USTER HVI 1000: Principles of Fiber Testing

Last Updated on 06/01/2021

USTER® HVI 1000 is the global reference tool for cotton classification, producing accurate and reliable results. It is the only cotton classification instrument in the world. USTER HVI 1000 rapidly provides full reports on eleven important quality characteristics describing the length, strength, fineness, color, and moisture content of the fiber.

Functions of HVI 1000:
The USTER HVI 1000 measures the most important cotton fiber properties for cotton classing purposes (and high-throughput requirements for spinning mills.) These are length, uniformity, short fiber index, micronaire, maturity index, strength, elongation, color and trash, and moisture content.

Features of USTER HVI 1000:
The following features are provided with the USTER HVI 1000:

Main Equipment: Length/Strength, Moisture Content, Micronaire and Color/Trash Instruments.

Computer Software: The USTER HVI 1000 is a menu driven design that allows quick access and selection of testing, setup, calibration, and data management. These features include:

• Windows XP operating system with icon-based software
• Simple user interface
• Error messages for troubleshooting
• Network capabilities

Computer Hardware: Computer system with 2.8 GHz PC with 512 MB RAM, P&P Sound Card, DVD-R drive, 1.44 MB (3.5-inch) Floppy Disk Drive, 60 GB or better hard drive, and Pentium P4 processor. Besides,

• Keyboard with Integrated Touchpad
• 17” High Resolution Flat Panel LCD Monitor with Integrated Sound Bar
• Balance
• Printer
• Integrated Bar Code Scanner

Barcode Reader (M700)

• UPS – Uninterrupted Power Supply device
• UV Module
• NEP Module

Additional features: Safety interlocks to prevent injury from un-authorized entry to the instrument

• Relative humidity and temperature probe
• Moisture measurement
• Easily accessible Lint Waste Box with two separate access doors
• Computer System easily removed for service
• Configuration can be straight line configuration or “L” configuration
• Industrial brushed stainless-steel top and work surfaces
• Single point adjustable brush pressure
• Integrated air enclosure around balance to eliminate influences of air turbulence
• Password protected operational software
• Complete Operator Manual included

Laboratory Temperature: These specifications are for the ambient conditions referenced below. If the airline will be subjected to temperatures that could promote condensation, a water filter attached to the airline inside the lab is recommended to remove any condensation that may occur.

Ambient Conditions: According to ISO 139, the following ambient conditions must be maintained in the laboratory in order to get repeatable and comparable test results:

• Temperature: 20±2°C; 65 °F to 72 °F
• Relative Humidity: 65±2%

For consistent test results, fiber samples should be conditioned in the laboratory environment with the above-mentioned ambient conditions for 24 hours. Samples should be laid out openly in the laboratory, and taken out of plastic bags, in order for the cotton to fully condition to the environment.

Test parameters of HVI: there are three modules in USTER HVI 1000

• MIC module (MIC and maturity
• Length and strength module (Upper Half Mean Length, Uniformity Index, Short Fiber Index, strength, elongation)
• Color and trash module (Rd, +b, color grade, trash grade, trash area, trash count, moisture)

By the HVI 100% cotton samples in the form of bale or opened and cleaned material (card mat) are measured.

Principles of Fiber Testing Using USTER HVI 1000:

Sample preparation: The fibro gram method is preferred while preparing the sample for fiber length estimation. The sample has to be presented to the measuring zone by clamping the fibers at a random catch point. Here the fibrosampler is used. The test specimen obtained using the fibro sampler/comb combination is a beard of fibers with individual fibers projecting to different length from the clamping point. In HVI, the strength testing is also done on the same beard of fibers with individual fibers projecting to different lengths from the clamping point. In HVI, strength testing is also done on the same beard of fibers prepared for length measurement. While using the low volume instrument -fibro stelo for strength measurement, the sampling is done on the separate fiber bundles, of which 15 mm long is prepared after remounting the short fibers by combing. For micronaire testing, a sample of cotton weighing approximately 8.5-11.5 grams is used. For color testing, random mass of fibers sufficient to cover the test window is used for measurement.

• Sample weight for MIC measurement-8.5 gm (range 8.5-11.5 gm)
• Sample weight for another test- 30-40 gm to cover the test window

Measurements and Calculations:

Micronaire: Micronaire Reading

Measuring principle: Measured by relating airflow resistance to the specific surface of fibers.

The micronaire module of HVI uses the airflow method to estimate the fineness value of cotton. A sample known weight is compressed in a cylinder to known volume and subjected to an air current at a known pressure. The rate of airflow through this porous plug of fiber is taken to be a measure of the fineness of cotton. The number of fibers in a given weight of cotton will be more in the case of finer fibers than in the case of coarser fibers. If air is blown through these samples, the plug containing finer fibers will be found to offer a greater resistance than the plug with coarser fibers. This is due to the fact that the total surface area in the case of the former will be greater than the latter and hence the drag on the air flowing past will be more. This differentiating factor is made use of to indirectly measure the fineness of cotton.

The instrument operates as follows. The chamber lid is closed; a piston at the chamber bottom compresses the fiber to a fixed and known volume. A regulated stream of air is then forced through the sample and the pressure drop across the sample is applied to a differential pressure transducer. The transducer outputs an analog signal voltage proportional to the pressure drop. This analogue voltage is applied to an analogue to digital converter, which outputs a digital signal representing the voltage. Cotton with known fineness values is tested and the voltages obtained are used to obtain the calibration curve, which is used for all subsequent testing to display the cotton fineness.

The fineness is expressed in the form of a parameter called the micronaire value, which is defined as the weight of one inch of the fiber in micrograms. Maturity of cotton also influences the micronaire value.

Maturity measurement: Maturity Index (Mat)
Measuring principle: Calculated using a sophisticated algorithm based on several HVI™ measurements. Maturity indicates the degree of cell wall thickness within a cotton sample. The HVI SPECTRUM Maturity index correlates very well to the AFIS Maturity Ratio and the reference method of microscopy (cross-sectional analysis).

Length: Upper Half Mean Length, Uniformity Index, Short Fiber Index

Measuring principle: Measured optically in a tapered fiber beard which is automatically prepared, carded, and brushed.

Upper Half Mean Length (Len):
The by weight measurement of the Upper Half Mean Length is calculated from the Fibrogram. A fiber beard of randomly clamped fibers is scanned optically across its length and the Fibrogram is drive from it. The Upper Half Mean Length corresponds to the classer’s staple length as well as to the AFIS Upper Quartile length by weight. Please note that a length range is assigned in inches for each length staple or code. The ranges calculated in millimeters do not line up exactly due to the conversion calculation. However, inches or 32nds are mainly used for staple length determination in the international cotton tread and are therefore binding.

Uniformity Index (Unf):
The uniformity index expresses the ratio of the mean length to the upper half mean length. It is an indication of the distribution of fiber length within the Fibrogram.

Uniformity index = Mean Length/upper half mean length.

Short Fiber Index (SFI):
The short fiber index is a value that is calculated using a sophisticated algorithm. The Fibrogram is mathematically converted to a length distribution curve. The SIF is an indication of the amount of fibers (%) that are less to than 0.5 inch (12.7mm) in length. It correlates very well to the AFIS short fiber content by weight (SFC).

Strength (Strength, Elongation):
Measuring principle: Strength is measured physically by clamping a fiber bundle between 2 pairs of clamps at known distance. The second pair of clamps pulls away from the first pair at a constant speed until the fiber bundle breaks. The distance it travels, extending the fiber bundle before breakage, is reported as elongation. The bundle strength is breaking strength of the cotton fibers in grams per tex. The fineness is calculated from the micronaire value. The fiber beard is broken at a continuous deformation rate (CRE= Constant Rate of Extension) and with a 1/8-inch distance between the clamps.

Elongation (Elg):
Elongation is a measure of the elastic behavior of the fibers in the bundle. The fibers are clamped in the bundle with a 1/8-inch distance between the clamps. The first pair of clamps is stationary and the back pair of clamps is pulled away at a constant rate. The distance the fibers extend before they break is recorded and expressed as a percentage elongation.

Moisture (Moist):
Measuring principle: Moisture content of the cotton sample at the time of testing, using conductive moisture probe. Moisture is the percentage of water that is present in the sample being tested. Moisture in the cotton varies with time, temperature, and humidity to which the samples have been exposed. Consistent moisture is necessary to maintain HVI SPECTRUM test result on the same level of accuracy and precision. The best level precision and accuracy are obtained when sample moisture has an average of 6.5% – 8%.

Color: Rd (Whiteness), +b (Yellowness), Color Grade

Measuring principle:
Measured optically by different color filters, converted to USDA Upland or Pima Color Grades or regional customized color chart.

Reflectance (Rd): This value expresses the whiteness of the light that is reflected by the cotton fibers. It corresponds to the reflectance (Rd) represented in the Nickerson/hunter color chart. It is used in conjunction with yellowness (+b) to determine the instrument-measured color grade of cotton.

Yellowness (+b): This value expresses the yellowness of the light that that is reflected by the cotton fibers. The yellowness (+b) of the sample is determined by using a yellow fiber. It corresponds to the +b value represented in the Nickerson/Hunter color chart. The yellowness is used in conjunction with the reflectance (Rd) value to determine the instrument-measured color grade of the cotton.

Color Grade (C Grade): The color grade of a cotton sample is determined in a two-filter colorimeter. This objective method was developed by Nickerson and Hunter in the early 1940s to check the USDA cotton grade standards. Today, it is intended to completely replace the subjective visual grade standards. Today, it is intended to completely replace the subjected visual grade determined by the cotton classer.

Trash: Particle Count, % Surface Area Covered by Trash, Trash Code

Measuring principle: Measured optically by utilizing a digital camera, and converted to USDA trash grades or customized regional trash standards.

Trash Count (Tr cnt): Trash is measured on the same glass window as the color measurement. The sample is illuminated form underneath the glass window, and a black and white CCD camera analyzes the changes in pixels. All particles that cover the glass window are counted one by one and the results are expressed in trash particle counts per surface area.

Trash Area (Tr Area): The area that is covered by a trash particle is measured at the same time the particle is counted. The area that is covered by single particle is summed up with all areas of the other particles counted on the surface glass window. The result is expressed as “%Area”.

For example, a small number of trash counts can result in a high “%Area” value if the particles are large. On the country, a high number of particles counts with a small “%Area” value indicate the trash is smaller in size (i.e. pepper trash).

Trash Grade (Tr Grade): This is the trash or leaf grade that is determined by calibrating the USTER HVI 1000 with known sample (i.e. trash standards). These samples are usually numbered from 1 to 7 with increasing amount of trash as the number gets large. The standards used for calibration can be supplied by the USDA or established by the official cotton standards agency in any cotton producing country.

Basic statistic: When analyzing test result of the USTER HVI 1000 some basic statistic is important. The three terms used most often in analyzing test results are:

• Average or mean value
• Standard deviation
• Coefficient of variation or CV value

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Mazharul Islam Kiron

Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. Mr. Kiron is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.

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