Medical Molding

When it comes to healthcare, there is no room for error. Medical plastic parts are subject to the most stringent quality tests, from the development phase to high volume production. Medical products range from disposable packaging, syringes, petri dishes and test tubes to parts for sensoric and diagnostic equipment and plastic implants. There is a large variety of medical grade plastics, most of which are sensitive and can only be molded within a very specific processing window.

Rheo-Pro® hot runner systems are ideal for the production of medical parts since they cut production costs dramatically by eliminating cold runners, including related part handling and regrind material. Hot runners also keep the molding operation clean as the molding cells produce only parts.

Valve Gating

Valve gating is usually the first option to consider when molding medical parts. Valve gate systems improve part quality by delivering crisp, clean gate marks. For example, a PP container cap with a metal foil insert and an elastomere over-mold. The over molded elastomere film is a 0.3mm thick layer that is direct-valve-gated as a secondary shot with a volume equivalent to only one plastic pellet 10mg². Applications like this are possible because of the accuracy of advanced valve gate systems that can deliver the repeatability of shot volume (within the milligram tolerance range) and the quality of the gate vestige (± 0.05 mm pin position).

Valve gating reduces cycle time. It is often the preferred method for producing medical parts because a valve gate offers more controlled processing conditions than thermal gating or side gating. However, different applications sometimes require different solutions.

Thermal Gating

Thermal gating or hot tip gating offers a lesser investment in the mold compared to the cost of valve gating but hot tips have a tighter processing window and these molds are more sensitive to operate. The resulting gate vestige often becomes a critical element for medical parts because the gate is a micro-fracture of up to 1.0 mm diameter right on the part surface. These hot tip gate nozzles are only applicable where a gate vestige is permissible on the part and only small parts qualify for hot tip gates between 1 and 50 grams of weight depending on the material. This is certainly a point of specification prior to the hot runner design. Materials with a brittle fracture such a PMMA and PS should not be hot tip gated for medical parts whereas ductile fractures with PC, PP, PE are more suitable for hot tip gates especially when they can be sunken into a dimple in the part surface. With nozzles as small as 12 mm diameter.

Multi-tip Nozzles

Rheo-Pro® multi-tip nozzles such as the M05 and M05VG are compact and cost efficient. One nozzle with up to six tips can gate a cluster of parts. Pictured below is an X-manifold with four 6-fold multi-tip nozzles, representing a very compact 24-cavity mold. This mold operates with PSU (polysulfon) at 380˚C melt temperature and 180˚C mold temperature producing 20 mg medical parts at a 5 sec cycle time.

A 36-cavity mold for insulin syringe needle protector caps illustrates the compactness of mold design with multi-tip nozzles. This compact mold with 290 x 390 mm (11.5" x 15.5") has the capacity to reproduce 150 million parts per year without regrind. The hot runner performs maintenance free for several 10 million cycles. The gate vestige rests safely in a 0.6 mm deep dimple.

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		High Cavity Valve Gating Micro Molding Side Gating Specialty Gating Multi-tip Nozzles Thermal Gating

In this case, as with many applications, careful consideration has to be given for the calculation of the melt residence time in the barrel and melt channels. This is of particular importance for heat sensitive materials and additives such as color pigments, nucleators, clarifiers, lubricants, stabilizers and so on.

Ease of mold maintenance is important. Fast access to tips, heaters, thermocouples and gates is made possible by stripping the cavity plate onto the core side while the mod remains inside the machine.

Side Gating Solutions

The Rheo-Pro® SG Series nozzle is specifically engineered for high cavity molds that require multiple side (or edge) gating into the walls of the cavity. It is an ideal solution for long and tall tubular parts such as syringe barrels and medical applicators.

SG Series systems are easy to install. The unique nozzle design reduces the mold cost significantly in comparison to other more cumbersome side gating methods, such as disks, where the cavity inserts must shift towards the nozzle tip, creating an unnecessarily complicated hotrunner assembly.

Custom Engineered Tips

Standard nozzle tips are not always able to produce parts with difficult gating situations. Some plastic parts allow only side gating with edge gates or internal gating. Mold Hotrunner Solutions® offers custom gating solutions and custom gate or nozzle tip designs.

High Cavity Molding

High cavity hot runners are required for production volumes exceeding tens or even hundreds of millions of parts per year. A 32-cavity mold at a cycle time of 6 seconds can produce between 150 million to 200 million parts in a 24/7 operation. Mold down time is not an option for such a production. But when such a mold produces extremely thin wall, small parts in polycarbonate (PC) at an injection pressure of 2500 bar (35,000 psi) and the part weight is only 70 mg, then only the hotrunner with the best micro-nozzles can perform. Medical hot runner systems, especially, require absolute reliability, perfect functionality as well as a high degree of flexibility for special and innovative designs.