January 18, 2010
Did you know that a sewing needle should be threaded from only one direction? That’s because the punched eyelet has a small burr on one side. Whether sewing by hand or by machine, whether stitching together pieces of cloth fabric for a quilt, leather for boots, interweaving space shuttle tile together or closing a wound, the performance of a needle is dependent on its design and its heat treatment; edge retention, toughness, springiness, and durability are critically important.
In the Beginning
According to legend, people started sewing as early as 20,000 years ago, during the last Ice Age. Early man joined skins and fur together using needles made of bone and horn with animal sinew for thread. It has been reported by Chinese archaeologists that the tomb of a minor official of the Han Dynasty (202 BC- AD 220) has been found to contain a sewing kit complete with thimble. Around the 14th century, iron needles were invented, and by the 15th century, there were eyed needles. Later, sewing needles were made of steel and even stainless steel, as they still are today. In 1790, the first workable sewing machine was invented and patented by the British inventor Thomas Saint. Early steel needles were precious and rusted easily, so sewers kept their needles in good condition by running them through emery (aluminum oxide) and storing them in wool. Because modern needles are plated, no such treatment is necessary.
How a Needle is Made
Today, more than 20 steps are needed to manufacture sewing needles. Needles are typically made two at a time from coils of steel wire. The wire is straightened and cut to twice the required length. Through a grinding process, points are formed at both ends. The needle is turned repeatedly during grinding until the point is fine and even. The care taken during this step is one of the key differences between a high and lower quality needle. Next, the eyes are stamped into the wire near the middle; two flat areas are stamped first, with the perfectly sized eyes punched through by another machine. Another piece of wire is drawn through the holes (like dental floss after a cleaning) so when the needle wire is cut apart, two needles remain, hanging from the wire. Their heads are smoothed and rounded. The bodies are checked for straightness, hardened and tempered, polished for smoothness, and finally plated.
Annealing, hardening, quenching, and tempering are heat treatments used on needles to enhance rigidity, develop toughness, and avoid brittleness.
Annealing is used to soften the needle and make it easier to shape by forging, stamping, and machining. The tough, springy form of the final needle is achieved by austenitizing followed by quenching, typically in heated oil, and tempering. Needles are often run in shaker hearth or vibratory tube furnaces so that they will progress through the furnace in a single spaced layer and can be quenched individually. Tempering, usually done in air or in a nitrogen atmosphere, produces the desired level of toughness and flexibility.
So the next time you see a needle, know that a great deal of effort has gone into this simple tool and that its design, manufacture, and heat treatment has been customized around its intended use. IH