Why Contour Edge-Banding Machine Design Is Critical For A Quality Finish
Most cabinet shops find edge banding one of the more challenging processes.
This is because of two key reasons. Firstly the fine finish tolerances you need to deliver a high quality result. And secondly the difficulty in working with the combination of panel, edge-band and glue.
There are two distinct types of edge-banding:
- Straight line edge-banding (SLE)
Example of a Straight Line Edge-Banding Machine
- Contour (or curved) edge-banding (CE)
Example of a Curved Edge-Banding Machine
Straight line edge-banding is used for standard square or rectangular panels with straight sides. Contour edge-banding is needed for panels with curved edges that have been cut with a CNC* machine.
Edge-banding machines are very mechanical. And they’re made more complex because of a large range of adjustments the operator needs to make to achieve a quality finish.
The critical things for straight line edge-banding are:
- Skilled operators
- Banding glue and panel quality
- Stable machine
Get these three things right and you have the essence of a successful, high-quality straight line edge-band
While straight line edge-banding is difficult, it’s far more challenging to get a high quality result with contour edge-banding.
Contour edge-banding raises the difficulty, because not only do you need to work with a curved edge, you also have to overcome band memory.
What is band memory and why is it important?
This is the edge-band’s natural tendency, when released, to spring back to a near-straight state. On a straight line edge-bander the glue force needed to hold the band straight is minimal. However on a contour edge-bander, the glue must provide much higher grip to bond the band tightly to the panel contours.
As the corner radius becomes smaller, the force the glue has to apply increases significantly. This is because the edge-banding process has to overcome increasing band memory. The easiest way to see this for yourself is to take some banding material and try to hold it tight against the board around a small radius or wireway. Where gaps appear between the band and panel, press them down with your finger and see how much force is required. This is the adhesion force the glue needs to deliver to bond the band securely to the panel. And it has to achieve this in a very short time before the roller rolls off that section.
All modern edge-banders are a continuous rolling processes.
This means there is a critical relationship between roller pressure, edge-band feed speed, glue open time* and glue tack strength*. In contour edge-banding, the relationship between machine, edge-band, pressure and glue is much more important because of the issue of band memory.
Unlike straight line edge-banders, where all machines use the same basic process, in contour edge-banding there are many different machine types. So having a good understanding of the intricacies of contour banding makes choosing the right machine easier.
One of the most important details is how close the glue unit is to the first pressure roller.
This is because tight corners mean the feed rate must be slower to allow the glue to tack-off to overcome the tension of the band memory. The longer the distance between the glue application and the first pressure roller (pressing the band to the panel), the greater the effect of variations in air temperature, feed speed, band characteristics etc.
This means the operator must have a solid understanding of how these factors relate to product quality, and must be able to make the appropriate adjustments. The best contour edge-banding operators understand their craft in a similar way that solid wood machinists understand the characteristics of their machines and the wood.
Also don’t compromise on glue quality.
Glue is the link between the board and the band. A high quality glue will make up for a lot of inconsistencies in band and board quality.
See also: Why Is Glue Type So Important In Contour Edge-Banding?
So in summary
It’s important, when purchasing a contour edge-bander, to have an understanding of the challenges faced when you’re bending rigid banding materials around complex shapes.
The most successful cabinet shops choose the best quality edge-banding machines they can afford, ideally with a short distance between the glue applicator and the first pressure roller, use high quality glue, and invest in the best quality operators.
DEFINITIONS
- CNC –Computer Numerical Control.
- Open time – Length of time the glue remains tacky after application to the band. Note: the characteristics of the band can also affect the open time as different band materials have different heat absorption characteristics. Those which draw heat quicker will reduce the open time.
- Tack Strength –This is the instant strength of the glue when the band is first pressed to the panel. Also known as green strength. This is critical in contour banding applications to prevent the band memory causing the band to pull away – or pop – when the pressure roller passes over the band. The heat absorption characteristics and temperature of the band and panel can significantly affect the tack strength. For example, if the band or panel are very hot before being pressed together, the tack strength is compromised.