page_title: Paper machine
section_title: Forming section or wet end
hierarchical_section_title: Paper machine / Operation / Forming section or wet end
caption_attribution_description: Local call number: c002311 Title: [A worker overseeing a papermaking machine at a paper mill near Pensacola] Date: 1947. Physical descrip: 1 photoprint&#160;: b&amp;w&#160;; 4 x 5 in. Series Title: (Commerce Collection.) Repository: State Library and Archives of Florida, 500 S. Bronough St., Tallahassee, FL 32399-0250 USA. Contact: 850-245-6700. Archives@dos.state.fl.us Persistent URL: [1]
context_page_description: A paper machine is an industrial machine which is used in the pulp and paper industry
  to create paper in large quantities at high speed. Modern paper-making machines are based on the principles of the Fourdrinier Machine, which uses a moving woven mesh to create a continuous paper web by filtering out the fibres held in a paper stock and producing a continuously moving wet mat of fibre. This is dried in the machine to produce a strong paper web.
  The basic process is an industrialised version of the historical process of hand paper-making, which could not satisfy the demands of developing modern society for large quantities of a printing and writing substrate. The first modern paper machine was invented in Britain by Henry and Sealy Fourdrinier, and patented in 1806.
  The same process is used to produce paperboard on a paperboard machine.
context_section_description: From the machine chest stock is pumped to a head tank, commonly called a "head tank" or stuff box, whose purpose is to maintain a constant head (pressure) on the fiber slurry or stock as it feeds the basis weight valve.  The stuff box also provides a means allowing air bubbles to escape. The consistency of the pulp slurry at the stuff box is in the 3% range.  Flow from the stuff box is by gravity and is controlled by the basis weight valve on its way to the fan pump suction where it is injected into the main flow of water to the fan pump.  The main flow of water pumped by the fan pump is from a whitewater chest or tank that collects all the water drained from the forming section of the paper machine. Before the fiber stream from the stuff box is introduced, the whitewater is very low in fiber content.  The whitewater is constantly recirculated by the fan pump through the headbox and recollected from the wire pit and various other tanks and chests that receive drainage from the forming wire and vacuum assisted drainage from suction boxes and wet fiber web handling rolls.  On the way to the head box the pulp slurry may pass through centrifugal cleaners, which remove heavy contaminants like sand, and screens, which break up fibre clumps and remove oversized debris. The fan pump ultimately feeds the headbox, whether or not any centrifugal cleaners or screens are present.
  The purpose of the headbox is create turbulence to keep the fibers from clumping together and to uniformly distribute the slurry across the width of the wire. Wood fibers have a tendency to attract one another, forming clumps, the effect being called flocculation.  Flocculation is lessened by lowering consistency and or by agitating the slurry; however, de-flocculation becomes very difficult at much above 0.5% consistency.  Minimizing the degree of flocculation when forming is important to physical properties of paper.
  The consistency in the headbox is typically under 0.4% for most paper grades, with longer fibres requiring lower consistency than short fibres.  Higher consistency causes more fibres to be oriented in the z direction, while lower consistency promotes fibre orientation in the x-y direction. Higher consistency promotes higher calliper (thickness) and stiffness, lower consistency promotes higher tensile and some other strength properties and also improves formation (uniformity).  Many sheet properties continue to improve down to below 0.1% consistency; however, this is an impractical amount of water to handle. (Most paper machine run a higher headbox consistency than optimum because they have been sped up over time without replacing the fan pump and headbox. There is also an economic trade off with high pumping costs for lower consistency).
  The stock slurry, often called white water at this point, exits the head box through a rectangular opening of adjustable height called the slice, the white water stream being called the jet and it is pressurized on high speed machines so as to land gently on the moving fabric loop or wire at a speed typically between plus or minus 3% of the wire speed, called rush and drag respectively.  Excessive rush or drag causes more orientation of fibres in the machine direction and gives differing physical properties in machine and cross directions; however, this phenomenon is not completely avoidable on Fourdrinier machines.
  On lower speed machines at 700 feet per minute, gravity and the height of the stock in the headbox creates sufficient pressure to form the jet through the opening of the slice.  The height of the stock is the head, which gives the headbox its name.  The speed of the jet compared to the speed of the wire is known as the jet-to-wire ratio.  When the jet-to-wire ratio is less than unity, the fibres in the stock become drawn out in the machine direction.  On slower machines where sufficient liquid remains in the stock before draining out, the wire can be driven back and forth with a process known as shake.  This provides some measure of randomizing the direction of the fibres and gives the sheet more u
caption: A worker inspecting wet, bleached wood pulp on an old-fashioned Hollander pulper or "beater".
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