Flame Treaters for BOPP Line

The roll’s surface temperature is a fundamental parameter in the uniformity the treated surface.

Poor attention to this component can cause:

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

EsseCi has solved these problems by designing treatment rolls with an active radial system in which the distribution of cooling water in the input and outlet positions is able to almost completely compensate the centrifugal force. Moreover, a labyrinth system guarantees the uniformity of the surface temperature along the entire roll surface.

The nip serves to achieve a flat film on the treated roll surface, free from bubbles or air trapped beneath the film, wrinkles or any other mechanical defect on the film exterior. The pinching against the treatment roll must be uniform and constant, whilst the nip roll dynamic profile must reflect the dynamic profile treatment roll.
The outcome depends on the static and dynamic balancing of both rolls and on the position of the nip roll in respect of the treatment roll. The best position is that shown in Image 1, where the nip roll is slightly over the treatment roll and the nip roll surface is straight. Different positions could involve using a bowed nip roll profile (bombeè), in order to compensate the arrow due to the weight of the nip itself.

Several tests have proven that the best flame for plastic material treatment is an oxidising flame in which a small quantity (0.5-3 %) of free oxygen is present. The simplest system to achieve such a flame is the pre-mixer set-up, just like a car carburettor. Once you find the right balance between air and gas, the issue then becomes how to maintain this ratio over time.

Today, generators designed and created by EsseCi to produce combustible mixtures (gas/air) necessary for feeding the burner are made from a gas supply tube and a fan that sucks air from the environment, pushing it inside a venturi that contains the air and gas mixer. Once the mixture has been formed in a controlled composition and quantity, it is sent to the Esseci burner on the Treatment Station. The flow of gas necessary to obtain an established ratio and quantity of gas/air mixture for the flame treatment is regulated by means of the special GOG device and the GCV1 valve, driven by the Jonoflame J combustion analyser through the TIC1 temperature regulator. The Jonoflame analyser is composed of a combustion chamber in which a small amount of the gaseous mixture, directed towards the burner, feeds a burner nozzle. To ensure proper operation, the mixture pressure sent to the nozzle must be controlled.

This system permits real time control of the mixture composition used, expressed in terms of a temperature. This combustion temperature is in fact calculated on the basis of the air/gas mixture ratio; the higher the combustion temperature, the richer the mixture is in gas. Mixtures that contain an excess of air (lean gas mixtures) produce flames in the Jonoflame that are transparent violet in colour, whilst gas rich mixtures generate flames in the Jonoflame with a greenish hue that appear surrounded by mist.

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