Precision cubed

Deutsche Version

Ipsen opens up new ways for heat treatment

Ipsen has created a special system for heat treating gearbox parts on behalf of Mercedes-Benz. The three-row pusher system requires comparatively little floor space but can nevertheless perform well – and all with particularly low power consumption.

Kleve, January 2014

The new Ipsen system for the heat treatment of gearbox parts, crown wheels and drive pinion wheels was moved into the Mercedes gearbox plant in Mettingen in the Neckar Valley in autumn 2013. The move was made all the more difficult by the site conditions since there was very little space around the planned three-row pusher furnace. Using a highly integrated feed mechanism it was possible, however, to install all the systems and components required for the heat treatment process in a very compact area. The high and low temperature furnaces, cleaning systems and quenching equipment were linked to form complex units while still providing good flexibility for various types of heat treatment for workpieces.

High-temperature furnace with single extraction door and oil bathThe workpiece charges are initially fed into the system manually using semi-automatic powered roller tracks for loading and unloading before they pass into the automatic charge storage conveyors. The charge temperature is raised in the preoxidation furnace to around 450°C. An intermediate transport unit then moves the charges into the entrance vestibule of the high temperature furnace. After then being pushed into the furnace’s heat treatment chamber, the charges are initially heated in the three-row heating zone to the carburizing temperature of over 900°C.

The subsequent three-row carburizing zone then takes care of the actual carburizing process in protective gas during which the carbon content for the surface of the workpieces precisely to suit requirements. The benefits of this are obvious – the three-row operation means that several charges can be treated at any one time which clearly helps to reduce cycle times so as to make the system more profitable.

At the end of the carburizing zone, the charges are once again transferred to a single-row hardening zone. At the end of this they are either quenched in an oil bath with two chambers which are separated by a gas-tight seal, or the charges pass through a quenching process in a downstream, fully automatic press hardening system with the charges mechanically prestressed in the press. This produces a distortion-free finish for large workpieces such as crown wheels with a diameter of over 30 centimeters and overall ensures that the finished components are true to size.

Control cabinetFinally all the workpieces can be transported fully automatically once again for further processing. All the workpieces undergo efficient cleaning in the subsequent three-zone post-washing machine after which they are dried. To make the final processes easier, it is possible to remove individual workpieces or alternatively certain parts of the charge for straightening and then return them to the process or to transport directly back to the two-row tempering furnace. The charges are returned to the loading and unloading track at the start of the system via the final cooling section with subsequent final storage section.

Overall, the complete Ipsen system comprises the following units:

  • Preoxidation furnace with an operating temperature of 450°C
  • High temperature heat treatment furnace with an operating temperature of up to 950°C comprising the following equipment:
    • Entry gate
    • Three-row heating zone
    • Three-row carburizing zone
    • Single-row hardening zone
    • Gas-tight intermediate doors
    • Discharge station for individual press-hardened parts
  • Oil bath with two separate immersion baths
  • Fully automatic Heess press hardening system
  • Three-zone post-washing machine
  • Tempering furnace
  • Various transport units

There is permanent pressure in the heat treatment furnace

Three-row heating zone with pusher deviceThe pusher furnace described here has three rows in all its main operating zones and is the first continuous heat treatment furnace from IPSEN to feature the new, patented “Lock up” system. This system is characterized by an entrance vestibule and an oil bath which are both separated from the heat treatment chamber in the pusher furnace by gas-tight doors. Using special gas guiding systems on the furnace, this principle means that for the first time it is possible to feed all charges in and out of the furnace without interfering with the furnace atmosphere. The furnace atmosphere thus fluctuates less in terms of temperature and carbon content. The result is precise, straight-line characteristics which are easy to monitor and can be adjusted accurately. “The charge is right” as the experts put it.

Another benefit is that the intergranular oxidation (igo) on the workpieces is minimized – after all these workpieces are primarily high quality precision gearbox components such as crown wheels and drive pinion wheels for gearboxes and axles which are designed for a service life of several decades.

A further advantage of the system with the gas-tight separation of the working chambers in the furnace is the reduced consumption of protective gas. This benefit is as a result of the fact that the pressure in the heat treatment chamber does not drop while the charge is being fed in and out of it. The pressure only has to be adjusted in the vestibules before the charges continue on the transport belts.

High efficiency using “Ecofire-Preheat”

A process known as “Ecofire-Preheat” which has been patented by Ipsen takes a very large step forwards in terms of improving energy efficiency. This particularly innovative process means that the endogas used to fill the furnace chamber is not simply lost by burning it off. In the past, simply burning it off has been standard procedure in all similar furnace systems resulting in both high temperatures around the furnace and large bills for process gases.

Now though, “Ecofire-Preheat” uses the surplus endogas in the preheating furnace as a combustion gas via strictly controlled process steps. This means that the process gas is recycled in a way so that it can be used. The major progress of this is in the costs. An Ipsen system with Ecofire-Preheat makes for savings in process gas costs of over 20,000 euros over the course of a year on a three-shift operation basis. The system therefore pays for itself within only a few years of use, depending on the size of the furnace.

To ensure that workpieces do not get cold

Another supporting measure to help the furnace system to be operated particularly economically is Ipsen’s new insulation technology. With a wall thickness of 40 to 50 centimeters in the main sections of the furnace system, micro porous material is used for rear insulation, material that surpasses all previous materials in terms of its insulation effect. The principle of this material is essentially that with its enormously high temperature resistance of up to 1100°C very few air molecules remain insulated within the tiny chambers. Compared to conventional designs, this results in a reduction in waste heat of up to 30 percent which is demonstrated by comparatively lower process costs.

Time-tested, durable Ipsen masonry consisting of refractory bricks continue to be used as front insulation for the walls, floor and ceilings. The hearth floor elements are made of high strength SIC materials and provide a very long service life.

All are equal in the flow diagram of the protective gas atmosphere

Equipping the entire system with sophisticated circulation equipment ensures both the homogeneous distribution of the protective gas in the heat treatment chambers and also a generous flow of reactive gases around the workpiece. The improved aerodynamics and the use of the latest burner technology ensure excellent uniformity and outstanding reproducibility of the heat treatment results.

Less is more

It should be mentioned that against the backdrop of the energy-saving principle of Ipsen’s new furnace technology, the massive energy consumption of heat treatment systems is not just a tricky topic from the point of view of the environment and costs. In fact, a new “Energy Using Products Directive” (EuP Directive) is currently passing through the normal committee stages at the EU Commission. Alongside the existing Ecodesign Directive 2005/32 EC, the resulting directive will result in the imposition of stringent requirements on the energy consumption of heat treatment systems in the near future.

The general public is not really aware at the present that almost 40 percent of energy used in industry in Germany is actually consumed in industrial furnaces. This appetite for energy is at least as striking in this respect as it is for the balance sheets of the companies concerned. The turnover generated by all this energy amounts to around 30 billion euros for all the companies concerned every year. In view of the rapid increase in global energy demand, we can certainly assume that prices will continue to rise.

Ipsen will continue to work on creating economical systems for handling energy. You can expect Ipsen to continue to produce particularly demanding solutions for handling energy as a valuable resource and also for reducing the running costs of these systems.

Please visit us at www.ipsen.de for more information, background details, interviews and additional comments.

This text is approved for immediate use. The photographs may also be used with the approved press material for publication purposes with the note “Source: Ipsen”.

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