Percussion Piston Notches for Rock Drill Cavitation

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Solution Overview

Problem

Rock drilling machines experience cavitation in the work space due to premature tank pressure buildup when the percussion piston's impact point moves, leading to erosion, as conventional control edges fail to manage pressure medium flow effectively.

Innovation Solution

The percussion piston features a control edge with notches that allow pressure medium to flow before the control edge passes the corresponding edge on the distributor, enabling a controlled state change and reducing cavitation by providing a larger cross-sectional area for pressure medium flow.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a control edge of the percussion piston passes by a corresponding control edge of the cylinder before an optimal impact point (advance), then the distributor starts moving to close the pressure channel, but this causes tank pressure to exist in the work space when the percussion piston is still moving towards the impact point, leading to cavitation and erosion

Engineering Contradiction:

ImprovereliabilityVSAvoidcavitation and erosion

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The notches on the control edge enable preliminary action by allowing pressure medium to flow through them before the main control edge passes the corresponding cylinder edge. This preliminary flow action prepares the pressure distribution in advance, preventing the harmful tank pressure buildup that causes cavitation and erosion during the impact phase.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The control edge is segmented by incorporating notches that create separate flow paths. This segmentation allows different regions of the control edge to perform different functions: the notches handle preliminary pressure equalization while the main control edge surface manages the primary flow control, thereby preventing cavitation without compromising reliability.

Inventive Principle:

Principle #1Segmentation

2Reliability

If the distributor starts moving to close the pressure channel before the optimal impact point, then reliability is improved, but the pressure channel closes prematurely causing harmful tank pressure in the work space

Engineering Contradiction:

Improvefunctioning reliabilityVSAvoidtank pressure in work space

Core Design Contradiction:

ReliabilityVSStress or pressure

Solution Approach 1:

The notches act as intermediary flow paths that mediate between the high-pressure supply and the work space. They provide a controlled intermediate stage for pressure equalization, allowing the distributor to move without creating harmful tank pressure buildup in the work space, thus maintaining reliability while avoiding excessive pressure stress.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Device complexity

If the control edge is designed without notches, then the structure is simpler, but the pressure medium flow is insufficient causing cavitation when the impact point moves

Engineering Contradiction:

Improvecontrol edge structureVSAvoidcavitation prevention

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

Inventive Principle:

Principle #1Segmentation

Applied Scientific Principles

This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.

Function Achieved in This Case

This design ensures a smooth state change for the distributor, reducing cavitation and erosion by allowing pressure medium to flow through notches on the control edge of the percussion piston, thereby optimizing the timing of work phases in rock drilling machines.

Implementation Method 1

pressure medium can flow through notches provided on a control edge of the percussion piston before the actual control edge of the percussion piston passes by a corresponding control edge provided on a pilot cylinder or the distributor

Methodology Applied

Scientific EffectPressure medium flow: Pressure Gradient

Implementation Method 2

This causes cavitation in work space causing erosion

Methodology Applied

Scientific EffectCavitation: Cavitation

Data Source

PatentEP3023199B1Percussion piston and method of use

Publication Date: 2019.02.27 SANDVIK MINING & CONSTR OY

Figure 1~2
Figure 3~4d
Figure 5

AI summary

Percussion piston (1) for a rock drill machine (2) that comprises a pilot cylinder (3), a distributor (4) and pressure medium comprises a control edge (5) configurable to cause a change in the position of the distributor (4) in a direction parallel to the axial direction of the percussion piston (1) as the percussion piston moves in the impact direction (A) in relation to the pilot cylinder. The control edge (5) of the percussion piston comprises at least one notch (6) provided on the outer peripheral (7) of the control edge and arrangeable to cause a start of a state change for the distributor (4) before the control edge of the percussion piston passes by a corresponding control edge (8) provided on the distributor or the pilot cylinder