A double bed circular knitting machine has two needle beds, It’s similar to a double flat knitting machine. The only difference is, that here the needle is placed in a circular panel. It could be a cylinder or a disc. We can categorize double bed circular knitting machines into two rib machines and interlocking machines. In terms of design and look both looks similar, but only the arrangement of needles on the two beds are different
1.Rib Machine
The Rib machine has two beds, one is called Cylinder and the other one is Dial where the needles are placed, The dial and cylinder would actively take part in the knitting process to create a double jersey fabric. Slots and tricks are created in a radial direction on a dial. Needles are placed on the slots, and the direction of movement is along the radius. No sinker element is required for a double bed circular knitting machine.
The vertical cylinder also has slots and tricks and each of these slots is equipped with needles, this is how the arrangement of two beds is done in a circular knitting machine. Cylinder needles are doing reciprocation in the vertical directions. On the dial, the needle is doing the reciprocation along the radial direction. While doing the reciprocation they are not striking each other, because both the needle set should not face each other. The position of the slot on the cylinder and the dial are shifted so they should not collide during the knitting process. One set of needles is displaced laterally by half pitch so they can smoothly do the knitting action. And all the needles are actively participating in the knitting process.
Fabric formation and Needle action on a Double bed Circular knitting Machine
The fabric is produced at a 45-degree angle with either cylinder or dial. Whenever one set of needles doing the action the stem of other needles is providing the support, which means when the dial needle is moving forward the loops are connected with the stem of cylinder needles. The stem of this needle is doing the function of sinkers so there is no requirement for the sinker in a double bed circular knitting machine. Which is the fundamental difference compared to a single bed circular knitting machine
Multi feeder Machine
In this type of machine, multiple cams are being placed along the circumference. At the same rotation, a single needle can create a multiple number of loops. So productivity on this particular knitting machine is high.
Compared to flatbed, where you have to first complete the entire reciprocation and then you have to return to make the second course. Here you can simultaneously create multiple numbers of course in one rotation. It’s done by multiple cams along the circumference
2.Interlocking Machine
In terms of design and look both rib and interlock are similar, but the arrangement of needles is different. This machine also has two different beds, one is a cylinder and the other is the dial. The only difference between rib machines is the placement of needles and the type of needles which is used in the interlock machines. Interlock fabrics are being used in t-shirts ,undergarments, pressure garments
In the Rib machine needles are placed in such a way that they do not face each other. The beds have laterally shifted half-pitch with the opposite bed. But in the case of the Interlock machine dial and cylinder are facing each other. When the cylinder needle will go top the dial is not doing anything and when the dial is doing an active movement then the cylinder is resting on the cylinder bed, In this particular machine, at a particular location, only half of the needles are active because these two needle beds are facing each other so if the cylinder and dial if they are active at the same location they can hit each other. Whenever the cylinder needles are taking part dial is resting; or when the dial is taking part, the cylinder is resting.
Another difference is the position of needles and they have two sets of needles on the same bed, On the same bed it has long butt and short butt needles. In one case but is at the highest position and in the other case butt is at the lowest position. So these type of needle is called long butt needle and short butt needle. And these two needles are placed alternatively on each of these beds.
Placement of Needles in a Interlock Machine
The dial short butt needle is facing cylinder long butt needles and the cylinder short butt needle is facing dials long butt needles. Alternating needles are selected from each of the beds, when dial needles are active, the corresponding opposite cylinder needle is inactive and vice versa, So they should not hit during the knitting actions. This is how the interlock needle arrangement is different from a rib needle arrangement.
The interlock machine has two cam tracks for long butt needles and short butt needles.This type of cam arrangement is for both dial and cylinder beds. So short butt needles catch the feeder yarn at an even position and Long butt needles catch the feeder yarn at an odd position
Gating
The placement of needles on the needle beds is called Gating
