Appearance
The coolant tank must hold 3–10× the pump flow rate to settle chips, dissipate heat, and provide stable pump inlet conditions. An undersized tank causes temperature rise, pump cavitation, and rapid coolant degradation. Size it right the first time.
Tank Sizing
Capacity Formula
Minimum tank capacity (litres) = Pump flow rate (L/min) × 3 to 10| Pump Flow Rate | Minimum Tank | Recommended Tank | Application |
|---|---|---|---|
| 50 L/min | 150 L | 300–500 L | Small gun drilling |
| 200 L/min | 600 L | 1,000–2,000 L | Medium gun drilling |
| 500 L/min | 1,500 L | 3,000–5,000 L | BTA drilling |
| 1,000 L/min | 3,000 L | 5,000–10,000 L | Large BTA drilling |
Additional Capacity Factors
| Factor | Additional Capacity Required |
|---|---|
| Heavy chip load (> 10% chip-to-coolant ratio) | +50% |
| High ambient temperature (> 30°C shop) | +30% |
| Extended unattended operation (lights-out) | +50% |
| Fine filtration (10 µm or finer) | +30% |
| Multiple machines sharing one system | +100% (per additional machine) |
Baffle Design
Purpose of Baffles
Baffles serve three functions:
- Direct flow — route returning coolant from the return side to the pump inlet side
- Settle chips — reduce flow velocity so chips drop out of suspension
- Prevent short-circuiting — stop return flow from going directly to the pump inlet
Baffle Configuration
| Baffle Type | Configuration | Effectiveness |
|---|---|---|
| Single weir | One vertical plate at 2/3 tank length | Basic |
| Double weir | Two plates, creating three chambers | Good |
| Labyrinth | Multiple offset plates | Best |
| Full-height with bottom gap | Forces flow downward through settled chips | Sludge re-suspension risk |
Recommended Design
A double-weir configuration with three chambers:
┌──────────────┬──────────────┬──────────────┐
│ Return │ Settling │ Clean │
│ Chamber │ Chamber │ Chamber │
│ (chip-heavy) │ (baffle) │ (pump inlet) │
│ │ │ │
│ ↓ Return │ ← Flow over weir → │
│ │ │ → To pump │
└──────────────┴──────────────┴──────────────┘Baffle Specifications
| Parameter | Specification |
|---|---|
| Weir height | 60–80% of tank depth |
| Gap between baffle bottom and tank floor | 100–200 mm |
| Distance from baffle to tank wall | 200–500 mm |
| Number of baffles | Minimum 2 |
Return Flow Management
Return Line Entry
| Design Feature | Purpose |
|---|---|
| Return below coolant surface (100–200 mm) | Reduces splashing and aeration |
| Return line at opposite end from pump inlet | Maximises residence time |
| Diffuser or spreader on return outlet | Reduces flow velocity, aids chip settling |
| Return angled away from pump inlet | Directs flow toward settling chamber |
Chip Settlement
Tip: Chip settlement is a function of flow velocity, not just tank size. Keep horizontal flow velocity below 0.15 m/s in the settling chamber for steel chips, and below 0.10 m/s for aluminium chips.
Temperature Control
Temperature Rise Causes
| Factor | Temperature Contribution |
|---|---|
| Pump energy (heat from pump motor) | 3–8°C above ambient |
| Cutting zone heat transferred to coolant | 1–3°C above ambient |
| Chip heat transfer to coolant | 1–5°C above ambient |
| Total typical temperature rise | 5–15°C above ambient |
Cooling Methods
| Method | Cooling Capacity | Cost | Best For |
|---|---|---|---|
| Tank surface radiation | 0.5–1 kW per 1,000 L | $0 (passive) | Low-volume, intermittent use |
| Radiator / fan cooler | 5–20 kW | $3,000–10,000 | Most production machines |
| Chiller (refrigeration) | 10–100 kW | $10,000–40,000 | Tight temperature control |
| Heat exchanger (plant water) | 10–50 kW | $5,000–15,000 | Plants with central cooling |
Recommended Coolant Temperature
- Optimal range: 20–30°C
- Maximum recommended: 40°C (above 40°C, coolant degrades faster and operator comfort decreases)
- Temperature stability: ±2°C for precision drilling (diameter tolerance IT7 or better)
Sludge Removal
| Method | Effectiveness | Cost | Maintenance |
|---|---|---|---|
| Manual (scoop during cleaning) | Low | $0 | Labour-intensive |
| Sloped bottom + drain valve | Good | $0 (design feature) | Periodic draining |
| Drag conveyor in tank | Excellent | $5,000–15,000 | Mechanical, occasional jam |
| Automatic sludge scraper | Excellent | $10,000–30,000 | Low maintenance |
Tank Bottom Design
- Slope bottom 1:20 to 1:30 toward the drain
- Place drain at the lowest point
- Provide cleanout access (minimum 300 mm × 300 mm)
- Coat interior with epoxy for corrosion resistance
FAQ
How big should my coolant tank be?
Minimum 3× pump flow rate in litres per minute. For a 200 L/min pump, use a 600 L minimum tank. For production drilling, 5–10× is recommended for better temperature stability and chip settling.
Can I use a standard machine tool coolant tank for deep hole drilling?
No. Standard machine tool coolant tanks are designed for flood coolant (low pressure, low volume) and are too small for deep hole drilling. They lack the capacity, baffle configuration, and chip settling volume required.
How often should I clean the coolant tank?
Schedule depends on chip volume. Typical intervals: light-duty (monthly), medium-duty (weekly), heavy BTA with large chip volume (every 2–3 days). Monitor sludge accumulation and adjust schedule accordingly.
Should the tank be above or below the machine?
Below the machine (pit-mounted) is preferred for deep hole drilling. Gravity return of coolant (required for high-volume chip evacuation) needs the return line to slope downward. Pit mounting also saves floor space.
Why does my coolant temperature keep rising during production?
The tank capacity may be too small for the heat load, or the chip load may be too high for the tank's settling capacity. Check if coolant is short-circuiting from return to pump inlet (baffle issue) and verify the chiller or cooler is functioning.
Coolant tank design depends on pump flow rate, chip volume, heat load, and available floor space. Consult with a coolant system specialist for custom designs. This article reflects industry practice as of 2026.