Bearings, Seals, and Lubrication Systems

Bearings, Seals, and Lubrication Systems

Chapter Introduction

This chapter covers one of the most heavily tested areas on the Red Seal exam for the industrial mechanic (millwright) trade. Bearings, seals, and lubrication systems are at the heart of rotating equipment reliability. You must not only know the types and functions, but also master installation procedures, clearance calculations, tolerances, and lubrication intervals. This chapter is structured to follow the logic of the exam: theory, practical application, calculations, then common traps.

Bearings: Classification and Fundamental Principles

Definition and Role

A bearing is a mechanical component that allows rotation or linear movement between two parts while reducing friction and supporting loads. It transmits forces between the shaft and the housing while maintaining precise positioning.

Main Classification

Standard Bearing Designation System

The ISO designation system (ISO 15 standard) is essential. A bearing of type 6205 is decoded as follows:

Bore rule: for codes 00, 01, 02, 03, the bores are 10, 12, 15, 17 mm respectively. From code 04 onward, multiply by 5 to get the bore in millimetres.

Example: bearing 6310 → bore = 10 × 5 = 50 mm. Bearing 6200 → bore = 10 mm (code 00).

Internal Clearance and Tolerances

The internal clearance of a bearing is the total possible movement of one ring relative to the other, without load. The standardized clearance classes are:

Exam trap: a mounting with a tight fit on the shaft (interference) reduces internal clearance. If the application generates heat, you must choose a C3 or C4 clearance to compensate.

Fits and Mounting

Recommended fits depend on which ring is rotating:

Fit tolerances follow the ISO 286 standard. Common classes:

Hot mounting procedure: heat the inner ring in an oven or by induction to a maximum temperature of 120 °C (beyond this, there is a risk of tempering the steel). Never heat directly with a torch on the bearing.

Cold mounting procedure: use a press and a mounting tube that applies pressure only to the ring receiving the interference fit. Never strike the bearing directly with a hammer.

Misalignment and Runout

Runout is measured with a dial indicator. Typical tolerances for a 50 mm shaft:

Excessive misalignment causes overheating, vibration, and premature failure. Alignment methods (laser or dial indicators) are covered in another chapter, but remember that angular misalignment and parallel misalignment must be corrected simultaneously.

Seals

Role and Classification

Seals prevent lubricant leaks and the entry of contaminants. They are classified as:

O-Rings

Standards: AS568A (American series) or ISO 3601. Common materials:

Compression rule: an O-ring must be compressed by 10 to 25% of its cross-section diameter. Excessive compression causes extrusion; insufficient compression causes leakage.

Lip Seals (Shaft Seals)

The standard lip seal (type TC, SC, etc.) is used for rotating shafts. Components: sealing lip, helical spring, metal casing.

Installation rules:

Maximum surface speed: a standard lip seal supports approximately 15 m/s. Beyond this, use a labyrinth seal or a mechanical seal.

Mechanical Seals

Used in centrifugal pumps and agitators. They operate with two flat faces (rotating and stationary) held in contact by a spring and fluid pressure.

Types:

Installation rules:

Labyrinth Seals

Non-contacting, they create a tortuous path that retains lubricant and blocks contaminants. Used for high speeds or heavily contaminated environments. They require precise radial clearance (often 0.25 to 0.50 mm) and must never rub.

Lubrication Systems

Roles of Lubrication

Types of Lubricants

Viscosity and Viscosity Index

Viscosity is a fluid's resistance to flow. It is measured in cSt (centistokes) at 40 °C for the ISO VG classification.

Selection rule: a standard ball bearing requires a minimum viscosity of 13 cSt at the contact point. If the actual viscosity is lower, you must switch to a more viscous oil or to a grease with a thicker base oil.

The viscosity index (VI) indicates the stability of viscosity with temperature. A high VI (≥ 100) means viscosity changes little with temperature.

Grease Lubrication: NLGI Classification

Grease quantity for a bearing:

The initial grease quantity should be approximately 30 to 40% of the bearing's free volume. For a ball bearing, the free volume is approximately:

V = (π × D × B) / 4

Where D = outside diameter (mm), B = width (mm), V = volume (mm³).

Example: bearing 6205 (D = 52 mm, B = 15 mm):

V = (π × 52 × 15) / 4 = 612.6 mm³

Initial grease = 0.35 × 612.6 ≈ 214 mm³ (approximately 0.2 ml).

Regreasing Intervals

The basic formula for the regreasing interval (in hours) for a ball bearing:

t = K × (14 × 10⁶) / (n × √(d))

Where:

Example: ball bearing (K = 0.9), bore 40 mm, speed 1500 rpm:

t = 0.9 × (14 × 10⁶) / (1500 × √40) = 0.9 × 14,000,000 / (1500 × 6.32) = 12,600,000 / 9,487 ≈ 1328 hours

This result is a baseline; you must reduce it by half if the temperature exceeds 70 °C, and divide it by 4 if the environment is dusty.

Automatic Lubrication Systems

Oil Analysis

Oil analysis is a predictive maintenance technique. Key parameters:

Applicable Canadian Standards and Codes

Canadian Electrical Code (CE Code)

The Canadian Electrical Code, Part I (CSA C22.1) applies to electrical installations. For industrial mechanics, the relevant rules concern motors and rotating equipment:

CSA B149.1 — Natural Gas and Propane Code

This code applies to gas installations. For the industrial mechanic, it is relevant when installing gas compressors, pumps, or burners:

CSA B51 — Boiler, Pressure Vessel, and Pressure Piping Code

This code applies to pressure vessels. Circulation pumps, mechanical seals, and associated lubrication systems must comply with safety requirements.

Relevant ISO Standards

Installation and Maintenance Procedures

Bearing Installation Procedure on a Shaft

Lip Seal Replacement Procedure

Lubrication System Verification

Common Traps to Avoid

Summary

Final Exam Tips

Good luck with your preparation. Mastering this chapter will give you a solid foundation for passing the Red Seal exam.