Industry visual standards

The glazing industry works to a prescribed acceptable visual quality standard for installed glazing. Glasscraft uses these visual quality acceptability guides to determine an acceptable level of glass appearance in the home.

Avoiding dispute between our customers and home owners

Based on the Glass and Glazing Federation’s (GGF) various publications concerning the visual acceptable quality of glass, there are basic rules that need to be understood and accepted to avoid disputes between our customers and the home owner. A common sense approach needs to be taken and an understanding that modern processed glass is not going to be flawless.

When inspecting the glass the following needs to be undertaken and explained:

1. View the glass from inside the room standing a minimum of 3m away facing the glass. This is because under normal everyday situations, looking through windows is usually at a distance and not from close up – say within 6 inches of the glass.

2. Look through the glass and not at it. This is expected as normal as the glass is there to enable a view beyond the window, not stopping at it.

3. Do not inspect in direct sunlight. This is because the direct sun will be refracted by the coating and any tiny imperfections in the glass surface, highlighting items that cannot be seen in normal conditions.

4. Ensure the glass is clean and dry inside and out. It is impossible to check glass that has rain, dust or condensation up on it, mixing up these elements with potential problems.

5. Ignore the 50mm perimeter of the glass. This is because when looking through windows, the eye is drawn to central areas and one doesn’t look through the edge of glazing when viewing. (Obviously large obtrusive marks in the perimeter are not acceptable.)

Using this as a guide, only items that are intrusive to the view are deemed as poor quality glass. This may include marks in the coating, deep scratches that are clearly visible, multiple and clustered imperfections on the glass surface or processing marks such as fingerprints!

Glasscraft quality department is often asked to attend homes where the glass is actually ok and acceptable. This is usually because the customer is worried that the glass may be faulty or doesn’t understand the nature of the issue.

  • Patterns in condensation – normal hydrophobic processing deposits.
  • Swirls in the glass when the sun shines – normal refraction of light by low e coatings
  • Hairline marks in the surface – low e marks only visible from a few inches away.
  • Lead discolouring – normal oxidation of the surface
  • Distorted reflections – normal movement to convex or concave position of the glass due to air pressure and temperature changes. (deflection)

Glasscraft – crafted with quality in mind

Glasscraft  is quality conscious and endeavours to deliver high quality products. If we should have any quality issues, we address these in co-operation with our customers so we both can understand how the issue has arisen and avoid repeats.

Modern glass is highly sensitive and processing is intensive. A sealed unit will undergo many processes from its component part preparation to final assembly.

A toughened unit, for example, starts life as individual components travelling across continents. The glass is sourced in the UK and comes into our factory in packs of 20+ sheets measuring 3210mm x 2550mm. These packs are off loaded using over head cranes. The individual sheets are then transported to our cutting tables and optimised to achieve the least waste.

Low e products have to be edge deleted (have the low e coating ground off around the perimeter), as well as undergo the cutting wheels. The individual rectangles/shapes of glass are then snapped out of the sheet and stacked in order for the next process.

Toughening begins with the stacked glass having the edges arissed (ground smooth to avoid breakage). This is done by automated sanding belts. This creates glass particles that are washed off the surface before toughening. The glass is then placed into our furnace in the same order and blast heated to round about 600°C for approximately 3 minutes.

It then moves on rollers to the cooling section of the furnace and cold air is blasted onto the surface to rapidly temper the glass. If both the clear piece and low e piece of glass survive to this point, they are paired up ready for the sealing process.

Meanwhile, in a different part of the factory, a spacer frame has been assembled. The 5m lengths of spacer tube are chopped into the correct lengths to make the cavity of the glazing. Desiccant is blown into the spacer tubes and the frame is assembled. This frame then has the PIB applied to its edge at a temperature of about 110°C.

The frame is transported to the assembly area on the line ready to be applied to the glass. The glass is now at the beginning of the assembly process. Each piece is put onto our vertical production line at the beginning, to enter the washing process.

Still in specific order, the glass enters a high speed washer that has 6-brushes (3 each side) that move into contact with the glass surface. These are special soft coat brushes to prevent scratching. The water is not any old tap water! It is purified water that is PH neutral with the lime scale content removed; it has been cleaned after leaving the tap by a reverse osmosis water treatment plant. This is similar to desalination plants seen in arid desert countries.

Both pieces of glass travel along the line and are inspected prior to the spacer bar being applied. The spacer is positioned using the alignment rack to achieve even sealant depths. The pieces of glass then pass in to the gas press and are literally squashed together under specific pressure limits to form the primary seal with the PIB and the glass.

Once squashed, they are joined together and the edge is then sealed using our precision robot. Once finished, labels and protection pads are applied and the sealed unit is left on a drying rack for the sealant to cure. It is then sorted in to customer deliveries and put on ‘A’ frames to be loaded on to our wagons.

At our customers, the pallets may be fork lifted off or hand-picked and stored into their warehouse. At this point, the journey is not over. The sealed unit is then put in the back of a glaziers van and taken to its final home. The window frame is fixed in place and the sealed unit is placed in the frame and beads are hammered into the frame to keep them it in place.

After all that, it must then last 10-years minimum and resist heat, cold, rain, wind, boisterous children, window cleaners, pets and wildlife to keep the occupants warm dry and safe. It’s a tough life!