Surface Roughness.ppt.Here we learn About surface roughness

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Lab#5: Surface Roughness Test

 To understand surface roughness terminology and its
parameters.
 To be able to use surface roughness measurement instrument.
 To know how PERTHOMETER M1 can be used to measure
surface roughness
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 Surface finish is a characteristic of any machined surface. It is
sometimes called surface texture or roughness.
 The design engineer is usually the person that decides what
the surface finish of a work piece should be. They base their
reasoning on what the work piece is supposed to do.
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 There are two principal reasons for surface control:
 To reduce friction: When a film of lubricant must be
maintained between two moving parts, the surface
irregularities must be small enough so they will not
penetrate the oil film under the most severe operating
conditions.
 To control wear: Surface finish is also important to the wear
service of certain parts that are subject to dry friction, such
as machine-tools bits, threading dies, stamping dies, rolls,
clutch plates, and brake drums.
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 Roughness is a measurement of the small-scale variations in
the height of a physical surface. It consists of surface
irregularities which result from the various machining process.
These irregularities combine to form surface texture.
 This is in contrast to large-scale variations, which may be either
part of the geometry of the surface or unwanted 'waviness'.
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 Roughness is sometimes:
 An undesirable property, as it may cause friction, wear,
drag and fatigue,
 A beneficial property, as it allows surfaces to trap
lubricants and prevents them from welding together

 Roughness Height: It is the height of the irregularities with respect to a
reference line. It is measured in millimeters or microns or micro inches. It is
also known as the height of unevenness.
 Roughness Width: The roughness width is the distance parallel to the
nominal surface between successive peaks or ridges which constitute the
predominate pattern of the roughness.
 Roughness Width Cut Off: The greatest spacing of respective surface
irregularities to be included in the measurement of the average roughness
height. It should always be greater than the roughness width in order to
obtain the total roughness height rating. It is used to differentiate between
roughness and waviness. The cut-off length should be at least 2.5 times
the peak-to-peak spacing of the profile roughness. This means that at least
two peaks and valleys are found in each cut-off length.
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 Lay: the direction of predominant surface pattern produced and it reflects the
machining operation used to produce it. Roughness is measured perpendicular to
the lay.
 Waviness: the irregularities which are outside the roughness width cut off values.
Waviness is the widely spaced component of the surface texture. This may be the
result of work piece or tool deflection during machining, vibrations or tool runout.
 Waviness Height : the peak to valley distance of the surface profile, measured in
millimeters.
 Waviness Width: the peak to peak distance of the surface profile, measured in
millimeters.
 Arithmetic Average (AA): A close approximation of the arithmetic average roughness-
height can be calculated from the profile chart of the surface. Averaging from a
mean centerline may also be automatically performed by electronic instruments
using appropriate circuitry through a meter or chart recorder.
 Root Mean Square (RMS or Rq ) :can be calculated as shown below. Its numerical
value is about 11% higher than that of AA.
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 H: Swedish height. The roughness between two predefined reference lines.
 ISO Flatness: Areal flatness deviation. The measure of surface deviation from
perfectly flat. It is the distance between two parallel planes obtained by applying a
Chebychev fit to the surface data.
 Pt ISO: Total peak-to-valley profile height. The distance between the highest peak
and the deepest valley over the entire evaluation length. The profile data has form
removed but is unfiltered.
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 R3z: Base roughness depth. The distance between the third highest peak and the
third lowest valley. A peak is a portion of the surface above the mean line and
between center line crossings.
 R3z ISO: Base roughness profile depth. The height of the 3rd
highest peak from the
3rd
lowest valley per sampling length. The base roughness depth is found in five
sampling lengths and then averaged.
 Rmax ISO: Maximum peak-to-valley profile height. The greatest peak-to-valley distance
within any one sampling length.
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 Ra: Arithmetical mean deviation. The average roughness or deviation of all points
from a plane fit to the test part surface. The average roughness is the area between
the roughness profile and its center line divided by the evaluation length. This is the
parameter that has been used universally for many years and the European and ISO
standards now more generally use Rz
 Rq (RMS): Root-mean-square (RMS) roughness. The average of the measured height
deviations taken within the evaluation length or area and measured from the mean
linear surface
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

L
q dx
x
z
L
R
0
2
)
(
1

 Rv (Valley): Lowest valley. The maximum distance between the mean line and the
lowest point within the sample. It is the maximum data point height below the mean
line through the entire data set.
 Rp (Peak): Highest peak. The maximum distance between the mean line and the
highest point within the sample. It is the maximum data point height above the mean
line through the entire data set.
 Rt (PV): Maximum peak-to-valley height. The absolute value between the highest and
lowest peaks.
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v
p
t R
R
R 


 Rtm: Mean peak-to-valley roughness. It is determined by the difference between the
highest peak and the lowest valley within multiple samples in the evaluation area.
For profile data it is based on five sample lengths. ISO, n=5
 Ry (Rmax): Maximum peak-to-valley roughness. The vertical distance between the top
of the highest peak and the bottom of the deepest valley within the sampling length.
It is the maximum of all the peak-to-valley values.
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n
Z
Z
Z
R n
tm




...
2
1

 Rz: Ten-point height. The average absolute value of the five highest peaks and the
five lowest valleys over the evaluation length.
 Rz ISO: Average peak-to-valley profile roughness. The average peak-to-valley
roughness based on one peak and one valley per sampling length. The single largest
deviation is found in five sampling lengths and then averaged
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5
)
...
(
)
...
( 5
2
1
5
2
1 V
V
V
p
P
P
Rz

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
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

 Perthometer
It is characterized by a multitude of functions. After carrying out a
measurement, periodic and non-periodic profiles can be identified and the
cutoff set according to standards automatically, such that unintentional
non-standard measurements are excluded
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 Measuring range up to 150 µm (6000 µin)
 Measuring units µm/µin selectable
 Standards: DIN/ISO/JIS
 Tracing lengths 1,75 mm; 5,6 mm; 17,5 mm (0,07 in; 0,22 in; 0,7 in)
 Cutoff 0,25 mm/0,8 mm/2,5 mm (0,01 in/0,032 in/0,100 in)
 Reduced cutoff selectable
 Number of sampling lengths selectable from 1 to 5
 Automatic selection of filter and tracing length confirming to standards
 Phase-corrected profile filter as per DIN EN ISO 11562
 Parameters as per DIN/ISO/SEP: Ra, Rz, Rmax, RPc and JIS: Ra, Rz
 Automatic scaling according to the profile amplitude
 Printing of roughness profile and measuring record
 Dynamic pick-up calibration
 Blocking of instrument settings to prevent unintentional modifications
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Parameter Value
Total length( Lt) 5.6 mm
Cut-off length (Lc) 0.8mm
Measured Length (Lm) 5.6-(2*0.8)=4mm
Average Roughness (Ra) 0.937µm
Average Roughness Depth (Rz) 6.26 µm
Maximum peak-to-valley (Rmax) 6.89 µm
RPc (0.2,-0.2) 90/c
Vertical Scale Division 2.5 µm
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Parameter Value
Total length( Lt) 1.75 mm
Cut-off length (Lc) 0.25mm
Measured Length (Lm) (1.75 – 2 (0.25)) = 1.25mm
Average Roughness (Ra) 0.9555µm
Average Roughness Depth (Rz) 6.22 µm
Maximum peak-to-valley (Rmax) 9.14 µm
RPc (2.5,-2.5) 16 / c
Vertical Scale Division 5 µm
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Surface Roughness.ppt.Here we learn About surface roughness

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