Volume 40, Issue 6 June 2005
Up to the Test
Quality Control Basics for Laminated Glass
by Mark P. Gold
When it comes to starting a quality control laboratory or taking over an existing program, companies often ask for recommendations to support this effort. There are two levels of quality control testing that need to be addressed in any manufacturing endeavor: process control and product control. Both are equally important. Process control normally takes the form of statistical evaluation of operating conditions and equipment. Product quality control involves testing a particular property or performance of the product at a frequency that is statistically significant. This article will answer the questions of why, what and how to perform product testing of laminated glass.
In the laminated glass industry, quality control testing often is done because the product’s performance is mandated by codes or regulations. Fabricators throughout the industry may implement a quality control program for a variety of reasons: the need to maintain process integrity, assuring customer satisfaction and verifying product application performances. However, within the laminated glass business, it is equally important to implement a rigorous quality control program because the end users often insist on proof that these products meet minimum performance levels. An appropriately-designed and implemented quality control program can not only provide the needed validation for a product’s use in a specific market, but can also protect against liability claims.
Most code-driven product applications require the periodic testing of laminated glass products to assure continual compliance with code required performances.
Once a decision has been made to launch an internal testing program, the next step is determining the necessary testing. The following are primary reasons for deciding which tests to conduct:
• Internal analysis;
• Customer direction; and
• Regulatory or code requirements.
Testing based on internal issues responds to known manufacturing process variables and test performance properties that are most effected by process variations. For example, if your process allows glass edge alignment variations over time, you might implement testing that responds to lay-up equipment concerns.
Customer-driven tests focus on product quality issues that customers often consider critical for use, such as laminate dimensions. In such a situation, several millimeters of size variation may not affect product performance but may be significant relative to framing or other end-user requirement.
Regulatory or code-based tests are often the most critical product quality control components because the performance parameters validated by these tests usually are the reason the product was specified. When it comes to selecting the tests to implement, as well as the sample preparation protocols and test procedures, the only acceptable guidance should be determined through standards or codes. Although relying on the standard or code for determining the test protocol sounds logical and straightforward, it is often not easy.
Such an effort requires identifying and locating the appropriate code or standard. In architectural glazing, there are numerous codes and standards that may apply (see sidebar above right). Usually the market application will help identify the code requirement. (ASTM International’s standards and test procedures are available for download from www.ASTM.org. These documents are primary sources for test equipment design and procedures for a range of laminated glass testing.)
Safety Glazing Standards
The two most broadly specified architectural safety glazing performance standards are ANSI Z97.1 and the Consumer Products Safety Commission (CPSC) 16 CFR 1201. Though they are different, there are commonalities between the two.
ANSI Z97.1 is a voluntary test method for safety glazing in buildings that tests for impact and durability. The durability testing requires both a short term test (conducted by boiling a laminate for two hours) and a longer term aging test. The CPSC test details the federally mandated requirements for safety glazing in doors and also requires impact and durability testing.
Specialized product performance requirements from the now well-known “hurricane test” (ASTM E 1996) to the lesser known bullet resistance (UL-972), high security (ASTM F 1233) or blast testing (ASTM F 1642) also have a component requiring impact testing.
A Closer Look
In examining the many laminated glass test procedures and performance requirements, it is apparent that durability and impact performance testing are common to most. In response to these code-driven requirements, such testing is a must for any laminated glass quality control laboratory program.
Durability testing is used to simulate the long-term exposure of the laminate. The boil test evaluates whether or not air was removed sufficiently from the laminate prior to autoclaving, thereby assuring bubbles will not form during the life of the product. This test requires boiling a sample of the laminate in water for two hours. The laminate is then inspected for bubble formation. Any bubbles that appear more than a ˝ inch from an edge or a crack constitutes a boil failure, indicating that the pre-press de-air process was likely insufficient to guarantee long-term product durability. More extensive accelerated durability testing can be done by exposure to artificial light in equipment such as weather-o-meters, fade-o-meters or other accelerated weathering equipment.
Impact testing predicts the penetration resistance of the laminates. Insufficient penetration resistance usually indicates incorrect interlayer to glass adhesion. The test requirements, whether impacted from 12 or 48 inches with the pendulum impact or with the 5-pound ball drop, are detailed in the test protocols. Because impact requirements are a portion of most performance requirements, quality control test labs should be equipped to perform some type of product performance impact.
When to Outsource
Heavy financial investments are not necessary to implement this testing. For example, a second story stairwell, or even a safely secured ladder, can provide sufficient elevation for launching the 5-pound ball drop test.
The more costly, difficult or time-consuming tests can often be contracted to commercial laboratories that, in addition to providing product performance testing, can also provide third-party certification. However, if quality control tests are outsourced, internal testing that correlates to the external test results should still be done to verify product consistency.
As a final note, understanding the factors that influence test results is as important as properly identifying and performing the tests. All too often non-conforming test results are traced to the test itself, rather than to the product. In impact testing, for example, sample temperature at impact can strongly affect the test results, so testing at the specified temperature is critical to the accuracy of the test results.
Although there are many properties for which laminated glass should be tested, every quality control program needs to focus on testing those performance parameters that are required and predict fitness for use. Most standards require impact and durability testing so inclusion of these tests is a minimal requirement when setting up a quality control program.
Mark Gold is the manager of applications and new business development for Solutia’s Saflex business group. He is a former quality control lab supervisor and is a member of the SAE Safety Glazing Standards Committee.
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