Curtain Coating

It is a well-known fact that the other person's coating method is better than one's own. The reason for this is that you know all the problems with yours, but you just see the elegant simplicity of the other.

One of the strengths of TopCoat is that it can give you a clear NO. There are times when the laws of physics are against you and it just isn't worth fighting. If you didn't know this then you might spend many hours (and $$$) trying to do something which just couldn't be done.

The example here illustrates these two facts. A TopCoat user was frustrated with his current coating technique. Whilst looking through a book on coating techniques he realised that Curtain coating was just what he needed. Fortunately for him, he had TopCoat available and in less than 10min discovered that Curtain could never be of any use. That 10min saved him a lot of trouble and he was able to put all his energies into a different method which, happily, solved his problems.

He wanted to coat 10µm wet at 10m/min (this was a very special application) and he entered the values into the Curtain modeller:

In TopCoat something in red is always bad news. In this case there was the mysterious message that the Weber number was <2 and so the curtain was probably unstable. Even he knew that the curtain would have to be stable for a good coating, but he had never heard of a Weber number.

TopCoat never leaves you in the dark. He was quickly able to find in the text the following:

In addition he was able to find out what each of the parameters in the Weber calculation meant.

More importantly he was able to play with the sliders to see what he would need to do to get a stable curtain. He found that he had to be coating >100µm wet and at a speed >40m/min to get a stable curtain:

But as he knew that his maximum possible thickness was about 12µm and his maximum speed about 15m/min he realised that Curtain could never work for him.

We don't like to hear a No. But it's better to find out sooner rather than later.

On the positive side, it's good to know that Curtain comes alive at high speeds and is a wonderful technique for those in that regime.