Keeping it clean

Cleanroom molding is essential for serving the medical segment, and various options exist for manufacturing anything from discrete components to complex assemblies in a pristine environment. So what cleanroom alternative should you choose? 
It very much depends on your application and business strategy.

What may appear to be the simplest solution to medical molding is to locate the entire machine in a cleanroom. This is best suited for molders that are operating several machines under cleanroom conditions and need to integrate large assembly systems into the cleanroom concept, according to Jochen Hirt, application department manager at Arburg (Shanghai) Co. However, this solution can only obtain ISO 7 standard at best, which is essentially equivalent to the Class 10,000 U.S. Federal standard typically required as a minimum for cleanroom molding. Good manufacturing practice (GMP) standards are generally also required for cleanroom molding, and these specify maximum bacterial count in addition to particle count. GMP Level C equates to ISO 7.

One issue with the fully integrated approach is, “If the cleanroom malfunctions and air quality is adversely affected, you have to shut down all your machines,” says Jack Liu, application engineering manager at Demag Plastics Machinery (Ningbo) Co. Ltd. A more flexible and lower-cost solution is to enclose only the mold space in a cleanroom environment by installing a laminar flow element on top of the machine’s clamping end. The clean air module is mounted on a traveling frame above the clamping unit, allowing easy mold installation from above.

In its simplest form, parts are molded in this mini-cleanroom area and dropped onto a covered conveyor that then transports them to a cleanroom attachment for robotic and/or manual assembly and packing. “Being much smaller, ISO 5 is attainable in this attachment,” says Liu.

With this modular clean air hood solution, the ambient air is drawn in via radial fans and clean air is produced via a pre-filter and a suspended matter filter (HEPA H14). An integrated ionization module produces ionized air, which ensures the neutralization of electrically charged components. This reduces electrostatic charging of the molded parts. Through the permanent air flow, a high level of air circulation is ensured within the clamping unit. The fan also creates an overpressure in the interior of the mold, which effectively prevents the penetration of particles from the ambient air.

Needless to say, for fragile parts that might be damaged by free-fall and a sorter flap, robotic takeout is essential. The cleanroom area must therefore be expanded to encompass the robot and conveyor placement area. Arburg’s solution here is a cleanroom production cell with its Multilift H horizontally operating robotic system.

KraussMaffei Technologies GmbH (Munich, Germany) has a different take on this option in that the robot accesses the mold space from an adjacent cleanroom. The overpressure in the white room causes the clean air to flow through the tunnel and flow out through the chute on the injection machine. The production area is isolated from the rest of the machine. This solution achieves ISO 6/7 standards.

Room in a room
KraussMaffei also offers a room-in-room solution whereby the clamping end of the machine protrudes into a sealed cleanroom. This option can cater to cleanliness up to the ISO 5 standard. For mold changing, service, and repairs, the machine is retracted on rails until the clamp is in the gray room area and the white room is completely sealed off by a second metal plate at the front of the clamp end.

This solution was adopted by Rexam Pharma GmbH (Neuenburg, Germany) for molding vials from cyclic olefin copolymer (COC) with TPE closures for injectables. The ready-to-fill vials leave the cleanroom closed and packed. Thomas Hörl, who oversees product and technology management at KraussMaffei, notes that when molding takes place under GMP Class B (ISO 5) conditions, the surrounding gray room area should be at least GMP Class C (ISO 7). Production in a Class 5 cleanroom makes post-mold cleaning or sterilization unnecessary in many applications, although it may be stipulated by end users.

Demag’s decentralized solution for incorporating an injection machine plus automation into a cleanroom is dubbed a cleanroom cabinet with roof construction. Takeout and assembly/packing are carried out under an ISO 7 environment. The machine may also be enclosed in the cabinet in its entirety.

Using a decentralized approach, Arburg’s Hirt says that newcomers to cleanroom molding can benefit in that they can start with just one machine and add cleanroom capacity as they go. “If individual machines are temporarily not required for cleanroom production, they may be undocked to produce standard parts,” he adds.

Cleanroom-customized machines
Workers are the main source of particulate contaminants, accounting for around 40% of emissions in a cleanroom, and removing them from the equation, or at least minimizing their presence, goes a long way toward eliminating particles. The next largest source on the list is the injection machine itself, and here, various techniques exist to minimize contamination. While Demag’s Liu says that fully hydraulic machines are capable of achieving ISO 7 standards when contained in cleanrooms, all-electric machines can operate at up to ISO 5 standards if water-cooled.

“Fan cooling is not as good for cleanroom environments, although ISO 6 is technically achievable,” says Liu, who adds that direct-drive is also preferable over belt-drive. Antistat metal coatings and PVC coatings for mobile elements are also employed, while use of perforated metal sheet minimizes air turbulence in the mold space.

“During production under cleanroom conditions, it is very important that the [hydraulic] machine can be cleaned easily,” says Arburg’s Hirt. “For this purpose, the distributor manifolds of the hydraulic circuit can be contained in a powder-coated sheet metal housing located at the machine base. This allows the injection molding machine to be kept clean much more effectively.” Further, raising the machine by 100 mm using anti-vibration pads makes cleaning under the machine considerably easier.

Closer to the tool, multiple cooling circuits can be routed directly to the fixed or moving mold platen for the mold cooling. “This tidy routing prevents unnecessary trailing of the hoses,” says Hirt. Powder coating is also used throughout Arburg machines for wear and scratch resistance. Hirt insists that a properly configured hydraulic machine can run in a cleanroom equally as well as a hybrid or all-electric machine.

KraussMaffei recommends its EX Series all-electric machines for medical molding applications. The Z-toggle has only eight pivot points, all of which are lubricated with completely encapsulated circulating oil. All drives are water-cooled, and plasticating and injection are driven by two coupled direct drives. —Stephen Moore