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SCHOTT has a command of the entire value chain, from customer-specific material development and highly- precise final processing to extremely accurate measurement technology:

Melting/Glass Manufacturing

With more than 125 years of experience in the area of optics and glass manufacturing, SCHOTT is today the last company in the Western world that actually still melts glass. SCHOTT was the world’s first special glass manufacturer to introduce continuous tank melting way back in 1911.

Glass is melted in four phases:
  1. Fusing: The batch consisting of high-purity raw materials that has been placed inside the furnace is heated up inside it. Then, a chemical reaction takes place --> formation of a molten mass.
  2. Purification: Elimination of the bubbles created by chemical reactions.
  3. Homogenizing: Stirring of the bubble-free melt.
  4. Casting & Hot Forming: Liquid glass exits the feeder and is molded into bars, rods or blocks.
SCHOTT employs the following melting techniques:

Tank Melting:  

This technique has been optimized for mass manufacturing. Not only blocks and bars, but also large round plates (Ø up to 1 m) can be melted.

Main characteristics:
- optimal usage of raw materials
- higher energy efficiency
 
Crucible Melting:  

This technique is mainly used to manufacture glasses with outstanding optical properties. SCHOTT reacts to individual customer requests quite flexibly and offers different dimensions.

Main characteristics:
- well-suited for glasses with outstanding optical properties
- smaller volumes possible
 
Up-Draw Process:  

This method is used to manufacture thin and flat glass. In this method, a glass ribbon is drawn up through the annealing furnace from the bottom to the top by various rollers.

Main characteristics:
- outstanding surface quality
- broad range of thicknesses ranging from 0.8 mm to 10 mm
- high flexibility with respect to both output and width
 
Down-Draw Process:  

The down-draw process is used to manufacture thin and ultra-thin glass. This calls for a glass ribbon to be drawn down through the annealing furnace by several rollers.

Main characteristics:
- fire-polished surfaces with a surface roughness < 1 nm
- broad spectrum of thicknesses from 1.1 mm up to 25 µm
- rapid adjustment to accommodate different types of glass
- high flexibility with respect to both output and thicknesses
 
Up-Draw Process
Down-Draw Process

Fine Annealing & Ceramization

Even more precise settings for predefined key properties are achieved by running extremely precise temperature-time programs, for instance on the refractive index, dispersion and tension with optical glass by using the fine annealing referred to here and by way of ceramization for the expansion coefficient of ZERODUR®. SCHOTT has determined the dependence of the properties on shifts in temperature over time quite accurately. This reliable data coupled with profound process expertise makes it possible to keep the target values within extremely narrow tolerances and achieve unmatched homogeneity.

CNC Machining

CNC (Computerized Numerical Control) machined components are converted into complex geometrical shapes inside CNC machines with the help of modern CAD software. These include CNC sawing and CNC grinding.

Sawing is used in mass manufacturing and to achieve dimensional accuracy. Grinding makes it possible to manufacture workpieces with a maximum diameter of up to 4.25 m. Carefully-trained employees and extremely precise processes developed by us, together with strict quality controls, result in products of the highest quality and precision.

Pressings

Pressed blanks are shaped into optical glasses with matte or naturally blank surfaces with the help of hot processing under pressure. Pressings already come in the shape of the optical components, lens pressings, prism pressings, etc. to be used later on.

Polishing

SCHOTT is capable of polishing all of its products, including zinc sulfide and infrared chalcogenide glasses.

Our company uses two different polishing techniques:

a.) Polishing by way of mechanical means used for optical components
b.) Fire-polishing performed while the glass is being manufactured, for thin glasses, for instance

SCHOTT offers single- and double-sided polishing to produce plano and plano-plano-parallel components (with a max. diameter of up to 650 mm, for instance) as well as single-sided polishing of spherical and aspherical surfaces.

Coating

SCHOTT offers standard and customer-specific coatings, whereby various coating techniques are used to produce a wave spectrum of between 200 nm and 3,000 nm.

The portfolio includes the following types of coatings:
  • Anti-reflective coatings
  • Permanent, anti-reflective and oleophobic coatings (CONTURAN® DARO)
  • Protective coatings
  • Multi-layer interference coatings
  • Reflective coatings
  • Conductive coatings
  • Anti-fog coatings
  • Sol gel coatings
  • Magnetron sputtering
  • Thermal evaporation
  • Hot reactive electron beam evaporation
  • Ion-assisted evaporation
  • Reactive ion plating
These thin coatings can be applied to many different optical materials by way of evaporation under high vacuum using dipping techniques or cathode sputtering.

Cementing & Framing

With cementing, two or three optical components (lenses or glass plates, for instance) are bonded together with the help of special synthetic resins or mechanical techniques. For example, when two or three lens elements are cemented together, they produce achromatic doublets or triplets that limit the effect of spherical and chromatic aberration.

With framing, optical elements, for example filters, are typically given a frame made of metal or plastic that makes it easier to use them in the customer’s devices.

Metrology

SCHOTT is capable of performing extremely accurate and comprehensive measurements on bubbles, striae, transmission, the refraction index and coefficients of expansion by using various measurement techniques and the respective instruments, such as the V-block refractometer, the high-precision spectral goniometer “URIS” or the high-precision dilatometer.

Furthermore, SCHOTT has access to even more measurement techniques and instruments that support processes along the value chain, for instance evenness interferometers or 3-D coordinate measurement devices.

The respective measurement data is available to meet customer-specific demands.