Tuesday, January 16, 2018

Parts and Working Principle of Round Knife Cutting Machine

Round Knife Cutting Machine:
Round knife machines are used to cut large and medium size components with a simple shape from low fabric spreads (1–12 fabric plies) or to cut single articles from 1 or 2 material plies. The machine is moved along the cut contours while the fabric spread remains in a fixed position. Round knife machines are the most effective for cutting slippery materials as the rotary movement of the knife ensures the continuous compression of the fabric plies. Round knife cutters are lighter (between 3 and 11 kg) than straight knife machines and are therefore easier to move.

You can also like: Straight Knife Fabric Cutting Machine: Parts, Feature, Advantages and Disadvantages

Main parts of round knife cutting machine:
A round knife machine consists of the following main parts: 1. Motor, 2. Electrical cable, 3. Handle, 4. Knife sharpener, 5. Safety shield, 6. Rotary knife blade, 7. Base plate with rollers (see Fig-1).

Fig-1:  Image (a) and diagram (b) of a round knife cutting machine. See text for explanation of components.
Important parts of round knife machine are described below:

The round knife:
The cutting device is a circular knife with a blade sharpened along one side. The knife rotates and cuts the fabric only in the downward direction. The diameter of the knife can vary from 80–200 mm. The larger the knife diameter, the larger, heavier and more powerful is the machine and therefore the less manoeuverable. The most widely used machines are those with 100 mm and 110 mm knives. Blades of different shapes are used for cutting different materials. Round blades are used to cut light fabrics but polygonal blades with 4, 6, 8 and 10 sides are used to cut thicker and harder materials (see Fig-2). The knives may have one or two rotation speeds. Because the cutting device is round, the height of the cut spread can be only approximately one-quarter of the knife diameter.

Fig-2: Shapes of a round knife: smooth (a), four bows (b) and 10 bows (c).
The knife sharpener:
The machine has a built in blade sharpening system which uses replaceable emery stones. It is necessary to stop the cutting process during sharpening. The frequency of sharpening depends on the material being cut and on the knife blade.

The base plate and its rollers:
The lowest possible base plate profile is necessary to ensure the stability of the machine. The base plate facilitates the manoeuverability of the machine and minimises the risk of deforming the material plies during the work process. Independently moving rollers are fixed under the base plate to ensure easy movement of the machine.

The cable:
An electrical cable supplies the motor with electricity. During the cutting process, it must be secured away from the surface of the cutting table to avoid the possibility of electric shock.

Safety devices:
The machine has a front safety shield to protect the operator’s hands from the knife blade. It may also be equipped with an auto stop trigger which switches off the power when the operator’s hand is removed from the lever. A separate on/off switch is situated on the top of the machine. During the cutting process, the operator must wear special protective gloves.

Advantages of round knife cutting machine:

  1. Easy to handle & operate.
  2. Suitable for cutting single ply as well as multilayer (say 20-30layers).
  3. Suitable for gentle curve line cutting.
  4. Suitable for small scale cutting.
  5. To cut the larger part of the garments.
  6. With a same r.p.m. its efficiency is 10 times greater than the straight knife.
  7. Round knife cutting machine is specially used to cut suit of fashion garment.
Disadvantages of working with a round knife machine:
The round shape of the cutting device significantly limits the height of the cut spread which can be no more than approximately one-quarter of the knife diameter. As the surface of the cutting device is large, the machine has limited manoeuverability. It cannot make an abrupt change in the cutting direction or cut contours with a large degree of curvature. Because of the round shape of the cutting device, the machine cannot be used to cut notches.

You can also like: Different Types of Fabric Cutting Machines Used in Apparel Manufacturing

Rotary shears/small round knife cutting machine:
Special small sized round knife cutting machines are available for cutting single or multiple plies of material (for spreads up to 10 mm), shown in Fig-3.

  • These differ in shape, have a small diameter knife (typically 50 mm) and are light in weight (0.5–1.5 kg). The machines may be mains or battery powered.
  • Smallest and most widely used rotary shears are perfect upgrade to or replacement for, manual shears. Streamlined, lightweight construction helps eliminate operator fatigue.
  • Built-in sharpener mechanism for ease of use.
  • Equipped with round blade for general use, or optionally with a hexagon or four-sided blade for difficult-to-cut materials.
Parts and functions of mini round knife machine:
Fig-3: Parts of small sized round knife cutting machine
  • Knife – Generally round knife used to cut the fabric. Based on the type of application variations in the knife like hexagonal can be preferred.
  • Knife guard – A small metal rod in front of the knife to avoid direct contact of hands with the knife during the cutting process
  • Lock screw – Knife lock screw is the essential part, which holds the knife in position. The screw needs to be removed while changing the knife every time.
  • Carbon bushes – Carbon bushes are inside the body and motor cases. The bushes need to be replaced after every 200–500 h of used based on the manufacturers.
  • Sharpening mechanism – Knife sharpening mechanism is on the both sides of the blade. The mechanism need to be cleaned after every usage. Dust accumulation in the device will reduce the sharpening efficiency and hence the cutter efficiency.
  • Base plate – The base plate is the plate which moves under the fabric plies during the cutting process. The base plates can be removed and replaced with cutting guides sometime.
  • Body/handle – The machine body is a plastic outer cover of electrical motor assembly which is also used as a handle to operate the machine. But machines are available with long handles too. The working of small round knife cutting machine is shown in Fig-4.
Fabric cutting using small round knife cutting machine
Fig-4: Fabric cutting using small round knife cutting machine.