Curved, finished and complete – What you should know about architectural stretch forming

Henry Ford Int MI

Henry Ford Museum in Greenfield Village, Dearborn, Michigan, built in 1929, was renovated with large, arched top windows using stretch-formed, finished aluminum framing members 
Credit: Courtesy of Wausau Window and Wall Systems

Stretch forming was invented during the 1940s with the rise of the aerospace industry for the curving of aluminum aircraft parts to reduce weight, and thereby, fuel consumption. It expanded into car components and eventually, into the architectural industry. Architects and designers pursued new opportunities to create curved facades and building components.

The process of stretch forming is more of an art, than a science. It takes years of experience to become a skilled craftsperson that can stretch form consistent, successful, curved aluminum components for architectural projects.

Form-on-maching-WEB

Stretch forming is a metal bending process in which a lineal shape, such as an aluminum extrusion, is stretched and bent simultaneously over a form, called a die.

Stretch forming is a metal bending process in which a lineal shape, such as an aluminum extrusion, is stretched and bent simultaneously over a form, called a die. Each form is built to the required radius. These forms may be customized for a special curvature and used only once, or re-used for more popular, repeating arcs.

Opportunities with stretch forming

Stretch forming capabilities typically include portions of circles, including half-circles and eyebrows, ellipses and arched shapes. These shapes can be formed with straight leg sections at one or both ends of the curve. This method of curving eliminates several conventional fabrication and welding steps.

The variety of shapes and cross-sections that can be stretch-formed is almost unlimited – from muntin bars and panning for windows, cladding and spirals for handrails, large mullions for building envelopes to serpentine shapes for canopies. Stretch forming allows architects, designers and builders to realize forms as graceful as they are sturdy and functional.

In most cases, the stretch-formed aluminum component’s curvature is so highly precise that even intricate multi-components and snap-together curtain wall components can be formed from metal without loss of section properties or original design function.

To achieve this level of precision, the basic stretch-forming machine has two arms or carriage beams that hold multiple-positioning gripping jaws. Both ends of the extrusion are inserted into the gripper jaws and stretched to their yield point. The jaws are attached to hydraulic tension cylinders that stretch the extrusion. The arms swing by rotating on large, machined pins with bearings that allow the extrusion to wrap around and against the form. This produces perfectly contoured products, while limiting or even eliminating wrinkling inside the arc. When the wrapping is completed, the stretch force is released and the gripper jaws are opened.

operator-WEB

It takes years of experience to become a skilled craftsperson that can stretch form consistent, successful, curved aluminum components for architectural projects.

Stretch forming maintains close and consistent tolerances with excellent repeatability, and alignments of complex profiles and compound curves. There should be no visible surface marring, distortion or ripples. These benefits inherent in the stretch forming process yield a smooth and even surface. Each component must meet the project’s specifications and warranty conditions.

Structural vs. non-structural application

Aluminum has proven to be a suitable, reliable material for load-bearing structures for more than 100 years. However, the application of the parts being curved dictates the process used.

PARQ-Vancouver-all-stretchforming-(3WEB

Vancouver’s PARQ Resort and Casino features a 23,000-square-foot façade with curved corners and curtainwall details made possible with stretch-formed aluminum framing members finished in clear anodize.
Credit: Courtesy of Gamma North Corporation

After being pushed through an extrusion press, extrusions are cut and placed into a tempering oven to harden and give them structural integrity. When they are fully hardened to a T5 or T6 temper, they are too hard to curve. If the parts to be curved have been fully tempered, they will need to be annealed before curving. To do this, the part is placed in a large oven and heated to a peak temperature range of 700 to 800 degrees Fahrenheit for two to three hours.

Annealing makes the extrusion soft again—enabling it to be curved. Metal that is annealed cannot be hardened again. Once it is softened, it will remain soft. In applications where the parts are expected to carry a structural load or have another structural application, annealing generally is not an acceptable practice.

PARQ-Vancouver-all-stretchforming-(8WEBFor structural or load-bearing applications, the best practice is to have extrusions tempered to a soft state of T1, T4 or to a T52 state. Material tempered to a T1 or T4 can be bent without annealing, and can be tempered after the curving process to a T5 or T6 that is typical in structural applications. T52 is a very stable temper and can be curved without annealing, and it maintains its properties after curving without the need for additional tempering.

Painted or anodized finishes

Similar to the curving process, the end-use application of the part will determine the best practice for how curved parts should be finished. If an extrusion has been painted or anodized, and has been tempered to a T5 or T6 hardness before being curved, the parts will need to be annealed. The high heat associated with the annealing process likely will cause painted finishes to burn and anodized finishes to discolor or craze. For this reason, when parts require annealing, it is best to finish them after the curving process has been completed.

Orlando-_-ITF-WEB

Orlando International Airport’s new South Intermodal Terminal Facility showcases a segmented barrel vault skylight featuring aluminum framing that has been stretch formed, thermally improved and finished in Bright Silver 70% PVDF architectural coatings.
Credit: Greater Orlando Aviation Authority

For extrusions tempered to a T1, T4 or T52 hardness, parts can be finished before curving. However, some marring or slight damage to the finished surface should be expected due to the parts being stretched across the form’s hard surface during the curving process. Depending on the tightness of the radius, anodic coatings also may craze or discolor as a result of being curved. If the T1 or T4 tempered extrusions require oven-aged tempering after curving, the high heat will likely damage the coating.

complicated-extrusion-curve-WEB

The stretch forming process yields a smooth and even surface with each component meeting the project’s specifications and warranty conditions.

Regardless of the effect the curving process has on the finish, nearly all manufacturer and applicator warranties are voided when extrusions or brake metal are finished prior to curving. To obtain the best finish quality and to keep parts fully warranted, it is best to finish after curving—regardless of the temper of the extrusion. The American Architectural Manufacturers Association (AAMA) publishes industry-accepted specification standards for anodize and paint finishing of architectural aluminum components.

Thermally improved curves

Rolled-TB-Extrusion-web136At least one U.S. finishing and service provider also offers thermal improvement services for curved and radius, finished aluminum extrusions backed with an industry-leading warranty. The thermal improvement processes may be specified as either a full pour-and-debridge of radius material, both structural and non-structural, or a fully crimped thermal strut system. The service provider places no restrictions to the degree of curvature, and finishes may be specified in liquid paint, powder coat or anodize.

Installing the thermal barrier in the metal after it has been curved helps minimize stress on the thermal barrier and ensures performance as specified. Choosing the thermal strut system provides the additional design flexibility of dual finishing, where the interior and exterior surfaces may be finished in different colors and formulations.

Ensure that aluminum products’ thermal improvement options strictly comply with its material suppliers’ standards and AAMA’s quality assurance processing guidelines. For optimal quality and convenience, some finishers provide a single-source solution where stretch forming, thermal improvement and finishing are synchronized and retain the full warranty. When available, utilizing the finisher’s trucks also can reduce material handling and packaging to minimize the opportunity for damage, while saving costs and time.

Overhead-camera-no-curves-WEB

The basic stretch-forming machine has two arms or carriage beams that hold multiple-positioning gripping jaws. Photos courtesy of Southern Stretch Forming

 

Construction Specifier column addresses “Avoiding Color Variation with Anodize Finishes”

champagne range sample

Linetec Champagne anodize range sample

Learning from failures are some of the most difficult and most valuable lessons. Many times, failures can be avoided if we turned to those with more experience for advice. The Failures column in the January issue of Construction Specifier takes this approach issue and shares advice on “Avoiding Color Variation with Anodize Finishes.”

Authored by Linetec’s Tammy Schroeder explains the variables affecting color in the anodize process, and the challenges of achieving an exact color from run to run and load to load.

To minimize color variation, she offers five tips:

  1. Maintain metal consistency – The easiest way to ensure this is to work with one metal source/extruder per project and request all metal come from one lot of material.
  2. Do not mix aluminum alloys, as even mixed tempers will not produce uniform results – For best results, use 6063 alloys for extrusions and 5005 for flat sheet stock and fabricated parts. When structural alloy is required, 6061 and 5052 can be used, but will not give similarly acceptable results.
  3. Perform as much bending and forming as possible prior to finishing – Anodic films are very hard, and as a result most post-production bending causes the film to “craze,” which produces a series of small cracks in the finish, giving it a spider-web like appearance.
  4. Be aware of anodizing’s effect on welds – The heat developed from the welding process changes the metallurgy on nearby metal or heat-affected zones, causing localized discoloration (i.e. halo effect), so one should use the proper 5356 alloy welding wire and lowest heat possible.
  5. Select an anodizer that uses automation – This helps to reduce inconsistencies in the process.
dark bronze range sampeles

Linetec dark bronze anodize range samples

Click here to read the whole Failures column, and please contact us for personalized service in avoiding color variation and selecting the correct finish for your next project.

AAMA updates paint specifications to -17

AAMA-proud memberThe American Architectural Manufacturers Association (AAMA) regularly reviews and updates its specification documents, including for painted coatings. The association’s Aluminum Material Council’s Finishes Committee has adjusted AAMA 2603, 2604 and 2605. The most current versions are denoted as 2603-17A, 2604-17A and 2605-17A.

What’s changed?

In the updated AAMA specifications, the procedure rating the adhesion of coatings to different substrates (via tape test) has been removed. Those standards are still required to meet AAMA’s guidelines, but now Section 8.4 Peel Adhesion refers the reader to ASTM D3359 to find the details on tape testing. These AAMA specifications also reference ASTM D3359-17 for the new requirements for tapes used in adhesion testing.

Section 8.4.1 now clarifies that all tests shall be performed in the sequence they appear in the document. Connected to this, the order of testing has been changed in the specifications. References to subsections of 8.4 also have been updated in Section 5.5.

What’s remains the same?

As a member of AAMA, Linetec stays up to date on these stringent industry standards and documents. We are committed to ensuring our customers’ finishing specifications are met on every project.

For a quick refresher, here’s what to remember about AAMA 2603, 2604 and 2605:

AAMA 2603 – typical for interior specifications

Required to show only “slight” fade and chalking after one year, AAMA 2603 has no specifications for gloss retention and erosion resistance. Baked enamel (acrylic/polyester) paints should meet AAMA 2603. These painted finishes are less expensive than fluoropolymer resin-based coatings, but have poor resistance to color fading and chalking. Baked enamel coatings are harder than fluoropolymer and can be used for interior application where color retention is not required.

AAMA 2604 – an “intermediate” specification

AAMA 2604 specifications are more demanding. If a finish qualifies, then five years after its application the color must have faded no more than 5 Delta E, the chalking no greater than 8, the finish still retain 30% of its gloss and no more than 10% of it has eroded. This finish will provide good color and gloss retention. It also will provide good hardness and abrasion resistance. Painted finishes meeting this specification typically are a 50% fluoropolymer resin-based coatings and are commonly applied on aluminum storefront framing, entrances or other high-traffic areas.

AAMA 2605 – the specification for high-performance exteriors

Ten years after it has been applied, an AAMA 2605 paint will have faded no more than 5 Delta E, the chalking will be no higher than 8, 50% of its gloss will still be retained and only 10% of the film will have eroded. These finishes exhibit outstanding resistance to humidity, color change, chalk, gloss loss and chemicals. Painted finishes meeting this specification typically are a 70% fluoropolymer resin-based coatings and are commonly applied on aluminum framing and systems for monumental architectural projects.

For personalized assistance in selecting and specifying the right coating for your aluminum building products, please contact Linetec’s regional sales managers , email sales@linetec.com or call 888-717-1472.

To download the latest version of these, or any, AAMA documents, visit the AAMA Publication Store

What are common paint defects? How do you minimize them?

ILRegatta_MagellanSelecting the proper architectural paint for a project’s architectural aluminum products can ensure a visually pleasing result for years to come. Even when the correct painted coating is chosen, other factors can cause unforeseen defects to the aluminum product’s surface. Here are some common flaws that may occur, and how to correct or avoid them.

Pretreat the Metal, Dry Thoroughly

The condition of the surface to be coated plays a big role in the final product. The presence of oil, grease or other contaminants can cause adhesion failure in the paint. This could result in the topcoat peeling or flaking off. The rolling process of tubes and extrusions also can leave such a residue. For architectural finishes applied at a paint facility, baking of the paint after application is required, any reside not removed prior to painting, may run, or leach out, from beneath the coating, damaging both the paint and metal.

Your finishing applicator can avoid these flaws by pretreating the metal before paint ever touches it. Using a combination of high-power water rinses, high-temperature acid clean, etch and desmut and a chromium phosphate coating will remove most contaminants and increase the corrosion-resistance of the aluminum. A thorough drying process afterward will ensure that any remaining moisture is evaporated and that the finishers have an ideal surface on which to work.

Know Your Oil

Non-water soluble oils can lead to “fisheye” problems. Fisheye is a defect where circular depressions or “craters” appears in the finish. Most pretreatment systems are not equipped to remove these oils in advance, so if you suspect them to be present on your surface, be sure to discuss this with your finisher.

Watch for Corrosion

If the metal was stored outside before painting, it may suffer from corrosion in spots, which will stain in areas after being finished. Corrosion can be minimized or removed entirely by sanding the affected areas of the metal prior to finishing.

spray application4Apply with Care and Control

The process of paint application also can cause defects to appear later. Blisters or “pops” can appear beneath the surface of the finish after the curing process is complete, if there wasn’t enough flash off time before baking. Inconsistent coloring can occur in the paint if its application was inconsistent or the thickness of the finish varies across the surface. This will result in a coat that has color variation throughout, particularly if viewed from different angles.

These flaws can be avoided by quality-controlled, standard operating procedures for paint application on the part of the finishers. By applying the coating consistently throughout the process, the finishers can ensure less variation in the end product. A combination of automated spray equipment and painting specialists, helps to ensures an even, gradual coating application to prevent film build-up.

Send a Sample

If you are still concerned about the opportunity for defects in your architectural paint, consider sending a sample sheet of the metal that will be used to your finisher, as a mock-up, in advance. By applying the exact process that would be use for your actual project, any potential flaws can be identified and corrected in advance.

ArchResourceImage-arch resource center

Learn more about Linetec’s quality control and paint finishing services by clicking here . For personalized assistance in selecting the right coating for your aluminum building products, please contact Linetec’s regional sales managers , email sales@linetec.com or call  888-717-1472

.

 

Anodize Nickel Test

Linetec-dark-bronze-Ano-nickel-rub-2blue-web

Nickel Test

When extreme hardness is required for aluminum building components, such as in high-traffic areas, like entranceways and railings, an AAMA 611-14 anodized aluminum finish should be specified.

The hardness of anodized aluminum rivals that of the diamond.

This “Nickel Test” demonstrates why a Class I high-performance anodize coating is the perfect choice for exterior architectural applications.

Architectural Paint Data Sheet

Process  .  Warranty  .  AAMA Specifications  .  Guide Spec

Architectural-Paint-Data-Sheet-1Download complete data sheet

High-performance fluoropolymer resin-based coatings may be defined as a thin layer of plastic film containing resin, binder and pigments that is applied to the surface of an object to provide protection and a decorative organic coating. The exact composition of a particular paint coating is often complex and proprietary.

Fluoropolymer resin-based coatings provide protection against… read more

High-Performance Architectural Paint Process

Paint systems are designed to be applied over clean metal that has been properly pretreated.

Without a proper pretreatment, delamination will likely happen within the first year of installation. To prevent, and warranty against, this type of failure a chrome-type pretreatment is recommended.    read more

ArchResourceImage-LinkedInStrengths of High-Performance Paint

  • Color Retention (UV resistance)
  • Salt-spray resistance
  • Vast array of color choices
  • Paint protects and maintains the structural integrity of the aluminum
  • Field touch-up / repainting capabilities
  • Small-batch and custom color capabilities – fast and cost effective

Paint Warranty

Projects painted by Linetec, utilizing liquid PVDF resin-based coatings, are warranted by the strength of both Linetec and the paint manufacturer. Linetec’s documented testing allows us to offer warranties of 10 years, on high-performance (AAMA 2605) coatings, with confidence that your product will perform as intended.

In some cases, with prior approval and a minimal up-charge, Linetec can offer an extended warranty up to 20 years on AAMA 2605 coatings. read more

AAMA Specifications

In order to ensure the paint performance expected for an architectural / commercial application, AAMA 2605 specification should be referenced along with the paint color.

Beyond the stringent standards and regulations, Linetec offers a downloadable guide spec with specifiable differences that contribute to a project’s long life, durability and sustainability.   read more

Damaged_Anodize-McDonalds door-brickwashCleaning and Maintaining your Aluminum Finish Guide

This paper discusses the recommended care of painted and anodized finishes on architectural metal and examines three levels of concern: care and cleaning, minor repairs, and more complex refinishing.             read more

Construction Specifier shares Linetec’s anodizing expertise

Flapper2-webThe April issue of Construction Specifier features “Five Factors for Variation in and Anodize Finish,” authored by Linetec’s Tammy Schroeder.

The six-page educational article describes the anodizing process and key considerations to minimize color variation. These essential factors include:

  • Aluminum alloys and their alloying elements
  • Mixing aluminum alloys means mixed results
  • Primary vs. secondary aluminum
  • Chemistry of the anodize process
  • Surface preparations

Construction Specifications Institute members received the printed magazine, and all can view the feature online, page 62.

After April, please visit https://www.constructionspecifier.com to create a free account and access the archived digital editions.

Follow the links to learn more about Linetec’s anodize process and how we ensure the most consistent color.