Type RR, Silicon Carbide Heating Elements | I Squared R Element Co., Inc.

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.

Category: Starbar

RR and RA Brochure

(PDF, 629KB)

Sizing Breakdown

Item #	Diameter	Max Overall Length	Hot Zone (Electrical Resistance)	Cold End (Electrical Resistance)
RR-3/8-10	3/8 Inch 10 mm	26 Inch 660 mm	0.3486 Ohms/Inch 0.01372 Ohms/mm	0.01743 Ohms/Inch 0.000686 Ohms/mm
RR-7/16-11	7/16 Inch 11 mm	36 Inch 915 mm	0.2563 Ohms/Inch 0.01009 Ohms/mm	0.01282 Ohms/Inch 0.000505 Ohms/mm
RR-1/2-13	1/2 Inch 13 mm	42 Inch 1090 mm	0.1963 Ohms/Inch 0.00773 Ohms/mm	0.00982 Ohms/Inch 0.000387 Ohms/mm
RR-5/8-16	5/8 Inch 16 mm	50 Inch 1250 mm	0.1262 Ohms/Inch 0.00497 Ohms/mm	0.00631 Ohms/Inch 0.000248 Ohms/mm
RR-3/4-19	3/4 Inch 19 mm	62 Inch 1575 mm	0.0865 Ohms/Inch 0.00341 Ohms/mm	0.00433 Ohms/Inch 0.00017 Ohms/mm
RR-1-25	1/1 Inch 25 mm	74 Inch 1900 mm	0.05 Ohms/Inch 0.00197 Ohms/mm	0.0025 Ohms/Inch 0.000098 Ohms/mm
RR-1-1/4-32	1-1/4 Inch 32 mm	86 Inch 2210 mm	0.0343 Ohms/Inch 0.00134 Ohms/mm	0.00171 Ohms/Inch 0.000067 Ohms/mm
RR-1-3/8-35	1-3/8 Inch 35 mm	90 Inch 2290 mm	0.027 Ohms/Inch 0.00106 Ohms/mm	0.00135 Ohms/Inch 0.000053 Ohms/mm
RR-1-1/2-38	1-1/2 Inch 38 mm	92 Inch 2340 mm	0.0234 Ohms/Inch 0.00092 Ohms/mm	0.00117 Ohms/Inch 0.000046 Ohms/mm
RR-1-3/4-45	1-3/4 Inch 45 mm	104 Inch 2670 mm	0.0165 Ohms/Inch 0.00065 Ohms/mm	0.00082 Ohms/Inch 0.000032 Ohms/mm
RR-2-1/8-54	2-1/8 Inch 54 mm	130 Inch 3300 mm	0.015 Ohms/Inch 0.00059 Ohms/mm	0.00075 Ohms/Inch 0.00003 Ohms/mm
RR-2-3/4-70	2-3/4 Inch 70 mm	130 Inch 3300 mm	.007298 Ohms/Inch	.00052 Ohms/Inch

Mounting

There are no restrictions on the mounting positions of Starbars, although the horizontal and vertical positions are the more common. Extreme caution should be used when mounting to ensure that the Starbars are not placed in tension. There should be adequate freedom to allow for the furnace and Starbars expand and contract independently.

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.

Table B Recommended Minimum Refractory Hole Size
Minimum Hole Diameter Based on Refractory Wall Thickness
Starbar Diameter		100	150	200	300	400	3	5	6.5	9	13.5
MM	Inch	MM	MM	MM	MM	MM	Inch	Inch	Inch	Inch	Inch
10	3/8	15	15	16			9/16	9/16	5/8
11	7/16	16	17	18	20		5/8	11/16	11/16	3/4
13	1/2	18	19	20	22	–	11/16	3/4	3/4	13/16	–
16	5/8	21	22	23	25	–	13/16	7/8	7/8	15/16	–
19	3/4	25	25	26	28	–	15/16	1	1	1-1/16	–
25	1	31	32	33	35	37	1-3/16	1-3/16	1-1/4	1-1/4	1-7/16
32	1-1/4	38	39	40	42	44	1-1/2	1-1/2	1-9/16	1-9/16	1-11/16
35	1-3/8	41	42	43	45	47	1-5/8	1-5/8	1-11/16	1-11/16	1-13/16
38	1-1/2	44	44	46	48	50	1-3/4	1-3/4	1-13/16	1-7/8	1-15/16
45	1-3/4	51	52	53	55	57	2	2-1/16	2-1/16	2-1/8	2-3/16
54	2-1/8	61	62	63	65	67	2-3/8	2-7/16	2-7/16	2-1/2	2-9/16

Specifications

Operating Temperatures

In an air or inert atmosphere of argon or helium the one piece Starbars can be operated at furnace control temperatures up to 3100°F (1700°C), the three piece Starbar up to 2600°F (1425°C). In reducing atmospheres the maximum operating temperature is 2500°F (1370°C), see Figure 1. There is a protective coating of silicon dioxide on the silicon carbide. Hydrogen reduces this coating and causes the Starbar to deteriorate. Very dry or very wet hydrogen is detrimental to long service life.

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.

Engineering Information

Superior Performance

Starbars will give you superior performance due to their high density – approximately 2.4 gms/cc. This gives the Starbar very slow aging characteristics and additional strength.

interchangeability

Starbars are interchangeable with all silicon carbide heating elements manufactured in the United States as well as higher resistance heating elements manufactured for the Asian and European markets. It is important to provide the nominal electrical resistance when ordering Starbars. Please contact us, before attempting to substitute.

Electrical Characteristics

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).

Electrical Loading

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.

Power Supply

Ease of Replacement

Starbars can be replaced while the furnace is at operating temperature. The power to the Starbars being changed should be shut off, the spring clips and aluminum braid released, and the old Starbar removed. The new Starbar should be inserted smoothly through the hot furnace with sufficient speed to insure that the aluminum is not melted off the terminal end but not so fast as to cause thermal shock.

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

Service life

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)
Atmosphere
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.

availabilty

Starbars can be shipped from stock, or two to three weeks after receipt of an order.

custom conFiguration

RA configuration
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.