34 Safety First
Rolling Glare Shield for Steelmaking Applications
Hazards are ever-present in the In 2016, MacPherson and Company, ordering and/or buying industrial steel plant environment, and a manufacturer of specialty safety glass do not have a basic knowledge a heightened awareness and glass for extreme heat and impact in of the different properties of glass. emphasis on safety is a necessary the molten metal industries, devel- Therefore it is important to review priority for our industry. This oped the rolling glare shield as an properties of different safety glass in monthly column, coordinated by added layer of safety designed to steel manufacturing environments. members of the AIST Safety & cut the radiant light hazard in mol- The most dangerous phase of Health Technology Committee, ten metal applications. This article steelmaking is during the charg- focuses on procedures and explains how the rolling glare shield ing phase. The second-most dan- practices to promote a safe works plus its relationship to other gerous is when the molten metal working environment for everyone. layers of safety glass. The shield is in motion. Steelmaking has two is another safety layer behind the threats: severe radiant energy that infrared-reflecting glass for block- is present from the melting through ing radiant heat energy and the the casting operation and the occa- impact safety glass for stopping sional reactions with water that debris in molten metal reactions causes explosions while in the mol- (Fig. 1). ten phase. Knowledge of steelmaking com- The term “safety glass” refers to bined with understanding the any type of glass designed for safety, properties and strengths of differ- but generally it falls into just two ent glasses is critical in engineer- types. The first, monolithic glass, ing windows for the steel industry. breaks into tiny pieces as opposed Author Most people commonly view glass to sharp shards when broken (Fig. Jane MacPherson as glass; however, the design of win- 2). In order for glass to break in a MacPherson Engineering Inc. dba dow systems for critical steelmaking dice pattern, the glass needs to be MacPherson and Company, Berea, Ohio, USA areas requires the proper selection tempered. The process of temper- [email protected] of glass with varied properties and ing glass is similar to the tempering strengths. Durability, serviceability, process in steel in that it rearranges comfort, and the operator’s safety the molecules to achieve a specific and health are important consider- strength and flexibility. Tempering ations for designing industrial win- glass is a way to dramatically change dow systems. It is best to rely on an the microstructure and strengthen expert to determine the best options, the glass. Quenching allows the out- as a sizable percentage of people side surface glass to cool rapidly associated with, operating behind, and at the same time allows for the
Figure 1 AIST.ORG I
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AUG 2017 Safety layers between the operator and molten metal applications. 35 Figure 2 Figure 3
Break patterns in tempered versus annealed glass. Example of iridescent IRR coating on glass. interior of the glass to cool slowly. This puts the outer minimal thermal shock. This is the most commonly surfaces into compression and the middle into tension. used glass in steelmaking applications. The second recognized safety glass is laminated glass, which is a composite of glass and laminate Tempered Borosilicate With IRR (BPS Heat Shield) — material. This glass remains in one piece after being This also has a pyrolytic coating to reduce the radi- fractured. The laminated glass can vary in strength ant energy transfer through the glass. BPS has low by using a variety of thicknesses of glass and laminat- thermal expansion. Tempered BPS heat shield will ing material. For steelmaking operations, it is a good outperform tempered soda lime IRR glass in extreme choice to use glass featuring infrared-reflective (IRR) thermal shock environments, but is not a safety glass coatings for the heat-side glass for elevated radiant since it does not dice when broken. It has a maximum energy environments. IRR coating is birefringent, operating temperature of approximately 550°F at the which gives an iridescent reflection on the glass surface area. It is desirable in applications less than 50 (Fig. 3). feet from molten steel, especially with the possibility There are three varieties of glass that are ideal for of thermal shock. molten metal applications as the outer heat shield on the heat side of the operator’s enclosure: tem- Glass Ceramic — This is not a safety glass because it pered IRR, tempered borosilicate with IRR and glass has a near-zero expansion coefficient and cannot be ceramic. tempered. This glass will sustain 1,100°F at surface area and performs well against thermal shock. This Tempered Infrared-Reflecting Glass — This soda lime glass is available in clear or with an IRR coating. Glass glass will dice into small pieces when broken. It has ceramic is normally used less than 15 feet from mol- a pyrolytic coating to reduce radiant energy and is ten steel. serviceable up to 400°F at the surface area. This is a useful product for most applications in areas with One can tell the difference between common (soda lime) glass and the other glass products when looking at the edge. (Fig. 4) The edge of soda lime glass will appear as a green color and the edge of borosilicate Figure 4 and glass ceramic will appear clear. Note that this discussion is only about the outer 0.25-inch glass for operator enclosures in hot applica- tions. Laminated safety glass is popular in many mill settings because the local glass installer can cut and
install the same day as needed. The 0.25-inch-thick AUG 2017 laminated glass is annealed and not tempered, there- fore it can be cut on-site. The downside to 0.25-inch I
laminated glass is it will crack at a much lower thermal IRON & STEEL TECHNOLOGY stress and more frequently, making it a costlier prod- uct over a short period of time. In addition, 0.25-inch laminated glass does not have IRR coating. A com- parison property chart (Table 1) reflects the varieties of outer heat-side glass that would be appropriate for I hot metal applications. AIST.ORG After reducing the radiant energy entering the cab, Edge comparison between glass types. the next layer of safety recommended is an industrial 36 AUG 2017 I IRON & STEEL TECHNOLOGY I AIST.ORG The rolling glare shield. glare rolling The Safety First temperature inner layers with an additional IRR coat IRR additional an with layers inner temperature concussion and impacts from hot metal reactions reactions hot from metal impacts and concussion either the SAFE-SHIELD ing and is tested to resist penetration at least 3,000 3,000 at least penetration resist to tested is and ing impact/explosion-resistant composite safety glass like like glass composite safety impact/explosion-resistant ft-lbs. HOOGOVENS offers maximum protection and and protection maximum offers HOOGOVENS ft-lbs. high- offers SAFE-SHIELD steelmaking. found in safety glass. These products are designed to stop the stop the to designed are products These glass. safety 0° –300°Cx10 expansion Coefficient ofthermal Nominal thickness Industrial use glass Type oftempered Comparison of Chart Properties Table 1 (%) Light transmission (scale 1–10) flex andimpact Mechanical strength temperature (°F) Maximum sustained (scale 1–10) thermal shock Withstands from 2,800°Fsource infrared radiation Transmission %of Figure 5
–7 radiant energy For minimal Soda lime Tempered 0.25 inch reflecting infrared 93.5 400 81 28 9 4 ® or HOOGOVENS or
For shortradiant BPS energy blast Borosilicate heat shield 0.22 inch ® 32.5 tempered 550 85 30 6 6 ® impact RADIANT For long-sleeve radiant energy Crystallized shield clear 0.25 inch ceramic 1,100 80 10 30 3 3 - ® heat operator’s clear viewing. operator’s viewing. clear only a short time of use. of use. ashort time only are a workable solution but tend to have issues after after aworkable solution but tendare have issues to glare shield, together with flip-down or pull-down or pull-down flip-down shield, with together glare flip-down shades and pull-down shades. The rolling rolling The shades. pull-down and shades flip-down shades, mediates the blinding light that interrupts the the interrupts light that blinding the mediates shades, The rolling glare shield can be paired up with PPE up with paired be shield can glare rolling The IRR coating. IRR PPE flip-down shades is the continual cost continual the is shades PPE flip-down avail acommercially is shade Polymer film Duct taping a green or blue glass to the the to or blue a green glass taping Duct off the glass; it eventually renders the glass glass renders the it eventually glass; the off bubbles it quickly windows, on steelmaking Lexan is not ideal for hot metal glass even for not for glass is ideal hot metal Lexan Therefore, temperature. that above is often of any strength highest impact the offers not have the flip-downs. Another issue with with issue Another not flip-downs. have the protec personal solution is Another unusable. radiant light associated with steelmaking and and steelmaking with light associated radiant using temperature softening Vicat The ness. orrecommended steelmaking hot in metal tion equipment (PPE) flip-down shades that that shades equipmenttion (PPE) flip-down then cracks and becomes difficult to scrape scrape to difficult becomes and cracks then be replaced frequently. Finally, another com another frequently. replaced be Finally, need to and lost regularly are these because tested repeatedly to resist penetration with with penetration resist to repeatedly tested the explosion-resistance safety layer. safety explosion-resistance the (120°F). 49°C around steel Most begins tion the over times 250 product with transparent but not layers does inner feature temperature when maintenance needed to use the pulpit. pulpit. the needed use to when maintenance cabs crane the in light forwhite operators mon solution used is pull-down shades. These These shades. pull-down is mon solution used molten metals. metals. molten ambient applications’ temperature making B120method 145°C is (295°F), deforma and inside and people temporarily in the area will will area the in people temporarily and inside hat tend not a hard pulpits wear to the in ing can turn toward the reduction of blinding of blinding reduction the toward turn can focus addressed, are threats impact extreme drawbacks for flip-down shades is those work those is shades for flip-down drawbacks removed inconvenient provedily and be to first the was EAF the in of glass pane inner goal. this of achieving methods improvised sheet thick equal in of glass strength impact attaches to all operators’ helmets. Some minor minor Some helmets. operators’ all to attaches able used product for When automobiles. applications. Lexan is a polycarbonate that that apolycarbonate is Lexan applications. high- has HOOGOVENS ft-lbs. 4,000 at least an added safety layer to block the damaging damaging layer the block to safety added an of manufacturing the during pulpits and solution encountered. This glass was not eas was glass solution encountered. This as designed shield was glare rolling steel. The After ensuring both radiant heat and radiant both ensuring After Over the years, there have been many many have been there years, the Over Lexan is a type of safety glass that is not is that glass of safety atype is Lexan ------37
The rolling glare shield was developed out of the protecting operator’s eyes during radiant light events need in the industry for a better solution for radiant and eliminating distracting and harmful light trans- white light defusing. The purpose is to protect the missions. The rolling glare shield, when used in a operator from the damaging bright white light in the crane cab, increases the ability for the operator’s steelmaking process without losing its strength and eyes to adjust and better see the environment below properties as it filters the difference between molten on either side of the ladle, as it diffuses light while steel and slag. The system allows the rolling glare traveling down the aisle. The shield also reduces the shield to roll quickly in place for charging, pouring double-image issue in the glass created by light bounc- or other blinding applications. When the work is com- ing off the double heat-reflecting glass. The rolling pleted, the rolling glare shield can easily be moved track system maximizes ease of use and serviceability. out of the way. It is positioned inside of the window system, shielding from the heat and impact. Since it is made of industrial-grade material, it is able to take References the heavy use seen in steel mills. 1. The Corning Museum of Glass, Corning, N.Y., USA. The shield reduces the strain on the eyes, improves 2. Schott Glass Specification Sheet 2005. workers’ productivity and reduces accidents by 3. Lexan Specification Sheet 2015. F
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