Retrofitting permeability meters to eliminate mercury seals.

Sand lab engineers develop a map to replace banned mercury seals in dated sand permeability testers with effective air seals.

Foundrymen continually rely on durable equipment in foundry sand testing laboratories for reproducible and accurate molding and core sand data. Advances in more recently developed permeability testing equipment include solid state circuitry and an "O-ring" seal to eliminate the mercury seal used on older drum-type permeability meters. Some sand testing laboratories, however, still use this serviceable but dated equipment, which may pose environmental hazards.

Sand permeability testing is a vital tool in the battle against gas-related defects. Many durable, accurate permeability testers, such as the one shown in Fig. 1, are still used in countless foundries to measure air flow through sand mixtures.

These instruments perform well, but most use mercury to maintain the airtight seal necessary in the air chamber below the sand sample. Air, under constant pressure (10 grams/sq cm of water), flows through an orifice into the open end of this chamber and through the sand specimen being tested. This outflow of air is measured and converted to a relative value of a specimen's permeability.

Because OSHA banned mercury from work areas, eliminating the mercury seal is a workplace necessity. Retrofitting these serviceable units also made economic sense to sand laboratory engineers Wayne Armstrong and Phillip Stacy at ACIPCO, Birmingham, Alabama.

In the absence of retrofit kits from the original equipment suppliers, the two engineers developed a modification that replaces the mercury seal with an efficient, effective and inexpensive air chamber.

Several simple, easily found materials are required. Shown in Fig. 3, these include:

* copper tubing, 7/8-in. OD x 2-1/8-in. long; (A)

* 7/8-in. copper cap with two 1/4-in. holes drilled in its side near the top; (B)

* a No. 11 solid rubber stopper with a 7/8-in. hole cut with a No. 11 cork borer, (C)

* a 4-1/4-in. x 1/16 in. metal disk, copper or steel, with a 7/8-in. center drilled hole; (D)

* rubber heater hose, 7/8-in. ID x 2 5/8-in. long; (E)

* two heater hose clamps, size 12, or two Snapper clamps, SNP 28. (F)

Preparation

Preparation steps for modifying the permeability meter include:

* record machine readings before modification, using a standard permeability test tube;

* remove water from tank;

* carefully remove (and conserve) mercury and the push rod from push rod holder;

* remove plug from air chamber with a 1-1/8-in. deep-well socket;

* examine check valve in plug--do not remove;

* remove the top check valve and mercury float by removing the 3/8-in. nut from the valve stem inside the air chamber tube;

* clean air chamber, replace the plug with the bottom check valve;

* clean water tank and mercury well.

Installation

To complete the modification of the permeability meter, follow these steps:

* put the heater hose over the tube in the well, seating it in the bottom of the well;

* place clamps on hose;

* insert copper tube in the hose until it is firmly against the well tube;

* remove cover disk and tighten both hose clamps;

* place cover disk over the copper tube;

* moisten the hole in the rubber stopper and place the large diameter of the stopper over the copper tube;

* if measured correctly, about 3/8-1/2 in. of the tube will protrude above the rubber stopper;

* fill the tank to the proper level with water, replace the air tank and the push rod into the rod holder;

* leak test connection by pressing a No. 3 solid rubber stopper into open end of copper tube;

* raise air tank 3-4 in. and release it; if the air tank level is unchanged, there are no leaks;

* remove No. 3 rubber stopper and lower air tank;

* place copper cap with the 1/4-in. holes over the end of the tube;

* cap should be snug but removable; copper cap allows air during use to flow freely from air the chamber without dislodging.

After completing the modification, compare the results of the recorded values of the modified permeability against the values obtained before modification. They should be identical.