The Sock Testing Consortium compiled the following information after two and one half years of intensive tests and analytical study on test methods and equipment available to the industry.
General Information
All standards should be set between the manufacturer and their customer. The study to date has only involved testing between the same stretch machine types. No correlation has been established between different stretch machine types.
Fit to Size / Stretch Dimensions
- Finished socks should be tested for FIT on appropriate NAHM forms both before and after 3 launderings (following AATCC test method 135) -- excluding the use of the Durometer due to its unacceptable and excessive variation within test sample groups. (refer to the Use of NAHM Forms page)
- Once FIT has been determined using the appropriate NAHM sizing form(s), a "statistically sound" stretch machine should be used to document standard "stretch" dimensions at specified measurement points.
Stretch Equipment
- A "Statistically Sound" stretch machine implies that its data is proven statistically reproducible both within the machine as well as from machine-to-machine. This applies to every component of the stretch machine be that cross and or length stretch.
- All standards set between the manufacturer and their customer must specify the equipment used, the specific measurement points, and their dimensions. At this time, no correlation tests have been run between different equipment types.
- This publication contains sizing equipment that has been tested and the results from the machines are statistically reproducible from machine to machine given appropriate calibration procedures and verification of such.
- Note that the sizing equipment manufacturer is responsible for insuring that their manufacturing processes maintain the reliability of the machines beyond the testing phase.
Machine Calibration
- The machine must have calibration procedures that can be verified by the user as a measure of force.
- Calibration of the machine should be maintained on a basis described in the Use Procedure for each machine.
- Each day confirm calibration of the machine by running 10 stretches with the test spring supplied by the machine vendor. If the readings are within specified tolerance begin your sock measurements.
- Once per month confirm that the test spring is pulling the same by measuring it’s extension at 10 pounds (10 lb. weight supplied). Compare that reading to the measurement taken when the spring was new. When a difference is noted, replace the spring with a new one from the machine supplier.
Measurement Points
- Each sock can only be measured once.
- Begin with length stretch and then measure cross stretch on each sock
- Cross stretch measurement of the foot should always be taken through the toe (cut out in finished socks).
- All measurements on any given profile should always be made at the same precise "location". "Location" means the same point down the sock in courses and around the sock in needles. It is important to have the sock symmetrical, front to back or side to side, when loading onto stretch equipment.
- Prevent any excess fabric from creating any drag on the sizing machine. Fabric on stretch machine at measurement point should be free to move, without constraint due to excess or folded-over fabric.
New Equipment and Modified Sizing Equipment
- New or modified approved sizing machines that become available can and will be tested at the Hosiery Technology Center utilizing a documented test procedure. Data tested will be evaluated by the Sock Testing Consortium for the machines’ final disposition. This applies to every component of the stretch machine, be that cross and or length stretch. Both fabric and test spring should be tested so that no possible mounting or operator error could be introduced
- Conditions/Parameters of Test
- The material used for test fabric will be a 100 % non-plated CPM tube.
- The test spring is currently being developed.
- A minimum of 3 machines will be needed for testing.
- 20 test runs on each measurement (length and cross).
- Analysis of Test Data:
- Comparison of Averages, standard deviation and Coefficient of variation (CV)% to compare within machine variation.
- Analysis of Variance (Anova) test to compare between machine variations must also be run at 95% confidence level.
- Results of the Anova test must show no significant difference between machines when comparing the F-test verses F-calculated numbers for the machines.
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