Internal Bore Surface: Diameter Tolerance H8/H9

Component Specifications

Definition

The internal bore surface is the precisely finished cylindrical interior of a cylinder barrel in hydraulic or pneumatic systems. This critical component provides the sliding interface for the piston and piston seals, maintaining fluid containment and ensuring linear motion with minimal friction. Surface finish, dimensional accuracy, and geometric tolerances directly impact system efficiency, leakage prevention, and component longevity.

Working Principle

The internal bore surface functions as both a guiding mechanism and sealing interface. During operation, the piston moves along this surface while hydraulic pressure acts upon it. The surface must maintain consistent clearance with piston seals to prevent fluid bypass while minimizing friction through optimized surface texture and hardness properties.

Materials

Typically manufactured from cold-drawn seamless steel tubing (ASTM A519), hardened steel (42CrMo4), or stainless steel (304/316). Common specifications include: hardness 58-62 HRC for hardened surfaces, surface roughness Ra 0.2-0.4 μm, and straightness tolerance of 0.02 mm per 300 mm length.

Technical Parameters

Parameter	Typical range	Notes & selection driver
Hardness	58-62 HRC
Roundness	0.01 mm max
Straightness	0.02 mm/300 mm
Surface Roughness	Ra 0.2-0.4 μm
Surface Treatment	Chrome plating (20-40 μm) or nitriding
Diameter Tolerance	H8/H9

Ranges are indicative industry figures for RFQ preparation, not a supplier commitment. Confirm every value and standard with the legal manufacturer before ordering.

Standards

ISO 3320, ISO 4394-1, DIN 24334, DIN 24540

Parent Products

This component is used in the following industrial products

Cylinder Barrel

The main cylindrical body of a hydraulic actuator cylinder that contains the hydraulic fluid and guides the piston movement.

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Engineering Analysis

Risks & Mitigation

Surface scoring from contamination
Corrosion in harsh environments
Geometric distortion under load
Premature seal wear from improper finish

FMEA Triads

Trigger: Contaminants in hydraulic fluid
Failure: Surface scoring and increased friction
Mitigation: Implement proper filtration systems (10 μm or better), regular fluid analysis, and contamination control procedures

Trigger: Inadequate surface hardness
Failure: Accelerated wear and reduced service life
Mitigation: Specify proper material grades, apply surface treatments (chrome plating/nitriding), and conduct hardness testing

Trigger: Geometric inaccuracies (taper, ovality)
Failure: Seal leakage and uneven wear patterns
Mitigation: Implement precision honing processes, use SPC monitoring, and conduct comprehensive geometric verification

Industrial Ecosystem

Compatible With

Typical Suppliers & Equivalents

Compliance & Inspection

Tolerance

Diameter tolerance H8/H9 per ISO 286, roundness ≤0.01 mm, straightness ≤0.02 mm/300 mm

Test Method

Coordinate measuring machines (CMM) for geometry, surface profilometers for roughness, ultrasonic thickness gauges for plating, and pressure testing for seal integrity

Procurement Evaluation Criteria

A practical evidence checklist for RFQ preparation and supplier evaluation.

Technical documentation

Request current drawings, revision history, and a signed specification sheet.

Manufacturing capability

Verify equipment lists, process limits, capacity, and representative production evidence.

Inspection readiness

Confirm test methods, calibrated equipment, sampling plans, and traceable reports.

Supplier transparency

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Manufacturers of Internal Bore Surface

Manufacturer profiles associated with Internal Bore Surface.

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Compiled and source-reviewed by the CNFX editorial team. Each manufacturer above links to the page on that company's own website where the product is listed, with the date we checked it. How we source and review

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The main frame is the primary structural component of a hydraulic press, providing rigidity and stability to withstand high compressive forces during metal forming operations.

Shaft Bearing

Precision component supporting rotating shafts in vibration motors to reduce friction and maintain alignment.

Seal Groove

Precision-machined groove in aluminum bearing housings designed to accommodate sealing elements for fluid containment and contamination prevention.

Frequently Asked Questions

What surface finish is required for hydraulic cylinder bores?

Hydraulic cylinder bores typically require Ra 0.2-0.4 μm surface finish achieved through honing. This provides optimal seal performance while minimizing friction and wear.

Why is chrome plating applied to cylinder bores?

Chrome plating (20-40 μm thickness) provides corrosion resistance, reduces friction, increases hardness, and extends service life by protecting against abrasive wear and chemical attack from hydraulic fluids.

How is bore straightness measured and controlled?

Bore straightness is measured using laser alignment systems or precision mandrels with dial indicators. Control is maintained through proper machining techniques, stress relief, and thermal management during manufacturing.

Data Basis

Editorial classification, named public sources where available, and source-reviewed manufacturer records. See the editorial policy.

Preliminary Technical Classification

This page supports structured research, RFQ preparation, and supplier evaluation. It does not replace buyer-led supplier qualification, standards review, or technical approval.

Internal Bore Surface