Parker Glass LLC
6327 SW Capitol Hwy.
STE C PMB# 251
Portland, Oregon 97239
 
Jason and Paul at the Sonoran Glass Art Academy with Columbia glass furnace in background.
Jason Marstall and Paul Anders-Stout teaching the Roll Up the Fun class at the Sonoran Glass Art Academy in Tucson, Arizona, January, 2010. The Columbia electric glass furnace from Parker Glass in background.
One hundred pound glass furnace on wheels Build Your Own
Electric Glass Furnace

A 100 pound pot furnace from a kit.
Common knowledge is that furnaces with coiled resistence elements need the elements replaced in less than a year. Many people replace elements after only 30 days of use. The life of elements is based on:

proportion of elements to melting chamber to volume of glass

refractory material supporting the elements

correct method of installment

firing method of elements

separation of elements from the glass enviroment

continuous use of the elements

The free standing crucible is generally considered a better quality method of melting glass. The problems develop when the crucible cracks and deposits glass on the furnace refractory, resulting in a worthless crucible and a damaged furnace. Alternatives have been melting in bricks or invested crucibles. These methods give a longer life than a single free standing crucible, but impart cords to the glass and eventually require the whole furnace to be replaced. The method of glass furnace construction directly relates to life of the crucible and the life of the elements.

There is no complete answer to the cost of operation when applying heat to glass in a refractory material. The 100 pound wire melter is an intermediate size glass furnace. When considering the initial cost of electric glass melting there are less and more expensive methods. The least expensive method is the soft brick hobby kiln. The down side is that for production use they are underfired, the element life is shortened by contact with the soft brick and method of firing, and the soft brick is destroyed with glass contact. They also are limited quantity of glass, but are suitable for melting small quantities of color for short periods of time.

The more expensive methods than a coiled resistence wire melter are silicon carbide elements and molydenum elements. These furnaces have the ability to melt 300-400 pounds of glass, the cost and firing methods are similar with the molybdenum furnace requiring an added transformer. The firing chamber is above the glass, requiring an area close to twice the volume of the glass. Both methods also require industrial electrical supply.

The Columbia glass furnace from Parker Glass is a coiled resistence element furnace which uses the technology of the less expensive hobby kilns and the more expensive industrial element furnaces.

This furnace was designed around elements that were capable of melting one hundred pounds of glass for a small glass melting shop. For larger facilities it is capable of melting color or as a back up for their larger furnaces.

The Columbia glass furnace draws 240 volt, 45 amps, from a 60 amp circuit breaker, not much more than a full sized electric water heater.

Removing the lid and the top insulating ring from the furnace allows easy access to the crucible system and the elements.

Without the crucible this furnace can be used for firing large pate de verre pieces and glass may be added to the mold by lifting the lid and charging cold glass.

The stainless steel metal parts surrounding the furnace and above the crucible are stainless steel which transmit less heat and do not break down under high heat.
The Columbia glass furnace from Parker Glass LLC.

A steel decking on steel wheels is the base for insulating brick and a hard refractory pan. The hard refractory pan will withstand hot glass spills, unlike a soft brick kiln, and is aided by a layer of silica sand covered by spent fiber, which soaks up glass and is easy to remove.

Nine hard refractory pieces make up the element holders and these pieces are keyed into the hard refractory pan.

This refractory is then wrapped with 2600F degree fiber, 2300F degree fiber, and the stainless steel exterior.
Refractories for the Columbia glass furnace.

Like a soft brick hobby kiln, the coiled resistence elements lay in a groove. This furnace interior is a hard refractory material and not an insulating brick. Hard refractory is a strong holding base for the elements and the elements are not prone to fluxing from impurities in the soft brick. Soft brick also breaks easily allowing elements to fall on others and short circuit.

Inserted through the furnace wall is a small type R thermocouple. This size thermocouple is used because it reads temperature changes quicker than the larger thermocouple so often used.

Elements and thermocouple in place.

The Columbia glass furnace has two electrical boxes. One is a keyed control box with a toggle switch, setpoint controller, cartridge fuse, and plug in thermocouple recepticle. It operates on 120 volt, 15 amp circuit.

The other is a keyed 240 volt, 45 amp relay box with a 60 amp shut off switch, three cooling fans, an infra red safety relay, a silicon controlled rectifier(SCR), ammeter and coil, all with their own quick blow cartridge fuses, and a 50 amp recepticle for the furnace. When the lid of this furnace is lifted the infra red relay shuts off all power to the furnace, eliminating any possible current or leaks to the furnace. Because of the crucible system loss of heat to the heating chamber when the lid is open is minimal.

The configuration in the control boxes are necessary not only for safety, but also for prolonging the life of elements. Soft brick kilns use contactor relays for off/on power to the elements. Power supplied in this manner rapidly heats the elements to their full temperature and then shuts them off. This shortens element life similar to rapidly turning on and off an incandescent light bulb.

Like the more expensive silicon carbide and molybdenum furnaces this furnace uses an SCR relay. The power is always on and the voltage is regulated to add or lessen heat according to the required temperature, prolonging the life of the elements.

Unanswered questions? Click below.
control box 50 amp recepticle on control box.
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