In the Shop: Liquid Miracles

October 28, 2011 09:48 AM
In the Shop: Liquid Miracles

Modern chemistry provides farmers an assortment of versatile sealants and adhesives to use during repairs. Room-temperature vulcanizing (RTV) silicone sealants cure at room temperature without the need for baking or special curing agents.

They cure by reacting with water vapor in the air. The higher the humidity, the faster RTV silicone cures (as long as the air temperature is above the minimum level noted on the product label).

RTV silicones can replace paper or fiber gaskets in many situations. They are resistant to water and oil, but some break down if exposed to gasoline or lighter distillates. Read labels carefully before using RTV silicones with gasoline fuel systems or similar applications.

Some RTV silicones have a strong vinegar odor. The distinctive odor is produced by an acidic chemical reaction as the product cures. The acidic vapors can corrode bare metal, so use RTV silicones with care near electronics or computer boards with exposed circuitry.

Oxygen sensors on car and truck engines have been damaged by acidic vapors from RTV silicones that were used to gasket other engine components. Use only RTV silicones that are labeled "oxygen sensor-safe."

Apply RTV silicones to clean bare metal to ensure they make an optimum seal. A 1⁄8" bead should produce a seal without squeezing excess sealant inside components.

For maximum sealing efficiency, connect, join or attach components before the bead of sealant "skins" over. Components sealed with RTV silicone can usually be returned to low-pressure service in a few hours. Allow 24 hours for full curing and the most durable seal.

Color-coded miracle workers. Thread-locking compounds are another liquid miracle worker commonly found in farm shops. They are generally color-coded according to strength: purple for low strength, blue for medium strength and red for high strength. Blue, medium-strength thread-locking compound is the "go-to" product for making sure nuts and bolts on farm equipment stay tight.

Thread-locking compounds are anaerobic adhesives that cure in the absence of oxygen. If a nut or bolt is left loose, it will become sticky. But tighten the nut or bolt so all oxygen is squeezed from between the threads, and the thread-locking product reacts with the bare ferrous metal of the fastener to form a strong bond.

Oily residue, rust and paint can inhibit the reaction that turns drops of thread-locking compound into vibration-resistant glue. For that reason, clean used nuts and bolts with brake cleaner or contact cleaner for optimum contact between bare metal and the thread-locking compound.

Fasteners made of nonferrous metals (aluminum or plated steel) might require special primers and curing agents to ensure maximum strength.

A few tricks can help you optimize the strength of fasteners when using thread-locking compound:

  • When possible, apply to the bolt rather than to the nut.
  • Coat only the threads of the bolt where the nut will be seated, not the entire length of threads.
  • When threading a bolt into a casting, apply the compound to the leading threads of the bolt.

Most fasteners "locked" with low- or medium-strength thread-locking compound can be disassembled with a hand wrench. To disassemble fasteners that were joined using high-strength thread-locking compound, apply heat to melt the compound and disassemble while the components are hot.

Machinery that has been repaired using thread-locking compound can be immediately returned to service if the nuts and bolts were tightened to recommended torque. The thread-locking compound doesn’t make them tight—it merely keeps them tight.

Cool Tool of the Month

To ensure leak-free repairs, mating surfaces must be cleaned of residual gasket material and sealant. Screwdrivers and pocketknives risk gouging and do not get surfaces perfectly clean. For $20, a three-piece gasket remover set offers sharp straight edges to remove old gasket material and sealant. One flexible wide blade, one flexible narrow blade and a rigid, beveled, narrow blade (with a metal-capped handle) make removal fast and easy.

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