A reliable process functionality is vital to horizontal mixing equipment, but the efficient cleaning process of the system is now becoming increasingly important. Today's hygienic requirements are no longer limited to the pharmaceutical industry, as integrated cleaning systems are now more often requested for new equipment in the food, cosmetics and chemical industries.
Through the cleaning process, manufacturers put a particular focus on the prevention of cross-contamination by allergens, flavours and active ingredients during product changeovers as well as the elimination of potential microbiological contamination.
Cleaning systems for process-related equipment can be divided into two categories: semi-automatic WIP systems (Wash-in-Place) and fully automatic CIP systems (Clean-in-Place). The latter does not require any manual cleaning steps.
Horizontal mixing systems generally use a WIP system because minor manual steps—removing a filter or installing a drainage cone on the machine outlet—are frequently required. Chemical disinfection of the system can be performed after machine cleaning as needed. This method is referred to as a SIP system (Sterilisation-in-Place).
Complex cleaning process
The cleaning process comprises the removal of the residue of any remaining product and material build-up in the entire mixing drum. For this purpose, the air purged seals of the mixing shaft and choppers will be flushed with water to prevent the ingress of cleaning liquid into the seals.
Afterwards, the horizontal mixer is cleaned successively from top to bottom. For this purpose, all sockets on top of the machine are equipped with cleaning nozzles, which are either firmly welded on the inside of the socket or can be positioned on the device as a separate washing adapter.
It is also possible to install automated retractable cleaning nozzles. Filters are generally thoroughly moistened while installing and then removed for further cleaning in a dishwasher or an ultrasonic bath.
Automatic cleaning of the mixer discharge is a more sophisticated process due to the complex geometry of the discharge door
The rinsing water used for cleaning the sockets is collected in the mixing drum and later used for cleaning the mixer interior, which requires a filling level of 10%-20% with the cleaning agent.
The mixing drum itself is cleaned using the mixing shaft. It rotates forwards and backwards, effectively ensuring intense and turbulent contact between the mixer inner surface and the cleaning media. If necessary, any product residue remaining in the mixer can be soaked during this process.
Mixing systems with higher volumes use additional rotating jet cleaners to maintain a reasonable water consumption per cleaning cycle. For this process, it is possible to use both freshwater or closed-loop circulation mode.
Automatic cleaning of the mixer discharge is a more sophisticated process due to the complex geometry of the discharge door, driveshaft and sealing surfaces. A combination of static cleaning nozzles and a centrally located rotating spray ball, as well as opening and closing the door in interval mode have proven successful for intense cleaning of all surfaces. Any wastewater created by the cleaning process is discharged through a drainage cone installed at the mixer discharge.
Schematic diagram of a WIP system with typical rinsing points on a horizontal Ploughshare Mixer. Source: Lödige
Depending on product solubility and the machine's degree of soiling, the cleaning process can be performed in multiple steps using cold, warm or purified water. Automatic metered addition of various cleaning agents, as well as a final chemical disinfection step, are also available. Thermal sterilisation by steam can also be performed, if the mixer is designed with the necessary equipment.
Final drying of the mixer with conditioned ambient air is possible, which can be supported by using hot water during the previous cleaning steps. Quicker alternatives such as blowing out the entire system with heated compressed air, or using blowers combined with air dehumidifiers—also referred to as absorption dryers—have proven useful.
Modular structure of the cleaning systems
All WIP, CIP or SIP systems for horizontal mixers have a modular structure that enables them to meet any customer- and product-specific task requirements. Each cleaning process is defined based on the mixer design and product properties and saved as a recipe in the machine control system making it reproducible.
The light of the UV lamp exposes all potential for optimisation. Source: Lödige
A riboflavin test is used to ensure correct functionality of the cleaning system (e.g. number and positioning of the nozzles) as well as the correct parametrisation of the cleaning process (e.g. water volumes, rinsing times, etc.).
Riboflavin glows if it is illuminated with ultraviolet light, and it's used as a tracer for visual inspection. However, this test is only an indicator of cleaning effectiveness. It cannot be used to validate the cleaning process.
Cleaning horizontal mixers with semi-automatic WIP systems is a complex process. Modular solutions cover such a wide range of tasks that they can reliably fulfil any industry-specific requirements in pharmaceutical production as well as those in the food, cosmetics and chemical industries.
N.B. This article is featured in the September 2019 issue of Cleanroom Technology. The latest digital edition is available online.