Preparation time

Definition

Set-up time – also known as ‘changeover time’ – refers, in production and process engineering, to the period between the last good product of a completed batch and the first good product of the following batch.

It encompasses all preparation, changeover and post-processing operations required to prepare a machine, plant or work system for the next production order following the completion of the previous one, and, where necessary, to return it to a defined initial state.

In the context of mixers, set-up time includes all the work required to make the mixer operational again and compliant with specifications following a product or formulation change: emptying, cleaning, drying, any tool changes, parameterisation of the control system, and quality assurance prior to the start of the new batch.

Characteristics of set-up time

Non-value-adding time

No value is added during set-up time: the mixer does not produce any saleable products, but continues to incur fixed costs for staff, plant capital, floor space and, where applicable, energy. In labour and time management, set-up time is regarded as part of the order time required for setting up and changing over the work system, without itself being part of the execution time.

Internal and external set-up time

For the purposes of analysis and optimisation, a distinction is made between:

• Internal set-up time: Activities that can only be carried out whilst the machine is at a standstill, such as opening the mixer, cleaning the interior, changing tools or carrying out manual inspections.
• External set-up time: Activities that can be prepared whilst production is running, such as preparing the next batch of raw materials, pre-weighing components, preparing cleaning agents or configuring parameters away from the production line.

The systematic shift from internal to external set-up operations is at the heart of the SMED (Single Minute Exchange of Die) methodology, an established approach for significantly reducing set-up times.

Components of set-up time for mixers

Emptying the residual contents from the mixing vessel

Complete discharge of the previous batch. Suitable mixers offer a high degree of discharge thanks to their conical base geometry and design with minimal dead space, thereby reducing the cleaning effort.

Cleaning

Removal of product residues to prevent cross-contamination, particularly in food, pharmaceutical and chemical applications:

• Dry cleaning: Suction, blowing or sweeping out of residues
• Wet cleaning (WIP/CIP): Automated cleaning-in-place or washing-in-place systems with spray nozzles, rinsing and subsequent drying

Drying after wet cleaning

Ensuring a dry condition suitable for the product before new powder batches are loaded.

Tool and component changeover

Replacement or adjustment of mixing elements, seals or discharge fittings to optimise the process for different product properties.

Control system parameterisation

Loading the new formulation into the control system, setting speeds, mixing times, temperature control and, where applicable, further process steps such as dispersion or granulation.

Test run and quality approval

Test run to check functionality and leak-tightness; where necessary, in-process checks such as homogeneity and moisture content; and approval of the plant for the production of the new batch in accordance with specifications.

Depending on the product characteristics – such as being sticky, hygroscopic, toxic or allergenic – cleaning and testing processes can account for a significantly larger proportion of the total set-up time.

Impact of design on set-up time

Vertical mixers offer design advantages over many horizontal mixing systems that have a positive impact on set-up time:

• high discharge efficiency due to conical or funnel-shaped vessel geometry
• good accessibility from above via large inspection and cleaning doors for manual checks and cleaning tasks
• reduced surface area for material build-up due to central mixing tools and predominantly vertical surfaces, which minimises powder build-up and the need for cleaning
• CIP and WIP capability with the appropriate equipment, enabling automated, reproducible cleaning processes with minimal staff involvement

A consistent hygienic design – polished surfaces, the avoidance of dead spaces, no horizontal resting surfaces, and suitable sealing and flange designs – further shortens cleaning and inspection times whilst enhancing cleanability and product safety.

Economic significance and optimisation

Significance for productivity and OEE

Set-up time is a key factor in overall equipment effectiveness. Every minute that the mixer is idle due to set-up procedures reduces the net available production time, whilst fixed costs continue to accrue.

Example: Four product changes per day, each with a set-up time of 60 minutes, result in 240 minutes – that is, four hours of downtime daily. Reducing this to 40 minutes per changeover frees up 80 minutes of additional production time per day – without investing in additional machine capacity.

Benefits of short set-up times

• greater flexibility: cost-effective production of small batch sizes and frequent product changes, for example for bespoke formulations or seasonal products
• reduced production costs: shorter downtimes lower unit costs, as fixed plant and labour costs are spread across a larger volume produced
• faster responsiveness: production can react at short notice to market demands, supply bottlenecks or recipe changes
• improved hygiene and product safety: standardised, efficient changeover and cleaning processes minimise cross-contamination
• Health and safety and ergonomics: easily accessible, hygienically designed mixers with quick-change systems and automated cleaning solutions reduce physically demanding tasks

Typical optimisation measures

• SMED methodology: systematic analysis and separation of internal and external set-up operations, standardisation of processes, reduction of manual steps and travel times
• automated cleaning systems: integrated spray nozzles, programmed wash cycles and defined drying phases for reproducible cleaning results
• Formulation and parameter management via the control system and higher-level production systems: centralised management and rapid loading of production formulations, automatic setting of process parameters and documentation of batch changes
• Quick-change systems: tool-free or low-tool assembly systems for mixing elements, seals and discharge fittings

• Smart production planning: Sequencing of production orders by product family, colour or hygiene requirements, so that time-consuming cleaning is carried out only when actually necessary

   

Related terms

Order time, batch changeover, CIP and WIP, OEE, SMED, cross-contamination, downtime.

When designing and evaluating mixers, in addition to the mixing quality itself, a transparent breakdown of the expected set-up, discharge and cleaning times should always be required. These times often have a greater impact on long-term operating costs, flexibility and the overall economic utilisation of the plant than the purchase price.