Leak testing has long been an integral part of the quality assurance programs for assemblers in a wide range of industries. Medical devices, heating and air-conditioning equipment, components for airplanes and automobiles-the number of assemblies that must contain or repel a gas or liquid staggers the imagination.
What follows are some examples of how today’s leading leak-test equipment providers are helping their customers improve the bottom line.
Medical PrecisionHistorically, the medical device industry has used conventional mechanical methods for testing products. However, in recent years manufacturers have increasingly turned to electronic testing systems to improve the sensitivity and reliability of their processes.
Electronic leak-testing equipment manufacturer InterTech Development Co., for example, recently created a cutting-edge system to ensure the reliability of an on-demand oxygen delivery system being assembled by one of its customers.
According to InterTech Development president Jacques Hoffman, the company had previously relied on a number of failure-prone mechanical valves to create the vacuum levels required to test the reliability of its oxygen delivery devices.
However, these products are now tested with an electronic system that measures the triggering sensitivity of the device and calibrates vacuum levels to preclude both false triggering and difficulty in triggering, at the rate of 18 parts per hour.
In operation, the system runs each device through a number of tests, including an auto triggering test to ensure the device does not trigger unintentionally; a pulse verification test to ensure that all pulse settings meet their required volume limits; and a low battery test to ensure that sensitivity and pulse volumes are within customer-specified limits.
Small CavitiesAnother challenge when leak testing many medical devices is their size. Products such as catheters and vials contain very small volumes. This places much greater demands on the testing equipment than those encountered with more moderately sized products.
To overcome these problems, a catheter manufacturer has incorporated a SigPOD leak-test system from test equipment manufacturer Sciemetric Instruments Inc.
The SigPOD system includes a number of features tailored specifically to testing medical devices, including a smaller footprint so that it can be located as close to the product being tested as possible; signature analysis performance to catch defects and help diagnose systemic problems; and full, serialized traceability.
Sciemetric engineers have also equipped the system with air-piloted check valves, which can be powered by the controller instead of a pneumatics module. The result is less heat within the system, promoting thermal stability and more constant test conditions.
Gas ManagementAssemblers have two basic options for leak testing. They can either pressurize or depressurize the cavity or container being tested and then look for pressure changes over time. Or, they can fill or surround the part with a tracer gas and then use a sensor to see if any gas ends up where it doesn’t belong-which would indicate a leak.
Helium is a popular tracer gas, because it is safe and its low molecular weight allows it to quickly permeate the various nooks and crannies of a test part. However, for helium testing to be effective, the gas must be used carefully and correctly.
“Often very little thought is given to how helium tracer gas is introduced during a leak test,” says John McLaren, marketing manager for test equipment manufacturer Varian Inc. “Poor helium management can lead to missed leaks, false rejects and wasted helium.”
Recently, the company worked with a manufacturer of automotive air-conditioning condensers that was having just these kinds of problems. To help solve them, the company implemented Varian’s Charge Management System (CMS), a tool that enhances the quality of leak testing by giving operators complete control of the charging portion each leak test operation.
The CMS allows manufacturers to perform proof, or pressure, tests and verify assembly integrity; to fully evacuate each component before it is tested to ensure correct helium distribution within the test volume; and to introduce the correct charge along with the right proportion of helium.
According to McLaren, correctly evacuating all gases prior to testing was especially important, because these gases can act as a “plug,” delaying or preventing helium from reaching the leak. By evacuating the air from the test space, manufacturers can also use less helium for each test, reducing their consumables costs.
No More BubblesIncredibly, plenty of manufacturers still dunk their products in a water tank to make sure they don’t leak. For example, an ammunition manufacturer only recently upgraded its leak-test methods to cut down on scrap.
Historically, the company would dunk a sampling of its bullets in a water tank to see if they emitted any bubbles. No bubbles meant the company was assembling good bullets.
Alas, there was just one problem. The rounds that the company dunked all had to be thrown away to ensure its customers didn’t receive any ordinance that may have been compromised by getting wet. There had to be a better way.
To solve the problem, the company installed a four-station test stand from test equipment designer and builder Cincinnati Test Systems. The stand accommodates both 7.62 millimeter and 50 caliber rounds.
To run the system, an operator first loads a round into one of four separate nests and then manually lifts and locks each nest into place. A sensor in the tooling recognizes which size round is being tested and sends a start signal to the appropriate Sentinel I-24 leak test instrument, which automatically selects the correct test program.
The Sentinel I-24 initiates the test sequence by sending an output signal to a tooling valve, which supplies air to the CTS Connect air-actuated connector and seals the round in the test chamber. As a first step, the system conducts a volumetric fill test under vacuum to detect any gross defect in the completely sealed round. It then conducts a vacuum decay leak test to identify any measurable leaks in the round.
Background NoiseRecently, an electronic components manufacturer was having problems guaranteeing the integrity of a multipin connector that it fills with helium before welding the assembly closed. Specifically, because the company’s leak detector was located adjacent to the helium filling and welding station, there was a lot of background helium in the area.
To solve the problem, the company installed a SmartTest HLT572 gas analyzer from Pfeiffer Vacuum. The system features a dry pump that is immune to helium contamination and a pair of independent compression chambers to resist back-streaming of light gases.
In operation, after the connector assembly has been filled with helium and welded shut, an operator places it in a flapper box to perform the leak test. If the part exceeds the company’s leak rate specification, it is removed to a fixture where a sniffer probe on the SmartTest HLT572 is used to determine if the leak is in the weld or one of the 16 pins. Epoxy is then applied to plug the leak, after which the part is checked again. If the part still leaks, the process is repeated until the part is right.
Leak Testing BatteriesPrompted by rising fuel costs and millions in aid from the U.S. Department of Energy, car manufacturers are scrambling to develop a new generation of efficient electric and hybrid cars. This, in turn, has generated tremendous interest in lithium-ion batteries as a means of storing energy onboard the new vehicles.
Unfortunately, lithium ion batteries have to be extraordinarily leak-tight if they are to function correctly.
To accommodate these high demands, a number of companies have begun using the Adixen ASM 182 leak detector from Alcatel Vacuum Technology Inc. The system is completely self-contained and uses helium gas, which allows manufacturers to pinpoint even the smallest leaks in as little as a few seconds.
The system can also store all test data, providing traceability, and helping manufacturers quickly identify any systemic problems in their processes as they ramp up production.
Cost-Benefit Catheter TestingAs is the case with all manufacturing processes, there is a cost as well as a benefit to leak testing. Granted, installing the best leak testing system money can buy will ensure your product is gas or watertight. But does this make sense from a cost standpoint?
To find an effective middle ground, a medical device manufacturer now uses a hydrogen-based system from ATEQ to leak test its surgical balloon catheters. The ATEQ leak tester uses a mixture of 5 percent hydrogen and 95 percent nitrogen to detect leaks as small as 0.05 standard cubic centimeters per minute, about 80 times smaller than what had been possible with an air-based test.
Although hydrogen-based testing is not as sensitive as helium-based testing, the equipment is substantially less expensive. Hydrogen is also abundant, while helium is in short supply and expensive. Although hydrogen gas is highly inflammable, it is safe when used in low concentrations.
To perform each leak test, an operator first pulls a vacuum on a catheter to ensure there is no accumulation of air preventing the hydrogen mixture from reaching potential leaks. At the same time, the instrument pulling the vacuum performs a vacuum-decay test to detect the presence of any larger leaks. This is important because a large leak, if pressurized with the hydrogen mixture, would contaminate the test environment and hold up further leak testing for a few minutes as the excess hydrogen was removed.
After a balloon catheter has passed the vacuum decay test, it is pressurized with the hydrogen mixture and placed in a chamber where the instrument then looks for any changes in hydrogen concentration that indicate leakage.