Bell Furnace by Therelek

Bell furnaces are removable retort type furnace which is lowered over the load and hearth. The inner retort is placed over the loaded hearth sealed at the bottom and provided with a constant protective atmosphere. The outer heating shell is then lowered over the assembly.


A bell furnace with an outer heating shell holds several retorts. In case of dense hearth loadings, a motor-driven fan for circulating the atmosphere inside the retort provides more rapid uniform heating.

The workload is placed on an elevated refractory metal hearth that rests on an insulated base clad with an alloy plate material. A water-cooled circumferential flange and vacuum gasket are located on the vacuum-tight base cover adjacent to the heated zone.

A retort made with heavy walled heat-resisting alloys covers the workload. A flange at the bottom of the retort fits on top of the base gasket to provide a vacuum-tight enclosure. The bell-shaped furnace equipped with internal electrical heating elements is lowered into position over the retort by a vertical hoist.

The vacuum pumping system is connected through the insulated base since this furnace cannot be heated or cooled rapidly even after rooming the bell-shaped vessel. The production rates and the number of thermal cycles within a given time period are limited. The hot retort will support the entire pressure of the external atmosphere for the wall being heavy. The operating temperature of these furnaces is limited to 925 °C.

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Features & Specifications

Title Description
Temperature Range Up to 1100°C (Bell Annealing Furnace) & Up to 1500°C (Bell Jar Furnace)
Standard Applications Wire annealing, Annealing, Isothermal Annealing, Brazing, Sintering, Vacuum Hardening, Vacuum Stress Relieving, Vacuum Tempering, Laboratory Applications
Insulation Vacuum Formed Ceramic Fibre Boards / Ceramic Fibre Blanket & Module / Refractory Brick Lining
Heating Media Options Electric/Gas Fired/Oil Fired
Heating Elements Nichrome Wire / Special Alloy Resistance Heating Wire / Silicon Carbide Rod Type
Furnace Classification Class 2/Class 3
Instrumentation options Thyristor, Programmable Temperature Controller, Temperature Recorder, PLC, SCADA, HMI

Types of Bell Furnace

Bell Annealing Furnace

Bell Annealer brings in excellent temperature uniformity, consistent quality and good production rates.

Bell Annealing Furnace

Bell Jar Furnace

Therelek’s Bell furnace is designed with optimal performance for high sensitivity and delicate components.

Bell Jar Furnace


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