Project Description
Introduction
In high-performance motion control and suspension systems, the geometric precision and structural integrity of the damper housing directly dictate ride quality, component longevity, and operational safety. Fushun Steel Tube specializes in manufacturing precision cold-drawn seamless steel tubes featuring a specialized outer-round and inner-oval cross-section, complete with CNC-machined inner chamfered ends.
This engineered profile solves critical damping challenges. The concentric outer diameter ensures seamless integration with standard mounts, dust covers, and coil springs. Meanwhile, the precision-drawn inner oval cavity acts as a natural anti-rotation guide for piston rods and optimizes hydraulic fluid dynamics during compression and rebound cycles.
The integrated inner chamfers eliminate sharp edges, protecting delicate seals during assembly and preparing the tube ends for leak-proof welding or crimping. Manufactured from premium low-to-medium carbon steels, these tubes deliver exceptional dimensional stability, superior fatigue resistance, and consistent internal surface quality.
Whether you are developing MacPherson struts for passenger vehicles, heavy-duty cabin dampers for agricultural machinery, or industrial vibration isolators, our ready-to-assemble tubing provides a reliable foundation for next-generation damping solutions. Tell us your specifications, and our engineering team will match you with the optimal material and tolerance package.
Engineered Profile & Geometry
The unique outer-round and inner-oval configuration is achieved through multi-pass cold drawing over custom tungsten carbide mandrels. This process guarantees strict concentricity and a uniform wall thickness distribution, which are critical for high-cycle fatigue performance in dynamic damping environments. Unlike standard round bores, the internal oval profile naturally restricts piston rod rotation without requiring external guide mechanisms, simplifying assembly and reducing overall system weight.
Applications
Our outer-round, inner-oval seamless tubes are engineered for direct integration into high-demand damping and motion control assemblies. Typical product-level applications include:
- Automotive Suspension Components: MacPherson strut housings, twin-tube shock absorber cylinders, mono-tube damper bodies, and electronic damping control sensor housings.
- Commercial & Off-Highway Vehicles: Heavy-duty truck cabin stabilizers, tractor seat suspension cylinders, combine harvester header dampers, and construction equipment vibration isolators.
- Industrial Motion Control: Automated conveyor line shock absorbers, robotic arm damping cylinders, press machine buffer tubes, and heavy-duty door closers.
- Consumer & Specialty Equipment: High-capacity washing machine drum stabilizers, commercial fitness equipment resistance cylinders, adjustable medical bed actuators, and railway bogie secondary dampers.
- Pneumatic & Hydraulic Actuators: Anti-rotation pneumatic cylinders, compact hydraulic rams, and linear motion guide sleeves requiring precise internal profiling.
For specialized corrosion-resistant environments, we also offer compatible geometries in our stainless steel tube series, while high-temperature variants align with our boiler tube manufacturing standards.
Specifications & Standards
Our shock absorber tubes are manufactured in strict compliance with globally recognized standards for cold-drawn seamless mechanical tubing. The carbon steel grades utilized in this product line are covered under the following specifications:
- ASTM/ASME: ASTM A519 Seamless Carbon and Alloy Steel Mechanical Tubing – Grades 1010, 1020, 1026, 1035, 1045
- EN/DIN: DIN 2391 Seamless Precision Steel Tubes / EN 10305-1 – Grades E235, E255, E355 / C10E, C22E, C45E
- GB/T: GB/T 3639 Cold Drawn or Cold Rolled Precision Seamless Steel Tubes – Grades 10#, 20#, 35#, 45#
- JIS: JIS G3445 Carbon Steel Tubes for Machine Structural Purposes – Grades STKM 11A, STKM 12A, STKM 13A
- ISO: ISO 10763 Hydraulic fluid power – Seamless precision steel tubes
All tubes are supplied as seamless cold-drawn products. Welded alternatives are not offered for this specific inner-oval geometry due to the stringent structural and fatigue requirements of dynamic damping applications.
Available Sizes & Delivery
Fushun Steel Tube offers flexible manufacturing capabilities to support both prototyping and high-volume production runs. Our standard supply parameters for outer-round/inner-oval shock absorber tubes include:
- Cold-Drawn Precision Tubes
- OD 20 mm – 120 mm | WT 1.5 mm – 6.0 mm | Length 2,000 mm – 6,000 mm (or fixed cut lengths)
- Hot-Rolled Seamless Mother Tubes
- OD 50 mm – 200 mm | WT 4.0 mm – 15.0 mm | Length 4,000 mm – 12,000 mm (for further machining)
- Tolerance Grades
- Cold-drawn tubes achieve OD tolerance ±0.05 mm to ±0.10 mm and WT tolerance ±5% to ±8%, depending on the specified ovality ratio and wall thickness.
- Ready Stock
- Common dimensions in SAE 1020 / 20# and SAE 1045 / 45# are available from inventory, with dispatch within 7 days.
- Custom Specifications
- Non-standard OD/WT combinations or proprietary inner-oval profiles require a minimum order quantity (MOQ) of 2–3 tons, with a production lead time of 25–35 days.
We welcome small-batch trial runs for new product development and engineering validation. Multi-ton project orders benefit from optimized pricing and phased delivery schedules tailored to your assembly line requirements.
Chemical Composition
| Grade (GB / ASTM / EN) | C | Mn | Si | P (≤) | S (≤) | Cr (≤) | Ni (≤) |
|---|---|---|---|---|---|---|---|
| 10# / SAE 1010 / C10E | 0.07–0.13 | 0.30–0.60 | 0.17–0.37 | 0.035 | 0.035 | 0.15 | 0.25 |
| 20# / SAE 1020 / C22E | 0.17–0.23 | 0.35–0.65 | 0.17–0.37 | 0.035 | 0.035 | 0.25 | 0.25 |
| 35# / SAE 1035 / C35E | 0.32–0.39 | 0.50–0.80 | 0.17–0.37 | 0.035 | 0.035 | 0.25 | 0.25 |
| 45# / SAE 1045 / C45E | 0.42–0.50 | 0.50–0.80 | 0.17–0.37 | 0.035 | 0.035 | 0.25 | 0.25 |
| 60# / SAE 1060 / C60E | 0.57–0.65 | 0.50–0.80 | 0.17–0.37 | 0.035 | 0.035 | 0.25 | 0.25 |
Composition ranges represent standard specifications for cold-drawn mechanical tubing. Residual elements are controlled within standard limits. Specific heat analysis can be tightened upon request for critical damping applications.
Manufacturing Process
Our production workflow integrates controlled metallurgy with precision cold-working to guarantee consistent performance in dynamic damping environments. Primary smelting utilizes an EAF + LF + VD route to ensure low gas content and high purity. For applications requiring exceptional fatigue life, ESR or PESR refining is available.
Tube manufacturing begins with hot-rolled seamless shells, which undergo spheroidize annealing, pickling, and phosphating before multi-pass cold drawing. Custom tungsten carbide mandrels are employed to form the precise inner-oval profile while maintaining strict concentricity. Following cold working, tubes undergo controlled stress-relief annealing to eliminate residual stresses and stabilize dimensions.
Finally, CNC machining produces the inner chamfered ends, and internal surfaces are polished or honed to specification. We work closely with your engineering team to select the optimal smelting route, drawing schedule, and thermal treatment that aligns with your performance targets and budget.
Mechanical Properties
| Grade | Condition | Tensile Strength (MPa) | Yield Strength (MPa) | Elongation (%) | Hardness (HBW) |
|---|---|---|---|---|---|
| 10# / SAE 1010 | Cold Drawn + Stress Relieved | ≥ 380 | ≥ 280 | ≥ 15 | 105–130 |
| 20# / SAE 1020 | Cold Drawn + Stress Relieved | ≥ 420 | ≥ 320 | ≥ 12 | 120–150 |
| 35# / SAE 1035 | Cold Drawn + Stress Relieved | ≥ 520 | ≥ 400 | ≥ 10 | 150–180 |
| 45# / SAE 1045 | Cold Drawn + Stress Relieved | ≥ 580 | ≥ 450 | ≥ 8 | 170–210 |
| 60# / SAE 1060 | Cold Drawn + Stress Relieved | ≥ 650 | ≥ 500 | ≥ 7 | 190–230 |
Data represents typical longitudinal test results for cold-drawn tubes with wall thickness ≤ 10 mm. Properties can be adjusted through customized heat treatment cycles to meet specific fatigue or formability requirements.
Heat Treatment
| Treatment Type | Temperature Range | Cooling Method | Purpose & Application Notes |
|---|---|---|---|
| Stress Relief Annealing | 550–650°C | Air or Furnace | Eliminates cold-work stresses, stabilizes oval geometry, prevents warping during welding/crimping. Standard for shock absorber tubes. |
| Spheroidize Annealing | 680–720°C | Furnace Cool | Softens medium/high carbon grades (35#–60#) for improved cold formability and machining prior to final assembly. |
| Normalizing | 850–900°C | Air Cool | Refines grain structure, restores uniform mechanical properties after hot rolling or heavy cold reduction. |
| Quenching & Tempering | 820–860°C (Q) / 400–600°C (T) | Oil/Water (Q) / Air (T) | Applied to 45# and 60# grades for heavy-duty dampers requiring high yield strength and impact resistance. Controlled atmosphere recommended. |
Surface Finish & Tolerances
We supply shock absorber tubes in multiple surface conditions to match your assembly requirements. Hot-rolled mother tubes are available as-rolled or pickled. Cold-drawn precision tubes feature a bright, scale-free finish with typical internal surface roughness of Ra 0.8–1.6 μm, achievable down to Ra 0.4 μm through roller burnishing or honing.
Standard OD tolerances range from ±0.05 mm to ±0.10 mm, with wall thickness controlled within ±5%. The proprietary inner-oval profile maintains a consistent contour tolerance of ±0.08 mm along the full length. CNC-machined inner chamfers are held to ±0.1 mm dimensional accuracy with a burr-free edge transition.
External surfaces can be turned, ground, or coated with phosphate/zinc per your specification. All dimensional and surface parameters are verified prior to dispatch to ensure drop-in compatibility with your piston and seal assemblies.
Quality Assurance & Testing
Quality is embedded at every stage of our manufacturing process. Incoming raw materials undergo full spectrometric analysis to verify chemistry compliance. During cold drawing, laser micrometers and ultrasonic wall-thickness gauges monitor dimensions in real time. Finished tubes are subjected to a comprehensive inspection protocol:
- Non-Destructive Testing (NDT): 100% Eddy Current Testing (ET) and Ultrasonic Testing (UT) to detect surface and subsurface discontinuities.
- Hydrostatic & Proof Testing: Pressure testing performed per standard requirements to verify structural integrity under simulated damping loads.
- Mechanical & Metallographic Validation: Tensile, hardness, and flattening/flaring tests conducted on each heat lot. Grain size and decarburization depth are verified via microscopic examination.
- Geometric Verification: CMM and optical profilometers validate inner-oval contour, straightness (≤ 1.0 mm/m), and chamfer angles.
All shipments include an EN 10204 3.1 Mill Test Certificate. EN 10204 3.2 certification with independent witness testing is available upon request. Our facility operates under ISO 9001 quality management, and we readily accommodate third-party inspections by SGS, TÜV, or BV.
Packing & Shipping
Proper packaging is critical to preserving the precision geometry and surface quality of shock absorber tubes during transit. Hot-rolled tubes are coated with anti-rust oil, bundled with steel straps, and fitted with end protectors. Cold-drawn bright and chamfered tubes receive individual plastic end caps, followed by VCI anti-corrosion paper or shrink wrapping.
Tubes are then securely packed in fumigated wooden crates or reinforced steel frames to prevent bending or surface abrasion. We support global shipping via sea freight, air cargo, or cross-border land transport, with full container load (FCL) and less-than-container load (LCL) options. Custom shipping marks, barcode labeling, and lot-traceability tags are applied per your procurement requirements.
Frequently Asked Questions
- Can you manufacture custom inner-oval profiles and non-standard OD/WT combinations?
- Yes. We design and machine custom tungsten carbide mandrels to produce proprietary inner-oval ratios, flat-sided profiles, or multi-lobed internal geometries. Non-standard dimensions are supported with an MOQ of 2–3 tons, and our engineering team will review your drawings to confirm tooling feasibility.
- What heat treatment condition is recommended for automotive shock absorber tubes?
- For most passenger vehicle and light commercial applications, cold-drawn plus stress-relieved annealing (550–650°C) provides the optimal balance of yield strength, dimensional stability, and weldability. Heavy-duty or off-road applications may benefit from normalized or quenched & tempered conditions to handle higher impact loads.
- How do you ensure the inner chamfer does not damage seals during assembly?
- All chamfered ends are CNC-machined and deburred to a strict edge-break specification. We verify the transition radius and surface finish using optical inspection, ensuring a smooth, snag-free entry for piston seals, Teflon bands, and O-rings, which significantly reduces assembly defect rates.
- What is the typical lead time for prototyping versus mass production?
- Standard sizes from ready stock ship within 7 days. Custom tooling and trial batches require 25–35 days for first-article delivery. Once tooling is validated, mass production cycles are optimized to 15–20 days, with phased shipments available for long-term contracts.
- Do you provide material traceability and third-party certification?
- Every tube lot is fully traceable from steelmaking to final inspection. We supply EN 10204 3.1 certificates as standard, and can arrange EN 10204 3.2 certification or independent third-party testing (SGS, TÜV, BV) to meet your OEM audit requirements.
