PHYSICAL PRINCIPLES
Essentially, glueing is the bonding of parts by means of an adhesive layer. The adhesive hardens by means of drying or a chemical reaction and thus holds the glued materials together. Two factors influence the strength of a bond:
ADHESION (INTERFACE ADHESION)
Good adhesion is achieved when there is close contact between the surface of the workpiece and the adhesive. This is only possible when there are no foreign substances in the gap. The glued surfaces must be clean and free from grease and dust. Adhesion is improved by roughing up the material surface with sandpaper, as this cleans foreign bodies from the workpiece and increases surface area.
COHESION (INNER STABILITY)
Cohesions refers to how the glued parts (molecules) hold together.
The greater the cohesion, the greater the stability of the adhesive.
When glueing, cohesion is put to optimal use when the adhesive is not applied excessively thickly.
THE RIGHT PREPARATION
Step 1
Clean any dirt, rust, paint residues and other foreign bodies from the surface.
Step 2
Rough up the surface by sanding.
Step 3
Thoroughly remove any grease from the surfaces to be glued. Examples of products that are suitable for this are acetone, alcohol or cellulose thinner.
Step 4
Allow the areas to be glued to dry.
Step 5
Do not touch the prepared surfaces any more to avoid the transfer of oil from your skin.
Step 6
Apply the adhesive in a thin, even layer (note the flash-off time in case of contact adhesives).
Step 7
Keep dirt and dust away from surfaces that have been freshly coated with adhesive.
Step 8
Stop any sanding work etc. until the parts are joined.
WHAT YOU HAVE TO BEAR IN MIND
Designing glued surfaces based on shape and size
Among other factors, the type of load is vital in determining the adhesion of a glue. Using simple methods, weak glued joints can be increased and made more stable. Hold the parts to be glued together and move them in a manner that mirrors the force of the subsequent load. This will tell you which forces are acting in which directions and will thus enable you to determine the type of load.
BUTT JOINT
In case of a low load/tensile stress, choose the butt joint.
SCARFING
In case of greater loads, increase the size of the surfaces to be glued by means of scarfing.
SCARFING
In case of greater loads, increase the size of the surfaces to be glued by means of scarfing.
SINGLE STRAP JOINT
In case of greater loads, increase the size of the surfaces to be glued using a single strap joint.
DOUBLE STRAP JOINT
In case of greater loads, increase the size of the surfaces to be glued using a double strap joint.
GAP LOADING
Here an uneven load is applied to the entire glued surface (perpendicular to the glued surface). Reinforce as with the tensile load, or place a cuff around it.
PEEL LOADING
Flexible materials can roll roll up from the glued surface as a result of peeling forces. The glued surfaces can be reinforced to counteract peel loading by:
a)
Glueing on a reinforced strip of material.
b)
Running the flexible part around the edge of the more rigid part.
c)
Rounding off at-risk edges.
