Many film converters operate older blown film lines that still produce good quality but lack modern automation. The good news is that an Inline auto film thickness control system can be retrofitted to most existing lines, transforming their performance without buying a new extruder. This article provides a practical guide to retrofitting an Inline auto film thickness control system.

The first step is assessing your current die. The Inline auto film thickness control system requires that the die bolts can be motorized. Many conventional dies have manual bolts with a standard thread size (e.g., M8 or M10). Motorized replacement bolts are available for most die brands. However, if the die body is worn or warped, retrofitting may not give good results because the die itself is not round. In that case, consider replacing the die with a new one designed for automatic control. Die diameters from 80mm to 300mm can be retrofitted. The number of bolts depends on die size; a 150mm die typically has 24 bolts.

The second step is selecting a mounting location for the thickness gauge. The gauge can measure the film either on the bubble (before collapsing) or on the flat film after collapsing. Bubble measurement is more common because it catches thickness variations earlier and is not affected by flattening distortion. However, the gauge must be mounted on a traversing mechanism that moves around the bubble or across the bubble width. This requires space around the bubble tower. For lines with limited space, a post-collapse gauge that measures the flat film is acceptable. Post-collapse gauges are easier to install but have slower response because the measurement point is farther from the die.

The third step is wiring and control integration. The Inline auto film thickness control system includes a computer cabinet, power supplies for the motorized bolts, and communication cables. The system needs to know the line speed and possibly the haul-off speed to correlate measurements with die bolt positions. It can receive these signals from the line's existing PLC via analog or digital inputs. If the line has no PLC, the system can operate with a separate encoder on the nip roll. Installation time for a retrofit is typically 2 to 5 days, depending on the number of bolts and the complexity of the gauge mounting.

After hardware installation, the system must be calibrated. The Inline auto film thickness control system requires a baseline profile: running the line at steady state, the operator measures the film thickness manually at several points around the circumference to create a reference. The controller then learns the relationship between each bolt's position and its effect on thickness. This “mapping” process takes about an hour. Once mapped, the system can start automatic control.

Retrofit cost varies widely. A basic system with 24 thermal bolts and a single-point capacitive gauge might cost $25,000. A full system with 48 stepper bolts and a traversing IR gauge could exceed $80,000. However, the payback period for retrofit is often shorter than for a new line because the existing extruder and downstream equipment are already paid for. Many converters report payback in 4 to 8 months solely from material savings.

Potential challenges include mechanical clearance for the gauge traverser, electrical panel space, and operator training. Older lines may have low-quality die heaters that cause temperature variation, which affects thickness. It is advisable to service the die and replace any faulty heater bands before installing the Inline auto film thickness control system. Also, operators need training on the new interface; they must learn how to set target profiles, interpret the display, and handle alarm conditions.

In summary, retrofitting an Inline auto film thickness control system is a cost-effective way to modernize an existing blown film line. It brings the benefits of waste reduction, quality improvement, and easier changeovers without the capital expense of a new extruder. With careful planning and professional installation, most lines can be upgraded successfully, delivering a rapid return on investment.