Hygienic Design of Load Cells and Equipment for the Food, Pharmaceutical and Chemical Process Industries

Recently, the requirements for production and packaging plants in the food industry have undergone a fundamental transformation. This is partly due to the increasing automation of these plants. But it is also due to a change in consumer attitudes, with customers increasingly demanding fresh products without preservatives. As a result, it is becoming more and more essential to design production environments in line with hygiene factors to ensure consumer safety.

Hygienic design reduces the ability of micro-organisms such as bacteria or fungi to deposit themselves and multiply. In addition, it enables equipment to be cleaned quickly and thoroughly, cutting both the risk of cross-contamination – between different medicines, for instance – and downtimes to a minimum.

To ensure hygienic plant design, as well as solid technical expertise, engineers also require an understanding of microbiology. They need to consider the properties and size of micro-organisms – especially how they behave on surfaces – and their growth in gaps, crevices and dead space.

Eliminating Micro-Organisms From the Process

As far as possible, consumers would like to buy food that is fresh, untreated and free from preservatives, such as smoothies from pureed fruit and fresh vegetable juice. In order to create these convenience products, it has to be virtually impossible for micro-organisms to get in during the production process.

To guarantee a production environment that is as hygienic as possible, the plants and components involved must satisfy certain requirements. The framework for action is defined by various guidelines, laws and organizations. The European Hygienic Engineering & Design Group (EHEDG) is worthy of particular attention. This consortium of manufacturers, food producers and research institutes is working on concrete guidelines to bring about maximum hygiene in food production.

European Hygienic Engineering & Design Group (EHEDG)

The EHEDG was founded in 1989 as an expert community that aims to raise awareness of the importance of hygiene in food processing and packaging. In Germany, around 100 companies and institutions are members of the EHEDG. Its main task is to promote hygienic engineering and design in all areas of food production. The organization develops appropriate guidelines and also provides certification. Furthermore, the EHEDG supports European legislation that requires food to be handled, processed and packaged hygienically, using hygienic machinery, and in a hygienic environment (EC Directive 2006/42/EC for machinery, EN 1672-2 and EN ISO 14159 for hygiene requirements).

HBM is also a member of the European Engineering & Design Group.

Basic Requirements for Hygienic Design

The hygienic design of plants focuses less on areas in which the risk of contamination is largely excluded. Instead, areas where direct or indirect product contamination is possible are a high priority. The aim is to recognize and avoid possible problem areas in order to guarantee high product safety. Consequently, the areas of plants for hygiene-sensitive production or aseptic packaging that are in contact with the product require an “easy to clean” design.

The easiest possible cleaning of all plants and components is achieved by using the appropriate materials, and by the geometry and surface design of the individual parts. Moreover, correct assembly that avoids angles, gaps and dead space is extremely important. In addition, plants must be easy to disassemble, clean, and put back together again.

What are the basic principles for a hygienic plant design*?

Yoghurt filling machine — Filling of yoghurt: Hygienically designed plants are especially important for the dairy industry.

Select and use suitable, approved and easily cleaned materials with the highest possible corrosion resistance
Produce sufficiently smooth, hygienic and easily cleaned surfaces and finishes
Minimize or optimize avoidable visible gaps, dents or protrusions (e.g. on static or dynamic seals) that are difficult to clean
Avoid pores, crevices, gaps and all types of defects, even those not visible to the eye, on surfaces, fixed and moving joints, and bearings
Design the geometry of components to optimize flow and avoid eddy formation due to delamination and dead water zones
Avoid any kind of dead space that is difficult or impossible to clean
Ensure the self-emptying or automatic drainage of all relevant areas.

In addition to these requirements, steps must also be taken to ensure that the materials used are physiologically harmless and food-compatible.

Aseptic Weighing Systems as the Gold Standard of Hygienic Design

Hygienic design is not always the same. For example, the German Mechanical Engineering Association (Verband Deutscher Maschinen- und Anlagenbau e. V., VDMA) have defined five different classes of Hygienic filling machines for liquid and viscous foods. Aseptic machines are at the top end of the spectrum and must therefore meet far more stringent requirements criteria than merely “hygienically designed” or “semiaseptic” plants or “ultraclean designs”.

The different requirements are primarily based on what kind of product is being processed. They are particularly strict as regards filling and packaging plants for juice, juice drinks and dairy products. Here, the avoidance of product contamination has to be guaranteed without the use of preservatives or aggressive cleaning agents.

The hygienic design guidelines from the EHEDG help companies by setting out the basic principles of hygienic design, which must be complied with when engineering and building equipment for food production. Here is an extract:

To avoid contamination, only tempered and electro-polished stainless steels with Ra<0.8um can be used. Smooth surfaces prevent the formation of coatings and adherence of product residues and increase the effectiveness of cleaning. Even frames and housings must be manufactured using high-quality stainless steels to avoid corrosion and contamination. Cleaned weld seams are mandatory, as is easy and user-friendly cleaning using trolleys or lifting mechanisms. In addition, all the applicable handling requirements regarding easy cleaning must be satisfied; in particular, there must not be any gaps or crevices.

These requirements apply to the entire weighing system, including all its parts, such as load cells.

Component Certification

The EHEDG also issues certificates confirming that components fulfill the legal provisions and are therefore suitable for use in the food industry. There are certificates for open and closed processes, and for cleaning in place and cleaning out of place.

In all these cases, the EHEDG checks the extent to which components can be cleaned, using suitable test methods it has devised itself. Components are deliberately exposed to bacteria, dried and then cleaned. In a further step, a culture medium with a pH indicator, in which bacteria can reproduce, is used to test whether any bacteria remain in or on the component after cleaning. If the color changes, this indicates that bacteria were still present despite cleaning.

Typical components that are EHEDG-certified include valves, pumps and sensors. Plant engineers deploying components with EHEDG certification are then able to meet the hygiene requirements of the EU Machinery Directive.

Hygienic conditions when bottling drinking water — Drinking water requires a hygienic bottling environment since no preservatives can be used

Hygienic Load Cells From HBM

The HBM portfolio includes two EHEDG-certified single point load cells: the PW27A and PW37P. To meet the EHEDG’s stringent cleanability requirements, they are hermetically encapsulated and made entirely of stainless steel. They are therefore guaranteed to be compatible with all the common cleaning agents and disinfectants used in the food and pharmaceutical industries.

The PW27A and PW37P are designed to be especially easy to clean. Their geometry was engineered to ensure that neither dirt nor product residues can accumulate. The load cells have a laser-inscribed marking on their surface, dispensing with the need for the usual adhesive labels and enabling thorough cleaning of the surface.

In the food industry, daily cleaning with cleaning agents, disinfectants and high-pressure steam jets is standard. This is why HBM single point load cells also have an IP rating of IP68 or IP67K.

Conclusion

Hygienic design is playing an increasingly important role in the food and pharmaceutical industries. Thanks to its new load cells with EHEDG certification, sensor and measurement technology specialist HBM can position itself in the market as a supplier to the highly demanding food and pharmaceutical sector. Plant engineers who integrate these load cells in their applications can be safe in the knowledge that they will comply with the relevant legislation.

_{*Source: Dr. Ing. Gerhard Hauser “Hygiene” in “Handbuch der Fülltechnik”, Behr’s Verlag, Hamburg 2004}