Coolant in deep hole drilling performs three critical functions: chip evacuation, guide pad lubrication, and heat dissipation. The coolant system is often the most expensive auxiliary system in a deep hole drilling installation.
| Method | Pressure | Flow Rate | Key Note |
|---|---|---|---|
| Gundrilling (D <5mm) | 100–200 bar | 2–8 L/min | Smaller diameters need higher pressure and finer filtration |
| Gundrilling (D 5–20mm) | 50–120 bar | 8–60 L/min | Most common gundrilling range |
| Gundrilling (D >20mm) | 30–80 bar | 60–200 L/min | Lower pressure but much more flow |
| BTA Drilling | 15–100 bar | 50–500+ L/min | High flow critical; pressure depends on depth |
| Ejector Drilling | 10–50 bar | 25–200+ L/min | Venturi effect needs volume flow more than pressure |
| Trepanning | 10–40 bar | 200–2200 L/min | Very high flow for large annular area |
| Skive & Roller Burnishing | 10–30 bar | 50–200 L/min | Mainly lubrication; chip load is low |
| Type | Pros | Cons | Best For |
|---|---|---|---|
| Neat oil (EP additives) | Excellent lubrication, rust protection, high film strength | High cost, degreasing step, fire risk, poor cooling | Gundrilling, BTA finishing, precision |
| Emulsion (3–10%) | Good cooling, low cost, fire-safe | Inferior lubrication, rust risk, bacterial growth | BTA roughing, general production, aluminum |
| Synthetic (water miscible) | Cleanliness, anti-bacterial, good cooling | Average lubrication, may foam at high pressure | Aluminum, cast iron, general machining |
| Semi-synthetic | Balance of lubrication and cooling | Moderate cost, may still foam | Good all-rounder for most deep hole work |
Filtration precision directly affects guide pad life, surface finish, and pump reliability. Insufficient filtration is the most common cause of premature guide pad failure.
| Application | Required Filtration | Risk If Insufficient |
|---|---|---|
| Gundrilling (precision) | ≤20 μm (15 rec.) | Guide pad scoring, short tool life, poor finish |
| Gundrilling D <5mm | ≤10 μm | Coolant passage blockage, catastrophic tool failure |
| BTA Drilling | ≤30 μm (20 rec.) | Guide pad wear, chip evacuation issues |
| Ejector Drilling | ≤50 μm | Nozzle blockage, loss of Venturi effect |
| Skive & Burnishing | ≤10 μm | Roller damage, poor surface finish |
| High-pressure pumps | ≤25 μm min. | Pump wear, seal failure, pressure loss |
| System | Pressure | Flow | Motor | Application |
|---|---|---|---|---|
| Small CNC retrofit | 20–70 bar | 33–41 L/min | 3–5.6 kW | Single ejector or small gundrill |
| Medium dedicated | 50–100 bar | 60–200 L/min | 11–22 kW | Production gundrilling or BTA |
| Large BTA system | 15–80 bar | 200–500 L/min | 22–45 kW | High-volume BTA production |
| Heavy trepanning | 10–40 bar | 500–2200 L/min | 45–90 kW | Large diameter trepanning |
Baffles for chip settling and foam control. Tangential return lines minimize aeration. Capacity 3–10× pump output.
Drum-type paper filter (15–50μm), magnetic separator for ferrous chips, or multi-stage bag/cartridge filter.
Centrifugal, screw, or plunger type as dictated by pressure/flow requirements.
Relief and regulation valves to protect system and allow adjustment. Accumulator/pulsation damper for plunger pumps.
Rotary union (rotating tools), pressure head BOZA (BTA), or connector block (ejector).
Chip conveyor, settling tank, return pump, secondary filtration. Heat exchanger or chiller for continuous operation.