Technology of Shearing
The function of a shearing machine is to cut the pile (or the yarn), present on a fabric surface, at a constant level of height. This operation can be applied to a wide range of fabrics and for a wide range of applications.
What kind of fabrics can I process on a shearing machine ?
The shearing machine can process a wide range of knitted fabrics, first of all we have to point out that knitted fabrics can not be processed in tubular form, on the shearing machine.
The effects of the shearing machine in the knitted fabrics can be various :
SHEARING THE PILE OF A RAISED FABRIC
This function is used to shorten and equalise the height of a raised fabric, to create more space for a subsequent raising or to have a final effect.
SHEARING THE PILE OF A AN ACRYLIC FUR
Acrylic furs need a complete finishing line that is composed of Tigering machines, Polishing machines and finally of Shearing machines. The shearing machine is placed in the middle and at the end of the finishing process, to cut the pile during its finishing and to give the final effect.
If we replace the cutting stand with a roller that bears a pattern design, only those parts of the fabric that correspond to the patter, will be sheared. A very nice effect with a design "sculpted” on the pile, will be the result.
CUTTING THE YARN OF A TERRY TOWEL OR OF A KNITTED VELOUR
A knitted fabric made with a terry machine, will have loops on its surface, if we cut the loops of this fabric, a very nice effect of velvet will be the result. In addition other effects like the acid burning are giving extra value to your finished fabrics.
Other applications cover the fields of cleaning a surface, like for example in grey fabrics before printing or in worsted fabrics, to remove any hairyness.
How does a Shearing machine work
|This operation is performed by a device called shearing unit. The
shearing unit is composed of two sharpened elements, that are working is
a similar way to a scissors.
The first element is a roller, with a certain number of blades (usually from 10 to 24 but can be less or more) fixed on it with an helical displacement, this roller is rolling on a flat blade; the contact between the helical blades and the ledger blade is giving the cutting function.
The rotation of the shearing roller on the flat blade, creates a continuous cutting effect and the point where the flat blade and the helical blades meet, is called the cutting point.
The fibres cut by the cutting operation are removed by a vacuum system, composed of a suction box, placed in the back of the shearing roller.
The fabric is brought in the cutting point by the cutting stand, the cutting stand may have different shapes according to the kind of fabric to process.
The distance between the cutting point and the cutting stand is called shearing height, and it is the height that the ensemble of fabric and pile, will have after shearing.
We have, in fact, to consider also the fabric thickness, when we calculate the desired height of the pile.
A key element for the good functioning and the optimal result of the
shearing operation is given by the position of each of these components
with each other:
• The shearing roller and the ledger blade,
• The shearing unit (shearing roller and ledger blade) with the cutting stand.
To do this, the shearing unit is equipped with a series of hand wheels and adjusting screws, that are setting all the reference positions of the various components.
It is no point to go deep in describing the various adjusting handwheels and screws, but we will stop a bit in one aspect of these adjustments.
As we said previously, the shearing unit is like a scissors; in order to have a good cut, for a scissors it is enough that the two blades are well sharpened and pressed in contact one with each other.
For the shearing unit this is a bit more complicated, there is a much higher cut efficiency and we have to make sure that this contact between the two blades is constant on all width.
Anyway, the key point for a good shearing efficiency is the perfect contact between the flat blade and the shearing roller.
The shearing process tends to wear the contact point between these two elements so the shearing quality will be worse after some time, in this case, there are two things to do :
1. Set the shearing unit
2. Perform sharpening of the blades.