Applications

Controlling the blow moulding process requires a complex balance between quality and speed based on the material used and the design of the product. Process control must take these characteristics into account in order to move the various electrical or hydraulic drives while managing complex recipes. In addition, the PLC must be able to support rapid changes in materials, offer integrated diagnostics and provide a rapid response in the event of deviations.

Stable rheological behaviour and dimensional consistency of the parison are achieved through rapid and uniform temperature control of the screw zones. The system must react to variations in load, material or environmental conditions, maintaining temperatures within tight tolerances. Inadequate control causes weight variations, surface defects and material degradation, reducing process repeatability.

The thickness profile of the parison influences the final quality of the container and the efficiency of the process. Uneven distribution can cause thin spots and sags or, conversely, unnecessary excess material that increases costs and reduces production efficiency. It is essential to control the position of the mandrel or bushing precisely, synchronising it with the screw and the blowing sequence to achieve uniformity and repeatability from cycle to cycle.

The mould closing phase is critical: it must be performed with precision and with the appropriate force to avoid joint defects, burrs and premature wear of the couplings. Imprecise closing can cause collisions, deformations or reduced service life of mechanical components. It is essential to monitor the position and speed of movement to ensure safety and quality.

The carriage must move in sync with the extrusion of the parison to avoid traction and deformation. Incorrect positioning compromises the quality of the piece and increases waste. Furthermore, non-optimised movement without acceleration monitoring leads to cycle lengthening and excessive mechanical stress.

During the blowing cycle, the blowpin enters the mould to blow compressed air and shape the parison against the cavity walls. Misaligned insertion or incorrect stroke can compromise neck closure, causing deformation or leaks. Furthermore, too rapid a descent risks damaging the mould or the part being formed. It is therefore necessary to precisely control the position of the nozzle throughout the cycle, synchronising it with the mould closure and blowing time.

After the blowing and cooling phase, the part must be removed from the mould in sync with the machine cycle. An uncontrolled movement of the arm can cause collisions with the mould or other moving parts, resulting in stoppages, damage or production waste. Accurate control of the position and speed of the picker is therefore essential to reduce cycle times, maintain the overall efficiency of the line and preserve the integrity of the part.

The filter protects the mould from impurities present in the molten polymer and prevents them from remaining in the product, therefore the filter gradually tends to clog. Clogging increases the upstream pressure and can compromise product quality or damage the line. Continuous measurement of the pressure before and after the filter allows the pressure differential to be calculated and alarms to be activated to guide the operator to take manual action or start automatic filter change systems.

The temperature and actual pressure of the molten polymer are critical parameters in the extrusion process, as they directly affect the viscosity of the material and its final mechanical and optical properties. Measuring the temperature in direct contact with the melt, rather than on the surface of the cylinder, provides a more accurate representation of the actual process conditions and, in combination with continuous pressure measurement, offers a significant advantage in rheological control.