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Machine Guarding
Plastics Machinery

 Interactive Safety Tour
Thermoforming Tour
Thermoforming Machines
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A typical roll-fed thermoforming machine
Figure 1. A typical roll-fed thermoforming machine.
 
Process flow diagram for roll-fed thermorforming.
Figure 2. Process flow diagram for roll-fed thermorforming.
Thermoforming is a manufacturing process using thermoplastic sheet or film. Employees load the roll of plastic sheet or film on the roll-fed thermoformer roll stand and then thread it through the end feed rollers. When the machine is activated, the plastic sheet or film is advanced into the oven for heating and then into the form station where the parts are formed and then advanced to the trim station.

In general, once the equipment is up and running in the automatic mode there is little employee involvement, other than starting new rolls (roll fed thermoforming), inspecting product, packaging and removing scrap materials, unless or until something goes wrong with the equipment or process that requires employees to take corrective action. During the forming and trimming production process, employees are not exposed to the hazardous areas of the machinery unless they reach into/over these guarded areas. Once the parts are formed and trimmed, they advance to the stacker that pushes the parts upward through the plastic web. The employee visually checks the parts for defects and packs them into cartons for shipment.

The plastic web is then automatically wound on the scrap rewinder or it can be trimmed and fed into a tub, conveyor, or directly in to a grinder. If the scrap is not fed directly into a grinder, it is typically baled and then manually fed into a web grinder/granulator.

Thermoforming equipment varies in complexity, size and cost from manufacturer to manufacturer, and ranges from simple inexpensive semi automated machines to highly automated systems. There are two types of thermoforming referred to in this module:
  • In-Line Thermoforming where a sheet of plastic is fed from an extruder to an oven by use of a guide rail and pin system. (Hazards that may be associated with the extrusion process are not addressed in this module.)
     
  • Roll-Fed Thermoforming (Figure 1) where a sheet of plastic is fed from a roll into the oven.
The following illustrate the areas where potential hazards may be found and possible solutions may be implemented when using thermoforming machines. The hazards that may be associated with servicing and maintenance (lockout/tagout) are not comprehensively addressed by this module.


Setup


Roll Handling
Roll handling may be a dangerous operation if performed with the wrong tools and/or equipment. Most injuries occur while employees are loading roll stock that may weigh from hundreds to thousands of pounds. The use of overhead material handling equipment is essential to load rolls of plastic on roll-fed thermoformers (Figure 3 and 4). In addition to loading rolls of plastic, form station tools are commonly installed and removed with the use of overhead hoists and trolleys. Improper use of overhead material handling equipment may result in injury to employees.

Potential Hazards
  • Falling rolls or equipment.
     
  • Exceeding the lifting capacity of all material handling equipment, including slings.
     
  • Mechanical failures of material handling equipment.
     
  • Pinch points between roll or tool and thermoformer frame.
     
  • Struck-by material or tool moving on the trolley.
Possible Solutions
  • Properly train employees to use and maintain material handling equipment.
     
  • Do not exceed the capacity of material handling equipment.
     
  • Do not work under suspended loads.
     
  • Properly maintain and inspect material handling equipment. Maintenance and inspection procedures need to be established in accordance with the manufacturer's recommendations.
     
  • Use lifting devices to help raise rolls of plastic and tooling off the floor (Figure 5).
Highlighted OSHA Standards Additional Resources
Overhead hoist operated by pendent.
Figure 3. Overhead hoist operated by pendent.

Overhead hoist operated by a pull chain.
Figure 4. Overhead hoist operated by a pull chain.

Manually operated lifting device that can help raise rolls of plastic and tooling off the floor.
Figure 5. Manually operated lifting device that can help raise rolls of plastic and tooling off the floor.


Feed End Handling
Rolls that have been loaded on the roll stand are threaded by an employee to the machine through end-feed rollers (also called the thread-up process). End-feed rollers are guarded or opened to avoid a wide range of injuries (Figure 6). There are multiple pinch points on the roll-fed feed-end unwind stand (Figure 8). Employees may be exposed to crushing, amputation, degloving, or scalping injuries that occur from hazards created by the movement of machine parts, and/or roll stock.

Potential Hazards
  • Crushing, pinching, amputation or degloving injuries may occur if hands or limbs are placed in feed mechanisms while the machine cycles (Figure 7).

  • Caught in moving machinery when loose clothing, hair or jewelry is caught by and pulled into the hazard area (i.e., guide rail and pin system or nip points).
     
  • Crushing, or pinching may occur if hands or fingers are caught under a rotating shaft that is not nested properly in groove (Figure 9).
Possible Solutions
  • Provide guarding solutions for the multiple pinch points (Figure 8) at the unwind stand. These may include:

    • Fixed barrier guards that require tools for removal.

    • Interlocked, moveable guards.
  • Use presence-sensing devices to stop machinery motion when employees enter hazardous areas.
     
  • Ensure rotating shaft is nested properly in its groove (Figure 9).
     
  • Ensure rotating shaft is properly guarded (fixed cap) or barricade area to prevent access.
Highlighted OSHA Standards  
Feed end - unwind stand from different angles.
Figure 6. Feed end - unwind stand from different angles.

Roll stand with roll stock. Rotating shaft is properly nested in groove.
Figure 7. Roll stand with roll stock. Rotating shaft is properly nested in groove.
 
Roll-Fed, Feed End - Unwind Stand with pinch points identified.
Figure 8. Roll-fed, feed end - unwind stand with pinch points identified.
 
Rotating shaft on unwind stand with arrows indicating nip points.
Figure 9. Rotating shaft on unwind stand with arrows indicating nip points.



Production


Form Station
A typical form station has the mold mounted on one platen and the pressure box mounted on the other. Vacuum holes in the mold and air pressure from the pressure box are used to produce highly defined plastic parts. The form station is often air operated. The toggle system has a flow control valve to adjust the speed at which they open or close and is used to extend and retract the forming station.

During the forming and trimming process, employees are not exposed to the hazardous areas of the machinery unless they reach into/over the guarded areas.
 
Potential Hazards
  • Hot surfaces that may cause burns.
     
  • Gases and vapors emitted from decomposing plastic.

  • Exposed electric wiring on adjacent heating oven components that may cause electric shocks.

  • Crushing, pinching, amputation or degloving injuries caused by moving machine (Figure 10).
Possible Solutions
  • Use guarding to prevent employee access to hazardous areas including:

    • Fixed barrier guards that require tools for removal (Figure 11).

    • Interlocked, moveable guards (Figure 12).
  • Use presence-sensing devices to stop machinery motion when employees enter hazardous areas.
     
  • Use locking, blocking, pinning and jacks to prevent release of stored energy.
     
  • Use appropriate personal protective equipment (PPE) as determined by the employer and noted in the work instructions.
Highlighted OSHA Standards
Top and bottom forming dye press components.
Figure 10. Top and bottom forming dye press components.
 
 Fixed barrier guard in place preventing access to moving parts.
Figure 11. Fixed barrier guard in place preventing access to moving parts.

Interlock guard is open preventing movement of machinery.
Figure 12. Interlocked guard is open preventing movement of machinery.


Trim Station
The trim station is often air operated and contains the cutting assembly. The cutting assembly on the trim station uses hydraulic pressure to finish the die cutting process. A toggle system is used to extend and retract the trim die. During the forming and trimming process, employees are not exposed to the hazardous areas of the machinery unless they reach into/over the guarded areas.

Potential Hazards
  • Crushing injuries or amputations may occur if hands or limbs are placed beneath the blades or between the molds or other hazardous areas while the machine cycles (Figure 13).

  • Cuts due to contact with sharp edges and blades (Figure 14).
     
  • Contact with live electric circuits that may cause electric shocks (Figure 14).
     
  • Burns caused by heated knife blade (Figure 14).
     
  • Contact with chains causing employee to be caught in machine.

  • Excessive noise level.
Possible Solutions
  • Follow lockout/tagout procedures during servicing, cleaning and other maintenance tasks.
     
  • Use proper tools and appropriate personal protective equipment (PPE) during servicing, cleaning and maintenance.
     
  • Use fixed barrier guards, interlocked gates, or adjustable barrier guards that are properly adjusted to prevent access (Figure 15 and 16).
     
  • Guard chains to prevent access (Figure 17).
Highlighted OSHA Standards  

Knife blade, live parts and hot surfaces may cause lacerations, crushing, electrical shock and burn injuries.
Figure 13. Knife blade, live parts and hot surfaces may cause lacerations, crushing, electrical shock and burn injuries.

Knife blade, live parts and hot surfaces may cause lacerations, crushing, electrical shock and burn injuries.
Figure 14. Knife blade, live parts and hot surfaces may cause lacerations, crushing, electrical shock and burn injuries.
 

Trim Station guarded by fixed barriers and interlocked gates to prevent access to knife blades or moving machinery. Figure 15. Trim Station guarded by fixed barriers and interlocked gates to prevent access to knife blades or moving machinery.
 
Ensure adjustable guards are properly adjusted to prevent access to knife blades.
Figure 16. Ensure that adjustable guards are properly adjusted to prevent access to knife blades.

Guard chain rails to prevent access. For illustrative purposes only, the guard has been removed to better see the hazard associated with the pins on the spiked chain and sprocket mechanism used to feed the plastic roll stock through the different stations of the thermoforming machine.
Figure 17. Guard chain rails to prevent access. For illustrative purposes only, the guard has been removed to better see the hazard associated with the pins on the spiked chain and sprocket mechanism used to feed the plastic roll stock through the different stations of the thermoforming machine.


Production - Pick End Process

Stacker
The stacker is a bottom tool that pushes the part upward through the web into a magazine for easy counting and removal. The tooling for the stacker is usually made from wood or aluminum and the operation can be automatically performed by a robotic process. Once the parts are formed and trimmed, they advance to the stacker which pushes the parts upward through the plastic web. The employees will then visually check the parts for defects and pack them into cartons for shipment.
 
Potential Hazards
  • Crushing injuries and amputations may occur if hands or limbs are placed into hazardous areas (Figure 17).

  • Struck-by moving machine parts, including robots (Figure 18).
     
  • Falls from unguarded platforms.
Possible Solutions
  • Install a top fixed guard on low-profile machines to prevent reaching in from the top.

  • Position adjustable guard to prevent access to discharge parts area (Figure 19).
     
  • Position operator workstation to prevent access to hazardous areas of machine.
     
  • Guard robots and other automation to prevent entering or reaching into their space during operation (Figure 20).
     
  • Install guardrail on platform.
Highlighted OSHA Standards
Stacker. Operator stands on platform to remove parts from basket.
Figure 17. Stacker. Operator stands on platform to remove parts from basket.
 
Robot picker/stacker replaces employee exposure to moving machinery. Figure 18. Robot picker/stacker replaces employee exposure to moving machinery.
  
Parts stacker with adjustable guard and pinch point identified Figure 19. Parts stacker with adjustable guard and pinch point identified.
 
 
Robot pictured with guards open. Figure 20. Robot pictured with guards open.


Manual Packing and Inspecting
Parts are visually checked for defects, counted, and packed into corrugated cartons. Due to machine configuration, platforms and/or steps are used to allow access to work areas. Work platforms may not be provided by the machinery manufacturer; however they may be fabricated by the end user.  It is important to provide an even work surface at an appropriate work height for the employee in order to prevent injury.
 

Potential Hazards
  • Falls from unguarded platforms.
     
  • Slips caused by slippery surfaces.

  • Trips due to contact with steps, packing material or auxiliary equipment.
     
  • Lacerations due to contact with sharp objects.

  • Injury to back and shoulders due to awkward body positions.
Possible Solutions
  • Use non-slip working surfaces and/or footwear.
     
  • Install guardrails whenever possible, at platform heights 4 feet or more above the adjacent floor or when adjacent to dangerous equipment.
     
  • Provide guardrails.
     
  • Secure steps and/or platforms to prevent movement.
     
  • Use uniform step size (slope).

  • Use stable chairs.

  • Encourage employee job rotation between pick end stations.
     
  • Provide steps and platforms with appropriate workstation height (Figures 21, 22, and 23).
     
  • Use appropriate personal protective equipment (PPE), such as gloves.
Highlighted OSHA Standards
Steps and platforms with guard rails to provide appropriate workstation height.
Figure 21. Steps and platforms with guardrails to provide appropriate workstation height.
 
Open platforms that are built up in between thermoformers to get personnel up to a proper work height.
Figure 22. Open platforms that are built up
in between thermoformers to get personnel
up to a proper work height.
 
Open platforms that are built up in between thermoformers to get personnel up to a proper work height.
Figure 23. Open platforms that are built up in between thermoformers to get personnel up to a proper work height.


Scrap Rewinder
The remaining skeletal trim scrap (Figure 24) is often rewound and collected for baling or grinding material off-line. The employee manually feeds the scrap into the rewinder (Figure 27 and 28), and removes the bale of material when the rewinder is full.

Potential Hazards
  • Pinch points caused by moving parts (Figure 25).

  • Awkward postures due to bending or reaching while pulling to remove roll.

  • Lacerations due to contact with sharp material or nips in plastic edges from pin chain.
Possible Solutions
  • Reposition the plastic scrap rewinder.
     
  • Use appropriate personal protective equipment (PPE), such as gloves and sleeves to prevent cuts from material nips when removing full rolls (Figure 26).

  • Use retractable knife or scissors to cut plastic webbing prior to removal.
Highlighted OSHA Standards

 
Web roll being started.
Figure 24. Web roll being started.

Web roll nearly full with pinch point identified.
Figure 25. Web roll nearly full with pinch point identified.

Employee with appropriate PPE (gloves, sleeves) removing full web roll.
Figure 26. Employee with appropriate PPE (gloves, sleeves) removing full web roll.
 
Empty web winder prior to starting the web roll, or following removal of full web roll.
Figure 27. Empty web winder prior to starting
the web roll, or following removal of full web roll.
Empty web roll prior to starting the web roll, or following removal of full web roll.
Figure 28. Empty web roll prior to starting the web roll, or following removal of full web roll.


Guillotine Cutter
A Guillotine Cutter (Figure 29) is often utilized to cut the skeletal trim scrap into sheets for easy collection and recycling, especially when the material is too thick to rewind. During the trimming process, employees are not exposed to the hazardous areas of the machinery unless they reach into/over these guarded areas.

Guillotine cutter. Figure 29. Guillotine cutter.
 
Guarded guillotine cutter.
Figure 30. Guarded guillotine cutter.
Potential Hazards
  • Nip points caused by moving machinery.

  • Crushing injuries, lacerations or amputations may occur if hands or limbs are placed beneath the knife blade.

  • Dust exposure from plastic dust created during the trimming process.
Possible Solutions
  • Install safeguarding such as barriers, light curtains and safety mats on all hazardous moving machine parts (Figure 30).

  • Provide guarding to prevent access to point of operation.
     
  • Use ventilation system to remove dust from work area.
Highlighted OSHA Standards


Web Grinders
Web grinders (granulators) (Figure 31) are a common way to dispose of web trim. Plastic scrap from the scrap rewinder is typically baled and then manually fed into a web grinder/granulator, where razor-sharp knives cut the plastic into small pieces to be recycled later. When grinding scrap roll stock, the grinder tends to pull the webbing into the grinder at a high rate.

Potential Hazards
  • Crushing injuries, lacerations and amputations due to direct access to the cutting knives, both rotary and stationery. Contact may occur if employees reach into the granulator.
Possible Solutions
  • Use energy control procedures to clean and inspect knives during changeovers of material type or material color.
     
  • Train employees to properly feed scrap roll stock into the grinder.

  • Manually turn rotor or flywheel to reposition machine parts that need cleaning. Apply energy control procedures before an employee performs any cleaning in order to prevent injuries, such as cuts and amputations.
     
  • Install safeguarding such as barriers, light curtains and safety mats on machinery to protect employees from all hazardous moving machine parts.
     
  • Provide anti-kickback flaps in feed throat.
     
  • Provide proximity guarding to prevent access from feed chute to rotating knives (Figure 32).
Highlighted OSHA Standards
Web grinders.
Figure 31. Web grinders.
 
 Web grinder with proximity guard identified. Figure 32. Web grinder with proximity guard identified.



Chain Rail
The chain rails contain a horizontally advancing, spiked chain and sprocket system. The chain spikes pierce the plastic sheet being fed into the machine. The chain draws the sheet through the oven, form station and trim station. Properly guarded chain rails prevent employee access to moving machinery.
 
Potential Hazards
  • Caught in unguarded, moving chains and sprockets, which may result in punctures, lacerations, or amputations.
Possible Solutions
  • Guard chain to prevent access (Figure 33).
     
  • Utilize lockout/tagout procedures.
     
  • Avoid loose clothing and jewelry; confine long hair.
Highlighted OSHA Standards
Guard chain rail to prevent access. For illustrative purposes only, the guard has been removed to better see the hazard associated with the pins on the spiked chain and sprocket mechanism used to feed the plastic roll stock through the different stations of the thermoforming machine.
Figure 33. Guard chain rail to prevent access. For illustrative purposes only, the guard has been removed to better see the hazard associated with the pins on the spiked chain and sprocket mechanism used to feed the plastic roll stock through the different stations of the thermoforming machine.


Heating Oven
There are five types of heaters commonly used on thermoforming machines: rod, ceramic, infrared, quartz and gas catalytic. They are setup in zones within the oven (Figure 34) for the gradual heating of materials. If the material is heated too fast, it will sag on the lower heaters and cause a burnout. During the forming process, employees are not exposed to the hazardous area of the machinery unless they reach into/over the guarded areas.

Potential Hazards
  • Burns caused by hot surfaces.
     
  • Gases and vapors emitted from plastic decomposition may be irritating to eyes and respiratory tract if employees are exposed.
     
  • Exposed electric wiring on heating elements that may cause electric shocks.
     
  • Crushing and pinch points caused by moving machine parts (Figure 35).
Possible Solutions
  • Follow lockout/tagout procedures during servicing, cleaning and other maintenance activities.

  • Provide adequate ventilation (Figure 36). Ventilation hoods are used to remove potentially irritating gases, vapors and smoke should a burnout take place.

  • Use proper tools to conduct servicing, cleaning and other maintenance tasks.
     
  • Use appropriate personal protective equipment (PPE) as determined by the employer and noted in the work instructions.

  • Use access doors and other guards to eliminate exposure to hazardous areas.
Highlighted OSHA Standards
Side view of heating oven area with access doors (guards) open.
Figure 34. Side view of heating oven area with access doors (guards) open.
 
Thermal and crushing hazards between two oven heating surfaces.
Figure 35. Thermal and crushing hazards between two oven heating surfaces.

Powered hoods are used to remove potentially irritating gases, vapors and smoke should a burnout take place.
Figure 36. Powered hoods are used to remove potentially irritating gases, vapors and smoke should a burnout take place.



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