high temperature electric muffle furnace with atmosphere | cyky

Chamber,  automatic, vacuum, high-temperature electric muffle furnace with a protective atmosphere in a nitrogen (argon) environment for brazing metal-glass products and heat treating parts at temperatures up to 1150 ° C

high temperature electric muffle furnace

high temperature electric muffle furnace Key parameters and dimensions

A possible atmosphere in the workspace is nitrogen or argon;

Muffle working space (diameter × depth) – at least 350 × 450 mm

Overall dimensions of the furnace with stand (Width × Depth × Height) – no more than 1000 × 1200 × 1950 mm;

The width of the furnace with a gas shield is not more than 1450 mm;

Overall dimensions of the control cabinet (Width × Depth × Height) – not more than 700 × 500 × 1700 mm;

(the dimensions of the equipment are due to the installation of the old furnace in place of the layout);

The mass of the furnace (without loading) – no more than 650 kg;

Type of heating – electric;

Main technical, economic and operational indicators

Operating temperature range – (200-1100) ° С;

Maximum temperature – 1200 ° C;

Range of working temperatures during the work in vacuum – (200-400) ° C;

The error in setting the temperature according to the volume of the working chamber is ± 7 ° C;

Accuracy of temperature maintenance – ± 3 ° С

Pumping out the muffle at a temperature of not higher than 100 ° C;

Working overpressure in the muffle – (1-5) mbar (0.001-0.005 kgf / cm2) (heating with gas supply);

The gas pressure at the entrance to the gas shield is not more than (0.3-0.5) kgf / cm2;

The residual pressure in the muffle during evacuation is not more than -0.9 kgf / cm2;

Inlet cooling water pressure – (2.5-3.0) kgf / cm2;

Nominal temperature of cooling water at the inlet – (+ 5 … + 20) ° С;

Maximum outlet water temperature – not more than 50 ° С;

Nominal volumetric flow rate of water – not more than 0.15 m³ / h;

Construction requirements, installation and technical requirements

The heating chamber should be rectangular in shape and lined with refractory thermal insulation. Powerful supports for fixing the muffle should be located at the bottom of the heating chamber. The front frame of the heating chamber should be made of heat-insulating plates. Plates in front should be covered with steel sheet with a hole for installing the muffle.

The muffle must be cylindrical and welded from sheet steel. The muffle must have two horizontal floors (shelves) and provide loading (16-20) of parts in devices with dimensions: Ø90 mm, height – 120mm.

The muffle must have a hermetically sealed opening with a diameter of at least 10 mm, for introducing control thermocouples into the working area of ​​the muffle (3-5) to certify the furnace.

The muffle flange should protrude from the furnace body forward and have a water cooling jacket. From the back of the furnace, gas supply and exhaust pipes must be introduced into the muffle. Gas supply to the muffle should be made under the lower shelf through a gas distribution device, which ensures filling the entire space of the furnace with gas and does not have “blind” places where there is no update of the supply of protective gas.

To completely fill the muffle with gas, the shelves should consist of separate ceramic plates spaced from each other and from the walls of the muffle. The gas pressure during heating and cooling should be maintained automatically within (1-5) mbar (0.001-0.005 kgf / cm2) and regulated by a rotameter. The whole process must take place in a flowing protective gas.

The gas outlet must be in the upper part, with the flow around the blocking labyrinth septum. In order to be able to evacuate, a nozzle connected to the vacuum pump must be cut into the lower tube. During evacuation, gas from the furnace muffle through the heat exchanger must be sucked off by a vacuum pump placed on a stand. The following must be installed in the vacuum line: manovacuum meter, solenoid valves, pressure sensors. After evacuation, the muffle should be filled with gas by direct feed, bypassing the flowmeters. After filling the muffle with inert gas, the necessary excess gas pressure in the furnace should be maintained automatically.

The gas flow rate at a dosed supply must be regulated by flow valves with an indication on the rotameters. To maintain overpressure in the muffle, the gas discharge pipe must have a pressure regulating valve, a manometer, and an overpressure relief valve.

The furnace door must be mounted on cantilever brackets with two support axes welded to the frame. When opening the oven, the lid must be retracted to the right side by hand – by turning around the axis. In this case, the internal heated part of the lid should always be directed in the opposite direction from the thermist.

high temperature electric muffle furnace must be heated by heaters made in the form of spirals worn on ceramic tubes. The tubes should be fastened around the edges in the supporting posts, and in intermediate positions are fixed by cantilever tubes mounted in the lining. Heaters should be located horizontally along the walls of the heating chamber along the entire height of the heating chamber and on the hearth. For accelerated cooling of the muffle with products, the furnace must be equipped with a purge fan, which is designed to blow air on the outer wall of the muffle and a duct system with drive dampers for supplying cooling air from the workshop room.

The fan must be installed on the stand, and the dampers on the furnace must provide the cooling speed set by the programmer in automatic mode and allow cooling the charge with parts from T = (1050 ± 10) ° C to T = (180 ± 10) ° C for (30-45) minutes.

high temperature electric muffle furnace control system must be fully mounted in the control cabinet, which must be installed next to the furnace and connected to it with cables.

The following must be installed in the control cabinet: PLC with an operator panel, temperature recorder, current indicator, logic elements, all power electrical equipment and other devices that ensure the operation of the electric furnace.

The control cabinet must provide the ability to quickly remove any instrumentation, control and recording devices.

The electric furnace must be equipped with a gas shield for supplying gas to the furnace and provide evacuation of the muffle, accelerated purge of the muffle with inert gas (bypassing the flowmeters), regulation of gas flow. The gas switchboard must have: pressure gauges, rotameters, control and shutoff valves, solenoid valves.

The gas shield must be installed on the stove to the left of the door.

The electric furnace must have emergency protection and blocking against unacceptable situations:

– protection against exceeding the permissible temperature;

– protection against breakage of the thermoelectric converter (thermocouple);

– blocking (shutdown) of heaters when opening a door;

– control of a break (or circuit) in power circuits using three-channel current indicators;

– monitoring the uniformity of the load distribution in phases, monitoring the correct operation of all power keys;

– diagnosis of malfunctions in the operation of the electric furnace and their interpretation on the operator panel;

– gas discharge in excess of the permissible pressure.

The electric furnace should be equipped with an automatic control system – ACS built using a programmable logic controller – PLC, which provides temperature control and all actuators of the electric furnace:

– PLC-based ACS must provide fully automatic maintenance of the specified modes of the electric furnace, as well as programmatically implement other heat treatment modes (if necessary) without making changes to the electric and electronic systems of the furnace;

– PLC-based ACS must have two independent temperature measurement channels: one channel is intended only for control according to specified programs, the second one should provide monitoring and recording of temperature conditions, as well as protection against unacceptable temperature values. The control system uses two temperature converters of type N, which do not contain precious metals;

– ACS based on the PLC using the operator panel should display on the mimic diagram: the status of all actuators of the furnace (open, closed, on, faulty, etc.), as well as the direction of flow in the gas lines. The operator panel should display all deviations and irregularities in the operation of the electric furnace, which will simply and clearly inform the personnel about all the problems that have occurred in the electric furnace;

– An ACS based on a PLC should implement a special function of heating an electric furnace according to a given mode with setting coordinates TIME-TEMPERATURE in 16 sections. ACS of an electric furnace should have a convenient graphical interface for setting heating modes and may contain in memory several programs that can be opened from the main menu.

In the delivery state of the furnace, the ACS must be programmed for three main heat treatment modes:

Mode number 1.

  1. Evacuation to minus (0.9-1.0) kgf / cm2 for 10 minutes.
  2. Inert gas discharge.
  3. Evacuation to minus (0.9-1.0) kgf / cm2.d. Heating to T = (400 ± 15) ° C for (60 ± 15) min.
  4. Exposure at T = (400 ± 15) ° C for (30 ± 5) min.
  5. Supply of flowing gas pressure (0.1-0.3) kgf / cm2.
  6. Heating to T = (880 ± 15) ° C for (70 ± 15) min.
  7. Heating to T = (900 ± 15) ° C for (40 ± 15) min.
  8. Exposure at T = (900 ± 15) ° C for (20-30) min.
  9. Heating to T = (950 ± 10) ° C for (40 ± 15) min.
  10. Exposure at T = (950 ± 10) ° C for (1-3) min.
  11. Cooling to T = (70 ± 20) ° C for (100-120) min.
  12. Turning off the gas supply at T = (70 ± 20) ° C.

Mode No. 2.

  1. Evacuation to minus (0.9-1.0) kgf / cm2 for 10 minutes.
  2. Inert gas discharge.

с. Evacuation to minus (0.9-1.0) kgf / cm2.

  1. Heating to T = (400 ± 10) ° C for (20-30) min.
  2. Exposure at T = (400 ± 10) ° C for (20-30) min.
  3. Supply of flowing gas pressure (0.1-0.3) kgf / cm2.
  4. Heating to T = (900 ± 20) ° C for (40-60) min.
  5. Heating to T = (1050 ± 10) ° C for (20-30) min.
  6. Exposure at T = (1050 ± 10) ° C for (5-10) min.
  7. Cooling to T = (580 ± 10) ° C for (40-50) min.
  8. Cooling to T = (180 ± 10) ° C for (60-70) min.
  9. Turning off the gas supply at T = (180 ± 10) ° C.

Mode number 3.

  1. Evacuation to minus (0.9-1.0) kgf / cm2 for 10 minutes.
  2. Inert gas discharge.
  3. Evacuation to minus (0.9-1.0) kgf / cm2.
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