used to
determine thecompressive strength. When conducting the test the
hammer should be held at right angles to the surface which in turn
should be flat and smooth. The rebound reading will be affected by
the orientation of the hammer, when used in a vertical position (on
the underside of a suspended slab for example) gravity will
increase the rebound distance of the mass and vice versa for a test
conducted on a floor slab. The Schmidt hammer is an arbitrary scale
ranging from 10 to 100. Schmidt hammers are available from their
original manufacturers in several different energy ranges. These
include: (i) Type L-0.735 Nm impact energy, (ii) Type N-2.207 Nm
impact energy; and (iii) Type M-29.43 Nm impact energy.The test is
also sensitive to other factors: Local variation in the sample. To
minimize this it is recommended to take a selection of readings and
take an average value. Water content of the sample, a saturated
material will give different results from a dry one.Prior to
testing, the Schmidt hammer should be calibrated using a
calibration test anvil supplied by the manufacturer for that
purpose. 12 readings should be taken, dropping the highest and
lowest, and then take the average of the ten remaining. Using this
method of testing is classed as indirect as it does not give a
direct measurement of the strength of the material. It simply gives
an indication based on surface properties, it is only suitable for
making comparisons between samples.This test method for testing
concrete is governed by ASTM C805. ASTM D5873 describes the
procedure for testing of rock.
Roll hardness testerFrom Wikipedia, the free encyclopediaAroll
hardness testeris a device to measure the roll hardness, hardness
profile and hardness variation of paper rolls.Contents[hide]
1Method 2Standards 3Application 4See also 5ReferencesMethod[edit]In
the preparation phase, the plunger, guide bar and guide disk are
pushed forward by the compression spring. At the end of the
movement the hammer mass is hooked by the pawl. During the loading
phase the hammer is pushed towards the surface in a controlled
movement. The hammer mass remains locked in place by the pawl. This
has the effect of stretching the impact spring to put it under
tension. Impact Rebound: At the very end of the movement, the pawl
spring releases the hammer mass. The impact spring contracts
causing the hammer mass to strike against the plunger. This is the
impact. The hammer mass then rebounds back to the body of the
hammer and distance travelled is recorded on the scale. The rebound
distance depends directly on the hardness of the roll under test: A
softer roll will absorb more of the impact energy and the rebound
distance will be less. A harder roll will reflect more of the
impact energy and the rebound distance will
increase.Standards[edit] TAPPIT 834 om-07: Determination of
containerboard roll hardness TAPPITIP 1004-01: TAPPI Roll Number
for inventory/tracking systems and bar codesApplication[edit]Roll
hardness is one of the most important parameters when deciding
whether a paper roll is good or bad. A roll that is wound too
softly can go out of round when handled. A roll that is wound too
hard, on the other hand, can crack during transportation.[1]These
variations are difficult to detect. Above all, it is typically the
variation in hardness across a given roll that relates most
directly to such converting issues with soft edges being perhaps
the biggest contributor.[2]See also[edit] Paper mill Pulp (paper)
Tablet hardness testingReferences[edit]1. Jump up^Black Clawson
Converting Machinery, "The Art of Winding Good Rolls".2. Jump
up^TAPPI Standard T 834 om-07Categories: Hardness instruments
Tablet hardness testingFrom Wikipedia, the free
encyclopediaTablet hardness testing, is alaboratory techniqueused
by thepharmaceuticalindustry to test the breaking point and
structural integrity of atablet"under conditions of storage,
transportation, and handling before usage"[1]The breaking point of
a tablet is based on its shape.[2]It is similar
tofriabilitytesting,[1]but they are not the same thing.Tablet
hardness testers first appeared in the 1930s.[3]In the 1950s, the
Strong-Cobb tester was introduced. It was patented by Robert
Albrecht on July 21, 1953.[4]and used an air pump. The tablet
breaking force was based on arbitrary units referred to as
Strong-Cobbs.[3]The new one gave readings that were inconsistent to
those given by the older testers.[3]Later, electro-mechanical
testing machines were introduced. They often include mechanisms
like motor drives, and the ability to send measurements to a
computer or printer.[3]There are 2 main processes to test tablet
hardness: compression testing and 3 point bend testing. For
compression testing, the analyst generally aligns the tablet in a
repeatable way,[2]and the tablet is squeezed by 2 jaws. The first
machines continually applied force with a spring and screw thread
until the tablet started to break.[3]When the tablet fractured, the
hardness was read with a sliding scale.[3]Contents[hide] 1List of
common hardness testers 2Units of measurement 3Sources 4Further
readingList of common hardness testers[edit]There are several
devices used to perform this task: TheMonsantotester was developed
50 years ago. The design consists of "a barrel containing a
compressible spring held between 2 plungers". The tablet is placed
on the lower plunger, and the upper plunger is lowered onto
it.[5][1] The Strong-Cobb tester forces an anvil against a
stationary platform. Results are viewed from a hydraulic
gauge.[5]The results are very similar to that of the Monsanto
tester.[6] ThePfizertester compresses tablet between a holding
anvil and a piston connected to a force-reading gauge when
itsplier-like handles are gripped.[5] Erweka tester tests a tablet
placed on the lower anvil and a weight moving along a rail
transmits pressure slowly to the tablet.[5] The Dr.Schleuniger
Pharmatron tester operates in a horizontal position. An electric
motor drives an anvil to compress a tablet at a constant rate. The
tablet is pushed against a stationary anvil until it fractures. A
reading is taken from a scale indicator.[5]Units of
measurement[edit]Theunits of measurementof tablet hardness mostly
follows standards used in materials testing theInternational System
of Units. Kilogram (kg) The kilogram is recognized by the SI system
as the primary unit of mass. Newton (N) The Newton is the SI unit
of force; the standard for tablet hardness testing. 9.807 Newtons =
1 kilogram. Pound (lb) Technically a unit of mass but can also be
used for force and should be written as pound force or lbf in this
case. Sometimes used for tablet strength testing in North America,
but it is not an SI unit. 1 kilogram = 2.204 pounds. Kilopond (kp)
Not to be confused with a pound. A unit of force also called a
kilogram of force. Still used today in some applications, but not
recognized by the SI system. 1 kilopond = 1 kgf. Strong-Cobb (SC)
Anad hocunit of force which is a legacy of one of the first tablet
hardness testing machines.[4]Although the SC is arbitrary, it was
recognized as the international standard from the 1950s to the
1980s. 1 Strong-Cobb represented roughly 0.7 kilogram of force or
about 7newtons.[7]Although the Strong-Cobb unit is arbitrarily
based on the dial reading of a hardness tester, it became an
international standard for tablet hardness in the 1950s until it
was superseded by testers using SI units in the 1980s.[6]The
Strong-Cobb is a unit with a very unusual name for a unit of
measurement since it is named after the company, Strong-Cobb Inc.
The inventor of the hardness tester was Robert Albrecht,[4]the
plant engineer for the Strong-Cobb Company. He sold the patent to
the company for $1.00.Sources[edit]1. ^Jump up to:abcJoseph Price
Remington (2006).Remington: The Science And Practice Of Pharmacy.
Lippincott Williams & Wilkins.ISBN0781746736.2. ^Jump up
to:ab"Tablet hardness testing". Sotax. Retrieved16 February2013.3.
^Jump up to:abcdef"Some Information on Tablet Hardness Testing".
Engineering Systems. Retrieved16 February2013.4. ^Jump up
to:abcRobert Albrecht (Jul 21, 1953)."Tablet Hardness Testing
Machine". United States Patent Office. Retrieved16 February2013.US
26459365. ^Jump up to:abcde"Quality control of solid dosage form".
Scribd. Retrieved16 February2013.6. ^Jump up to:abMcCallum, A.,
Buchter, J. and Albrecht, R. (1955). "Comparison and correlation of
the Strong Cobb and the Monsanto tablet hardness testers".Journal
of the American Pharmaceutical Association44(2):
8385.doi:10.1002/jps.3030440208.PMID14353719.7. Jump up^Russ
Rowlett (September 1, 2004)."How Many? A Dictionary of Units of
Measurement". University of North Carolina. Retrieved16
February2013.Further reading[edit] J. E. Rees and P. J. Rue
(1978)."Work Required to Cause Failure of Tablets in Diametral
Compression".Drug Development & Industrial Pharmacy4(2):
131156. Retrieved16 February2013. American Society for the Testing
of Materials (ASTM), Designation: E407, 'Standard Practices for
Force Verification of Testing Machines'.Categories: Hardness tests
Measuring instruments Laboratory techniques Pharmacology
Tablet hardness testingFrom Wikipedia, the free
encyclopediaTablet hardness testing, is alaboratory techniqueused
by thepharmaceuticalindustry to test the breaking point and
structural integrity of atablet"under conditions of storage,
transportation, and handling before usage"[1]The breaking point of
a tablet is based on its shape.[2]It is similar
tofriabilitytesting,[1]but they are not the same thing.Tablet
hardness testers first appeared in the 1930s.[3]In the 1950s, the
Strong-Cobb tester was introduced. It was patented by Robert
Albrecht on July 21, 1953.[4]and used an air pump. The tablet
breaking force was based on arbitrary units referred to as
Strong-Cobbs.[3]The new one gave readings that were inconsistent to
those given by the older testers.[3]Later, electro-mechanical
testing machines were introduced. They often include mechanisms
like motor drives, and the ability to send measurements to a
computer or printer.[3]There are 2 main processes to test tablet
hardness: compression testing and 3 point bend testing. For
compression testing, the analyst generally aligns the tablet in a
repeatable way,[2]and the tablet is squeezed by 2 jaws. The first
machines continually applied force with a spring and screw thread
until the tablet started to break.[3]When the tablet fractured, the
hardness was read with a sliding scale.[3]Contents[hide] 1List of
common hardness testers 2Units of measurement 3Sources 4Further
readingList of common hardness testers[edit]There are several
devices used to perform this task: TheMonsantotester was developed
50 years ago. The design consists of "a barrel containing a
compressible spring held between 2 plungers". The tablet is placed
on the lower plunger, and the upper plunger is lowered onto
it.[5][1] The Strong-Cobb tester forces an anvil against a
stationary platform. Results are viewed from a hydraulic
gauge.[5]The results are very similar to that of the Monsanto
tester.[6] ThePfizertester compresses tablet between a holding
anvil and a piston connected to a force-reading gauge when
itsplier-like handles are gripped.[5] Erweka tester tests a tablet
placed on the lower anvil and a weight moving along a rail
transmits pressure slowly to the tablet.[5] The Dr.Schleuniger
Pharmatron tester operates in a horizontal position. An electric
motor drives an anvil to compress a tablet at a constant rate. The
tablet is pushed against a stationary anvil until it fractures. A
reading is taken from a scale indicator.[5]Units of
measurement[edit]Theunits of measurementof tablet hardness mostly
follows standards used in materials testing theInternational System
of Units. Kilogram (kg) The kilogram is recognized by the SI system
as the primary unit of mass. Newton (N) The Newton is the SI unit
of force; the standard for tablet hardness testing. 9.807 Newtons =
1 kilogram. Pound (lb) Technically a unit of mass but can also be
used for force and should be written as pound force or lbf in this
case. Sometimes used for tablet strength testing in North America,
but it is not an SI unit. 1 kilogram = 2.204 pounds. Kilopond (kp)
Not to be confused with a pound. A unit of force also called a
kilogram of force. Still used today in some applications, but not
recognized by the SI system. 1 kilopond = 1 kgf. Strong-Cobb (SC)
Anad hocunit of force which is a legacy of one of the first tablet
hardness testing machines.[4]Although the SC is arbitrary, it was
recognized as the international standard from the 1950s to the
1980s. 1 Strong-Cobb represented roughly 0.7 kilogram of force or
about 7newtons.[7]Although the Strong-Cobb unit is arbitrarily
based on the dial reading of a hardness tester, it became an
international standard for tablet hardness in the 1950s until it
was superseded by testers using SI units in the 1980s.[6]The
Strong-Cobb is a unit with a very unusual name for a unit of
measurement since it is named after the company, Strong-Cobb Inc.
The inventor of the hardness tester was Robert Albrecht,[4]the
plant engineer for the Strong-Cobb Company. He sold the patent to
the company for $1.00.Sources[edit]1. ^Jump up to:abcJoseph Price
Remington (2006).Remington: The Science And Practice Of Pharmacy.
Lippincott Williams & Wilkins.ISBN0781746736.2. ^Jump up
to:ab"Tablet hardness testing". Sotax. Retrieved16 February2013.3.
^Jump up to:abcdef"Some Information on Tablet Hardness Testing".
Engineering Systems. Retrieved16 February2013.4. ^Jump up
to:abcRobert Albrecht (Jul 21, 1953)."Tablet Hardness Testing
Machine". United States Patent Office. Retrieved16 February2013.US
26459365. ^Jump up to:abcde"Quality control of solid dosage form".
Scribd. Retrieved16 February2013.6. ^Jump up to:abMcCallum, A.,
Buchter, J. and Albrecht, R. (1955). "Comparison and correlation of
the Strong Cobb and the Monsanto tablet hardness testers".Journal
of the American Pharmaceutical Association44(2):
8385.doi:10.1002/jps.3030440208.PMID14353719.7. Jump up^Russ
Rowlett (September 1, 2004)."How Many? A Dictionary of Units of
Measurement". University of North Carolina. Retrieved16
February2013.Further reading[edit] J. E. Rees and P. J. Rue
(1978)."Work Required to Cause Failure of Tablets in Diametral
Compression".Drug Development & Industrial Pharmacy4(2):
131156. Retrieved16 February2013. American Society for the Testing
of Materials (ASTM), Designation: E407, 'Standard Practices for
Force Verification of Testing Machines'.Categories: Hardness tests
Measuring instruments Laboratory techniques Pharmacology
Persoz pendulumFrom Wikipedia, the free encyclopedia
Persoz pendulumAPersoz pendulumis a device used for
measuringhardness of materials. The instrument consists of
apendulumwhich is free to swing on two balls resting on a coated
test panel. The pendulum hardness test is based on the principle
that theamplitudeof the pendulum'soscillationwill decrease more
quickly when supported on a softer surface. The hardness of any
given coating is given by the number of oscillations made by the
pendulum within the specified limits of amplitude determined by
accurately positioned photo sensors. An electronic counter records
the number of swings made by the pendulumConstruction[edit]
Persoz pendulum deviceThe pendulum consists of balls which rest
on the coating under test and form thefulcrum. The Persoz pendulum
is very similar to theKonig pendulum. Both employ the same
principle, that is the softer the coating the more the pendulum
oscillations are damped and the shorter the time needed for the
amplitude of oscillation to be reduced by a specified amount. The
two pendulums differ in shape, mass and oscillation time, and there
is no general relationship between the results obtained using the
two pieces of equipment. In either case, the test simply involves
noting the time in seconds for the amplitude of swing to decrease
from either 6 to 3degrees(Konig pendulum) or 12 to 4 degrees
(Persoz pendulum).[1]References[edit]1. Jump up^PRA. Mechanical
Properties. Accessed: May 6, 2015.Categories: Hardness instruments
Materials science Pendulums Coatings
