Clean Air! ...Breathing Protection

Air breathing protection, we all know we only get one set of lungs so lets talk about how to protect them. There’s some decisions to make when purchasing air protection equipment and some things to consider like pricing, facial hair, and comfort just to mention a few. Let’s start with the basics, you are either going to bring in outside clean air to the painting area through an ambient pump or use the compressed air being supplied by your compressor.

Both types are known as Supplied Air Respirators (SAR) because you are supplying positive air pressure to the mask. The ambient air pump is going to be a bit more money because it has it’s own ambient air pump, but a cleaner system because of it’s separate air supply line. Very important that you place the pump in a clean non contaminated area free of any type of exhaust or gases. 

The system that uses the compressed air source is also an excellent system and most painters prefer this system because of the comfort of only having to carry one air hose. Just remember that the air is coming from your compressor and depending on the age and condition of the compressor the amount of contaminants in the line are going to vary. With these setups it’s vital to install the pickup line after a series of good quality filters to eliminate the particles and contaminants in the line but before any desiccant filter.

The next level of air protection falls under Air Protection Respirators (APR) and these can either be full masks or half masks that use either a single or double element cartridge where the air must pass before you breath it. Depending on what type of product you are spraying you can purchase many types of cartridge filters with varying degrees of protection. Unlike the previous systems mentioned these mask must be seal tested to insure there is a solid seal where the mask touches your skin. This is important because as you breath you are causing a vacuum (negative pressure) within the mask and if the seal is not correct you are breathing in Volatile Organic Compounds (VOC).

The pros and cons, obviously pricing as compared to the other systems but on the flip side you have to make sure and replace the cartridges on a regular basis. Don’t assume that if you aren't using the mask or haven’t used it in a while that the cartridges are still good. Most of the cartridge elements are typically carbon and as soon as you open and install them on the mask the life of the cartridge diminishes whether you use the mask or not.    

If you're a die hard fan of Duck Dynasty and have the facial hair to prove it then here’s where you might have to settle for a system where you’ll get a proper fit like a full mask.

Lastly, working our way down to your everyday bondo, sanding and shop dust you’ll be using your elastic band dust mask and there are varying degrees of quality here also.

Just keep in mind that air protection is crucial, in paint products it’s actually the chemicals within the solvents that you can't smell that do the most harm, like isocyanates. These are the products that show their effect on your body and nervous system later in life. Any two component catalyst system whether primer, bases or topcoats has harmful chemicals that weren't meant to be inhaled.  

Does That Color Look Right? ...Color Matching

Color matching, it's an art as much as a science. Even with all the tools at a painters disposal, they all have to be used correctly to try and achieve a match. Not only do painters have the task of matching newer difficult colors but also the correct texture on the finish. If that wasn't enough you have weathered finishes and different types of materials to spray that cause colors to look different. These are just some not all, of the issues a painter deals with on a daily basis.

So let's start at the beginning of the process and talk about the original paint on the vehicle. When vehicle manufacturers decide in what color choices they will offer a particular vehicle they also decide on what paint manufacturer will supply them with those colors. During the years that those colors are offered on a vehicle numerous paint manufacturers may have been used as suppliers. Keep in mind that this process of supply and demand is on a global scale, add to that paint batch variances within the same paint manufacturers. This is only one contributor to color variance.

Paint manufacturers are aware of these variances and try to keep up with formula updates as quickly as possible. This is why certain colors will have alternates offered and they are usually also chipped to make picking one easier.  These are only tools that are offered to help but by no means an exact science.

Let's address some other issues. So you've decided that a certain alternate was a close match and you have the paint jobber mix that color for you or you have an intermix system setup in shop.

If something as simple as mixing the toners on the machine is not performed prior to mixing the color you could be off on the mix. Let's take this a step further not only could you be off on that color but every color you make with that toner thereafter because the pigment proportions will be off on the toner.

Some simple mistakes that can be corrected are not using spray out cards before applying a color. Do you want to spray out a pint of paint on a panel, step back and then decide it didn't match. Spray out a card which you can use to make notes on and keep for future use. If the color needs to be adjusted then we are looking for things like Value (lightness or darkness), Hue (color), and Chroma (intensity, richness, saturation). A lot can be written about this and I won't go into it here.

The color is a blendable match and you're ready to spray. Well before we go spray happy lets cover some things. No color is ever a perfect match, it may look that way but when you get it under different lighting conditions and you run into that eventual picky customer you are going to have to redo some jobs. Word of advice don't butt match paint jobs, go that little bit extra and always blend into adjacent panels or find the right places to cut off the blend.

Lighting conditions is also a big issue at shops. Owners typically don't feel they need to spend money on this but if the math was done on how much money is spent on re do's because of improper lighting this would be an easy sell.

Listen I'm one of the first that will admit to wearing my fare share of blue socks when I thought they were black. Well, same damn thing but now we're talking hundreds of dollars worth of paint products. If the light is wrong the color is wrong. There are many vendors that sell sunlight equivalent tubes that can replace your current spray booth tubes and will give you the true color you need to see when matching, not after you roll the car out into the sunlight.  

Matching the selection of colors that are coming out in the automotive world is truly becoming more of an art, but if you use all the tools at your disposal and stick with the proven blending techniques the odds will be in your favor.

Spray Booths & Air Flow Designs

Spray Booths have evolved quite a bit since the original early Cross drafts and I would venture to say that a lot of that change and improvement came not only from changes in paint technology but also stricter regulations concerning VOC emissions. 

When I say changes in paint technologies for those of us that are old enough to recall, the lacquer days were very forgiving. Dirt and overspray were not a problem, sanding the finish and laying on another coat would fix most problems or just buffing it with rubbing compound and a wool pad would do the trick.

Those paints went by the wayside and in came the sophisticated 2 and 3 stage paints with tricky and delicate application methods and beautiful long lasting finishes that were here to stay. One requirement for these new paints was a clean environment to apply them and with that the paint booth business grew.

Down draft, Semi down draft, Side draft or Cross draft, these different types of Automotive spray booth all get their names from the direction the air flows when it enters and exits the booth. The only exception to this might be an open face booth which has only a plenum that consist of filters and exhaust fan to filter and remove paint overspray from the shop. These are most often used to cut in parts so as to not tie up the painter or the production in the main booth. They are sometimes used in combination with plastic curtains as a makeshift small booth.

 

Prep Station and Prep Station with Side Curtains

Cross draft

The original and still very much used Cross draft booth is your basic entry level booth. The concept here is that air flows from the entry double door which is typically where the air entry filters are placed and crosses the vehicle and then gets filtered again on the way out to remove the overspray paint before being exhausted out of the shop. The downside to this design is the dragging of the overspray across already painted surfaces and producing dry dull finishes. A good painter will compensate for this and paint from the air entry side to the exhaust side, and paints over any overspray to avoid this issue.

You will see all kinds of modifications to the Cross draft design by manufactures to try and improve on the design while still offering an affordable booth. There's also a Reverse Cross draft where the doors are moved to the exhaust side to try and control dirt from entering through the entry doors and this is accomplished by changing the design of the exhaust plenum to a bridge instead of a box so the vehicle can enter from the other end of the booth. If dirt enters through the doors it's caught by the exhaust filters instead of dragged across the paint finish.

Cross draft

Reversed Cross draft

Down draft

The Down draft concept was designed with the idea of eliminating the paint overspray problem that existed with the Cross draft.  These fall into two major groups, the original take on this design which entailed a lot of floor work because the booth rested flush with the floor and the air had to be vented under the booth. The later models were elevated with raised floors and the down flow concept could still be accomplished without the floor work.

Down draft with raised floor

Conventional Down draft

There's of course many variations to the Downdraft design, Semi down draft is one where the air enters through the ceiling but exits like a Cross draft. Side down draft is another where air enters through the ceiling but exits through the bottom of the side walls eliminating the need to elevate the booth. 

There has definitely not been a shortness of ideas and designs from manufacturers here and they're usually all on display at the Autobody convention on a yearly basis for you to get a closer look at.

Side Down draft

Positive and Negative pressure

In plain terms the booth fans either push air into the booth or pull air through it. The importance of this is that a positive pressure booth by design is a cleaner booth. Depending on what part of the country you're located you'll quite often see a heater unit along with what's called the air makeup unit. This not only produces the positive air pressure in the booth but also warms the intake air in cool weather before it enters the booth. On booths with baking capabilities the heating unit is designed to elevate temperatures high enough to bake the applied finishes at the recommended times and temperatures.

Most of your basic Cross drafts are negative pressure booths and on these types of booth you don't want anyone entering or leaving the booth when there's painting in process, you'll notice that when side doors are opened the air will be drawn in not out and with it plenty of dirt.

Some of the issues that I most often see and should address here regardless of the type of booth are as follows. Maintenance is number one, often I see beautiful expensive booth that are not maintained properly and it's almost a shame to spend that kind of money and still get low quality paint finishes due to dirt. Filter replacement and booth cleaning need to be on a schedule that fits the production and volume of vehicles flowing through the booth, it will only help improve your final product.

Proper quality and installation of filters, on your Cross draft intake filters there's usually a front and a back side, one's sticky and the other is not. This helps in trapping dirt as it enters the filter, many times have I seen them installed backwards. As important are door seals on Cross drafts, if they're worn and torn it presents a steady stream of dirt and contaminants. A good way to check for any openings in the booth due to wear and tear is to get inside, close it and turn off the lights, you'll easily see if light is coming in through any holes, if so then dirt is also making it's way in. Fix and seal these holes and you will not only see improvements in your finishes but also a happier polishing and finishing department.

Finally an important thing to remember when purchasing and installing a spray booth is placement. Carefully consider where you will place the booth or you might pay dearly later with many filter changes and dirt contamination. Install booths away from areas where there will be sanding or the use of any chemicals that are airborne and might enter the spray area.

Clean, Dry Air... How? Drains, Traps and filters

If you read my previous article then you know by now that moisture is simply an unavoidable by product of compressing air for shop use, and depending on what part of the country and the time of year, some will tend to have more water than others. This will consist of a mixture of water, oil and rust and depending on the age of your compressor and the humidity in your area you’ll have more or less of one of those substances.

So how do we control these and stop them from ruining our tools and contaminating paint jobs, well let’s start at the main source the compressor. Somewhere on the bottom of every receiver tank is a manual valve which is placed there so you can occasionally drain the tank of the water build up. Not all, but in most shops we unfortunately do not have remembering to drain the compressor as a number one priority on the to do list. Well the good news is there are options to remedy this.

Here is one of those rare scenarios where spending more money might not be the better way, let me explain. You can install an electric timed drain valve system that will open at certain intervals and drain the tank. Down side is you have to supply power to it and it’s on a timer that has no correlation to compressor use. That equates to the compressor being drained whether you’re using it or not and that equates to unnecessary dollars spent. A less expensive alternative is a float and valve system which basically opens only when there’s water at the bottom of the tank.

Moving on away from the compressor to our traps, but before I do here’s a quick tip "compressors vibrate a lot!" and because of this always remember to use a flexible connection from the compressor to the lines or over time you will have a line failure due to vibration. See example below.  

Traps, a simple trick to eliminate a lot of the water in your lines and all it takes is a little plumbing skill. Whatever extra cost of piping and time it takes will pay for itself many times over in longer tool life and desiccant filter replacements.

Below you’ll see a drawing (Sharpe spray equipment) put out in the market decades ago that does a pretty good job of explaining traps. There are 5 key points I want to address here, first unless you’re going all out and buying a refrigerated air dryer then do not place any outlet or air filter anywhere near the compressor outlet. The reason for this is that you still have warm air coming directly out of the compressor receiver and you need to give the air some distance to cool or any filter you install nearby will be ineffective.

Next, notice they are suggesting a slight sloop in the main line, you don’t want any water hanging out up there vacationing, you need those lines to naturally drain and stay dry. Following the main line you’ll find that the first outlet faces up not down, let gravity do it’s job and keep the water on the pipe and not filtering down your outlet pipe. All this takes is two extra elbows to accomplish. Following that same first outlet downward notice that the filters are not installed directly under the pipe, there has been tees installed along the down pipe, it’s a lot harder for water to go sideways then downward, again gravity working for you.

Lastly, if you want the best driest air for your paint spraying lines then install your expensive desiccant filters the farthest from your compressor this will give you a better chance at having the driest air and getting longer life out of your desiccant filters.

The only other thing I would add to this configuration would be to close these lines in a closed loop system so you have a balanced airflow and you don’t lose significant pressure if a worker starts using a high cfm tool along the line while you're in the middle of a paint job.

Let's Air out a few things about Compressors

There are several categories that compressors fall into, but when we talk about compressing air to use for tools in your typical shop or garage 99.9% of the compressors that are used are piston type compressors, so that is what we'll focus on here. Compressors range in size from your tiny portables used for small airbrushing jobs to your massive 10 to 25 hp compressors typically used at the larger production shops.

Now to the nuts and bolts, within the piston or reciprocating type compressors as they're called in fancy terms, there are two major differences 1 stage and 2 stage. This has nothing to do with how many pistons are in the compressor, so let's explain the difference. When we talk about a 1 stage compressor we're referring to the way it compresses the air into the storage tank or receiver. A 1 stage compressor accomplishes this in a single stroke of the piston, on the down stroke it sucks in the air controlled through a set of valves and on the upstroke it compresses the air into the tank. 

There are upsides and downsides no pun intended, to a 1 stage compressor the upside mainly being the price because it's a simple system and a lot less expensive to produce. These are for your small application type uses and they range from low HP to around the 5 HP range. When shopping for these type of compressors don't be fooled by tank size or some of the hyped numbers that manufactures put on the labels they can be easily inflated by changing pulley sizes of the motor and increasing the revolutions on the compressor.

Which now leads us to the down side of a 1 stage compressor, and that's in the way they compress the air in a single stroke into the tank. They generate a lot more heat, and a by product of that is condensation which leads to water in the storage tank and lines.
As pressure builds in the tank these compressors have to work harder to continue to fill the tank and are not as efficient at doing so. Don't misunderstand 1 stage compressors are fine, just know that you get what you pay for and they are only suited for the correct applications. If you over work them you'll have to contend with a lot of moisture in your lines and a compressor that won't last very long.

                                                

On to 2 stage compressors, you have very few manufactures producing 2 stage compressors in the low HP range because people looking in that range are typically looking at price not so much the quality. Your typical 2 stage compressor will start at 5 hp on up. What makes a 2 stage compressor a more efficient system is in how it compresses the air into the tank, the first larger piston compresses the air to a mid range level and then passes it through an inter-cooler system. This inter-cooler can be as simple as a piece of copper tubing to a sophisticated series of pipes with fins to help cool the air before it enters into the next smaller piston. Then the second phase of the compression hence 2 stage, is the further compression within that second piston to a higher compression level and into the tank.

Since the air is compressed in 2 stages it is done so without generating as much heat therefore enters the tank cooler which causes less moisture. 

Also the revolutions that they typically run are much lower which causes less strain on the components which gives you a longer lasting compressor.

Do You Have "Enough" Air?

My goal here and in the following blogs I post will always be to try and bring useful information to everyone from the Do-it-yourselfers to the guys doing this for a living. Now I'm aware that on every topic I cover there could be volumes of more information written but for the sake of simplicity I want to stay brief and cover the essentials.

In my years in the field I have seen some crazy stuff, don't believe me try this one on for size. I once saw a guy at a bodyshop I believe it was in Columbia somewhere using a combination of a lawnmower engine and a vehicle A/C compressor to produce enough air to spray paint a vehicle. Wish I knew years earlier I'd be writing a Blog I sure would have snapped a picture of that setup. Human ingenuity it's a beautiful thing.    

So to the point "Enough" air, the topic I'm going to cover is air Volume. There are many issues and contaminants that will ruin a paint job but one of the biggest problems that won't go away unless you do it right from the beginning is your shops air supply lines. You can add expensive and sophisticated filters along the way to solve water and moisture problems in your paint, but the quantity of air just won't be there if you don't get it right when you lay down your air lines.

There are diagrams and design ideas out there from companies like Devilbiss and Binks, they will show you the right diameter to use from the air source (compressor) depending on how far you are going with the air lines. Along the way you can add water traps that won't cost you much more in plumbing and will save you hundreds of headaches and dollars in filters and paint problems.

This problem isn't just for the big boys at the shops. If you are a hobbyist with a portable compressor and are using any type of High Volume spray gun or air tool that consumes a lot of air, and decided you didn't want to spring for the air hose that was a little bigger and a little more money because the other would work just fine. You could have the same problem. Specially if you thought connecting two 25 footers would get you to the painting area without having to carry the compressor out there.

Here's an example of this the way I was first told years ago, basic science say you have 2 balloons one is full the other isn't and they are both connected by a valve in the middle, lets say you open the valve what's going to happen? You are correct, they are both going to balance out, equal air pressure in both. Let's say the valve connecting both balloons has a very tiny hole, hence your small air lines or hose diameter, the air pressure will balance out but it will take a little longer.

So how does this look in action in the shop or in your garage? You look at your air gauge on the wall or at your spray gun and the pressure looks fine but you pull the trigger and you just can't maintain the pressure the gun manufacturer suggested you use. Here is where pressure and volume are noticed. You'll get your pressure back when you release the trigger because the pressure balances out like in the balloon example but the amount that you need can't flow through your small lines or air hose. Try giving a garden hose to a firefighter putting out a fire and you'll get a hard fast lesson in volume.

The terms to learn here if you're interested are CFM -cubic feet per minute, this is the amount that's moving through your air lines "Volume", and PSI - pounds per square inch, this is the measure of "Pressure".

Please feel free to post any specific questions or problems you might be having in regards to any of these issues and I'll make sure to answer you.   

Next time we'll get into a couple of the different types of compressors and how big is big enough.