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Nip Impressions´┐Ż is Paperitalo Publications' flagship publication.  Published every Thursday afternoon (US Eastern Time), Nip Impressions´┐Ż is eagerly read by pulp and paper professionals around the world.

9 Jul 5: Materials 6: Paper Hoods



We are going to continue to explore non-traditional materials for a while.


But first, remember this from the early days of our work here at LGMI:  2/3 of the weight of an installed paper machine is in structures and foundations to support the rest.  So, our interest in alternative materials for the paper machine itself not only can provide a superior machine, but also drastically reduce the overall weight (and cost) of the installed facility.


So, why not paperboard for dryer hood skins?  


It always struck me (Jim) that machine tools are made of steel, yet machine tools are used to shape steel.  Hence, if we are making paper, what parts of our machine can be made of the product it produces?


Dryer hoods come to mind.  If wallboard, which consists of two sheets of paper sandwiching a layer of gypsum, can be made with a fire rating of three hours or more, surely we can make a machine hood of triple wall corrugated, properly treated for fire resistance and wet strength.


What would be the advantages?  One that is easy to see, is in the case of emergency, a hole could be cut in such a material with a stout knife.  


Also, an integrated containerboard company could easily make new panels themselves.  And possibly repulp the old ones (depending on the added chemicals).


In some cases, aluminum hoods are attacked by chemicals in the air contained in the hood.  The paperboard hood may be designed to be more resistant to these.


Can you think of any other advantages?


Any comments?  Let us know by sending an email to [email protected]
with "LGMI Frontiers" in the subject line.
From last week:

 Hi Jim and Brian;


I don't understand your disclaimer "We are not talking about some sort of FRP structure here, but a headbox whose main material of construction is a resin specifically designed for this purpose." 


FRP thermosetting plastics, as shown by GM in the Corvette, Boeing and others making stealth aircraft, etc, readily provide the dimensional stability and chemical inertness required for a headbox.  An FRP laminate could have a Halar (ECTFE) or other high performance corrosion liner for complete non-stick properties, resisting microbiological growth and other causes of boilouts and other biocidal additions.  


Industrial thermoplastics like PET, polysulfone, polycarbonate  and even laminated glass (like car windshields) readily resist modest temperatures for paper-making without any loss of stiffness or strength.


Headbox construction for various products could consist of bolting together molded segments with carefully designed fluid dynamics properties for a variety of widths with a metal slice lip bolted in place if it it decided - though I doubt it should be - that only a metal slice lip is acceptable.  Plastic shapes can be structurally supported with an external skeletal frame to ensure long term dimensional stability. 


I proposed a crosslinked HDPE headbox approach chamber to P&G about 7 years ago precisely because it provides all the critical functions and properties they expect from a stainless steel unit with the engineering plastic fastened to a metal (SS) exoskeleton.  The idea was too avante garde even though the non-metal equipment was 1/6 as heavy as a SS unit and was immune to crevice corrosion in seams and corners.


By the way, ALL white water piping around a paper machine can be plastic - CPVC being an obvious choice since it is rated to 210F and can be overwrapped with FRP for super stiffness.  Solid Halar pipe or dual-laminate Halar/FRP wrap pipe would be permanently clean since nothing sticks to the surface.


However, before you/we can persuade anyone to construct a modern headbox from better, light-weight, non-metal materials, we might first consider our inability to persuade the industry (other than IPPEL in Brazil) to make rotating pressure vessels (dryer cans) from welded steel instead of material  - gray cast iron - everyone KNOWS to be unacceptably dangerous and devoid of any redeeming properties.  Continuation of this idiotic and unsafe practice supports your frequent observations on the dearth of quality management and intelligent leadership in the industry.  I've been sorely tempted after each dryer explosion to request OSHA or at least one insurance company to ban new gray iron dryers, but instead have pledged to work around them as if they are potentially fatal bombs.  


I hope this commentary contributes a tiny shred of encouragement to your LGMI mission, especially your persistent efforts to educate and inspire an industry that is too stupid to appreciate your insights or to realize how perilous its existence is.


Have a safe, healthy and productive summer.


Best regards,


Dave Bennett




LGMI Design Practices
As always, your comments will be appreciated.
Think light!


Brian Brogdon, Ph.D.
Executive Director




Jim Thompson

Send us your comments by emailing Brian Brogdon
or Jim Thompson!

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