Glass Forms Available From SEM-COM


SEM-COM Glass Powders

Most glass powders are made from glass chips (or frit) and have the physical property values of the glass composition selected.  The chips are reduced to a powder by grinding in a ball mill where glass is charged into a rotating ceramic housing containing rods or balls that roll and impact the chips to reduce them and achieve the particle size desired.  The quantity of the charge to the ball mill and the grinding time are selected to control particle size of the desired product.  Average particle size can be extremely important so our screening and sub micron measurement devices are necessary to qualify these products.

Glass powders have a wide spectrum of applications.  They serve as a sealant material for such products as closures for color TV, hermetic power feed-throughs, coatings for enameled ceramic ware, decoration for tumblers, electronic preforms, tape buildup systems for electronic components, etc.  Certain glass powders can be mixed with various other material to produce semi conductor coatings for active electronic components.  There are many other applications for the list of glass powders that we supply.


SEM-COM Micro-Tubing

We consider glass items having uniform cross section along one axis as 'micro' when cross section dimensions fall below 0.125".  Precision is stressed by forming and then machining a large glass part to precise cross sectional dimensions.  The part can then be reduced in size by a secondary forming operation done under tightly controlled temperatures.  This second process is known as redraw attenuation where the cross section is reduced to the smaller dimension in a ratio that maintains the original starting shape of the larger part. The beauty of this process sequence lies in the many options possible. Some of these options are as follows:
  • Different glass compositions can be selected to provide properties such as a desired expansion coefficient, dielectric performance, color, sealant temperature, etc.
  • Cross sections can be either tubing or solid and range from cylindrical to square, triangular, hexagon, oval, 'V' shaped, etc.  Bores can be centered or off-center.
  • Final parts are cut into length and dimensions closely held.  Parts can have ends polished, parallels within 1/2 wavelength of light, and be free of scratches, digs or chips.
  • Identical small parts can be produced in relatively large volume.

We entertain difficult precision part fabrication and can maintain costs at a fair reflection of fabrication difficulty when there is adequate disclosure about application.


SEM-COM Cast Products

Cast products of glass include bars, billets, cylindrical rods, and other shapes that involve a mold that accepts a stream of glass. Molds are filled and opened to release a cooled product ready for annealing.  Annealing is the controlled cooling that must follow casting to bring the part down to room temperature without breaking.  Resulting product uses are manifold, both in a finished form and as a starting form for secondary processes.

Requisites for casting include the choice of a composition and physical properties that are needed in the final product.  The glass chosen must be able to be melted and made homogenous and attain a viscosity and temperature suited to pouring into a stream without air entrapment.  The material must also be stable enough at operating temperatures to avoid crystallization or other phase changes.

Continuous cast products are those that are cast from a furnace directly into a mold, forming rod or slab shapes. The bottom of the mold is open, allowing for a continuous length of cooled, semi-solid glass to exit the bottom without opening the mold.  A section of the cast part, upon sufficient cooling is then cleaved from the continuous ribbon and sent to the annealer.  Rod for fiber optic applications can be made this way to assist in achieving near optical quality.


SEM-COM Glass Frit and Chips

Many SEM-COM glasses can be supplied in frit or chip form for final processing by the customer.

Chips are formed by passing the molten glass through water cooled stainless steel rollers which cools and flattens the glass into a thin ribbon that breaks up into small chips. Glass in this form can easily be converted into a fine powder in a normal ball or pebble mill.

An alternate method to rapidly cool the molten glass is to drop direct the hot glass stream into a DI water bath whereupon small beads of glass or "frit" are formed. This method is referred to as water fritting.

The choice depends the glass composition and the type of particle size reduction process that is used.



SEM-COM Bulk Preforms

SEM-COM manufactures bulk glass preforms to customer's specified shapes and sizes. These preforms may be further processed by the customer to a final configuration or in some cases used "as is".

Shapes can vary from pellets as shown here to small lengths of tubing, or cast pieces. Forming processes can include casting, up-draw or down-draw, core drilling or slicing.

Glass characteristics are tailored to the specific application and can include both vitreous and crystallizing types. In the latter case the crystallizing usually is done after the preform has been manufactured.



SEM-COM Capillary Tubing

SEM-COM produces both sodium and pH capillary tubing. This micro-tubing made from special glass compositions is supplied with typical outside diameters of about 0.050" (1.2mm) and inside diameters of about 0.030" (.75mm) or less. These dimensions are tailored to a specific customer's specs. This high quality tubing is made using a carefully controlled re-draw process that produces uniform wall thicknesses.

Capillary tubing is normally sold in 12 inch lengths however other configurations can be supplied upon request.