1.) Carefully unpack the MoSI2 elements from the packaging material in the master carton. Several individual cartons (5 or 6) will be taped together in the master carton. Lift the bundle out of the master carton and lay it on a table or flat surface.
2.) Cut the tape holding the individual cartons together and lay each individual carton flat on the table, with the chip box edge up. Cut the tape and allow the chip box to open. Carefully remove the two or three layers of foam exposing the individual element.
3.) When unpacking individual elements care should be taken to avoid any bending or twisting of the element. DO NOT squeeze the aluminum sprayed ends together.
4.) Place the element horizontally on a table and insert the terminal ends in the passage brick ensuring that the correct length of terminal ends are protruding from the top of the brick. Do not remove the wooden spacer until the terminal ends have been inserted in the brick. Then remove the spacer. Be careful not to scratch the glaze coating on the Lu section.
5.) Pack the appropriate grade ceramic fiber loosely into the terminal holes approximately .5" to 1" in from the cold face. DO NOT pack too tightly; allow for expansion. This packing is only to prevent heat from chimneying out attacking the terminal straps.
6.) Attach the element holders to each terminal leg and tighten in place. Be sure each leg has the same dimension from the top of the holder to the end of the leg. Be careful not to twist or bend the element during this process. When determining the position of the element holder it is critical that the tapered section between the heating section and the terminal end be completely below the hot face of the lining. If any part of the tapered section is in the refractory lining it may overheat causing element failure or refractory damage.
7.) Connect the aluminum braided strap to the terminal ends of the element. Do not bend or twist the element during this procedure. Be sure to connect the strap to the element before attaching the strap to the bus bar.
8.) The element is now ready for installation into the furnace.
9.) Once the element is positioned in the furnace, connect the terminal strap to the bus bar. Do not pack insulating material in the terminal compartment (over the braid) or the braid will get too hot and fail.
10.) Now check the element to be sure it is free to expand and contract on heating.
11.) Turn the power on to the elements and bring them up to temperature. To grow the protective glaze on the elements, the elements should be raised to a temperature of 1200ºC and operated at this temperature for about 15 minutes.
The 1200ºC should be obtained in 1 to 3 minutes. The furnace does not have to reach temperature, only the elements. This can be accomplished with the door open or closed.
We caution that the amperes through individual elements not be exceeded, 3/6--75 amps, 4/9-- 115 amps, 6/12--200 amps, 9/18--365 amps, 12/24--560 amps. 12.) After the initial heat up, turn the power off and check that both the element holders and the braid connections are tight.
Sometimes expansion takes place on heating, resulting in loose connections. Be sure the element has not slipped or cocked in the terminal holes, by checking that both terminal ends are equal.
Distance to wall
It is important that the distance between wall and heat- ing zone of the element is large enough to avoid contact. In the case of long elements at high temperatures, electro- magnetic forces and bad centering when installing the elements may cause the elements to come in contact with the walls, causing damage.
The minimum distance, between the heating zone of the element and the furnace walls depends on the length of the element (see the figures to the right).
When installed along the wall it is:
For Le < 1000 mm (39.4 in); e = Le /20
For Le < 300 mm; e = min. 15 mm (0.6 in)
For Le > 1000 mm (39.4 in); e = min. 50 mm (1.97 in)
When installed perpendicular to the wall, the deformation due to the electromagnetic forces must also be considered. The reason is that the deformation causes reduc tion of the distance between part of the heating zone and the wall. After calculating the magnitude of deformation , the distance E can be calculated and e is estimated in the same way as for elements installed parallel to the wall.
A – a
Emin = e+ 2
Distance to bottom
In order to prevent the elements from coming into contact with any material deposited on the bottom of the furnace and to compensate for the elongation of the elements at high temperatures, the recommended vertical distance h between the element bend and the furnace floor should be at least:
h ≥ Le ; min. 10 mm 20
Distance between elements
Minimum distances, b, between adjacent elements are given in the figure on the below page “Necessary distances”.
Necessary distance,b,to counteract the effect of the electromagnetic force on QS heating elements
Deformation of QS heating elements due to electromagnetic forces valid for all sizes
Important istallation parameters for passage brick and skewbrick
Hole diameter of passage brick
Recommended min. width of opening in skew brick, w
The minimum length of opening A is calculated according to the diagram above
Vertically mounted elements
The exceptional properties of QS MOSI2 elements can best be utilized when the elements freely radiate in the furnace chamber.
U-shaped elements fitted through the furnace roof and vertically suspended in the furnace should be considered as the standard design for a QS MOSI2 furnace . The elements are normally placed along the side walls, but in wide furnaces it may be necessary to place elements across the width of the furnace to provide the power required.
Certain furnace designs do not permit elements to be fit- ted through the roof. The internal height of the furnace may be such that more than one level of elements must be installed. In these cases elements with bent terminals or heating zones are available .
Horizontally mounted elements
In some types of furnaces where the roof height is low, horizontally installed QS MOSI2 elements may be the most economical and efficient alternative.
As QS MOSI2 elements start to soften at tempera- tures around 1200°C , they must generally be supported when used horizontally. This limits their maximum operating temperature because of possible reactions with the supporting material. If a reaction occurs between the silica layer on the element and the supporting brick, the element may adhere to the brick and fracture when cooling down. Even when suitable dense bricks of sillimanite or mullite type are used,
the maximum element temperature must not exceed 1600°C (2910°F). Sillimanite or mullite grains (≈ 3 mm/0.12 in) can be used on the supporting surface where applicable.
Brick lined furnaces
To facilitate the installation of QS MOSI2 elements in brick lined furnaces, passage bricks are used. They are installed in openings in the roof or side wall (fig. 1 and 2). The passage bricks mounted through the roof often rests on a skew brick, which has oval holes for the elements. The passage bricks are made of heavy duty insulating firebrick of a quality matched to the furnace temperature.
Ceramic fiber lined furnaces.
In fiber lined industrial furnaces, e.g. forging furnaces, if passage plugs of fiber or refractory bricks are used, then the complete element assembly also needs to be supported by the furnace roof or side walls.
In small fiber lined furnaces, e.g. laboratory furnaces, it may be sufficient to introduce the QS ele- ments through slots in the insulation and fill the space around and between the terminals with loose ceramic fiber .
In furnaces for temperatures above 1700°C (3090°F), it is important to relieve the hot face lining of the roof from the weight of the element assembly. It is recommended to use a divided passage plug of ceramic fiber or a passage plug supported by the cold side of the roof .
The weight of the element sets is carried by the outer lining. Especially useful in furnaces for very high temprrature.