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- All About Bob Smith CA

About CA

courtesy of Bob Smith Industries

Cyanoacrylates (CAs) have become the adhesive of choice for most hobby and household applications. High quality CAs such as INSTA-CURE™, when used properly, form bonds that in many cases are stronger than the material that is being adhered. INSTA-CURE™ is a highly refined CA. CAs are reactive monomers that chemically link (polymerize) when pressed into a thin film. The very thin layer of water moisture present on most surfaces acts as an alkali, or weak base, which is the catalyst that results in bonding; however, the presence of detectable amounts of water usually degrades the performance of CAs.

Safe Use of CA Adhesives

Before using any adhesive, adequate ventilation of your work area needs to be addressed. A window or door should be open and/or a small fan placed to circulate the air over your workbench. When using CA, especially super-thin INSTA-CURE, always loosen the top and then retighten it before carefully cutting off the end of the nozzle. This relieves any pressure that may have built-up inside the bottle that could cause the CA to spurt out. This is definitely an issue when CA is used at higher altitudes. Never have the bottle pointing close to your face while opening it.

The fumes produced by CA are an evaporated form of the CA itself. Develop a habit of never having your face above the objects that you are bonding together. Always keep them well in front of you. The fumes that rise during the curing process, while not toxic, can be very irritating to the eyes and nose. Repeated heavy exposure can cause some people to become sensitized to the fumes. For these people, any exposure to CA fumes can result in cold or flu-type symptoms. If you find yourself falling into this category there are two options. First, you can switch to another adhesive such as BSI's odorless SUPER-GOLD. Second, you can use protective gear such as a respirator. 3-M makes a dual-cartridge paint spray mask (R-6211) with #6001 Organic Vapor Cartridges that works very well in preventing adverse reactions to CA. 3M 5010 pre-filters can be attached for additional protection.

Cyanoacrylates do not have an adverse effect on body tissue. The heat that is generated when CA comes in contact with human skin can result in some burning, however. Do not wipe-off CA that gets on your hands with a dry paper towel! Most paper towels seem to have just the right chemistry to instantly set off CA with a resultant burst of heat. While not dangerous, this can be very uncomfortable. The primary difference in CA's developed for medical use is the very low heat that is produced when they cure.

CA or CyA?

Readers of model magazines have probably noticed that they are split down the middle on how their editors prefer to abbreviate cyanoacrylate. They use CA or CyA. BSI will always use the proper designation, which is CA. One editor says he uses CyA to avoid confusion with the postal designation for the state of California. Since we are talking chemicals and not states, CyA is the symbol for Cyclosporine A. Case closed.

Bonding Plywood

The manufacturing process that produces plywood can sometimes leave a tiny layer on the outside surfaces that inhibits bonding. Plywood should therefore be lightly sanded before bonding to produce the best results. Lite-ply is the most difficult plywood to bond. It soaks up thin CA like a sponge. Thicker CA's such as MAXI-CURE are what achieve the best results with plywood. Strength tests of such bonds usually result in the plywood delaminating before the glue joint gives way.

BSI’s CA Tops are Clog-Free

Bob Smith Industries’ CA tops are acknowledged to be the best available. To achieve the best clog-free results, modelers should follow some basic procedures. Initially, the top should be loosened and then re-tightened to relieve any pressure inside the bottle. Then the most important step is to use a sharp hobby knife of razor blade to cleanly cut off the tip of the top. A rough edge here invites clogging. Squeezing the upright bottle after use will blow air through the top and assures a clear nozzle. If the top is allowed to touch the surface on which accelerator has been applied, a hardening of the glue at the tip will usually occur. Flexing the tip and using your fingernail to remove the hardened CA usually gets the CA flowing again. If a top is abused to the point it cannot be unclogged, soaking it overnight in acetone will return it to as good as new condition. Of course, we also have replacement tips and tops available here at Sirius Rocketry.

What to use?

INSTA-CURE™

has a water-thin viscosity that wicks deep into joints by capillary action and cures in a matter of a few seconds. Surfaces to be bonded must be tight fitting and should be held together while you apply the CA around the edges of the seam. At the moment CAs cure, they give off a vapor that can irritate the nose and eyes, so be prepared. Thin CAs work very well on balsa since they penetrate into the wood and form more than just a surface bond.

INSTA-CURE+™

is a higher viscosity CA for loose fitting joints in which the adhesive must bridge gaps. Normally, the thicker CA is applied to one surface and then the parts are held tightly together for about 5 to 15 seconds. For large surface areas, including those with close fitting joints such as laminations, INSTA-CURE+ ™ should also be used. To prevent premature curing, don’t spread the glue into a thin film. Lay down a serpentine bead with about 1" separations on one surface, then assemble the parts, letting the pressure spread the CA out.

MAXI-CURE™

extra thick CA is the best CA for most plastics, including GE’s Lexan MAXI-CURE™ is the best choice for plastic model assembly. When used with INSTA-SET™, it works better than any putty for modifying or filling voids. It can be carved with a knife or razor blade and sanded and feathered to form a finish indistinguishable from plastic.

MAXI-CURE™

bonds fiberglass, hardwood, metal and rubber better than any other hobby adhesive. For gluing to the inside, clothtextured surface of fiberglass, scrape the area to be bonded with a razor blade or coarse sandpaper before using MAXI-CURE™ or any other adhesive. It also is best for bonding the tires for R/C cars.

INSTA-SET™

is a catalyst which acts as an accelerator that allows CAs to quickly cure in thick layers by enhancing the alkaline conditions during polymerization. INSTA-SET™ in a spray bottle is normally used to cure the CA that flows from joints when parts are pressed together. Applying an additional bead of thick CA along a seam and then curing it with INSTA-SET™ significantly enhances a joint’s strength. For difficult to bond materials, INSTA-SET™ can be applied to one surface and CA to the opposite surface. When brought together, they will bond instantly. INSTA-SET™ is formulated with a strawberry scent and activates CA in 6 to 8 seconds without any degrading of the CAs strength, which can occur with many other accelerators. It is compatible with all surfaces, even clear plastic and white foam.

UN-CURE™

debonder will soften cured CA. If parts are bonded incorrectly or your fingers are stuck together, a few drops of UN-CURE™ will dissolve the CA in about a minute. Apply on bonded skin and roll apart fingers. Once stuck, use acetone to clean off softened CA, then wash off with soap and water.
 

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