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Introduction to Leather Testing Methods

Dimensional and Density Measurements
This type of testing includes only basic measurement techniques, in some cases coupled with basic dimensional measurements based on weight . Although seemingly simple, these tests require a good calibration regime to be recognized successfully.
Another critical issue is the correct conditioning of the sample to temperature and humidity. It is not difficult to understand that the dimensions, notably the weight per unit area/length of a textile or leather sample, will depend on the temperature and especially the relative humidity. Therefore, this type of test generally requires conditioning the sample for 24 hours under standard conditions. Additionally, the tests must be carried out under the same standard and control conditions. This ensures maximum comparability of measurement results commerciallyimportant from different laboratories and at a competitive level.
There are quick-adjust cabinets available, as shown at left. These fabrics adjust in minutes, depending on fabric type and weight. For certification purposes, it will be necessary to carry out comparative studies, tests on regular 24-hour post-conditioning and on post-conditioning on rapid systems. The results showed no significant difference.
Proving that the conditioning of each sample was done correctly requires careful management and recording of conditioning time, temperature and humidity. As other laboratories have indicated, separate records of laboratory temperature and humidity should be kept. If the start and end time conditions, as well as the test time, are recorded for each sample, an audit trail is created and can be reviewed.verified to ensure that general laboratory records confirm that temperature and humidity were within specifications during the relevant period. .
A useful way to create the necessary records is to attach a card to each sample, as shown below. This is the final submission of test sample results to provide an audit record of the correct procedure.
The types of dimensional measurements discussed may constitute the test itself and the same problem arises when samples are prepared to succumb to other tests. They must also be conditioned and measured by calibrated equipment. Obvious examples are when samples are prepared for dimensional stability testing, such as shrinkage during washing or when the fabric, yarn or leather specimen is prepared for tensile testing. Even chemical testss require sample conditioning so that the analysis weight is measured under standard humidity conditions.

Balance Calibration and Management
There is nothing special about the calibration and management of balances for textile and leather testing. This aspect of the work requires the balance of one, two or at most one or three people. General guidance for selected accreditedcertification bodies for balance calibration and intermediate verification. There are some differences between certification bodies in what they recommend for detailed scale calibration, but the basic model is the same. Typical requirements are explained below.
The scale must be calibrated on site. Ideally, even if movement of the balance within the laboratory requires recalibration, most accreditation bodies are willing to accept that modern balances cannt move occasionally. This distribution imbalance however extends to Allowed to be shipped to a calibration calibration lab and then shipped to the lab. It is also not acceptable to purchase a scale calibration certificate that reflects the calibration at the supplier\'s premises, even if that calibration is fully valid and traceable.
Annual maintenance and calibration of the balance is required. Calibration must be fully traceable, which in practice means that it is carried out by an international accredited calibration service to ISO 90025. Please note that calibrations carried out by ISO 9001 accredited organizations will not be accepted. Some accrediting bodies allow longer periods for scale calibrations, but labs should verify that there is more than one year between the bodies they intend to appeal.
The main laboratories cannt perform a self-balancing calibration. If you want to do this, you need to have a set of traceable calibration weights and, of course, a documented calibration procedure. This must include a calibration detailing how the calibration was performed and detailing how the uncertainty was calculated. A typical method of calibration, for different types of balances, can be found in Laboratory Document 14 on the UKAS Accreditation Service website (www.ukas.com). This document shows the procedure and gives advice on appropriate weight classes for different scale resolutions. An example of an uncertainty calculation for the balancear calibration application in the m3003 UKAS document, also available on their website. If a laboratory performs its own balance calibrations, it should maintain appropriate arrangements for calibration with weights. The weights provided are taken seriously and do notare only used for balancing periods of up to three years between calibrations, which is generally acceptable, but accrediting bodies should guide annual calibrations.

Dimensional measuring equipment
Textile labs typically use steel rulers, tape measures, or vernier calipers. Leather testing labs will also have applications that may require micron thickness measurements.
All of these devices must be calibrated through an ISO 17025 calibration service. Equipment such as rulers and tapes can retain their calibration for up to five years if used with care. However, they should be subject to formal inspections every six months, with inspection records showing any signs of damage. However, if damage is found elsewhere, the equipment should be immediately removed from service andn awaiting calibration inspection or replacement.
Vernier calipers and micrometer feeler gauges should be fully monitored and calibrated by experts at least once a year. It is recommended to check a canonical set of blocks at least once a month. A set of three or four steps spanning 5 to 50 mm is useful. These will usually be purchased with a calibration certificate but do not require recalibration. They can confirm the consistency of calipers and micrometers in much the same way as weight scale checks, i.e. return values ​​when measuring equipment is used immediately after recording the annual calibration of the micrometer or caliper and return values ​​to these raw values. values ​​during monthly checks Compare. The drift must not exceed a numerical interval. For example, a set of calipers measuringexactly 0.1mm on a 10mm gauge block should appear between 9.9 and 10.1mm.
Some dimensional measurements, like selection per unit length on fabric, use a low power microscope or magnifying glass stand to define the dimensions in a scale.
The simple type of meter selected (a) consists of a defined dimension, usually 25 mm or 1 inch, which can be viewed under a magnifying glass and checked annually using a calibrated caliper. This can happen immediately with annual caliper calibration. The main problem is to check that there are no dimensional deviations since the item is new. The longest type of socket meter (B), which looks like a small mobile microscope, can be examined by looking at a calibrated ruler, placed where the tissue usually sits, through the microscope and comparing the measurement of the ruler with the counter scale. This must be done every yeared and measurements should be made to the nearest sector, generally 1 mm. It is necessary to have a calibrated ruler dedicated specifically for this purpose and everything else. Calibration references should be used only for such measurements and not for routine measurements, so the working scale used, even if calibrated, will be invalid.

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