Availability
Definition
Availability refers to the proportion of the scheduled time during which a plant is actually operational and capable of delivering the required output. In process and mixing technology, the term therefore describes how often and for how long a system is operational under real operating conditions.
Availability as a percentage = actual operating time ÷ scheduled production time × 100
For the operator, high availability means that the plant runs when it is needed – reliably, predictably and with consistent product quality.
Key influencing factors
Technical availability
This describes the purely technical condition of the plant, independent of organisational factors such as a lack of materials or staff. In the case of mixers, the following components in particular influence technical availability:
- Mixing tool
- Drive unit and gearbox
- Sealing system
- Sensors and control system
- Discharge components and valves
Operational availability
This also encompasses all operational and organisational factors, for example set-up times, cleaning intervals during product changes, material provision and operator interventions.
Reliability
The longer a plant’s trouble-free running time, the higher its availability. In maintenance, this is often described using the MTBF (Mean Time Between Failures), i.e. the average time between two failures.
Maintainability
Short repair and maintenance times directly improve availability. The MTTR (Mean Time To Repair) indicates how long it takes on average for a fault to be rectified and the system to be back in operation. A maintenance-friendly design, good accessibility and a rapid supply of spare parts reduce this figure.
Cleaning and changeover times
Particularly when product changes are frequent, cleaning and changeovers are often the biggest factors influencing effective plant availability. A plant designed for rapid cleaning significantly reduces downtime.
Distinction from OEE
Availability is one of the three factors of Overall Equipment Effectiveness (OEE), alongside performance and quality. It answers solely the question of whether the plant is running. Whether it is running at the intended speed and whether the output meets specifications are captured by the other two factors. High availability alone is therefore not proof of high productivity.
Significance in practice
Production planning and on-time delivery
High availability forms the basis for reliable production plans and robust delivery commitments. In the food, pharmaceutical and chemical industries, any unplanned downtime leads directly to production losses.
Cost-effectiveness
As availability is factored into the OEE on a multiplicative basis, even small improvements can have noticeable economic effects.
Design features for high availability
- low-wear mixing tools
- low-maintenance seals on shaft passages
- good accessibility for cleaning and servicing
- CIP- and WIP-compatible designs
- robust drive technology with sufficient reserve capacity
- sensor technology for condition-based maintenance
Maintenance strategies
- Preventive maintenance: planned measures reduce the risk of unplanned breakdowns.
- Condition-based maintenance: Monitoring of vibration, temperature and current consumption provides early indications of wear.
- Predictive maintenance: Data-based predictions help to schedule maintenance before a breakdown occurs.
Spare parts availability: Well-organised wear-part kits reduce repair times and increase effective availability.
Typical application scenario
For plants with frequent formula or product changes, cleaning-related availability is particularly important. A vertical mixer with good discharge characteristics and an accessible mixing chamber can significantly reduce cleaning time and thus get the plant back into production more quickly.
Guidance for the user
High availability is not merely a technical parameter, but a direct driver of productivity, on-time delivery and cost-effectiveness. When selecting a mixer, it is therefore worth considering not only mixing quality and performance, but also design details that minimise maintenance, cleaning and repair times.