Spray Finishing and Touch-Ups Summer 2024

Overview of Spray Finishing and Touch-Ups

• Covers equipment, materials, and techniques for spray finishing
• Divided into two parts: theory and practical

Air Compressors

• Supply clean, dry air to various shop equipment
• Type and size of compressor depend on spray equipment used
• Components:
  • Motor and air pump to force air into storage tank
  • Storage tank to hold compressed air
• Properties:
  • Pressure (typically stated in psi)
  • Delivery rate (flow rate) in CFM at a specific pressure
  • Storage volume (in gallons or liters)

Humidity and Compressors

• Air holds water vapor (moisture), and humidity is the amount of water vapor in air
• Maximum water vapor air can hold depends on temperature and pressure
• Compressors and water:
  • Compressed air cannot hold as much water, so water collects in the storage tank
  • When air is released, it expands and cools, causing condensation in air lines

Types of Air Compressors

• Piston type:
  • Creates air pressure through reciprocating piston action
  • Single stage (one cylinder) or two stage (two cylinders) configurations
• Rotary screw type:
  • Uses intermeshing helical rotors in a twin bore case
  • Quieter and has a higher CFM than piston type, but more expensive

Compressors and Sawdust

• Sawdust can clog air intake filter, so it's best to feed air from outside the shop
• Compressors create heat, so they are equipped with cooling fins (radiator)

Compressed Air Components

• Filter: removes water or debris from the air system
• Oiler/Lubricator: adds oil mist to air line for tools that require lubrication

The Spray Booth

• Enclosed area with lighting, filters, and an exhaust fan for applying spray finishes
• Reasons to use a spray booth:
  • Control overspray
  • Reduce contamination of wet finish
  • Protect finisher from harmful gases
  • Reduce risk of explosion/fire
  • Protect environment from airborne products

Types of Spray Booths

• Down draft: draws air from above and directs it out through filters in the floor
• Cross draft/draft through: draws air from one end and out through a filter wall
• Waterfall/waterwash: uses a running sheet of water to absorb overspray and airborne products

Make-Up Air Unit

• Introduces filtered and heated air to compensate for exhausted air from the spray booth
• Prevents negative pressure and cold temperatures in the shop

Air Velocity and Lighting

• Air must move through the booth with sufficient velocity to carry away overspray and toxic vapors
• Measuring and controlling velocity using a manometer
• Proper lighting is essential for applying a finish; lighting must meet explosion-proof requirements

Spray Booth Maintenance and Rules

• Monitor manometer and clean filters when required
• Keep lighting clean and free of overspray
• Keep floors and walls clean of dust and overspray
• Tidy up regularly and dispose of rags properly
• Follow safety rules, including wearing PPE and avoiding smoking and open flames

Spray Systems

• Definitions:
  • Overspray: application of a finish onto an unintended location
  • Transfer Efficiency (TE): percentage of material that adheres to the substrate
• Basic operating principle: take liquid finish, break it up into small droplets, and propel them toward a workpiece

Creating Droplets and Making Liquid Flow

• Atomization: breaking up bulk liquids into droplets
• Means of making liquid flow:
  • Gravity
  • Suction
  • Pressurized container
  • Pump

Types of Spray Systems

• Conventional spray guns:
  • Gravity feed
  • Siphon (suction) feed
• Pressure pot system
• HVLP (High Volume Low Pressure) turbine system
• Airless spraying
• Air-assisted airless spraying
• 3M Paint Preparation System (PPS)

Controlling Sheen with Flattening Agent

• Solid particles stirred into a finish to reduce sheen
• Particles create micro-roughness on surface, scattering light randomly
• Most finishes available with flattening agent included

Troubleshooting

• Air cap orientation affects spray pattern shape
• Spray patterns are a function of air flow setting and fluid (material) setting### Troubleshooting Spray Gun Issues
• Rotating air cap 180 degrees to diagnose issues: if defect rotates, the issue is with the air cap; if it doesn't rotate, the issue is with the fluid tip or needle.
• Importance of even coverage: moving the gun parallel to the workpiece ensures even coverage; rotating the gun can cause uneven coverage.

Common Issues with Spray Guns

• Pulsating or fluttering finish: caused by tipping the gun too far, blocking the vent hole, and preventing air from entering the cup; resolve by cleaning the vent hole.

Respiratory Protection

• Importance of respirators: protect against particulate hazards and chemical gasses.
• Factors to consider when selecting a respirator: type of hazard, level of exposure.

Respiratory Equipment Types

• Negative Pressure: relies on the wearer's lungs to pull air through the cartridge or filter; requires fit testing, seal checks, and can be affected by facial hair.
• Positive Pressure: equipment pushes air to the hood or facepiece; can be powered air or supplied air, and may be loose or tight fitting.

Self Contained Breathing Apparatus (SCBA)

• Definition: user carries the source of clean air with them in a tank.
• Key characteristics: provides a self-contained source of clean air, independent of the surrounding environment.

Filter vs. Cartridge

• Filters: remove particles from the air.
• Cartridges: remove chemical gasses from the air; some cartridges also include a filter.

Choosing a Filter

• Letter meaning: N-Class filters are not resistant to oil, R-Class filters are oil-resistant, and P-Class filters are oil-proof.
• Number meaning: '95' filters out at least 95% of airborne particles, '99' filters out at least 99%, and '100' filters out at least 99.97%.

Choosing a Cartridge

• Colour-coded label: black for organic vapors, white for acid gasses, yellow for both, and green for ammonia or methylamine.

Maintenance and Replacement

• When to change a cartridge or filter: when it's clogged, when the established time of usage elapses, or when you smell or taste the contaminate.