TechArchive

Original article date: April 1998

Advice for machine builders from Smartscan on how to stay within the law by safeguarding end-of-line packaging machinery and similar equipment.

Over the past decade, a significant amount of European legislation has been implemented into UK law, together with a miscellany of supporting harmonised standards. And although basic safety standards are not affected by the new laws, they have amplified basic requirements and placed more explicit duties on manufacturers, suppliers and users.

End-of-line packaging machines present significant potential hazards. They are large, generally operate automatically and have openings large enough to allow the passage of pallet loads and therefore provide potential for unauthorised access. Accidents can be caused by entry into the working parts of the machines if proper control of the energy sources is not considered.

A series of “C” standards relating to end-of-line packaging machines is currently being developed by European Committee CEN/TC 146. The first in the series concerning this type of machinery is EN415-4: Palletisers and de-palletisers, due for publication this year. Standards which lay out requirements for other machine types, including pallet stretch wrapping and pallet strapping machines, are likely to be available within the next two to three years.

End-of-line packaging machinery also falls directly under the scope of the Machinery Directive, or the Supply of Machinery (Safety) Regulations in the UK. It is a requirement that designers, manufacturers, suppliers and users of these machines consider hazards associated with all phases of machine life, including commissioning and decommissioning, setting or process changeover, adjustment, use (including starting and shut down), maintenance and cleaning.

End-of-line packaging machines are often linked together to form a fully automated system. For example, a pallet de-stacker, palletiser and stretch wrapper. In such cases, the requirements of ISO standard 11161:1994 (E) should also be applied. ISO 11161 specifies safety requirements for integrated machinery systems.

Protection must be provided to prevent access to the working parts. The danger zone(s) of end-of-line packaging machines are normally enclosed within an area referred to as the interior zone(s) and uses one or a combination of the following safeguarding techniques:

• fixed enclosing guards
• fixed distance guards, including type-approved safety light curtains
• electro-sensitive trip devices, including type-approved safety light curtains

Generally, these machines are safeguarded with fixed fences surrounding the periphery of the machine. Access to the interior zone is normally through an interlocked gate or light curtain. If pallet conveyors are provided for automatically feeding loaded pallets into and out of the danger area, then light curtains positioned across conveyors at pallet infeed and outfeed zones and normally used.

When a person requires access into the interior zones, such as for machine setting, process correction or maintenance, the operation of the safeguards must be fully effective. The guards should provide the same measure of safety for persons who are forced to disturb the safeguarding requirements effective during normal operation.

Mechanical fixed guarding must be designed and constructed to prevent any part of the body from reaching the dangerous parts of the machinery. It should be robust, sufficient to withstand the stresses of the process and environmental conditions and withstand forces, providing containment of the product under all conditions.

Conventional perimeter fencing is made from rigid panels at least 2m high, securely fastened to the floor or some convenient structure and positioned so that it is not possible to reach any dangerous parts of machinery. It should only be possible to remove fixed fencing with the aid of a tool. In certain cases, if there is a risk of injury, fences may need to extend above 2m, to at least the full height of a hoist, lift table, film carriage mechanism or the higher-most reach of a robot arm.

The fencing and its fixings should be strong enough for the particular need. For most purposes, a hollow section steel framework in-filled with mesh is satisfactory. The in-filling should be made from sheet steel or plastic panels, reinforced if necessary.

In extreme cases, where it is foreseeable that the normal access opening is either not large enough or is inconveniently placed for maintenance work, sections of the fencing may be made de-mountable, providing they can only be removed with the aid of a tool.

Inside the interior zone(s), all dangerous parts of the power transmission components – gears, belts, sprockets, etc.) which are likely to be in motion when a person is inside the interior zone, must be protected by fixed guards.

Steel perforated and mesh guards are often suitable for packaging machinery, as this can be of rigid construction and provide vision into the safeguarded area for observation of the machine’s process. However, it is unlikely to be suitable in areas where hygiene is a consideration. The perforation of the mesh should be of a dimension that will not allow a finger or any part of the body to pass through and touch any potentially dangerous moving part of the machine within the safeguarded area.

Clear plastic may be used for guarding as an alternative to mesh. Plastic sheets available for safeguarding applications include polycarbonate, PVC, cellulose acetate and acrylic sheet.

The mechanical properties of most plastics may be adversely affected by heat, cold or contamination in the form of cleaning and sterilising agents. If in doubt, materials suppliers should be consulted to ensure that the material chosen is suitable for the intended application.

Different types of plastic sheet have differing impact strengths. When considering materials of equal thickness, polycarbonate is strongest, followed by rigid PVC, cellulose acetate and acrylic sheet.

Normally, guards are fastened to the floor. The number and spacing of the fixing points must be adequate to ensure stability and rigidity of the guard. It is recommended that clearance under the guard should be provided for cleaning and maintenance of spillages. The height of the clearance, from floor level to the guard structure, should never exceed 300mm.

For further information on fixed guarding, refer to drat European Standard prEN 953 – general requirements for the design and construction of guards – fixed and moveable.

When it is necessary for materials to be fed through the guard during the work process, openings should be sufficient only to allow the passage of these materials, but should not create a trap between the material and the guard. These openings normally allow for the passage of individual products or unit loads. They must never be of a dimension large enough to allow a person access into the safeguarded area unless additional safeguards are provided. If access to the dangerous parts cannot be safely prevented by the use of a fixed enclosing guard with a plain opening, then a tunnel of sufficient length should be provided.

This may be achieved by positioning the guard at the required safety distance which extends outwards from it. The effectiveness of a guard with an opening should be judged by a reach test, towards the potentially dangerous parts. This test must be carried out with the machinery at rest and in a safe condition.

When regular access is required to interior zone(s), such as for maintenance, servicing or the passage of palletised loads, the fencing may be provided with:

• sliding or hinged interlocking access gates; and/or
• an opening protected by an electro-sensitive protective device.

An interlocking guard is one which is a moveable part, the movement of which is interconnected to the power or control system of the machine. It should be connected to the machine controls, so that until the guard is closed, the interlock prevents the machinery from operating by interrupting the power system.

The interlocking system may be either mechanical, electrical, hydraulic, pneumatic or any combination.

Re-closing and locking of gates must not cause automatic restart of the machine. Restart must require positive operator action, such as a manual restart button or key.

A free booklet from Smartscan sets out recommendations for safeguarding end-of-line packaging machines from design through to installation, operation and maintenance.

• Smartscan
• 01536 401313

April 1998