TPT 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.

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July 2013