Portable
Instruments (OFDA2000 and Fleecescan)
OFDA2000 and Fleecescan are two instruments developed
in Australia for on-farm fleece testing with the objectives
of separating superfine wool from flocks of fine-wool sheep
and assisting with genetic selection based on fineness characteristics.
The reason for the former practice is a premium paid for
superfine wool. One of the problems of measuring purely
for marketing reasons was in many cases when the superfine
wool was removed from the clip, the remaining wool had a
higher micron with a lower market value. The additional
labor and testing expense to separate the superfine wool
is not always economically justifiable.
The OFDA2000 and Fleecescan are not approved by IWTO or
ASTM. Wools separated into different micron ranges by these
instruments still have to be core sampled and tested by
IWTO and/or ASTM approved methods and instruments when offered
for sale.
The OFDA2000 measures the dimensions of raw (i.e., greasy
and dirty) fibers and then uses a constant correction factor
(within a "mob") to estimate the true dimensions.
This correction factor is measured and calculated on-site
and is typically the average of 30 samples. Since the cleanliness
of every sample measured is different, this practice limits
the accuracy of individual measurements.
The OFDA2000 has a built-in compensator for temperature
and relative humidity that adjusts for the ambient air at
the testing location. Thus it can only be properly used
on samples that have been given time to reach equilibrium
with the ambient air. OFDA2000 is not suitable for testing
raw, unconditioned samples at a central location since raw
samples from different areas of the country contain varying
amounts of moisture that affect fiber diameter. Also, it
would not be possible to use an appropriate grease correction
factor. The only way to accurately test wool or other animal
fibers is for the samples to be washed, dried, and conditioned
at standard conditions for testing textiles, a worldwide
requirement.
The OFDA2000 tests fewer than 100 fibers (depending on
the fiber diameter and staple length) from tip to base in
five millimeter increments for a total of about 1500 measurements.
It produces a fiber profile reflecting aging, health/production
status, and environmental conditions the animal was subjected
to during the growth of that particular staple length. Typically,
a mid-side sample is measured to estimate the average fiber
diameter of the whole fleece. Other (more accessible) locations
(e.g., the pin bone) have also been investigated.
The OFDA2000 uses the same basic technology as its parent
the OFDA 100 with the exception of measuring multiple fibers
in profile. The OFDA 100 is actually capable of measuring
one fiber at a time in profile but this measurement is slow
and tedious, and probably only used by researchers.
The Fleecescan is transported in a trailer. This system
minicores each fleece and chemically cleanses the sample
that is then tested on a specially designed LaserScan heavily
protected to avoid damage as it is being moved.
Genetic Selection Tool
Yocom-McColl uses both LaserScan and OFDA 100 to test fiber
of individual animals. We can measure average fiber diameter,
diameter distribution, spin fineness, curvature, curvature
distribution, and comfort factor on the LaserScan. Using
the OFDA 100, we measure all of the above plus medullation
on white or light-colored animals. Comfort factor is the
percentage of fibers greater than 30 microns subtracted
from 100 percent (in other words, a marketer’s positive
"spin" on the original term "prickle factor".
We test individual animals using two millimeter snippets
obtained across the base of the two inch square submitted
sample. In this way, we are able to provide estimates of
the genetic uniformity of the sample at a precise environmental
time.
The Laserscan and the OFDA 100 test from 2,000 to 4,000
individual snippets per sample either core sampled (minicored)
or guillotined. When guillotined at the base of the staple,
all fibers measured were produced at the same time and in
the same environment. Such a measurement indicates the genetic
fineness and uniformity of the animal (at a specific age)
that can be extremely valuable for selection purposes.
Neither LaserScan nor OFDA measure relaxed staple length.
Yocom-McColl measures average staple length on an Agritest
instrument according to IWTO 30 on relaxed, conditioned
staples.
Fiber Testing Terminology
Normal Distribution
The graph of a normal distribution, the normal curve, is
a bell-shaped curve. Many biological phenomena including
animal fiber diameter distributions for single-coated animals,
result in data distributed in a close approximation to normal.
Hence, statistics applicable to normally distributed populations
(mean, standard deviation, and coefficient of variation)
are used to define these fiber diameter distributions. The
normal curve is symmetric about a vertical center line.
This center line passes through the value (the high point
of the bell) that is the mean, median and the mode of the
distribution. A normal distribution is completely determined
when its mean and standard deviation are known.
Approximately sixty-eight percent of all measurements lie
within one standard deviation of the mean and approximately
95.0 percent of all measurements lie within two standard
deviations of the mean. More than 99.5 percent of all measurements
will lie within three standard deviations of the mean.
Fiber Diameter Measurement and Distribution
Fiber diameter is measured in microns. One micron is equal
to 1/1,000,000th of a meter or 1/25,400th of one inch. Mean
Fiber Diameter (MFD) is in common use internationally. MFD,
Standard Deviation (SD) and Coefficient of Variation (CV)
all relate to the (approximate) normal distribution of the
animal fiber diameters. SD characterizes dispersion of individual
measurements around the mean.
In a normal population, 66% of the individual values lie
within one SD of the mean, 95% within two SD’s and
99% within 2.6 SD’s. Since SD tends to increase with
increasing MFD, some people prefer to use CV (=SD*100/MFD)
as a method of comparing variability about different sized
means.
Comfort Factor
Comfort factor is the percentage of fibers over 30 microns
subtracted from 100 percent. Ten percent of fibers over
30 microns corresponds to a comfort factor of 90 percent.
Curvature
Fiber curvature is related to crimp. Average Fiber Curvature
(AFC) is determined by the measurement of two millimeter
(2mm) snippets in degrees per millimeter (deg/mm). The greater
the number of degrees per millimeter, the finer the crimp.
For wool, low curvature is described as less than 50 deg/mm,
medium curvature as the range of 60-90 deg/mm, and high
curvature as greater than100 deg/mm.
Typical values might be illustrated by a 30 micron Crossbred
wool fleece with typically low curvature and broader crimp
with a frequency of approximately two crimps/cm. In contrast,
a 21 micron Merino fleece typically has a medium curvature
and a medium crimp with a frequency of approximately four
(4) crimps/cm. A 16 micron Superfine Merino fleece typically
has a high curvature and a fine crimp with a frequency of
approximately seven (7) crimps/cm.
Definition of Medullation
A medullated fiber is an animal fiber that in its original
state includes a medulla. A medulla in mammalian hair fibers
is the more or less continuous cellular marrow inside the
cortical layer in most medium and coarse alpaca fibers.
By definition (ASTM), a kemp fiber is a medullated fiber
in which the diameter of the medulla is 60% or more of the
diameter of the fiber.
Medullation Measurement
Medullation measurement can be performed using either a
projection microscope or the OFDA 100. Using IWTO nomenclature,
a kemp fiber is classified as an “objectionable fiber”
when measured on the OFDA 100. The OFDA100 measures opacity
and therefore only white or light colored fibers can be
measured. A reasonable assumption is that colored fibers
have similar levels of medullated fibers as their white
and pastel counterparts.
Spinning Fineness
This number (expressed in microns) provides an estimate
of the performance of the sample when it is spun into yarn
by combining the measured mean fiber diameter (MFD) and
the measured coefficient of variation (CV). The original
theory comes from Martindale, but the formula used comes
from Butler and Dolling and normalizes the equation so that
the spinning fineness is the same as the MFD when the CV
is 24%.
Length & Strength
Length is measured in millimeters (mm) and the reported
measurements readjusted to an annual growth period. Strength
is measured in Newtons/kilotex (N/ktex) and is the force
(measured in Newtons) required to break a staple of a given
thickness (measured in kilotex). On the earth’s surface,
one kilogram exerts a force of 9.8 Newtons (= 1kg * acceleration
due to gravity measured in meters/second2). Kilotex indicates
thickness in terms of mass per unit length expressed as
kg/km.
Intrinsically, alpaca fibers appear to be very strong, an
average of 50 N/ktex or better is not unusual. From a processing
point of view, a mean staple strength greater than 30 N/ktex
is considered adequate for pro-cessing wool on today’s
high-speed equipment.
Resistance to Compression
The resistance to compression (RTC) of alpaca fibers is
measured in kilopascals (Kpa). A pascal (Pa) is a unit of
pressure equivalent to the force of one Newton per square
meter. In the commercial sector, RTC values >11 kPa are
considered high, 8 to 11 kPa medium, and <8 kPa is low.
The intrinsic resistance to compression of alpaca is low
because of the relatively low levels of crimp. Thus, alpaca
is not suited to end-uses that require high resistance to
compression (or high bulk).
Position of Break
Truly sound fibers break in the middle section of the staple.
Intrinsically, alpaca fibers appear to be very strong, in
the 50 N/ktex range. A mean staple strength greater than
30 N/ktex is considered adequate for processing wool on
today’s high-speed equipment.
Clean Yield
Yield is based on bone-dry, extractives-free wool (alpaca)
fiber or wool (alpaca) base (WB). Many different “commercial”
yields are used in the international marketing of wool fibers.
These are values calculated to predict the amount of clean
fiber obtained after commercial scouring and/or after combing.
Allowances are typically made for grease, ash, vegetable
matter, and moisture. Various percentages of moisture are
added in these calculations of commercial yield, which in
some cases (very clean wool or some alpaca yields) may result
in the clean yield exceeding 100%. |
