■ preparation of the fiber materials (disolving, thickening / diluting, refining, cleaning, mixing)
■ addition of pigments and chemical additives (dependent on paper grade)
■ sheet or web forming on an endless wire
■ pressing between felts & rolls
■ drying on steam heated cylinders
■ possibly surface application of starch / chemical additives
■ smoothing by calendering
■ converting (cutting&forming paper reels, or sheet cutting)
From Raw Materials to the finished Paper Product (Source VOITH Paper)
The Papermaking Process starts with the delivery of the raw material of the stock components. The first main production step is a more or less complex and extensive Stock preparation (defibering, beating, fractionating, cleaning), followed by some after-treatment and stock storage, before the diluted stock suspension flow to the web forming, wet press and drying parts of the papermachine. In the last finishing step the paper sheet will be sometimes coated and / or calendered for improved surface.
Directly after the paper stock suspension (approx. 1 kg solid stock is diluted by 100 liters process water) is leaving the headbox. the suspension is distributed across the machine width onto the wire. On the wire section the sususpension is formed into an endless web by dewatering.
Since the invention of the fourdrinier wire section by Robert, Donkin and Fourdrinier in 1799-1804 a range of web forming principles have been developed. The three most important types are shown below:
3 Examples of Web Forming Principles (Source: VOITH Paper)
Water is, beside fibers, the key component in pulp and paper manufacturing and fulfills numerous functions in the process:
► transport medium
► for cleaning and cooling
► as a lubricant
► as the "binding agent" for forming hydrogen bonds between the fibers within the paper sheet
In earlier times paper was produced with a high specific fresh water consumption in the range of 100 to 500 m³/ton paper. For economic and, in the last decades, also for ecological reasons, the average water consumption has been significantly reduced (e.g. in Middle Europe to an average of 12 m³/ton paper). This dramatic reduction was only feasible by the increasing the closure of the process internal water circuits. This means, that the former fresh water consumers in the pulp and paper mill are now fed by clarified circuit water.
Process Water Recycling-Efficient and Eco-friendly (Source: VOITH Paper). Water is ,besides fibers, the key component in pulp and paper manufacturing. It is necessary for dissolving pulp and recovered paper, to transfer pigments in slurry form, to dilute chemical additves, then for treatment and transport of the paper stock in the stock prepration part and last not least to get an uniform paper web on the wire and as finished paper sheet.