Tubes

CYLINDER TUBES : PRODUCTION FACILITIES

STELMI:WORLD LEADER IN QUANTITYThe production capacity installed corresponds to more than 12.000 tons per year of skived and roller burnished / honed tubes.

All the equipment have been designed and built by Stelmi, taking a great advantage of a 25 years long production experience.

Stelmi equipment machines the tube horizontally; the tube turns and the tool translates, carried at one end of the boring bar. Rotation and translation may be varied continuously. Machining the tube horizontally means an easier control of the tube itself from both sides and an easier positioning for long tubes. The machining operation is fully automated.

CYLINDER TUBES : PRODUCTION TECHNOLOGY

Stelmi produces skived and roller burnished/ honed tubes with high performances for all the applications in hydraulic or pneumatic industry, in petrochemical and thermohydraulic fields.

Stelmi ensures the highest uniformity of properties for each batch. Thanks to the peculiar process, the internal diameter and the out of roundness are kept constant all along the length of the tube. A technological know-how in continuous improvement allows to machine even the largest and longest tubes with great performances. The quality in terms of roughness and bearing ratio of the surface outperforms the conventional honing, offering longer gaskets life.

SKIVED AND ROLLER BURNISHED STEEL TUBESStelmi machines cold drawn steel tubes, seamless DIN 2391.C, steel grade St 52, or welded DIN 2393, steel grade St52.3, in stress relieved conditions (BK+S).Tubes are ready to be used, with inside diameter in tolerance H8. The surface roughness values are Ra < 0.2 ?m, Rt < 3.0 ?m, TPI > 60% at a depth of 0,25 ?m. The lengths are between 5 and 9 m., the straightness is better than 0.5/1000 mm. Tubes with mechanical properties and straightness higher than the standard ones also available.

HONED STEEL TUBESThe tubes are hot rolled according to DIN 2448/1629, the steel grade is St52. On request St52.3 N (normalised tubes). Stelmi offers these tubes for special sizes and for all the diameters > 200 mm. The largest
inside machinable diameter is 650 mm. Lengths are normally those requested by the Customers.Tubes are ready to be used, with tolerance H8 on inside diameter. The inside surface roughness is Ra < 0.4 ?m.For
heavy applications Stelmi can supply also forged tubes, eventually with collar (dia. max. 1000mm), turned outside.


Two technologies are in use: traditional honing and skiving and roller burnishing process. Stelmi machines cylinder tubes operating with both technologies selecting the most suitable for the different diameters and applications.

HONINGHoning is the oldest process, still widely in use. A boring operation is always performed before honing. Honing tool works by stones or other abrasive means; the honing operation is made by very long strokes, back and forth, of the tool itself, placed at one end of the boring bar. In order to ensure a good quality by honing, the material removal must be at least 0.1/ 0.3 mm, depending on the quality of the base material. An advantage of the honing process is the fact that the tooling is cheap and can be easily adjusted to different diameters.

SKIVING AND ROLLER BURNISHINGThe skiving and roller burnishing in Stelmi is something basically different from the traditional honing. Machining is performed by a combined tool; the skiving corresponds to the forward stroke, whilst the roller burnishing operation is carried out during the return stroke, thanks to the new tool configuration. The combined tool skives the internal surface by cutting, simultaneously, two chips not lower than 0.2 mm thick, more than what is usually done by honing, ensuring a defect free surface.

Roller burnishing also means an improvement in surface hardness.

CYLINDER TUBES : SURFACE QUALITY

PROCESS EVALUATION
Compared with honing, skiving and roller burnishing process offers not only a better accuracy but also a better surface quality.
A comparison between standard production samples is shown hereafter; skived and roller burnished material has a lower Ra and Rz and a better bearing factor. The picture displays a 60% Tpi achieved, by honing, at a depth of 1,39 ?m The same Tpi value can be found at a depth of only 0,17 ?m thanks to the skiving and roller burnishing process. The shown differences are very important for the gaskets life; for honed tubes, after 100 working hours the gaskets are already 50% worn out. This is due to the fact that the gaskets operate like a “tool”,
working to smooth the small, sharp peaks resulting from the honing operation. This phenomenon is unknown for skived and roller burnished tubes.The superior surface quality offered by the skived and roller burnished tubes is essential when a cylinder operates at high speed. The skived and roller burnished surface is superior also for
very slow displacements, avoiding the “stick-slip” phenomena. Honed surfaces on the opposite require frequent gaskets maintenanaces.

HONED TUBE

SKIVED AND ROLLER BURNISHED TUBE


STELMI TUBES : ADVANTAGES

A well proven and consolidated technology that assures

top quality level
outstanding constant performances

A well organized and efficient service that assures:

good planning
well respected delivery terms

CYLINDER TUBES : STEEL GRADES IN USE

COLD DRAWN TUBES
(DIN 2391, seamless; DIN 2393, welded)

CHEMICAL ANALYSIS

MECHANICAL PROPERTIES

HOT ROLLED TUBES
(DIN 2448 / 1629)

CHEMICAL ANALYSIS

 

MECHANICAL PROPERTIES.

CYLINDER TUBES : MANUFACTURING PROGRAM

STELMI PRODUCTS
Stelmi manufacturing program for cylinder tubes in metric sizes is given hereafter; the base material are cold drawn tubes, seamless or welded.
Common sizes are listed in bold characters
Standard tolerance: H8

IMPERIAL SIZESStelmi manufacturing program for cylinder tubes in imperial sizes is given hereafter; the base material are cold drawn tubes, seamless or welded. The common sizes are listed in bold characters
Standard i.d. tolerance : H8.