Heat treatment furnaces are divided into periodic types (integral-quench furnaces, pit furnaces, bell furnaces) and continuous types (mesh belt furnaces, pusher furnaces, roller hearth furnaces, rotary hearth furnaces) according to production methods. The integral-quench furnace is flexible and suitable for carburizing and quenching of many types; the mesh belt furnace is suitable for large-volume quenching of small parts such as fasteners; the push-rod furnace is suitable for large-volume carburizing of gears; and the pit-type furnace is suitable for long shafts and nitriding. The sealing methods and atmosphere zoning of different furnace types determine the difficulty and strategy of atmosphere control.
- Periodic type: integral-quench furnace, pit furnace, bell furnace, flexible but the consistency needs to be controlled between batches
- Continuous type: mesh belt furnace, pusher furnace, roller hearth furnace, large output, requires stable atmosphere partitioning
- The furnace type determines the sealing, air inlet point and oxygen probe placement location
- Multi-furnace workshops are suitable for centralized gas supply and unified monitoring
Periodic furnace
Sealed box type integral-quench furnace (Integral Quench Furnace) It consists of a heating chamber and a front chamber with an oil tank. The parts are heated and carburized in a protective atmosphere and then directly dropped into the oil tank for quenching. The advantage is that it is flexible and has a wide range of processes, and can be carburized, carbonitrided, and quenched; the disadvantage is that the atmosphere needs to be re-established in each furnace, air will enter when the door is opened, and the recovery time affects the quality consistency. integral-quench furnaces often form production lines, along with cleaning machines, tempering furnaces and automatic transfer vehicles.
pit furnace The furnace is vertical and the parts are hung and loaded. Suitable for deep carburizing of long shafts and large gears, as well as gas nitriding (pit nitriding furnace). The main seal is the furnace cover, and the atmosphere circulation in the furnace relies on the fan.
bell furnace It is mostly used for annealing wire rods and steel strip coils, often with hydrogen or nitrogen-hydrogen protective atmosphere.
Continuous furnace
Mesh belt furnace The parts are laid on a heat-resistant steel mesh belt and continuously pass through the heating zone and fall into the quenching tank. Mainly used for fasteners, stamping parts, and small bearing parts. The inlet and outlet are usually closed with fire curtains, and the atmosphere flows in zones in the furnace, and the areas near the outlet and inlet are easily affected by air.
push rod stove The material tray is pushed forward by the push rod in sequence, with multi-zone control, suitable for mass carburizing of automobile gears and other equipment. Different temperatures and carbon potentials can be set in each zone, which requires high atmosphere partitioning and flow balance.
Roller hearth furnace / rotary hearth furnace Parts or trays move on roller conveyors or rotating furnace bottoms, which are suitable for large-size parts or situations where quenching (such as pressure quenching) is required piece by piece.
The relationship between furnace type and atmosphere control
| Furnace type | Difficulties in atmosphere control | Control considerations |
|---|---|---|
| Integral-quench furnace | Open the door to take in air and rebuild the atmosphere in each furnace | Reasonable recovery time, enriched gas adjustment, door seal maintenance |
| Mesh belt furnace | Air infiltration at the inlet and outlet and air cross-flow between areas | flame curtain, air inlet point distribution, probes arranged by area |
| push rod stove | Different regions have different carbon potential needs | Zoning control and traffic balancing |
| Well type nitriding furnace | Ammonia decomposition rate, Kn uniformity | Hydrogen probe measurement, ammonia/diluent gas ratio control |
Shop-level perspective
When there are a dozen to several dozen controlled-atmosphere furnaces in a workshop, independent atmosphere preparation in a single furnace (such as methanol dripping from each furnace) will cause hazardous chemical management and consistency problems. The use of large gas production endothermic gas generators for centralized gas supply, unified pipelines and unified data monitoring is the choice of many large heat treatment plants. For example, Gauss Control has equipped 30 different types of controlled atmosphere equipment of Zhejiang Qiujing Technology with 3 RX generators rated at 160 m³/h each and a complete set of gas supply piping.
Frequently asked questions
How long does it take for the carbon potential to recover after the integral-quench furnace opens the door?
Depending on the furnace volume, atmosphere flow, parts loading and door seal condition, it usually takes several minutes to more than ten minutes. The control system should reasonably adjust the enriched gas during the recovery period and mark the recovery period in the record.
How many oxygen probes need to be installed in a mesh belt furnace?
At least one should be installed in the main heating/carburizing area; when the furnace is long or the partition processes are different, it is recommended to set up a probe in each control area and monitor the air infiltration in the exit area.
How to choose between pusher furnace and integral-quench furnace line?
When the variety is single and the batch size is large, the pusher furnace is more efficient; when the variety is multiple and the batch size changes greatly, the integral-quench furnace line is more flexible. Also consider quenching method, site and investment.