Cold tank stripping employing methylene chloride is the fastest conventional method of removing a reasonably broad spectrum of paint types.

Components are immersed in methylene chloride, usually blended with activators and inhibitors provided by most specialty chemical manufacturers. Strip time ranges from five minutes to about four hours to remove paint from a batch of components. Rinsing of components, followed by the application of a rust inhibitor (on ferrous components) complete the process.

Because methylene chloride is so effective, the price of materials and labor in a per part costing formula is quite attractive. The capital required to install the necessary environmental controls however, will be substantial.

The surface quality is good, as long as steps are taken to battle the on-set of oxidation. As well, less than thorough rinsing can leave trapped chemicals in some complicated components.

The delivery of finished components back to the paint line is good since (depending on tank size) a large batch of parts can be processed in a relatively short period of time.

It is important to note that you should consult a credible environmental consulting firm to discuss your intention to explore methylene chloride stripping. In addition to accommodating current environmental, as well as health and safety regulations, it’s advisable to consider future government intentions.

The use of strong alkalines or caustics in immersion tanks at temperatures from 130F° to 200F° is also effective on many varieties of coatings.

Although invariably slower than cold tank strippers, they are much easier to deal with from a disposal, environmental and heath and safety perspective.

The price per part is good due to batch processing and lower chemical purchase and disposal costs.

Depending on the type of coating and the substrate, the surface quality is good. Coating is often removed completely. Again, employ proper rinsing to ensure undesirable chemicals do not enter the paint line.

Delivery may be a problem, depending on how quickly the components need to be returned to the paint line. Dwell or immersion time is often about eight hours.

This process poses much reduced health risks versus methylene chloride.

The painted part is exposed to large volumes of high velocity abrasive particles, such as sand, glass bead or steel grit.

The abrasive is propelled either by air pressure or by a motor-powered wheel. The paint is chipped off by the abrasive. The abrasive is recycled through a separator that removes paint dust and broken-down abrasive to a dust collector, and returns good clean abrasive back into the hopper.

Generally, in an air blast system, the price to process a part is quite high compared to a batch-type system. Wheel blast systems provide a batch-type process and can be economical and even less expensive than chemical processes — there is no rinsing stage at the end of the process, as is required with chemical stripping.

The surface condition could be described as a non-directional finish or texture. In some applications, this is advantageous because it provides an excellent surface for paint adhesion. It is the best finish for bonding because a minute layer of steel and its scale or contaminants are virtually removed to expose a new surface. Although this is an advantage in many applications, it may be a disadvantage if a very thin layer of paint and a smooth surface are the desired results.

Delivery depends on the type of process (a manual air blast or an automated wheel blast). In most cases, the production rate of a manual air blast process is slower than the painting process itself. In an automated wheel blast process however, hundreds of parts can be completely cleaned in 10 to 20 minutes. In removing heat treat scale or rust, hundreds of parts can be cleaned in two to five minutes.

This is a process where heat is applied to a batch of components (commonly referred to as burn off) and turns the paint to ash.

The two main methods of applying the heat are: in a specially designed oven with temperatures in the 600F° to 900F° range; or in a bath of molten salt operating at similar temperatures. A rust inhibitive rinse stage is required.

Price-wise, the process can be quite attractive again, due to the batch type process.

In terms of delivery, the transfer efficiency in a salt bath is very efficient, allowing much better cycle times (often minutes) versus conventional burn off ovens (hours). Keep in mind that molten salt equipment is capital intensive.

This process is similar to abrasive blasting, in that the stripping action is accomplished by a particle propelled by air or a motor-powered wheel to remove paint.

The similarities end there. Plastic media is softer than your steel parts but harder than the paint. There is no change to steel and often none to non-ferrous substrates as well. In fact, conversion coatings remain intact. You are left with a surface exactly as it was before it entered the paint chamber. Because it is a dry process (often referred to as "dry stripping"), the occurrence of any flash rust is rare.

Plastic media blasting has its roots in the aircraft industry, where large volumes of chemical strippers were required to strip the large surface area of an aircraft. Huge costs were involved due to the purchase and disposal cost of the chemicals. Plastic media is used and re-used (10 to 20 times) until it is carried as dust over to a dust collection system.

This can be an expensive method, as it is usually manual. It has its applications for high value parts, complicated conversion coatings that cannot be removed, or for chemically sensitive parts.

The quality of the stripped surface is by far the best of any stripping process. This is a strong statement, but steel and most non-ferrous parts are left in the condition they originally entered the paint line. As well, there is no fear of chemicals hiding in seams and coming out during cure after re-painting.

Delivery is one drawback. Production rates are slower than a typical paint process. A stripping facility’s capacity may have to be probed before embarking on this process.