The task was to rejuvenate a slitter rewinder that was not performing as expected. The machine, at least 60 years old, was still using many of its original mechanical features, with the exception of some new slitting blades, a changed motor, and brake. The slitter was used to rewind 500 mm diameter multiple slit widths from reels 2.6 m wide and 2.5 m in diameter. The main issues were the density of the reels and the difficulty in separating the slit reels once the wind was complete.
Old System
The slitter rewinder was running with a single drive motor, a gear difference between the two bottom surface rewind rollers, and a belt drive to the rider roll. The only adjustable parameters were the running speed and the brake torque off the unwind. In standard surface slitter rewinders, the principle of winding a dense reel involves the web coming up between the main drive rollers and wrapping around 85% of the core before coming into contact with the second surface roller. However, in our customer's application, the machine could not be run this way.
Disadvantages
The machine had limited adjustability, with only the running speed and brake torque off the unwind being adjustable.
The density of the finished slit reel was inconsistent, leading to issues in the final product.
The slit reels were difficult to separate once the wind was complete, causing delays and inefficiencies in the production process.
New System
To address the customer's issues, we decided to fit separate drive motors for both the two main drive rollers and the surface roller. The surface roller was rubber-covered to ensure it had more impact on the tightness of the finished reel. To eliminate the pulsing in the web, which was causing the slit reels to overlap and become difficult to separate, we installed a new linear dancer. This acted as a shock absorber to the eccentric load. We also added a closed loop control system to make the brake more active and smooth out the pulsing in the web. Three new square frame AC drive motors, with encoders and gearboxes, were fitted into a very tight space to ensure all aspects of the speed and torque could be controlled through the new drive control system. After tuning, we increased the running speed to 510m/min, a more than 20% increase.
The equipment was installed in 2015 and has been providing excellent service ever since. The solution, a result of collaboration between us, the customer, and other stakeholders, has given a very old machine a new lease of life and resulted in significant payback.
Advantages
The separate drive motors for the two main drive rollers and the surface roller allowed for better control and consistency in the winding process.
The rubber-covered surface roller improved the tightness of the finished reel.
The new linear dancer and closed loop control system eliminated the pulsing in the web, making the slit reels easier to separate and improving the overall efficiency of the process.
The new drive control system allowed for better control of speed and torque, and increased the running speed by more than 20%.
