Heat Soak Testing - Viracon

surface compressionRESPONSE TO NICKEL SULFIDE INCLUSIONSEven though annealed glass may have nickel sulfideinclusions present, breakage from these inclusions isunlikely due to the very low residual stresses inannealed glass. The same can be said of heatstrengthened glass which has carefully controlledsurface compression levels. ASTM C 1048, which is theindustry standard for heat treated glass, requires heatstrengthened glass to have a surface compression withinthe range of 3,500 psi to 7,500 psi. Viracon producesheat strengthened glass with a surface compression levelof 4,000 psi to 7,000 psi in order to minimize thepotential for nickel sulfide breakage.Viracon has been producing heat strengthened glass withsurface compressions within a range of 4,000 psi to7,000 psi since 1985 and within this time, has notexperienced a single incidence of spontaneous breakagein heat strengthened glass. Tempered glass, according toASTM C 1048, must have a surface compression levelgreater than 10,000 psi. As a result of the high residualstresses in tempered glass, the potential for inclusionbreakage exists.the heat soak processWhen glass is heat treated, these nickel sulphide inclusionsundergo a phase change as a function of time andtemperature. If located near the central tension core of theglass, the expansion of these inclusions may providesufficient stresses to produce spontaneous breakage. Theinclusion expands at a rate greater than the glass andliterally causes the glass to break from within.When tempered glass is heat soak tested, the glass is placedin an oven and subjected to temperatures of 550°F±50°F(290°C±10°C). Careful temperature controls must beenforced to establish when the hold time or dwell timebegins. The dwell time at peak temperature is anothercritical factor in the heat soak process. Viracon hasdetermined that a two hour dwell time is capable ofreducing the potential for spontaneous breakage in heatsoak tested glass to 5 lites per 1000 (5/1000).glass in serviceShould breakage exceed 5 lites per 1000, Viracon willreplace the glass at no charge and pay for the cost ofreplacement labor.The heat soak test provided by Viracon is offered at aminimal charge to provide greater assurance against nickelsulfide breakage. When compared to the actual cost ofreplacing broken tempered glass in the field, there issubstantial justification for the additional process charges.We realize that there are situations where tempered glasssimply must be used because of its superior strength andbreak-safe characteristics. In these situations, we feelcompelled to provide this alternative service as a meansto avoid the potentially serious occurrences ofspontaneous breakage.glass solutionsTHE LEADER IN GLASS FABRICATIONAs an international company, Viracon offers the mostcomplete range of high-performance architectural glassproducts available worldwide. We’re a company that notonly fabricates glass, we’re also a company that deliversdesign, aesthetic, budget and performance solutions forclient projects. Our success is reflected in our long-lastingclient relationships, which have given Viracon a visiblepresence on skylines around the world, including Asia,Africa, Australia, Europe, North America, South Americaand the Middle East.Since 1970, Viracon has expanded its facilities to performmore glass fabricating processes at a single site than anyother fabricator in the world. We believe in selling glasssolutions, which means helping clients explore all theoptions for each step of a project. Our complete productline includes tempered, heat-strengthened, insulating,laminated, silkscreened, spandrel, hurricane-resistant,acoustical and high-performance coated glass.At Viracon, we have been offering the heat soak test since1984 and we have not had a single incidence ofspontaneous breakage occur in heat soak tested glass.With the two hour dwell time, we are confident that wehave minimized the potential for breakage to its lowestlevel. Viracon offers a heat soaked tempered glasswarranty for breakage due to verifiable NiS inclusions.For more information on heat soak testing or additional literature, call 800-533-2080 (e-mail:glass@viracon.com).

This publication describes Viracon’s heat-soakingmethods for tempered glass products, as well as thebenefits of heat-strengthened glass to help you analyzepossible design options and applications. To obtainwarranty information, contact Viracon’s ArchitecturalInside Sales or Technical Services Department.The information contained in this publication ispresented in good faith. It is believed to be accurateat the time of publication. Viracon reserves the rightto change product specifications without notice andwithout incurring obligation.www.viracon.com800 Park DriveOwatonna, MN 55060507.451.9555800.533.2080 (Toll Free)507.444.3555 (Within the U.S.A.)507.451.2178 (Outside the U.S.A.)E-Mail: glass@viracon.comCopyright © 2003 Viracon. All Rights Reserved.VTT-010C VRJC0104