In brief
On an extrusion line, the hazard changes along the line: the rotating screw at the feed hopper, hot melt and pressure at the head and die, entrapment at the haul-off and winder, and the granulator blades on pelletising lines. Most accidents happen not during production but during a "quick intervention". Guarding, interlocking and energy isolation rules should be written separately for each zone, and head opening and blade cleaning should be tied to instructions.
Extruder safety: reading the line zone by zone
Extruder safety is the safety not of a single machine but of a line of machines in series. Raw material enters through the feed hopper, is melted by a screw rotating inside a heated barrel and is forced under pressure through the head and die. Then, via the cooling bath, haul-off, cutter or winder, the product becomes pipe, profile, sheet, film or pellets. On recycling and compounding lines, a granulator is added at the start of the line and a pelletiser at the end.
In plants in Bursa and the surrounding area supplying plastic products to the automotive supply industry, construction and packaging, these lines usually run continuously for long periods. Accidents also mostly happen not during production but during intervention: pushing material bridged in the hopper, pulling melt hanging from the die, straightening a profile slipping in the haul-off, cleaning the granulator by hand. The risk assessment should therefore divide the line into zones and deal with the intervention work in each zone separately.
| Zone | Main hazard | Key measure |
|---|---|---|
| Feed hopper and throat | Rotating screw, dosing unit, dust | Fixed grille, hopper opening from which the screw cannot be reached, interlocked lid |
| Barrel and heater bands | Hot surfaces, electricity | Heat-insulated cover, warning sign, closed junction boxes |
| Head, screen changer and die | Hot melt, pressurised ejection | Pressure gauge and limiter, head opening instruction, face shield |
| Cooling bath | Slips, water and electricity | Floor drainage, non-slip surface, residual current protection |
| Haul-off (caterpillar or belt) | Entrapment, drawing-in | Enclosed guard, interlocked cover, emergency stop |
| Cutter or saw | Cuts | Enclosed cutting unit, blade that stops when the cover is opened |
| Winder | Entanglement, drawing-in | Guard preventing access to the rotating reel |
| Granulator and pelletiser | Access to blades, noise, dust | Long feed chute, cover that does not open until the rotor has stopped |
The legal framework is Annex I of the Regulation on Health and Safety Requirements for the Use of Work Equipment. Where there is a risk of contact with moving parts, it requires guards that prevent access to the danger zone (2.8), measures that prevent approach to or contact with parts at high temperature (2.10), and maintenance to be carried out with the equipment switched off, the energy supply disconnected and all movement stopped (2.13). Guards must be such that they cannot easily be removed or defeated (2.8.1).
The feed hopper and dosing
At the bottom of the feed hopper, in the throat area, the screw rotates. When someone intervenes in the hopper by hand or with a rod, the hand, glove or rod can be drawn into the screw. There must be a fixed grille at the hopper opening, and this grille must not be removed "so the material flows faster". If material often bridges, the solution is not pushing it by hand but technical arrangements such as drying, a vibrator or an agitator.
On lines with vacuum loaders and dosing units, filling and cleaning done by climbing on top of the hoppers also bring a risk of working at height. Determine the need for platforms, ladders and guardrails according to how often this work is done. For dust released when emptying masterbatch and additive powders, local exhaust ventilation and respiratory protection are assessed.
The heater bands and temperature sensors (thermocouples) along the barrel are a second risk group. The junction boxes of heater bands must not be left open, and cables must be routed so they do not touch hot surfaces. Heater bands or sensors are not changed before the barrel has cooled and the energy has been isolated. The insulating cover on the barrel must not be a surface the operator leans on or leaves tools on while working.
In the cooling bath and vacuum calibrator section, the floor is constantly wet. Edges that reduce splashing and overflow, regularly emptied drainage and a non-slip floor are needed, as is residual current protection for the bath pumps and electrical connections.
The extrusion head and die: burns and pressurised melt
The head and die area is the hottest point on the line. Extrusion head burns happen in two ways: contact with a hot metal surface and molten plastic sticking to the skin. Because the melt sticks to the skin, the burn deepens; in first aid, the burned area is cooled with plenty of water and the stuck plastic is not forcibly pulled off. For burn supplies in the cabinet, see our article on the first aid cabinet.
A less well known but more serious hazard is the ejection of melt under pressure. Pressure can build up in front of the head because of frozen material in the barrel, a blocked screen or a cold start. If the head or screen changer is opened in this situation, melt and gas suddenly escape. Measures:
- The gauge showing head pressure and the limiter that stops the screw on overpressure must be in working order and not bypassed.
- The screw must not be started before the barrel heaters have reached their set point.
- Nobody should stand directly in front of the die when the head is opened; the operator should use a face shield, heat-resistant gloves and long-sleeved clothing.
- Overheating materials such as PVC can release irritant gases; local exhaust ventilation should be considered at the head area.
Entrapment at the haul-off, cutter and winder
The haul-off unit pulls the product at a constant speed between two caterpillars or belts. The gap between the caterpillars is exactly where hand and finger entrapment will happen. When a profile slips or the product is being threaded through the line for the first time, the operator tends to put a hand into this area. The haul-off should be inside an enclosed guard, movement should stop when the cover is opened, and a low-speed hold-to-run control should be preferred for initial threading.
At the winder, the hazard is entanglement. When film, cable or hose is being wound, the rotating reel can catch a glove, the end of a garment or a wrist. Reel changes and end threading are done with the winder stopped; nobody works in this section with loose clothing, jewellery or untied long hair. On saw or guillotine cutters, the blade must stop when the cutting unit cover is opened. Chips and flash at the cutter are removed not by hand but with a brush or vacuum.
The pelletising line and the granulator
A plastic granulator reduces scrap parts and production waste with rotating blades. Accidents usually happen when pushing a jammed part by hand, opening the cover before the rotor has fully stopped, and during blade cleaning. The rotor keeps turning for a while after the energy is cut; the cover lock must not open until the rotor has stopped. The feed chute must be long enough and shaped so that the hand cannot reach the blades, and a push stick must be used for jammed parts.
On a pelletising line, the molten strands coming out of the die pass through a cooling bath and are then fed into the pelletiser by hand. When feeding the strands, the hand approaches the pelletiser's infeed rollers; a fixed guide and low speed should be used for this job. Granulators can be the noisiest point on the line; determine exposure by measurement and arrange the use of hearing protection according to the result. For the method, see our article on workplace noise measurement.
Work instruction for head and screen changes
Screen and die changes are routine jobs, but each time they require opening a hot, pressurised system. The instruction should be short and posted next to the line:
- Stop the screw; see on the gauge that head pressure has fallen to zero.
- Inform the line supervisor and clear the area in front of the die.
- Put on a face shield, heat-resistant gloves and long-sleeved clothing.
- Open the head or screen changer in the order given in the instruction, without bringing your face in line with the opening.
- Place hot screen and die parts on a heat-resistant stand and leave a "hot" warning on them.
- After closing the head, do not start the screw until you have seen the heaters reach their set point.
- Start at low speed and watch the first melt coming out from the side of the die.
This instruction should be demonstrated at the line during the new operator's hands-on training. For similar risks in the mould area, see our article on plastic injection moulding machine safety, and for guard types, machine guards.
In its OHS specialist service, Bursa Sistemer examines extrusion and pelletising lines zone by zone and enters the findings into the risk assessment. Other topics for the sector are on our chemicals and plastics page. You can see your workplace's specialist and physician times with the OHS obligation calculator.
Frequently Asked Questions
Is it mandatory to fit a grille to the feed hopper?
The Regulation on Work Equipment requires a guard preventing access to the danger zone wherever there is a risk of contact with moving parts. If the screw can be reached through the hopper opening, a grille or equivalent guard is required; this guard must not be easy to remove.
Why does melt spurt out when the head is opened?
Frozen material, a blocked screen or a cold start can build up pressure in front of the head. The head must not be opened before the pressure gauge has fallen to zero, and nobody should stand in front of the die when it is opened.
Why should the granulator cover not be opened straight away?
The rotor keeps turning for a while after the energy is cut. The cover lock must not open until the rotor has stopped, and blade work must be done with lockout and tagout.
Is an extrusion line subject to periodic inspection?
Extruders and granulators do not appear as separate items in the Annex III tables. However, equipment on the line that is listed in the tables, such as compressed air receivers, lifting equipment, electrical installations and ventilation, is inspected at least once a year unless the standard or the manufacturer's instructions give a shorter interval. The machine's own maintenance is carried out according to the manufacturer's instructions.
A certified specialist matched to your hazard class: site inspections, approved logbook, training plan, annual plan and report follow-up.
Bursa SİSTEMER OSGB Technical Team — written from the field experience of our OHS specialists and workplace physicians. Legal information is valid as of the publication/update date; contact us for an assessment specific to your business.