How to Make a Sealed Unit

An insulated glass (IG) sealed unit is made with two panes of glass (although triple glazing and even quadruple glazing with three or four panes of glass are also available) which are separated with a spacer frame made from tube or foam spacer (tube can be bent or cut and corner keyed). The spacer frame is fixed onto the two panes of glass with a primary sealant. A spacer tube is filled with desiccant on two to four sides of the frame (foam spacer is manufactured with a desiccant compound included) and then a secondary sealant is applied to the back of the spacer to seal the unit. Insulated glass sealed units can also be gas filled to improve their thermal efficiency.

It is generally accepted that a unit which achieves a higher Window Energy Rating is constructed similarly to our own high performance superior double glazed sealed unit - one low-e glass pane and the other glass pane float or low-iron. You then have various options in terms of gas-filling, warm edge spacer, desiccant and sealant. Whether you apply single or dual seal, it's the care you take over the construction and the choice of the components that you make that will help to guarantee the longevity of your sealed unit. Thermoseal Group is the UK's leading manufacturer and supplier of insulated glass sealed unit components, as well as and sealed unit manufacturing machinery. Please click here to view our full range of glass machinery and click here to view our extensive range of over 2,000 components, including our highest performance warm edge spacers Thermobar and Thermoflex.

Glass Preparation

• The two panes of glass that will be used to make the sealed unit are measured and cut to size either by hand or using an automatic cutting table. This reduces waste and manpower.
• Thermoseal Group supplies machines for removing the low-e perimeter (soft coat) surface coating from the edge of a glass panel prior to its use in an insulated glass sealed unit. Edge deletion is necessary because the low-e coating on the glass surface affects adhesion with insulated glass sealants. Removal of the edge coating means that the sealant can bond directly to the glass. Please confirm this requirement with your glass supplier.
• Glass panes are then fed through a glass washer/dryer using demineralised or deionised water. After being washed they are thoroughly inspected by the operator. For leaded units, the leading is applied to the glass which is then fed through the washer a second time. We supply a range of glass washers, both horizontal and vertical, as well as water purification units/treatment plants (essential for soft coat), demineralising units and the resin.
• If bevels have been applied to the glass they are now 'cured' using a UV lamp or bench (these can be supplied by Thermoseal Group). Thermoseal Group supplies a range of DecraLed® bevels, lead and colour film, as well as a range of tools and accessories for applying these to the glass.

Spacer Frame Construction

• Tubular Spacer bar can either be bent or cut and used with corner keys to construct a frame to be used to create an airspace between the two panes of glass in a double glazing sealed unit. The width of the spacer bar determines the cavity depth within the sealed unit. Spacer tubes can be made with aluminium, steel or warm edge options. Thermoseal Group supplies a wide range of spacers including Thermobar and Thermoflex warm edge, aluminium, and steel.
  • Spacer Bar Bending - A length of spacer is cut to size and three or four corners bent to create a rectangular frame (spacer tubes can also be curved for unusual shaped glass sealed units). The two ends of bar are then joined either using one corner key (3 bent corners) or with a straight connector (4 bent corners) for a join along the length of the spacer tube. Thermoseal Group supplies a range of spacer bar bending machines as well as the accessories they require. Please note that some spacer tubes are more suitable for bending than others.
  • Spacer Bar Cut and Corner Keys - Four lengths of spacer are cut to the correct length (standard size is 24mm shorter than the glass size) and then joined together with compatible corner keys to create a rectangular framework. Thermoseal Group supplies a range of spacer bar saws, blades and compatible accessories.
• Foam Spacer such as Thermoflex is not constructed into a spacer frame before being sealed between the two panes of glass. It is applied directly to one of the glass panes using its pre-applied adhesive side tape. Foam spacer, as well as machinery, tools and accessories for use with foam spacer can all be supplied by Thermoseal Group.
• Georgian Bar grids are constructed and fixed to the spacer systems. To create an authentic multi-pane window, a spacer grid is constructed using duplex fittings or a Interbar system. Equipment for preparing and stapling Georgian spacer bar is available from Thermoseal Group including staple tables, mitre machines, bending machines and saws. A wide range of Georgian Bar and accessories is also available, as well as Aluminium and UPVC Surface Mount Georgian Bar.

Desiccant Filling

• Desiccant Filling - The completed spacer frame is filled with desiccant. This adsorbs any moisture that may trapped in-between the two panes of glass during manufacture, or which finds a way into the sealed unit throughout the lifetime of the unit. It is standard practice in cut and corner key units that two of the four spacer tubes are filled with desiccant. With most warm edge systems it is recommended that at least three sides are filled as the internal diameter of the tube is smaller than aluminium spacer tubes. Thermoseal Group supplies a range of desiccants and also manual and automatic desiccant dispensers to fill spacer tubes. It is important that you purchase a pure 3A desiccant such as Eurosiv to ensure the longevity of your sealed units. Ask about our desiccant testing service and test kits we can supply.

Primary Seal

• Polyisobutylene or PIB is applied to both edges of the spacer tube framework. This is then carefully pressed in place in-between the two panes of glass. PIB can be hand applied, but is usually applied using a PIB machine. Care should be taken to ensure PIB covers the joints where key and bar meet. Thermoseal Group supplies a range of PIB, including our own-brand Euroseal PIB, and a range of PIB machines suitable for small and large IG manufacturers.  

Secondary Seal

There are various options of secondary sealant which can be applied to the outer edge of IG units to provide a dual seal.

• Hotmelt (most popular secondary sealant used in the UK market) - one component sealant applied at 170-190°C has no curing time. Simply wait to cool down and glaze. Euroseal Hot Melt is Thermoseal Group’s own high quality brand.
• Polysulfide (PS) 2-component chemically curing sealant.
• Polyurethane (PU) 2-component chemically curing sealant.
• Silicone one or two part chemically curing sealant.

Various ranges of all of the above sealants are supplied by Thermoseal Group, as well as a variety of machines suitable for applying each sealant including: Hot Melt Extruders and replacement guns; Glass Sealing Tables; PS and PU Mixing and Silicone Dispensing Pumps; and digital thermometers (for checking the application temperature of your sealant).

Gas Filling

Gas filling is a means of improving the thermal efficiency of your IG unit to produce a high performance glass sealed unit. In fact, if you gas-fill your units, it is possible to achieve a 'C' rating under the UK Window Energy Rating Scheme (WER) with some window profiles using traditional aluminium spacer bar. However, you should explore your warm edge spacer options. Please click here to see our recommended high performance unit and range of warm edge spacers available from Thermoseal Group. There is also a wide range of marketing support material available.

Thermoseal Group supplies a range of gas fillers for filling Argon (Ar), Krypton (Kr) and Xenon gas (Xe). There is a fast-fill feature available. In addition, gas hole drilling and gas testing equipment is available.

Vertical Gas Filling

This is the most efficient form of gas filling a double glazed unit. Two 5mm holes are drilled as close as possible to either end of one side of the spacer bar which does not contain any desiccant. Alternatively special gas corner keys with pre-drilled holes can be used.

The sealed unit is then constructed with the primary seal and positioned vertically - either with one of the drilled holes positioned vertically above the other, or with both holes at the top.

Recent evidence has shown us that it is ideal to use a displacement filler unit positioned vertically with both holes at the top as per the image below. As well as being an easier method, it is quicker to fill and ensures less gas leakage during manufacture but requires the use of a gas filler with a suction facility on. - you can do this using displacement as long as the gas can escape through the hole with the sensor in it as fast as you are pumping it in. This method is good for Krypton at around 8-10 liters per minute.

All NM Gas/Multigas Fillers from Thermoseal Group are rapid fillers with suction. The unit is positioned with the holes uppermost on the horizontal edge. The probes are pushed through the holes. If the primary seal is applied correctly the gas cannot leak out as the holes are uppermost.

Once the unit has been filled with the chosen gas, the holes are closed with end rivets or plastic plugs. If you are using a secondary sealant, this can now be applied.

Horizontal Gas Filling - ideal for Hot Melt Users

This method allows you to perform the gas filling function through one hole in the perimeter of the spacer bar frame or through a single gas key.

The chosen gas is injected into the hole with a unique gas probe which has an in-built gas sensor to indicate when the unit is filled with gas.

Although this method is slower than vertical filling, it is useful for certain production methods:

• For filling spacer bar which is bent. A single gas key can be used and the profile is easily filled through a hole in this key).
• For Hot Melt users. Manufacturers can seal all four sides of the sealed unit leaving a gap on one corner, then without moving the unit from the clamp table they can fill it with gas and insert a plug in the key to seal it up.

Safe Handling

The completed unit can then be taped around the edges in order to facilitate safe handling by the fitters, and stored on a glass rack ready for delivery/collection. A variety of suitable tapes and racking can be supplied by Thermoseal Group.

Production Lines and Fully Automated Machinery

We have put together some insulated glass sealed unit manufacturing packages suitable for starting up your own sealed unit manufacturing business. These packages are a guideline of the equipment you will require to set up a sealed unit manufacturing business. However, if there is a specific package of machinery and tools you require then we can supply individual machines or parts for the following machines: Production Lines and Spacer Bar Gantry's; Panel Press Machines; Roller Press Machines; Spacer Bar Alignment Racks; Tilting Tables and many more. Please click here to view the range of new and used machinery we have available. Please note that we may be able to supply additional glass machinery which is not yet detailed on our website, so please don't hesitate to contact us with your requirements.

EN1279 Certification

Sealed unit manufacturers trading within the EU must consider this European standard for manufacturing insulated glass sealed units. It has 6 parts as follows:

Part 1 of the standard deals with a number of key issues for all manufacturers of insulating glass units in building. It covers the system description, which describes the properties and performance of the products being manufactured.  

Part 2 is for air-filled units and requires the manufacturer to have a set of units tested to determine their resistance and moisture ingress.  

Part 3 for gas-filled units (normally Argon) and requires the manufacturer to have a set of units tested to determine their ability to retain the gas, and hence the claimed thermal performance improvement for the working life of the unit. 

Please note that building regulations suggest that the majority of double glazed sealed units will need to be gas-filled to meet energy efficiency guidelines and achieve higher Window Energy Ratings (WERs). This test can take up to six months from application, so apply now so that you can continue to supply insulated glass sealed units which meet the demand for WERs.

A few tips for making sealed units to meet EN1279 part 3 standards:

• Limit the number of paths for escape of gas where possible and ensure that corners, joints and staple holes are secured to limit gas loss. It is unlikely that you will be able to meet the requirements of part 3 without using a dual seal system - i.e. PIB as an inner sealant.  If you don't have a PIB machine, ask us about purchasing your spacer bar with pre-applied PIB.
• Try using hand-applied PIB as a primary seal to bond your unit together.
• Once your unit is filled with gas, plug and fill gas holes as soon as possible to limit the gas loss during manufacture.
• To achieve the best sealant bond ensure that the sealant is at its optimum temperature for application and that the glass is warm and dry.

Part 4 for sealants (to be supplied by sealant suppliers).

Part 5 is the legal part of the standard and all other parts support part 5.

Part 6 describes a minimum factory production control systems and describes the required periodic testing.

Please note that the words 'Normative' and 'Informative' are often used in European standards so note the meaning of these as follows:

• Normative means that there is a legal requirement to carry out the instruction.
• lnformative means for information only. However, it is often advisable to conform to these requirements as the whole standard represents a legal requirement.