Ask the Expert: When Should I Split and Clean my Fluid Coating Die?

Using proper cleaning tools is essential to avoid damaging the die. Recommended materials include: 

• Clean, lint-free rags
• Compatible solvents or die soap (for heated applications)
• Copper gauze or SOS pads without steel or added cleaning agents 
• Brass pick tools and brass scrapers
• Only use materials softer than steel. This typically includes copper, brass, bronze, aluminum, and wood. 

Materials to avoid include: 

• Steel wool 
• Scotch-Brite pads
• Sandpaper
• Steel tools
• Power tools 

When cleaning, always use side-to-side motions, not in the direction of flow. If minor scratches occur, keeping them perpendicular to flow helps reduce the risk of coating defects. 

What to Look for During Cleaning

Splitting and cleaning a die provides a valuable opportunity to inspect internal conditions. While cleaning the flow channel, look for: 

• Gelling or charring of material 
• Contamination buildup 
• Signs of degraded material

Over time, buildup can adhere to the flow channel and release unpredictably, leading to coating defects such as lines or streaks. 
Pay close attention to the lip land and lip faces. Excess buildup in these areas can alter the effective die opening, impact coat weight uniformity, and cause unstable coating edges. 

Inspecting for Wear and Damage

A split and clean is a good time to closely inspect the flow channel of the die, the lip seats where the lips mate to the die, and the lips at the lip exit for any physical damage that may have happened over time.  Typically, physical damage is caused by using the incorrect tools, the incorrect use of the correct tools, or normal wear overtime. Wear from simply just operating will usually show up as scratching on the lip face, dulling of the lip edge radius, and knicks on the lip edge radius. Damage from operating comes from contaminates that get carried onto the substrate, from the substrate itself, or even improper operating setting. Physical damage in the flow channel allows for areas that fluid can easily get hung up on and then start to degrade. Physical damage that is close to the lip exit or on the lip face will likely leave a line in the coating. The only way that physical damage can be corrected is with a refurbishment of the die or the lip set. 

The examples below are of a worn and damaged die that is experiencing an unstable edge and an unstable coat weight uniformity. The buildup of charred/degraded material on the lip land and lip faces are changing the dimensions of the lip opening and the distance of the lip to the roll. This will in turn have an influence on the coat weight uniformity. The buildup on the lip face can prevent clean fluid release, further affecting coating stability. 

 
Additional Maintenance Checks
Since lines are often shut down while splitting a die open and cleaning it, there are other items that can be looked at to help ensure smooth coating operation. This is a good time to look at the lip adjustments (if the die is equipped) to ensure that none are at the top/bottom of their range and that all adjustments are operating correctly. If there have been issues with adjustments prior to the split and clean, adjustments are maxed out on travel, or if the adjustments do not have smooth operation, it would be a good time to reset the adjustments. Taking time to lubricate moving parts on the positioning system should be done at this time as well. The last items that should be inspected during a split and clean are the heaters (if equipped).  Testing the ohms for each heat zone and ensuring the proper resistance can help pinpoint any issues that may be experienced with heating the die.  

Extended Time Between Changes

 Consistent, small maintenance steps can significantly extend the time between major cleanings:  

• Wipe the die lips whenever the line stops and the die is pulled away from the roll
• Use a brass feeler gauge or shim to lightly scrape lip lands during purging
• Perform a thorough exterior lip cleaning at the end of each shift

These quick actions help prevent buildup and maintain coating quality without adding significant downtime. Every coating process is different, and maintenance schedules should reflect that. If you begin to see contamination exiting the die, reduced coating quality, or poor gauge uniformity, it's likely time for a thorough cleaning. Proactive maintenance not only improves performance but also reduces unplanned downtime and extends the overall life of your equipment.

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