Learn how bearings, belts, chains, couplings, gears, hydraulics, pneumatics and pumps work, how they fail, and how maintenance teams lubricate, plan PM work, rig loads and weld safely.

Mechanical Systems & Maintenance

## Why it matters

Lubrication is the cheapest maintenance there is and one of the biggest causes of failure when done badly. Too little lubricant and metal touches metal; too much and bearings overheat; the wrong type, or the right type contaminated with dirt and water, and parts wear fast. Many plants have a lubrication technician role for exactly this reason.

## What lubricants do

A lubricant separates moving surfaces with a film, reduces friction and wear, carries away heat, protects against rust and, in the case of grease, helps seal out dirt. In a rolling bearing the oil film is thinner than a human hair, so a few particles of grit can break through it.

## Oil

Oil is used where speeds or temperatures are high, where heat must be carried away, or where a circulating system already exists: gearboxes, hydraulic systems, compressors and large plain bearings.

**Viscosity** is the oil's resistance to flow, the single most important property. Industrial oils are graded by the **ISO VG** system: the number is the viscosity in centistokes at 40 °C. ISO VG 32 and 46 are common hydraulic oils; VG 220 and 320 are common gear oils. Higher loads and slower speeds need thicker oil; higher speeds need thinner oil. The **viscosity index** tells you how much viscosity changes with temperature.

Additives matter too: anti-wear, extreme pressure (EP) additives for gears, rust and oxidation inhibitors, anti-foam. Oils are not interchangeable just because the viscosity matches.

## Grease

Grease is oil held in a thickener, like a sponge holding water. It stays in place, so it suits bearings that cannot have an oil bath, open gears and parts that are hard to reach.

- **NLGI grade** measures stiffness. NLGI 2 is the most common general-purpose bearing grease. NLGI 0 or 00 are soft greases for centralized systems; 3 is stiffer.
- **Thickener type** (lithium complex, polyurea, calcium sulfonate, aluminum complex and others) affects water resistance, temperature range and compatibility.
- **Base oil viscosity** still matters, just as it does for oil.

**Compatibility**: mixing greases with incompatible thickeners can make the mixture soften and run out or harden. When changing a grease type, purge the old grease out and check the manufacturer's compatibility chart.

## How much grease, how often?

Bearing makers publish formulas and charts. A widely used starting point for the amount when regreasing a rolling bearing from the side is:

```text
grease (grams) = 0.005 × D × B
```

where D is the bearing outside diameter and B its width, both in millimeters.

**Worked example.** A 6310 bearing is 110 mm OD and 27 mm wide.

```text
grease = 0.005 × 110 × 27 ≈ 15 g
```

A typical grease gun gives roughly 1 to 1.5 g per stroke, so weigh a few strokes of your own gun. Here that is around 10 to 15 strokes, not "until it comes out the seal".

**Intervals** depend on bearing size and speed, temperature, load and contamination. Manufacturer charts give a base interval, which you shorten for heat (a common rule halves it for every 15 °C above about 70 °C), vertical shafts, vibration, dust or water. Then you adjust with experience: condition monitoring such as ultrasound can tell you when a bearing actually needs grease.

## Good lubrication practice

- **Clean before and after**: wipe the grease fitting and the gun tip. Fit caps to fittings.
- **Label everything**: color-coded tags on fittings and matching containers stop mix-ups.
- **Store properly**: sealed containers, indoors, first in first out. Use filtered transfer containers for oil, not open buckets.
- **Check, do not just add**: sight glasses on gearboxes, oil condition (color, smell, water), breathers and seals.
- **Oil analysis** on important machines finds wear metals, water and degraded additives long before failure.
- **Record it in the CMMS**: what, where, how much, when.

## Common mistakes

- **Over-greasing**: the most common error. Excess grease churns, heats the bearing and pushes past seals. In electric motors it can get into the windings.
- Mixing incompatible greases.
- Using a general grease where a high-temperature or food-grade (NSF H1) one is specified.
- Topping up a gearbox with whatever oil is nearby.
- Greasing a sealed-for-life bearing that has no fitting by drilling it.

## Safety

Lubrication routes often take you close to moving machinery. Many plants let trained staff grease some points while running, through extended lines outside the guards, but only where the site procedure says so; everything else needs lockout. Grease guns develop very high pressure: never point one at anyone, and treat injection injuries as emergencies. Read the safety data sheet for each lubricant.

## Recap

- Oil for speed, heat and circulating systems; grease where the lubricant must stay put.
- ISO VG = viscosity at 40 °C; NLGI grade = grease stiffness.
- Regrease amount ≈ 0.005 × D × B grams; intervals shorten with heat and contamination.
- Clean, labeled, recorded and not overdone.

## Try it

Open the **Do** tab and take the quiz on choosing a lubricant and interval.


Choose between oil and grease, read viscosity and NLGI grades, and set a sensible relubrication amount and interval.

Lubrication

What are the main differences between grease and oil?

Lubrication Basics

Create an Assets sheet with columns: asset ID, description, make/model, location, criticality (1-3). Add your chosen equipment.

Look up the owner's manual (most are free online) and list the maintenance tasks and intervals the manufacturer recommends.

Create a Work Orders sheet with the fields from the reading: WO number, asset, type, frequency, priority, estimated time, safety, parts/tools.

Write the safety line first: how the equipment is made safe (unplugged and plug kept with you, engine off and cooled, wheels chocked). Keep it specific.

Write 4 to 8 numbered tasks. Each task must be specific and measurable, with a spec where possible (for example, tire pressure 50-60 psi from the sidewall).

Add a Readings section with blank cells for at least two measurements you would record each time.

If it is safe and simple (for example, checking bicycle tire pressure and chain wear with a ruler), carry out the inspection tasks only and record the readings.

Fill in Findings and write one follow-up corrective work order for anything you would fix later.

Ask someone else to read your work order and tell you one task that was unclear. Rewrite it.

## Why it matters

A plant that only fixes things when they break spends nights and weekends on emergency repairs, buys parts at rush prices and loses production. Planned maintenance flips that around. Mechanics do not just do the work: they write and improve the PM tasks, record what they find and close work orders in the computerized maintenance management system (CMMS). Good records are how a team learns.

## Maintenance strategies

- **Reactive (run to failure)**: fix it when it breaks. Fine for cheap, non-critical items such as a light bulb in an office. Expensive for anything that stops production.
- **Preventive (PM)**: tasks on a fixed schedule, by calendar (every month) or by usage (every 500 operating hours). Examples: change filters, grease bearings, inspect belts.
- **Predictive / condition-based (PdM)**: measure the machine's condition (vibration, temperature, oil analysis, ultrasound) and act when the data shows a problem developing. You will see more of this in the PLC course's reliability lesson.
- **Reliability-centered maintenance (RCM)**: a structured method that asks how each asset can fail and what the consequences are, then picks the right strategy for each failure mode.

Most plants mix all of these. The skill is matching the strategy to the asset's criticality.

## Key metrics

- **MTBF** (mean time between failures) = operating time / number of failures. Higher is better.
- **MTTR** (mean time to repair) = total repair time / number of repairs. Lower is better.
- **PM compliance** = PMs completed on time / PMs scheduled. Many teams target 90 percent or more.
- **Planned vs reactive ratio**: the share of maintenance hours that were planned.

**Worked example.** A conveyor ran 2,000 hours last quarter and failed 4 times, with repairs of 3, 5, 2 and 6 hours.

```text
MTBF = 2,000 / 4 = 500 hours
MTTR = (3 + 5 + 2 + 6) / 4 = 4 hours
```

## What a CMMS does

A CMMS is a database of the plant's maintenance. Typical records:

- **Assets** in a hierarchy (site, area, line, machine, component), each with an ID, make, model, serial number, criticality and manuals.
- **Work orders**: requests, corrective repairs and PMs, with status (requested, approved, scheduled, in progress, complete, closed).
- **PM schedules** that generate work orders automatically.
- **Parts inventory** with stock levels, bin locations and reorder points.
- **Labor and history**: who did what, how long it took, what was found.

Common systems include IBM Maximo, SAP PM, Fiix, Limble and UpKeep, and many small shops use spreadsheets. The concepts are the same.

## Anatomy of a good PM work order

```text
WO number:     PM-0412          Asset: CNV-03 Conveyor 3 drive
Type:          Preventive       Frequency: every 4 weeks / 500 h
Priority:      3 (routine)      Estimated time: 45 min, 1 mechanic
Safety:        LOTO per procedure LOTO-CNV-03; gloves, safety glasses
Parts/tools:   Belt tension gauge, grease gun (NLGI 2), straightedge
Tasks:
  1. Lock out and verify zero energy at the drive disconnect.
  2. Inspect V-belts for cracks, glazing, wear. Record condition.
  3. Measure belt deflection force. Spec: 4-6 lbf at 0.5 in. Record.
  4. Check sheave alignment with straightedge. Record OK / adjusted.
  5. Grease both pillow block bearings: 6 strokes each. Record.
  6. Refit guard, remove locks per procedure, test run, listen.
Readings:      Tension ____ lbf   Bearing temp after run ____ °C
Findings:      _______________________________________________
Follow-up WO:  _______________________________________________
Completed by / date / actual time: ___________________________
```

Notice what makes it good:

- **Specific and measurable**: "measure deflection force, spec 4 to 6 lbf", not "check belts".
- **Safety first**: the lockout procedure is referenced by number.
- **Parts and tools listed** so the mechanic does not walk back to the crib.
- **Readings recorded**, so trends show up over months.
- **A place for findings and follow-up work**, so a worn belt becomes a planned corrective order, not a breakdown next week.

## Closing the loop

The work order is not done when the wrench goes down. Record actual time, parts used, readings and what you found, then close it. Failure codes (problem, cause, remedy) on corrective orders let the team spot repeat failures. If a PM never finds anything, it may be too frequent; if failures happen between PMs, it may be too infrequent or checking the wrong things.

## Common mistakes

- Vague tasks such as "inspect pump" that two mechanics would do differently.
- Signing off a PM without recording readings.
- Pencil-whipping: marking tasks done that were not done. It hides real problems and can be a safety issue.
- Never reviewing PMs after they are written.

## Beyond the platform

Industrial machinery mechanic roles usually require an apprenticeship or an associate degree in industrial maintenance with supervised hours, plus site lockout and qualified-person training. Optional credentials include NIMS (https://www.nims-skills.org/) and SMRP's CMRT (https://smrp.org/). Registered apprenticeships are listed at https://www.apprenticeship.gov/ (Checked on 2026-10-23.)

## Recap

- Match strategy to criticality: reactive, preventive, predictive, RCM.
- MTBF = operating time / failures; MTTR = repair time / repairs.
- A good PM work order is specific, measurable, safety-first and records readings.

## Try it

Open the **Do** tab to write your own PM work order.


Compare maintenance strategies and write a preventive maintenance work order the way a CMMS stores it.

Preventive maintenance and CMMS

What is Preventative Maintenance?

What is a CMMS?

Write the load weight and add an allowance for rigging hardware (assume 30 lb). Write the total.

Sketch the lift: hook above the motor's center, two sling legs down to the lugs. Label the sling length (6 ft = 72 in) and half the lug spacing (15 in).

Find the vertical height of each leg with Pythagoras: height = square root of (72² − 15²). Then find the angle from horizontal: sin(angle) = height / 72.

Calculate the tension per leg: (total load / 2) / sin(angle). Compare it with each sling's WLL. Is it OK?

Check the shackles (3/4 ton = 1,500 lb) and the hoist (2 tons = 4,000 lb) against the loads they will see. Note which item has the smallest margin.

Now imagine the only slings available are 18 in long. Recalculate the angle and tension. Write whether the lift is still acceptable and why.

Write the area controls: barricade, who is the single signal person, the travel path, and where the cart is chocked.

Write the pre-lift inspection checklist for the slings, shackles and hoist from the reading.

## Why it matters

Millwrights and machinery mechanics install, move and remove heavy equipment: motors, gearboxes, pumps, whole machines. Lifting is where small mistakes become fatal ones: a sling cut on a sharp edge, a hook loaded on its tip, a load that weighs twice what someone guessed. This lesson is awareness only. Before you rig or signal a lift for real, your employer must train you and, for many lifts, certify you as a **qualified rigger** under OSHA rules.

## The lift plan

Every lift, even a routine one, follows the same thinking. Complex or critical lifts get a written plan signed by a competent person.

1. **Know the weight.** Use the nameplate, drawings or manufacturer data. If you must estimate, calculate volume × density and round up. Add the weight of rigging hardware.
2. **Find the center of gravity (CG).** The hook must be directly above the CG or the load will tilt or swing when it lifts.
3. **Choose the hitch and slings**, accounting for the sling angle.
4. **Check every capacity**: hoist or crane, hook, slings, shackles, eyebolts, beam or gantry.
5. **Plan the path and landing**: overhead obstructions, floor loading, blocking at the landing spot.
6. **Control the area**: barricades, a single designated signal person, nobody under the load.
7. **Inspect** all rigging before use and remove anything damaged from service.

## Weight estimates

Steel weighs about 490 lb per cubic foot (about 7,850 kg per cubic meter). A solid steel plate 4 ft × 2 ft × 2 in is 4 × 2 × (2/12) = 1.33 ft³, so about 650 lb. Machines are mostly air and castings, so use the nameplate or shipping weight when you can.

## Hitches

- **Vertical**: one sling straight down. Full rated capacity, but the load can spin.
- **Choker**: the sling wraps around the load and through itself. Capacity drops, typically to about 75 to 80 percent of vertical for a standard choke.
- **Basket**: the sling goes under the load with both eyes on the hook. Capacity can be up to twice vertical when the legs are vertical, but only if the load is balanced and cannot slip out.

Always use the manufacturer's tag on the sling, which lists capacity for each hitch.

## Sling angle: the critical calculation

When two sling legs spread out from the hook, each leg carries more than half the load. The flatter the angle, the higher the tension.

```text
tension per leg = (load / number of legs) / sin(angle from horizontal)
```

```text
Angle from horizontal   Load multiplier per leg
90 degrees (vertical)   1.000
60 degrees              1.155
45 degrees              1.414
30 degrees              2.000
```

**Worked example.** A 2,000 lb gearbox is lifted with a two-leg bridle at 45 degrees.

```text
tension per leg = (2,000 / 2) / sin(45°) = 1,000 / 0.707 ≈ 1,414 lb
```

Each leg needs a working load limit (WLL) of at least 1,414 lb, not 1,000 lb. At 30 degrees each leg would see 2,000 lb, the full load. Many sites forbid angles below 30 degrees; aim for 60 degrees or steeper. You can estimate the angle from the sling length and the vertical height: sin(angle) = height / sling length.

## Hardware

- **Slings**: wire rope, alloy chain (only grade 80 or higher for overhead lifting), synthetic web and round slings. Every sling must carry a legible capacity tag.
- **Shackles**: the pin must be fully seated; load the bow in line, not sideways.
- **Eyebolts**: shouldered eyebolts lose much of their capacity when loaded at an angle; use them in line with the shank or use swivel hoist rings.
- **Hooks**: load in the bowl, never on the tip; the latch must work.

## Inspecting rigging

Remove from service: slings without a tag; web slings with cuts, burns, holes or exposed red warning yarns; wire rope with broken wires, kinks, birdcaging or crushing; chain with stretched, nicked or bent links; hooks with a throat opening that has grown or a twisted tip. Protect slings from sharp edges with softeners.

## Moving machinery without a crane

Mechanics also use machinery skates, toe jacks, pry bars, come-alongs and gantries. The same rules apply: know the weight, keep below rated capacity, keep hands and feet out from under the load, and crib (block) a raised load before anyone reaches under it.

## Common mistakes

- Guessing the weight.
- Ignoring sling angle, so each leg is overloaded.
- Standing under or beside a suspended load, or riding a load.
- Using a sling with a missing tag "because it looks fine".
- More than one person giving signals.

## Rules and training

OSHA covers slings in 1910.184 (general industry) and rigging equipment in 1926.251 (construction), with crane rules in 1926 Subpart CC: https://www.osha.gov/cranes-derricks. ASME B30.9 covers slings: https://www.asme.org/codes-standards/find-codes-standards/b30-9-slings. Rigger and signal person certifications are offered by bodies such as NCCCO: https://www.nccco.org/ (Checked on 2026-10-23.)

## Recap

- Know the weight and CG, choose the hitch, then check every capacity.
- Tension per leg = (load / legs) / sin(angle); 30 degrees doubles the load on each leg.
- Inspect and tag; protect from edges; one signal person; nobody under the load.
- Real lifts require employer training and, for many, a qualified rigger.

## Try it

Open the **Do** tab and plan a lift on paper.


Plan a safe lift on paper: estimate the load, account for sling angle, check rated capacities and control the area.

Rigging and moving machinery

Basic Rigging Terms You Should Know

Do's and Don'ts for Loading a Hook | Tips for Safe Rigging with Cranes & Overhead Lifting

## Why it matters

Maintenance mechanics fabricate brackets and guards, repair cracked frames, build up worn shafts and cut out seized parts. Even mechanics who are not certified welders need to know the processes, read a weld symbol on a drawing, and set up hot work so it does not start a fire. This lesson is awareness only: welding and cutting must be learned hands-on in a supervised shop or class, and hot work in a plant requires a permit.

## Arc welding processes

All of these melt the base metal and a filler with an electric arc, and shield the molten pool from air.

- **SMAW (shielded metal arc, "stick")**: a flux-coated rod. The flux burns to make shielding gas and slag. Portable, tolerant of dirty steel and wind, good for structural repairs outdoors. Slower, with slag to chip off.
- **GMAW (gas metal arc, "MIG")**: a wire fed continuously through a gun, shielded by gas (often argon and CO₂ mix for steel). Fast and easy to learn, common in fabrication shops. Needs clean metal and still air.
- **FCAW (flux-cored arc)**: like MIG with a flux-filled wire, with or without extra gas. Good penetration and usable outdoors.
- **GTAW (gas tungsten arc, "TIG")**: a non-consumable tungsten electrode with a separate filler rod, shielded by argon. Slow but very precise and clean; used for stainless steel, aluminum, thin material and critical welds.

A quick rule: stick for outdoor and dirty work, MIG for speed in the shop, TIG for precision and non-ferrous metals.

## Cutting and other processes

- **Oxy-fuel cutting**: an oxygen and fuel-gas (acetylene, propane) flame preheats steel, then a jet of oxygen burns through it. Also used for heating and brazing.
- **Plasma cutting**: an electric arc and compressed gas cut any conductive metal, including stainless and aluminum, quickly and cleanly.
- **Brazing and soldering**: join parts with a filler metal that melts below the base metal, without melting the base metal.
- **Grinding** prepares joints and finishes welds. Abrasive wheels have maximum speeds and must be guarded.

## Joints and weld symbols

Common joints are butt, tee, lap, corner and edge. On drawings, the American Welding Society (AWS A2.4) symbol tells you what to make:

- A horizontal **reference line** with an **arrow** pointing to the joint.
- The weld symbol **below** the line means the weld goes on the arrow side; **above** means the other side.
- A triangle is a **fillet** weld; the number to its left is the leg size (for example, 1/4 in).
- A flag at the bend means weld in the **field** (on site); a circle means weld **all around**.

## Weld quality

Good welds have consistent width and ripple, proper fusion into both pieces and no cracks. Defects include **porosity** (gas holes, often from dirty metal or lost shielding gas), **undercut** (a groove melted into the base metal), **lack of fusion**, **cracks** and **slag inclusions**. Structural and pressure welds are made to a written procedure by a certified welder and inspected.

## Hazards and controls

- **Arc radiation**: ultraviolet and infrared light burn eyes ("arc eye") and skin within seconds. Use a welding helmet with the correct shade, flame-resistant clothing covering all skin and welding screens to protect people nearby.
- **Fumes and gases**: welding fume contains metal oxides; stainless steel releases hexavalent chromium, galvanized steel releases zinc oxide, and some coatings release toxic gases. Use local exhaust ventilation and, where required, respirators. Never weld on degreased parts still wet with chlorinated solvent.
- **Electric shock**: keep cables, gloves and clothing dry and in good repair; never stand in water.
- **Fire and explosion**: sparks travel up to 35 ft (about 11 m) and fall through cracks. Never weld or cut containers that held flammables unless cleaned and certified safe.
- **Compressed gas cylinders**: secure upright, caps on when not in use, oxygen stored away from fuel gases, regulators and hoses with flashback arrestors.
- **Burns and hot metal**: mark hot parts "HOT".

## Hot work permits

In a plant, welding, cutting and grinding outside a designated shop needs a **hot work permit** (NFPA 51B). The permit confirms that combustibles within 35 ft are removed or covered, a **fire watch** with an extinguisher is in place during the work and for a set time afterwards (often at least 30 to 60 minutes), sprinklers and detectors are handled correctly, and the area is checked before the permit closes.

## Beyond the platform

Learn welding in a supervised school, community college or apprenticeship shop. Certification is commonly through AWS (https://www.aws.org/) or employer procedure tests. OSHA's welding, cutting and brazing rules: https://www.osha.gov/welding-cutting-brazing. NFPA 51B for hot work: https://www.nfpa.org/codes-and-standards/nfpa-51b-standard-development/51b (Checked on 2026-10-23.)

## Common mistakes

- Watching an arc without a helmet, even for a moment.
- Welding near combustibles without a permit or fire watch.
- Welding galvanized or coated parts without removing the coating and ventilating.
- Leaving oxygen and acetylene cylinders unsecured or with regulators loose.

## Recap

- Stick for outdoor and dirty work, MIG for speed, flux core for penetration outdoors, TIG for precision and non-ferrous metals.
- Weld symbol below the reference line = arrow side; triangle = fillet weld.
- Control arc light, fumes, shock, fire and cylinders.
- Hot work outside the shop needs a permit and a fire watch; real welding needs supervised training.

## Try it

Open the **Do** tab and take the quiz on welding processes and safety rules.


Name the main welding and cutting processes, what each is used for, and the hazards and controls that come with them.

Welding and fabrication basics

Welding Basics for Beginners

4 Types of Welding Explained: MIG vs TIG vs Stick vs Flux Core

Lubrication, preventive maintenance and CMMS work orders, rigging and moving machinery, and welding and fabrication basics.