SLITTING KNIFE CLEARANCE - DeeTee group

No. 3N(oe.)9w(.de).fw.:.e0.1f./:0011/2/0040/92013

Determination to Establish Excellence
Through Efficiency and Expertise

SLITTING KNIFE
CLEARANCE

SLITTING CLEARANCE :

Proper knife clearance minimizes burr, increases knife's life by reducing wear and tear. It
also reduces stress on the machine and improves slit width tolerance.

While slitting, knives cut partially through the metal. The material then fractures, the rest
of the way. The angle of the fracture is same, regardless of the metal being processed. The
thickness and tensile strength of the metal determine knife clearance.

WHAT HAPPENS IN SLITTING : UPPER KNIFE

As the metal strip enters the knives (step 1 Strip Step 3
in diagram), the strip penetrates the knives (step 2) 2 Step
until the forces exceed the ultimate tensile strength
of the material and the strip separates (step 3). The 1
penetration forms nick at strip edge and the Step
separation is called the break. The depth of
penetration is determined by the ultimate tensile LOWER KNIFE
strength of the material and its relationship to the
yield strength and the thickness of the strip.

STEP 1 STEP 2 STEP 3

Start of cut At instant of parting At instant of parting

Knife Knife Knife

Strip C (Horizontal Nick Nick Break Break
Knife Knife Knife
Clearance) C (Horizontal C (Horizontal

Clearance) Clearance)

Fig: Progressive Knife Action

DeeTee Industries Limited, Unit-1 (Tooling Division)

28/33, Pologround Industrial Estate, Indore-452 015 (INDIA) Ph. : (0091-731) 4296777 Fax : (0091-731) 4296766
e-mail: [email protected] web site : www.deeteegroup.com

DeeTee stands for total quality movement

BSI

When knife clearance is correct and the knives are in good condition, a good slit edge will
be produced. The ideal slit edge will have:

l A shiny penetration zone (or nick)
l A smooth, matte grey separation zone (the break)
l A relatively straight demarcation line between the two zones

1. HORIZONTAL CLEARANCE OF THE SLITTER KNIVES :

The most important factor in achieving an ideal slit edge Knife
is the horizontal clearance between a pair of slitter knives. The
proper horizontal clearance depends primarily on the: Strip

l Thickness of the material C (Horizontal
l Tensile strength of the material
Clearance)
In general, as the gauge of the strip and/or its tensile
strength increases, so should the horizontal clearance between Knife
the knife faces.
Clearance to Produce
Other important factors that must be taken into account Ideal Slit Edge
when choosing the horizontal clearance are:

l The condition of the equipment
l Arbor parallelism
l Condition of the Arbor bearing
l Arbor deflection

1.1 KNIVES SET TOO CLOSELY OR TIGHTLY (Lesser horizontal clearance) :

When the knives are set too close together, some material Knife
is left on the slit edge at the instant of parting. This may be either
sheared off or folded over as the strip passes the knives. As Shelf
evident, you will see slivers or filings around the machine.

When clearance is too tight, the slit edge that results will Strip
have:
C (Horizontal
l A deeper than normal nick
Clearance)

l A smaller than usual break Knife

l A burr on the bottom edge Clearance Too Tight

Because more force than normal is required to separate

the strip when knives are too tight, the knives tend to chip off. Unnecessary forces are imparted to

the strip and to the slitter head itself.

1.2 KNIVES SET TOO FAR APART (Excess horizontal clearance) :

When the knives are set too far apart, strip tears. The resulting edge may have:
l No noticeable nick
l A heavy roll over on the top of the strip
l A heavy burr on the bottom of the strip

It is easy to see the roll over and the burr on the slit edge. Knife
In effect, the slitter knives are acting as bending dies.

The quality of the slit edge and knife life will depend Burr
largely on the care with which setting between knives is made.
Strip
There is an optimum knife setting for every thickness and Knife
type of metal. When we speak of knife setting, we mean both
horizontal clearance and vertical clearance. The clearance,
vertical and horizontal, must be considered together because one
affects the other.

Clearance Too Wide

1.3 VERTICAL KNIFE POSITION

The vertical relation of the top and the bottom knives is also an important factor in
producing a quality slit edge. The correct vertical position depends on the strip gauge. Its tensile
strength and the condition of the equipment. The horizontal clearance is also important in setting
vertical position. If horizontal clearance is either too tight or loose, more vertical overlap will be
needed to separate the strip, which can lead to problem.

(Vertical Knife Knife Knife
Clearance)

V

(No Vertical
Clearance)

V

(Vertical
Overlap)

V

C C C

(Horizontal (Horizontal (Horizontal
Clearance) Clearance) Clearance)

Case 1 Case 2 Case 3
Vertical Clearance No Vertical Clearance or Overlap Vertical Overlap

A general rule is to bring the arbors together until cut is produced, then close them a little
more to compensate for such factors as:

l Variation in strip thickness
l Condition of bearings
l Tolerance on slitter knives outer diameter and bore
l Tolerance in arbor positioning device
l Arbor deflection
l Knife wear etc.

Overlap should always be minimized. Too much overlap can cause differential between the
linear speed of the strip and the linear speed of the knife at the point where the strip contacts it.
When the speed of the knives and the speed of the strip do not match, there is an increase in heat
resulting from friction between knives and strip. This heat can cause the knives to lose hardness
by tempering, which results in knife failure. This frictional heat also leads to welding of the
slivers to the knife face (commonly called pick-up).

Knife Setting - Horizontal knife clearance 'C'
v/s thickness of material to be slit.
First of all Arbor coller perpendicularity
should be checked within .02 mm. No exact setting 3.0
can be determined except through trial and
experience, because of the variables involved. 2.5 HighCA2llo0y%, SotfaMtihneil1ced5ksinu%sem&sosASfoiltllihfocsiyoctnrkSipnSteeteeseslslsof Strip
These include the type of material being slit, arbor 2.0
deflection (if any), slitter speed, quality of slit edge 1.5
required and condition of slitting line.
1.0
The horizontal setting is made first, Good .5 M7il.d5%Steoef lthickness of Strip
practice demands that knives be accurately ground,
and that the distance rings and nuts be smooth and 0
free from nicks. 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

When Setting up Slitter arbors, it is essential Strip thickness in mm
that the knives and distance rings be perfectly
clean and dry. The upper arbor should be raised so After the Set up has been completed and
that the knives will pass freely, and then the slitter secured by a locking nut, bring down the top arbor
Knives and distance rings can be setup. so that the knives overlap and check the clearance
between the adjacent knives. They should be
Vertical knife clearance 'V' checked with a feeler gauge in at least four
v/s thickness of material to be slit. positions around the circumference of the Knives.
It may be necessary to readjust the clearance
Positive between Knives.
.7 (i.e overlap)
.6 (1.4,0.6) In adjusting the arbors for vertical clearance,
the initial setting should be such that the Knives
.5 vÞÞ are neither overlapped nor separated, but set to
5.0 6.0 7.0 8.0 zero clearance. After the material is fed into the
Vertical knife clearance "V" in mm .4 slitter, the knives are overlapped until they begin to
(8.0,-0.6) cut. It is common practice to have the knives
.3 overlap about one half of the thickness of the
material being slit, for light gauges. As the
.2 thickness increases, the overlap decreases. For
thick material, the knives are usually separated
.1 from each other vertically.

0 +
-
1.0 2.0 3.0 4.0
.1

.2 Strip thickness in mm

.3

.4 ÞÞ

.5 v

.6

.7 Negative

Note : Please remove rust preventive oil before setting the tooling. After use, Knives and rings should be properly oiled.

Tools WHICH LAST LONGER - Slitting Line Tooling, Tube/Section Mill Rolls, Tube Cut Off
Knives, Cold Rolling Mill Rolls, Leveller Rolls, Fins, Steel Centers, Friction Saws, Shear Blades,
H.S.S. Saws & C.T. Saw Bodies, 20 Hi Mill Rolls.