Objective:To show the method for stripping old paint, and to learn what paint may be used on 3AL cylinders. To understand the limit for heat curing paint on a 3AL cylinder.

REPAINTING ALUMINUM SCUBA CYLINDERS
Frequent use of Aluminum alloy cylinders in the typical diving environment often contributes to their developing an unsightly, worn paint surface. Divers may desire to restore their cylinders to a like-new finish but are hesitant to do anything because of the much publicized explosions in 1980 which resulted from two heat cured, repainted aluminum scuba cylinders.

Luxfer USA Limited, of Riverside, California, provides information so that cautious, informed cylinder service professionals can safely refinish aluminum cylinders. A renewed finish is not necessary to a cylinders function, but of course, it looks nice. It is imperative however, that under no circumstances should caustic, metal damaging paint strippers be employed. Furthermore, paint which are not compatible with 6351 aluminum alloy or require heat curing at temperatures of 300 degrees F. (148.9 C.) , or higher should not be used. The methods mentioned here do not apply to composite aluminum cylinders.


Stripping Compounds:
Certain paint strippers may be safely used on aluminum scuba cylinders to remove existing paint and adhesive. The stripping chemical should be a brush applied gel type rather than an immersion type when only a few cylinders are being stripped, because of the large volume of stripper needed for the latter treatment.

Prior to using any stripper, consult the manufacturer s complete specifications and instructions. Confirm the stripping chemical you have chosen is compatible with aluminum. If there is any doubt, contact the manufacturer for technical information and test the stripper on a small piece of scrap aluminum.

Luxfer, reports that CYL-STRIP, produced by Spatz Paint Company (1601 North Broadway, St. Louis, Missouri, 63102) and ZIP STRIP, produced by Star Bronze Company (803 South Mahoning, Alliance, Ohio, 44601) are satisfactory gel strippers for their cylinders.

Zip Strip is widely distributed throughout the U.S. in paint stores and building supply outlets. It is sold in pints, quarts, larger sizes and spray containers. Cyl-Strip, on the other hand is not widely distributed so may be purchased directly from the manufacturer in 5-gallon containers.

Gel strippers typically are applied by brush, allowed to stand, and then are removed by water wash or with a steel wool pad. However, some cylinder distributor decals and old visual inspection stickers require additional Zip Strip applications. Clean, dry cylinders are then ready for the painting steps.

Safety precautions must be observed to ensure that the stripping chemical does not come in direct contact with user. Methylene chloride, the action ingredient of many paint strippers, is caustic and may cause burns to the skin and eyes. Wear full cover clothing, protective gloves, an eye shield and, where specified, a respirator.


Selecting Paint:
Air dried automotive type paints were, at one time, used on aluminum cylinders. While a number of brands may be suitable, DuPont produces two that Luxfer considers appropriate. Both IMRON, a polyurethane enamel, and CENTARI, an acrylic enamel, may br found at auto repaint supply stores. The application and safety instructions should be precisely followed. The IMRON label indicates it is only available to professional, trained painters. Both Imron and Centari paints must be mixed with activators just prior to use. Cleaning solvents ant undercoats also are specified. Required paint spray equipment and operator safety apparatus exceed that normally available to most divers. Therefore, the paint application is not recommended for individuals. Those who are prepared for the work and cost of cylinder refurbishing should prepare the cylinder for painting by a professional automotive paint shop.


Heat Concerns:
The DuPont Co., states that, almost always, Imron is applied by automotive paint shops without artificial heat. Printed specifications require that forced heat paint curing must be done at less than 250 degrees F.(121.1 C.), somewhat below the temperature limit for aluminum cylinders. However, DO NOT, UNDER ANY CIRCUMSTANCES, HEAT CURE THE PAINT. Instead, leave the painted cylinder in the clean, warm, dust free, and well-ventilated painting room for at least two days.

Initially, the stripped cylinders are scuffed using a fine sandpaper, then PREP-SOL, a paint thinner, may be wiped over the metal to remove particles. Observe safety precautions provided by manufacturer when using solvents. Twine attached to the masked valve will allow the tank to be suspended for painting.

Apply two coats of primer-sealer. With Imron paint, use 225 S cleaner followed by 226 S conversion coating. Then apply Corlar Epoxy Primer, a suitable self-etching chemical. After drying according to instructions, Imron should be applied in 2 light coats by spray gun. One quart (.95 l), should be sufficient for about 4 cylinders. Be sure to follow the complete instructions for the products you choose to use.

Be warned, visual cylinder inspectors, especially those trained at PSI Visual Cylinder Inspection Training seminars are alert to, and most wary of, cylinders repainted by owners. The cylinder owner should be prepared to explain to air station operators how the like-new appearing cylinder was refinished.

Last updated 25 Feb 98

For comments/suggestions send an e-mail to: Dennis P. Reed