Thread for footwear upper

 

Thread for footwear upper is a long, thin strand of cotton, nylon, or other fibers used in sewing or weaving upper components of shoes.

Qualities of the thread for footwear upper required for footwear manufacturing is:

(i) High Strength: Thread should be strong enough to be able to penetrate two or more layers of leather without breaking.

(ii) Stretches: Thread should be stretchable enough to withstand all shoemaking process without any breakage.

(iii) Elasticity: Thread should be elastic enough so that the a seam can recover well after stretching and not become loose in wear.

(iv) No shrinkage/expansion when exposed to heat or when wet.

(v) High flexibility and resistance to flex cracking.

(vi) Uniform thickness to avoid snagging during stitching.

(vii) Non- slip property to prevent run back.

(viii) Good abrasion resistance to withstand rubbing in wear and high-speed stitching.

(ix) Resistance to needle heat.

(x) Resistance to bacteria.

(xi) Resistance to damage from sunlight.

(xii) Colorfastness.

(xiii) Ability to take dyes.

(xiv) Retain a good appearance in finished seams

Quality checks of thread for footwear uppers are:

To produce uniform, strong, dyed and the lubricated thread of different thicknesses, is a long process which requires continuous quality control checks, which are:

· Yarn evenness.

 · Yarn strength.

 · Twist levels and regularity.

 · Plied thread strength.

 · Shade matching.

 · Lubrication.

 · Finished appearance.

Thread Classification and Material

Threads are made from fibers and these fibers that are used to make industrial sewing threads come from two major sources: fibers could be man-made or natural.

Natural Fibers:

• it comes from plants and animals and is spun or twisted into yarns, as it is the most common natural fiber used to make the thread.

• natural fibers include silk, wool, jute, hemp, and linen.

Synthetic Fibers:

• are made from various chemicals or regenerated from cellulose such as wood pulp and cotton waste.

• examples are polyester, nylon, etc.

• synthetic fibers based on their sewing ability, seam performance, ease of dying, colorfastness, and pricing.

Thread Twist: Fibers are twisted to make fine yarns/filaments. This twist produces coherence, strength, and flexibility – the essentials of a sewing thread. 

This twist is balanced by a reverse twist when two or more yarns are joined together to form a thread otherwise the individual plies would separate while sewing.

• Anti-clockwise twist produces an S-twist thread whereas clockwise twist produces Z-twist. 

• The twist is defined in terms of the no. of twists inserted cm. If the twist is too much, the thread gets lively, and if too less the yarns will open up and fray.

• Threads are mainly produced in 2,3 or 4 ply.

Thread Numbering/Sizing System

There are two methods to size a thread:

(i) Fixed Length System: It is the weight in grams of a fixed length of thread so, the heavier the thread, the higher the number. This system is used for silks and rayon.

(ii) Fixed Weight System: It is the length of thread in meters of a fixed weight of thread so, the finer the thread higher the number.

The threads can also be sized according to its text value, which is the weight in grams of 1000 meters of the thread.

Thread consumption formula

It is very important to know the amount of thread that has been consumed in a product so you can:

•  estimate the number of cones needed, and
• calculate the cost of thread that is needed to manufacture the finished product.

  Formula: 

  

         for thread consumption for a lock stitch machine = [{2 * (material thickness + stitch length)* stitches/cm} + 10] – 15% wastage allowance.       

                                                          

Example:

Length of seam = 50 cm (0.5 metre)

Stitch class = 301 Lock stitch

 total thread usage per cm of seam = 2.5 cm

Total thread consumption = 50 cm x  2.5= 125 cm

Estimated Needle thread =125 x 0.50 = 62.5 cm

Estimated Loop thread = 125 x 0.50 = 62.5 cm

Add 10% wastage = 125 cm x 1.10 = 137.5 cm of thread per seam

The choice of thread depends upon the type of :

•  Seam
•  Material
•  Needle
•  Purpose

upon which it is used.