Have you ever wondered, as you followed behind a log truck, just where the logs were being taken and what was going to be done with them? Most often, the logs are being taken to a paper mill to be made into paper. The logs will see many different machines before it becomes paper. Let’s take a look at the machines used in the making of paper.
The first thing the logs go into is a large metal vat filled with water, where it is tumbled. This helps remove the bark from the log. The next machine is called a chipper. The chipper has a rotating steel blade, much like a huge fan, that chops the logs into tiny pieces. These pieces are much easier to work with than the large logs.
The chips then go by a conveyor belt into the top of a machine called a digester. The digester is like a giant cooking pot. Chemicals are added to the chips inside the digester to help remove the parts of the wood that is not necessary for paper. This process is called cooking and causes the unnecessary parts to dissolve. Once the remainder of the chips passes completely through the digester, the chips are rinsed to rid them of the added chemicals. What remains is called pulp.
This pulp is brown in color and paper producers need it to be white. The pulp, therefore, passes through a series of vats filled with various bleaching chemicals, sometimes a different set in each vat. There are at least three separate vats used, and more if necessary.
Once the pulp is as white as possible, it goes into the refiner. The refiner has a series of rotating, serrated metal disks that work like a blender on the pulp, making it even finer than before. The length of time the pulp is in here will depend on the type of wood it comes from, as some woods are thicker than others. The pulp needs to be very fine to work in the paper machine, which comes next.
The paper machine is a very complicated piece of machinery with many parts, all with their own names and functions. This is where the actual paper sheets are formed. The head box is where the pulp first enters. Here, water and fillers are added and the pulp travels through a long, narrow tube onto the wire. The wire is actually a continuously moving piece of either wire or plastic mesh. The pulp travels over this and excess liquid is drained from it. Once the pulp reaches the end, it goes through a set of rollers, called the felt, where even more water is squeezed out.
The fibers leave this pressing section and enter drying cylinders. These are large metal cylinders which are heated internally with steam. The paper passes through this area several times before it is completely dry and ready for the calendar, which presses the paper to make sure it is smooth. It is then rolled onto a large roll and exits the paper machine.
The rolled paper is transferred to yet another roller. Some paper is packaged and sent out like this, but others continue on to other machines. There is a supercalendar, which further smooths the paper and adds a gloss to it. This machine consists of steel and hard cotton rollers that the paper passes through.
Some of the paper goes through an embossing machine to be imprinted and others go through a cutter. The rolled paper enters one end of the cutter and comes out the other end already cut into sheets. These sheets are counted by the machine and packaged, ready for shipment.
Today’s paper mills have much more complicated machinery than those of yesterday. They enable more paper to be produced in less time, with less human involvement. We can only guess what tomorrow will bring.
