Electrostatic Spraying

Electrostatic painting standard in the Automotive Industry for over 25 years. Car makers found that if you magnetically charged the particles of paint that you were spraying on a car body, these would be attracted to the metal and produce a uniform cover of paint with excellent adhesion. This meant that the paint job was of better quality, less paint was used to cover the same surface, and the overspray, that cloud of drifting paint particles that got on everything and everyone was reduced to a minimum, thus making the operation safer and more comfortable for the workers.

For electrostatics to work properly, the paint spray is blown through an electrostatic field (very much like the “Force Fields” on Star Trek). The droplets have to travel through at high speed so that they draw the electrostatic charge out of the field with them and do not give it a chance to return to the field. Once out of the nozzle, the droplets forming the spray cloud (pattern) are carrying the electrostatic charge, this charge is looking for a place to land and will be attracted to the nearest grounded surface.

Again, for electrostatic attraction to take place the “target” surface must be grounded and have magnetic attraction, as in the case of the car body, which is steel that has been degreased and prepared for painting. If you were to cover the car body with a nylon cover, the droplets would look for another exposed metallic surface to land on before going towards the “insulated” body, unless they were aimed directly at that car body, in which case they would depose in very much the same manner of a conventional (non charged) spray.

Electrostatic attraction can enhance spray coverage

One of the advantages of Electrostatic Spray is that when the droplets in the cloud are attracted to the target surface, the magnetism of an area of the surface covered by a charged droplet is canceled out by the charge of the droplet and therefore the other droplets flying around in the cloud will look for another area that still has attraction. This means that with electrostatics, one can obtain a much more uniform coverage than with conventional spray patterns. i.e.: minimum amount of drips and runs: a good looking paint job.

There are some areas and cases where it is said that Electrostatics work very well, but basically in agriculture there is an absence of good magnetized target areas. We are spraying plants and trees, which, although grounded, are not metallic and therefore have very low conductivity values. In addition, some plants, especially those in warmer, sub tropical climes, have naturally more waxy surfaces on the leaves. therefore presenting a barrier to charged particles very much like we did when we covered the car body in a nylon sheet.

In Electrostatic Spraying, we are trying to get better deposition of the chemicals we are spraying onto the leaves of the plants. This is especially true in the case of row crops and vegetables in the ground, as the area of most importance for coverage is the underside of the leaf and this is also the most difficult to reach with conventional systems.

Using Electrostatics we hope to drift a relatively turbulent cloud of spray into the foliage and have it envelop and adhere uniformly to the surfaces because the magnetism of electrostatics would attract the charged particles in the spray cloud to the hard to reach areas of the leaves, fruit, flowers and stems. However, depending on how the spray is directed, chances are that the particles in question will be attracted to the soil, since it is grounded, and is more conductive of electrical charges than the target vegetation.

One of the signs of electrostatics in ag spray is the absence of overspray and drift. In other words, most of the spray cloud is being attracted to either the target or the ground, and therefore does not remain in suspension in the air over the crop like a conventional spray cloud would. This is also true in air-blast spraying where the cloud is directed upwards into the tree canopies and, if there is attraction, seldom rises over the tops of the trees.

Electrostatic spraying has been quite successful in tree crops, especially in drier climates and with fruit crops such as apples and pears. Many growers in Washington state, Michigan and upper New York State have been successfully using electrostatics for many years. Their success is due in part to the climate and the fact that apple and pear leaves have little or no waxy protection on their surfaces, reducing that insulating effect that I discussed previously when I referred to more tropical crops.

The more tropical the plant, the more it will protect its stoma with waxy like substances on the cuticle as a natural defense against the effects of heat, disease and insects. As this protective layer thickens, there is less conductivity through the plant’s leaf surface, which reduces its ability to transfer the electrostatic charge necessary to attract the charged particle of spray.

There has also been considerable success with directed spray equipment such as stake tomatoes and other trellis type sprayers. The spray pattern is directed at the crop either horizontally or at an upwards angle, away from the ground, and at a relatively close proximity to the actual foliar target. Thus the charged droplets will depose on the target before being attracted to other surfaces. This is especially evident in stake grown crops where the spray heads are positioned on both sides of the row and simultaneously spray at each other so to speak. Using electrostatics in this type of application, has produced very good results both in coverage and chemical savings, while radically eliminating drift and other hazards.

The same cannot be said for low lying vegetable crops such as cucurbits, snap beans a other produce that grows close to the soil. When the electrostatic spray pattern is directed at those plants, the majority of the spray is attracted to the ground, and not the plant. The only redeeming feature of this would be a reduction in drift. The fact that plastic is used to cover the beds does not seem to have much effect in insulating the charges from the ground because the in-rows are not covered and generally have some vegetation that will definitely attract the charged particles in the spray cloud directed at the crop.

Another phenomena occurs with ornamental and nursery crops. Most materials grown in greenhouses and shadehouses are grown on benches off the ground and in plastic pots and liners. In addition, larger ornamentals are grown in pots on the ground, but the ground is covered in poly or nylon ground cover material, and the pots are plastic.

There is little or no possibility of these crops having any contact with the ground, hence they are not grounded and therefore not capable of drawing an electrostatic charge out of the ground to meet the charge borne by the charged particles in the electrostatic spray. Consequently: no attraction and the electrostatic spray becomes a pulverized cloud similar to that produced by a conventional sprayer.

How To Tell if Electrostatics Are Working?

A good test to see if your system is functioning properly is to watch the spray cloud. If the cloud seems not to drift away from the target and stays down around the crop, electrostatics may be working. Away to verify this is to switch the power on and off and look for changes in the cloud pattern. If you start with the switch off and watch the spray cloud, and then turn the power on, the spray cloud produced from that moment on, should be noticeably more concentrated in the direction the crop and there should be little or no drift away from the targets. If this is not the case, check that the sprayer is grounded. (a chain dragging from the steel frame would be adequate).

For electrostatics to work, the sprayer producing the electrically charged particles must be grounded. If that does not correct the problem, check your electrical supply and make sure the “field” is active. If there is no charge in the “field” through which the droplets have to pass, they will not be charged.

Speaking of electrical charges, the successful electrostatic machines generate their field with solid state power units that are capable of producing up to 20,000 volts. These units require substantial power sources to operate, such as tractor electrics or small generators and are either row-crop or grove-type sprayers.

My jury is still out on the hand held models. I have not been able to make them perform, especially in the areas that they are most used: Ornamentals and bedding plants. Some of the manufacturers have very impressive demonstrations that show just how electrostatics can be so more effective than conventional spray systems. Remember, demonstrations are just that, and designed to showcase the product. You are the final judge. You are the user and the one that will have to live with the decision and grow the crop.