Chapter 15 Shop and Equipment Preparation

Objectives Describe the recommended maintenance program for a spray booth Explain the importance of proper material atomization, viscosity, and temperature Measure the viscosity of material using a Zahn cup Describe the advantages of a captive spray gun system

Objectives (continued) Operate and maintain a spray gun Complete a spray pattern test Explain the use of electronic or computerized mixing scales Adjust a spray gun to prepare for refinishing a vehicle

Introduction Sloppy shop conditions will usually result in a sloppy paint job Variables that affect refinishing operation include spraying environment and spraying equipment and their adjustments Professional painting technician will spend more time maintaining shop and equipment than on any other single task

Painting Environment Proper painting environment –Must be clean to keep dirt out of paint –Must have proper temperature and humidity to allow paint to cure –Must have proper light –Must have right air pressure to send clan air to spray gun Dirt can be controlled with dustless vacuum and sanding systems

Painting Environment (continued) Dirt can be controlled by cleaning vehicle before bringing it into shop Have paint prep area separate from body repair area, and use prep stations Maintain compressed air system’s filters and water traps Prepare equipment by cleaning spray booth and checking its filters Drain moisture from compressed air system and check filters and dryers

Figure This chart shows the major steps for preparing equipment and the painting area.

Preparing Spray Booth If booth is not clean, foreign matter may enter a fresh finish, requiring you to sand out debris and redo area Spray booth must be clean, with a constant temperature, daylight corrected lighting, and proper air movement Regular program of cleaning, filter replacement, examining seals and lighting is important for spray booth operation Manometer indicates when intake filters are overloaded

Figure Airflow through the booth and filters helps keep any dirt from entering wet paint.

Preparing Spray Booth (continued) Weekly spray booth cleaning includes –Vacuum top of spray booth –Secure access doors and blow off interior walls –Clean light fixtures and check lighting Monthly spray booth cleaning includes –Inspect spray booth for air leaks, and inspect and clean sprinkler heads Annual spray booth cleaning includes –Clean and oil plenum chamber and fan blade –Inspect exhaust stack for paint buildup

Prep with Vehicle in Booth After driving vehicle into spray booth close booth doors tightly Turn on air filtration system and allow it to run for a few minutes Tack rag entire vehicle to remove any loose dust and debris If booth doors must be opened, be sure exhaust fan and air supply are turned off Clothing and gloves should be clean and lint- free

Mixing and Storage Area Prep Paint mixing room should provide a safe, clean, well-lit area to store, mix and reduce paint Paint mixing area may have a painter prep area Federal and local laws dictate type of mixing area shop must have Mixing area must have adequate ventilation and fire protection Must have proper mixing and measuring equipment

Preparing Spray Equipment To prepare spray equipment –Clean equipment, and set it up with proper fluid needle, nozzle and air cap –Adjust temperature and air pressure –Make a test spray pattern To avoid air supply problems –Check and replace oil and water filters and traps –Drain moisture from system daily Atomization breaks paint into a spray of tiny uniform droplets

Preparing Spray Equipment (continued) Atomization takes three phases Stage 1: material passes through fluid tip and is surrounded by air from annular ring Stage 2: material stream is hit with jets of air from containment holes Stage 3: material is struck by jets of air from air cap horns, which hit material from opposite sides

Figure Note the three stages of atomization shown by this cutaway view of a spray gun.

Spray Gun Parts Review Spray gun air cap directs compressed air into material to atomize it and form spray pattern When pattern control knob is closed, spray pattern is round –As it is opened, spray pattern becomes oblong Fluid nozzle forms and internal seat for fluid needle, allowing it to open or shut off Fluid control knob changes distance fluid needle moves from its seat to control flow

Figure Compare basic types of spray guns.

Mixing Paint and Solvent A percentage reduction means that each material must be added in certain proportions –If paint requires 50 percent reduction, one part reducer must be mixed with two parts paint Mixing by parts means that for a specific volume of paint, a specific amount of another material must be added –If you are mixing a gallon of paint, a 25% reduction means you add one quart of reducer

Mixing Paint and Solvent (continued) Proportional numbers denote amount of material needed –4:1:1 might mean 4 parts color, one part hardener and one part solvent Mixing chart converts a percentage into how many parts of each material must be mixed

Using Mixing Sticks Graduated mixing sticks have scale markings that indicate correct proportions Use a can, pail or container with straight sides, large enough to hold all material for job Place mixing stick in container and pour amount of paint you will use Stop pouring when paint is even with number on stick, for quantity needed

Using Mixing Sticks (continued) Pour in hardener until it is even with same number in next column on stick Pour in final ingredient until it aligns with same number in last column Mix thoroughly, and fill spray gun Always use a paint strainer over cup to keep contaminants out of spray gun

Viscosity Viscosity is the thickness or ability to resist flow of the paint, primer or clear Measured with a viscosity cup – a Ford cup or a Zahn cup Paint manufacturer gives a recommended viscosity in viscosity cup seconds If material drains too quickly, you have added too much solvent If material drains too slowly it needs more solvent

Using a Zahn Viscosity Cup To use a Zahn viscosity cup –After mixing paint, submerge the viscosity cup –After removing cup, release flow of paint and trigger stopwatch –When stream of paint breaks, stop the watch A graduated mixing cup is a clear plastic cup with paint ratio markings for mixing materials Computerized mixing scales automatically indicate how much of each paint ingredient to use by weight

Paint Temperature Temperature of shop and work surface influence smoothness of finish Pull vehicle into shop and booth long enough that its surfaces warm up Never spray warm paint on a cold surface, or cool paint on a hot surface Hot weather solvent slows solvent evaporation Cold weather solvent speeds solvent evaporation

Captive Spray Gun System In a captive spray gun system, individual guns are used for applying each type of material Separate guns are used for primers, sealers, basecoats and clearcoats A good spray pattern should deposit an even oval-shaped mist of liquid on the surface Three basic adjustments for proper spray pattern, wetness and air pressure –Air pressure, pattern control, fluid control

Figure The fluid control knob on the spray gun controls the volume of color, primer, or clear leaving the gun.

Captive Spray Gun System (continued) Install a gun-mounted pressure gauge to measure and adjust the air pressure Optimum air pressure is lowest needed for proper atomization, flow rate, pattern width Set size of spray pattern with pattern control knob Use fluid control knob to adjust amount of fluid leaving spray gun

Spray Pattern Test Spray pattern test checks spray on a piece of paper before painting vehicle –Spray pattern that is heavy in the middle means too little air flow –Divided spray pattern means too much air flow

Spray Pattern Test (continued) Too much paint at top, bottom, or to one side might be a restriction at fluid needle or air cap horn Test spray for uniformity of paint distribution Flood pattern, and if all adjustments are correct, runs will be almost equal in length

(C) Heavy center pattern Figure With the cap turned sideways on the gun, test spray further. Spray a heavy coat of paint onto the test paper to flood the pattern. Inspect the length of the runs. If all adjustments are correct, the runs will be almost equal in length. (B) Split pattern. (A) Balanced pattern.

Summary Painter must have a good painting environment These variables must be addressed: cleanliness, temperature/humidity, light, compressed air/pressure Atomization breaks paint into a spray of tiny uniform droplets When properly applied, droplets flow together to create an even film thickness with a mirrorlike gloss

Summary (continued) Proper atomization is essential when working with today’s basecoat-clearcoat finishes Paint viscosity refers to paint’s thickness or ability to resist flow Viscosity can be measured with a Ford cup or a Zahn cup –Zahn cup is more common and less expensive In a captive spray gun system, individual guns are set up and used for applying each type of material