TEMPERATURE MEASUREMENTS IN TEMPERING

Tempered glass – sometimes called toughened or – is glass which has been heat-treated and then rapidly cooled, in a controlled manner, in an air quench section. This process makes the glass much more resilient than plain flat glass. Producing tempered glass free of visual distortions requires a uniform temperature to be achieved across the whole surface of each glass lite. This requires accurate temperature monitoring across the entire width of the glass. USES OF TEMPERED GLASS WHY IS GLASS TEMPERED?

AUTOMOTIVE WINDOWS

PLAIN GLASS TEMPERED APPLIANCES Plain glass is easily broken and breaks glass, which inflicts replacement SUCH AS OVEN DOORS into shards which can cause serious costs on suppliers and affects their injury. reputation for providing a quality AND REFRIGERATOR FOR BUILDINGS product. Tempered glass is much harder to break and, if broken, it produces small, Distortions are particularly noticeable SHELVES harmless dice-shaped pieces. This in architectural glass, which is also one makes tempered glass ideally suited of the largest markets for tempered Over-extending the heating to applications where human safety is glass. time may reduce breakages, an issue. but can have a negative effect The only way to ensure the glass is free on the glass quality. However, if the process is not properly of visual deformities is to ensure the monitored and controlled, the heat same uniform temperature is reached treatment involved in tempering can over the entire surface of each lite. introduce visual distortions. GLASS DOORS AND Generally, customers reject distorted SHOWER DOORS DISTORTED DISTORTION FREE

MOBILE PHONE AND GLASS COOKWARE TABLET SCREENS

02 Glass tempering safety application note WWW.AMETEK-LAND.COM 03 THE TEMPERING PROCESS AN ACCURATE SURFACE MEASUREMENT Before tempering, the glass must be standard is 620oC). It then undergoes go into compression, providing the cut to the desired size, as operations rapid, high-pressure cooling through tempered glass with its strength. such as etching or edging after the blasts from air nozzles. Ideally, each sheet of glass should heat treatment can result in strength This process, called quenching, lasts have minimal temperature variation. reductions or product failure. just seconds and cools the outer This provides the same even The glass is examined for surface of the glass much more quickly across the glass, ensuring distortion- imperfections, then the sharp edges than the centre. As the centre cools, free viewing. are removed by an abrasive, such as it tries to pull back from the outer A thermal image of each lite as it enters sandpaper, and the glass is washed. surfaces. the quench allows adjustment of the Next, the glass is heated in a tempering The result is that the centre remains heating profile to maintain a uniform oven to more than 600oC (the industry in tension, while the outer surfaces glass temperature.

LOW EMISSIVITY THERMAL IMAGES INFRARED MEASUREMENT TECHNOLOGY These thermal images show Low Emissivity (Low E) glass lites using the AMETEK Land measurement system, The gap between the furnace exit and visible radiation from entering the compensation value cannot be used o the air quench entrance can be very building. It also retains existing heat for all glass types. with a temperature scale set to 620 C, LOW EMISSIVITY o narrow, often as small as 10 cm, so a inside the building, reducing energy ±5 C. Measurements within this range Using an imaging system with linescanner is the ideal instrument to costs for the end user. are shown in green. Hotter areas are highly stable electronics and use at this point. yellow or red, while colder areas are blue. Low E glass does not emit much of sufficient gain to compensate for The lites were travelling from left to Glass lites entering the tempering its energy, and there are hundreds of Low E glass is essential to achieve right. Most of the glass is close to furnace are often a mixture of different grades, all with different accurate compensated temperature 620 oC and appears green, but the sizes and are randomly placed. A emissivity values, so a single measurement of each batch. leading edge is yellow, closer to 640 oC. linescanner such as the AMETEK Land Towards the tail in the middle there is a LSP-HD 50 can easily monitor the glass LSP-HD 50 colder blue area at around 610 oC. This as it passes through the narrow gap, is sufficient variation to cause concern scanning continuously across all the for a tempered glass manufacturer. THERMAL IMAGES OF LOW E GLASS glass lites, typically at 150 scans per second. In this set of images, a much more on the hotter side of the furnace will Single-spot thermometers are not even temperature profile has been draw heat away from this area, evening suited to this measurement, as they achieved, though as the yellow colour out the temperature. may miss the glass lites and cannot EVEN TEMPERATURE PROFILE o indicates, it is around 15 C higher. This monitor for a uniform temperature Batch timing and other thermal may also cause concern. across the width of the glass. controls can also be adjusted to Thermal images produced for each reliably produce lites with a uniform Two or three temperature bias sensors – batch of lites effectively provide a thermal profile within the required typically the AMETEK Land SOLOnet SN5 SOLOnet temperature profile of the furnace. temperature range. – may be installed on the underside of Trends from batch to batch can reveal the process to provide a compensating By measuring the true temperature of if one side of the furnace is running measurement for any surface coating on Low E glass, the thermal profile of the cooler than the other. the glass. furnace can thus be controlled in an Changing the distribution of lites is often informed way, ensuring the consistent In recent years, Low E glass has been the simplest way to adjust the furnace production of high-quality, distortion- increasingly used for windows. Low E THERMAL IMAGES OF LOW E GLASS temperature profile – placing larger lites free glass. glass prevents much of the sun’s non- LSP-HD 50 MOUNTED ABOVE THE GAP BETWEEN THE FURNACE EXIT AND BEFORE THE QUENCH

04 Glass tempering safety application note WWW.AMETEK-LAND.COM 05 CHALLENGES OF LOW THE LSP-HD 50 LINESCANNER

o EMISSIVITY GLASS The LSP-HD 50 can A compact infrared linescanner, the 70 C. A mounting/cooling assembly is operate accurately LSP-HD 50 can provide highly accurate available. temperature measurements even with cooling in ambient Highly stable electronics provide when the gap between the furnace conditions up to 60oC. the LSP-HD 50 with sufficient gain to and air quench is a narrow one. compensate for very low emissivities, It is able to scan 1000 data points below 0.3. at 150 scans per second, enabling When viewing Low E glass, an detection of the smallest temperature IN ADDITION TO GLASS innovative reflector plate fits to the variations, and is plug-and-play TEMPERING, THE LSP-HD 50 underside surface of the LSP-HD 50 compatible with LANDSCAN WCA IS IDEAL FOR MEASUREMENTS enclosure. software for advanced analysis. ON GLASS FLOAT LINES, This deflects much of the hot The LSP-HD 50 operates accurately FORMING AND BENDING updraft at the furnace exit, and also without cooling in ambient conditions prevents the LSP-HD 50 from seeing PROCESSES, GLASS up to 60 oC and will continue to its own reflection, ensuring accurate COATING AND SOLAR PANEL operate outside its specifications up to measurements. MANUFACTURE.

GLASS FLOAT LINES FORMING AND BENDING PROCESSES SOLAR PANEL

Mapping Low Emissivity (Low E) glass emissivity compensation is required. two or three underside sensors – is can be a challenge. Infrared applied. Only one of the sensors needs In addition, Low E glass is produced in LSP-HD 50 FEATURES AND BENEFITS thermometers are non-contact to have seen the glass lite for this to the same furnaces as uncoated instruments that sense emitted work correctly. glass, so there is a huge variation radiation and convert the received in emissivity for any temperature Operators typically mark the input signals into an accurate temperature measurement system to cope with. roller with stripes to ensure a lite will FEATURES BENEFITS measurement. Low emissivity means pass over at least one of the sensors. there is very little emitted radiation for AMETEK Land’s solution compensates High-resolution optical system Full-width measurement helps identify & analyse problems the infrared instrument to measure. for each batch of glass and the This ‘true temperature’ system is a big emissivity value of that specific batch. advantage to users of the LSP-HD 50, Industry-leading 150 Hz scan speed Process modelling improves process control When emissivity is low, reflectivity is First, a contact closure signal is taken enabling the manufacturer to produce high, so background sources of Designed to operate in harsh industrial environments Accurate thermal records for product quality data from the furnace controls, signalling better quality tempered glass with radiation can easily add extraneous the start of the batch exiting the fewer visual distortions, reducing Plug-and-play installation via single Ethernet cable Real-time thermal displays signals to the measurement. An furnace, and the end of the batch. waste product, increasing profit, and Range of data output formats Easy connection to process control system incorrect estimate of emissivity enhancing reputation. may lead to very large errors in Then, the underside temperature temperature reading, so active correction – as measured by one,

06 Glass tempering safety application note WWW.AMETEK-LAND.COM 07 AMETEK LAND SOLUTIONS FOR GLASS TEMPERING:

LSP-HD 50 SOLOnet SN5 FLT5A Ethernet-controlled compact Highly accurate, cost-effective Flexible, accurate infrared infrared linescanner, designed to single-spot infrared pyrometers, pyrometer specifically designed produce advanced thermal images easily customised to meet for surface temperature on moving processes. precise measurement and control measurements on glass float line requirements. applications.

FIXED SPOT FIXED SPOT LINESCANNING PYROMETERS PYROMETERS

LSP-HD A FAMILY OF HIGH SPEED, HIGH RESOLUTION NON-CONTACT AMETEK Land’s AMECare Performance Services ensure peak performance INFRARED LINESCANNERS and maximum return on investment over the life of your equipment. i 20 to 1500 °C / 68 to 2732 °F We will deliver this by: AMETEK Land’s global service network • Proactively maintaining your provides unparalleled after-sales equipment to maximize availability. services to ensure you get the best performance and value from your • Optimizing solutions to meet your AMETEK Land products. Our dedicated unique applications. service centre teams and on-site • Enhancing user skills by providing engineers are trained to deliver the access to product and application highest standard of commissioning, experts. maintenance and after-sales support. QUALITY CUSTOMER SOLUTIONS

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