Volume 7, Issue 9 - October 2006

Choose Wisely
There Are Several Factors to Consider When Selecting IG Production Lines
by Kevin Zuege

Insulating glass (IG) production lines come in varied layouts and orientations—no two are exactly alike. A vertical line may work best for a glass wholesaler producing a variety of large commercial and residential IG units. Alternatively, a horizontal line may be best for door and window producers looking for high volume when producing small- to medium-sized units.

Determining the best layout involves consideration of numerous other variables in addition to insulating glass unit size. Fabricators need to consider the required throughput, staff availability, line layout, size, shape, cost, materials, labor efficiency, floor space, level of automation and a multitude of other inputs.

A general rule of thumb in system design is to add as many viable processes to the line as possible to optimize efficiency. A high level of inline processing capabilities allows glass to move through the system as far as possible before any batching occurs. Ideally, the glass could move all the way through the production line—from washing to final formation as a sealed, gas-filled IG unit or possibly unit glazing with certain non-curing IG systems—before being batched for transportation. The goal is a one-piece flow system that also has reasonable cycle times, minimal waste and high productivity.

A fabricator’s ability to achieve true one-piece flow, or at least a variant that minimizes batching, rests on optimization of a number of important variables specific to his operation.

Layout Orientations
IG lines are constructed in three basic layout orientations: horizontal, vertical and hybrid configurations, which may combine horizontal and vertical components.

Each system orientation has its place. The best system for an operation depends completely on its company’s business–whether it is a commercial IG wholesaler or a window fabricator. The difference in classifications creates a dichotomy in production line orientations that follows a distinct geographical pattern.

For example, the North American window market is comprised predominantly of door and window fabricators producing residential single-hung and double-hung windows. These fabricators make relatively small IG units with dimensions averaging from less than 26 inches to 40 inches and glass thicknesses of .093 or .125 inches. Small IG units are fabricated in horizontal, vertical and hybrid systems. However, smaller units can be processed at the highest efficiency on horizontal production equipment due to the higher capacity of parallel processing, which allows two streams of glass to run rapidly through the same equipment in tandem. Because of this efficiency, horizontal lines currently dominate the North American market. 

In Europe, where large primary and independent IG wholesalers dominate the IG supply chain and relatively few window fabricators produce their own IG units (which are sized larger), the opposite is true. More than 85 percent of the market uses vertical lines. Further, glass wholesalers process a steady mix of commercial and residential IG units on the same production lines. Vertical lines allow for easier handling of these larger, heavier glass lites. The same is true for patio doors and picture windows in both Europe and North America. However, high-volume production capacity is limited compared to two-stream horizontal lines.

Hybrid lines are finding a niche in both North America and Europe. These vertical lines allow for parallel processing of glass combined with either horizontal or vertical spacer application.

System Flow
The flow of glass in the form of serial or parallel processing is a primary indicator of a system’s throughput potential. System productivity levels can vary greatly among these processing capabilities for each line orientation. 

Serial processing lines are only capable of sending one stream of glass through the production line at a time and can be found in vertical and horizontal configurations. The lites flow either in “top, bottom” or “bottom, top” sequences, depending on the set-up.

This constraint may increase IG unit cycle times between 5 seconds and 10 seconds per unit compared to other lines. Glass lites move through the system directly in line, and serial feeding cannot be broken.

Parallel processing permits two streams of glass—the tops and bottoms of the IG units—to flow through the line in tandem. While one lite is being applied with spacer material, its top lite bypasses the application station to the topping station in anticipation of receiving the applied lite.

Parallel processing exists on horizontal and hybrid lines, but horizontal lines offer more opportunities for highly efficient production. This is possible due to a shared application bed that allows for near continuous flow of glass. 

Hybrid processing lines have a separate flow area for the topping lite that moves the lite in a vertical orientation behind the application station while its mate is applied with spacer material. The bypass allows the top lite to keep moving while the applied lite is stationary.

Automation Levels
Adding degrees of automation to a line can further augment efficiency and reduce labor costs. The European market uses a high percentage of automated vertical lines. North America is following closely behind with increased installation of automated vertical lines as well as automated horizontal lines, which offer high-efficiency production of smaller IG unit sizes.

Equipment providers offer a variety of options for manual, semi-automated and fully automated IG production lines. Efficiencies can be optimized in relation to spacer application, muntin placement, gas filling and dual sealing.

Spacer Application. Efficient application of flexible and rigid spacers is a matter of choosing the appropriate level of automation for a particular need.

Horizontal spacer application on horizontal and hybrid lines may be performed manually or with automation. Vertical application usually requires full automation, although rigid spacer bars applied on vertical systems must usually be hand-fed into the application station, which increases labor. Application of flexible spacers in a vertical orientation is quite rare, and has an insignificant share of the market.

Grid Placement. Muntin bar placement traditionally is a manual process, but automated applications do exist on a limited basis. Some production lines provide position assistance to ensure accurate grid alignment. 

Another effective grid assistance tool is found on automated lines using rigid spacer bars. These lines punch a notch or hole directly into the spacer bar, depending on the end clip being used to attach the grid.

Alternative methods for grid placement, such as projection lasers and parallel placement, are less effective and have a higher potential for human error than systems that use CNC control to mark or punch the spacer at an identified perimeter location. As operators place grids, the beam may be obstructed, causing difficulties for proper alignment. Manually-based parallel placement relies on using the application table grid layout to position the glass and muntins. Glass must be aligned precisely and squared with the table grid for proper muntin alignment.

Gas Filling. Highly productive systems offer gas processing cycle times in the range of 20 seconds to 28 seconds. All highly productive, one-piece flow gas filling systems are vertical and rely on two basic methods of filling, “cryogenic fluid” filling and “turbulent flow” filling. The turbulent flow filling method uses more gas and has higher unit cycle times compared to the cryogenic gas filling method. Batch systems make up the balance in use.

Dual Sealing. An increasing trend in IG production is adding a curing sealant around the perimeter of the unit. This additional layer of sealant material increases the moisture vapor transmission path and provides additional stability.

Most automated-dual sealing equipment is vertical in nature. Therefore, IG manufacturers interested in dual-sealing methods are likely candidates for vertical or hybrid lines to keep the benefits of one-piece flow.

Line Footprints/Floor Space
Available plant space–and its physical layout–may also be a determining factor for an appropriate IG production line layout.

Horizontal lines are typically blocky and short. Vertical systems are linear and long. A comparison of square footage may be relatively similar between two layouts with similar capabilities.

A long, narrow plant may be better suited to a vertical line. However, it is important to note that while several vertical stations can be placed against a wall, other ancillary stations may extend out from the wall and eat up floor space. For instance, a rigid spacer bar operation will require stations for spacer cutting and bending, desiccant filling, PIB extrusion and application, an overhead conveyer and spacer storage areas, all of which change the linear layout to become blockier. Flexibility and thorough planning is key.

In IG production, there is a strong desire to minimize human intervention. This is achieved through the progressive use of automation in system designs. The wide variety of available manufacturing methods enables manufacturers to use as few as one or two operators on a line, while some systems require in excess of ten operators.

Flexible spacer lines require between two and seven operators, while rigid spacer lines average five to 15 operators. Labor efficiency is maximized on production lines that produce high units per man-hour (UPMH).

Capital Investment
IG production lines can range anywhere from $100,000 to more than $2 million (USD). As a fabricator selects a base line for investment, he should work with his equipment provider to discuss current and future needs.

Kevin Zuege serves as director of technical services for Truseal Technologies Inc. in Beachwood, Ohio. 

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