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Sealed Units FAQ

How is a sealed unit made?

1. The two glass panes that will be used to make the sealed unit are measured and cut. Usually one pane is low iron and the other planitherm. glass cutting tableglass cutting table
2. Optimised information (to reduce the amount of wastage) is entered electronically into the cutting table computer. The operator enables the table to cut the low iron glass first, once this process is done the operator then switches to the cutting head/edge deletion mode in order to cut the Planitherm.

Once these two processes are completed the Planitherm sheet is paired up with its low iron partner.

When using Planitherm glass, the cutting table computer engages the edge deletion tool which removes a 10mm strip from the perimeter of the soft coating from the edge of the glass, in order for the hot melt (added in a later stage) to adhere to the glass. The computer then engages the cutting head to actually cut the sheets.cutting table computercutting head

3. This is the spacer cutting station. The spacer bar is cut to the correct length using our automatic digital saw. The width of the spacer bar determines the cavity depth within the sealed unit. The spacer bar can be of different colours, e.g. black, silver, and is made from aluminium or composite materials. The completed frame is filled with desiccant which absorbs any moisture that may build up between the two panes of glass. As with our cutting table, safety is very important to us. The saw comes from underneath the spacer bar and cuts upwards to that it is never exposed at any point to the operator and further is pedal operated. Cutting The SpacerCutting Machine Computer
4. If the glass requires extra detailing such as bevels, lead, Georgian bar, colours or pictures added to it, they pass into our lead department for the necessary processing. After which they are then ready for washing and drying.

If bevels have been applied to the glass they are now 'cured' using a UV light unit. This takes approximately 10 seconds to cure the bevels, instead of the 12 hours it would take without it. 'Curing' the bevels

5. The glass panes are then fed through the automatic washer/dryer using demineralised water. After being washed they are thoroughly inspected by the operator and then labeled with their correct size and specification. For leaded units, the leading is applied to the glass which is then fed through the washer a second time. washer/dryerwasher/dryer
6. Once washed and dried the glass is then transferred to the clamp roller table where a Bostik hot melt sealant is applied at 185ºc into the cavity around the edges of the glass. This forms an air tight seal between the two panes. At this stage the unit can be filled with Argon gas if required. Assembly Machine Applying The Sealant
7. The completed unit is then taped around the edges in order to facilitate safe handling by the fitters. It is at this point the unit receives its final inspection and a quality stamp applied, before finally being stored on a glass rack ready for delivery/collection. Glass Rack

Properties of PLANITHERM TOTAL+ Glass

Planitherm Total+ Glass

Christie Glass uses PLANITHERM TOTAL+ glass from Saint-Gobain Glass.

PLANITHERM is a new generation of energy saving window glass and the most energy efficient available. Its advanced coating technology reflects radiated heat back into the room, rather than allowing it to escape through the windows. At the same time, PLANITHERM allows free heat and light from the sun to pass through the glass.

PLANITHERM TOTAL+ is one of the most energy efficiency glass products available helping to improve the window energy ratings of your glazing and making your home more comfortable.


  • Improved thermal insulation - reduces heat loss more effectively than traditional low-E coatings.
  • Promotes passive solar heat gain - free heat from the sun passes easily through the glass helping to warm your home.
  • Improved energy efficiency - reduced need for heating helps to save energy and protect the environment whilst saving you money on heating bills.
  • More comfortable rooms- improved thermal insulation means fewer cold spots and drafts near windows and doors.
  • Less condensation- the inner surface of the glass stays warmer reducing internal condensation and prolonging the life of your window.

The value of Argon filling

When gas is introduced into the cavity of a double glazed unit, it reduces the heat conductance between the panes. This helps to keep heat in during the winter and out in the summer. When used in conjunction with Planitherm Total+ glass on the inside of the sealed unit the thermal insulation is greatly improved.

The pairing of Argon gas and Planitherm Total+ glass can achieve an improvement in thermal performance of approximately 50% over a standard sealed unit.

In addition to its excellent heat insulation properties, Argon gas is sunlight stable, colourless and odourless, non corrosive, and is non-toxic.

When is toughened/safety glass required?

The shaded areas in below diagram shows the areas in which safety glass must be used. Glass used in these areas must comply with BS 6206.

Safety Glass Areas

Where only part of a unit contains a shaded location the whole of that unit must comply with BS 6206.

Safety glass is 5 times stronger than normal glass, and is ideal for vulnerable ground and first floor installations, and also most importantly for conservatories.

On impact safety glass disintegrates into small granular pieces which are not sharp, thus reducing the risk of injury.

Pilkington 'K' Glass

Pilkington K Glass

We can also supply Pilkington 'K' glass.

Pilkington 'K' glass varies from normal clear glass in that one side of the glass has a special metal coating known as a low emissitivity coating.

This very fine metal coating allows shortwave radiation through, such as sunlight, but reflects longwave radiation such as heat from fires and radiators.

This coating also makes the surface warmer to the touch and condensation is also reduced.

The Pilkington 'K' glass is said to be up to 30% more efficient in its insulation than other types of double glazing.

This of course results in reducing your fuel bills and makes your home much more comfortable.

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