Edge Delete Solutions for High Performance ‘Low E’ / Solar Control Glass
Innovations in ‘Low E’ glass coatings are making the process of Edge Deletion much more challenging, from single layer / multi-layer coatings (commonly known as offline coated products), and the applications for which the glass is designed, all making the types of coating available becoming thicker and harder to remove.
This is especially the case with the new EasyPro from Saint-Gobain Glass which we will go into more information later on in this article.
What is ‘Low E’ Glass?
Low E (Low Emissivity) Glass involves metal particles being deposited onto the glass surface inside a vacuum. Coated Glass offers a very low solar factor when compared to standard non-coated glass, making it very desirable for homes and commercial buildings – due to its insulating properties (see Fig. 1).
The coating layer is applied by Magnetron Sputtering Vapor Deposition (MSVD) which usually contains Silver. The name ‘Soft Coat’ is given to the glass because of the susceptible nature of the coating being accidentally removed, damaged, or to corrode due to the sliver base.
Why do we need to remove the coating?
These glass panels will be made into a double or triple glazed ‘unit’, which involves ‘gluing’ these panes together using various types of sealant. As the soft coat is susceptible to corrosion this coating must be removed from the outer edge of the glass prior to gluing, so we are bonding to the substrate (glass) and not the silver based coating. If this is not done, moisture from the sealant and the external environment will corrode the silver, resulting in delamination (moisture inside the unit).
So, how do we remove it?
An important part of the glass industry is the Edge Deletion process. This involves the removal or stripping of the Soft Coat using an Edge Deletion Wheel. Edge deletion is normally done on the cutting table of which there are 4 main OEM’s - Hegla, Lisec, Botero & Bystronic. Although there are subtle differences between these machines all manufacturers delete and cut the glass in a similar way. See below a typical Cutting Table (Fig. 2):
The edge deletion wheel traverses across the glass jumbo on a CNC controlled bridge (above). The grinding head motor usually spins the wheel at a speed of around 2000 rpm and the wheel is pneumatically pushed against the glass surface with anywhere from 1 to 3 bar of pressure. As the cutting head travels across the glass surface in its pre-programmed pattern, the wheel removes the coating. The main adjustable parameters for this process are very simple: traverse speed, grinding head pressure, and sometimes wheel rotational speed.
See below 2 examples of edge deletion quality. Fig. 3 shows unsuccessful deletion with much of the coating left on the glass surface, where Fig. 4 shows the coating completely removed.
Fig. 3 - Unsuccesful edge deletion
Fig. 4 - Successful edge deletion
Inspection is normally a visual check, but a secondary inspection can be done with a fuse tester / multi meter as pictured below. If the green led is lit, then the deletion is not sufficient (Fig. 5). If the green led is not lit, then the surface is not conductive and has been deleted successfully (Fig. 6).
Fig. 5 – Showing conductivity
Fig. 6 – No conductivity
EasyPro - New innovation from Saint-Gobain Glass – What is it?
EasyPro is a revolutionary new temporary surface protection which is designed to deliver effective protection against damage as well as ageing from deposition of the coating until tempering. A Polymer deposition is deposited after the coating process and simply burns away during the hardening process. This new coating creates new challenges for the already difficult edge deletion process as now there are 2 types of coating which must be removed – EasyPro layer and the Silver coatings. Saint-Gobain Glass has tested all available types of Edge Deletion Wheels extensively and found that no wheel in today’s market can do this to a satisfactory level. This is why they approached Saint-Gobain Abrasives for assistance and we present the newly developed Edge Deletion Wheel - Norton Edge Delete Pro.
For more information please contact your local Norton Represenative.
Application Engineer, Saint-Gobain Abrasives