| "Gluing" two substrates is just that, you
are taking two pieces of something and adhering them together with a
different substance.
The first adhesives were
natural gums and other plant resins or
saps used as far back as 50,000 years ago. Over the centuries,
animal glues came to be made by rendering things like horse teeth and
hooves.
Native Americans of the eastern United States used a mixture of spruce
gum and fat as adhesives to fashion waterproof seams in their birch bark
canoes. In
medieval times, egg whites were used as glue to decorate
parchments with
gold leaf. The first actual glue factory was founded in Holland in the
early 1700s.
As the modern
world evolved, materials such as bones, starch,
fish, and
casein ('sticky protein' in milk & cheese) were introduced to the gluing
recipe. Over time, glues have improved greatly on the flexibility,
toughness, curing rate and chemical resistance of their predecessors.
Still, while gluing is highly useful and
greatly convenient, it's grip often degrades over time and may eventually
delaminate. |
Chemical Welding, also called 'chemical bonding', refers to any of
several forces or mechanisms, especially the ionic bond, covalent bond,
and metallic bond, by which atoms or ions are bound in a molecule or
crystal.
Chemical welding occurs by application of
a 'reactive adhesive', usually as a thin film, to the surfaces being joined.
It works either by chemical bonding with the surface material or by
in-situ hardening as two reactant chemicals complete a polymerization
reaction. Reactive adhesives include two-part epoxy
and isocyanate.
Distinctly different from the type of
adhesion that results from mechanical 'gluing' in which the adhesive works
its way into small pores of the substrate and 'sticks' the two surfaces
together, with chemical welding the bond occurs at the molecular level.
Examination of such bonds with an
electron microscope reveal that an actual fusion of the two surfaces takes
place after which it is impossible to discern where one material ends and
another begins. ~~~
|
This
massive pultruded frame is assembled with chemical welding.