Porosity sealants fill tiny imperfections in cast metal, powdered metal, plastic and ceramic parts. Parts that are filled correctly are leak-proof and can be machined.

Low-viscosity resin sealants don't leave residue on parts. As a result, parts can go directly onto an assembly line, according to manufacturers.

Perhaps most importantly for distributors selling to manufacturers of gears, motors and machine tools, porosity sealants can be used on powdered metal, plastics, ceramics and other porous substrates, as well as hot-formed castings. Manufacturers of porosity sealants are making improvements that will open more doors for distributors.

New products present opportunities to sell to clients who have not used sealants. They also offer opportunities to solve some of the porosity sealing problems inherent in older products, like filling more holes per cycle and stopping more leaks, said Harry Arnon, president of Hernon Manufacturing Co., a maker of industrial adhesives and sealants.

Porosity sealants have a wide range of uses in the automotive industry where powdered metal components must go through many machining, cleaning and plating operations, Arnon said. There are two types of sealing processes.

"Anaerobic curing involves parts dipped into a resin tank and sealed in a vacuum," he said. "The resin is sucked into cavities. The parts are washed and put in an activator tank, hardening the resin and sealing the surface."

The hardened resin becomes a solid plastic with properties of a lubricant. It aids machining, eliminating interrupted cuts that break down cutting tools. However, the washing process is long and requires using surfactants to break down resins, an environmentally unfriendly procedure.

The second process — heat curing — involves spinning excess resin out of parts and dipping in water at 90° C, just under boiling, Arnon said. This process is less complicated than anaerobics, but many products like plastics can't be heated to boiling.

Two new products address the problems: an anaerobic sealant that washes cleaner and faster without surfactants, and a product that will cure at about 70° C, allowing more varied-material castings to be filled and saving electric energy. Arnon said that more plants are willing to look at using the porosity filling process now that "greener" options are available.

Riechman Crosby Hays Co., a distributor based in Memphis, Tenn., runs an integrated supply operation for a customer who makes aluminum boat transoms. The company was using a product that did not fill all the pores and left "leakers," according to site manager Jim Miles. That product also needed to be shipped and stored under refrigeration, he said.

"Leakers are castings that show holes when put under pressure. The cycle time was also cut in half, from 12 minutes to six minutes. The improved product needs no refrigeration and no mixing, saving the customer a lot of expense," Miles said.

The end user produces about 140 castings each day and completes most of the finishing processes before checking each for leaks, so it is all the more important that leakers be kept to a minimum. This customer uses a heat-curing process sealant and has yet to find a leaker when using the new product, Miles said.

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