The polyurethane processing for panel air filters (flexible foam)for high yield (free of all defects) is very critical and sensitive on account of Polyurethane making chemistry, short reaction times, process conditions, ambient temperature and humidity , equipment dispensing-mixing precision and moulds' surface quality, moulds' temperature and uniformity impacting the defects in filters like pin holes, short filling, over filling or growth, skin damage, loose skin, voids, hardness variations, shrink marks, knit lines etc. Research is conducted to study and establish a correlation between various parameters so that process settings can be altered to ensure minimum variation to output in spite of variation in inputs and noise to the system. THE market in India for polyurethane panel air filters is growing in line with the automotive growth in 4 wheelers and two wheelers with an additional volume for the after sales market generally with one to two filters per year per vehicle. The challenge for the organized sector, manufacturing these filters as suppliers to the OEMs is high productivity coupled with high yield. Typically the limiting process for productivity in the filter production will be the floor to floor time at the dispensing station which can be called as the constraint or bottleneck of the production line. The low yield is on account of a process which is too sensitive to Polyurethane making chemistry, short reaction times, process conditions, ambient temperature and humidity , equipment dispensing-mixing precision and moulds' surface quality, moulds' temperature and uniformity impacting the defects in filters like pin holes, short filling, over filling or growth, skin damage, loose skin, voids, hardness variations, shrink marks, knit lines etc. The current defects' percentage is about 35% for a medium size rectangular filter on account of above defects. To improve the overall productivity coupled with high yield, a research is conducted to study the correlation of various parameters on the presence of defects or the extent of defects. The research is mainly being done in the following area- a) Three-dimensional topographical analysis of foam surface texture, cream time changes and hardness as a function of mould temperature and its uniformity within the mould. b) The surface hardness of the foam at various points on the product as a function of mixing ratio and controlled growth through varying grammage for definite inputs of raw materials. c) The density and hardness of the foam as a function of the nucleation of Polyol. d) The texture of the molded foam surface as a function of the type, concentration, spread and application process of mould release agent. Currently the results of various experiments and observations are directing in making concrete hypothesis leading towards defining processes to make the panel filters free of various defects. We hope to draw conclusions in the above research areas by and proving the same over a new production line which is expected to run with a production speed of about 600 filters per hour.
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