Reel & Roll Handling How to Audit a Dual Knife Rotary Cutter
Maxson Automatic Machinery provides a comprehensive guide on how to audit a dual knife rotary cutter
D
ual knife rotary cutter technology enjoys a higher installed base in the Industry than a generation ago. Quieter, delivering a cleaner cut and not requiring sheet squarenenss adjustment, “double fly” cutters provide significant advantages over the less costly stationary bed knife cutter design.
Here is a step-by-step process to audit a dual knife rotary cutter:
The cutter section converts a web into a finished sheet – accurately, squarely and as cleanly as possible. Before auditing the cutter, record parameters while the sheeter is in production. Specifically: l Measure sheet length of at the last 10 knife revolutions during acceleration or deceleration l Confirm sheet length monitor readout for the same 10 cuts (check against actual) l Record the thickness and description of the material converted l Evaluate the leading, trailing and slit edges of the sheets measured The recorded data and sheet samples serve as historical benchmark information to identify machinery performance. Typically, it is during acceleration and deceleration that sheet length variation is greatest. Measuring sheets cut during speed changes provides insight as to the integrity of the cutter drive and the unwind’s tension control. To begin the audit, lock out and tag out the sheeter.
SHEET LENGTH ACCURACY In the dual knife rotary design, a microprocessor governs the knife motor’s drive, so that the average rate during each knife revolution maintains a proportional speed relative to the draw drum’ surface speed. Although the motion control is very precise, slop in the drive belts, gears or couplings between motors and cylinders can also create sheet length variation. So, to tighten up sheet length accuracy, the inspection needs to focus on a methodical review of the gear train from the motor to the knife revolver: l Couplings are fastened to the shaft and properly aligned
l All keys are securely seated into journals l Bearings within the drive train: – are properly lubricated – in operating condition – set screws are tightened l Gears
– Lubrication level in the bearing housings are inspected
– Gear teeth are inspected for wear – Properly set for minimal backlash l Drive belts inspected for wear – Broken cords – Worn timing belt l Belt take ups aligned and tightened
SLIT AND CUT QUALITY
An inspection of the slitting and cutting sections should concentrate on: Slitting – Sharpness of the top slitter blades; maintaining the top slitter setting per manufacturer’ specifications; integrity of the pneumatic connections and controls, if used; trueness and condition of bottom slitter rings; consistency of the slitter drive.
Cross cut quality – sharpness of the cross- cutting knives; full working complement of knife adjusting hardware; proper position of the before knife doctor board system from draw drum to cut point; test knife revolvers’ preload bearing’ settings; test knife revolvers’ gearing back lash. Beyond inspecting the slitting section, the cutter assembly, the doctor board arrangement and the cutter drive here are four other systems that an audit should address the following:
LEAD IN ROLL ARRANGEMENT The lead in roll section insures a wrinkle free flow into the cutter. It also establishes the wrap angle over the lower slitter rings. Be sure the roll(s) are level across the width of the cutter and that the vertical position allows for optimum slit quality.
DRAW DRUM SECTION
The rubber covered squeeze roll loaded against the draw drum pulls the web into the cutter. If the nip pressure is insufficient or there is slippage at the pull rolls, sheet
length variation can occur. Inspect the surface of the squeeze roll to make sure it is not glazed over and slippery.
Confirm the pneumatic controls that raise and lower the squeeze roll and vary the nip pressure are in operating order and there are no air leaks.
ELECTRICAL SYSTEM
Electrical malfunctions generally make themselves known; though identifying the cause and remedying the situation can be time consuming. An audit should address the cleanliness of the electrical enclosure and the connections therein of the drives and logic control modules.
In particular, examine the enclosure’s cooling system and associated filters, cleaning the panel’s interior of dust buildup. External to the electrical enclosures, verify the operation of all push buttons, counters, monitors and sensors. If there is a Human Machine Interface (HMI), confirm that it is working properly and that all screens are accessible.
SAFETY
Certainly, not least in the review of the cutter is validating the safety systems. All mechanical guards should be securely in place. Safety interlocks should be functioning and not disabled. The functionality of the emergency stop chain is to be verified.
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maxsonautomatic.com
convertermag.com
February 2021
29
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