TUBES FOR CYLINDERS
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CYLINDER TUBES COLD DRAWN TUBES
(DIN 2391, seamless; DIN 2393, welded)
i.d. mm
Machining operation
20 up to 210
Skiving and roller burnishing
St 52– STE 460 on request
> 220 or special dia
Boring and honing
St 52 –on request MV450 / 20MnV6 W
St 52
Steel grade BK+S or NBK
Similar to UNI Fe510D- BS 5242/ HP 5 – SS 212, common steel grade for cylinder tubes
Ste460 BS 5242 /HP 6 – SS 2142 , for heavy duty applications
CHEMICAL ANALYSIS
MECHANICAL PROPERTIES
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HOT ROLLED TUBES ( DIN 2448 / 1629 ) ST similar to UNI Fe 510 UNI 7729 – TU 52.B easy weldability , common use MW 450 / similar to TAM HB 470 AR microalloyed Vanadium steel, with higher yield and excellent weldability
52 20MNV6
CHEMICAL ANALYSIS
MECHANICAL PROPERTIES
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TECHNOLOGIES
Two technologies are in use: traditional HONING AND SKIVING AND ROLLER BURNISHING PROCESS. We use both technologies selecting the most suitable for the different diameters and applications
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MATERIAL It is common practice to identify by the DIN symbols the heat treatment conditions in which the material is going to be delivered. We list these symbols hereafter indicating, by arrows, which is the influence that each heat treatment condition is going to have on the mechanical properties
The machinability depends on the chemical analysis too. SPECIFIC HEAT TREATMENS G Spheroidising; the temperature is kept long under Ac1 in order to generate globular carbides BG Heat treated in such a way to obtain a well defined metallurgical structure (ferrite + pearlite) BF Heat treatment to obtain an higher U.T.S. value V Quenched and tempered to obtain the best mechanical properties and impact values. W Hot rolled condition
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TECHNICAL SPECIFICATIONS
HOT ROLLED TUBES
COLD DRAWN TUBES
Steel grades and heat treatment conditions DIN ST 52 hot rolled
DIN ST 52 BK+S (stress relieved)
Manufacturing specification DIN 2448 / 1629
DIN 2391- C ( seamless) Straightness
0,5 : 1.000 mm drawing processing 0,1 : 1.000 mm thrust processing
0,5 :1000 mm Excentricity +/-7,5% of the wall thickness (smls tube) +/-3% of the whole thickness (welded tubes)
+ / - 12,5 % of the wall thickness
i.d. Tolerance H8
H8 i.d. Surface Roughness
Ra = 0.4 µm Rt = 3 µm (honed)
Ra = 0.2 µm Rt = 3 µm (skived and roller burnished) i.d. Bearing Ratio Tp
>= 60% at 1,39 µm of depth (honed
>= 60% at 0,17 µm of depth (skived and roller burnished )
i.d. Surface Hardness 150 up to 200 HB (honed)
190 up to 245 HB (skived and roller burnished)
Manufacturing lengths 3 / 9 meters
5 / 9 meters
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SURFACE QUALITY 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 µm The same Tpi value can be found at a depth of only 0,17 µm 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 maintenances. HONED TUBE
SKIVED AND ROLLER BURNISHED TUBE
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The 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 I.D. TOLERANCE : H8.
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The 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.
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