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1) Number of nip passed

The greater the number of nip passes, the greater the number of times the sheet is subjected to calendering, and the higher the natural calendering effect. However, according to the structure of the calender, this seems to be due to the pressure zone, that is, the number of rollers, so the result of high line pressure.

Some people make the paper pass through different number of nip under the same online pressure. The results show that the number of nip is more and the effect is good. In fact, it is the effect of prolonging the calendering time.

2) Line pressure

The greater the line pressure, the stronger the compression effect generated in the nip, and the better the transfer effect.

However, it must be pointed out that the improvement of its effect is limited. When it exceeds a certain limit, the calendering effect is not improved, and the mechanical strength of the paper sheet will be greatly reduced.

3) Vehicle speed

General speed increases, the calender effect will be reduced. This is because the paper sheet also has the properties similar to the so-called viscoelastic substance such as asphalt, that is, under the action of force, the longer the action time, the softer and easier to deform, and the shorter the action time, the harder and more elastic.

When the vehicle speed is high, the paper sheet instantly passes through the nip, so it is harder and more elastic, and the calendering effect is reduced. Therefore, the increase of vehicle speed often requires that the line pressure should also be increased, and the number of rollers should also be increased accordingly. Some high-speed paper machines even set up two calender machines to extend the calender time.

4) Moisture

When the water content of the paper increases, the plasticity increases, which is conducive to calendering, but when the water is too large, it will be compressed too tightly, which greatly increases the transparency, and the paper looks dark, that is, the phenomenon of blackening. Therefore, the water content is generally controlled at 6 to 8%.

In production, it is often found that the calendering effect is not good due to the over-drying of the paper sheet. Moreover, if the load of the drying part of the machine is not enough, and when over-drying occurs due to strong drying, adjusting the drying steam pressure often causes large fluctuations. At this time, a steam nozzle can be set on the calender to properly moisten the paper sheet and improve the calender effect.

5) Temperature

The higher the temperature of the nip, the more conducive to the plastic deformation of the paper sheet, thus contributing to the improvement of the calendering effect.

Practice has proved that at a higher temperature, a better calendering effect can be obtained under a lower line pressure and a smaller number of passes through the nip, which can greatly reduce the side effects such as the reduction of paper strength caused by mechanical pressing.

The recent development of high-temperature calendering technology, through various types of hot calender roller (steam heating, electromagnetic heating and hot water heating) can make the roller temperature up to 200 ℃, at this time the inside of the paper to maintain a low temperature, and the inside of the paper does not produce large compression deformation, so the paper sheet strength loss is very small.

This high-temperature calendering technology requires that the effect of the roller on the paper sheet must be uniform, otherwise it is difficult to make the thickness uniform under low pressure, thus seriously affecting the uniformity of the paper sheet calendering. Therefore, the processing and medium-high design of the roller are very strict, and the paper sheet itself requires very good uniformity, which limits its application in general paper machines.

This calendering technology can be used in conjunction with controllable medium and high rolls, as well as with wire gripper machines using a flow-collecting headbox with stepped diffusers and flutters.

6) Type of calender roll

The calender roller of the ordinary paper machine calender is a hard cold cast iron roller. For the paper with uneven surface, the roller surface will only contact the convex part of the surface, but not the lower part.

The tightness of the contact part increases, and the enhanced pressure forms a light spot, making the surface characteristics uneven. Soft calendering technology uses the degeneration of elastic rollers to absorb the unevenness of the paper surface, so that the paper surface is completely in contact with the iron roller surface. After calendering, the tightness of the paper sheet changes gently and continuously, and the surface characteristics of the paper sheet are invalid. In addition, the pressing area is wide, the pressing time is long, and the specific pressure is relatively reduced, which can reduce the thickness less (the strength loss is small), while the smoothness is improved.

7) The nature of the paper

Generally speaking, the paper is relatively soft and plastic, it is easy to produce a good transfer effect in the nip, which is conducive to improving the calendering effect.

For example, newsprint, although the fiber is quite hard, but because of the soft and porous, coupled with the fine components, easy to move and deform each other, so its calendering effect is better than the more brittle and hard straw pulp;

The moderately beaten paper stock has better calendering effect than the unbeaten paper stock due to its enhanced plasticity and better paper uniformity.

The plasticity of soft pulp is better than that of hard pulp, so the calendering effect is also better, but the pulp with high beating degree and softer pulp is more prone to black pressing. The plasticity of the filled paper sheet is enhanced, so the calendering effect is improved.