To ensure the manufacture of consistently high-quality, high-performance glass components and products, it’s critical to utilize optical specifications. These are useful in two ways: First, they establish an acceptable standard by which a glass surface must perform; second, they can help determine the amount of time, money, and labor that should be spent on the manufacturing process.
Below are a few key optical specifications to take into consideration when working with glass surfaces.
The requirements for surface quality are as varied as the applications for glass surfaces. For instance, in industrial settings, the bar set for surface quality is not as high as it would be for work with lasers. Surface quality refers solely to the cosmetic quality of a glass surface — whether it has any marks, divots, scratches, and so on. While such imperfections may not necessarily impact performance, it’s still important to consider how long-term effects, such as general wear and tear, may impact the appearance and overall quality of the glass.
Surface quality is reflected by two numbers: the scratch number, which is determined by comparing scratches on a surface to a set of standard scratches under controlled lighting conditions, and the dig number, which is calculated at the diameter of the dig in microns divided by 10. For example, 60-40 reflects precision quality, and is a common surface quality value in research and industrial sectors. The lower the number, the higher the quality of the product. Industries and applications working with lasers aim for a higher standard of 10-5.
MIL-O-13830A and MIL-O-13830B standards are the most commonly applied for surface quality, but there’s also a more complex standard, ISO 10110, which allows designers some level of control and eliminates much of the guesswork for inspectors.
Surface flatness is the measure of how flat a surface is; this test is critical for glass products such as windows, mirrors, and plano-lens. The surface flatness test accounts for surface deviations such as ripples, bows, and other imperfections, which are measured in waves — the multiple of the wavelength from the reference surface. In this case, the higher the digit, the more precise the product. To determine surface flatness, the surface being tested is compared to a high-quality, highly precise flat reference product — referred to as an optical flat — and examined for deviations by comparing the two surfaces.
To compare the surface, the optical surface at hand is placed against the optical flat. When they are placed against each other, fringes — more specifically, “Newton’s fringes” — will appear, and the shape of these fringes will determine the flatness. Evenly spaced, straight, and parallel fringes indicate that the surface being tested is at least as flat as the optical flat. Curved fringes indicate subpar glass flatness.
This specification applies to curved optical surfaces — surfaces with power — and is tested similarly to flatness; the curved surface is stacked against a reference surface, a highly calibrated reference gauge. The air gaps created by the interference provide information on the deviation between the surfaces of the test model and the reference model. The deviations create a series of rings, referred to as Newton’s rings. The more there are, the more pronounced the deviation from the reference model.
The irregularity specification is used to describe the deviation of a test surface’s shape from the shape of its corresponding reference surface. The measurement is obtained using the same test conducted for power, but this test focuses on the sphericity of the circular fringes, which are determined by comparing the test and reference surfaces. Still, irregularity is often described as a ratio to power. For example, if the power of a surface is more than five fringes, detecting smaller irregularities (less than one fringe) is often difficult; therefore, the irregularity is reflected through this ratio of power to irregularity. In this particular example, the ratio would be 5:1.
During polishing processes, there’s always a risk of small irregularities occurring on the surface of the glass. Surface finish testing, or surface roughness testing, is used to measure these irregularities at the end stage of product manufacturing. Tolerances for surface-finish quality range from 50Å RMS, which represents typical quality, to 20Å RMS, which represents precision quality, and 5Å RMS, representing high quality.
This test will have varying degrees of importance depending on the eventual application of the glass product at hand. Surfaces intended for use in lasers and intense heat would demand a much higher surface finish than applications that don’t require the same level of precision or are less concerned with the inevitable wear that occurs in rougher surfaces.
Obtaining and understanding optical specifications can allow for significant cost and time savings for designers and suppliers alike. While none of these tests are required by any regulatory body, it’s critical to work with suppliers and manufacturers who uphold these standards in order to cut down on surface rejections and defects — and, therefore, reduce overall costs and lead times.
Swift Glass provides a wide range of testing services to ensure our products are of the highest possible quality and precision. Our team offers full-service precision optical glass component fabrication services for all types of high-volume projects.
Glass is among the most versatile of materials. Depending on its composition, treatment, and manufacture, it can be customized for high performance in countless applications.
In order to get the right fit for your next glass project, remember to consult properties such as the corrosion resistance, thermal properties, viscosity, dielectric properties and refractive index of potential materials. These properties tell a lot about how a material reacts to its environment, which is especially important for your application’s performance.
Sample Material: Borosilicate
When compared to other types of glass, borosilicate has a high corrosion resistance to acid, but a low corrosion resistance to weathering. Its thermal expansion is very low, and its volume resistivity and thermal shock resistance are both high — but not the highest. Its light transmission is excellent.
Pyrex® and Borofloat® are common types of borosilicate, though both Schott and Corning craft a series of variations with increasingly specific properties.
What does all of that mean?
Because of its resistance to high temperatures and chemical corrosion, borosilicate makes an excellent material for the biomedical and research industries. It’s also an ideal material for optical, lighting and industrial applications.
Because this is a glass that demonstrates strength without being the absolute strongest, borosilicate is an affordable material, making it extremely popular in many industries. Of all possible glass materials, it’s the Swift Glass choice for all of our annular edge glass. Its edges can be ground specially to be sealed in a flange for biomedical, research, optical, optoelectronic, photonics and analytical applications.
Other Material Options
For the toughest situations, traditional glass materials may not be enough — no matter how naturally strong. Thermal tempering and chemical strengthening can further prepare glass for high-intensity applications, such as:
High Pressure Windows
Industrial and Residential Doors
The additional safety and dependability offered by tempered glass serves many industries, from automotive to medicine.
Resources for Selecting Materials
For quick reference, the Swift Team has assembled a Glass Material Properties Chart addressing some of our most popular material choices, ranging all the way from soda lime glass to fused silica. We also offer material consulting from our team of experts, as well as tempering services for specialty projects.
Computers, optical and other technological manufacturing industries require glass wafers as a carrier substrate for safe fabricating of delicate products like thin silicon wafers.
Glass wafers are also essential to the semiconductor, electronics, and biotech industries in a variety of applications.
Making Glass Wafers
Glass wafers are highly technical products that demand a highly technical production process, often requiring their own proprietary technologies. Here’s how Swift Glass utilizes its expert team and technology to craft these complex products:
Glass wafers begin with the highest quality glass. We typically work with Borofloat, Borosilicate, Quartz, and Eagle XG, selecting the most consistent glass sheet from the best batches. Wafers are cut from these sheets to be further processed.
The carefully selected and cut material is then ground to build out the wafer’s general shape.
The edge profile of the wafer is machined to specifications with the use of diamond tools. For example, a wafer could be crafted with a flat or notch, depending upon the design, and with an edge profile that is either flat-ground or pencil-ground. The notch, if designed, serves as a precise locator.
The product is lapped, and the profile accuracy gets checked.
Glass wafer inspection must be highly controlled in order to guaranteeprecision — the product is taken to a clean room with climate control, and the profile is recorded by laser.
The laser passes over the glass three times while another gauge reads the wafer’s total thickness variation (TTV). The larger the wafer, the more critical the TTV.
Glass Wafers from Swift Glass
After more than eighty years of glass manufacturing, the Swift Glass Team has developed highly specialized design and production capabilities. We are proud to take on the complex challenges that come with specialty products like glass wafers.
Swift Glass will be joining its glass manufacturing peers at the prestigious SPIE Optifab 2015 exhibition and conference next week in Rochester, New York.
The SPIE Optifab exhibition is the largest optical fabrication event in North America and acts as a forum to share and discuss the latest techniques and tools for the optical fabrication industry.
The event includes over 100 technical talks, covering glass manufacturing topics such as grinding and polishing, optical fabrication of freeform surfaces, metrology, optical materials, cleaning and coating, optical design, optical engineering, meter-class optics, and molded optics.
Swift Glass will be bringing our knowledge of glass fabrication to the forefront in our own exhibition. We will showcase a piece of chemically-straightened glass at Booth 504, and will have a team of highly skilled and experienced employees on hand to answer questions and provide information about the capabilities that we specialize in.
Optifab 2015 takes place from October 12-15 at the Joseph A. Floreano Rochester Riverside Convention Center, located at 123 E Main St. in Rochester, New York. Presentations will run from 8am until 6pm, daily.
Come join us in celebrating optical fabrication and learn about all the capabilities and materials Swift Glass works with. Contact us today to learn more about the event.
Swift Glass among the Region’s Optical and Photonics Specialists
Vice President Joe Biden recently visited Rochester, the “optics capital of the world,” to announce that our region has been chosen to host a new $600-million Integrated Photonics Center.
The creation of a national photonics institute means more than jobs and industrial growth; it’s the beginning of the next generation of American manufacturing.
Photonics research contributes to the function of countless daily tools: smartphones, high-speed Internet and wireless controllers, to start. It is closely related to optics: technology harnesses light for the development of smaller, faster and more energy-efficient devices.
Photonics touches a broad spectrum of industries: for example, manufacturing, global information technology, telecommunications, medicine, energy and national defense.
The idea is to transition devices from electron-based operations to using photons, or light. This includes the transfer of data from the internet, phones, TV, and radio with tools like lasers, fiber optics and optical detectors.
As a longstanding member of the optical community — and as a close neighbor to Rochester — Swift Glass is proud to have the specialized skills to bring new designs like these to life with working products and system components. Our glass materials alone carry unique traits applicable in modern technology, but our custom fabrication capabilities are where real innovation happens.
The skilled technical team at Swift specializes in every step of development, from prototyping to large-scale part production. Our state-of-the-art machining solutions and capabilities include:
Bending and Convexing
Cutting and Drilling
Double Sided Lapping & Polishing
Flat Polish and Pencil Polish Edging
We’re proud to have spent eighty years here in the Rochester area, sharing in the research, technology and thriving energy of the optical industry. As the oldest supplier of tempered glass in the United States, it’s inspiring to see these types of developments in the industry
Lighting, appliances and optics are part of the Swift Glass DNA, and we can’t wait to see what technology is to come. If you’re working on a custom project or prototype of your own, reach out to the team today — they’d be happy to help.
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