Application information

12.1      General

Baril’s range of products can be applied with most spraying equipment. In addition, a number of products can also be applied by roller. This chapter provides an overview of the most common spraying equipment, and a brief description is provided below of the working principle behind such equipment. The following application methods are dealt with:

 

pneumatic spraying (conventional air spraying);

airless spraying;

airmix spraying;

hot spraying;

electrostatic spraying;

two-component spraying;

HVLP spraying;

roller and brush.

12.2      Pneumatic/Conventional (air) spraying

This method of applying paint has been used for a long time, and the basic principle is relatively simple. The technical performance of the equipment is still being improved, but the basic concept is the same. Pneumatic spraying, also referred to as air spraying, is based on the injection of paint into a powerful stream of air. The spray pistol, with a top or bottom reservoir, is particularly suited for smaller jobs and/or paintwork involving a great many colour changes. Models with the paint reservoir on the bottom have a greater capacity and allow the operator to work longer without refilling. For larger surfaces, spray pistols are available with a separate pressure-fed reservoir of 2 to 300 litre.

In order to ensure that this spraying technique provides a good result, it is important to first adjust the viscosity of the paint to a suitable level. The amount of paint lost due to overspray with this method is quite large. Most of the products supplied by Baril Coatings can be applied using this method. Every product data sheet includes a guideline for paint viscosity under the header "application information." This spraying method does not make it possible to realize large coating thicknesses in a single process run.

12.3      Airless spraying

 

Airless spraying was developed to make it possible to cover large areas with thicker paint coatings in a single run. In airless spraying, the paint is converted into a fine spray mist as it is forced through the spray opening under high pressure (150 - 250 bar). Many of the products supplied by Baril Coatings can be applied using this method. Every product data sheet specifies the viscosity to which the paint must be adjusted for airless spraying under the header "application information." Polyurethane paints can be applied via airless spraying, but extra attention must be paid to the layer thickness in that case. If a layer is applied in one run which is too thick, it will result in blistering (trapped air) and foam formation as well as a somewhat matt paint finish, thereby reducing the glossiness of the coating.

 

12.4      Airmix spraying

 

Airmix spraying is, in principle, the same as airless spraying. The only difference is that airmix spraying also makes use of compressed air, which is why it is also referred to as air-supporting spraying. In this method, an airless pump applies a pressure of circa 50 bar to the paint. During the application stage, an additional 1 – 1.5 bar of compressed air is added to achieve an improved spray pattern. The application information for this spraying method is also included on the product data sheet. The layer thickness that can be realized in one paint run using this method is less than with airless spraying. This application method is more effective when it comes to obtaining optimum results with the application of polyurethane paints.

 

12.5      Hot spraying

 

Hot spraying can be used in combination with airless and airmix spraying. It is particularly useful for very viscous paint products which must be applied so as to achieve a specific layer thickness. In this method, the paint is first heated to 40° to 70° in order to obtain a suitable working viscosity. This makes it unnecessary to thin the paint. The paint is heated in a painting block (hot airless), which is connected to the airless or airmix equipment.

 

12.6      Electrostatic spraying

 

The working principle behind this spraying method is that particles with differing electrical charges attract each other. The paint is first converted into a spray mist with the help of pneumatic or airless equipment, after which it is given a negative charge with the help of an electrode and then sprayed onto an object with a positive earth connection.

As the paint particles are attracted to the object, they also end up on the back side of the object, substantially reducing paint loss, in particular for jobs done in the open. Some objects with unfavourable/complex shapes only need to be sprayed from one side.

 

12.7      Two-component spraying

 

This application method is rapidly gaining ground due to the development of low-solvent and solvent-free products, which are often supplied as two-component systems. The paint itself and the curing agent are delivered in the proper ratio via separate channels and then mixed inside or just before reaching the pistol. Application is done with pneumatic or airless equipment, if necessary with the addition of heat.

 

12.8      HVLP spraying

 

HVLP (High Volume Low Pressure) spraying has been used for some time by firms specialized in painting and finishing. When an HVLP spray pistol is used, the resulting mist is coarser than with an air pistol. Due to the larger volume of air, the paint particles in the jet of paint are larger, and more paint reaches the object. The HVLP spray method does not provide the same end result as air spraying. But the coarser spray pattern is not noticeable in painting plasterwork. The coarser spray pattern is also not a problem when silky gloss or matt paints are used.

 

12.9      Roller and brush

 

Everyone is familiar with the application of paint using a brush. It's a labour-intensive painting method. Working with paint rollers makes it possible to apply layers of paint more quickly. This method is particularly suitable for painting large and flat surfaces. When using a roller, one needs to make sure that the layer of paint applied is thick enough. In order to achieve good results, it is necessary to thin the paint down to a special level, as specified in the product data sheet.

 

12.10    Possible problems associated with various spraying methods

Every spraying method has its own specific and special instructions for achieving the best results. Nevertheless, the spray pattern and end result may not always be in line with one's expectations..

The overview presented below is intended to help you quickly recognize and solve the most common types of problems and to ensure that you obtain the desired result.

Problem	Cause	Visual effect	Action to take
Tailing	Insufficient pressure or insufficient thinning down	Hard lines in spray pattern	Increase pressure or use smaller nozzle or thin down
Spatter in spray pattern	Trapped air during mixing; new batch of paint	Air bubbles on surface of paint film	Thin down somewhat; remove air from paint by waiting or straining
No flat or vertical spray pattern	Old tip or nozzle;          dirt in pistol	Round or angled spray pattern	Replace tip or nozzle; clean pistol
Jerky, jolting	False air inflow, leak in pump	Irregular pattern/width and spray pattern	Check couplings and feed lines
Craters or pinholing	Oil leaking from pump	Craters in the paint film which open up on the surface	Flush and clean out the pump with clean material; avoid contamination
Poor flow pattern	Paint is too thick or sticky and unfavorable viscosity	Appearance is not smooth cellulite appearance	Thin down paint or decrease nozzle diameter and increase pressure
Dripping	Spraying excessively thick layers; maximum pot life reached (above critical point)	Local drips in places where extra-thick layer applied	Thin down paint to enable more even application

12.11    Amount of paint consumed

 

In order to correctly calculate the quantity of paint that will be consumed during spray paint application, it is necessary to take a certain level of paint loss into account. The table below provides an overview of the loss percentages associated with various spraying methods. The figures given are intended to serve only as a rough guide.

 

 

*This viscosity is realized by increasing the temperature of the paint.

In some cases, the application loss can be much higher, for example when spray painting openwork objects (e.g. balcony fencing).

 

All the information needed to obtain good application results are included on the product data sheet. The information is intended to serve only as a guideline. During paint application processes, various factors play an important role including: temperature, humidity, working conditions, nozzle diameter and angle.

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