Cylinder Block and Valve Plate for A6VM215

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Product details

1. Model Matching & Product Overview

A6VM215 is a 215cc bent-axis variable displacement piston motor from Rexroth A6VM Series 71, widely used in closed-circuit hydrostatic transmissions for rotary drilling rigs, tunneling machines, winches and mining hoists. The cylinder block (rotor) and valve plate form the core friction pair of the motor, which directly determine volumetric efficiency, torque output and overall service life. It withstands continuous operating pressure up to 350 bar and peak intermittent pressure of 400 bar.

Basic Dimension Parameters

1. Cylinder Block: Outer diameter 133 mm, total length 86.5 mm, central shaft bore φ27, with 9 equal piston through-holes; sintered bronze wear-resistant lining on end face.

2. Valve Plate: Outer diameter 108 mm, locating boss diameter φ22, dual arc kidney-shaped ports, built-in pre-pressure damping grooves and cavitation buffer triangular grooves.

2. Cylinder Block (Rotor): Structure, Material & Function

2.1 Structural Composition

- Forged steel substrate with sintered bimetallic bronze wear layer on the sliding end face, equally divided into 9 piston chambers.

- Central splined bore connects drive shaft; each piston chamber houses piston, slipper and retainer plate. Central spring pushes the cylinder block tightly against the valve plate for sealing.

- Tiny damping holes at the bottom of piston chambers balance internal pressure and mitigate high-pressure shock.

2.2 Material & Processing

- Substrate: 40CrNiMo alloy forged steel, quenched and tempered to hardness HRC 58~62, resistant to high-pressure deformation.

- Sliding end face: High-lead powder metallurgy bronze sintered layer, storing hydraulic oil in micropores to form static pressure oil film and reduce dry friction.

- Mirror honed piston bores with precise clearance to control internal leakage.

2.3 Core Functions

1. Accommodate reciprocating motion of 9 piston assemblies; variable bent-axis angle adjusts piston stroke to realize stepless displacement from 0 to 215 cc/rev.

2. Slide against valve plate end face to distribute high-pressure inlet and low-pressure return oil.

3. Transfer hydraulic torque to drive shaft for load output.

2.4 Common Failure Modes

1. Scratches or honeycomb cavitation pits on bronze lining (caused by air suction or insufficient charge pressure).

2. Deep scratches inside piston bores, excessive clearance, sharply reduced volumetric efficiency and insufficient output torque.

3. Unilateral inclined wear and grooves on end face (misaligned drive shaft or damaged bearings).

4. Peeling or delamination of bronze layer (long-term oil temperature over 90℃ or contaminated fluid).

3. Valve Plate: Structure, Material & Function

3.1 Core Structural Design

1. Dual arc kidney ports: Correspond to motor high-pressure port A and low-pressure port B, supporting bidirectional rotation.

2. Triangular buffer damping grooves (pre-charging slots): Gradually boost/release pressure during piston chamber switching, eliminate pressure shock, reduce noise and prevent cavitation.

3. Wide sealing land between high/low pressure ports to isolate pressure zones and restrict internal leakage.

4. Central locating boss for coaxial alignment with cylinder block to guarantee full flat contact.

3.2 Material & Processing

- Base material: High-carbon chrome bearing steel, carburized and quenched, ultra-precise mirror grinding on sliding surface.

- Flatness ≤0.003 mm, surface roughness Ra ≤0.02, forming uniform static oil film under high pressure; excellent wear and cavitation resistance for high-temperature closed circuits.

3.3 Operating Principle

The cylinder block rotates with the drive shaft, and piston chambers sweep across high/low pressure ports on valve plate sequentially:

- High-pressure oil enters piston chambers to extend pistons and generate driving torque.

- Pistons retract while aligned with low-pressure ports for oil return.

Buffer slots eliminate abrupt pressure fluctuation to cut down pulsation, vibration and cavitation damage.

3.4 Typical Valve Plate Failures

1. Circular wear grooves or mirror surface scratches on sealing land, severe internal leakage and weak motor power.

2. Cavitation perforation or edge spalling on triangular buffer grooves, accompanied by loud abnormal noise and vibration.

3. Warped flat surface from long-term overpressure or overheating, causing partial sealing failure.

4. Matching Requirements for Cylinder Block & Valve Plate Friction Pair

1. Pair Grinding Rule

The bronze sliding face of cylinder block and valve plate are factory-lapped matched pairs. Single-piece replacement is forbidden; mismatched spare parts lead to poor contact, rapid wear and overheating.

2. Static Oil Film Precondition

Charge pressure ≥20 bar, fluid cleanliness Class NAS 8 or better. The oil film is only several microns thick; solid contaminants will scratch sliding surfaces instantly.

3. Preload Force

Central spring maintains continuous compression force to separate surfaces at zero speed or low pressure and avoid instantaneous dry friction.

5. Root Causes of Damage

1. Fluid contamination: Metal particles and dust scratch friction surfaces severely.

2. Air entrainment / insufficient charge pressure: Cavitation forms honeycomb corrosion pits.

3. Frequent peak pressure overload at 400 bar, breaking protective oil film.

4. Sustained oil temperature above 95℃, oil film failure and accelerated bronze lining wear.

5. Excessive clearance of drive shaft and bearings, cylinder block wobble and unilateral valve plate wear.

6. Replacement & Assembly Specifications

1. Replacement Standard

Full set replacement is mandatory if bronze lining wear depth >0.05 mm, valve plate groove depth >0.03 mm, or cavitation perforation exists. Minor scratches can be repaired by professional surface lapping.

2. Pre-assembly Cleaning

Thoroughly flush all oil galleries, piston chambers and valve plate slots to remove metal debris.

3. Lubrication Before Assembly

Coat sliding surfaces evenly with matched hydraulic oil; dry assembly is prohibited.

4. Coaxiality Control

Drive shaft, cylinder block and valve plate must maintain perfect concentricity to avoid inclined wear.

5. Synchronous Replacement

When renewing cylinder block and valve plate, replace pistons, slippers, retainer plate and all sealing kits together.

7. Applicable Equipment & Working Conditions

- Main winch / rotary head motors of rotary drilling rigs

- Travel and loader drive motors for tunneling machines

- Closed-circuit motors for mining winches and crane hoists

- Auxiliary drives for large road milling machines and shield tunneling equipment