The RR Starbar is a resistance type silicon carbide heating element. Starbars are rod shaped or tubular depending on the diameter. They have a central heating section referred to as a hot zone and two terminal sections called cold ends. There are two types of RR Starbars. (1) The cold ends are impregnated with silicon metal - referred to as one piece, and (2) low resistance cold ends which are furnace welded to the hot zone - referred to as a three piece or LRE (Low Resistance End) type. This lower electrical resistance cold end causes them to operate at a lower temperature. The extremities of the elements are metallized with aluminum to provide a low resistance contact surface to which the electrical connections are made using braided aluminum straps.
RR and RA Brochure
|Item #||Diameter||Max Overall Length||Hot Zone (Electrical Resistance)||Cold End (Electrical Resistance)|
|RR-3/8-10||3/8 Inch |
|26 Inch |
|0.3486 Ohms/Inch |
|.007298 Ohms/Inch||.00052 Ohms/Inch|
When mounting Starbars vertically they must be supported on the lower end by electrically insulated supports.
Starbars should have their heating sections centered in the furnace chamber so that no portion of the heating section extends into the furnace wall. A conical or truncated cone shaped recess 1/2 inch (13 mm) deep is sometimes located on each interior wall where the Starbar passes through. This allows the hot zone to radiate properly and helps maintain a uniform temperature in the kiln.
Recommended Minimum Refractory Hole Size
|Minimum Hole Diameter Based on Refractory Wall Thickness|
Nitrogen atmosphere applications are limited to 2500°F (1370°C) and 20 to 30 watts per square inch (3.1 to 4.6 watts per square centimeter) maximum surface watt loading. Too high of a surface temperature will result in a silicon nitride reaction. A thermally insulative layer forms around the Starbar resulting in very high surface temperatures which damage the Starbars.
The silicon carbide Starbar is a linear type resistance heater that converts electrical energy to heat energy – Joule’s Law W = I2 x R, (W = power in watts, I = current in amperes, R = resistance in ohms).
Starbars are not sized to a specific wattage output like metallic heating elements. The amount of energy that a Starbar is capable of converting from electrical to heat energy depends on the ambient furnace temperature and atmosphere in which the Starbar.
Ease of Replacement
recommended starbar spacing
X = 2 x Starbar Diameter is the Minimum, 1.5 x Starbar Diameter is the absolute Minimum and requires a reduced Starbar Surface Watt Loading
Z = S ÷ 1.41 Minimum for Stationary Loads
Z = S ÷ 1.73 Minimum for Moving Loads
S = 2 x Starbar
Starbars increase gradually in resistance with use. This characteristic of increasing in resistance is called aging. Aging is a function of the following:
- Operating temperature
- Electrical loading (usually expressed in watts per square inch or watts per square centimeter of Starbar radiating surface)
- Type of operation (continuous or intermittent)
- Operating and maintenance techniques
Furnace heating chamber
The furnace heated chamber dimension, which the Starbar spans, can be the same as the hot zone length of the Starbar as shown by the Starbars under the load in Figure 3. Alternately the furnace heating chamber dimension, which the Starbar spans, can be one inch (25 mm) less than the effective heating length of the Starbar. In this case there must be a 45° conical recess in the furnace wall as shown in Figure 3 for the Starbars above the load. Recommended terminal hole diameters for various refractory walls and Starbar sizes are shown in Table B.
Starbars should not be placed closer than two Starbar diameters to each other or one and one half Starbar diameters to a wall or other reflecting body. If the Starbar is not able to dissipate heat energy equally in all directions, it may cause local overheating and possible failure.
The formula for computing the recommended Starbar spacing to obtain an even temperature gradient on the product being heated is shown in Figure 3.
Specifications & Matching
Starbars have a manufactured tolerance of plus or minus 20% on the nominal resistance. All Starbars are calibrated at least twice prior to shipping to ensure their being within specifications. The calibrated amperage of each Starbar is marked on the carton and right hand end of each Starbar. When installing, arrange Starbars with amperage values as close to each other as available. Longer service life will be obtained when series connected Starbars are matched in resistance. Starbars are shipped as closely matched as possible.
Special sizes and shapes are available. Cold ends can be different lengths. This, for example, would be applicable for furnaces with arched roofs that require longer cold ends through the roof and shorter through the floor.