Concrete Mixer processes and Safeguarding requirements
Why effective safeguarding is essential around moving components and access points
Concrete mixers are used to combine cement, aggregates, water, and additives into a uniform concrete mix. Depending on the equipment, the process may include loading, mixing, discharge, cleaning, and maintenance, often involving rotating drums, shafts, paddles, conveyors, or discharge mechanisms.
These moving components create hazards such as entanglement, crushing, shearing, and unexpected movement. Effective safeguarding typically combines fixed guarding around hazardous areas with controlled access points for cleaning, inspection, and maintenance.
Where regular access is required, interlocking or trapped-key systems can be used to help ensure access is only possible under controlled conditions.
Built for Harsh Industrial Environments
Trapped-key interlock systems are well suited to concrete processing environments where dust, debris, and vibration can affect conventional electrical components.
Key advantages include:
- Robust mechanical design for dusty environments
- No wiring required at access hatches
- High safety performance up to SIL 3, Category 4, and PL e
- Reliable access control for cleaning, inspection, and maintenance
This makes trapped-key interlocking a practical option where durability, simplicity, and high safety integrity are required.
Practical application of machine safeguarding devices to concrete mixers
Bolt lock
Bolt lock with three access keys.
Mechanical door lock
De-activation of manual crane operation.
Signal Lamp
The signal lamp indicates that the mixer is operational.
The isolating switch is
turned to the off position.
The first access key
is turned and taken out.
The pin is shot
to lock the isolating switch in
the off position.
The access key is
entered into the shutter latch
to unlock it.
The access key remains
locked as long as the
shutter is open.
Securing concrete mixers in accordance with the Machinery Directive can be achieved using a trapped-key interlock system. Access through mixer hatches is only permitted after the power supply has been electrically or mechanically isolated.
The trapped-key sequence links machine isolation directly to hatch access: the key is released only after isolation, used to unlock the hatch, and remains trapped while the hatch is open. This prevents the normal operating sequence from being restored until the hatch is closed, locked, and the key is returned.
For inspection or cleaning under manual operation, limited movement can be permitted when the mixer is equipped with a frequency inverter and a two-hand control console, for example at a maximum of 10% power for up to 10 seconds.
Safeguarding standards and regulations for concrete mixers
Hazards involved when using a concrete mixer
EN 12151:2007
This standard addresses the significant hazards associated with machinery used for the preparation, batching, and mixing of concrete and mortar.
Covers risks from moving parts, access to hazardous areas, and machine operation, providing an application-specific safety framework for protective measures.
Design guidelines for safety interlocking devices
ISO 14119:2024
ISO 14119 applies where guards, doors, or access points are fitted with interlocking devices.
This defines principles for selecting and designing interlocks so that access to a hazardous area is controlled and machine operation is linked to the status of the guard.
For concrete mixers, this is especially relevant where operators require regular access for cleaning, inspection, or maintenance.
Prevention of unexpected start-up
ISO 14118:2017
ISO 14118 focuses on preventing machinery from starting or re-energizing unexpectedly when personnel are exposed to hazardous areas.
Particularly important for concrete mixers during activities such as cleaning, clearing blockages, inspection, and maintenance, where personnel may be close to or inside the machine and unexpected movement could create serious risk.
Products used in this application:
Frequently asked questions about safeguarding concrete mixers
Yes. Trapped-key interlocks can be used to control access to mixer hatches by ensuring the machine is isolated before entry is permitted. They help reduce the risk of unexpected movement or restart during cleaning, inspection, and maintenance, while providing a robust solution for demanding industrial environments.
The mixer is first electrically or mechanically isolated. This releases a key, which is then used to unlock the access hatch. The key remains trapped while the hatch is open and can only be returned once the hatch has been closed and secured.
A correctly designed trapped-key system prevents the normal operating sequence from being restored while the access hatch is open. Restart is only possible after the hatch is closed, locked, and the key is returned.
Isolation helps prevent hazardous movement or unexpected energisation while personnel are entering, inspecting, cleaning, or maintaining the mixer. It creates a controlled condition before access is permitted.
Yes. Trapped-key systems can be configured to control multiple hatches or access points. The key sequence can ensure that all required conditions are met before access is granted and before normal operation can resume.
Where the application allows it, controlled manual movement can be provided through a frequency inverter in combination with a two-hand control console. This allows restricted operation under defined conditions while maintaining controlled access.
Yes. Mechanical trapped-key systems are well suited to dusty, high-vibration, and demanding industrial environments because they provide robust access control without relying solely on electronic sensing at each access point.
Relevant requirements may include the Machinery Directive or applicable machinery legislation, ISO 14119 for interlocking devices associated with guards, and other standards covering access control, guarding, and prevention of unexpected start-up.
