Bonding of edgings
1. What is the ideal temperature for the hot melt adhesive?
The theme of “adhesives” is extraordinarily complex. In the OSTERMANN range there is a variety of different products available for the most diverse requirements. That’s why this is the answer for only a standard EVA hot melt adhesive. The ideal temperature for this is about 190 – 210 degrees C in the glue pot, preferably higher rather than too cold, since the temperature decreases right up to the application roll.
Special tip: Producers should not rely on the temperature indicator in the display but should check the temperature in the glue pot and on the application roller regularly.
2. What other reasons could there be for the adhesive not sticking?
When edgings don’t stick it could be that the heating unit of the machine is defective. This happens sometimes even on new machines. In this case the required temperature of the hot melt adhesive is not reached. It’s a good idea to measure the hot melt adhesive. For this you can use for example an infra-red thermometer, which can measure temperatures from -18 to +260 degrees C at the push of a button. It is important to measure not only the temperature in the glue pot but also the temperature where the glue is to be applied.
Special tip: For regular checks you can purchase a high quality IR thermometer from OSTERMANN.
3. Why should the pressure on the first roll be checked regularly?
If there is not enough pressure applied to the edging on the first roll and the joint is not closed immediately, then the edging doesn’t stick properly. The reason is that the adhesive is not fully in contact with the board. Even on the second roll the adhesive has then cooled down too much to spread sufficiently and make a strong bond between the board and edging.
Special tip: You can check the adhesive application and the roll pressure with OSTERMANN’s transparent test edging without primer. This test edging is available in 23 and 43 mm widths and in 0.4 mm thickness.
4. What should you keep in mind when processing real wood veneer?
Real wood veneer edgings have fundamentally more residual stress. Here the adhesive has to do more. Although the edgings can be glued mechanically by the usual hot melt adhesives (EVA, PUR, PO) and manually with Kantol special glue, they require more glue to be applied. All OSTERMANN thick veneers (1 and 2mm) have primer. Compared to veneer edgings without primer, primed edgings show much better adhesive qualities. For mechanical processing OSTERMANN recommends a glue application of about 200 – 300 g/m.
Special tip: With some glueing machines the roll direction can be reversed. This results in more adhesive being applied and so to better adhesion of real wood veneer edgings.
5. Why are OSTERMANN edgings primed? What is that anyway?
Plastic edgings and thick veneers are always primed at OSTERMANN. The so-called primer is an adhesive agent. It ensures the best adhesion between edging and glue. You can see under UV light whether an edging is primed or not. OSTERMANN’s thin veneers and end grain edgings have a thin fleece on the back instead of a primer. This ensures not only better adhesion but serves also as splinter protection.
Special tip: See for yourself and compare the chip pull after removing a veneer edge with and without pre-applied primer!
6. PUR or EVA adhesive: which is better?
In most businesses EVA hot melt adhesive is used and fulfils the requirements reliably. However, OSTERMANN experts recommend PUR adhesive because of its clearly better adhesive qualities (water resistance, thinner bond line, higher bond strength). Many businesses are concerned about cleaning the machine after using PUR, but the hot melt adhesive glue pot is easy to clean after cooling with the help of the blue cleaner. However, you must not forget to do this.
Special tip: It’s also possible without the cleaner. Carefully remove the PUR residue, run the leftover edging through, until there is no more adhesive on the roll and then apply EVA glue to edging again.