The Problem of Pooling
A very common problem in dip coating is “pooling” or the “edge effect”. Gravity pulls excess liquid to the bottom edge of your part, making the film too thick in that area.
This thick edge can crack during drying or fail to cure properly. It ruins both the appearance and the quality of your product.
Why Constant Speed Fails
Standard dip coaters pull the part out at one steady speed from start to finish. However, this constant speed cannot stop pooling.
The issue happens at the exact moment the part leaves the liquid. As the part exits, surface tension grabs the liquid and drags it along the bottom edge. Gravity then turns this extra liquid into a thick bead at the very bottom.
Old Methods and Their Limits
In the past, engineers tried manual tricks to fix this:
- Touch-off:
Briefly touching the bottom edge to the liquid surface or a cloth to wick the liquid away. - Slanted Withdrawal:
Tilting the part to let the liquid drain from a single corner.
The problem is that these manual methods depend on human skill. They lack repeatability. For precise nano-level coatings or mass production, you cannot rely on manual work.
The Modern Solution: Linear Withdrawal (Variable Speed)
The smartest way to stop pooling automatically is to change the pulling speed at the very end of the process.
By precisely speeding up or slowing down just as the part exits the liquid, you can control the surface tension. This encourages the excess liquid to flow smoothly back into the tank instead of sticking to the edge.
Automate with SDI’s Linear Dip Coater
Our Linear Dip Coater features a programmable drive system. You can easily set multiple speed change points during the pull.
Whether you are coating flat plates, 3D shapes, or tubes, you can program a custom speed profile that matches your part. This guarantees an even coat from top to bottom every single time.
If you use thick liquids or make precise electronic parts, upgrading to a variable speed (linear) system is the best way to boost your yield.
▼ Specialized in Variable Speed Withdrawal! Learn more about Linear Dip Coater (LD1304S2)
https://www.sdicompany.com/en/dipcoater/ld1304s2.php