Integrated frame & glass

Abstract

To provide for continuous line production from glass/frame profile cutting to window assembly, our company has developed a new fenestration system that integrates frame and glass technology. The proprietary system features two new core technologies, which are trade named Friction Corner Welding and Fusion Assembly Systems.

Friction Corner Welding is ‘a rapid means of joining thermoplastic profiles' and involves the use of a corner web that is vibrated back and forth very rapidly. The framing profiles are pressured against the web, generating heat and melting plastic to form a welded joint. Through the incorporation of various design features into the web, mechanical flash removal is eliminated and this allows for welding around insulating glass (IG) units. With this fast heat friction process, the overall cycle time is 85 per cent less than with conventional hot plate welding,

Fusion Assembly is ‘the technology of glass and frame integration'. Using a U-channel profile, the welded frame assembly is continuously adhered to both sides of the IG unit using twin sealant beads. By stiffening the frame through the adhered IG unit, structural performance is enhanced and this results in simplified profile design and reduced material use. By eliminating the use glazing stops, there are further material and labour cost savings.

Each core technology has required the development of two new pieces of automated equipment that has been engineered in partnership with two European equipment manufacturers, Bystronic Glass and Sturtz Machinery. These two new pieces of automated equipment have been designed to link to IG production and provide for high volume production of 800 sash frame window assemblies per eight-hour shift.

For the architectural market, the combination of Friction Corner Welding and Fusion Assembly allows for the development of new fenestration products that feature advanced composite thermoplastic frame materials.

Conventional Vinyl Window Production

At present, vinyl (PVC-U) windows are manufactured using a batch production process with the IG unit and sash frames being separately manufactured. The IG units are then manually installed within the sash frames and because this process cannot be easily automated, it is a key bottleneck within the present window production process.

Friction Corner Welding

Although vibration welding is a well established technique for joining together two separate thermoplastic components, the new Friction Corner Welding technology allows for the joining together of two thermoplastic extrusions by means of a third intermediary element that is known as a corner web. This third corner web element has to be made from material that is compatible with the thermoplastic extruded profile material. The corner web is vibrated through an amplitude ranging from 0.6 to 1.2 mm at a frequency of 200 to 240 Hz to create frictional heat between the web and the two extruded profiles. To generate heat, pressure has to be applied during the welding process and this required pressure is between 3.5 and 14 bars (50 -200 psi). Sophisticated control systems are used to optimise the process by varying the pressure during the welding cycle, that is about two seconds in length. The overall process is controlled through measuring the amount of material that is melted with the recommended combined melt depth being 0.5 to 1.5mm.

In addition to being produced from compatible thermoplastic material, the corner web element needs to be stiff and flat as it is the major element and datum for all operations. The corner web elements are injection moulded and are individually designed to match the profile shape of the mitre cut profile joints.

With the new Friction Corner Welding process, there is only minimal melted material residue or flash produced. By incorporating various design features into the web, the flow of this melted material can be controlled and a clean joint-line aesthetic can be created.

By eliminating corner cleaning, there are a number of important advantages. First, coated and other decorative-finished profiles can be more easily welded as the coatings and finishes are not damaged during the corner cleaning process. Second, without the need for mechanical flash removal, there is the opportunity to introduce more complex shapes and profile designs. Third, there is a cleaner factory environment. Fourth, by incorporating various design features in the web (e.g. hardware holes), the need for secondary machining operations can be eliminated and this ensures that all messy fabricating operations are concentrated in one location.

In joining the profiles together, the web acts as a structural brace adding stiffness to the corner joint. A further advantage is that by providing an intermediary joining element, there is no need for the mitre cut profile walls to be matched up and this allows for different size profiles to be welded together. This means that like traditional wood windows, there can be a wide bottom rail and a narrow side jamb. The new welding technology also allows for the development of new visually distinctive joint designs including butt joints that imitate the appearance of traditional wood window assembly.

In addition to welding conventional PVC-U hollow profiles, the new Friction Corner Welding process can also be used to join thermoplastic materials that cannot be easily welded using conventional hot plate technology. These include: thermoplastic foam materials; wood fibre filled vinyl; solid profiles from recycled polystyrene, and composite glass fibre reinforced thermoplastic materials. Through special design features in the corner web, Friction Corner Welding technology also allows for hollow cavity profiles with very thin walls (1 mm) to be joined.

Friction CornerWelding technology was initially developed because of Intra's interest in welding glass fibre reinforced plastic profiles that have an expansion coefficient similar to glass. For these new composite thermoplastic materials, instead of using a simple web, Intra has developed a corner key technology. In contrast to the flat corner web, the corner key incorporates legs that are fitted into the mitre-cut ends of the hollow cavity profiles. The main flange of the corner key is friction corner welded to the profile ends and the two profile sides are then ultrasonically spot-welded to the key legs. The end result is a very strong and stiff corner joint.

The new Friction Corner Welding technology has been developed in partnership with Sturtz Machinery. The first equipment system that has been developed is an automated four-head welder with the capacity to produce 800 units per shift. A semi-automated single head welder is also being developed with the capacity to produce up to 400 units per shift. The development of an even higher volume four-head equipment system has been initiated and this new system will have the capacity to produce more than 2,000 sash frames per shift.

Fusion Assembly

With Fusion Assembly systems, the frame profiles are welded with the IG unit in position. To do this requires a U-shaped frame profile and a corner web that is designed to fit around the IG unit. Proprietary rubber centring blocks inserted in the frame profile hold the IG unit temporarily in position and help dampen vibrations during the welding process.

Note the reduced profile size and material required for Fusion Assembly.

After corner welding, reactive thermoplastic sealant material is inserted into the two gaps between the IG unit and the U-profile frame. This is achieved by means of automated sealant gunning equipment that has been developed by Bystronic Glass. Known as the Frame Sealer, the double head robotic equipment simultaneously applies twin sealant beads at very high speeds with the cycle time for a typical sash frame (600mm x 900mm) being 25 seconds. Through a three-pump system and a highly engineered nozzle design, the sealant material is very accurately and precisely applied, creating a smooth bead appearance even at the corners.

By adhering the U-shaped profile to either side of the IG unit, the unit is hung within the window sash frame assembly and so there is less weight and pressure on the bottom window rail.Strength and rigidity is also added to the window assembly and as a result of this improved structural performance, there is a reduced need for metal reinforcement. Even for very large window units, this need for metal reinforcement can be fully eliminated by substituting composite thermoplastic materials, which can now be corner welded due to the development of Friction Corner Welding technology.

With Fusion Assembly, less frame profiles are required for each window type and this means that there is less need for expensive profile dies and inventory costs are also reduced.

Integrated IG/Window Production

The combination of Friction Corner Welding and Fusion Assembly provides for a continuous process from glass/frame profile cutting to IG fabrication and window assembly. With a four head Friction Corner Welder, the cycle time is 25 seconds compared to a cycle time of 120 seconds for a conventional four head welder. The output is 800 units per shift, which is matched by the output of the twin head Frame Sealer. Through the use of reactive IG sealants, there is no cure time or holding time and the IG unit can be automatically transferred from IG production to frame assembly and then from frame assembly to glazing sealant application.

As a result of the continuous integrated IG/window production process, there is less material handling, less in-process inventory and less labour. For example with North American residential vinyl windows, there is typically a 70 per cent reduction in labour savings. The factory footprint of the new system is also typically 35 per cent less than current production systems. Even though there are higher levels of automation, overall equipment costs are not increased and this is because expensive equipment items such as corner cleaners are eliminated.

Through integrated production software, the new continuous production process allows for efficient, just-in-time production of custom vinyl windows. For typical residential windows, our objective is for an overall cycle time from glass/frame profile cutting to finished window assembly of 10 minutes or less and to achieve this ambitious goal requires further improvements and innovations in such critical tasks as hardware installation. In terms of the contribution of glass cutting and sorting to overall window assembly time, the new Bystronic vertical glass cutting system is an important new development because there is no need to cut up a full glass sheet in order to supply a different sheet thickness.

Summary

Friction Corner Welding and Fusion Assembly are two new fenestration products that have been developed to integrate glass and frame technology. By allowing for a continuous window assembly process, these two system technologies provide both labour and material cost savings. In combination with composite glass fibre-filled thermoplastic materials, these two new technologies also provide the opportunity to develop new architectural fenestration products that offer improved design performance and unique product aesthetics.