By David Gecic (Dave the Oven Guy) – Custom Designed Chemicals
The nature and composition of ash residues vary with different operations. Local laws vary from location to location. This information may not specifically apply to any operation. It should not be used as the sole determinant of how to handle any specific situation.
Thermally removing paints, “burning them off”, creates ash.
Ash is the solid (non-gaseous) residue left after burning. It varies widely in its character. Fine powdery ash easily suspends in the air. This ash also deposits in other areas of the oven. It can deposit on walls and in the oxidizer (afterburner) chamber. In some operations it is referred to as “fly ash”. It can be emitted through the stack if the oven is not working properly. It easily spreads through the air into other areas of the plant.
Courser heavier ash remains in the bottom of the oven. This is “bottom ash”. This ash spreads throughout the plant but with more difficulty. There are also slag-type ashes that contain melted metallic materials.
Ash Composition
Paints contain numerous ingredients. Generally, these fall into four types: pigments, solvents, fillers, and binders. Heat cleaning removes as much volatile material as possible. The burn-off process volatilizes most of the binders and solvents. However, the ash is not always completely combusted. In practical terms sometimes some combustible material remains.
So, what is the ash left behind made of? It consists of inorganic materials and small amounts of un-burned organic or semi-organic material. Inorganic pigments and fillers remain. These are, for example: silicates, silica, titanium dioxide, zinc phosphate, iron oxide, and a wide variety of other materials. Some are hazardous and need to be handled as a hazardous substance. However, most paint ash consists of non-hazardous materials. They can be disposed of in a local landfill.
Some inorganic pigments are hazardous wastes. Zinc primers may contribute enough zinc to the ash that it may need special handling. Unknown paints can be a problem as the composition may have hazardous waste materials. Older material may have lead residues.
The ash itself tends to be alkaline in nature and some pigments will have a substantial amount of alkalinity. This may make it very irritating to workers. It also can be abrasive and affect equipment.
A customer received a job stripping off a large number of bicycles from a foreign company. The paint had a lead pigment that showed up months later in their discharge water. The clean-up was a problem. Ash residue should be suspected in cases like this unless you have a captive shop where all processed paints are known.
Disposal of Ash Residues
Regulations vary from state to state and from local to local jurisdiction but usually differ only in small details. In 1997 the state of Illinois created Section 22.48 of the Illinois Environmental Protection Act. This allows disposal of non-hazardous industrial waste with municipal waste. This means that it can be disposed of with other material as regular “garbage.” But the ash must meet certain criteria.
Every jurisdiction uses their own definitions. In general paint ash can be classified as non-hazardous if it is a solid, contains no heavy metals or other pollutants, and was not considered a hazardous material prior to burn off. It must be dry. Paint residue cleaned with a pressure washer must be dried before disposed.
If a coating contains a highly dangerous material such as dioxin, which makes it a hazardous substance, burning it off, can legally create a hazardous waste. These paints require a special permission to process. So even if the extremely hazardous substance is no longer present the EPA and local authorities can still classify it as hazardous. These cases are rare and unusual. In a properly working oven, these substances are totally removed. Regulators are normally extremely flexible in these instances. But it is always best to check.
Safety Data Sheets
The company which produces the ash must be able to prove that the waste is non-hazardous and keep records of their process. They should keep on file any SDS available on the paints they are processing.
Before a paint is processed a review of the Safety Data Sheets can determine if there are any hazardous ingredients. The SDS should be retained for the company records. These records must be kept for a minimum of three years. While it is not necessary to report these on a day by day basis, they should be available on demand to the EPA, the waste hauler, or the landfill itself. Again, they are usually flexible with these rules But, if the material is a hazardous waste the generator of the ash is responsible. Documentation can protect the operator.
Hazardous Waste
Any ingredient which would create a hazardous waste should appear on the SDS. Not all substances that appear on an SDS will be hazardous or will remain in the ash. All solvent materials will be removed during the cure process and will not be present. These include substances such as acetone, glycols, alcohols, and mineral spirits. In general, these materials will be gone before they can even get into the oven.
Organic pigments will usually be destroyed by the burn off process. All inorganic pigments should be considered to remain in the paint ash. But pigments such as: zinc phosphate and other zinc compounds, strontium chromate and other compounds which contain chrome or chromates, cobalt compounds, lead compounds, copper compounds, nickel compounds, manganese compounds, cadmium compounds and mercury compounds can all create a hazardous waste. It depends on the amount.
Any material containing a metal constituent may be suspected of being a pollutant. Most compounds of magnesium, calcium, aluminum and iron are considered non-hazardous. Zirconium is usually considered not hazardous. Molybdenum may or not be considered hazardous. Titanium is usually not considered hazardous (by the EPA).
With a little experience and education, it is easy to determine what substances will make a material hazardous. Your oven company representative can answer any question about the hazards of a material you may have.
Oven Cleaning
Ash is an irritant to operators. Sweeping the ash from the oven is an effectively removes the ash. However, ash easily suspends in the air. Using a good shop vacuum is more effective. Gentle brushing removes ash from walls.
Dust masks can be used to prevent breathing of the residues. Because of the size of the particles, a high quality mask must be used. OSHA considers white titanium dioxide pigments a hazard.
Ash residues that have spread through the plant should be swept and then wet mopped to clean the ash.
Removing Ash Residues from Surfaces
Sometimes dropping the work onto the ground is enough to knock ash off a surface. Some people use a simple water hose to remove the ash. Others have used a water hose on parts that are still hot and the effect of the water boiling off the parts can remove ash.
Some paint pigments such as titanium dioxide are one of the most tightly adherent pigments. It is the common white ash that remains of the surface of many parts. Generally, it requires some sort of mechanical removal. This can be physical scrubbing, media blasting or pressure washing.
Removal of a hazardous material by a high-pressure wash system or other means may produce wash water which is hazardous, so it is a good idea to investigate the hazards of the material prior to burn off so there is a method of handling any solutions which may require more processing.
The wash water itself may contain too much suspended solids (turbidity) to be discharged down the drain. If this is the only problem it can be filtered or allowed to settle before discharging.
Chemicals
If a pressure washer alone does not remove the ash there are numerous types of chemicals which help clean the ash. One of the most effective ways to remove ash is a short immersion in an acid which tends to break the surface bond of the pigments and a simple low-pressure water rinse can then remove them from the surface. These acids do not need to be extremely hazardous materials but the stronger the acid the faster it will work. In addition an acid can remove any surface oxidation that occurs during the burn-off.
Using an acid in a spray wash system is a very effective way to remove ash residues. The higher the pressure the less acid is needed.
The lowest hazard way to clean off the ash is to use special detergent wetting agents which can help to wet and remove the ash. Alkaline materials also have an effect.
Flash Rusting
Flash rusting of parts is often a problem. The formulation of the chemical can manage the flash-rust to a degree but in extremely high humidity conditions a water-soluble rust inhibitor may be needed.
Examples of Ash Removal
My first real experience with ash removal was a company using a high-pressure wand system. They were almost getting the results they needed. A simple high-wetting detergent additive gave them excellent results. I also added a little bit of rust protection as a bonus.
Then there was Harley. They processed large amounts of burned off parts through a batch cabinet washer. It was a new system. The washer had the ability to have two different tanks with a fresh water rinse in between. Great results were obtained using a highly acidic product, a rinse with a small amount of neutralizer in it that was discharged to their waste treatment system, and an effective neutralizer/rust preventative.
It is not unusual that a multi-stage cabinet washer will have heavy chemical usage due to less effective rinsing. It requires frequent recharging and creates a moderate amount of sludge that is difficult to handle.
But my work showed that acid products that attack the metal, usually but not solely stronger acids, improved the results in direct relationship to the amount of attack on the metal. Detergents that wet certain pigments more than the metal were the most effective.
I have seen very effective overhead conveyor washers remove ash. Especially when there are consistent shaped parts and nozzles could be adjusted to give good impingement of chemical solutions. One novel, very well working line had a station where a pressure wand attachment could be used to hit areas that the washer missed. An operator stood in a booth and spray the areas that were not getting reached by the regular washer.
Belt washers can be effective but often the conveyor belts can block the solution from reaching parts of the work.
Ultrasonic Cleaning
Ultrasonic tanks work very well. However, I usually recommend an acidic soak tank prior to the ultrasonic tank. Using the ultrasonic in the rinse tank is usually very effective. Alternately a single ultrasonic tank with a good detergent/rust preventative product. An ultrasonic tank develops pigment sludge. This requires removal on a regular basis.. Large amounts of sludge could become re-suspended or absorb some of the ultrasonic activity. It the ultrasonic is in the rinse, the tank is easier and cheaper to clean. A still chemical processing tank followed by an ultrasonic rinse removes the ash in the rinse tank. This saves on chemicals.
Useful Chemicals
Custom Designed Chemicals has several options to help remove ash residues from surfaces. Our most popular product is Ash Cleaner 1. This product is a moderately strong acid/wetting agent combination that works in both spray and immersion applications. One very effective process uses Ash Cleaner 1 in an immersion situation followed by a pressure spray rinse. The acid breaks the bond of the pigments of the surface and the pressure wash removes them.
Although Ash Cleaner 1 works well in spray situations, using an acid in a spray wand process can discharge acid down the drain. This could be a problem for most users. Using an acidic product could require neutralization or require collecting the water.
One of the advantages of using an immersion tank is that the bond with the pigments can be broken in the acidic solution. Then the loosened pigments could be removed with a simple water rinse. Often a pressure washer is not needed. The rinse water usually dilutes the acidic surface enough that discharge is not a problem. An immersion tank of this type tends to have a long bath life. Over time heavy metals may build up in the tank from the processed metals. As a result the tank may need to be processed as a waste. The rinse removes most of the solids. Very little deposits in the tank.
Ash Cleaner 2 is a mildly alkaline material for high pressure spray situations. It is a mixture of detergents which wet the surface pigments including titanium dioxide. It has some rust protective ability.
Ash Cleaner 3 is a safer more expensive mild acid product that takes longer to remove ash residues. It can sometimes be discharged down the drain.
Final Word on Ash
The nature and composition of ash residues vary widely with different operations. Local laws vary from location to location. This information may not apply to any specific operation. It should not be used as the sole determination of how to handle any situation. However, more than likely all the paint you encounter is non-hazardous and can be disposed of easily and cheaply.
If you need help with an ash cleaning problem, please give CDC a call at 312-550-7083.
Social tagging: ash > Burn-off > paint removal