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Horizontal Injection Molding Machines
Horizontal Injection Molding Machines
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Figure 1. Employee opening operator's gate.
Figure 1. Employee opening operator's gate.

Thermoplastic injection molding machines produce molded plastic parts by converting plastic pellets into molten material, injecting the molten plastic into a mold, and cooling the plastic material. The mold consists of two halves. One half is connected to a movable platen and the other is connected to a stationary platen. As the machine prepares to inject molten plastic into the mold, the platens close and press the mold halves tightly together. When the plastic is cooled, the movable platen retracts, and the solidified plastic parts are removed.

Operator Involvement

The operator may need to open the operator's gate and remove plastic parts from the mold. The operator may also be required to operate the control panel interface. Tasks associated with the injection molding process include:

Potential Hazards

  • Crushing injuries or amputations may occur if hands or limbs are placed between mold halves or other hazardous areas while machine cycles. This can occur if the operator or other person:

    • Reaches into the machine to loosen a part that is stuck (for example, while interlocks have been removed or bypassed).

    • Inadvertently or purposefully reaches around, under, or over guards into hazardous areas.

    • Operates a machine with missing or inoperable guards or interlocks.

    • Is not familiar with the equipment.

Possible Solutions

  • Ensure that an operator's (safety) gate is installed to block operator access to moving parts while the machine is in normal production. Use interlocks (mechanical, electrical, hydraulic) that prevent the mold from closing when the gate is open.

  • Do not remove, alter, or attempt to otherwise bypass a safety interlock.

  • Do not attempt to reach around, under, or over a guard. If a person standing on the floor can reach over the machine into the mold area, install a top guard that is fixed or interlocked.

  • Access the mold cavity via the operator's gate and do not remove a fixed guard during normal operation.

  • Provide training on the safety hazards and features of the injection molding machine for all employees who will operate or work with it.

  • Lockout/tagout the machine prior to servicing and maintenance work.

Figure 5. An employee follows lockout/tagout procedures for plastics machinery needing repair. Figure 6. An employee changes the mold of an injection molding machine. If exposed to potential injury from hazardous energy, follow the lockout/tagout procedure.

Potential Hazards

  • Electric shock, amputation, or crushing may result from a service or maintenance worker:

    • Removing guards, bypassing safeguards, and

    • Relying on interlocks rather than lockout/tagout procedures.

Possible Solutions

  • Follow lockout/tagout procedures during service or maintenance. Some machine guarding safety devices may be sufficient during normal operations, but may not be permitted to be used during servicing and maintenance work. Lockout/tagout must be performed if activities require the employee to:

    • Remove or bypass a guard or safety device, or

    • Place any part of the body into the mold area or an associated danger zone.

    NOTE: The lockout/tagout standard makes a limited exception for minor service activities that take place during normal production operations when they are routine, repetitive and which are integral to the use of the equipment for production, provided that the work is performed using alternative measures that provide effective employee protection.

Figure 7. A guard equipped with safety signs covers the barrel of the injection unit.

Potential Hazards:

  • Skin burns from contact with the heated barrel or burns from splatter of hot plastic and gases/vapors.

  • Hands or limbs caught in machine while loosening trapped materials at feed throat.

  • Slips, trips, and falls at material feed location.

Possible Solutions:

  • The injection unit and other accessible parts posing thermal hazards should be insulated or guarded. Place warning signs where hot parts are necessarily exposed.

  • Place a fixed guard (usually a grid) or a distance guard (usually the hopper) at the feed throat. Do not place your hand into the feed throat.

  • Wear appropriate personal protective equipment (PPE), such as a heat-resistant gloves, long-sleeved shirt and eye/face protection, when necessary.

  • Use a ladder, rolling stairs, platform, or other safe means to access the hopper or feed throat area. Do not climb on the machine.

  • Ensure that proper ventilation and exhaust systems are in place to help prevent inhalation of harmful gases and vapors.
  • Consult manufacturer's material safety data sheets (MSDS).
  • Wear heat-resistant personal protective equipment (PPE) to prevent burns from contact with hot surfaces or splatter of hot plastic and gases, when necessary.
  • Follow good housekeeping procedures and keep floors clean to prevent slips, trips, and falls due to spilled pellets on the work floor.
  • Apply engineering controls or hearing conservation programs as necessary to control noise. For more information, see OSHA's Occupational Noise Exposure Safety and Health Topics Page.