TPT July 2013

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96 July 2013
Article
The air technology to achieve
the most of PVC-O pipes
By Mr Ignacio Muñoz, Molecor Tech CEO
Molecular orientation has been known since the 1950s and
the systems for PVC-O piping to this day are clearly defined
in two ways – in batch and in line systems, both having their
own advantages and disadvantages.
In batch systems orientation is produced by means of the
expansion of a feedstock pipe against the wall of a tubular
mould, which provides the final diameter to the pipe.
On the other hand there is the in line system, where the
orientation is produced by expanding the pipe by means of a
rigid mandrel, a flexible device or others, during the extrusion
process.
In batch systems advantages are:
• Maximum degree of orientation recognised by the
standards.
• High stability because the conditioning of the pipe is carried
out piece by piece.
• Big range of products: this kind of system allows most of
the geometries and large wall thickness and diameters,
making it possible to design pipes of any pressure or
diameter.
In line systems brought a clear improvement with regards to
the disadvantages of the in batch systems mainly in:
• Orientation integrated in the line drastically reduces the
cost of manufacturing PVC-O pipes.
• Lay-outs in a linear shape, easy to adapt to standard
factories.
In spite of these evident advantages, in batch systems were
inefficient mainly because of their low output per mould
and the high manufacturing costs due to labour and a high
consumption of energy.
During the process of orientation the plastic has to be heated
up and cooled down 80°C at the same time the mould and
the water involved needs to be heated and cooled and this is
the reason behind its high energy consumption. Considering
the specific heat for three materials (water 1 Kcal/Kg °C,
Steel 0,11 Kcal/Kg °C, PVC 0,26 Kcal/Kg °C) we consider the
following formula.
Nowadays when the world is in crisis the manufacturer
has to juggle to make their business profitable. The new
air based system developed for bi-oriented PVC pipes
brings excellent opportunities for PVC-O, improving
performances and savings in raw material and becoming
the key for competing in the market.
Q = α · m· ΔT
Where:
Q: Heat; Energy consume
Α: Specific Heat
ΔT: Variation in Temperature
m: Mass
From this, we know that only 0.7 per cent of the energy
applied in the process is really used to condition the plastic.
A novel project was started with the only purpose of gathering
the best advantages from both systems: a highly stable
process allowing the highest orientation and thus reporting
important savings in raw material, being efficient at the same
time, easy to use, and fully compatible with any lay-outs.
After a thorough research and taking into consideration all the
improvements that needed to be implemented the conclusion
was that water could not be the means of orientation and the
use of air would be the key for success.
A new air-based system for PVC-O
From the beginning the system to improve was the in batch
system, mainly because of the stability and the target class
500. The main points to be improved were: speed and
reduction of energy, of needed space and labour.
The use of air brings many advantages: the process is clean,
and safe, and leakages do not pose a problem. The process with
air spares the use of expensive stainless steel or anticorrosive
material. The process is faster because the conditioners of air,
in this case, are much faster than the water ones.