These machines are awesome! Especially for a corraddict since these machines are so open – unlike the single facer with negative or positive pressure – that they allow you to see and measure everything.
One would expect that just because these machines are so accessible that they would be in a very good mechanical state, but I see more of the opposite in the field, not too good maintained equipment with serious maintenance issues.
Incoming steam pressure in the single facer at the litholaminator.
Let’s start with the incoming steam. Most cases one runs with 14 bar incoming steam. That’s in most cases just too much and the more one goes to smaller flutes the more difficult this becomes with this amount of heat. At one customer we were able to go to 9 bar without seeing a drastic change. So even going lower in pressure when running N flute is possible.
Quote: “We cannot run with steam pressures lower than 14 bar”.
Question (me) : “Can you explain why ?”
Answer: “Because it is so…. “
Question: “Did you try to run with lower heat/ lower starch amount?”
Answer: “ No”, or “Board will not glue” or “We will have too much warp” etc.
A most interesting answer : “We can’t apply less heat on the single facer because then we need to use less glue and this results in too dry board that will cracks in converting.” ?!
We all know that higher temperatures /steam pressures results automatically in a higher starch demand, ending up with at the end of the day a wetter single facer web.
And how do we get then a flat sheet after laminating with Poly Vinyl Acrylic glue (PVA glue)?
Mostly we will apply too much glue to enable us to create flat board. (The 50% water in the PVA glue will balance the sheet with the high humidity of single faced web). So then we get almost perfect flat sheets but very wet and with a huge amount of washboarding.
So one creates very wet board that one also needs to flip flop to get flatness.
An additional problem with this way of running is that through the hydrodynamic forces of the glue one tends to apply more glue in the middle then on the edges. Many mechanical solutions have been tried to overcome this, but one this phenomenon cannot completely be suppressed.
To be able to apply low amounts of glue on has to have a single facer in perfect mechanical state.
As an example I will show you some pictures of what can cause serious problems in a litholam line:
The iodine coloring of the fluting in the picture above does not look good. In the light colored area’s one could obtain a lack of glue. If that happens the operator has no other choice then to increase the glue, but then this will result in an overload of glue in the darker areas.
This is resulting in applying more PVA glue on the PVA glue station to get the board back in balance. (flat).
Another risk of applying too much heat and starch, caused by damaged equipment, is splashing or spraying of glue in the flute valley, where there is even no contact with the liner.
So the message here is to make sure that the equipment is in good shape.
Running Lower grammages as fluting and inner liner
There is a tendency to use lower grammages. The prerequisites to be able to run low grammages like 70 g fluting and 60 g liner are:
- Positive mentality of the crew to do its best, and accept change.
- Good starches and good PVA glue (mostly not the cheapest)
- Equipment in a perfect state: glue rollers, blades, corrugating rollers
- POSSIBILITY TO REDUCE THE STEAM PRESSURE IN SINGLE FACER
The same prerequisites are valid for running aereated glues. These allow you to save big time in glue consumption but also in the total drying time of your laminated sheets (less PVA glue used, less water, hence less drying time). But mostly one does not succeed because one of the four conditions above have not been met.
So one ends up using 230 g as a top sheet in order to cover up the imperfections in the laminator or the crew’s mentality. Have you ever made the calculation if you could run 160 g as top sheet?