Spray Finishing and Touch-Ups Summer Semester 2024 PDF

Spray Finishing and Touch-Ups SUMMER SEMESTER 2024 Overview Equipment, materials, and techniques for Spray Finishing Two Parts ○ Theory portion ○ Practical portion Theory Topics Air compressors Film thickness Spray...

Spray Finishing and Touch-Ups SUMMER SEMESTER 2024 Overview Equipment, materials, and techniques for Spray Finishing Two Parts ○ Theory portion ○ Practical portion Theory Topics Air compressors Film thickness Spray booths Types of finishes Spray systems Lacquer finish defects Respirators Rubbing a finish Viscosity Shading stains and toners Air Compressors A supply of clean, dry air is required by many pieces of shop equipment 1 Type / size of a compressor required for spray finishing will depend on the selected spray equipment Air Compressor A device that uses a motor / air pump to force air into a storage tank Air amount in storage tank increases → Tank pressure rises ○ Motor shuts off when tank pressure reaches upper pressure limit Compressed air is held in tank until used Air amount in storage tank decreases → Tank pressure drops ○ Motors turns back on when tank pressure reaches lower pressure limit 2 Compressed Air / Compressor Properties Pressure ○ Typically stated in pounds per square inch (psi) Delivery Rate (Flow Rate) ○ Typically stated in cubic feet per minute (CFM) ○ Usually stated at a specific pressure → ie. 8 CFM @ 40 psi ○ A measure of effectiveness of the air pump ○ Indicates how quick the storage tank will fill Storage Volume 3  ○ Typically stated in gallons or litres Humidity Air can ‘hold’ water vapor (moisture) Humidity → The amount of water vapor in the air ○ The maximum amount of water vapor that air can hold depends on the temperature of the air Cold air holds less water vapor than warm air Temp drops → Condensation ○ The maximum amount of water vapor that air can hold also depends on the air pressure Air at a high pressure holds less water than air at a low pressure Compressors and Water When air is compressed → Pressure increases ○ When pressure increases, air cannot hold as much water → Collects in the storage tank When air is released from storage tank → Air expands ○ Water temperature drops → Condensation forms in air lines Depending on the relative humidity, compressor tanks and air lines will likely collect water Types of Air Compressors 4  1. Piston Type a. Creates air pressure through the action of a reciprocating piston i. As piston moves down → Air drawn through an intake valve ii. As piston moves upward → Air is compressed iii. Now compressed air discharged through an exhaust valve into storage tank b. Single Stage Piston i. Air is drawn from atmosphere and compressed to final pressure with a single stroke ii. Tank pressure typically kept between 100 psi and 125 psi (Actual values vary from model to model and manufacturer to manufacturer) iii. Various configurations 1. Single Stage – Single Cylinder 5  2. Single Stage – Multiple Cylinders a. Higher CFM compared to single stage – single cylinder c. Two Stage Piston i. Two cylinders – One large cylinder + one small cylinder ii. Air compressed in two separate steps 1. Same process as single stage compressor → intermediate pressurized air (~100 psi) 2. Pressurized air enters second, smaller cylinder → Air compressed further → Higher pressure (~175 psi) iii. Pressurized air delivered to storage tank iv. Advantage → More air can be storage in same size tank due to higher tank pressure v. Disadvantage → Cost 2. Rotary Screw Type a. Utilize two intermeshing helical rotors in a twin bore case b. Air is compressed between one convex and one concave rotor c. Trapped volume of air is decreased → Pressure increases 6  d. Compared to piston air compressors i. Much quieter ii. Higher CFM → Very quick fill / recharge times iii. More expensive Compressors and Sawdust Sawdust can clog air intake filter ○ Air intake fed from outside of shop is best Compressors create a lot of heat ○ Equipped with cooling fins (radiator) ○ Sawdust on cooling fins reduces cooling efficiency Compressed Air Components Filter Filters water or debris from air system 7 Oiler / Lubricator Some air tools require lubrication Options ○ Periodic manual application ○ Automatic Oiler installed in compressed air system – Adds oil mist to air line Supplies oil to tools in a system which can use oil without contamination DO NOT use an automatic oiler with spray finishing equipment 8 Drip Leg Low point in air system used to drain system of any condensed water 9 Compressor Maintenance 1. Drain water from air storage tank 2. Check compressor oil 3. Clean air intake and cooling fins The Spray Booth Spray Booth – An enclosed (or partially enclosed) area with lighting, filters, and an exhaust fan used for applying spray finishes Overspray – The application of a finish on to an unintended location Reasons to Use 1. Control overspray 2. Reduce contamination of wet finish 3. Protect finisher from harmful gases 4. Reduced risk of explosion / fire 5. Protect environment from airborne product Types of Spray Booths Down Draft ○ Draws in air from above and directs it out through filters located in the floor ○ Reduced overspray as material is not drawn across booth / across the workpiece ○ High setup cost and large space requirement Cross Draft / Draft Through ○ Draws air from one end of the booth across and out through a filter wall ○ Can be open face or fitted with doors 10  Doors are fitted with intake filters to minimize dust in the booth ○ Available in many sizes ○ Low setup cost ○ Low maintenance Waterfall / Waterwash ○ Dry filters replaced by running sheet of water ○ Overspray mixes with water, absorbs airborne product ○ Very expensive setup ○ High maintenance ○ Best performance in chemical absorption Make-Up Air Unit Volume of air exhausted from a spray booth is significant ○ In cold weather, the temperature in the shop may become irregular and uncomfortable ○ Can create a negative pressure in the shop To prevent these conditions, sufficient ‘make-up’ air must be introduced to compensate for the exhausted air An air replacement unit can be installed → Supplies filtered and heated air to compensate for air exhausted by the spray booth exhaust fan Types of Filters Exhaust filters vary in quality and cost Filters must allow a minimum CFM through the booth, depends on the area Cheaper, low quality filters can… ○ Clog faster and reduce efficiency of the booth ○ Be ineffective → Results in coating o finish in plenum and on fan 11 Air Velocity Air must move through the booth with sufficient velocity to carry away overspray and toxic vapours ○ Too Low Causes potentially dangerous working conditions, especially when material contains toxic elements Low quality finish (overspray lands on piece) Increases maintenance costs (overspray coats spray booth) ○ Too High Wastes power and energy required to heat make-up air Will dry finish too quickly Measuring and Controlling Velocity Use a manometer – Measures resistance through filters To adjust airflow ○ Adjust speed of fan ○ Adjust pitch of blades on fan if unit is equipped with adjustable blades ○ Control air baffle on exhaust Spray Booth Lighting Proper lighting important when applying a finish ○ Reflections in finish can help access how evenly finish was applied, spot defects Lighting must meet explosion proof requirements if spraying solvent based finishes Ensure lighting is kept clean / free of overspray Spray Booth Maintenance 12  Monitor manometer → Clean filters when required Keep lighting clean of dust and overspray Keep floors and walls clean of dust and overspray Tidy up on a ongoing basis ○ Dispose of rags properly ○ Do not store chemicals in booth ○ Do not store unnecessary items in booth Spray Booth Rules Proper PPE → Respirator Masks at all times No smoking or sources of ignition (including electric tools) Do not enter booth unless you are dust free No food, drinks, or other contaminants in booth Clean up when done ○ Clean out guns ○ Properly dispose of any rags No excess chemicals in booth – Do not use spray booth for chemical storage Make sure chemicals and equipment are properly grounded Spray Systems Definitions: Overspray – the application of a finish onto an unintended location Transfer Efficiency (TE) – the amount of material that adheres to the substrate compared to the amount of material that was sprayed through the applicator toward the substrate, expressed as a percentage ○ A low TE results in increased material cost, and increased labour Basic Operating Principle Take liquid finish Break it up into small droplets 13  Propel droplets toward a workpiece to coat it Creating Droplets Atomization – the process of breaking up bulk liquids into droplets Options ○ Force liquid through a mechanical nozzle to create droplets (ie. water hose) Not ideal for spraying furniture as droplets are too large ○ Add a stream of air to break up forced liquid droplets into even finer droplets Making Liquid Flow Gravity Suction Pressurized Container (ie. super soaker water gun) Pump A Spray System combines a means of making the liquid finish flow with a means of atomizing the finish. Types of Spray Systems 1. Conventional Spray Guns ○ Gravity Feed Material is fed from a container above the gun via gravity Liquid is atomized with compressed air 14  Pros Well suited to praying both thin and thicker materials Relatively quick cleanup Cons Can be cumbersome in tight spaces due to large cup mounted above the gun Can be top heavy when filled with finish Must be held upright to avoid spilling material Small Capacity →Must stop and refill often ○ Siphon (Suction) Feed Material is fed from a container below the gun via vacuum or suction Liquid is atomized with compressed air Pros Well suited to spraying thinner material Relatively quick cleanup Cons Can be cumbersome in tight spaces due to large cup mounted below the gun Must be held upright or material will spill Uses more compressed air than a gravity gun (must generate enough vacuum to draw material from the cup) Small Capacity → Must stop and refill often 15  ○ Parts of a Conventional Spray Gun Fluid Tip / Nozzle and Fluid Needle Fluid needle seals the opening the in the fluid tip Fluid flows through the opening in the fluid tip as the fluid needle is pulled pack Air Cap and Fluid Tip Stream of fluid leaves the fluid tip and is atomized by jets of air from the air cap Shape of the spray pattern is determined by the amount of air and orientation of the air cap The air cap, fluid tip, and fluid needle are typically a matched set Comes in different sizes Required size depends on material being sprayed 2. Pressure Pot System ○ Gun + separate storage container for material 16  ○ Uses a gun similar to a conventional spray gun but without the cup ○ Liquid is atomized with compressed air ○ Container is pressurized to feed material to the gun when trigger is depressed ○ Some containers can be fitted with agitators (mechanical or air driven) ○ Two regulators on most tanks – One controlling air into tank and one controlling air out to the gun ○ Pros Material to be sprayed is not carried on the gun → Gun is light and can be used in more confined areas Various container sizes (1L, 5L, 20L, etc.) Can be used for adhesives (contact cement) as well ○ Cons Care should be taken not to exceed the recommended pressure rating of the tank Long change over due to amount of cleaning needed 3. HVLP Turbine System ○ ‘HVLP’ – High Volume Low Pressure Pressure is less than 10 psi ○ HVLP Gun + Electric Turbine Turbine generates the required airflow → Does not require a separate source of compressed air 17  Air travels through a series of fans → Each fan stage boosts the air pressure HVLP Guns Have larger passageways to accommodate the higher volume of air moving through the gun under lower pressure Available as siphon feed or gravity feed Liquid is atomized with a stream of low pressure air a. Lower pressure → Less overspray → High TE Cup is often pressurized to help with flow of material Can be configured with pressure pot systems Can be used with shop compressors, however, the airflow requirements is usually problematic Some supplies offer Reduced Pressure (RP) guns which are not true HVLP 4. Airless Spraying ○ Does not require compressed air ○ High pressure diaphragm pump generates suction to draw material from the container and forces the material through the gun ○ Spray Tip / Nozzle breaks the stream of fluid into ‘small’ droplets that form the spray pattern ○ Pros Good for spraying large areas of extremely thick material (ie. paint) 18  ○ Cons Compressed air IS NOT used for atomization → Larger droplets / lower quality finish compared to systems using air for atomization Not for refined finishing →’Orange Peel’ is a common problem 5. Air-Assisted Airless Spraying ○ Air driven piston pump draws material from storage container and feeds it to the gun ○ Material is atomized at the air cap using pump pressure plus compressed air (“Air Assisted”) ○ Pros Utilizes a double-action displacement pump → Very even flow of material Material to be sprayed is not carried on the gun → Gun is light and can be used in more confined areas Can spray directly out of 5 gallon pails (no pressure pot required) Suitable for both thick and thin material Large quantity of material can be applied quickly with a high quality finish ○ Cons Expensive 6. 3M Paint Preparation System (PPS) ○ A variant of conventional gravity / siphon feed guns 19  ○ Gun Options Dedicated PPS gun from 3M (gravity feed) Adapters which allow other conversion of other guns to the PPS system ○ Pros Uses interchangeable / disposable liners which allows for faster color changing and cleaning Liner is sealed and collapses as liquid is removed → No air, gun can be held in any orientation ○ Cons Small Capacity → Must stop and refill often High initial and ongoing cost Controlling Sheen w/ Flattening Agent Solid particles stirred into a finish to reduce sheen ○ More flattening agent → Lower sheen Particles nearly transparent Creates a micro-roughness on surface that scatters light randomly Most finishes available with flattening agent included Flattening agent must be kept suspended in finish while spraying ○ Stir often or use an automatic agitator (manual or air-driven) Troubleshooting Air Cap Orientation Air from horns of air cap will change spray pattern shape Spray Patterns 20  Pattern from a spray gun is a function of Air Flow setting and Fluid (Material) setting Right or Left Heavy Spray Pattern Could be caused by: a. Blocked jet on air cap; b. Debris on Fluid tip / needle To Assess: a. Rotate air cap 180 degrees If defect rotates → Issue is with air cap If defect does not rotate → Issue is with fluid tip / needle Even Coverage Rotating gun will result in uneven coverage 21  Gun should be moved parallel to workpiece Pulsating / Fluttering Conventional spray guns usually have a vent hole in cup lid ○ Allows air to enter cup as fluid level drops Tipping gun too far can cause finish to cover hole and dry ○ Blockage prevents air from entering cup through vent Results in pulsating or fluttering of finish leaving gun Resolve issue by cleaning vent hole Respirators Can help protect against: Particulate hazards Chemical gasses Selection of respirator type based on: Type of hazard Level of exposure 22 Respiratory Equipment Types Negative Pressure Relies on the wearer (lungs) to pull air through the cartridge or filter Potential to put strain on the wearer Tight fitting ○ Fit testing required ○ Users must perform seal checks before every use ○ Potential issues with facial hair Positive Pressure Equipment pushes air to the hood or facepiece ○ Powered Air 23  Battery powered blower to pull air through filter / cartridge ○ Supplied Air Bring in clean air through a hose from a source outside the contaminated area May be loose fitting or tight fitting Facial hair compatible SCBA “Self Contained Breathing Apparatus” User carries the source of clean air with them in a tank 24 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 => Filter Resistance to Oily Mists N-Class Filters ○ NOT resistance to oil R-Class Filters ○ Oil resistant ○ May only be used against oily mists for up to eight hours P-Class Filters ○ Oil proof Manufacturer will state any time use limitations Number Meaning => Filtration Efficiency ‘95’ ○ Capable of filtering out at least 95% of airborne particles ‘99’ ○ Capable of filtering out at least 99% of airborne particles ‘100’ ○ Capable of filtering out at least 99.97% of airborne particles Choosing a Cartridge 25 Colour Coded Label Black ○ Approved for Organic Vapors (OV) from solvents (ie. paints and thinners) White ○ Approved for acid gasses (ie. chlorine, hydrogen sulfide, and sulfur dioxide) Yellow ○ Approved for both OV’s and acid gasses Green ○ Approved for ammonia or methylamine When to Change a Cartridge or Filter Once filter is clogged or you have a hard time breathing Once established time of usage elapses Once you smell or taste the contaminate (make sure mask is fit on correctly first) 26