The injection molding machine gets all the attention. Visitors tour the plant and watch the machines cycle, mesmerized by the rhythm of molds opening and closing. Meanwhile, the dryer in the corner, the conveyor running overhead, and the chiller humming in the back room go unnoticed. Yet when production stops because moisture in the material caused splay defects, or when cycle times creep up because the cooling water temperature drifted, the real importance of auxiliary equipment becomes painfully clear.
A molding machine is the visible centerpiece of production, but it cannot function without the support systems that prepare material, control temperature, and handle finished parts. Auxiliary equipment represents a significant capital investment, typically 30 to 50 percent of the machine cost, and its proper selection, sizing, and maintenance determine whether the expensive machine in the middle of the cell runs efficiently or sits idle while someone troubleshoots preventable problems.
Material Drying Systems
Hygroscopic plastics absorb moisture from the atmosphere. Nylon, polycarbonate, PET, PBT, and ABS all require drying before processing. Running wet material produces defects ranging from cosmetic splay marks to structural weakness from hydrolytic degradation. No amount of process adjustment compensates for moisture in the material.
Desiccant dryers are the industry standard for hygroscopic materials. These systems pass heated air through a desiccant bed that removes moisture, then direct the dry air through a hopper containing the plastic pellets. The desiccant regenerates on a timed cycle, with dual beds allowing continuous operation. Dewpoint measurements indicate drying effectiveness, with targets typically around negative 40 degrees Fahrenheit for demanding materials like polycarbonate.
Hot air dryers work for non-hygroscopic materials that simply need to be warm and surface-dry. They lack desiccant beds and cannot achieve the low dewpoints required for moisture-sensitive resins. Using a hot air dryer on nylon or PC is a common mistake that produces immediate quality problems.
Compressed air dryers use the expansion of compressed air to achieve low dewpoints. They’re compact and suitable for smaller throughputs but have higher operating costs due to compressed air consumption.
Sizing a dryer involves matching airflow to throughput and ensuring adequate residence time in the hopper. Most materials require four hours of drying time at specified temperatures before processing. A dryer serving a machine consuming 100 pounds per hour needs a hopper holding at least 400 pounds to provide that four-hour residence time. Undersized hoppers are a common source of intermittent moisture problems that confuse troubleshooting efforts.
| Material | Drying Temperature | Minimum Time | Target Dewpoint |
|---|---|---|---|
| Nylon (PA6, PA66) | 175-185°F | 4-6 hours | -40°F |
| Polycarbonate | 250°F | 4 hours | -40°F |
| PET | 300-350°F | 4-6 hours | -40°F |
| ABS | 180°F | 2-4 hours | -20°F |
| PBT | 250°F | 4 hours | -40°F |
Monitoring systems on modern dryers track dewpoint, hopper temperature, and residence time. Data logging provides evidence for quality investigations when moisture-related defects appear. Without monitoring, troubleshooting moisture problems becomes guesswork.
Material Handling Systems
Moving plastic pellets from storage to machine hoppers seems straightforward until you consider the scale involved. A busy molding operation might process hundreds of thousands of pounds of material monthly across dozens of machines. Manual handling at this scale is impractical and introduces contamination risks.
Central conveying systems use vacuum to transport pellets from bulk storage through dedicated lines to machine hoppers. A central pump creates the vacuum, with automated sequencing directing material to machines as needed. These systems handle high throughput efficiently but require significant infrastructure investment: piping, pump stations, filter systems, and controls.
Machine-side loaders provide local vacuum conveying from boxes or drums to individual machine hoppers. They’re simpler and less expensive but require material handling to the machine location. For smaller operations or specialty materials used at single machines, they offer a practical solution.
Blending systems mix virgin material with regrind, color concentrates, or additives in controlled ratios. Gravimetric blenders measure by weight for precise ratios; volumetric blenders measure by volume and are less accurate but less expensive. Maintaining consistent blend ratios affects both material cost and part quality.
Material handling systems must prevent contamination, maintain material identity, and avoid degradation. Cross-contamination between materials causes serious quality problems, sometimes not detected until parts fail in the field. Color contamination from inadequate cleaning between material changes shows up immediately as rejected parts.
Line purging between material changes, filter maintenance, and grounding to prevent static buildup are essential practices. Neglected material handling systems gradually accumulate problems that manifest as inconsistent quality with no apparent cause.
Temperature Control Units
Mold temperature control is fundamental to part quality and cycle time. Water or oil circulates through channels in the mold, removing heat from the molten plastic and maintaining consistent mold surface temperature. Temperature control units (TCUs) heat or cool the circulating fluid to maintain setpoint.
Water-based TCUs handle temperatures up to about 300°F, suitable for most applications. They’re less expensive to operate and maintain than oil systems. Pressurized units extend the temperature range somewhat by preventing water from boiling.
Oil-based TCUs serve applications requiring higher mold temperatures, up to 600°F or more. They’re necessary for engineering resins that require elevated mold temperatures for proper crystallization or surface finish. Oil systems cost more, require more maintenance, and present safety considerations from hot oil handling.
Sizing temperature control units involves matching heating capacity to heat load at startup and cooling capacity to heat removal during steady-state operation. Undersized units struggle to maintain setpoint during production, causing mold temperature drift that shows up as inconsistent shrinkage and warpage.
Flow rate matters as much as temperature. Turbulent flow through mold cooling channels transfers heat more effectively than laminar flow. Monitoring flow rates at each circuit identifies restrictions from scale buildup or kinks in hoses before they affect part quality.
Common TCU problems include scale buildup in lines, pump wear reducing flow, and heater element failure. Preventive maintenance involving regular descaling, pump inspection, and heater testing prevents unexpected failures during production.
Chillers and Cooling Towers
Process cooling extends beyond individual mold TCUs to plant-wide systems that supply chilled water and reject heat from the building.
Central chillers produce chilled water, typically at 45 to 55°F, distributed throughout the plant. Sizing involves total heat load calculation from all connected equipment. Chillers are significant energy consumers, and their efficiency directly affects operating costs.
Portable chillers serve individual machines or small groups. They’re flexible and allow temperature control independent of plant systems, useful for specialty processes or when central capacity is limited.
Cooling towers reject heat from the chiller condensers or, in some plants, supply cooling water directly to molds. Tower water is typically warmer and less precisely controlled than chilled water, suitable for applications where tight temperature control is less critical.
Water treatment for cooling systems prevents scale, corrosion, and biological growth. Neglected water chemistry degrades heat transfer efficiency, damages equipment, and creates health risks from bacterial contamination. Most plants contract water treatment services to maintain proper chemistry.
System capacity should include margin for expansion and for unusually warm ambient conditions. A cooling system sized exactly for current load provides no headroom when production increases or when summer temperatures spike.
Granulators
Injection molding inherently produces scrap: runners, sprues, startup parts, and rejected production. Granulators reduce this material to pellet-sized pieces for reuse, turning waste into recovered value.
Beside-the-press granulators sit adjacent to molding machines and process runners and sprues immediately after each cycle. They offer convenience and immediate material recovery but generate noise and require floor space at each machine.
Central granulators serve multiple machines, with scrap collected and transported to a dedicated grinding area. They consolidate noise and dust in one location and can handle larger volumes, but require material handling infrastructure.
Blade maintenance determines regrind quality. Dull blades produce fines (dust-sized particles) and uneven pellet sizes that cause feed problems and quality issues. Sharp blades produce clean cuts and consistent regrind size. Blade inspection, sharpening, and replacement schedules are essential maintenance items.
Screen selection controls regrind particle size. Screens with holes matching virgin pellet size produce regrind that flows and feeds properly when blended with virgin material. Oversized or inconsistent regrind causes processing problems.
Granulator safety deserves special attention. These machines contain rapidly spinning blades with enough energy to cause severe injury. Interlocked guards, proper lockout procedures during cleaning and blade changes, and employee training prevent accidents.
Automation and Robotics
Automation removes human hands from repetitive tasks, improving consistency, reducing labor costs, and enabling operations during shifts without full staffing.
Part removal robots extract finished parts from the mold and place them on conveyors, in containers, or in downstream equipment. Three-axis Cartesian robots handle most applications; six-axis articulated robots provide flexibility for complex movements. Cycle time for robot operation adds directly to overall cycle time, so robot speed and efficiency matter for production rates.
Sprue pickers are simplified robots that remove only the runner and sprue, allowing parts to fall into bins below. They’re less expensive than full part-removal robots and suitable when part orientation doesn’t matter and drop damage isn’t a concern.
Insert loading systems place metal inserts, labels, or other components into the mold before each shot. They’re essential for overmolding applications and improve consistency compared to manual insert placement.
Automation payback depends on labor cost savings, quality improvements from consistency, and capacity gains from eliminating manual handling time. Simple payback calculations compare automation cost to labor savings, but total value includes quality and consistency benefits that are harder to quantify.
Integration between robots and molding machines requires communication interfaces for cycle coordination. Modern machines and robots communicate through standard protocols, but ensuring proper setup and verifying reliable handshaking deserves attention during installation.
The Systems Perspective
Auxiliary equipment functions as an integrated system supporting the molding machine. Each component must have adequate capacity, and capacities must match across the system.
A dryer undersized for the machine’s material consumption causes moisture problems regardless of how well the TCU, chiller, and robot perform. A cooling system at capacity can’t support additional machines even if material handling has excess capability. The system’s production capacity is limited by its weakest component.
Maintenance scheduling should coordinate across equipment. Material handling downtime for cleaning can align with dryer maintenance and cooling system service. Uncoordinated maintenance creates frequent short interruptions; coordinated maintenance minimizes total downtime.
Redundancy and backup plans prevent auxiliary equipment failures from stopping production. Critical systems like central chillers may justify backup capacity or emergency rental arrangements. Spare parts for frequently failing components, such as dryer heaters and TCU pump seals, should be stocked on-site.
The investment in auxiliary equipment supports every part produced over the life of the molding operation. Specifying appropriate equipment, maintaining it properly, and integrating it into a functional system separates efficient operations from those constantly fighting preventable problems.
Sources
- Rosato, Donald V. “Injection Molding Handbook.” Springer.
- Plastics Technology. “Auxiliary Equipment Guide.” https://www.ptonline.com/
- Conair Group. “Material Handling Systems.” https://www.conairgroup.com/
- Novatec. “Drying Technology.” https://www.novatec.com/
- Society of Plastics Engineers. “Injection Molding Division Technical Papers.”