T.M. Stewart, Inc.

Industrial Metal Sealant Co.

         Founded 1945

Impregnation Since 1962

                MICROPOROSITY & IMPREGNATION


Micro porosity in pressure-type castings costs American industry many millions of dollars annually. Pressure type castings must retain gases, liquid chemicals and other fluids under pressure. Examples of these industrial parts are: Fuel pumps, valves, carburetors hydraulic units, meters, motor parts, crank cases, microwave systems, gear housings & optical housings. These are but a few of the many parts that can be Impregnated.

A varying percentage of all pressure castings leak in spite of correct design, proper alloy selection and good foundry practice. Microporous flaws are particularly prevalent in low density metals such as aluminum and magnesium. The major causes of porosity are : (1) Inherent tendency of the metal toward microporosity, (2) Design requirements, (3) Intradentritic shrinkage, (4) Incorrect foundry techniques , and (5) Occluded gases.

While castings may leak before machining, experience indicates that most porosity occurs after the surface areas are cut away. The result is a serious loss of critical materials, labor and machining time. No one wants to design, cast or machine microporous or leaking castings, but it is generally understood that such losses are a fixed hazard in all types of pressure type castings. A foundry contracted to deliver 100% pressure tight castings must of necessity, estimate that a certain percentage of castings will be returned as leakers after machining, and figure into his costs the losses due to such rejects. Impregnation is also used for other purposes other than pressure tightness.

Another application is to prevent salts and other foreign materials in the pores from exiting and ruining a final finish or components in the parts. This process is also used to seal chrome plate. The polyester resin is inserted in the pores to prevent salts and alkalies from entering and deteriorating the plating. This gives the plating a longer life. Impregnation also prevents chrome plate leakage in hydraulic applications.

Ref : PS11501J & CPC 8220. We have preformed these specifications since 1978, on thousands of parts.

Impregnation is performed on a wide variety of parts. Some typical applications are: Gear housings that contain grease or oils, valves that contain liquids or gases, electronic housings that must not allow moisture to enter and ruin the components, hydraulic parts that must retain fluid pressure, lens housings that require no moisture from entering and causing distortion, air powered tool components, transmission cases, microwave components, vacuum pumps, compressor parts, chrome plated marine parts, parts that must be submerged in water or fluids, computer parts in super clean systems, fluid cooled parts, refrigeration and air conditioner parts, pipe fittings, and many other applications. When raw castings are impregnated, the pores are filled providing a smooth surface so drills and taps do not bind when penetrating the wall of the casting. Impregnation can also be used to bond a tight fitting bushing so it will not move.

Impregnation is a cost effective way of providing clean pressure tight parts.


Call or E-Mail us with your quotes or questions.

Impregnation service since 1962

Phone: (631) 893-0031 ** E-MAIL  otto@tmstewartinc.com

Monday thru Friday 5:00am thru 3:30PM EST

Attn: Bob Otto     

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