The Wagner Tips

7/31/2019 The Wagner Tips

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The Wagner Tips & Tricks: Standard application values

By: Martin Krssing, Manager WAGNER Applications Technology

In my capacity as manager of the Applications Technology Department at WAGNER, I have visitedcustomers all over the world. In this column, I would like to tell you about the most frequent problems Ihave been confronted with and - more particularly - about the solutions to these. Just take a regular look;it will definitely be worthwhile.

Gun Performance

The gun performance describes the area which a spray gun can coat in one minute.

This is how the gun performance is calculated:


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Powder Output Measurement

This measurement is of interest if you want to find out how the wear on wearing parts affects the powder consumption, or whether the individual guns deliver an equal amount of powder at the same setting. In order to measure the powderoutput an empty powder measuring bag is weighed and fixed to the gun. Then powder is sprayed through the gun forprecisely one minute. At the end the powder bag is weighed.

Die Dsensysteme

Fan spray nozzle

The Fan spray nozzle is widely used in modern coating plant. The reason for this is themore uniform coating and the greater effective depth.

Deflector cone

Deflector cones tend to generate a picture frame affect. The smaller the deflector plate the

less critical is this effect.

Wide fan spraynozzle

This nozzle system, also known colloquially as a duck's bill, is used for larger outputs ofpowder due to its geometry.

Tips & Tricks no. 1 - The choice of the right nozzle system

It is found again and again in practice that work pieces are being coated with completely unsuitable nozzle

systems. The result is usually an inadequate coating quality or an excessive consumption of powder.


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Fan spray nozzle (gap) for Corona und TriboFor complicated and deep objects

Powder output max. 150 - 200 g/min (Corona) Powder output max. 100 - 150 g/min (Tribo)

Wide fan spray nozzle for Corona and TriboFor surfaces and recesses

Powder output max. 300 g/min (Corona) Powder output max. 250 g/min (Tribo)

Deflector cone for Corona und Tribo For coating surfaces

Powder output max. 300 - 400 g/min (Corona) Powder output max. 200 250 g/min (Tribo)

When determining the correct nozzle system, the depth profile of the work piece is of decisive importance. Toget the best out of your coating equipment you should also attach great importance to the correct powderoutput.

The following illustration shows how to choose the optimal setting of your equipment for your work pieces:


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Tips & Tricks no. 2 - The electrically conductive powder hose

Who hasnt had it happen to them? You pick up a powder hose and suddenly itsliterally like being struck by lighting!

The problem:

During the coating process powder flows through the hose. Due to the frictioncaused by this, the hose becomes electrostatically charged. Since it is notearthed, it discharges as soon as the opportunity arises. An unsuspectingoperator can quickly become just such an opportunity.

The solution:

To resolve this problem the hose needs to be earthed but normally plastic is not electrically conductive. Thisis why those resourceful people at Wagner have come up with a powder hose with an electrically conductive

core, a vein of carbon running along the whole length of the hose.

When the new powder hose is used with a suitable injector (PI-P1 or PI-F1), the dischargesdescribed above finally become a thing of the past. With a few adaptations older injectors ofTypes PJ-2020PRS and PJ-D1 are also compatible with the new electrically conductive powderhose.

Tips & Tricks no. 3 - The Venturi principle, or how does the powder injector work?

The diagram below shows a cross section through a WAGNER powder injector:

The functional principle

Compressed air from the feed air connection is pushedthrough the injector nozzle (also known as the Venturinozzle) into the collector nozzle. The small diameter of

the nozzle ensures a high air velocity.

On its way through the injector the feed air passes across thepowder suction tube where it sucks in powder due to the vacuum.The air and the powder now continue to flow at a high velocity

through the collector nozzle into the powder hose and finally to thespray gun.


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Good to know: The powder particles must be delivered at a speed of around 12 m/sec in order to achieve a uniform

powder delivery and a soft cloud.

The secret of the air flows

The feed air is responsible for the powder quantity. In order to influence the powder velocity, dosage air is also required.

The air flow rate which you set on the controller consists partly of feed air and partly of dosage air.The ratio of dosage air to feed air has a great influence on the amount of powder delivered:

feed air high / dosage air low = large flow of powder

feed air low / dosage air high = small flow of powder

The sum of both air flows, i.e. the total air, and the powder velocity in the tube remain the same.

Wear

The abrasive effect of the powder/air mixture wears the collector nozzle over time. The powder speed decreases withIncreasing wear of the collector nozzle. The result is a reduction of the Venturi effect and consequently of the powder output.

New collector nozzle Worn collector nozzle

In order to maintain the desired powder output the experienced powder coater increases the feed air at this point. Normally,this measure works until the collector nozzle is completely worn and must be replaced.


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Typically, the life span of a collector nozzle lies between two weeks and one year (depending on the powder characteristics,the feed air quantity used etc.)

Tip:Dont forget to reduce the feed air again, as soon as you start using the new collector nozzle.Otherwise, there will be a significant wear right from the beginning.

Tips & Tricks Nr. 4 - The importance of the correct powder velocity

A wrongly set powder velocity in the powder hose can result in serious consequences.Too high a powder velocity means:

Increased wear in the injector and in the gun (nozzle wedge, nozzle body, gun attachment) Blow off effects when coating. Problem areas will be poorly coated due to poor air flow. Unnecessarily high air consumption.

If the speed is too low this will give rise to:

Powder deposits in the hose. Irregular powder output (spitting)

Only with the correct powder velocity do we get a homogeneous powder cloud.

So far so good. Now, how high is the correct powder velocity? How do you calculate the total air quantitynecessary for this? And how do you set this on the control unit? Find the answers in the next issues of our Tips& Tricks.

Tips & Tricks no. 5 - How to calculate the correct total air quantity


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As a rule the ideal powder velocity to is 10 - 15 m/s. To achieve this result you must calculate the total air. Thetwo crucial factors in this are the values for:

The internal diameter of the hose The velocity of the powder

For the sample calculation below we assume a powder velocity of12 m/s and an internal hose diameter of 9mm (r = 4.5 mm).

This is the formula:

and here's the calculation:

In real terms this means that you must set a total air figure (feed and dosage air together) of 2.7m3/h. Tomake things a little easier for you we have already calculated the total air quantity for the most commoninternal hose diameters:

Internal hose Powder velocity Total air

9 mm 12 m/sec 2.7 m3/h

10 mm 12 m/sec 3.4 m3/h

11 mm 12 m/sec 4.1 m3/h

12 mm 12 m/sec 4.9 m3/h

Learn how to set the total air in the next issue of our Tips & Tricks.

Tips & Tricks no. 6 - How to adjust the air flows

After we discussed how to calculate the correct total air quantity in the last issue of our Tips & Tricks, it's now time to have acloser look at the setting procedure of the results we have obtained.

Remember: The correct total air with different hose diameters

Internal hose Powder velocity Total air

9 mm 12 m/sec 2.7 m3/h

10 mm 12 m/sec 3.4 m3/h

11 mm 12 m/sec 4.1 m3/h

12 mm 12 m/sec 4.9 m3/h

Systems with automatic regulator (AFC in m3/h)

Here all you have to do is enter the total air through a keypad or by turning a swivel knob. The regulation then takes placeautomatically. The system operator can adjust the feed air, as required, to influence the size of the powder cloud.


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So that the velocity in the powder hose is kept constant, the dosage air is automatically regulated to suit.

First total air setting of manual coating systems

Injectors with orifice

The total air of plants with manual pressure

control valves is somewhat more complex toadjust, depending on the configurationinstallation. Let's take a look at it on the basis ofa concrete example with the following values:

Injector: PI-PF with orifice (recognizable from the black or partly black dosage air fitting)

Hose length: 6m / 20ft

Hose inside : 11 mm

Powder velocity: 12 m/s / 40 ft/sTotal air: 4.1 Nm3/h

Powder: Epoxy Polyester (E/P)

Target powder quantity100 g/min

1. Adjust the feed air until the desired powder cloud is obtained (e.g. 1 bar / 14.5 PSI).2. Check the feed pressure on the pressure gauge. The corresponding feed air quantity in Nm3/h can be read on the

outer scale of the pressure gauge.3. Calculate the dosage air quantity:

Total air (4.1 Nm3/h) - feed air (2.0 Nm3/h) = dosage air (2.1 Nm3/h)4. Now find the equivalent of the dosage air quantity on the pressure gauge and adjust accordingly

(2.1 Nm3/h = 1.5 bar / 21.75 PSI).

Feed air Dosage air

Increasing the powder throughput

1. Increase the feed air until the desired powder cloud is obtained (e.g. 2 bar / 29 PSI).2. Check the feed pressure on the pressure gauge. The corresponding feed air quantity in Nm3/h can be read on

the outer scale of the pressure gauge. Total air (4.1 Nm3/h) - feed air (3.2 Nm3/h) = dosage air (0.9 Nm3/h)3. Now find the equivalent of the dosage air quantity on the pressure gauge and adjust accordingly

(0.9 Nm3/h = 0.7 bar / 10 PSI).

These settings apply to our example and can significantly vary depending on the hose length, the specific weight of thePowder and other parameters.


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Feed air Dosage air

Injectors without orifice

Injectors without orifice are generally used with

automatic air flow control. They are less suitablefor systems with manual air adjustment. Thesetting range of the dosage air is very narrowhere and adjustments become a ratherpainstaking task.

This is how the dosage air would have to be set for the two examples above:

2.1 Nm3/h Dosage air 0.9 Nm3/h Dosage air

Bibliografia:

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he Powder Cycle

1. The Powder Center

Coating powder is best conveyed to the sprayguns if it is fluidized first. This is done in the Powder Feed Center,whose suction system (2) submerges into the container and ads fluidizing air to the powder. The container isplaced on a special shaker table. As soon as it begins to vibrate a homogenous powder-air mixtureforms.During the normal coating process powder is consumed, which leads to a lowering of the powder levelinside the container. A probe measures the level and lowers the suction system when required in order toensure a continuous powder flow. In the case of powder shortage, an alarm is triggered. Depending on the typeof powder feed center, the consumption of coating powder is compensated either automatically or by manuallyadding fresh powder into the container.

2. Powder Delivery

The fluidized powder is fed by the suction system (2) from the container to the injectors and finally to thesprayguns by means of fluidizing air. The amount of powder that flows to the guns can be increased by applying

more feeding air. The addition of dosage air speeds up the powder flow.If the feeding air is turned off and the dosage air is opened completely, the powder supply to the guns stops,while the powder hose will be flushed with air. As soon as the feeding air is turned on and the dosage air is setto a normal level, the powder starts flowing again.

3. The Sprayguns

Depending on the application, Tribo or Corona sprayguns are used for industrial powder coating. The powderparticles are charged inside the gun and then applied evenly to the object to be coated. Different shapes andobjects like wire goods, gratings or aluminum cross sections require different powder clouds for high qualitycoating. This is why sprayguns must be able to be equipped with a great variety of nozzles systems, such asdeflector cones, fan spray nozzles etc.

4. Powder recovery

A considerable amount of powder does not stick to the object during the coating process. The so calledoverspray is sucked from the spray booth through the exhaust air conduct (4) and conveyed to the cyclone (5).

5. Separating the powder-air mixture

The cyclone sets the powder-air mixture in rotation. This creates centrifugal forces which push the powderparticles outwards onto the cyclone walls. The powder subsequently slides onto the screen surface of thescreening unit, where coarse impurities are held back. By means of a peristaltic conveyer, the recycled powderis finally supplied back to the container in the powder feed center.

6. Filtering of the exhaust air

The cyclone sets the powder-air mixture in rotation. This creates centrifugal forces which push the powder

particles outwards onto the cyclone walls. The powder subsequently slides onto the screen surface of thescreening unit, where coarse impurities are held back. By means of a peristaltic conveyer, the recycled powder


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is finally supplied back to the container in the powder feed center.

7. Control

To control the complex workflows within a powder system, several types of controls can be applied. Therequirements for customer specific systems which are completely designed for special coating requirements arerising; systems need to be flexible and modular. Therefore WAGNER offers a wide range of modular control

systems that guarantee the perfect control technology for each customer.

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Powder feeding with injectors

WAGNER powder supply systems for spray guns rely on the Venturiprinciple. In these powder injectors, air (feed air) is blown into acollector nozzle via a so-called injector nozzle. A special geometrygenerates a vacuum that sucks in powder and conveys it downstream.

Dosing air is fed into the powder current in addition to the feed air. Thetotal quantity of air generates a homogeneous powder/air mixture. Theair quantity is dosed in such a manner that a suspension feed isgenerated in the powder hose that prevents the powder from settling.This is a requirement for constant powder delivery, homogeneousatomisation and optimal coating results without spitting.

WAGNER offers the right system for every application. The standard injectors excel in a high delivery rate. An

alternative is provided by the HiCoat ED system with its optimized geometry within the injector. This patentedsystem leads to a considerable reduction in the required air quantity and thus an enhanced transfer efficiency.

The feed systems are operated on a convenient control unit that automatically uses the right mixing ratiobetween the feed and dosage air, allowing the user to concentrate fully on the coating process.

Charging systems

1. Corona charging

Bei der Coronaaufladung setzen sich negativ geladene Luftionen whrend des Zerstaubungsprozesses an diePulverteilchen. Die Luftionen werden an der Hochspannungselektrode der Pulverpistole erzeugt. Die Erzeugungder Hochspannung erfolgt mit Hilfe einer Hochspannungskaskade, die in den Pistolenkrper eingebaut ist. DieHochspannung kann dabei in einem Bereich von 30 - 100 KV variiert werden. Die Hhe der Spannung istzugeschnitten auf die Geometrie der Werkstcke bzw. das verwendete Pulverlacksystem. Die aufgeladenenTeilchen bewegen sich nach der Aufladung entlang der Feldlinien auf das geerdete Werkstck zu.

Da die Feldliniendichte an den Kanten der Bauteile hher ist als auf denFlchen, kommt es hier zu hheren Pulverschichtdicken. Umgekehrt gibtes bei dreidimensionalen Bauteilen Bereiche, in die keine Feldlinieneindringen. In diesen Bereichen, den sogenannten Faraday'schenKfigen, wird daher Pulverlack nur sehr begrenzt abgeschieden. Bei derAbscheidung der Pulverlackschicht werden auch Luftionen mit in dieSchicht eingelagert. Hierdurch kommt es bei einer zu hohenLadungsdichte zu sogenannten Rcksprheffekten. Ziel ist daher, dieMinimierung dieser Luftionen, welche z.B. durch den Einsatz einerzustzlichen Erdung auf dem Pulverzerstuber erfolgt.

Die genannten Effekte konnen durch die modernen WAGNER Sprhsysteme HiCoat-C4 uber umfangreicheEinstellmglichkeiten der Hochspannung, der Strombegrenzung und der Kaskadenkennlinie auch bei

komplizierten Werkstcken reduziert werden. HiCoat-Pistolen sichern so ein optimales Beschichtungsergebnis.
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2. Die Triboaufladung

Das Tribo-Verfahren bedient sich der Reibungsaufladung. Hierbei wird das fluidisierte Pulver-/Luftgemisch ineinem Pulverrohr, zumeist PTFE, durch Reibung an der Rohrinnenwand positiv aufgeladen. Der Werkstoff PTFEeignet sich auf Grund seiner niedrigen elektrischen Ladungseigenschaften (negativ) zur Aufladung und wegen

der sehr guten Antihafteigenschaften zur Vermeidung vonAnsinterungen an der Wandung.

Bei der Reibungsaufladung im Pulverrohr entsteht eine gleichmigeAufladung bzw. Ladungstrennung. D.h. bei einer bestimmten Menge anpositiv aufgeladenen Pulverteilchen bleiben im Pulverrohr exakt gleichviele negativ aufgeladene Teilchen. Diese negative Ladung muss ausdem Sprhgert abgefhrt werden. Sie wird ber eine Messzelle geleitetund gibt als Tribo-Strom eine Aussage ber die Qualitt des Pulvers undder Aufladung.

Auf Grund der Aufladung durch Reibung bentigt dieses Verfahren einspezielles Tribo-Pulver. Bei WAGNER Tribo-Pistolen kann mittels einerspeziellen Tribo-Luft diese Aufladung beeinflusst bzw. verstrkt werden.So kann z.B. auch nur schwer aufladbares Pulver trotzdem gut appliziertwerden.

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