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Technical Data

• Typical Operating Characteristics
• Installation Methods

Electrical Characteristics

(GRAPH FROM BROCHURE)

Typical Resistance Temperature Characteristic of a Kanthal SiC Heating Element at Standard Calibration of 1960°F (1071°C)

Kanthal Globar elements have a negative resistance characteristic at temperatures to approximately 1,200°F (650°C). Above that temperature, the characteristic changes to positive and remains positive throughout the normal operating temperature range as shown in the accompanying graph. The curve as shown from room temperature to 1200°F is an average curve, since traces of impurities have a noticeable effect on the cold resistance. These impurities, however, are not a factor in the higher temperature range. Therefore, nominal resistance ( the value used when making calculations) is measured at 1960°F (1071°C).

All elements are tested in open air with an electrical loading of 100 watts per square inch (15.5 watts/cm²). The same test voltage is applied to any one size and the calibrated current is marked on the right-hand end of the element as well as on its individual shipping carton. The resistance of the elements should never be determined at room temperature.

Watt Loading

(GRAPH FROM BROCHURE)

Recommended Watt Loading for Kanthal Globar Elements

The watt load for an element is established by dividing the watt input by the square area of its radiating surface.

The recommended watt loadings of elements operated at various control temperatures are given in the accompanying graph.. The upper curve is used to select the number and size of elements for a given maximum input in atmospheres of air and inert atmospheres such as argon and helium. The lower curve applies to reducing atmospheres of hydrogen and nitrogen.

More favorable results can be obtained by conservative watt loadings.. The most satisfactory service is usually obtained with loadings in the range of 20 to 45 watts per square inch (3.1 to 7 watts per square centimeter) depending on temperature.

Atmospheres

Kanthal Globar elements can be operated at up to 3000°F (1650°C) in air and inert atmospheres. The maximum operating temperature for Globar^® Type LL elements is 2800°F (1538°C). Some atmospheres at certain temperatures shorten the element's life.. The dew point of the atmosphere and the watt loading on the element are also factors that combine to affect element life.

Kanthal Globar elements can be operated at up to 2370°F (1300°C) in hydrogen and disassociated ammonia atmospheres. In atmospheres containing nitrogen, silicon nitride will form if a temperature of 2500°F (1370°C) is exceeded. Exothermic gas can be used up to a carbon monoxide content of 18%. Methane and hydrocarbon vapors and certain atmospheres reduce element life.

In a carbonaceous atmosphere, Kanthal Globar elements will tend to pick up carbon. This is a slow process, and the resistance drop can be noted by a gradual increase in amperage. The carbon has no detrimental effect on the element. However, it can short-circuit sections of the element, thus increasing the electrical load on the remaining section and reducing the life. The carbon can be burned out by shutting off the atmosphere and introducing air into the furnace chamber at periodic intervals.

Excessive moisture, methane and hydrocarbon vapors should be kept out of the high-temperature zone of the furnace where the elements are located. The combination of element watt loading, temperature and atmosphere should be kept in balance at all times, and recommended limits should not be exceeded.

Kanthal Globar elements are easily installed. While they can be mounted horizontally or vertically, elements should be mounted centrally in a furnace chamber, and heating sections should be 1” (25mm) longer than the chamber span. The conical-shaped ½” (13mm) deep recess in the terminal holes at the inner wall allows the end of the heating section to radiate properly and helps maintain uniform temperature within the chamber.

The cold end terminals of elements mounted horizontally lie flat in the bottom of the terminal hole. Ceramic fiber insulation tucked around but not under the terminals will prevent heat from escaping through the terminal holes. Ceramic fiber paper or tubes that extend about halfway through the furnace wall can be used to prevent terminals from adhering to the brickwork because of process glazes. The use of insulating ceramic terminal tubes is recommended. See Element Accessories section.

(ILLUSTRATION FROM BROCHURE) Horizontal Installation

Vertically mounted elements should be centered in the terminal holes and supported by an insulating support at the lower terminal. Bulk ceramic fiber insulation, tucked around the top and bottom terminals, prevents a chimney effect. Ceramic fiber flanged tubes can also be used.

Elements must be mounted so they are free to expand and contract, and not be subject to tension or strain.

(ILLUSTRATION FROM BROCHURE) Vertical Installation with Arched Roof

(ILLUSTRATION FROM BROCHURE) Vertical Installation with Flat Roof

Terminal Hole Diameters

To allow sufficient clearance, the element terminal holes should be in line and of the same diameter shown in the accompanying table for standard wall thicknesses. Wall abrasion can result from sliding elements in and out of the chamber. Therefore, the holes through the insulating board should be enlarged. The terminal hole in the steel shell should provide sufficient clearance to prevent short circuits.

Terminal Hole Diameters

Recommended Element Spacing

To allow for the most efficient radiation, the minimum distance between element centers should be twice the element diameter. The minimum distance from the center line of an element to any wall should not be less than 1- times the element diameter. The recommended spacing for all Kanthal Globar elements is shown in the accompanying diagram.

(DIAGRAM FROM BROCHURE) Recommended Element Spacing Guidelines

Connections

Care must be used when placing the terminal straps and clamps on elements to help prevent breakage.

An aluminum strap should be wrapped around the terminal end of LL or SG elements and held in place by either M or C type spring clamps.

Type M clamps with wings are used when there is enough space available for the clamp to be fitted on the element without shorting of the electrical connection.. When the C clamp is required, the expanding tool is used to fit on the element in order to avoid mechanical shock.

Enough slack should be left in the straps to allow for element expansion.

Sufficient clearance should be left between the two when the furnace is up to temperature.

Installation Methods for SGR Elements

Kanthal Globar SGR elements can be mounted horizontally or vertically, projecting up or hanging down. The terminal assembly should be outside the furnace structure to keep it as cool as possible. No portion of the spiral heating section should extend into the refractory wall.

The element should be mounted in an insulating ceramic terminal tube to prevent possible shorting of the terminal ends, because full element voltage exists along the entire length of the terminal. The element should be mounted as shown in the accompanying diagrams. The slot in the terminal should not be in contact with the terminal tube or brickwork.

The terminal slot must remain free of any electrical conducting material, such as condensed metallic vapors, carbon, ceramic glazes, and other materials which lose their electrical insulating properties at high temperatures.

In some installations where elements are mounted horizontally, it may be necessary to support the tip end of the element in a blind hole drilled in the opposite wall of the chamber. The blind hole should be at least ½” (13mm) larger in diameter than the element and have a ½” deep conical recess for easy element installation. Special SGR elements, with longer, unspiraled sections at the extremity of the element should be used for this type of installation.

Recommended Element Spacing

Recommended element spacing for SGR elements is the same as for LL, SG and CR elements. Click here for details.

Terminal Hole Diameters

Recommended terminal hole diameters for all Kanthal Globar elements are shown in the accompanying table. However, insulating ceramic terminal tubes are highly recommended for use with SGR elements. When insulating ceramic terminal tubes are used, the diameter of the holes through the chamber wall is determined by the outside diameter of the terminal tube. When properly installed, the element, terminal tube and terminal hole should all have a snug fit. Click here for terminal tube dimensions.

(DIAGRAM FROM BROCHURE) Horizontal

(DIAGRAM FROM BROCHURE) Horizontal into Blind Hole

(DIAGRAM FROM BROCHURE) Hanging Down

(DIAGRAM FROM BROCHURE) Projecting Up

Physical Specifications (DIAGRAM FROM BROCHURE)

Element diameter (inches)	Dimensions (inches)					Terminal Strap Ampere Rate
	D	F	T	V	W
½	1-¾	½	1	1	2-1/8	25
5/8	1-¾	½	1	1	2-1/8	25
¾	2-¼	½	1	1	2-1/8	25
1	2-¼	½	1	1	2-1/8	50
1-¼	3	½	1-½	1	2-5/8	50
1-½	3	¾	1-½	1	2-5/8	50
1-¾	3-½	¾	1-½	1	2-5/8	100
2-1/8	4	1	1-½	1	2-5/8	100