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{"title":"Gas Spring Precision Steel Pipe 4 - 75mm OD With Polished Surface Treatment","imgUrl":"https:\/\/img.chinax.com\/nimg\/b1\/96\/2765f004f7df46070d60436108b3-200x200-1\/gas_spring_precision_steel_pipe_4_75mm_od_with_polished_surface_treatment.jpg","attrs":{"Brand Name":"TORICH","Model Number":"BS 6323-6\uff0cDIN 2393\uff0cASTM-A513-t6\uff0cN10305-2","Certification":"ISO9001","Place of Origin":"China"}}
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Round automotive precision steel tubes for shock absorber cylinders are manufactured by cold drawing or cold rolling to obtain controlled outside diameter, inside diameter, wall thickness and surface condition. They are intended particularly for shock absorber working cylinders where piston guidance, seal performance and dimensional consistency depend directly on tube geometry and bore quality.
EN 10305-1 seamless cold-drawn precision tubing is particularly suitable for this type of application because the standard defines dimensional accuracy, surface requirements, mechanical properties and delivery conditions. Typical materials include E215, E235 and E355, while E255 and E410 can be specified when different strength levels are required.
Cold rolled: typically up to ±0.05 mm; cold drawn: typically up to ±0.10 mm, depending on dimension and order specification
ID Tolerance
Can be controlled according to shock absorber cylinder drawing requirements
Wall Thickness Tolerance
According to applicable standard and dimensional combination
Straightness
Controlled according to EN 10305-1 or customer drawing
Cross Section
Round
Surface Condition
Bright, oiled, polished or phosphated as specified
Surface Roughness
EN 10305-1 specifies Ra ≤4 μm for applicable tubes with D ≤260 mm; tighter functional bore finish can be produced by additional processing
Heat Treatment / Delivery Condition
+C, +LC, +SR, +A, +N
DIN Traditional Delivery Designations
BK, BKW, BKS, GBK, NBK
Inspection Document
EN 10204 inspection certificate available according to order requirements
Primary Use
Automotive shock absorber working cylinder
Main Characteristics
Controlled Cylinder Geometry
Cold drawing or cold rolling improves dimensional consistency compared with conventional hot-finished tubing. For shock absorber cylinders, accurate control of inside diameter, outside diameter, ovality and wall eccentricity helps maintain stable piston-to-cylinder clearance throughout the working stroke.
For precision production, outside diameter tolerance can typically be controlled to ±0.05 mm on suitable cold-rolled dimensions. Tighter ID requirements should be specified directly on the customer's cylinder drawing because the functional bore, rather than only the OD, determines piston and seal clearance.
Defined Surface Roughness
EN 10305-1 requires smooth internal and external surfaces and specifies maximum roughness values. For tubes with outside diameter up to 260 mm, the standard specifies maximum Ra values of 4 μm under the applicable delivery conditions.
Shock absorber working cylinders may require a considerably finer functional inner surface than the general standard limit. Honing, skiving and roller burnishing or other bore-finishing processes can therefore be specified when low-friction piston and seal movement is required.
Stable Mechanical Properties
The final tube properties depend on both steel grade and delivery condition.
+C provides the highest cold-worked strength but relatively low ductility.
+LC uses a light final drawing pass after heat treatment and provides improved formability.
+SR is stress relieved after cold drawing and offers a balance between dimensional stability and mechanical strength.
+A is soft annealed for increased ductility.
+N is normalized and provides standardized strength and elongation values suitable for subsequent machining and forming.
Our Advantages
Functional ID Control for Piston and Seal Matching: For shock absorber cylinders, purchasing only by OD and wall thickness can result in unacceptable bore variation. The inside diameter directly affects piston clearance, seal contact and damping consistency. Production can therefore be controlled according to OD × ID or OD × wall thickness, with ID tolerance, ovality and wall eccentricity included in the inspection plan when specified on the drawing. Precision cylinder projects can use tighter dimensional requirements than the general commercial tube tolerance.
Bore Surface Can Be Matched to the Actual Cylinder Function: A general precision tube may satisfy dimensional requirements while still requiring additional bore processing for a hydraulic sliding surface. The required bore condition can therefore be defined separately from the general tube surface requirement. Cold-drawn, cold-rolled, honed or skived-and-roller-burnished conditions can be selected according to piston, guide and seal design. This avoids treating surface roughness as a purely cosmetic specification.
Grade and Delivery Condition Can Be Controlled Together: Mechanical properties cannot be determined from steel grade alone. Cold-worked and heat-treated conditions produce substantially different tensile strength, yield strength and elongation. Orders can therefore specify both the material grade and final delivery condition, for example E355+SR or E355+N, rather than simply specifying E355. Heat number identification and EN 10204 inspection documentation can also be agreed for production traceability.
Execution Standards
Standard
Scope
EN 10305-1
Seamless cold-drawn steel tubes for precision applications
DIN 2391
Traditional German specification for seamless precision steel tubes; commonly associated with St35, St45 and St52
ASTM A519
Seamless carbon and alloy steel mechanical tubing
JIS G 3445
Carbon steel tubes for machine structural purposes
GB/T 3639
Cold-drawn or cold-rolled precision seamless steel tubes
GOST 9567
Precision steel tubes with controlled dimensional accuracy
For new European projects, EN 10305-1 grade designations and delivery-condition symbols should normally be used instead of relying only on older DIN 2391 terminology.
Application
Automotive Shock Absorber Working Cylinder
The tube is used as the working cylinder of an automotive hydraulic shock absorber. Inside the cylinder, the piston assembly moves repeatedly through hydraulic oil while the piston seal maintains controlled contact with the bore. The cylinder tube therefore requires consistent internal diameter, low ovality, controlled wall eccentricity, adequate straightness and a smooth functional inner surface.
E235 and E355 precision steel tubes are commonly selected depending on required strength, tube dimensions and subsequent processing. Final material selection should be based on the shock absorber drawing, operating load, forming operations and required delivery condition.
Chemical Composition
Grade
Steel No.
C %
Si %
Mn %
P %
S %
Other Requirements
E215
1.0212
≤0.10
≤0.05
≤0.70
≤0.025
≤0.025
Al total ≥0.025
E235
1.0308
≤0.17
≤0.35
≤1.20
≤0.025
≤0.025
Al total ≥0.015
E255
1.0408
≤0.21
≤0.35
0.40-1.10
≤0.025
≤0.025
Annex A grade
E355
1.0580
≤0.22
≤0.55
≤1.60
≤0.025
≤0.025
Al total ≥0.020
E410
1.0509
0.16-0.22
0.10-0.50
1.30-1.70
≤0.030
≤0.035
V 0.08-0.15; Al 0.010-0.060; Nb ≤0.07; Ti ≤0.05
Mechanical Properties
Grade
Delivery Condition
Tensile Strength Rm
Upper Yield Strength ReH Min.
Elongation A Min.
E215
+N
290-430 MPa
215 MPa
30%
E235
+N
340-480 MPa
235 MPa
25%
E255
+N
440-570 MPa
255 MPa
21%
E355
+N
490-630 MPa
355 MPa
22%
E410
+N
550-700 MPa
410 MPa
22%
Delivery Conditions
Symbol
Traditional DIN Designation
Description
+C
BK
Cold drawn hard; no final heat treatment after final cold drawing
+LC
BKW
Cold drawn soft; final heat treatment followed by a light drawing pass
+SR
BKS
Cold drawn and stress relieved in a controlled atmosphere
+A
GBK
Soft annealed after final cold drawing
+N
NBK
Normalized after final cold drawing in a controlled atmosphere
Product Images
Frequently Asked Questions
Are you trading company or manufacturer?
Manufacturer, also can do trading.
How long is your delivery time?
Generally speaking, it is 10-15 days if the goods are in stock, or it is 30-40 days if the goods are not in stock, according to quantity.
Do you provide samples? Is it free or extra?
Yes, we could offer the sample for free charge but need pay the cost of freight.
What is your terms of payment?
Payment ≤ 2000 USD, 100% in advance. Payment ≥ 2000 USD, 30% T/T in advance, balance before shipment. If you have another question, please feel free to contact with me.
