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2K and 3K Coating Systems for OEM Product Finishers

Article 19 of 24

Recognizing and Containing Off-Ratio Material

Detecting suspect coating, establishing the containment boundary, correcting the process, and protecting the customer

Off Ratio Is a Product-Control Event

An off-ratio condition means that the reactive components were not delivered in the relationship required by the approved coating recipe. The result may remain liquid, appear normal, atomize properly, and produce an attractive film while failing to develop the required cure or performance.

When off-ratio material is suspected, the response must extend beyond the proportioner. Mixed material, hoses, applicators, test panels, work-in-process, completed parts, rework, production records, and potentially shipped product may all require evaluation.

Learning Objectives

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

• Define an off-ratio condition and explain why appearance alone cannot confirm acceptability.
• Recognize equipment alarms and physical signs associated with improper proportioning.
• Stop the process without destroying important evidence.
• Establish the beginning and end of the suspect-production window.
• Physically and electronically identify affected material and parts.
• Investigate potential material, equipment, control, and operating causes.
• Verify corrective action before authorizing production release.

A Good-Looking Film Can Still Be Off Ratio

Wet appearance, spray pattern, gloss, color, and initial tack are not reliable proof of chemical proportion. Some off-ratio coatings may not show an obvious problem until hours or days later.

Potential consequences include slow cure, soft film, brittleness, poor adhesion, reduced chemical resistance, loss of corrosion protection, staining, gloss change, print-through, intercoat failure, or premature field failure.

What Off Ratio Means

The coating manufacturer's specified ratio establishes the required relationship among the reactive components. The allowable tolerance must also come from the coating manufacturer, approved specification, or qualified process plan.

An off-ratio condition may involve:

• Too much or too little Component A
• Too much or too little hardener, catalyst, or Component B
• Incorrect Component C delivery
• The wrong resin, hardener, reducer, or additive
• Air or incompatible cleaner entering a component stream
• Poor mixing even though component quantities are correct
• A ratio setting based on the wrong volume-versus-weight interpretation

How the System May Detect a Problem

Depending on the dosing method, the controller may compare component volumes, meter pulses, pump strokes, dosing-cylinder movement, elapsed dose time, pressure, or another measurement with the programmed recipe.

The system may report:

• Ratio-high or ratio-low alarm
• Component A or B dose-time alarm
• No-flow or unexpected-flow condition
• High- or low-pressure alarm
• Empty-supply or pump-cavitation condition
• Meter, stroke-sensor, or valve fault
• Pot-life expiration
• Recipe, communication, or controller fault

The alarm identifies a condition the system could not accept or confirm. It does not automatically determine how much production was affected.

Physical Signs That Require Investigation

An operator or inspector may observe:

• Unexpected change in viscosity or material flow
• Unstable or changed spray pattern
• Color streaks or poor component blending
• Material that remains unusually wet, soft, tacky, or easily marked
• Unexpectedly rapid gelation
• Loss of gloss, wrinkling, lifting, or abnormal surface texture
• Abnormal adhesion or cure-test result
• Unexpected pressure or flow behavior
• One component container depleting faster or slower than expected
• Unusual residue, blockage, or cured material in the mixer or applicator

These observations can have other causes, but they should trigger a structured investigation rather than an informal adjustment.

First Response: Stop, Preserve, Contain

1. Stop: Prevent additional suspect coating from reaching production parts.
2. Preserve: Retain alarm history, controller data, recipes, pressures, raw test results, and material identification.
3. Contain: Identify and isolate all potentially affected material and product until an authorized disposition is made.

Do not repeatedly reset the controller, alter calibration factors, change alarm tolerances, flush away the evidence, or continue spraying in the hope that the condition corrects itself.

Establish the Suspect-Production Window

The containment window extends from the last verified acceptable condition to the first verified acceptable condition after correction.

Use Time, Volume, and Part Traceability

The alarm time alone may not define the beginning of the problem. A slow loss of supply, leaking valve, increasing restriction, failing meter, or incorrect recipe may affect material before the controller reaches its alarm limit.

Review:

• Controller and alarm history
• Ratio, flow, pressure, and dosing trends
• Recipe and material-selection records
• Component lot changes and replenishment times
• Robot, gun-trigger, booth, and conveyor records
• Part serial numbers, rack positions, work orders, and time stamps
• Operator observations and shift-handoff information
• Inspection and test results before and after the event

Physical Containment

Potentially affected product should be:

• Stopped from advancing to the next operation where practical
• Clearly identified with a hold or quarantine status
• Moved to a controlled area or physically segregated
• Blocked from packing, shipment, assembly, or customer release
• Listed by part number, quantity, serial number, rack, batch, or production time
• Protected from accidental mixing with acceptable production

Electronic hold status is valuable, but it should be supported by physical identification where product could otherwise be moved or shipped.

Contain the Material and Equipment

Containment also applies to coating and equipment. Potentially affected material may remain in the mix manifold, static mixer, regulator, filter, hoses, splitters, applicators, dump passages, and waste lines.

The response may require:

• Stopping further mixing and spraying
• Directing material to an approved collection point
• Purging or removing the entire affected mixed-path volume
• Inspecting for gel, contamination, or restricted passages
• Replacing mixers, filters, hoses, seals, or other affected components
• Identifying and controlling the collected material as waste or suspect material

Potential Causes of Off-Ratio Delivery

Preserve the Evidence

A useful investigation depends on accurate information. Before changing the process, preserve:

• The original alarm code and first-out alarm
• Controller screen photographs or downloaded event data
• Recipe number and revision
• Calibration factors and tolerance settings
• Component pressures, temperatures, and flow readings
• Material names, containers, labels, batches, and remaining quantities
• Unaltered ratio-check results and calculations
• Representative material samples where authorized
• Part identification and process records

Do not modify calibration values or alarm tolerances merely to produce a passing result. Record the original condition before any authorized adjustment.

Verify the Actual Ratio

Follow the equipment manufacturer's approved ratio-check procedure. Collect the components independently at the designated test points and compare the result with the coating manufacturer's required ratio and tolerance.

If the required ratio is volumetric but the components are collected by weight, convert each net weight to volume using its verified density. Do not compare raw weights directly with a volume ratio unless the approved procedure specifically permits it.

Repeat the test to establish reproducibility. One passing result after several failures does not by itself demonstrate a stable correction.

Testing Affected Coated Parts

Product testing should be selected by the coating manufacturer, specification, customer requirement, and qualified technical authority. Depending on the coating and service, evaluation may include cure, hardness, solvent resistance, adhesion, film thickness, gloss, color, chemical resistance, or other performance tests.

A simple surface check may not prove long-term performance. Passing one test does not automatically establish that all properties affected by incorrect chemistry are acceptable.

When the consequence of failure is significant or the actual ratio cannot be established, consultation with the coating manufacturer, customer, engineering authority, or qualified laboratory may be necessary before disposition.

Do Not Attempt to Repair Off-Ratio Material in the Equipment

Adding extra resin, hardener, catalyst, reducer, solvent, or fresh mixed coating to the common fluid path does not provide controlled correction. The actual composition and distribution inside the equipment are unknown.

Remove or purge the suspect material according to the approved procedure, correct the cause, and refill the system with verified material.

Corrective Action and Restart

Before restarting production:

1. Identify the initiating cause rather than only the resulting alarm.
2. Repair or correct the material, equipment, control, or procedural problem.
3. Inspect and clean the affected fluid path.
4. Restore the approved recipe, calibration, and alarm settings.
5. Prime and stabilize each required component circuit.
6. Complete a passing independent ratio verification.
7. Fill the mixed path and discard the validated transition volume.
8. Confirm stable ratio, pressure, flow, and alarm status.
9. Produce and inspect a representative test panel or first-off part.
10. Obtain authorized production release.

Product Disposition

Contained product should remain on hold until an authorized decision is documented. Possible dispositions may include:

• Release: Objective evidence demonstrates compliance with all applicable requirements.
• Rework: An approved procedure can restore the product without creating additional unacceptable conditions.
• Repair or concession: Used only when formally authorized by the responsible customer or technical authority.
• Reject or scrap: Compliance cannot be established or the product cannot be acceptably restored.

Production urgency, appearance, or the cost of rejection is not objective evidence that the coating meets its requirements.

Response Matrix

Documentation

The event record should include:

• Date, time, system, line, recipe, and work order
• Alarm code, first-out event, and operating data
• Material identity, batch, temperature, and supply condition
• Last-known-good and first-verified-good boundaries
• Affected part numbers, serial numbers, quantities, and locations
• Ratio-test data and calculations
• Investigation findings and identified cause
• Repairs, adjustments, flushing, and verification performed
• Product-testing results and technical decisions
• Disposition and release authorization
• Preventive action and assigned follow-up

Key Takeaways

• Off-ratio coating may look normal while failing to develop required properties.
• An alarm identifies a detected condition but does not automatically establish the full containment boundary.
• The immediate response is to stop, preserve evidence, and contain.
• The hold period extends from the last known good condition to the first verified good condition.
• Containment applies to coating, equipment, work-in-process, completed parts, and potentially shipped product.
• Raw alarm, recipe, calibration, ratio-test, and production data should be preserved.
• One cosmetic or cure check may not establish long-term coating performance.
• Production should resume only after correction, verification, containment, and authorized release.

Knowledge Check

1. Why can appearance alone not prove that a plural-component coating is on ratio?
2. What three actions should occur immediately when off-ratio material is suspected?
3. How is the suspect-production window established?
4. Why may the alarm time be later than the actual beginning of the problem?
5. Why should calibration factors and tolerances not be changed before the original condition is documented?
6. What must be completed before production is released after an off-ratio event?

Technical References and Further Study

• WAGNER TwinControl Operating Manual
• WAGNER TwinControl Electronic 2K Mixing System
• Graco Manual 312776 — ProMix 2KS Manual Systems Operation
• Graco ProMix Ratio-High Error Guidance
• Graco ProMix 3KS Ratio-Low Alarm Guidance
• Sames Cyclomix Micro Ratio Test Kit

Professional responsibility: Follow the coating manufacturer's approved ratio, tolerance, cure requirements, testing instructions, and written technical recommendations. Follow the proportioner manufacturer's alarm, ratio-check, flushing, pressure-relief, and service procedures. Product disposition should be made only by personnel authorized under the facility's quality system and applicable customer requirements.

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