Vetus Poly-wood Instructions D'installation page 12

3 Further processing methods
3.1 Bonding
The high chemical resistance of Poly-wood means that there is
no bite on the surfaces at room temperature and only adhesive
joins are possible. Pre-treatment of joint surfaces notably
improves wettability. This activation can be achieved by singe-
ing with a flame set to excess oxygen by dipping in a bath of
chromosulphuric acid at 60-80˚C or electric surface discharge.
See DVS Information Sheet 2204 page 2 'Sticking Polyolefins'
for detailed instructions on sticking polyolefins.
Experience to date has shown that the following adhesive is
suitable for bonding Poly-wood: 3M™ Scotch-Weld™ DP8005.
This is a two-part acrylic based adhesive. After the adhesive is
applied, substrates must be mated within the worklife of the
adhesive, 2-2.5 minutes for one-sided applications. The bonded
should be fixured or clamped for at least 2 hours. For further
information, please visit the website: www.3m.com/bonding.
3.2 Thermoforming
Poly-wood sheets can be processed by thermoforming, which
is often described - not entirely correctly - as a deep drawing
process. 'Deep drawing' is in fact a metalworking term and
means a process of deformation whereby the sheets are not
firmly clamped at the edges and can still flow. In thermoforming,
on the other hand, the edges are firmly clamped.
Heating, forming and cooling are all vital stages, but the qual-
ity of the semi-finished product is vitally important for the ther-
moforming process.
A controllable heating system will be required, designed to pro-
vide even heat to each point of the sheet. Excessive differences
of temperature cause surface flaws. Poly-wood is generally
heated on both sides.
Temperature range for forming Poly-wood: 140˚C - 150˚C
After heating the plates, the next stage is forming. In principle,
there are two methods:
- Negative forming into a female mould
- Forming over a male mould.
The process used will depend on wall thickness distribution and
finishing at the edges, and what side of the surface is designed
for use. To obtain an item with a stable form, formed parts
should cool in the mould. Various air cooling systems can be
used, e.g. water spray with air or cooled moulds.
Semi-finished products for thermoforming may not have any
major deviations of dimensions parallel to or across the direc-
tion of extrusion after maintaining at 170˚C (as per DIN 16925,
Section 4.5). In particular there should be not positive change in
dimensions in the cross direction. The level of shrinkage will
depend on sheet thickness.
The homogeneity of the semi-finished product is decisive for the
quality of the formed parts. Streaks, exudation marks and cor-
rugations, which can be overcome by smoothing rolls in the
extrusion process, show up again after thermoforming.
Homogeneity is tested by the shrinkage test.
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3.3 Printing
Surfaces of Poly-wood parts can be printed after correct
pre-treatment.
Colours and paints do not adhere readily to Poly-wood parts.
This necessitates intensive surface pre-treatment. Pre-treatment
is possible by ordinary or Corona discharge methods. Both
increase surface tension by producing polar groups within the
sheet surface. Only this makes any form of colour adhesion
possible. Pre-treatment should be carried out when at its most
effettive, i.e. immediately before printing. When parts are stored
far any length of time, pre-treatment should be repeated.
To print, the usual machines and processes are used such as
flexographic, rotogravure, offset and litho. Good adhesion and
even spread of colour depends on good pre-treatment.
3.4 Painting
We do not advise painting. Standard paints are more rigid and
harder than the thermoplastic material. Large expanses of paint
burst and come away from the material. If painting is required,
we recommend direct contact with the paint manufacturers.
3.5 Hot stamping
Surface pre-treatment is not required for hot stamping. Good
results are largely determined by print pressure, temperature
and contact time of the hobbing punch.
3.6 Hot gas welding
The process uses heated gas (usually air) to plasticise the orig-
inal material and filler and weld them to the joint surfaces under
a given pressure. The air is heated to the required temperature
by electric elements. The following rules should be followed for
optimum welding:
• Joint surfaces and weld rod should be cleaned before work-
ing
• Smooth, even surfaces improve seam quality
• Use correct welding nozzle with correct profile weld rod
• Seam should have no notches or fusion defects
• Weld rod and original material should be made of the same
material
• Take care to keep to the welding parameters.
Poly-wood hot gas welding parameters (guideline):
Weld gas temperature [˚C]
Material temperature [˚C]
Air flow [l/min]
Weld speed [cm/min] 50 - 70
ø weld rod [mm]
300
Min. 150
40 - 60
3 or 4
Poly-wood