Two-component materials — epoxy primers, PU fillers, acrylic-PU topcoats, 2K clear coats — are mixed with hardener seconds before they reach the part. From the moment they mix, pot life is running. Every design decision in a 2K system is a trade between accuracy, response time and how much mixed material you throw away.
Ratio accuracy, and why it is a specification
The mixing unit meters resin and hardener to a set ratio. Deviation shows up not at the gun but days later as soft film, poor chemical resistance or gloss loss — after the parts have shipped.
Metering is done by flow meters or by gear pumps driven by servo motors. On our adhesive and paint projects we specify servo gear-pump metering where the accuracy has to be demonstrable: on one glass-bonding cell the specification was 0–2,500 cc/min at ±0.3 %, and that figure was written into the acceptance test, not left as a catalogue claim.
Where the mixer sits
| Mixer position | Advantage | Cost |
|---|---|---|
| At the paint kitchen / wall | Simple, serviceable, low arm payload | A long length of mixed material in the line — large flush loss at every stop |
| On the robot arm (in-arm mixer) | Short mixed-material path, fast colour and material change, low waste | Wrist payload, hoses and maintenance access inside the booth |
| External mix at the applicator | Components meet only at the nozzle; minimal mixed material | Nozzle design and cleaning discipline; not suitable for every material |
Pot life is a production constraint, not a chemistry note
- The mixed material between the mixer and the gun has a clock on it. Line stoppages longer than the pot life mean an automatic flush — so the flush sequence has to be part of the PLC logic, not a manual procedure.
- The flush cycle consumes solvent and produces waste at a rate that scales with the mixed volume in the line. This is the real argument for an in-arm mixer on a line with frequent stops.
- Shift patterns matter: an end-of-shift flush is cheap; an unplanned two-hour stop with a wall-mounted mixer is not.
What we put in the offer
- The mixing and dosing unit by name — AccuFlo 2KP Pro for 2K, or the AccuFlo 1KP flow meter for 1K lines — with the ratio range and metering principle stated.
- Mixer position and the resulting mixed-material line volume.
- The flush and cleaning arrangement: solvent supply, cleaning tanks, waste collection.
- Hold-pressure valves, air treatment and paint circulation from the mixing room — the interface items that turn into change orders when they are omitted.
- The acceptance criterion for ratio accuracy, if the customer specification states one.
Frequently asked questions
Do I need 2K equipment if I only run 2K occasionally?
If the occasional run is a topcoat that defines the finish, yes — hand mixing into a pot defeats the repeatability you bought the robot for. If it is a rare variant, an external-mix arrangement or a separate manual station may be the cheaper answer.
How is ratio accuracy verified at acceptance?
By collecting and weighing timed samples of each component at the mixer over a defined output range. If accuracy is in your specification, put the test method in the contract — a percentage without a method is not testable.
Can the same robot run 1K and 2K materials?
Yes, with the fluid path built for it: separate circuits, a defined change and flush procedure, and enough wrist payload if a mixer is carried. It is a design decision at quotation stage, not a later addition.
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