Paper Basics

This is a general overview of the papermaking process. I won't go into great detail in any area, but if you would like more information on something let me know and I'll go into more in a later post.

There are four main areas in a paper mill: powerhouse, wood yard, pulp mill, and paper machine. Additional areas areas are roll fishing and converting.

The powerhouse is where the power is made, pretty obvious huh? Besides providing the mill with power the powerhouse also provides a key component in making paper, steam. Without steam no paper making would be taking place. It is necessary for the pulp mill and the paper machine. The powerhouse utilizes byproducts from the paper making process, as well as alternative fuels to create energy. The alternative fuels are dependent on what the powerhouse is permitted to burn. Some places use tire chips or chicken litter. I've also known some places to burn marijuana that had been confiscated by local law enforcement. Anyhow, the process of making energy is somewhat complicated. Basically fuel is burned to produce steam. The steam is then fed to turbine generators which make electricity.

The wood yard is where the wood comes in, again pretty obvious. Wood can be delivered in different ways. There are log trucks, train cars, and boats. It's too expensive to bring in by air, but they would if they could. The wood is delivered as long timbers, short timbers, or wood chips. If the wood is delivered as timbers, it must be debarked. This is done with a debarking drum. Once the timbers are debarked, they are then chipped with a chipper. The bark is sent to the powerhouse to burn as fuel. The wood is chipped into uniform chips. There is an optimum size for chips to efficiently make pulp. The chips are piled into chip piles. They are separated by wood type, hard wood or soft wood. That's pretty much the wood yard.

The pulp mill gets the chips from the wood yard and turns it into pulp. The chips are cooked in digesters to form pulp. The cooking process breaks down the chemicals, lignon, that hold the fibers together. After getting cooked or digested, the pulp is bleached if necessary. The pulp is then screened for quality, before being sent to the washer. The washing process gets rid of any residual chemicals and reclaims some of the chemicals used in the cooking process. After the pulp is washed, it is then screened a second time. Then it is sent to storage. From the storage tank it can be sent to a pulp dryer or to the paper machine. The pulp dryer dries the pulp in sheets or bales which can be sold or saved for use later.

On to the paper machine, this is where rubber hits the road so to speak. The pulp from the pulp mill comes over and is refined. The refining process fibrillates and cuts the fibers. The fibrillation referst the removal of the primary fiber wall and loosening of the internal structure. This makes the fiber more flexible and allows the fiber to absorb more water. Refiners are setup in series or parallel depending on the fiber being processed and the paper being made. From there the pulp is sent to a stock chest. Then the different kinds of stock and chemicals are mixed in a blend chest depending on the grade of paper being made. Note, not all machines have a blend chest. From there the mix is sent to the machine chest, which is essentially a holding tank or surge tank or large are in the pipe. Then it goes to a stuff box. The stuff box is important because it provides a constant pressure head for the basis weight valve which is between the stuff box and the fan pump. The fan pump pulls water from the wire pit, which is where all the water drains off from the table or forming section and the stock mixture from the stuff box and pumps it all to pressure screens. The pressure screens ensure the quality of the stock. Note, there is also some equipment in between to remove entrained air, I can discuss this in a future post. The accepts from the screens go to the headbox which delivers the stock to the forming section. The forming section can be a Fourdrinier which is flat or a gap former which is sandwiched between two fabrics. I can discuss the difference in a later post. The forming section is where the sheet is initially formed. As the sheet goes across the forming section water is drained off. From there it goes into a press section where the sheet is pressed to remove more water. After the press section is the primary dryer section where the sheet is dried. Then depending on the machine there can be breaker stacks or size presses in between. Again these can be discussed in a future post. At the end of the dryers is a calender stack. The calender stack smooths the sheet for a uniform thickness. Then the paper is rolled onto a reel. The jumbo reel is then cut into rolls with a winder. From there the paper is processed for shipping or sent to the converting area. The converting area converts the reels into reems of paper or notebooks for consumber use.

That was my brief overview of the process of making paper. There are many items I can discuss in further detail, but I'm not ready to write a book quite yet. The moral of the story is the things we take for granted often take alot of effort to make. So the next time you jot down a note or throw away a paper cup, think about what it took to make that simple convenience.