Skylight Frame Materials
- Basically an elaborate "pump" in the form of a large screw.
- A dry powder (PVC) is fed into the Feed section of the extruder barrel.
- The "Flights" or wings of the extruder screw force the material forward while applying pressure
and heat from the Heating Bands.
- As the material moves through the Compression Zone, additional heat and pressure is applied until the PVC
reaches a fusion point.
- The Vacuum Port draws out any moisture from the material in a vapor form. If any moisture remained, it would
cause bubbles (creating a weak frame for impacts) or blister during the extrusion process.
- The product then moves into the Metering Zone where even more heat and pressure is applied - at this point,
4,000 psi of pressure at 385° forces the PVC through the die.
The die is what gives the vinyl its shape. The molten material is forced through a series of dies that gradually create the final shape. They
are much wider and more complex than a "Playdough" die, or pasta die, even though these are often used as a reference as to how this
process is done. Dies are produced in-house or by contractor at an extrusion facility's tool shop. The material flows through the die at a rate
of up to 1000 lb of PVC vinyl per hour
The calibrators are where the material becomes solid. The calibrators hold the material's shape until it's stable and cooled. A vacuum actually
pulls the material against the calibrator "wall" to maintain the shape. A "puller" down the extrusion line is now pulling
the solid shape through the calibrator at the precise speed at which the molten material leaves the die "upstream." The material is
then cut to length.
Architectural Grade 6063 T5 Aluminum and sustainability
Aluminum's inherently sustainable characteristics combined with the extrusion process make extruded aluminum the green
building industry's material of choice for now and the future. Green building isn’t just a catchphrase; it implies a vital planet-preserving
future for the commercial and residential building-and-construction industries. Architects and builders are aggressively pursuing advanced technologies
based on sustainable design principles. Such tenets employ energy conservation, eco-friendly materials choices, and extensive reuse and recycling
practices to create environmentally responsible buildings that are more productive, healthier, and profitable places to live and work. Advanced
green design and building technologies are proving highly effective in lowering construction costs and reducing operating expenses. According
to the U.S. Departments of Energy and Transportation, buildings drain a staggering 39 percent of the nation’s total energy, while all transportation--including
cars--consumes 27 percent. Green buildings are rapidly gaining in acceptance, as public awareness grows and the global community develops alternative
energy sources and intensifies its efforts to ease global climate change. Aluminum, one of the most abundant elements in the earth’s crust,
is an ideal natural materials choice for sustainable buildings – not just in new construction, but also in retrofitting older buildings to improve
their energy performance. Aluminum is specified by architects for curtainwall systems, windows and doors, reflective “cool” roofing, solar-panel
framing, skylight framing, reflectors for interior lighting grids, elevator housing/framing, atriums, entryways, walkways, sun rooms, and heat
exchangers for air conditioning systems in both commercial and residential applications. Aluminum has always been a green building material,
and continues to offer key attributes that architects and builders want in a sustainable building, namely durability throughout a long life
cycle, structural strength in terms of elastic modulus/stiffness, and importantly, recyclability. At the end-of-life stage in a building, aluminum
is 100-percent recyclable, and may be reused in building components without any loss in quality. Thousands of green commercial, office, and
residential structures using aluminum emit less carbon dioxide, and are boosting the U.S. economy in a tangible way. The construction market
constitutes 14.2 percent of the U.S. GDP. And it is important to note that aluminum can be recycled repeatedly without losing its integrity.
From a green design perspective, aluminum’s reduced cost over a longer life cycle offers architects a viable economical choice. A whole-buildings
approach allows flexibility for balancing U-factors; for example, thermally-broken aluminum window frames may be used in combination with increased
insulation, HVAC efficiency, ambient lighting, high-tech glazing, etc., providing more options in designing the building envelope. Aluminum
resists the ravages of time, temperature, corrosion, humidity, and warping, adding to its incredibly long life cycle. Extruded-aluminum-framed
windows and Skylights with thermal barriers effectively insulate against condensation and are rigid and stable, operating with minimal maintenance
and a tight fit. Extruded aluminum alloys accept durable anodized finishes, which are inert materials that are not combustible and pose no health
risks. Energy efficiency in cooling buildings is also being redefined by all-aluminum microchannel heat exchangers used in commercial and residential
air conditioning units. This advanced technology delivers greater cooling capacity in a same-sized unit, compared to traditional copper-tube/aluminum-fin
technology. Microchannel heat exchangers employ a metallurgical interface with greater thermal efficiency and corrosion resistance.
The aluminum extrusion industry is actively engaging LEED-certified architects and builders, seeking to make extruded aluminum a priority materials
choice for a vast array of commercial applications. Aluminum is extremely light weight in relation to its strength. This allows builders to
do more with less material. It is aesthetically flexible, allowing numerous finish and color opportunities. Aluminum is inherently recyclable
and can be taken from the buildings in the future and brought back into the resource stream. Sustainability is now the investment of choice,
and green building products give an exceptionally good return on investment.” Earth-friendly extruded aluminum has the inherent characteristics
essential to sustainable construction.
This diagram shows the basic steps involved in extruding an aluminum profile. Process explained below
Aluminum Extrusion Process Overview
The aluminum extrusion process really begins with the design process, for it is the design of the product--based on its intended use--that determines
many of the ultimate production parameters. Questions regarding machinability, finishing, and environment of use will lead to the choice of
alloy to be extruded. The function of the profile will determine the design of its form and, hence, the design of the die that shapes it. Once
the design questions have been answered, the actual extrusion process begins with billet, the aluminum material from which profiles are extruded.
The billet must be softened by heat prior to extrusion. The heated billet is placed into the extrusion press, a powerful hydraulic device wherein
a ram pushes a dummy block that forces the softened metal through a precision opening, known as a die, to produce the desired shape.
Diagram of a typical horizontal hydraulic extrusion press; the direction of extrusion here is from left to right.
That is a simplified description of the process known as direct extrusion, which is the most common method in use today. Indirect extrusion
is a similar process, but with some important differences. In the direct extrusion process, the die is stationary and the ram forces the alloy
through the opening in the die. In the indirect process, the die is contained within the hollow ram, which moves into the stationary billet
from one end, forcing the metal to flow into the ram, acquiring the shape of the die as it does so. The extrusion process has been likened to
squeezing toothpaste out of a tube. When pressure is applied at the closed end, the paste is forced to flow through the open end, accepting
the round shape of the opening as it emerges. If the opening is flattened, the paste will emerge as a flat ribbon. Complex shapes can be produced
by complex openings. Bakers, for example, use a collection of shaped nozzles to decorate cakes with fancy bands of icing. They’re producing
extruded shapes. You can squeeze aluminum through a shaped opening, however, with the aid of a powerful hydraulic
press, producing an incredible variety of useful products with almost any shape imaginable.
These photos show a new length of extrudate; just emerging from the press (left)
and the production of a profile in progress (right).
Billet is the starting stock for the extrusion operation. Extrusion billet may be a solid or hollow form, commonly cylindrical, and is the length
charged into the extrusion press container. It is usually a cast product but may be a wrought product or powder compact. Often it is cut from
a longer length of alloyed aluminum, known as a log. Alloys are metals composed of more than one metallic element. Aluminum extrusion alloys
contain small amounts (usually less than five percent) of elements such as copper, manganese, silicon, magnesium, or zinc. These alloying elements
enhance the natural properties of aluminum and influence the extrusion process. Billet length varies according to a number of factors, including
the desired length of the finished profile, the extrusion ratio, the length of the runout, and the requirements of the extrusion press. Standard
lengths may run from about 26 inches (660 mm) up to 72 inches (1,830 mm). The outside diameter may range from 3 inches (76 mm) to 33 inches
(838 mm); 6-inch (155 mm) to 9-inch (228 mm) diameters are the most common. Once the shape of the final product has been identified, the proper
alloy selected, and the die prepared, to make ready for the actual extrusion process, the billet and extrusion tools are preheated. During extrusion,
the billet is still solid, but has been softened in a heating furnace. The melting point of aluminum varies with the purity of the metal, but
is approximately 1,220° Fahrenheit (660° Centigrade). Extrusion operations typically take place with billet heated to temperatures in excess
of 700°F (375°C), and--depending upon the alloy being extruded--as high as 930°F (500°C). The actual extrusion process begins when the ram starts
applying pressure to the billet within the container. Various hydraulic press designs are capable of exerting anywhere from 100 tons to 15,000
tons of pressure. This pressure capacity of a press determines how large an extrusion it can produce. The extrusion size is measured by its
longest cross-sectional dimension, sometimes referred to as its fit within a circumscribing circle diameter (CCD).As pressure is first applied,
the billet is crushed against the die, becoming shorter and wider until its expansion is restricted by full contact with the container walls.
Then, as the pressure increases, the soft (but still solid) metal has no place else to go and begins to squeeze out through the shaped orifice
of the die to emerge on the other side as a fully formed profile.
About 10 percent of the billet, including its outer skin, is left behind in the container. The completed extrusion is cut off at the die and the remainder of the metal is removed to
be recycled. After it leaves the die, the still-hot extrusion may be quenched, mechanically treated, and aged. Extrusion rates vary, depending
on the alloy used and the shape of the die. A hard alloy, given a complex shape, may emerge from the press as slowly as one or two feet per
minute; a soft alloy taking on a simple shape may be extruded at a rate of 180 feet per minute, or even faster. Depending on billet size and
die opening, a continuous extrusion as much as 200 feet long may be produced with each stroke of the press. The newly-formed extrusion is supported
on a runout conveyor as it leaves the press. Depending on the alloy, the extrusion is cooled after emerging from the die, either naturally or
through the use of air or water quenches. This is a critical step to ensure sufficient metallurgical properties after aging. The extrusion is
then transferred to a cooling table.
End view examples of various aluminum frame extrusions
A stretcher and/or straightener may be employed, after the profile has been quenched (cooled) to straighten the extrusion and correct any twisting
that may have occurred subsequent to extrusion. (The stretcher may also be used to impart cold work to the extrusion.) Conveyors feed the work
to the saw.
Typically, a finish cut saw is used to cut the profile to the specified commercial length. Circular saws are the most common in use today and
are generally similar to a radial arm saw that cuts across the profile at a perpendicular angle to the length of the extrusion. Other saws may
swing down onto the profile (like a power miter saw), or may operate more like a table saw, with the circular blade rising up to make the cut,
then dropping down below the table for the return pass.A typical, circular, finish cut saw may be 16 - 20 inches in diameter, with more than
a hundred carbide-tipped teeth. Larger saws are used for larger-diameter presses. Lubricated saws are equipped with delivery systems that feed
the lubricant through the teeth of the saw for optimal efficiency and cut surface. Automatic devices clamp profiles in place for sawing. Saw
chips are collected for later recycling.
Zinc Plated Galvanized Steel
The sheet steel used for manufacturing Skylight frames and flashing must abide by the following specifications: ASTM A36M, as with most Carbon
steels, A36 has a density of 0.28 lbm/cu in (7.8 g/cm3). A36 steel in plates with a thickness of less than 8 in (203 mm)
has a minimum yield strength of 36,000 psi (250 MPa) and ultimate tensile strength of 58,000–80,000 psi (400–550 MPa). Young's modulus
for A36 steel is 29×106 psi (200 GPa). Plates thicker than 8 in have a 32,000 psi (220 MPa) yield strength and the same ultimate tensile
strength. A36 is a standard carbon steel, without advanced alloying. Carbon steel, also called plain-carbon steel is steel where the main interstitial
alloying constituent is carbon. The American Iron and Steel Institute (AISI) defines carbon steel as: "Steel is considered to be carbon
steel when no minimum content is specified or required for chromium, cobalt, niobium, molybdenum, nickel, titanium, tungsten, vanadium or zirconium,
or any other element to be added to obtain a desired alloying effect; when the specified minimum for copper does not exceed 0.40 percent; or
when the maximum content specified for any of the following elements does not exceed the percentages noted: manganese 1.65, silicon 0.60, copper
This steel must also follow guidelines of ASTM A123 shown below.
The article is immersed in a bath of molten zinc between 815-850 F (435-455 C). During galvanizing, the zinc metallurgically bonds to the steel,
creating a series of highly abrasion-resistant zinc-iron alloy layers, commonly topped by a layer of impact-resistant pure zinc.
Example of a hot dip Galvanics bath
Galvanizing forms a metallurgical bond between the zinc and the underlying steel or iron, creating a barrier that is part of the metal itself.
During galvanizing, the molten zinc reacts with the surface of the steel or iron article to form a series of zinc/iron alloy layers. The figure
below is a photomicrograph of a galvanized steel coating cross-section and shows a typical coating microstructure consisting of three alloy
layers and a layer of pure metallic zinc. The hot-dip galvanized coating is intended for products fabricated into their final shape that will
be exposed to corrosive environmental conditions. Once a product has been hot-dip galvanized, any further fabrication, which very rarely occurs,
may have negative effects on the corrosion protection of the coating. The coating grade is defined as the required thickness of the coating
and is given in microns. Zinc coating thickness table is on the next page.
ASTM A 123/A 123M Requirements below
TABLE 2 Coating Thickness Grade*
* The values in micrometers (µm) are based on the Coating Grade. The other values are based on conversions using the following formulas: mils - µm x 0.03937; oz/ft² - µm x 0.02316; g/m² - µm x 7.067.
- Coating Thickness / Weight – dependent upon material category and steel thickness
- Finish – continuous, smooth, uniform
- Appearance – free from uncoated areas, blisters, flux deposits and gross dross inclusions as well as having no heavy zinc deposits
that interfere with intended use
- Adherence – the entire coating should have a strong adherence throughout the service life of galvanized steel