|
|
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.
|
|
|
Interactive Safety Tour |
Thermoforming
Machines
|
 |
 |
|
|
|
Figure 1. A typical roll-fed
thermoforming machine.
|
Figure 2. Process flow diagram for roll-fed thermorforming. |
|
|
|
The
hazards that may be associated with servicing and maintenance (lockout/tagout)
are not comprehensively addressed by this module. For additional
training materials on machine guarding and lockout/tagout issues
associated with thermoforming machines, see
Roll-fed and Inline Thermoforming Machine Safety Training Course.
|
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
|
Figure 3. Overhead hoist operated by pendent.
Figure 4. Overhead hoist operated by a pull chain.
Figure 5. Manually operated lifting device that can help
raise rolls of plastic and tooling off the floor. |
Additional Resources
-
OSHA Alliance
Program. Hoist Manufacturers Institute (2006).
- Hoist Operator’s Manual. HMI (2000). Also available as a 2.3MB
PDF,
61 pages.
- Hoist Inspection and
Hoist Maintenance Personnel Manual. HMI (2002). Also available as a 909KB
PDF,
81 pages.
- Recommended Practices for Hand Hoists. HMI (2006). Also available as a 56KB
PDF,
3 pages.
- Recommended Practices for Powered Hoists. HMI (2006). Also available as a 58KB
PDF,
3 pages.
|
|
|
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
|
Figure 6. Feed end - unwind stand from different angles.
Figure 7. Roll stand with roll
stock. Rotating shaft is properly nested in groove.
Figure 8. Roll-fed,
feed end - unwind stand with pinch points identified.
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
|
Figure 10. Top and bottom forming dye press components.
Figure 11. Fixed barrier guard
in place preventing access to moving parts.
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
|
Figure 13. 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.
|
Figure 15. Trim Station guarded by fixed barriers and interlocked gates to
prevent access to knife blades or moving machinery.
Figure 16. Ensure that adjustable guards are properly adjusted to
prevent access to knife blades.
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. |
|
|
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
|
Figure 17. Stacker. Operator stands on platform to
remove parts from basket.
 Figure
18.
Robot picker/stacker replaces employee exposure to moving machinery.
|
Figure 19. Parts stacker with adjustable guard and
pinch point identified.
 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
|
Figure 21. Steps and platforms with guardrails to provide appropriate
workstation height.
Figure 22. 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
|
Figure 24. Web roll being started.
Figure 25. Web roll nearly full with pinch point identified.
Figure 26. Employee with appropriate PPE (gloves, sleeves) removing full web roll.
|
Figure 27. Empty web winder 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.
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.
|
 Figure
29. Guillotine cutter.
Figure 30. Guarded guillotine cutter. |
|
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).
|
Figure 31. Web grinders.
 Figure
32. Web grinder with proximity guard identified.
|
|
Highlighted OSHA Standards
|
|
|
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
|
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
|
Figure 34. Side view of heating oven area with access doors (guards) open.
Figure 35. Thermal and crushing hazards between two oven heating surfaces.
Figure 36. Powered hoods are used to remove potentially irritating gases, vapors and smoke should a
burnout take place. |
|
|
|
|
|
Back to Top
