Case Studies: Force Tester Springs into Action
January 2, 2008
Bespak Ltd. (Buckinghamshire, United Kingdom) is a manufacturer of specialty medical devices for inhaled drug delivery and anaesthesia. The company manufactures more than 450 million complex devices each year, many of which are inhalers used to administer medicine to those with illnesses such as asthma and chronic obstructive pulmonary disease. Tensile and compressive helical springs form a key element of the operating mechanism of these devices. As a supplier quality control measure, Bespak performs free height test and compressive/tensile force tests on the springs to ensure conformance with specification. This is critical to guarantee correct functioning of the resultant device. The springs, which range from 20 to 120 millimeters, arrive at Bespak’s King’s Lynn site in the United Kingdom in six deliveries per week, and 30 to 50 samples from each batch must be tested.
This was previously performed using a gage mounted onto a manually operated test stand; however, the quality control team at Bespak found their needs outgrew this setup, and a more sophisticated testing solution was required. “It was necessary to take out as much as possible of the operator influence, which was evident in the manual system,” says Peter Haken, quality engineer at Bespak. “Spring suppliers had already changed to a much more repeatable system. This change would allow a more direct comparison between supplier and customer.”
To help Bespak obtain more accurate and repeatable measurement results, Mecmesin (Sterling, VA), a designer and supplier of force and torque measurement solutions, supplied a MultiTest 1-i computer-controlled force testing system, fitted with a 50-newton loadcell. This system, coupled with Mecmesin’s Emperor software, provides fully automated control of all test parameters, removing inaccuracies arising from manual force application.
To perform a compression test, the spring is loaded onto custom-made alignment pins. The loadcell (mounted on the system’s automated crosshead) then descends at a constant rate, stopping first to record the spring’s free height, then continuing to the specified test height, taking more than 2,000 readings per second to accurately map the spring’s compression profile. The results are exported to Microsoft Excel for analysis and subsequently uploaded onto the company’s quality module in its database for storage. Force profile charts are stored within the Emperor software for later viewing.
“We have used Mecmesin equipment for some years,” says Haken. “We now estimate that every second more than a thousand people rely on a Bespak device to help them breathe. And as our testing requirements have grown, so too has our relationship with the company. Today we rely upon their advanced test systems to guarantee the quality of our supplied materials.”