Selection of Slitting Line:

If you have purchased, or are going to purchase a new slitting line which is a large capital investment item, you have probably spent a lot of time with the machine builder or designer, obtaining the proper machine and accessories for your requirement. It is important that the machine be equipped with the best possible tooling as this is the heart of the slitting operation. Tooling can amount to approximately 1o to 15 percent of your total equipment cost, hence serious consideration must be given for selection of tooling.

1. Slitting Line Tooling consists of :

1.1 Slitting Knives
1.2 Distance Rings/ Spacers
1.3 Shims
1.4 Stripper Rings
1.5 Rubberised Spacers
1.6 Over Arm Seperator Discs
1.7 Distance Rings for Over Arm Seperator

F U N C T I O N S:

1.1 The rotary slitting knife is, without doubt the most important part of the set as it performs the actual cutting or slitting task. As its name implies, it is a circular knife with parallel faces. This produces two cutting edges per knife which can be used simultaneously or one at a time, depending on the mode of application.

1.2 Distance Rings are provided in order to maintain an accurately defined distance between two rotary slitting knives. As a rule distance rings have the same geometric form as the knives, although they are smaller in diameter in order to allow the knife to enter the material to be cut and to permit regrinding of knife. Accuracy of distance rings will decide the performance of slitting operation.

1.3 The shims are a special kind of distance rings. Generally they are lesser than 0.5 mm in thickness and are made of plastic or brass. Shims are utilized to get exact slit width.

1.4 The fourth functional part of the tool set is rubber ring. Its geometry is that of distance ring but it’s made or wear resistant rubber. This ring pushes the cut strips out from between the rotary slitting knives where, due to the overlapping of the side faces of the knives, strip has a tendency to get stuck.

1.5. Rubberised Spacers are a combination of spacers and rubber rings.

1.6 Seperating discs, running on separating shaft, separate the cut strips, so that they can be fed to individual winding coils. Because separating discs are subjected to heavy frictional wear, they are usually made from hardened tool steel and have a cross section which is tapered towards the outside diameter. AISI D2 is most recommended raw material. (For details please refer NV 11d).

1.7 Spacers for over arm separator are arranged between the separating discs so as to maintain a distance between the discs that equals the width of the strip.

2. KNIFE MATERIAL :

2.1 It should be clear, from physical point of view, that the selection of the knife material with regard to steel composition is governed primarily by the material to be cut. Because steel is to be cut by steel, the cutting quality is always the prime criteria for selection.

This means the knife material must be harder than the material to be cut. The second most important criteria for the material selection must therefore be the capability of holding its cutting edges, that is to say, the cutting quality under load must be impaired in anyway. Consequently the material suitable for knives is the kind of alloy steel that can be hardened in principle, can be hardened in depth and is resistant to plastic deformation under pressure.

2.2 When selecting the material, it is essential to decide which of these three main characteristics, namely hardness, tenacity and resistance to wear, should be given preference or which optimum combination of all three characteristics is desirable and possible.

2.3 The loads to which knives are subjected on a slitting line vary considerably, as the thickness of the material to be cut can vary from 0.05 mm to 20 mm. Besides thickness, the composition and tensile strength of the material to be cut also govern the loading on the slitting line. A general rule: the thinner the material to be cut, the higher can be the hardness of the knife.

2.4 There are four basic grades of steels used for slitting knives:

a. Shock Resistance Steel / Hot Die Steel.
b. High Carbon High Chrome Steel.
c. High Speed Steel.
d. Carbide Steel.

This is not to imply that thee are only four grades of steels used in the manufacture of knives. However, these are the basic classifications. From this, many compositions can be developed, depending on application and slitting requirement.

a. Shock resistance Steels/ Hot Die Steels are generally used, as the name implies, to resist shock. Cutters made out of these steels are used on the lines, slitting material more than 6 mm thickness in mild steel. As indicated in figure 2, this type of material has got the least wear resistance properties as compared to other knife materials.
  
OTHER ARTICLES

NON DESTRUCTIVE TESTING OF COLD ROLLING MILL ROLLS
SUB ZERO TREATMENT (Reduction in Retained Austenite)
TUBE CUT OFF KNIVES
TIGHTER MANUFACTURING TOLERANCE FOR ROTARY
CUTTER, SLITTING KNIFE AND SPACER.
CRYOGENIC TREATMENT
GUIDELINES FOR RAW MATERIAL SELECTION FOR SLITTING LINE TOOLING
SHEAR BLADES AND MACHINE KNIVES
PRECAUTION & ORDERING TIPS FOR FRICTION SAWS
FINS AN IMPORTANT COMPONENT OF TUBE MAKING
IMPORTANT FACTORS IN COLD ROLLING MILL ROLLS
DEE TEE FORGES YET AHEAD IN SEARCH OF EXCELLENCE
SLITTER TOOLING OVER ARM SEPARATORS