Process KnowledgeDisk disc spraying appears one side thick, one side thin or color yin and yang side, the correct first level of troubleshooting is not to repeatedly modify the high pressure, but to answer two questions:
Is the spray from the spinning disk circumferentially consistent?
Is the path and residence time of the workpiece through the spray symmetrical?
The spray is asymmetric, focusing on the paint, viscosity, distributor, disk surface, rotational speed, shaping gas, coaxiality and disk state; the path is asymmetric, focusing on the central position, distance, reciprocating trajectory, line speed, hanger rotation and multi-head superposition.
Only after these two sets of variables are basically normal, continue to check the electrostatic high voltage, actual current, workpiece grounding, paint batch, metal pigment orientation and oven temperature difference.
First confirm whether the spray is symmetrical, and then confirm whether the path is symmetrical.This makes it easier to find the true root cause and create a reproducible process window than tuning just one parameter.
Process KnowledgeThe stability of K polyurethane cup spraying cannot only look at the "correct A/B ratio" displayed on the controller, nor can the reaction be fully guaranteed by simply lengthening the static mixer.What is really needed is a continuous dynamic control chain:
The ratio specified in the formula is the instantaneous ratio of the → A/B → independent metering accuracy of the mixer inlet. The cumulative ratio within a → certain time window is the mixing uniformity and residence time distribution of the → static mixer→. The viscosity, flow rate and atomized → wet film leveling, flash drying, curing and final performance of the mixing material age → rotating cup end in the pipeline after the mixer.
Four boundaries must be defined first:
Static mixers do not correct mismatches. It can only further segment, reorganize and homogenize the A and B components that have already entered the mixer.If the upstream metering ratio is wrong, the better the mixing, the more evenly the error ratio will be distributed.
The cumulative ratio is correct, which does not mean that the instantaneous ratio is stable. Start-stop, color change, flow switching, valve hysteresis, pump pulsation, or short-term shortage may still spray local partial A or partial B material to the workpiece when the total average seems to be qualified.
Nominal residence time is not the actual reaction time of each piece of material. Static mixers and downstream tubing have dwell time distributions, channel differences, and dead volumes; materials continue to react during shutdown.
Dwell time is in the process window. Too short may result in inadequate mixing; too long may result in increased viscosity of the mixture, increased pressure drop, deterioration of atomization, increased gumming and cleaning loads.Can't take “longer” straight
Process KnowledgeThe Great Cyclone Recovery System cannot only be judged by "the greater the wind and the higher the pressure drop, the better the recovery".What really needs to be matched is:
The PSD offset → screening, contamination and film-forming quality access control of → primary recovery powder and secondary trapping powder of particles with → different grading efficiency in tangential flow field and residence time in → cyclones can be → actually recombined.
Among them, four boundaries should be established first:
The inlet wind speed determines whether the particles can be stably transported into the cyclone and the strength of the cyclone field, but there are applicable windows. Too low wind speed may cause pipeline deposition and penetration of usable powder to the second level; too high wind speed will significantly increase the risk of pressure drop, energy consumption, particle impact and re-entrainment, and does not guarantee that the separation efficiency will continue to increase in equal proportions.
The cyclone pressure drop is the result of the operating state and is not a quality indicator that can be set separately from the flow rate, geometry, powder load and measuring point. The same pressure drop may come from high flow, or it may come from clogging, dust build-up, air leakage, point change, or downstream resistance coupling.
The particle size distribution of the powder determines the classification difficulty of the cyclone. Larger, denser, and more agglomeratively stable particles are generally more susceptible to centrifugal separation; fine powder is more susceptible to secondary filtration with airflow, but the specific behavior is also influenced by particle shape, density, humidity, charged, agglomerated, and surface state.
The secondary trapping amount is not equal to the secondary powder reusable amount. The secondary powder must pass the PSD, contamination, fluidity, live, fluidization, screening and film-forming quality verification before it can be included in the qualified reuse amount.
Therefore,
Process KnowledgeWhether the conductive primer can improve the electrostatic spraying of non-metallic workpieces should not only look at "whether there is a spray primer", but also can not only look at a surface resistivity reading.What really requires closed-loop verification is:
Effective connection between the continuous → dry film structure and the cured → surface/volume conductive path → and the grounding of → the hanger Charge attenuation behavior → Electrostatic field stability and coating transfer performance.
There are four key judgments:
Coating rate first refers to effective area coverage and continuity, not just paint consumption or average film thickness. Locally exposed bottoms, pinholes, thin edges, and uneven zoning will cause the conductive network to be cut off, and the electrostatic effect may be unstable even if the average film thickness seems to be acceptable.
Surface resistivity is not the charge decay rate itself. The surface resistivity reflects the difficulty of conducting electricity along the coating surface; the charge decay time is also affected by the coating capacitance, area, film thickness, substrate, ground contact, temperature and humidity, and measurement structure.
The effect of the degree of curing on the conductivity is usually not a monotonous relationship. Residual moisture or solvent during undercuring may cause temporarily low readings, but accompanied by drift, adhesion, and risk of re-coating; overcuring may also alter resin shrinkage, conductive filler contact, or interlayer adhesion.The specific direction must be confirmed by the corresponding primer system and test.
“Lower resistance is better” is not a complete process goal. What is needed is to form a stable, uniform, repeatable discharge path from the spray area to the ground, while avoiding the illusion of localized silos, contact failures, and changes in test conditions.
Therefore, the conductive primer
Process KnowledgeThe final arrangement of sheet pigments such as aluminum powder and pearlescent mica in metal glitter paint cannot be obtained by increasing the rotation speed of the rotating cup, electrostatic voltage or "accelerating volatilization" alone.A more robust control logic is:
Establish a suitable atomization window with the rotating cup speed: the droplets are uniform and refined enough, but cannot be excessively dissolved, viscous or dry sprayed before reaching the workpiece.
Create a uniform deposition window with a stable but not too strong electric field: the focus is on controlling the trajectory, coating, and film thickness distribution, rather than understanding the electric field as a separate knob that directly “lays” the sheet pigment.
Establish a directional locking window with mixed solvents and flash drying conditions: the wet film should retain sufficient flow time so that the sheet pigment tends to be parallel to the substrate; then it should be adhered and locked in time to avoid continued drift, settlement or flow.
Therefore, what really needs to be optimized is the continuous process of “atomization — deposition - wet film flow — flash dry locking”, rather than three isolated parameters.
Process KnowledgeThe function of the fluidized bed powder barrel is not to "blow the powder as alive as possible", but to reduce the internal friction of the powder layer with a uniform and controlled rising airflow, so that the powder forms a loose state that can be stably absorbed by the powder pump. Insufficient fluidization can cause lumping, bridging, rat holes, and powder suction interruptions; excessive fluidization can cause large bubbles, furrows, powder tumbling, fine powder lifting, coarse and fine powder delamination, and powder suction concentration fluctuations. The permeability uniformity of the microplate determines whether the air flow at the bottom of the powder drum can be evenly distributed: local blockage, damage or edge leakage will form a high and low flow rate zone, which will periodically change the apparent density of the powder near the inlet of the powder pump. The effect on the primary powdering rate is usually indirect - it first affects the amount of powder per unit time, the powder-air ratio and the stability of the powder cloud, and then affects the powder charge-to-mass ratio, the spraying width, the film thickness uniformity, the over-spraying and the quality of the workpiece deposition. The flow rate of fluidized gas, the pressure drop of the microplate, the state of the powder layer, the coefficient of variation of the minute amount of powder and the one-time powdering rate calculated according to the unified boundary should be measured at the same time for selection and debugging, and the pressure gauge reading should not be looked at alone.
Process KnowledgeElectrostatic spraying voltage cannot be set using a fixed, one-size-fits-all value. First confirm the equipment type and manual specifications, then check grounding, gun distance, material feed, and atomization. Test incrementally based on flat surfaces, deep grooves, sharp corners, or recoating scenarios. Adjust only one variable at a time and record film thickness, appearance, and alarm conditions.
