When it comes to lubricating electric motor bushings, choosing the right lubricant is crucial for optimal performance and longevity. The lubricant prevents wear and tear, reduces friction, dissipates heat, and protects against rust and corrosion. With so many options on the market, determining the best lubricant for your specific application can be challenging.
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Quick Answers
Here are quick answers to common questions about lubricating electric motor bushings:
What are bushings?
Bushings are cylindrical liners that are inserted into housings to provide smooth rotary or linear motion. They protect shafts and absorb radial forces.
Why lubricate bushings?
Proper lubrication reduces friction and wear, dissipates heat, protects against corrosion, dampens noise, and extends the service life of bushings.
What factors determine the best lube?
Lubricant selection depends on the bushing material, operating speed, temperature range, environmental conditions, and desired service intervals.
What are common bushing lubricants?
Greases, oils, solid lubricants like graphite or molybdenum disulfide, and synthetic lubricants like PTFE are common. Greases are often preferred for their adhesion properties.
Bushing Lubrication Basics
Before selecting a lubricant, it’s important to understand some basics about bushings and how they are lubricated:
Bushing materials
Bushings are typically made from metals like bronze, cast iron, babbitt, or non-metallic materials like plastic or carbon. The bushing material impacts lubrication needs.
Clearance fit
The diametrical clearance between the bushing and shaft is important. Tighter fits require more viscous lubricants. Looser fits can handle lower viscosity lubricants.
Speed factors
High speeds generate more friction and heat which impact lubricant selection. Slower speeds allow wider viscosity ranges.
Loading conditions
Higher radial or thrust loads require lubricants capable of handling the increased pressures and stresses.
Temperatures
Temperature extremes influence lubricant viscosity and performance. High temperatures require higher viscosity lubricants that won’t thin out too much.
Contamination
Contaminants shorten lubricant life so electric motor bushings should use clean lubricants and be properly sealed.
Relubrication intervals
Lubricants with longer service intervals are preferred for bushings in difficult to access locations.
Choosing the Right Lubricant
With the basics covered, here are specific tips for selecting the optimal electric motor bushing lubricant:
Match viscosity to application
Viscosity is a lubricant’s most important property. Heavier viscosity oils or greases are needed for high speeds, temperatures, and loads. Lighter viscosity lubricants suffice for slower, cooler, lighter duty applications.
Consider base oil properties
Base oils like mineral oil, polyalphaolefin (PAO), esters, or silicone impact performance properties like viscosity index, resistance to oxidation, and pour point.
Use proper thickener type
Grease thickeners like lithium, calcium, aluminum, or polyurea offer different advantages. Ensure compatibility with bushings and base oil.
Check for specific approvals
Look for lubricants approved by electric motor manufacturers or that meet specifications like NLGI GC-LB for high temperature greases.
Review performance additives
Some lubricants contain special additives like EP, anti-wear, anti-rust, or anti-oxidant that enhance protection, life, efficiency.
Consider environmental factors
Temperature, moisture, chemicals, and particulate contaminants impact lubricant selection. Extreme environments require specialized lubricants.
Verify correct application method
Match lubricant to relubrication method – whether manual, automatic oiler, or grease packed for extended service.
Check manufacturer recommendations
Often the equipment OEM provides specific lubricant selections or requirements. It’s prudent to follow their guidelines.
Common Electric Motor Bushing Lubricants
Here are some of the most common lubricant choices for electric motor bushings:
Grease
Greases are commonly used for bushings due to their adhesive properties and ability to stay in place. NLGI GC-LB certified high temperature greases are frequently used. Lithium complex, calcium sulphonate, polyurea, silicone, and PFPE greases are options for harsh conditions.
Oil
For bushings with an active oiling system, lower viscosity electric motor oils are an option. They contain anti-wear additives and have viscosities around ISO 68-150. Synthetic oils perform better across temperature extremes.
Solid lubricants
Dry lubricants like molybdenum disulfide, graphite, PTFE, talc, and boron nitride can be used alone or added to greases. They reduce friction and handle high temperatures.
Synthetic
Synthetic oils and greases based on PAO, esters, silicone, PFPE, polyglycols, or synthetic hydrocarbons provide excellent high temperature stability for challenging conditions.
| Lubricant Type | Typical Products | Key Properties |
|---|---|---|
| Lithium grease | Mobil Polyrex EM, Chevron SRI | All-purpose performance, availability |
| Calcium sulphonate grease | Chevron Calsulf XT, Shell Gadus S5 V142W | High temperature, water resistance |
| Polyurea grease | Mobil SHC Polyrex EM, Kluber Staburags NBU 12 | Excellent high temp stability |
| Silicone grease | Dow Corning 44, Electrolube HSPL | High and low temp performance |
| Electric motor oil | Mobil DTE Oil Heavy Medium, Shell Morlina S4 B | Anti-wear, demulsibility |
| Synthetic oil | Mobil SHC Cibus, Kluber Klübersynth GH 6 oils | Premium stability, life |
| Solid lubricants | Molykote G-N Metal Assembly Paste | Extreme pressure, dry lubrication |
Application Methods
Proper re-lubrication procedures are also key to electric motor bushing performance. Here are some common lubricant application methods:
Manual
Grease is manually packed into bushings at periodic relubrication intervals based on hours run or date. This allows visual inspection when serviced.
Grease gun or pump
Grease dispensing systems connected to lubrication points provide a measured amount of grease when activated manually or at set intervals.
Oil drip feed
An oil reservoir continually supplies oil to bushings through lines and nozzle drip feeds. Feed rate is adjustable.
Oil circulating system
Oil is pumped and circulated from a reservoir through bushings and bearings then returned and filtered. Oil condition is constantly monitored.
Sealed for life
Some bushings are pre-packed with sufficient grease to last until bushing replacement is required. No re-lubrication is needed.
Key Considerations
Keep these important tips in mind when lubricating electric motor bushings:
- Follow OEM lubricant recommendations
- Select lubricants designed for electric motor service
- Match viscosity rating and fluid type to application
- Ensure lubricant provides rust and corrosion protection
- Consider relubrication accessibility and intervals
- Use clean lubricants and application tools
- Avoid mixing greases with different thickeners
- Re-lubricate at proper intervals based on hours run
- Inspect bushings during relubrication when possible
Conclusion
Choosing the optimal lubricant is critical to maximizing electric motor bushing life, efficiency, and reliability. While many lubricant types can work, the best choices consider bushing material, operating speeds, loads, temperatures, and environmental conditions. Matching the viscosity rating, base oil properties, thickener compatibility, and performance additives to the application is the key to optimal lubrication. Following OEM recommendations, proper relubrication procedures, and routine inspections ensures electric motor bushings continue running smoothly for a long service life.