Design experience of paper dryer screen
At present, the wet papermaking drying department has fully used dry nets, completely replacing the previous dry blankets, and various varieties are emerging in an endless stream, playing an active role in the development of the papermaking industry. This article summarizes and discusses the design experience of the products on the existing domestic market, in order to stimulate the development of the papermaking dryer net.
1. Performance requirements
From the perspective of overall performance, the papermaking dryer should be easy to install, good in air permeability, and ideal in service life.
1.1, easy installation
A small number of paper machines with narrow widths have a movable frame, and the use of dry nets generally uses an endless interface.
The end interface method is used in the fixed drying section. Its characteristics: convenient to surf the Internet, can be connected to the old net to lead the net, even if the old net is cut off, it is more convenient to directly thread the net. There are two main types of end joints: directly use the mesh body warp thread to form the joint, the wear-resistant high-strength wire is inserted in the middle of the ring, usually called the self-generating ring; the spiral ring is bound outside the mesh body warp, and the wear-resistant ring is penetrated High-strength wire, usually called spiral loop.
It is common to thread the dry net interface with a single thread. This requires good threading quality, small wear on the ring, sufficient toughness, and stability under large tension fluctuations.
1.2, ventilation requirements
The drying department requires good drying web stickers, small paper jitter, and at the same time satisfying the volatilization of moisture from the paper web.
One group and two groups require certain drying quality, but more importantly, it is to ensure the stability of the paper machine and the stability of the paper, so the air permeability is generally relatively low, the sticker surface is smooth, and the contact area is large; with a sizing part, sizing After the first group of drying requirements are similar to the first and second drying.
As the dryness and strength of the paper in the middle section of the drying section increase, the air permeability is required to increase, and at the same time, try to ensure the superior performance of the net sticker.
1.3, economic life
The dimensional stability of the drying fabric is required to be good, not to be loose, large deformation, small elongation during use, and small swing; the contact paper surface requires high flatness, and the height difference between the ring surface and the wire surface is small; the horizontal rigidity of the network body is high, and it is not easy to discount ; The net body has good anti-fouling performance, is not easy to be dirty, and is easy to clean; the contact surface of the paper and the net is large.
2. Selection of raw materials
Use ordinary or hydrolysis-resistant polyester monofilament on low-speed paper machines, use high-hydrolysis-resistant monofilaments on a large area on medium and high-speed paper machines, and use PPS or PEEK monofilaments on high-speed paper machines. In special cases, all use PPS or PEEK monofilaments. .
2.1, polyester monofilament
Polyester raw materials were the first to be widely used on dry nets, and so far are the most used and the most diverse processing techniques. On the basis of ensuring the characteristics of polyester, in order to increase its wear resistance and anti-aging performance, continuous improvement in technology. In terms of molecular weight and elastic modulus, polyester monofilaments are classified into high, medium and low, and the product series are abundant. In order to increase wear resistance, wear-resistant nylon and other powders are added in the production and processing, and anti-hydrolysis agents are added to delay aging under high temperature and high humidity environments.
2.2, PPS, PEEK monofilament
Polyphenylene sulfide (PPS) is better than polyester monofilament in high temperature resistance, abrasion resistance and aging resistance. Compared with polyester monofilament, it has insufficient stiffness and high cost. Therefore, it is rare to use PPS monofilament to make woven dry net or The spiral net is used in conjunction with polyester in a certain proportion in the processing of the net body.
Polyetheretherketone (PEEK) has high heat resistance (its deformation temperature is 300℃ after fiber reinforcement), hot water resistance (it can be used in steam at 200～260℃), fatigue resistance and creep resistance (it is a thermoplastic Among the highest), corrosion resistance (except for concentrated sulfuric acid and concentrated nitric acid, no solvent can corrode it), radiation resistance and flame retardancy, good mechanical strength and electrical insulation.
2.3, nylon monofilament
The drying part is rarely used, has superior abrasion resistance and low deformation, but its temperature resistance is worse than polyester. When the temperature requirement is not high, the cost is considered, and the wear resistance has special requirements, we can provide nylon monofilament dry net.
2.4, characteristic monofilament
According to special requirements, some or all of them are processed with special performance monofilament. If special anti-fouling performance is required, the use of general anti-fouling polyester monofilament cannot meet the requirements, and special anti-fouling monofilament is required; when special antistatic is required, antistatic monofilament is used.