Exhaust Recuperator

Exhaust Recuperator Leak Test Cell DR-104
Innovative fixture and seal design enables high-pressure leak testing on large, thin, flexible component with unstable sealing surfaces.

The Challenge
Two sizes of heat-exchanger segments are proof-tested at 70-110 psig. for seam integrity, then leak-tested to a limit of 272 sccm. under 30 psig. at a rate of 75 pph.

Test parts are flat, hollow assemblies designed to let hot air flow from one end to the other while heat dissipates through external fins. Two sidewalls of 31-gauge (0.0105.) stainless steel sheet are joined by a brazed seam around their perimeter, and spaced 0.303. apart by a corrugated stainless sheet that forms multiple internal channels to guide the airflow. Together, the sidewalls terminate in two rings of unequal size, with one ring at each end of the frame. The smaller size frame has 10.and 5. ID rings spaced on 28.centers; the larger frame has 13. and 8.5. ID rings spaced on 45. centers. In final assembly, multiple frames will be stacked to form tubular inflow and outflow manifolds.

Test fixtures must pressurize these parts through the larger ring’s open ID while sealing off the smaller ring’s ID, a requirement complicated by the instability of their flexible, thin-metal sealing surfaces.

Test Process
InterTech’s design answers the sealing challenge with a pneumatic, multi-jaw chuck that expands outward from the circular fixture holding each ring, wedging into the ring’s open ID to support both sidewall sealing surfaces simultaneously from the inside.

To avoid the need for high sealing forces to counteract test pressures, sealing fixtures on both sides of the ring automatically grip each other with a bayonet-type twist lock. An inner O-ring seal isolates most of the circular fixture's central area from the test circuit, confining test pressures to the outer edge of the fixture. This also speeds the test by reducing the test cavity volume and eliminating fixture creep.

The machine operator loads a test part horizontally between two circular fixtures positioned at each end of the part, then touches two start buttons. Small pneumatic clamps move in to hold both rings down on their fixtures while the support chucks expand, then the upper half of each fixture comes down and locks into the lower half. Soft silicone O-rings on upper and lower halves of both fixtures compensate for slight waviness or other imperfections on the part's thin stainless sealing surfaces.

An InterTech M-1075 Mass Flow Leak Detector applies proof pressure for five seconds, then vents the part and applies leak-test pressure for 10 seconds. Accepted parts are marked green, vented and released. Rejected parts are marked red and remain sealed under pressure so the operator can spray the part with a liquid soap solution to locate the leak before manually releasing it for rework.

For additional information, please contact InterTech Sales