Use of Lube Oil Cooler in Gear Box
The use of a lube oil cooler in a gearbox is a critical aspect of ensuring reliability and longevity, especially in high-power, high-speed, or continuous-duty applications.
Here’s a detailed explanation of its role, how it works, and why it’s necessary.
1. The Primary Purpose: Managing Heat
The fundamental job of a lube oil cooler in a gearbox is to remove excess heat from the lubricating oil.
- Source of Heat: The main source of heat in a gearbox is friction. This includes:
- Gear Meshing: As teeth engage and disengage, sliding and rolling friction generates significant heat.
- Churning: The gears sloshing through the oil sump creates fluid friction.
- Bearings: Friction within the support bearings also contributes to the overall heat load.
- Consequence of Overheating: If this heat is not removed, the oil temperature will rise to dangerous levels, leading to:
- Oil Degradation: The oil will oxidize, break down, and lose its lubricating properties (viscosity shears down).
- Component Damage: Loss of lubrication leads to increased wear, scouring, and pitting on gear teeth and bearings.
- Thermal Expansion: Excessive heat can cause the gearbox housing and components to expand beyond their design tolerances, leading to misalignment and potential seizure.
- Seal Failure: High heat rapidly degrades rubber and polymer seals, leading to leaks.
2. How it Works: The Cooling Process
The cooler is integrated into the gearbox’s lubrication system. The typical flow is as follows:
- Oil is Pumped: An oil pump (either dedicated or splash-fed) picks up oil from the gearbox sump (reservoir).
- Oil is Directed: Instead of going directly to the gears and bearings, the warm oil is first routed through the oil cooler.
- Heat Exchange: Inside the cooler, the hot gear oil transfers its heat to a cooling medium.
- Cooled Oil Returns: The now-cooled oil is fed back into the gearbox to lubricate and cool the components, and the cycle repeats.
. Types of Coolers Used in Gearboxes
The two most common types are:
A. Air Cooled Oil Cooler (Air-to-Oil)
- How it Works: The warm oil is pumped through a core of tubes with fins attached. A fan (electrically driven or mechanically driven from the gearbox itself) forces air over the fins, carrying the heat away.
- Pros: Simpler design, no risk of fluid mixing, self-contained.
- Cons: Cooling efficiency depends on ambient air temperature. Larger and louder than water-cooled versions.
- Common Applications: Mobile equipment (vehicle transmissions, axles), wind turbine gearboxes, industrial gearboxes where a water source is unavailable.
B. Water Cooled Oil Cooler (Shell-and-Tube or Plate Heat Exchanger)
- How it Works: The warm oil is pumped through one set of passages (e.g., the tubes). Cool water or coolant from an external source (like a plant cooling water loop or a separate radiator system) is pumped through the surrounding passages (the shell). Heat is transferred through the metal walls from the oil to the water.
- Common Applications: Marine gearboxes, large industrial gearboxes in factories, power generation equipment, steel mill drives.