Dowel welding of Canadian wood species

1

• 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
2
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).

3
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).

4
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.

4
5
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.

6
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
7
Materials and Methods

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

7
8
Results and discussion - Factorial analysis
Statistical analysis shows that A significant
effect of the quadruple interaction among the
species, IP, the RR and HD on tensile strength
9
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
10
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.

11
Results and discussion Temperature measurement
at welding line

• The temperatures reached during the welding
  process were
• 266 Tw Maple 323C
• 244 Tw Birch 308C

12
Results and discussion Welding line density
study
The weldline density appears to be in direct
relation with bond strength obtained.
13
Results and discussion SEM study
SEM study investigates the contact zone between
the dowel and the wood substrate across the
transverse sections
a)
b)
14
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 .
15
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).
16
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.

17
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.

18
Acknowledgment

• FQRNT
• FPInnovations
• CRIQ
• École du meuble et de lébenisterie

19
Thanks for your attention