While an annual doctor’s visit is widely accepted and recommended as a path to good health, no one really enjoys their personal “preventative maintenance.”
I submit, the same is true for preventive maintenance on equipment—particularly magnetic cylinders, which are so critical to achieving accurate, repeatable and predictable diecutting results.
Preventive maintenance takes planning and time to coordinate, yet it is a necessary and important path to the continued and successful performance of both equipment and operators, as well as uptime. We all realize there are many variables in the diecutting process, so our logical conclusion portends that controlling variables and standardizing processes, where possible, can be key to increased uptime!
One variable that is often overlooked is the “airgap/undercut” being out of tolerance on magnetic cylinders. Magnetic cylinders are very durable, but they are not indestructible. Magnetic cylinders can become out of tolerance either through physical damage or due to natural wear of the bearers over time. A magnetic cylinder that is out of tolerance can mislead an operator into believing he has a flexible die that is out of specification. This creates downtime in installing and removing the flexible die, as well as time and aggravation spent in re-ordering another die, only to achieve the same result. Out-of-tolerance magnetic cylinders will affect the die’s capability to perform its function precisely and efficiently, causing the die to cut uneven, too deep or too shallow into the liner.
In today’s industry the tolerances on magnetic cylinders, flexible dies and liners are held to within microns, but not knowing if the air gap/undercut of a magnetic cylinder is within specification can too often lead to costly and what should be avoidable downtime.
To avoid this pitfall and control such a variable on the press, an annual audit of all magnetic cylinders will allow standardization of the library of cylinders, while providing a detailed report of the tooling that is within tolerance and specification. In addition, magnetic cylinders that are on the cusp of needing repair can be identified and monitored. Finally, cylinders that are out of tolerance can be removed from inventory for repair or replacement.
The benefits that come from conducting a magnetic cylinder audit are:
- Inventory of all magnetic cylinders by press and tooth gear (repeat) listed out
- Cylinders that are creating downtime identified
- Exact register maintained
- Faster press speeds
- Competitive edge in diecutting quality and uptime
- Longer die life
Aspects of Audit
High-quality magnetic cylinders are comprised of a stainless steel body, in order to resist corrosion, along with hardened bearers and journals. All surfaces, bearers and journals are visually inspected for wear, damage or imperfections/flaws. All cylinders in inventory, regardless of manufacturer, should be evaluated. Each cylinder measured is identified by serial number, press model and gear tooth size for tracking purposes.
The purpose of the audit is to determine the airgap, or undercut as it is sometimes called, on both sides of the cylinder—from the surface of the bearer to the surface of the body—in order to identify if the cylinder falls within tolerance specifications.
The tool most often used when conducting an audit on-site is a high-quality dial indicator mounted within a special holder. Once the measurement of the cylinder is recorded on the audit report sheet, it is common to “grade” the cylinder’s condition by using the “traffic light” approach:
- Green indicates the magnetic cylinder is in good shape and within acceptable tolerances of +/-3 microns
- Yellow indicates the cylinder either has imperfections or is on the edge of being out of acceptable tolerances. Yellow-categorized cylinders should be monitored closely during continued use
- Red suggests that the magnetic cylinder should be pulled from inventory immediately, as the cylinder will create downtime issues for already being out of acceptable tolerance
When conducting an audit, there are several troubleshooting areas to look for, including:
- Discoloring of the bearers. This is typically a result of improper lubrication, although excess pressure can also be a cause. This will result in the bearers becoming a light straw color in appearance over time or, in the worst-case scenario, a blue color. As a result of improper lubrication, the magnetic cylinder heats up significantly while the press is running. The faster a magnetic cylinder runs without proper lubrication, the more heat will generate in the bearers. This results in cutting issues and reduces the life of the magnetic cylinder; it will also damage the bearer surface of the anvil base roll. During an audit, the anvil surface should always be inspected as a precaution
- Check the gear to make sure it is not worn or has any damaged teeth. Sometimes, it is possible for the pressure bridge bearing trucks to be misaligned and ride against, or on top of, the magnetic cylinder gear, damaging the teeth. The gear can also be damaged due to misalignment with the anvil base roll. If worn or damaged, a new gear will need to be ordered for replacement
- Check the journals for wear. If there are signs of wear or damage, it might be possible to replace the hardened race on the journal or if the journal is not hardened, it can be machined down and a hardened race added
- Visual inspection of the surface of the magnetic cylinder identifies scratches or deep pits in the body of the magnetic cylinder
- Visually inspect the magnets on the cylinder to make sure they are all intact and that there is no epoxy ooze/bleed due to the use of non-approved solvents to clean the cylinder. Methyl ethyl ketone (MEK) and acetate are not to be used to clean a magnetic cylinder, as they will slowly weaken the epoxy and deteriorate the cylinder, creating an uneven surface
- If “wobbling” or oscillation/runout of a magnetic cylinder or bearing block is noted while running in the press, it is a clear indication of a bent journal. The cylinder should be sent in for repair
Once the audit has been completed, the next step is to review the report to determine the number of potential replacements or repairs of magnetic cylinders that are necessary. Sometimes, a magnetic cylinder can be repaired, providing the refurbishment does not take the cylinder under the minimum diameter. Repairs can even include rectifying damaged magnets or bearers.
Next, consider developing a plan to implement the repairable or replacement cylinders in order to bring the inventory (or library) of tooling back into balance. Depending on the circumstances, options could range from replacing one or two magnetic cylinders per month, to all necessary replacements at one time.
Magnetic Cylinder Care & Maintenance
Proper care and handling of magnetic cylinders can add years of production life, as well as ensure the equipment will remain within specified tolerances. Magnetic cylinders are durable, but not indestructible. A magnetic cylinder will normally fail as a result of either damage or wear that can occur to its bearers.
Bearer wear is most commonly the result of the lack of lubrication or the use of excess pressure. The surface of a magnetic cylinder should be wiped down prior to applying a flexible die, to remove any small particles or debris that could get trapped between the flexible die and magnetic cylinder surface.
One of the best ways to do this is to wipe your hand gently across the cylinder surface. It is important to note that the cylinder should only be wiped down in one direction, so as not to move the debris back and forth across the cylinder. Once to the side, the debris can be removed quickly and efficiently with masking tape or tack cloth. Any debris on a cylinder that is caught under the flexible die ruins the precision that is needed to cut efficiently and effectively, as magnetic cylinders are manufactured to a precise level.
When a job is complete and it is time to remove the magnetic cylinder from the press, the cylinder needs to be cleaned thoroughly, removing any adhesive or ink that may have accumulated during the pressrun. A lint-free cloth and isopropyl alcohol are recommended to wipe and clean the cylinder. VCI paper or a light coat of oil should be applied to the magnetic cylinder during storage to prevent any possible corrosion from occurring.
In summary, identifying your magnetic cylinder inventory through an annual audit can be an effective way of controlling a variable within the diecutting process and creating uptime in the pressroom. In addition, care and maintenance are critical to continued performance of repeatability and predictability, resulting in profitability.
While certainly not as daunting as seeing a doctor, an audit, care and maintenance can be a healthy prescription to your bottom line!