Flame Treatment For Film Production

The surface temperature of the roll is a fundamental parameter involved in the uniformity of the treatment achieved on the treated surface.

Poor attention to this component can cause:

• Irregular temperature along the roller
• Too high Temperature difference between the roll surface and cooling water
• Water flow is not constant with respect to the rotation of the roller
• Difficulty in obtaining high heat exchange coefficients

EsseCi has solved these problems by designing treatment rolls so that the distribution of cooling water in the inlet and outlet positions, using an active radial system, is able to almost completely compensate the centrifugal force; moreover a labyrinth system guarantees the uniformity of the surface temperature along the roll surface.

The fuction of nip is to achieve the film flat on the trater roll surface, without bubbles or air trapped under the film and without wrinkles or any other mechanical defect on the film surfacd. The pinching against the treatment roll must be uniform and costant and the nip roll dinamic profile must be copy the treatment roll dimanic profile.
This result depends on the static and dinamic balancing of both rolls aand on the position of the nip-roll respect the treatment roll: the best position is that shown in the fig. 1, wherethe nip roll is slighrly over the treatment roll and the nip roll surface is straight. Different position could require a nip roll profile bowed (bombeè), in order to compensate the arrow due to the own weight of the nip.

Several test proved that the best flame for treatment of plastic materials is an oxiding flame, that is a flame where free oxygen is present in small quantity (0,5 -3 %). The simplest system to get such flame is the pre-mixer arrangement, like in a car carburator. Once you find the right balance between air and gas the problem has always been how to maintain this ratio over time.

Today the generator designed and realized by EsseCi, to generate combustible mixture (gas/air) necessary for feeding the burner, it is made from a gas supply pipe and a fan that sucks air from the environment, pushing it inside a venturi. In the venturi is the mixing between air and gas. The formed mixture, controlled in composition and quantity, is sent to the burner Esseci on Treatment Station. The flow of gas that is necessary to obtain an established ratio and quantity of gas/air mixture for flame treatment is regulated by means of the special GOG device and the GCV1 valve, driven by the Jonoflame J combustion analyzer through the TIC1 temperature regulator. The Jonoflame Analyser is composed of a combustion chamber where a small part of the gaseous mixture, directed to the burner, feeds a burner nozzle. To ensure proper operation, the mixture pressure sent to the nozzle must be controlled.

This system it enables the control, in real time, of mixture composition used, expressing this in terms of a temperature. This combustion temperature is in fact calculated on the basis of the air/gas mixture ratio; the higher is the combustion temperature and the richer in gas is the mixture. Mixtures that contain an excess of air (gas lean mixtures) produce flames in the Jonoflame trans- parent violet in colour, while gas rich mixtures generate flames in the Jonoflame that tend to a greenish colour and that appear surrounded by mist all around themselves.

The roll and burner cooling systems are constituted by a closed circuit in which a pump is sized so as to circulate the right amount of water in the unit. In circuits are connected to the temperature control systems, in order to keep it constant. The cooling medium is water which may come from the tower, shaft or chiller. The water is sent to a heat exchanger through an automatic control valve.