Nowadays mechanical forming (e.g. ClassiFormer by SUNDS-DEFIBRATOR) has gained a big share of the particleboard forming machinery business. The signer of this document knows this fact, but having been involved in windforming (2 years as technical manager of a particleboard factory using BISON-hydrodyn process and 3 years as a manager in a project for developing a windformer) knows so much symphaty with those who still have windformer and difficulties in this area, that he decided to make this page in hope that someone some day can get some help of it.

The signer have had the best possible opportunity to research and develop the windformer because RAUTE WOOD OY decided year 1989 to create a new windformer. In that purpose RAUTE built a complete forming line 1:1 (width 2560 mm) with windformer and mechanical former. (see picture above). Also the gluing station was built. RAUTE appointed me manager of this project and gave me "free hands" to develop a new windformer.

I started this project by testing the existing methods and noticed that none of them was completely satisfactory. One of the many weaknesses in the existing formers was that using of circulaiting air caused dust blockage in every tested air system. Using of dusty air was however one of the goals in this project. After these preliminary tests I noticed that I had to start this project from "the clean table".

In an early stage I noticed that the particleflow that falls into the airstream has to be almost homogenous for two reasons:

• denser spots in the storage bunker mirror in the formed mat
• Denser spots in the chip flow add the effect of making denser spots in formed mat also by disturbing the air stream.

I solved this problem by using horizontally , partly in between each other rotating "rakes" which spread the chips, dropped on one spot, evenly along the whole width of the storsge bunker (se picture attached). This equipment is small and cheap. The transverse density in chipmat in storage bunker varied + - 2% using this equipment

Second critical point in windforming station (as well in mechanical former) is discharging the chips into the airstream.
SCHENCK's method with its many cutting rollers is modest, but expensive, service demanding and sensitive to any even smaller defects in cutting rollers. Rapidly rotating spike roller is one of the worst solutions for this purpose. It causes turbulences in air and if any of the spikes is the least in wrong angle it causes "stripe" in the formed chipmat.

I solved this spot by using a roller made of wide spaced steel wire net. When this roller rotates slowly in front of the chipmat which comes from the storage bunker, it cuts an even chipflow from the edge (see picture). SUNDS-DEFIBRATOR has patented this method later.

Before coming into the airstream the chipfall must be broken to individual chips to make the airstream effective. For this purpose I used same kind of rotating steel wire net roller as for discharging (see picture).

In the same picture one can see also the best system that I found to regulate the forming result. It consists of 50 mm wide "lists" placed side by side. They can be lowered or lifted individually into the air stream. Lowering a list causes a thicker stripe in formed chipmat placed crosswise in same place as the list is. The lower the list is the higher is the stripe and vice versa.

This kind of equipment is necessary when using circulaiting air, because airflow through the perforated steelplate, which is used in this system , is not disturbed and therefore the holes in the plate remain open.

Now I have to say, that this system needs one essential element to work properly i.e. an even airstream. Perhaps the most difficult thing (for me anyway) was to get the airstream even concerning speed and direction through the whole cross-section of the windchamber. Yet this thing is necessary to achieve a perfect result. I found the solution to this problem after many failed attempts, and it is very simple and cheap. This system is not patented (unlike the preveous mentioned methods) and therefore I don't explain it here.

The funnel or any other device through which the air is blown into the windchamber is sensitive for dust accumulation. To prevent this I formed the walls of the funnel in this former curved (see picture). This shape (which by the way has same shape as the upper surface of an airplane wing) keeps the airstream in touch with the walls and prevents the dust to accumulate in the funnel.

Altogether I got with this former better results than I had ever seen before. E.g. the thickness variation across the final chip mat was + - 1.5 mm when the thicness of the mat was 45 mm with the capacity of 14 m3/m/h. This fact was also documented using ultrasonic sensor which scanned across the mat.

Also the trimming of this system is easy and quick. It took from me under 2 hours to achieve above mentioned result and these trimmings are lasting.

In this document I have concentrated only in larger units but if I would try to explain how to build a good windformer according to my opinion I could write a book of this matter. So many details it consists.

Though I don't want to tell in this document about my invention concerning the air system of this former, I don't want to keep this know how myself. If anyone is interested, my E-mail address is below.

Clicking here you find my background


Pertti Sairanen
pertti.sairanen@phnet.fi