Blind holes and cross-drilled holes are exactly the places a spray jet does not reach: it hits what it sees.
Cleaning and deburring components with cross-drilled holes and blind holes
1 · The challenge
Why cross-drilled holes and blind holes are difficult
On a component with cross-drilled holes and blind holes the contamination sits where the spray jet does not get to. Spraying produces spray shadow: not every surface is reachable — the jet hits what it sees. What it does not see stays untreated and becomes visible in the residual contamination verification.
A blind hole is one of the places a directed jet does not reach. But that is exactly where the residual contamination sits that is measured later — and exactly where spraying fails because of spray shadow.
At the bore intersection of two cross-drilled holes a second problem is added: that is where the burr forms, and no mechanical tool reaches any of these places. Four of the seven burr types we list sit at or in bores — there is no fixed standard burr type; the part geometry is what governs.
A burr that stays in a cross-drilled hole rarely remains a form deviation. It comes loose later and travels to where the component works — into oil and hydraulic channels, to valves, into pumps and gearboxes. A detached burr in the channel is therefore not only a deburring problem but a residual contamination problem.
The task does not depend on the individual component: internally branched housings, channels with cross-drilled holes, blind holes and bore intersections pose the same task — no matter whether the part later works in a gearbox or in an aero engine.
2 · Engineering considerations
What we base the system design on
- 01
Internal geometry
Blind holes, through-holes and internal channels with cross-drilled holes help decide the process: spraying produces spray shadow, not every surface is reachable. Many bores speak for lance technology — targeted instead of across the whole surface. - 02
Part geometry
Geometry, size and material come at the beginning — as does whether an individual part is processed or a batch of bulk parts. The more complex the geometry and the more bores and blind holes, the sooner immersion and flooding come into question instead of spraying. - 03
Workpiece fixture
With cross-drilled holes and blind holes the parts carrier is not an accessory but an essential part of the system concept. Its design engineering helps decide where spray shadow arises and whether the nozzles reach the component — especially with residual contamination requirements it is a decisive factor. - 04
Part orientation
How the component lies in the system helps decide whether the cleaning medium drains off again and how much effort the subsequent drying takes. A component with blind holes that lies horizontally on the workpiece carrier cannot drain: the water stands in the bore and goes into the drying in full. A different fixture — tilted or rotated — changes exactly that. The amount of liquid is therefore not an input value but a result of geometry and position. - 05
Residual contamination requirement
What has to be verified in cross-drilled holes and blind holes stands at the beginning of the system design, not at its end. The required residual contamination values act on the process, the filtration, the drying and the workpiece fixture at the same time. - 06
Deburring requirement
Whether deburring is additionally required is decided in the same technical clarification: where a burr is involved as well, water jet deburring is usually the better solution. At the bore intersection of two cross-drilled holes, that is the place no tool reaches mechanically. - 07
Drying
Bores and blind holes place the highest demands on the drying — residual moisture stands there where conventional drying is not enough. How dry the component has to leave the system determines the effort at the end of the process chain: recirculating air, infrared drying, air blow-off or vacuum drying, designed to suit the project.
3 · The system concepts
Which processes and system concepts come into question
Immersion cleaning
Where a directed jet does not reach the blind hole, immersion can lead to the result: it is not the process medium that is guided around the component, but the component that is lowered into the process medium — so the liquid also reaches areas no jet can aim at.
Flood washing
Where a directed jet does not reach concealed transitions and branched contours, flooding can come into question: the process medium is guided over and around the workpiece at high volume, and the effect arises from the surrounding amount of liquid instead of from the impact. Flooding is a process, not a machine type of its own.
Lance technology
Where a single cross-drilled hole has to be hit precisely, lance technology comes into question: the process medium is guided into the bore in a targeted way instead of across the component. Each lance has to match its bore and hit it reliably — the arrangement is designed for the specific component and is part of the design engineering.
Immersion cleaning systems
ZTFor complex components with many bores and blind holes the immersion cleaning system can make sense — everywhere that spraying leaves spray shadow and the process medium has to reach every place reliably.
Chamber cleaning systems
ZKFlooding processes run predominantly in chamber cleaning systems. Where individual bores additionally have to be flowed through in a targeted way, lance technology is added within them.
Water jet deburring
Where a burr root sits at the bore intersection of two cross-drilled holes, water jet deburring comes into question: the water jet needs no path for a tool, only one for the process medium.
Drying
Blind holes and internal bores are the critical case of drying — residual moisture stands there where conventional drying is not enough. Where the requirement is high, vacuum drying can be the answer to it; it is an option, not a process of its own.
The principle
Why several solutions are possible for this geometry
None of these assignments is a rule. Cross-drilled holes and blind holes say where the problem sits — not which system solves it: it is not the type of component that decides, but the process design. Depending on production volume, cycle time, residual contamination requirement and material flow, the same component can be better placed in a different system — there is no rule “component X, machine Y”. What you see here is the consideration, not its result.
4 · What else to consider
What else has to be clarified for cross-drilled holes and blind holes
- 01
Spray shadow is not a weakness of the system
Spraying produces spray shadow — regularly so with cross-drilled holes and blind holes. That is not a weakness of the system but a property of the process, and it belongs in the decision. - 02
Lance technology supplements, it does not replace
Lance technology does not replace cleaning across the surface: the surface is sprayed or flooded, the bores are lanced. In practice this is often a combined process in the same parts cleaning system. - 03
Ultrasonic cleaning is an option, not a process of its own
Ultrasonic cleaning is used predominantly together with immersion and flooding processes. It supplements them where wetting alone is not enough, but it does not replace them — and whether it makes sense in the specific case is decided by the system design. There is no blanket rule. - 04
A burr at the bore intersection is not a cleaning problem
If chips remain in bores and cross-drilled holes, that is a question of media routing. If a burr sits there at the bore intersection as well, it is not a cleaning problem but a deburring problem — and both are therefore considered together.
Questions and answers
Frequently asked questions about cross-drilled holes and blind holes
Why does a spray jet not reach the blind hole?
Is spray shadow a defect of the system?
Does lance technology replace cleaning across the surface?
Is ultrasonic cleaning the solution for blind holes?
How much liquid remains in the blind hole?
Direct contact
Hauptstraße 31
93186 Pettendorf
Pettendorf bei Regensburg
Fax +49 (0) 9409-777 3607
Technically responsible for this page: Günther Zippel — International Sales & Technical Consulting