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					  Dowel welding of Canadian wood species

Georgina Rodriguez1, Tatjana Stevanovic1, Pierre Blanchet1,2
  1Centre de Recherche sur le Bois, Département des Sciences du Bois et de la Forêt, Université Laval,

  2FPInnovations- FORINTEK,




                                                   September 29th 2009
    Introduction
•   Assembly techniques by dowel insertion are common in joining
    •   by percussion, pneumatic or manual means;
    •   adhesives, generally poly(vinyl acetate) (PVAc), are used.

•   Wood dowel bonding by high speed rotation welding
    •   without any adhesive;
    •    frictional energy required to make flow and merge the
        matrix polymer cell components (amorphous lignin and
        hemicelluloses).




                                                                     2
 Objectives

The aim of this study is
• determine the optimal set of welding parameters
  for two hardwood species:
   sugar maple (Acer saccharum)
   yellow birch (Betula alleghaniensis).
    Materials and Methods

•    Parameters
     •   Wood species: Sugar maple and yellow birch.
     •   Wood substrate with receiving holes: ø 7.67, 7.14, 7.37
         mm/depth 15 mm, (wood dowels ø 9.68 mm / length 80
         mm).
     •   Insertion of dowel into wood substrate perpendicularly to
         different plans: radial, tangential and diagonal.
     •   Rotational speed 1000, 1500 and 2500 rpm.


                                                               Receiving
                                                               hole
                                               Wooden
         Tangentiel
                                               dowel
         direction

                                   Diagonal
                                   direction                           5 mm   Wood substrate



                                                        15mm
                       Radial
                       direction
                                                                                               4
    Materials and Methods

•    Tensile strength
     •   by pulling the dowel out of the substrate according to
         standard ASTM-D 906-98:
     •   three conditions
          • dry (12% MC);
          • After 24 h cold water;
          • After 2 h hot water;
     •   comparison with PVAc adhesive.




                                                                  5
    Materials and Methods

•    Temperature measurements at welding line
     •   Type T thermocouples coupled with a Vishay data acquisition
         station (5100 model with 100 Hertz /canal frequency).




                                                                       6
    Materials and Methods

•    Welded joint analyses
    •   X-ray microdensitometry
    •   Scanning Electron Microscopy (SEM)
    •   Differential Scanning Calorimetry (DSC)




                                                  7
Results and discussion - Factorial analysis

 Source of variation       F-value             Pr  F
 Species                   877.59              <.0001
 Insertion plan (IP)       283.90              <.0001
 Hole diameter (HD)        81.89               <.0001
 Rotation rate (RR)        32.79               <.0001



 Statistical analysis shows that:
      • A significant effect of the quadruple interaction among the species,
      IP, the RR and HD on tensile strength;




                                                                               8
Results and discussion – Optimal combinations

  In both species (sugar maple and yellow birch) the best adhesion was
  obtained using:
            • 7.67 mm receiving hole diameter;
            • Insertion within the radial plan.


  at different speed rotations for two species :
            • 1000 rpm for sugar maple;
            • 1500 rpm for yellow birch.


  The highest tensile strength determined for welded joints was:
            • 9.2 ± 1.0 Mpa (max value 11 Mpa) for sugar maple;
            • 7.1 ± 1.1 Mpa (max value 8.2 Mpa) for yellow birch.

                                                                         9
Results and discussion – Tensile strengths of welded
dowels compared with glued joints




 • For birch comparable to those obtained with PVAc-glued joints.
 • For maple are superior to those obtained with PVAc adhesive.

 • Rotation-welded dowel joints appear to perform better than PVAc-glued
  joints at wet conditions.

                                                                           10
Results and discussion – Temperature
measurement at welding line




The temperatures reached during the welding process were:
• 266 ≤ Tw Maple ≤ 323°C
• 244 ≤ Tw Birch ≤ 308°C
Results and discussion – Welding line density
study




 The weldline density appears to be in direct relation with bond strength
  obtained.
                                                                            12
Results and discussion – SEM study


SEM study investigates the contact zone between the dowel and the wood
substrate across the transverse sections:




      a)                                    b)
Results and discussion – DSC study (Birch)




 A decrease of the two peak temperatures as well as a slight shift of LCC
 peak on the welded material .
   Results and discussion – DSC study (Maple)




An important increase and a shift to higher temperature of LCC part, as well
as less distinctive peak of amorphous polysaccharide part (shoulder).
 Conclusions

• Canadian wood species, sugar maple and yellow birch, can be
 successfully welded by high-speed rotation of wood dowels,
 without any adhesives.

• Wood species has been shown to be the most significant
 parameter determining the tensile strength of the welded
 samples.

• Better welded joints were obtained with sugar maple wood

• More uniform welding line provided better joint in case of sugar
 maple.

• Different chemical changes of wood components during the
 welding process were confirmed by DSC for two species.

                                                                     16
 Conclusions

• The strength of the joints obtained for the birch is comparable
 to that obtained by gluing with PVAc adhesive, whereas for the
 maple it is superior to that obtained with PVAc adhesive.

• For the two species, the water resistance performance of the
 welded wood samples was determined to be superior to that of
 the PVAc adhesive glued samples.

• While wood welding yields the required strength in a few
 seconds, to achieve the same result, it takes 24 h to glue
 with PVAc.


This is the major advantage of wood welding technology which
                   is still under development.
                                                                    17
Acknowledgment

• FQRNT
• FPInnovations
• CRIQ
• École du meuble et
  de l’ébenisterie
Thanks for your attention




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