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Portable Plural-Component Coating Systems for Contractors

Article 14 of 24

Plural-Component Spray Guns, Chambers, Tips, and Nozzles

The application gun must match the mixing method, coating chemistry, required output, operating pressure, spray pattern, and cleaning procedure of the complete plural-component system.

Two Different Gun Arrangements

Plural-component coatings are commonly applied through one of two fundamentally different arrangements. In the first, the components are mixed upstream and an airless, air-assisted airless, or airspray gun receives already mixed coating. In the second, separate components enter a specialized gun and are mixed by impingement immediately before atomization.

These guns, tips, chambers, and cleaning methods are not interchangeable. Contractors must identify the mixing method before selecting or servicing the gun.

Learning Objectives

After completing this article, the contractor should be able to:

• Distinguish a mixed-material spray gun from an impingement-mix plural-component gun.
• Select a gun with the required pressure, flow, material, and temperature ratings.
• Explain how airless tips and impingement-mixing chambers affect output and spray pattern.
• Recognize worn, obstructed, or incorrectly installed gun components.
• Perform safe shutdown, cleaning, inspection, and maintenance.
• Recognize conditions requiring immediate stop-work.

Mixed-Material Application Guns

In a conventional static-mix system, Components A and B combine at the mix manifold and pass through a static mixer before reaching the spray gun. The gun receives one stream of catalyzed coating.

The application gun may resemble equipment used for single-component coatings, but it must be suitable for the mixed coating's pressure, viscosity, temperature, solids content, abrasiveness, and available working time.

Every passage from the mix point through the gun and tip contains reacting material and must be included in the flushing plan.

Mixed-Material Gun Selection

Maximum Pressure Is a System Limit

The gun, tip guard, tip, swivel, whip hose, fittings, mixer housing, and every other downstream component must be rated for the maximum pressure the proportioner can generate.

Never combine a high-pressure proportioner with a lower-rated gun merely because the intended operating pressure is lower. A fault, blockage, incorrect setting, or closed valve can expose the gun to the system's maximum pressure.

Airless Spray Tips

An airless tip meters the mixed-material flow and shapes the spray pattern. Its orifice size, internal geometry, fan designation, condition, coating viscosity, and pressure all influence output and atomization.

Tip selection affects:

• Material flow rate
• Fan width at a specified spray distance
• Required atomizing pressure
• Film-build rate and applicator travel speed
• Overspray and transfer efficiency
• The production demand placed on the proportioner, heaters, and supply system

Tip Size Does Not Establish Mix Ratio

In a static-mix system, one spray tip controls the total flow of material after the components have been combined. Changing that tip changes mixed-material output and pressure demand; it does not intentionally change the A-to-B ratio.

If a tip change causes ratio or pressure alarms, the equipment may be operating outside its stable flow range or another restriction may be present. Diagnose the system rather than adjusting component ratio to accommodate the tip.

Tip Selection Procedure

1. Review the coating manufacturer's approved tip-size range and application method.
2. Determine required production, wet-film thickness, surface geometry, and working distance.
3. Confirm that the complete proportioning system can support the expected output.
4. Install an approved tip, seal, retainer, and guard rated for the gun pressure.
5. Begin at the lowest pressure that produces a complete, stable pattern.
6. Evaluate pattern uniformity, atomization, film build, overspray, and coating temperature.
7. Confirm ratio status and stable component pressures at production flow.
8. Record the approved tip and operating range in the application procedure.

Recognizing Tip Wear

Abrasive and high-solids coatings gradually enlarge the tip orifice and change the fan pattern. A worn tip may deliver substantially more material even though the pressure setting has not changed.

Possible signs of wear include:

• A narrower, heavier, or distorted fan
• Increasing material consumption
• Excessive wet-film thickness at normal travel speed
• Reduced control at edges or complex surfaces
• The proportioner cycles faster than expected
• Difficulty maintaining the approved production range

Replace a worn tip. Do not attempt to restore an orifice with a drill, wire, torch, file, or another unapproved tool.

Air-Assisted Airless and Airspray Guns

Some lower-pressure or finishing applications use air-assisted airless or airspray atomization after upstream plural-component mixing. These guns require correctly conditioned material and clean, regulated atomizing air.

Fluid-tip, needle, nozzle, and air-cap combinations must be selected as a system. Increasing atomizing air cannot correct off-ratio material, incomplete mixing, excessive viscosity, an unsuitable fluid nozzle, or a partially cured mixed path.

Impingement-Mix Spray Guns

An impingement-mix gun receives separate pressurized components. When the gun is triggered, the components enter precisely sized ports and collide at high velocity inside the mixing chamber. The mixed material then exits through a round, flat, or other approved pattern-forming outlet.

This arrangement minimizes mixed-material residence time and is commonly used for very fast-reacting materials that cannot remain in a static mixer and mixed-material hose.

Mixing Chambers and Impingement Ports

The mixing chamber contains the precisely manufactured component ports and pattern outlet. Chamber selection affects component flow, total output, pressure requirement, mixing energy, and spray-pattern shape.

Chamber selection must consider:

• The gun model and approved chamber family
• Required total mixed output
• Component ratio and equipment configuration
• Required round, flat, or special pattern
• Component temperature and viscosity
• Minimum dynamic pressure needed for complete impingement
• The proportioner's ability to maintain flow and pressure for both components

Do Not Alter Mixing-Chamber Ports

Impingement ports and pattern outlets are precision components. Enlarging them, drilling them, cleaning them with oversized tools, or mixing parts from unapproved chamber combinations changes flow and mixing performance.

Use only the cleaning tools, drill sizes, procedures, and replacement parts identified by the gun manufacturer. Cleaning tools remove contamination; they are not intended to resize ports.

Round, Flat, and Wide Patterns

Pattern labels are manufacturer-specific. Select chambers, tips, and nozzles from the current equipment documentation rather than assuming that similar numbers from different product families are equivalent.

Side Seals, Check Valves, and Screens

Impingement-mix guns commonly use side seals or equivalent components to control the separate component passages against the mixing chamber. Check valves and screens may protect those passages from reverse flow and contamination.

Wear or contamination can cause:

• Component leakage inside or outside the gun
• Cross-contamination and cured material
• Reduced component flow
• Unbalanced dynamic pressure
• Poor impingement and incomplete mixing
• Distorted spray pattern or material spit at trigger transitions

Air-Purge, Mechanical-Purge, and Solvent-Flush Designs

Each method requires its own gun construction, supporting equipment, inspection, and maintenance. Do not add solvent to an air- or mechanical-purge gun unless the manufacturer specifically approves the procedure.

High-Pressure Injection Hazard

High-pressure coating from a gun, hose, fitting, valve, or pinhole leak can penetrate skin. The injury may appear small while forcing toxic or reactive material deep into tissue. This is a surgical emergency.

• Never point the gun at any person or body part.
• Never place a hand over the tip, nozzle, or suspected leak.
• Never attempt to stop a leak with a glove, rag, tape, or body part.
• Keep the approved tip guard installed during spraying.
• Engage the trigger lock whenever the gun is not being sprayed.
• Follow the complete pressure-relief procedure before inspection, cleaning, or service.

If injection occurs, obtain immediate emergency medical treatment. Tell medical personnel exactly which coating component or mixed product was injected and provide the safety data sheet.

Clearing an Airless Tip Obstruction

Use the gun and reversible-tip manufacturer's approved procedure. Engage the trigger lock before rotating a reversible tip, direct the gun toward a safe waste location, restore the spray position after clearing, and evaluate why the obstruction occurred.

Never remove a tip, guard, chamber, nozzle, air cap, or fluid fitting while the equipment is pressurized. If the approved clearing procedure does not restore flow, perform the complete shutdown and pressure-relief procedure.

Grounding and Static Control

The gun is commonly grounded through connection to properly grounded, electrically conductive fluid hoses and equipment. Grounding continuity must extend through every approved connection.

Follow the equipment manual and applicable codes for grounding the proportioner, gun, hoses, workpiece, containers, and flushing pails. Use conductive metal containers where required and maintain metal-to-metal contact during flushing.

Daily Gun Inspection

• Confirm the gun model and pressure rating.
• Inspect the trigger, trigger lock, guard, handle, and fluid connections.
• Inspect hoses, swivels, electrical or air connections, and strain relief.
• Confirm the correct tip, nozzle, chamber, air cap, seal, and retaining parts.
• Check for dried coating, blockage, leakage, wear, and damaged sealing surfaces.
• Verify free operation only according to the manufacturer's safe test procedure.
• Confirm required purge air, mechanical purge, or flush supply.
• Verify grounding continuity where required.

Spray-Pattern Diagnosis

Gun Cleaning and Maintenance

1. Follow the approved shutdown, purge, flushing, and pressure-relief procedures.
2. Disconnect or isolate energy only as directed by the equipment manual.
3. Move the gun to a clean service area protected from component cross-contamination.
4. Use only approved cleaning materials, tools, lubricants, and repair parts.
5. Keep Component A and Component B parts separated and identified.
6. Inspect sealing surfaces, ports, needles, seats, side seals, screens, chambers, tips, and nozzles.
7. Replace worn or damaged components rather than altering them.
8. Reassemble using the specified orientation, lubricant, torque, and adjustment.
9. Complete required leakage, function, pressure, purge, ratio, and spray-pattern tests before production use.

Stop-Work Conditions

• The gun or any connected component has an inadequate or unknown pressure rating.
• The trigger lock, tip guard, purge system, or another required safety device is missing or inoperative.
• A gun, hose, swivel, fitting, chamber, or valve leaks.
• The correct tip, chamber, nozzle, seals, or gun configuration cannot be confirmed.
• The spray pattern changes suddenly without an identified cause.
• Component pressure or temperature is outside the approved impingement-mixing range.
• Cross-contamination or cured material is discovered inside a component passage.
• The gun cannot be cleaned or purged according to its approved procedure.
• Ratio, mixing quality, or cure cannot be verified.

Practical Field Rule

First identify whether the gun receives mixed material or mixes separate components internally. Then select every chamber, tip, nozzle, seal, hose, and cleaning method for that exact gun and material. Similar-looking parts are not proof of compatibility.

Technical References and Further Reading

These official resources provide additional information concerning mixed-material airless guns, impingement-mix guns, mixing chambers, spray tips, grounding, pressure relief, operation, and maintenance. Product references are educational examples and do not constitute an endorsement.

• Graco, XTR5+ and XTR7+ Airless Spray Guns—Instruction Manual: Official mixed-material airless-gun manual
• Graco, Fusion PC Plural-Component Spray Gun—Instructions: Official impingement-mix gun manual
• Graco, Fusion Mechanical-Purge Impingement-Mix Spray Gun: Official mechanical-purge gun manual
• Graco, Plural-Component Sprayers and Application Equipment: Official equipment and gun information
• WAGNER, Manual and Automatic Liquid-Coating Spray Guns: Official airless, AirCoat, and airspray application information
• OSHA, 29 CFR 1910.107, Spray Finishing Using Flammable and Combustible Materials: Spray-finishing, grounding, pumping, and material-handling requirements

Professional responsibility: Follow the coating manufacturer's current application method, pressure, temperature, output, tip, nozzle, chamber, mixing, working-time, and cure requirements. Follow the equipment manufacturer's approved gun configuration, pressure rating, grounding, purge, flushing, pressure-relief, cleaning, inspection, and maintenance procedures. Project specifications and applicable regulations also apply. Obtain written clarification whenever requirements conflict.

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