Press Release



(Press Release, September 2009)

Heat treatment technique gives high-load machine parts more resistance

Quality through production technology

The rotor of a 120 Watt air motor to rotates under load 11,000 times a minute. The air constantly rotates the rotor in the eccentric cylinder. Longevity, reliability and robustness are the quality signs of a modern powerful air-motor. If for example one exchanges the vanes for the first time after 1.000 operating hours, the rotor has moved about its own axis already 660 million times. The steel for such highly stressed machine parts must be especially resistant. Special hardening procedures improve the micro structure of the steel material and increase its mechanical resistance.

DEPRAG SCHULZ GMBH u. CO. KG is an internationally recognized manufacturer of air-motors, automation, screw-driving technology and power tools. Through decades of experience with materials, especially steel, DEPRAG has developed a high competence for its own heat treatment process. Not only components for the own production are subjected to the heat treatment technology in Amberg's special hardness procedures; DEPRAG also heat treats components for external clients as a special service.

Before they find their place in a motor, the steely rotors of the renowned air-motors from different DEPRAG product lines go through the heat treatment. DEPRAG employs a combined process, known as case hardening. This method is primarily used for high wear gear components, shafts, special purpose tooling and other machine parts.

Air vane motors operate according to one basic principle. Compressed air is used to set a rotor in motion inside an eccentric cylinder. Vanes, which are located in the rotor slots, are pressed outwards against the cylinder wall by the rising centrifugal force. This leads to the formation of chambers for the expanding air pressure. Through this expansion of the compressed supply air the pressure energy is transformed into kinetic energy and rotation is produced.

A resilient rotor in the airmotor is the prerequisite for the long-time function of the motor. The rotors are mounted into a clamping fixture; they are fully turned, milled and the rotor gearing is manufactured. After the hardening, the manufactured rotors are given their final measurement by highly exact polishers. The slots for the vanes are manufactured on a production machine, which was especially designed for DEPRAG and which guarantees the long life of the vanes.

DEPRAG Amberg uses the salt bath hardening procedure. As a prerequisite to the next step in the case hardening process, the steel rotor is immersed in a salt bath at temperatures of up to 950 degrees and held there over a certain time period. The surface layer of the steel is enriched with carbon through diffusion (carburized). The carbon content in a salt bath is particularly well regulated and therefore the results of this process on the work piece are very consistent. The usual case depth, depending on the component and customer specification, is between 00.5 and 1.5 millimeters.

After enrichment with carbon, the steel rotor is hardened and then tempered (relaxed). During hardening the steel is heated to the austenite phase (over 723 degrees Celsius) and then quickly cooled (quenched) in order to circumvent the pearlite and ferrite phases and reach the so-called hardened martensitic microstructure. The hardening procedure is followed by tempering (regulated reheating) process in order to give the steel back a certain degree of strength and ductility.

Salt bath heat treatment increases the mechanical characteristics of steel. Results are: increased rigidity of the component, wear resistance is heightened due to the surface hardening, core ductility is magnified, the load capacity is boosted and resilience toward alternating flexural stress and overload tolerance are improved. Salt bath hardening is recommended for the treatment of components used in precision engineering, tooling for applications in extreme heat and cold conditions and other highly stressed machine components, for example; the rotors on air vane motors.

A special treatment after the hardening process is tempering. Tempering involves the regulated reheating of the material to high temperatures (up to 700 degrees Celsius). The aim of this process is to give the steel the highest possible strength and at the same time increased ductility. Machine components which are subject to sudden loads and safety components which must withstand large distortions are recommended as candidates for this technique.

The annealing of steel is another heat treatment technology, that achieves a defined and for the processing necessary material qualities. Standard annealing, soft annealing, low-tension annealing and BG-annealing are some of the hardening techniques applied by DEPRAG. DEPRAG's production location in Lázne Belohrad in the Czech Republic also offers the economical and extremely reliable gas hardening for larger production batches in their gas hardening facility.

Distortion-free hardening of materials is almost impossible because of the alterations to the microstructure of steel. However, through decades of experience, the DEPRAG team is in a position to reduce the distortion to its absolute minimum. DEPRAG's heat treatment technique is certified according to the standard DIN EN ISO 9001 and is subject to strict quality control. The components receive a quality certificate after standing up to the Rockwell, Brinell and Vickers hardness tests. Either a digital or printed image displays the steel microstructure or the case depth from under the microscope. This is a destructive test and is used primarily for spot tests on large production batches

Extensive consultation and advice in the correct choice of material, heat treatment techniques and the proper observance of hardening regulations are included in the range of material treatment services provided in Amberg. The service also covers metallographic examinations and damage analysis. All normal heat treatable steels, and also in small quantities, highly-chrome-alloyed steel components with a maximum breadth of 280 millimeters and maximum length of 450 millimeters can be processed in the DEPRAG heat treatment facility up to 1300 degrees Celsius. The specialists at DEPRAG know that great importance is attached to flexibility and short reaction times.

DEPRAG SCHULZ GMBH & CO. KG is a well-known manufacturer of air motors, automation, screwdriving equipment and industrial power tools; employing around 600 employees in more than 50 countries. Their proficiency in heat treatment processing is mirrored by their equally professional approach to environmental protection. Extraction and filter systems keep the emissions, which are an unavoidable by-product from the process, under the limit values enforced by the Federal Emission Protection Law. The experts at DEPRAG not only produce top quality components, they put their ecological view into practice in all production methods.

Press Contact:

Dagmar Dübbelde
Carl-Schulz-Platz 1
D-92224 Amberg
Tel: 09621 371-343
Fax: 09621 371-199

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