Heat-Treated Glass
Manko is equipped with state-of-the-art tempering furnaces in each fabrication facility to provide large volumes of high quality glass. These furnaces incorporate modern convection technologies with ceramic rollers to provide precise uniform temperature controls to minimize distortions. Manko has the capability of heat-treating several different thicknesses of glass, ranging from 1/8” to 5/8".
The heat-treating process is broken down into four simple steps. First, begin by cleaning the outside edges of the annealed glass, if the glass is fabricated with a clean “machine-finish” edge already, it will bypass seaming. However, if not, the glass will need to have the edges seamed, this process helps eliminate unequal temperatures around the edge of the glass while in the furnace, which helps reduce glass breakage. After seaming, the glass moves to the washer, which cleans and removes any particles on the surface of the glass. The glass is then automatically moved to the furnace. In the furnace, the glass is heated to approximately 1,200° Fahrenheit, oscillating back and forth, for a specific period of time depending on the thickness, color and properties of the glass. Immediately following the furnace, the glass is automatically moved to the quench. The quench rapidly forces air onto both surfaces of the glass, cooling it quickly. This process puts the surface of the glass in a state of high compression and the central core in a tension state. The tension (core) area makes up the middle 60% of the thickness of the glass, the compression area encompasses the remaining 20% of the outer edges of the glass. It is in the quench where the end product becomes either fully tempered or heat-strengthened, depending on the amount of cool air forced onto the glass.
The heat-treating process is broken down into four simple steps. First, begin by cleaning the outside edges of the annealed glass, if the glass is fabricated with a clean “machine-finish” edge already, it will bypass seaming. However, if not, the glass will need to have the edges seamed, this process helps eliminate unequal temperatures around the edge of the glass while in the furnace, which helps reduce glass breakage. After seaming, the glass moves to the washer, which cleans and removes any particles on the surface of the glass. The glass is then automatically moved to the furnace. In the furnace, the glass is heated to approximately 1,200° Fahrenheit, oscillating back and forth, for a specific period of time depending on the thickness, color and properties of the glass. Immediately following the furnace, the glass is automatically moved to the quench. The quench rapidly forces air onto both surfaces of the glass, cooling it quickly. This process puts the surface of the glass in a state of high compression and the central core in a tension state. The tension (core) area makes up the middle 60% of the thickness of the glass, the compression area encompasses the remaining 20% of the outer edges of the glass. It is in the quench where the end product becomes either fully tempered or heat-strengthened, depending on the amount of cool air forced onto the glass.
All heat-treated glass will contain some level of distortion, including bowing, warping, and visual distortion. Many factors go into how much distortion will be apparent, including but not limited to the quality of the production process, project atmosphere conditions, as well as project installation conditions.
Fully Tempered glass is typically four times stronger than annealed glass with the same properties and can qualify as safety glazing. When broken, fully tempered glass breaks into small pieces, reducing the risk of serious cutting or piercing. In order for the product to meet safety glazing, the ten largest particles taken from a broken fully tempered lite of glass must weigh no more than the equivalent weight of 10 sq. in. of the original glass. Fully tempered glass is required to have either a minimum surface compression of 10,000psi or an edge compression of not less than 9,700 psi.
Heat-strengthened glass is typically two times stronger than annealed glass with the same properties. The break pattern of heat-strengthened glass varies by size and shape depending on the amount of surface and edge compression. The larger the compression psi is, the smaller the break particles are. By requirement, the surface compression of heat-strengthened glass is between 3,500 psi and 7,500 psi, however it does not meet safety glazing requirements.
Architectural glass fabricators should be consulted to confirm the ability of the specific glass construction to meet design parameters. Thermal and Mechanical stresses in glass, as well as glass deflection, must be reviewed to ensure a successful application. Typically, it is recommended that glass deflection of 1 inch (25 mm) or more be called to attention of design professionals and building owners for consideration of occupant comfort levels. Some glazing applications require thicker glass substrates in order to limit deflection.
When viewing heat-treated glass in certain conditions, a pattern of iridescent spots or darkish shadows may become visible this is called the strain or quench pattern of the glass and is related to the stresses introduced in the cooling process. Sharp angles, polarized light, thicker glass and applied coatings increase the visibility of the pattern.
Inherent visible characteristics are accentuated by the application of coatings to the glass. The visibility of distortion in solar control or reflective coated glass is greatly affected by surrounding conditions. If the reflected image is of a uniform blue sky the glass will appear extremely flat. If the same lite of glass is reflecting the multiple gridlines of an adjacent building, the reflection may appear to be distorted. viewing full size mock-ups, under typical job conditions and surrounding landscape, is highly recommended for user evaluation and expectation of reflective distortion.
*Information provided by GANA Glazing Manual
Manko’s heat-treated glass meets the following code requirements:
ASTM C 1048 – Standard Specification for Heat-Treated Flat Glass – Kind HS, Kind FT Coated and Uncoated Glass
ANSI Z97.1 – American National Standard for Safety Glazing Materials Used in Buildings – Safety Performance Specifications Method of Test
CPSC 16 CFR 1201 – Safety Standard for Architectural Glazing Materials
ASTM C 1048 – Standard Specification for Heat-Treated Flat Glass – Kind HS, Kind FT Coated and Uncoated Glass
ANSI Z97.1 – American National Standard for Safety Glazing Materials Used in Buildings – Safety Performance Specifications Method of Test
CPSC 16 CFR 1201 – Safety Standard for Architectural Glazing Materials
