Silcarb Recrystallized Private Limited

Silcarb boasts of a manufacturing plant spread across 2½ acres plot with all requisite facilities to manufacture products as per defined industry standards. Our state-of-the-art infrastructure, equipped with modern machinery and equipment enables us to manufacture a wide range of Silicon Carbide Heating Elements and custom made industrial furnaces.

Currently we are working on advanced ceramic as applied to heating systems.

Silcarb, An ISO 9001-2008 company is India's premier indigenous manufacturer of Silicon Carbide Heating Elements, with its plant located at Bangalore, South India

Silcarb's 'ALPHA ROD' Silicon Carbide Heating Elements Series is made of Re-Crystilliaized Alpha Silicon Carbide.

Silicarb's 'SPIROHEAT' Silicon carbide heating elements are made of Reaction bonded Silicon Carbide.

'Alpho Rods' and 'Spiroheat Elements' are available in different Configurations for connections from two ends or from one end.

The resistance of a silicon carbide element is difficult to measure at room temperature due to minor impurities, self heating and contact resistance. Also the green silicon carbide has a negative resistance temperature characteristic from room temperature to approximately 8000C. It turns positive at this point and remains so throughout its normal operating temperature range. A typical resistance temperature characteristic curve of a silicon carbide heating element is show in another Figure.k walled tubes. They have a central heating section referred to as a hot zone and two terminal sections called cold ends. The cold ends are impregnated with silicon metal to lower their resistance. This causes them to operate at a lower temperature. The extremities of the elements are metalized with aluminum to provide a low resistance contact surface to which the electrical connections are made with braided aluminum straps. Elements are described by giving the overall length, the heating section length, the diameter and resistance.

Electrical Characteristics of Spiroheat / Alpha Rod Elements

Installation and Maintenance

Silicon Carbide Heating Element : 

High Performance :

The Alpha Rod elements will give you superior performance due to their high density – approximately 2.4gms/cc. This gives the element very slow aging characteristics and additional strength.

Operating Temperatures :

The Alpha Rod Element s can be operated at furnace control temperatures up to 14500C in an air atmosphere or inert atmospheres of argon or helium. In reducing atmosphere the maximum recommended operating temperature is 13500c.

Electrical Characteristics :

The Alpha Rod Element is a linear resistance heater that converts electrical energy to heat energy(Joule’s LawW = 12R). W=power in watts, l = Current in amperes, R = resistance in ohms.

The heating elements are often referred to as self-bonded, for the lattice structure or bonds that hold the elements together are formed by recrystallizing the silicon carbide at very high temperatures. The elements are manufactured of green silicon carbide which is classed as an excess electron type semi-conductor.

The resistance of a silicon carbide element is difficult to measure at room temperature due to minor impurities, self heating and contact resistance. Also the green silicon carbide has a negative resistance temperature characteristic from room temperature to approximately 8000C. It turns positive at this point and remains so throughout its normal operating temperature range. A typical resistance temperature characteristic curve of a silicon carbide heating element is show in another figure..C.

Alpha Rod heating elements increase gradually in resistance with use. This characteristics of increasing in resistance is called aging. Aging is a function of the following :

• Operating temperature.
• Electrical loading – usually expressed in watts per square centimeter of element radiating surface
• Atmosphere
• Type of operation (continuous or intermittent)
• Operating and maintenance techniques

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

When mounting elements vertically they must be supported on the lower end by electrically insulated supports.

Alpha rod Elements 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 ½ inch deep is located on each interior wall where the element passes through. This allows the hot zone to radiate properly and helps maintain a uniform temperature in the kiln.

The resistance of Spiroheat / Alpha Rod Element varies with temperature as detailed in the figure below. From a relatively high value at room temperature it falls to a minimum at about 800 Degree C and then gradually rises up to its maximum operating temperature. The resistance value at 1400 Degree C will approximately by 10% more than its value at 800 Degree C. The Voltage across the element and the current passing through it should be measured at about 800⁰C to determine the resistance (V=IR).

Element Loading

The Operating temperature of the elements is dependent on both the furnace temperature and the specific element loading, normally expressed in watts per square centimeter of the Hot Zone area.

Operating Temperature

Spiroheat / Alpha Rod Elements may be operated in air at furnace temperature of upto 1450⁰C. Elements may also be used in neutral or reducing atmosphere but a lower temperature limit may be required. Maximum recommended operating temperatures for Spiroheat / Alpha Rod Elements in various process atmospheres.

Spiroheat / Alpha Rod elements are normally operated in air or other oxidizing atmospheres, as other gases may react with the element material or the protective glaze, thereby causing a reduction in element life. It is recommended that the manufacturer be consulted if the use of Spiroheat Element in a reducing atmosphere is being considered.

Water vapour has a serious effect on ‘Spiroheat / Alpah Rod Element’, by increasing, the oxidization of the material and hence the ageing rate. Furnaces should be thoroughly dried before the elements are installed but if it is essential to use the elements for drying, then the furnace should be well ventilated and no build up of steam should be allowed to occur.

Other process vapours many also adversely affect element life, either by chemically attacking the silicon carbide and the protective glaze of by condensing in the element support holes causing restriction and subsequent breakage. Most alkali vapours will have a detrimental effect, halogen gases, metal halides (e.g. Fluxes in aluminum furnaces) and also most of the metallic oxides. To minimize any attack an efficient extraction system should be incorporated to reduce the volatile concentration in the chamber to an acceptable level. This will also encourage an inflow of air over the element cold ends and minimize any condensation at these points.

Type DE & SE elements must be accurately positioned in the furnace to ensure that the hot zone does not enter the element support holes. It is important to ensure that elements are free to move in all directions and mounting holes must be aligned and sufficiently large to prevent restriction, for expansion during hot condition.

Type DE / Alpha Rod Elements

Special lead-in sleeves are available for each size of element. They should be fitted from the outside of the furnace in holes bored to a diameter which will ensure a loose fit. Sleeves should never be cemented into position.

If sleeves are not used then the element support holes should be about 3-6mm large than the element diameter for sizes up to 18mm about 8-10mm for larger sizes. For exceptionally thick furnace lining and where there is a possibility of volatiles condensing on the cold ends, a fairly large hole diameter should be used and the elements centralized by supporting them on a small ceramic fiber pad under cold end.

Special lead-in sleeves are recommended for use with SE elements to provide the correct alignment and support required. These sleeves should be of a loose fit and not commented into positions. Type SE 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 xtend into the refractory wall. The element should be mounted in a high Die-electric lead-in sleeve to prevent possible shorting of the terminal ends, because full element voltage exists along the entire length of the Terminal.

• The Correct size of elements should be chose at the design stage of the furnace. This is to ensure that the wattage loading does not exceed that shown in the Element loading graph.
• The element support holes must be of the right size, i.e. 3 to 6mm large than the element diameter upto 18mm and 8-10mm for larger sizes and should be installed along with ceramic lead-in sleeves for both type DE & SE Elements.
• The aluminum braid connections should be flexible and long enough to avoid any stress on the elements.
• Connecting spring steel clips tend to loose their tension over a period of use. Therefore, new clips should be used whenever an element is replaced.
• When elements are connected in series it must be ensured that they are well matched in resistance. Generally not more than 2 elements should be connected in series.
• If an element breaks prematurely due to mishandling it may be replaced with a new one. However, if the furnace has been run for a long period, it is preferable to replace the full set of elements owing to the incompatibility of resistance due to ageing. Partially aged elements may be stored for later use with others of the same resistance of elements must be determined when it is at red heat since the resistance between room temperature and 8000C is available.
• Always select the minimum voltage tapping to give the required furnace temperature.
• When starting with new elements always select the minimum voltage tapping available.
• When an element is used continuously as in the case of a tunnel Kiln, special glaze treatment is required. Please specify use while ordering. It is recommended that a chart of the elements resistances be maintained and the resistance values of the elements operating be entered every 15days. This helps to monitor the life of the elements and also to change if required any element that may have aged abnormally to retain the balance.
• As these elements are fragile, handle with care, particularly whilst fitting the braids and clamps
• Block off the annular space between the element and the surrounding refractory with ceramic fibre of glass wool to prevent heat loss at the cold ends.