The Process of Papermaking
The Process of papermaking has several stages — Raw material preparation & handling, Pulp manufacturing, Pulp Washing & Screening, Chemical recovery, Bleaching, Stock Preparation, and finally, Paper manufacturing or as we say — papermaking.
There are a number of steps involved in turning wood into pulp that could be classified as part of the paper making process, however, the process of papermaking is basically a 2-step process in which a fibrous raw material is first converted into pulp, and then the pulp is converted into paper. But in this article, we will focus on how the stock or pulp mixture gets made into paper.
A paper machine consists of a paper machine mainframe and auxiliary equipment. It is typically 10 to 25 feet wide, and can range in length anywhere from half a soccer field (50 yards) to the full length (100 yards). The machine has 2 main components — a wet end and a dry end.
- The pulp mixture along with water is dispersed across a forming fabric that looks like a huge mesh screen on the front end, or wet end, of the paper machine.
- During this process of papermaking — pulp is 99 percent water and one percent pulp. At the later stage of papermaking — Gravity, suction, and a mechanized vibration of the screen quickly begin to mremove 20 percent of the water, much of which can be re-used at the paper mill for next process of papermaking. All paper mills are advised to follow strict environmental guidelines for the volume and quality in papermaking.
- In the next process of papermaking on the wet end is the press section where even more water is extracted. With the water level still at 60 percent, the pulp mixture is squeezed through enormous cloth-wrapped cylinders known as wet felts. It is during this process of papermaking that the product starts to get its smoothness and thickness.
- Now, the paper enters the dryer portion after passing through the felts. It next passes through steam-heated dryers, leaving the product with a moisture content of 2-6 percent.
- In the next process of papermaking — a starch solution is applied to both sides of the sheet while passing through size press. (If you have ever used starch while ironing your clothes, you can get an idea of what is happening to the paper.) The use of starch solution on paper enhances its ability to resist water and ink penetration during the offset printing process. This process of papermaking gives the paper the ability to accept toners and liquid inks that used in various types of digital printing.
- In the next phase of papermaking — a big, heavy cylinder called the calendar stack await the roll that is forming. The cylinders apply pressure to the sheet to form the desired smoothness and caliper of the paper. The pressure on the calendar stack can be adjusted. More pressure yields smoother paper with less thickness.
- Then, the paper is coiled on a big reel called the winder at the end the machine. The paper reel is sliced into manageable size rolls as it travels to the winder. There are two types of roll formats: one that is sized for a web printing press for sheet fed machines, and the other that transforms rolls to be cut and packaged into cartons for a sheeting application. The winder offers the ability to customize sheeter roll sizes to maximize the efficiency and limit waste.