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| Circular Knitting Machine. |
Circular knitting is a construction of fabric or garments knitted on a circular knitting machine in tubular form. Knitted fabrics on large-diameter circular knitting machines are manufactured as endless tubular fabric with a circular array of knitting needles. In double-jersey machines, needles are arranged in both the cylinder and in the dial, while single-jersey machines use knitting-machine needles as well as sinkers. In shirtmaking on bodysize machines, for example, this eliminates lateral seams. This is particularly advantageous for skintight clothing.
A circular knitting machine is commonly used for single knits. Single knit is a knit fabric made on one set of needles. Circular knitting machines pull their yarn supply from creels located either above the machine or next to the machine. To make it easier for technicians to service the creels, it is more usual to locate creels at the side. In this position, less lint falls into knitting elements, larger packages can be used and more feeds can be placed on the machine. Whether the creel is at the side or at the top the principles for circular knitting are the same. Fed from above the knitting elements, yarns move from the yarn supply, or creel, through guides to stop motion controls above the machine.
Then back down through tension controls and yarn feeding devices to the knitting elements. Quality products can be produced only when stop motion and yarn feeding functions are properly set. The intricate action of knitting where needles form loops occurs in the middle of the machine between the take-up and the yarn feeding mechanism. Circular weft knitting needles are knit one after the other in a sequence for each yarn. Loops are formed horizontally by needles knitting around a cylinder knitting forming a tube. After the yarn is knit on the knitting elements, the knitted fabric is passed over a spreader mechanism through take-up rolls and is wound into a roll. This elliptical spreader distributed the take-up tension uniformly and enables the fabric to conform to a flat tube.
Typical application fields in circular knitting include the manufacture of outerwear such as T-shirts, leisure and sportswear, underwear and sleepwear, among them bra fabrics and technical textiles such as smart shirts.
Needle Action
Knitting machines are designed so that each needle can be placed in a groove cut into the outside of a metal cylinder. The cuts or grooves are also referred to as slots or tricks. The top edge of each groove is referred to as the verge. These cylinders are very precisely manufactured so that the diameter measured at any place is equal. Machines are classified by the number of cuts per linear inch. This is referred to as the cut or gauge of the machine. For example, an 8-gauge machine has 8 cuts per inch. The total number of cuts around the circumference of the cylinder would indicate the number of needles in the cylinder—the more needles, the wider the fabric.
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| Latched needle parts. |
Parts of a Latched Needle
At the top of each needle is a hook. Below this is a latch attached with a rivet. The bottom edge or cup of the latch is curved to fit over and completely close the hook. At the bottom of the needle is a butt that plays a part in controlling how needles activate, up or down. A needle with a latch is very efficient. When the latch needles are used to create weft knits, the knitting cycle can be completed without any auxiliary attachments.
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| Latched needle working cycle. |
How a Latched Needle Works
Rest – At rest or running position, a knit loop rests above or on the latch.
Clearing – As the needle moves up, the old loop, already formed, drops below and clears the latch.
Yarn Receiving – As the needle moves down, it receives the new yarn to begin forming a new stitch.
Cast Off or Knockover – The latch is knocked over by the old loop and this old loop is cast off.
Stitch Formation – The needle moves further down to fully form and complete the new stitch.
The amount of yarn used to form a new stitch determines the stitch length. This is important because stitch length affects the weight, width, and aesthetics of the fabric. On modern-day knitting machines, needles make millions of loops or stitches a day. Needles may need to be replaced due to wear but they usually last up to six months depending on the construction, yarn type, fiber type, and speed. Next, let’s take a look at what causes the needles to move up and down. The butt of the needle guides the needle through a path formed by cams. Each cam is designed to allow the needle to run straight or to move up and down.
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| Cam stages. |
Here’s how the needle travels through various stages:
Rest Cam – At the rest or running position, the needle runs straight over the rest cam.
Clearing Cam – When it hits the clearing cam, it rides up at a steep angle which forces the needle to rise and clear the old loop.
Stitch Cam – The needle drops when it contacts the stitch cam.
As it continues on its path, it catches the new yarn. It continues further down, pulling the new yarn far enough for a new loop or stitch to form as the old loop is cast off.
Upthrow Cam – The upthrow cam returns the needle to its resting position so it can begin the cycle again.
The machine has a cylinder that contains vertical grooves and slots to hold the needles that move.
Sinker
Between each pair of needles is a sinker. Sinkers control the movement of fabric as the machine knits. A sinker is a thin steel element with a distinctive shape. A sinker has a hold, a throat, a nose, and a butt with a place to insert a cam.
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| Sinker parts. |
As the needle goes up, the sinker moves in to catch the fabric in its throat. Since the fabric can’t go up with the rising needle, the old loop now clears the latch. When the hook catches a feeder yarn as the needle moves down, the sinker moves back out of the way and knockover, cast off, and stitch forming take place. As the new stitch is formed, the fabric rests on top of the nose.
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