Modular mold design for one of lightest vaccination syringes in the world
The worldwide demand for disposable vaccination syringes is constantly increasing. Werkzeugbau Ruhla GmbH, one of the leading suppliers of modular mold solutions for the medical industry, realized two high-cavity molds for the production of a three-part safety vaccination syringe in a short time with EWIKON as a partner in the hot runner sector.
Disposable vaccination syringes for standard vaccinations are needed in billions of units. The start of the vaccination campaigns against COVID-19 also has demand increasing additionally, so that production capacities must be further expanded worldwide. Injection molds that are available in short lead time and can produce vaccination syringes quickly, efficiently and with minimal material usage are therefore in demand.
In this context, Werkzeugbau Ruhla GmbH in Seebach, Thuringia, Germany, designed two 64-cavity full hot runner molds for the production of both the barrel and the piston of a three-part 0.5 ml safety vaccination syringe. The parts were made of PP and were for use in primary vaccinations. For many countries, the additional strict specifications of the World Health Organization (WHO) apply to vaccination syringes, in these cases vaccination syringes must be designed in such a way that multiple use are not possible.
As a specialist for medical precision mold solutions, Ruhla consistently relies on a modular concept with a high degree of standardization in mold construction. The design was developed and perfected in a long-standing partnership with their hot runner supplier, EWIKON. Its focus is on a compact and weight-optimized mold design with efficient cooling and high ease of maintenance, allowing for use in the smallest possible machine sizes. On the hot runner side, the mold relies on lateral direct gating with EWIKON’s high-performance HPS III-MH multi-tip nozzle concepts, which guarantee the high gating quality required for medical components.
Production of the syringe barrels utilize a radial nozzle specially developed for the syringe production. The nozzle features extended tip inserts and a particularly slim nozzle body whose length can be flexibly adapted to accommodate a wide variety of different part lengths.
"With this nozzle version, there is enough installation space between the nozzle body and the article contour to provide our mold inserts with a surrounding cavity cooling," explained Ruhla Managing Director Udo Köllner. "This design is standard for all our syringe molds and — in combination with inner cores that are also cooled — allows very short cycle times. The design of the mold inserts also makes them very easy to replace."
Production of the syringe plungers uses the linear version of the nozzle with a rectangle body installed in a row within the mold.
All mold solutions from Ruhla are developed with special attention to a high degree of maintainability, facilitating routine maintenance work even when used worldwide. An important contribution to maintainability is made by the EWIKON tip exchange concept, which enables the tip inserts to be easily replaced on the machine without having to dismantle the mold.
"In addition, there is the modular design, which integrates the nozzles including the complete wiring into a separate mold plate, which can simply be pulled off in case of a nozzle exchange", Köllner pointed out. "This makes the nozzle easily accessible and it can be dismantled in a particularly time-saving manner. Again, EWIKON supports us perfectly with a corresponding design of the wiring boxes with special plug-in connections."
The article design for both components of the syringe was optimized in close cooperation between Ruhla and the end customer. This resulted in the greatest possible material savings through reduced wall thickness and length.
"With a weight of only 1.1 g for the syringe barrel and 0.35 g for the plunger, we were able to save 25% of material compared to conventional vaccination syringes of the same size," said Ruhla Managing Director Lena Lüneburger, "which means we have one of the lightest syringes currently available on the market."
EWIKON provided support with part filling studies as well as with extensive calculations of pressure and shear in the hot runner system to ensure efficient mass production with short cycle times.
Two circular recesses are integrated into the wall of the syringe barrel to form defined locking positions for the plunger. When the syringe is drawn up, the plunger locks into the rear position when the filling volume of 0.5 ml is reached. The front locking position is reached once the injection of the vaccination dose is complete. If an attempt is made to fill the syringe a second time, the plunger will tear off at two defined predetermined breaking points rendering the syringe unusable. The syringe plunger was also consistently designed for low weight and maximum material savings by using a three-rib design. Additionally, the design of the three-part vaccination syringe requires no slide mechanism during demolding thus simplifying the mold construction considerably.
Despite the extremely high numbers of cavities, a very compact mold design could be realized. In both molds, eight nozzles are installed in either radial or linear version in two vertical rows of four. In the 446 x 596 mm syringe barrel mold, eight parts are arranged in a circle around each nozzle. The gating is done with heat-conductive tips angled at 60 degrees on the side wall of the cylinder close to the bearing of the inner core, in order to minimize core displacement.
In the syringe plunger mold, eight parts per nozzle are placed in two rows of four on both sides of the rectangular nozzle body. The plunger is gated on the grip plate. The mold dimensions are 546 x 596 mm. The hot runner technology for both molds was supplied by EWIKON as a complete hot half with integrated electrical wiring and connection technology and completed at Ruhla with the contour plates and the ejector side. Ruhla was able to realize the entire project from receipt of order, to pre-production testing in its own technical center, to delivery to the customer with a very short lead time of only 16 weeks. This was due to the high level of standardization in conjunction with modern production technology, including a fully automated production cell for electrodes. In addition, the expectations of a cycle time of approximately 10 s were fully met.
The delivery comes with a comprehensive service package, that not only includes the most common spare parts and a detailed operator's manual, but also detailed disassembly and assembly videos for the most important maintenance work. The overall concept proves to be convincing with another mold for the same syringe size already on order by an Asian customer and a 0.3 ml version, the common COVID-19 vaccination dose, is already in the works.
"This is where the advantages of our modular concept become apparent," said Lüneburger, "because even the smaller version can be realized quickly and easily by simply moving one of the recesses in the syringe barrel."
For more information, visit ewikonusa.com.