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1- Title
An important aspect is the knowledge of the sewing linear count, what allows to the same thread class, to choose what the best conditions for the article use are.
It's true that the count influences:
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The breaking strength of the sewing thread and so the seam resistance
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The choice of the needle size
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The filing up of the reel
The count can be expresses in several varieties:
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Tex
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Ne
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Nm
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Denier
Tex and Ne are the most used to the sewing threads.
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2-Twist
It's the number of thread turns around its axle, determines by its nominal measure length, that is before distortion.
The twist should be expressed by twist per meter, but it can also be expressed by twist per centimeter or twist by inch.
The direction of the twist it's very important. The twist can be in direction of the clock hands, twist Z, known as left twist, or on the opposite of the clock hands that forms twit S, known as right twist.
The Z twist is more suitable to the majority of the modern sewing machine, because a thread with S twist becomes distorted by the machine action, untwisting and breaking afterwards.
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3-Friction
It's the sliding of the thread in contact with a cylindrical form where opposite forces exist.
The frequent changing of needles is due to consume caused by the friction on the metal.
The needle heat and the abnormal frequent of breaks are also caused by the friction. The friction properties depend of the sewing thread quality and the finishing oils.
The oiling is very important because it diminishes the friction and protects the sewing thread against heat.
It's necessary in these cases to do an friction or sliding test of the thread on the metal, which allows the detection of the material consume of the thread, affecting its characteristics and life duration of the machine pieces.
Too much oiling can cause stains on the pieces, and create a big problem, oil cleaning is very expensive.
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4-Irregularity
The irregularity of the thread, that is the mass variation per length unit is considered a very important and critical factor. The irregularity can be found in any phase of the textile process, can appear in threads, rugs and ribbons.
The length and diameter of the fiber are very important properties to determine their behavior in the spinning process. There a great relationship between the irregularity of the thread and the medium length of the fiber.
The variations of the transversal section of the thread, such as napes, thin and thick stitches, are usually described as imperfections and there are analyzed parallel to the irregularity.
It's important to understand that all threads are someway irregular, being its value the determined factor for the product to be accepted or not by the consumer.
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5-Breaking Strength
It's the tension that breaks the thread, expressed in grams or kgs (force) or
centinewtons (1 gf=0, 98 CN). This varies lightly according to the specific
conditions under which the thread broke, for example, humidity, temperature,
load regime and longitude of the thread under strain.
So, all these conditions are precisely specified in all international tests.
These tests are done in labs under controlled atmosphere with automatic
machines, using electronic cells.
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6-Tenacity
Tenacity or relative resistance to break of a fibre or thread is obtained
dividing the resistance to break by the linear mass.
The thicker we produce a thread the more resistant it will be, of course.
But, the tenacity is theoretically independent to the linear mass of the thread
and can be used to compare the resistance of several fibres and thread
constructions. Tenacity can be expressed in many ways, for instance grams
(force) per denier (g/d), cN per Tex (cN/tex) or grams (force) per TEX (g/tex);
This last one is the most used.
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7-Breaking Extension
breaking extension it is the quantity of sewing extended until break, it is expressed in percentage of is original length.
8-Elasticity
This is he property of the thread through which tends to recover its original length, after being stretched to a certain point. For instance the gum recovers its original length, so it's highly elastic with an elastic recuperation of 100%.
One say that non stretched polyamide has high plasticity with zero elastic recuperation.
Valfios department of quality makes control tests of these parameters through samples and reference of the sewing thread.
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In English
