How does a spray booth work?
HOW TO ESTIMATE INFORMATION AND CHOOSE A SPRAY PAINT BOOTH?
We went through a historical moment. We have made a decision to buy a spray booth. We will form a real spray shop. We would like our invested finance resources to have a high refund rate. It is also important that the bought devices are modern, always efficient, safe, easy in use, have low exploitation costs, assure proper work parameters, are aesthetic, etc.
How to make a proper choice if the market is full of new offers and it is also possible to buy second handed devices?
Every supplier assures that devices delivered by him will exactly fulfil your expectations.
In case of cars, most of us knows what is air condition, ABS, air bag, electrical steering windows, seat belt stretcher, radio, ventilation, heated back window, engine, power engine, gearbox, turning moment, injection, turbo compressor, inter cooler, etc. But when we start talking about appliances like EDS, ASR even sellers in famous car showrooms get confused.
Do we understand what a spray booth producer says and what is the meaning of it, when he uses definitions such as: air flow speed, ventilator efficiency, extracting system, thermic power, delta T, isolation, air distribution system, ventilation system efficiency regulation, spraying phase, drying phase, ventilation, air circulation, exchanger with a linear flow, exchanger with a cross flow, metal base, floor bars, initial filters, ceiling filters, floor filters, coal filter, lighting intensity, light colour, etc?
While buying a car, do we care what engine it will have and if we are able to easily, fast and safely make an overtake manoeuvre on our crowdy roads? Is it important if the car has an air condition or a power steering?
Let us answer the question: while making such a serious decision is it only the price that matters or is it also important what do we get for this price?
Remember that spray booths watched from outside hardly have any difference and we have to make a decision if we buy it to bring jealousy with the owners of the neighbour garage or we buy it to assure a stable and safe working conditions for our workers.
We understand that this is a very difficult decision and that is why we have prepared this guide.
WHAT PARAMETERS CHARACTERIZE A SPRAY BOOTH?
The basic parameter is the spray booth's dimensions, because they determine the size of vehicles possible to spray paint. It would be difficult to work in the 5m length spray booth if the car is 4m long. That is why most of the spray booths have the length of 6 - 7 m and 4m width. This width is optimal and adapted to most of vehicles.
Everybody knows that is would be more comfortable to work in a 7m long spray booth. We should also understand that increasing a spray booth surface will bring the increase of ventilation system efficiency to assure a proper air flow speed. This will also increase the use of heating system that is necessary to assure a proper level of thermal jump ΔT. These factors cause the increase of exploitation costs. As you can see there are no technical obstacles to make a long and wild spray booth but there are high execution and exploitation costs.
There are no limits concerning the height of the spray booth. The higher it can be, more comfortable it is to work. The spray booth that is 3m high is much more comfortable that 2,6m because it can also serve trucks and buses. Increased height has no impact on the necessity of bringing a more efficient generator.
The following parameter that characterises spray booths is the ventilator's efficiency. It must be set to achieve at least an average value of 0,25 m/sec by a vertical air move (air flow speed). It means that the air together with a spray mist moves by the vertical move up and down 25cm/sec. After placing a vehicle in a spray booth the active spray booth surface decrease and flow speed rise in proportion to the surface decrease. Air flow speed depends on two factors: spray booth surface and used ventilators efficiency. German, French or Belgian spray booth producers use in their products exactly 0,25 m/sec flow speed and most of Italian or Spanish producers use 0,20 m/sec flow speed.
The problem is with the reliability of technical details given by producers, especially concerning ventilator's efficiency that is different depending on achieved pressure. Some producers give the values according to ventilators that are working without a load that means maximum values or with channels and filters resistance that means nominal values.
There is one more thing connected to the ventilator's efficiency and that is the environmental protection. There is The Highest Permissible Concentration of damaging substance exhausted by a spray booth. While one hour of spraying, no matter if in a garage or a spray booth, the same amount of lacquer material is released from the pistol. Ventilator's efficiency depend on the level of diluting exhausted dangerous and harmful substances.
The ventilator's efficiency is connected to the spray booth surface, air flow speed and also the ecological and safe working of the whole spray booth.
A correctly configured spray booth must be equipped with a separate ventilator system, with both ventilation and exhaust. Cheaper spray booths have only a ventilation ventilator system.
There is a heating system directly connected the ventilation system. It must be selected according to the device efficiency to assure a proper temperature increase (thermal jump ΔT). Thermal jump is an air temperature increase and that is the difference between the air sucked in to the spray booth (almost always from outside) and a maximum air temperature delivered to the inside of the spray booth after passing a heating system. If it is winter and the outside temperature is -15°C, and if the optimal temperature in the spray booth we want to achieve is 20°C we must achieve a thermal jump of 35°C. However the heating efficiency (power) will be different for various ventilator's efficiency.
Technically it does not cause any problems. It is possible to install a big heating system to achieve a thermal jump without any difficulties. We should think that in a climate conditions where we have about 2 weeks during the year a the temperature below -15°C, the use of a decent heating system is really necessary. Or maybe we should install a less efficient heating system that will not be able to work in very low temperatures but for the rest 95% of days in a year it will work with its full power.
The most profitable solution, for example in central/ northern europe, the use of the heating system that achieve a thermal jump of 26-27°C connected to a special system that lets the system increase temporary ΔT to about 35°C. This kind of solutions are used by some of famous spray booth producers and find application in spray booths utilised in northern countries (especially Scandinavia). It is the most rational solution of an efficient heating system.
One of the most important element for a proper system work is its foundation. The best solution is the so-called concrete basement channel. It is a lower air flow channel adequately shaped and with an adequate depth. It assures unlimited and even air flow. All traders will talk about problems concerning building this channel (made by an investor) and will suggest much easier solution like a metal base. Because of a small height (about 300 mm) of a metal base, it will be kind of a barrier for a proper air flow. A Metal base is only a replaceable solution. Sometimes it happens that - because of technical reasons - it is not possible to make a concrete channel. In spite of all a metal base is not so cheap.
The quantity, place, type and colour of the lightning are also very important elements. A person that works in a spray booth must have a possibility of identifying and comparing colours. That is why fluorescent light with a specially selected colour of emitted light is necessary. Lamps need a proper security class if when placed from the internal side. To ensure a proper brightness in the spray booth, it is necessary to use a sufficient amount of light points.
There are two ways of placing lamps in the spray booth. First is placing lamps on the slants between the spray booth wall and filter ceiling. It causes a higher light intensity in a work place and less quantity of installed lamps and fluorescent lights. In this case the ceiling filters cannot cover the entire ceiling and turbulences and air whirl may become a disadvantage.
Second option is placing a big amount of lamps in the wall panels, mostly in two lines. This solution gives opportunity to install ceiling filters with almost the same surface like a spray booth surface. The disadvantage is a double amount of the fluorescent light and much higher electricity use. This solution gives a very good distract and high light intensity in the spray booth.
The next question is: cheap or good?
An in between solution with very good parameters is placing lamps on the top of the slants and additional vertical lamps in the corners of the spray booth on the floor level. This gives a good intensity in the working area and does not create shadows on the surface of the sprayer's shadow. All the lights glas covers must be made from the safe glass.
HOW SPRAY BOOTHS ARE BUILT?
A spray booth is mostly made from panels on a self-supporting construction, isolated by different materials, like: polystyrene, foamy polyurethane, standard or ironed mineral wool.
Most of the producers isolate only the spray booth's walls. Famous producers also isolate roofs or even whole generators where the air with a temperature of 60°C. flows in a drying phase. There are also rumours that no isolation is necessary and this kind of spray booths exist in Europe. Imagine a late autumn and cold outside. In a body shop the temperature is 15°C . There is a recently sprayed car in a spray booth. The temperature inside the spray booth is 60°C. It means that the temperature difference is 45°C. Let's answer the question if there is a heat penetration through the spray booth's wall that is made from 1 mm metal steel.
Spray booth floor
The next thing that has a great impact on a device efficiency is the size of the floor grates, which are placed under the spray-stop floor filters. There are several solutions from the worst to the best.
A Narrow grate under a car - a little bit an archaic solution in the cheapest spray booths with a small ventilation system. A car surface blocks an air access to the outflow channels.
Two narrow grates placed under car wheels - more efficient solution because parts of the grates can be seen from the car side contour. It lets for a better air penetration to the exhaust channel.
Two narrow grates placed under car wheels connected to additional grates at the beginning and the end of the channel, a so called "RING" system - a similar solution as the previous one but gives a more efficient air flow also in the front and the back of the vehicle. It increases the result of an air fall and makes spray painting those parts be possible.
Above solutions requires placing the in car in a central and precise way to make an air fall to be most evenly spread. This kind of solutions dominates in devices with small efficiency ventilators (mostly one ventilator systems). Less floor filters on the surface is how an easier and faster result is achieved. But remember that having only this surface of filters, while spraying the same amount of spray paint, will make that the filters will get easily clogged. The consequence of this floor filter pollution is a high increase (especially in one ventilator spray booths) of hypertension in the spray booth that leads to a decrease in the air flow speed.
If this value decreases below 0,16 m/sec we will achieve similar conditions to the conditions in a garage with opened windows.
A floor with a big grated surface - mostly 5 x 3 m - is a very efficient solution, depriving all above mentioned faults.
A 100% grated floor - the best and the most expensive solution because of the big amount of platform grating and necessity of making support systems on which grates are placed.
ATTENTION - some of the producers use the two last solutions but still under the grated floor and filters they put metal sheet on the surface, leaving only two narrow grates under the car wheels. This kind of solution is carried out when using small efficiency ventilators.
Entering door to the spray booth - there are also differences in constructing the entering door. The entrance must make an easy entering possible and after closing the door, it should seal the spray booth so no air with harmful and dangerous substances would get out.
There are two basic ways of making doors. First - double wings door and second - triple wings door. Triple wings door take less place when opening because of the narrow door. One of the door wings works as a service door and must be equipped with a safety lock which allows the door to open under a pressure from inside in case of any crisis situation. When applying a double wings door it is necessary to install a separate service door. Every construction should include a circuital gasket and closing system, eg. bolting to ensure a proper door frame tightening. It is also good if the doors are thermally isolated.
ARE WE AWARE OF HOW THE SPRAY BOOTH WORKS?
Two main phases
There are two basic phases of work: spraying and drying phase.
The way of working in a spraying phase should be the same for safety and ventilation efficiency. An injection ventilator takes clean air from outside and guides it to the heat exchanger. There the air is heated and guided to the spray booth filtering assembly. Then it goes through the ceiling filters and enters the room with a vertical move up and down depending on the spray booth equipment.
It can also be "squeezed" through grates and floor filters and pushed out through the exhaust ventilation channel placed over the roof of the building (single inlet ventilator spray booth). It can also be drawn in by an extracting ventilator and pushed out through an exhaust ventilation channel over its buildings (double ventilator spray booth: inlet and exhaust) extracting spray booths). The air is deeply polluted that is why it can not be used in heating the spray booth.
In the drying phase individual devices work in different ways. It is caused by the necessity of achieving much higher temperature of 60-70°C. A temperature of 70-80°C will not be able to be achieved while using a heating system with a standard heating efficiency.
What can we do about it?
One solution would be to install a heating module with enormous power, but it would be totally unjustified economically. There are three solutions to the problem right now.
The simplest technical solution is to let only 20-25% of the initial ventilation efficiency value to flow through the heating exchanger. This amount of the air can be easily heated to the demanded temperature. The disadvantage is a very irregular drying of a vehicle. Vertical parts of the car body dry up much longer then a horizontal parts and the process of drying may be very long. In this solution the whole heated air is thrown to the atmosphere.
Other solution is a mechanical limitation of the inlet channel section that decreases the efficiency of ventilators to about 50%. Additionally it opens a cover between the inlet channel and the heat exchanger chamber that allows sucking in some amount of hot air through the air stream that is sucked in by the inlets. The air delivered to the heat exchanger is mixed with the hot air and that is why its temperature is much higher. It causes the air that flows through the heat exchanger can achieve a proper temperature increase. People who are connected a much higher quantity of hot air what incredibly improves and accelerates the drying process. Like in the previous solution, the hot air is evaporating into the atmosphere.
Next solution is a system, which causes that 90% of the air mass to circulate in a closed circuit. It is caused by a system with covers that automatically closes the inlet air and opens the connection of a inlet ventilator with a channel. A ventilator sucks in previously warmed air from the spray booth and again directs it to the spray booth through the heat exchanger where the temperature drops are supplemented. The cover that closes the inlet intentionally has a leak to assure 10% of fresh air that is necessary for the drying process. An extracting ventilator must work also in the drying phase to have a proper exhaust for the 10% added fresh intake air.
Which solution is the best for our customer? Lets use an example again. Lets imagine that we drive a car with 4 people. There is a winter and it is freezing outside. We drive several kilometres and the engine achieved a proper temperature. The driver puts on the heating and the ventilator on the lowest revolution. Will people sitting in the back feel warm? After what time?
And what will happen if a ventilator will be on the highest revolution? Will the heat appear faster?
Spray booths are much more technically complicated, equipped with electronic steering systems can also have an additional working functions:
A ventilation phase, after a spraying phase
A cool down phase that turns on automatically after the drying process
A special thermal energy saving system, which switches the spray booth automatically into a recirculation phase in case we stop the spraying process.
A visualisation system which reports damage on the controller
Possibility of installing a completely automatic hypertension regulation that is in the spray booth, to always ensure the same air flow speed.
Generator / aggregate
Let us go back to the end to the main point of the spray booth, which is a ventilation and heating unit called a generator or an aggregate.
Producers use as always different solutions based on technical possibilities and mostly costs of production. In most of cases this kind of generator is built as a self-supporting construction made from steel sheet metal adequately bended to achieve spatial profiles, connected on the place of assembly by rivets or self drilling screws and covers made from sheet metal. Individual parts of construction are connected and form a carrying structure for the heat exchanger, ventilator(s) and additional equipment, like: a recirculation cover (if occurs), pneumatic motor operators, servo-motors, support for air inlet, launchers and other parts that may occur in different constructions.
Such a solution is fast mass production, but its durability may depend largely on the integrity of the assembly. Ventilators have quite a lot of weight and spin at high speed. Done inaccurate, any installation can quickly take revenge.
Producers with a good reputation are companies with several years of tradition that do not specialise in making mass products. These companies always control the assembly and the correctness of installation. Their generators are built on the base of solid steel constructions, able to carry big load. It is delivered to the receiver in the form of ready to work units, which include all the necessary elements inside, like: ventilators, engines, covers, heating exchanger etc. It brings several problems connected with transportation and unloading of those devices.
The most essential parts of the generator are the ventilators and the heating exchanger.
A heat exchanger is necessary to "mediate" between a burner flame and the air given to the spray room. A burner placed on the exchanger's wall has a flame directed to the inside of the exchanger, to the burning chamber. Fumes are directed away to the exhaust chimney through the flame channels. The inlet air is guided through the inlet ventilator and is heated by the heat exchanger.
Most of the producers make exchangers with a simple construction, with fume channels made in the shape of vertical slots placed side by side in one line over the combustion chamber. In this kind of exchanger the air goes between those slots in a smooth, linear way.
Other constructions place rounded flame pipes over the burning chamber placed in several lines. In this kind of exchangers the flowing air must make a "snake" move. This causes the exchange surface to be very big.
Often we get asked about the fuel consumption of the burner. This value depends of course on the burner. In the heating systems of spray booths there are oil or gas burners. It is good if burners are from a known producer that could make proper tests of the product. Burner's power must be adjusted to the required power of the heating system.
A consumption of the fuel depends on the burner's power and on the work intensity. That means that if it’s cold outside, a burner must work longer to get the air to a proper temperature. If it works longer, it uses more fuel. That is why it is installed.
In the heating systems of spray booths, one can find following oil and gas burners:
First of all - the most common: The disadvantage of a big difference in temperature, even 3-4°C during a spraying phase. After setting a temperature of 20°C, the painter spray paints parts of the car in 17°C and in the next minute another part of the car in 23°C. Paint in these conditions will stick differently.
Secondly - if they have installed a proper steering element (eg. Spraytronic), they almost don’t have any of the above mentioned faults. This burner functions, depending on the demanded heat and operates in the first two stages. Gas burners can also have so called ‘flame unit system’. This is a very expensive solution, but assures a stable temperature.
Ventilators used in spray booths can be divided in:
- Single stream, directly on the motor shaft,
- Double stream , driven by a transmission belt.
However, These are always centrifugal ventilators. One stream ventilators are a good and cheap solution. They tolerate a relatively high pollution from the filters ceiling. They do not require any adjustments and actually don’t have a possibility to regulate the rotary speed and therefor also not the productivity.
Double stream ventilators are driven by a belt transmission that allows to change the ventilator’s efficiency by adjusting the transmission belt. It is important for example when the spray booth is located higher than sea level (which is often the case). These ventilators have a much higher efficiency per 1 kW of the engine power.
We hope that this information will allow you to find some guidance in all the offers you recieve. We must understand that most of the producers probably know how a spray both should be constructed to have a well-built efficient and properly working spray booth.
The other chapter is the reliability on the dealer. Mostly of these are hard working people with a professional knowledge. However there are companies, like in every environment, that works on the principle of fast profit and not respecting the client’s needs. Please ask us about any technical details and we are glad to verify technical aspects.