Public health authorities around the world now have an all-in-one, cost-effective tool to test water quality thanks to a highly automated approach rooted in an innovative two-shot overmolding process.
| New cartridge speeds water quality testing.
The product is a turnkey single-use water test cartridge system and automated monitoring system that determines water quality within 2 to 18 hours depending on level of contamination. It replaces a test that can take up to two weeks to determine the presence of E.coli and total coliform bacteria. Total coliforms include bacteria that are found in human or animal waste.
Development work started three years ago and led to innovations in polymers used, tooling, injection molding machinery and specially developed automated assembly equipment that completes six processes outside of the molding area, and then boxes the cartridges for shipment.
The ENDETEC TECTA automated microbiological testing system uses an instrument with built-in incubation, a special optical system, integrated user interface with interpretive software, and a test cartridge for the detection of E.coli and total coliforms. Design elements in the cartridge include a plastic vial with a living hinge and cap and an optically clear liquid silicone rubber (LSR) plug at the bottom of the vial.
The thermoplastics needed to be gamma sterilizable and clear. They also needed to be free of inhibitors that could prevent an optimal seal with the LSR. The plastics also could not interfere with the microbiological growth that takes place during the test process. That's an interesting twist because many plastics aimed at the healthcare market today incorporate antimicrobial agents to kill germs.
|LSR is overmolded on polypropylene.|
The plastic selected was a modified polypropylene and the LSR was an optically clear 1003 grade silicone.
In a quality-enhancing move that also cut costs, a decision was made to overmold the polymers, a difficult process because of the difference in their molding temperatures.
"The two-shot overmolding process was quickly adopted since it allows new formulas to bond to different substrates (such as silicone and plastic) most cost-effectively," said Greg Roembke, president of Roembke Mfg. & Design.
Special attention was required for the thermoplastic unit to meet the temperatures required to achieve a good cycle time. This was also necessary to produce an effective seal that would not leak fluid between the two polymeric sections. ENDETEC specified that no chemical bonding agent could be used.
Roembke and Engel collaborated in the developing of a two-shot molding cell. Roembke developed a single drop cold deck mold with a standard LSR valve gate design featuring side injection. Back injection is used for the thermoplastic.
The production Engel machine is a standard two-component machine using the smallest diameter screw possible (12 mm) in the injection unit. The wide platen on the machine accommodated a special ejector pattern for the tool. Dedicated servo valves were used on both ejection units with valve controls used for optimal speeds and pressures.
"Modification was also done to accommodate the side-change injection of the screw and barrel on the
|A special assembly system was developed.|
Pro Systems (Churubusco, IN) engineered turnkey automation into the machine using a six-axis robotic system. One of the steps requires placement of a water-soluble pouch containing pre-measured amounts of growth media that support the enrichment of any target bacteria present in the sample for each water test cartridge.
The process development required extensive testing in Roembke's 3,600 sq. ft. Application Center, which has seven injection molding presses with 35 to 200 tons of clamping force. Prototype tools were modified for the plastic vial and LSR component to test the system. One press molded the plastic vials, which then were transferred to the second press to apply the LSR. The primary machine used was Engel's Victory 200H/80L/160 Combi, a 160-ton single-cavity machine with wide platens equipped with two injection units.
The primary injection unit was used for thermoplastics and the secondary was used for LSR.
"Through our extensive prototyping and testing, the system was proven-out and set up for future expansion," Romebke said. "The single-cavity tool can be easily expanded to a four-cavity tool as sales ramp up to anticipated quadruple volume."
According to ENDETEC's VP of Operations, Doug Wilton, "The world-wide market potential for this new water monitoring technology is simply huge. We're already selling systems in North America, Europe and Asia with additional markets under development."