CASE STORY 1
For continuous hardening in furnace atmosphere
Factory was established in 1964 as an independent heat treatment company
The company operates today a number of different furnaces like rotary hearth, continuous rotary, continuous shaker, sealed quench, pit furnaces and induction furnaces, all elec- tric. The furnaces are equipped with QS (MoSi2) heating elements.
The production volume is about 35 tons/day and the plant is operated on a continuous base 24 hours per day, at present for ﬁve days per week. Maximizes process control with four separately zones. Most of the customers are found in the automotive industry all . The process control of the furnaces is completely computerised and monitored from a central unit. This contributes to a very high efﬁciency and quality and less need of manpower. The total number of employees is about 30.
One of the ﬁrst furnaces installed was a salt bath furnace for nitrating and carbonitriding, with limited production capacity and an old process control system. The furnace did not meet the demands of company any longer and a decision was made to replace this furnace with a completely new integrated hardening line. Company have used QS heating elements in their sealed quench furnaces directly in the furnace atmosphere for many years with very good experiences, and would prefer to have the new line heated in the same way.
The lifetime of the elements was in average 6-8 monthes, and the high power resulted in a very short recovery time after charging and consequently a high and reliable production. A similar performance was expected for the new line as the atmosphere and temperature would be the same.
The new line was designed and built by the Italian furnace builder . It consists of a high temperature furnace for carbonizing and carbonitriding, a quenching unit, cleaning and tempering.
The total power is 240 kW with QS MoSi2 heating elements. The elements are powered by a transformer and connect four elements in series in three groups per phase. The maximum temperature is 940°C (1720°F), although the process run by company nor-mally requires 900–920°C (1650–1690°F). Each element is of the 1700 type, with a heating zone length of 670 mm (26.4 in), rated between 4177–5842 W. Zone 1 and 4 are using 12/24 and zone 2 and 3 6/12 elements. (Dimension in mm of the heating zone diameter/terminal diameter.) The furnace is equipped with a mufﬂ e and the elements are installed vertically from the roof between the lining and the mufﬂe.
The atmosphere is an endothermic mixture of natural gas, N2, methanol, cracked ammonia, CO and air. The carbon potential is 1.0–1.1%.
Qs heating elements are the only electric elements that can be operated directly in the furnace atmosphere without using any protection tube.
The new line is easily controlled through the whole pro- duction process. This is due to four separately controlled zones in the new line.
CASE STORY 2
For ,high flexibility and productivity in decorating kilns
A well known company, is a large producer of porcelain, gift items and table- ware. A high proportion of its products are exported
Factory has three electric front-loaded, fiber insu- lated kilns, designed and built by the furnace builder Prins Ovenbau BV, Holland, for decorating porcelain at 1015°C (1860°F) in air atmosphere.
Usable chamber size is about 10 m3 (353 ft3). One firing cycle takes about 14 hours. The porcelain products are stacked in several layers on ceramic stands, each 650 mm (25.6 in) wide.
Factory wanted to achieve a better result for their products in terms of colors and quality. This was achievable through a higher and more even tempera- ture in the furnace. Another factor that was important both for working environment and the result of the pro- duction, was to minimize the level of combustion gases from the gas heated kilns.
Total installed power in each kiln is 450 kW generatedby six rows of eight QS molybdenum disilicide (MoSi2) heating elements of the 1700 6/12 type. The heating zone length, Le, is 1250 mm (49.2 in) and the terminal length, Lu, is 315 mm (12.4 in). Each element is rated at 9.375 kW.
The eight elements in each row are connected in series to line voltage without transformers and regulated by phase angle thyristors. The porcelain products are biscuit fi red in direct heated gas kilns.
The heat transferred from the heating zones of the elements to the furnace load is relatively minor. The majority of the heat transfer onto the products is radiant energy reflected from the furnace interior – walls, roof, floor, kiln furniture and also the products themselves. When firing ceramic products an even temperature gradient is very important and the refl ected radiation contributes to this evenness, which cannot be achieved in a gas heated kiln.
With QS MOSI2 heating elements on bothsides of the product stands, the required evenness of temperature throughout the kiln is achieved. The radiation energy reflected is of such magnitude that the additional metallic floor elements once installed, are not needed.
The experience from the Gmundener installation is that the decorating enamel becomes brighter when fired in an electric kiln with an air atmosphere, compared to direct gas heated kilns. Some metal oxides in the enamel such as copper oxide, cannot be fired in gas heated kilns as the correct color balance cannot be obtained.
Another advantage of electric kilns is the absence of the combustion gases, which are produced in gas heat- ed kilns. Electric kilns are, therefore, environmentally friendly. The yield of the decorating firing is normally 100% when the enamel is correctly applied.
A heating system, based on QS MOSI2 heating elements, has due to high and even quality a long lifetime. In addition, their high density makes them resistant to chemical attacks. The heating system for kilns, when assessed in terms of cycle time, energy cost and total economy can equal the performance of direct gas heated kilns.
CASE STORY 3
For high quality and improved economics in the glass industry
Factory is famous throughout the world for the artistic excellence and technical quality of its crystal glass and crystal artware. factory traces its his- tory back to the 18th century. An electrically heated feeder with QS molybdenum disilicide (MoSi ) heating elements has been playing its part in maintaining the superb quality of products.
Factory wanted to install a new feeder to be able to reduce energy costs, boost the yield and improve the working conditions
A feeder and forebays was installed and were heated by 111 QS elements. The total power is 350 kW, and the production capacity is three tonnes per day
QS MoSi heating elements are monitoredautomatically by a computer that measures and re- cords the temperature in several parts of the feeder and in the forebays
Melting is carried out in an oil-heated tank furnace. The tank is connected to a feeder forehearth which has forebays.
The feeder has proved its worth over the years. All of the original objectives have been met, and the cost per unit of glass produced has also dropped, in spite of the in- creased cost of electrical energy. The quality of the glass has also been maintained at a consistently high level.
The heating system guarantees temperature control that is as precise as it is simple. No stoppages in production, no combustion by-products to spoil the brilliance of the glass, and nothing to impair the efficiency and economy of production. The molten glass is maintained at uniform temperature and a consistent viscosity throughout.