Cementing - Nitriding

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Types of Equipment in Use

Electric resistance multipurpose shaft furnaces enable chemical and thermal processing of metals. They are particularly suitable to :

• Cementing and nitriding in a process atmosphere
• Box quenching
• Tempering and annealing in a process atmosphere

Description:

The working area is separated from heating with a metal muffle of creep-resisting steel. The muffle is closed with a cover. The muffle and the cover are sealed with silicon rubber placed in a water-cooled labyrinth. A fan and working media supply inlets are fitted in the furnace cover. The fan circulates the process atmosphere and thus promotes even temperature distribution in the furnace. A circulation sheets in the muffle improve the distribution of the atmosphere in the working area. The furnace lining is of light-mass materials and fibrous insulation, which provides for low heat losses and better economy of the operation. The cover is lifted by a hydraulic cylinder and moving aside manually. The furnace heating input is controlled by a semiconductor switching element (solid state relay). This electric connection provides for the heating longer service life and decreases the peaks in power demand. The temperature in the furnace is measured by a calibrated thermocouples and controlled by a microprocessor programmable controller.. If requested, also instruments communicated with PC or another master control system may be supplied.

Process:

The furnace is designed for fast after-cooling of the charge under the atmosphere or charge controlled cooling.

It may be provided in two options:

• 1. Installing of a cooling shaft. The charge closed in a muffle with a lid is transferred by crane manipulator and subsequently cooled down in a protective atmosphere
• 2. A system providing for a complete system of cementing and controlled cooling of the charge is fitted in the furnace. The fan blows cold air in, on the muffle. The warm air from the furnace area is conducted outside the hall through exhaust flanges in the upper part of the furnace under the lid. The cooling system is controlled by electromagnetic flap valves controlled from the temperature controllers according to an appropriate curve as required.

Nitriding (CAK 3,5.5/10 – PBS TURBO s.r.o. Velká Bíteš)

Nitriding in gaseous atmosphere takes place at the temperatures of 500 – 550°C, in ammonia atmosphere. Atomic nitrogen is produced in result of ammonia cracking in the retort and diffuses to the charge surface layer. Effects on the nitriding process are produced by precise control of the gas quantity dosing. Where high quality of heat processing is required, use of process continuous control and an analyser is recommended for use. Ammonia and industrial nitrogen are the working media.

The chemical and heat process is controlled by a control system including any elements required for the automated process, i.e. appropriate sensors, temperature programmable controller, nitriding controller, ammonia analyser, gas distribution controls, control software with various levels of display and the process recording by means of a PC.

Cementing (CAK 8.15/10 – Nová Huť a.s. Ostrava)

Chemical and heat process is controlled by a control system including an atmosphere composition sensor, temperature and carburising programmable controller, gas distribution controls, control software with various levels of display and the process recording a PC included.

Working media are hydrocarbon liquid (methanol), carrying gas (natural gas or propane-butane) , industrial nitrogen, pressure air.

• Cementing speed: 0.1 – 0.15 mm/hr
• Cementing range: 0.1-2.5 mm

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