Food and beverage processing industries represent some of the most rigorous operating environments for sealing components. Seals in these applications are frequently faced with temperature and pressure extremes, with no margin for error when it comes to long-term hygienic sealing performance. The impact of process media and chemicals used in cleaning and sterilization can also have a significant effect on seal lifetime and reliability. In food and beverage processing, hygiene is the most critically important factor above all else. Compromised sealing systems must be diagnosed and isolated quickly and efficiently before risk translates to the end consumers.
Steps can be taken to minimize any risk factors associated with the failure of hygienic sealing. This article explores some of these steps in more detail, helping equipment operators, engineers and maintenance teams get more from their process lines and keep consumers safer.
What are the biggest sealing challenges around process contamination?
The purpose of elastomeric sealing components in food and beverage processing equipment is to handle aggressive thermal and chemical conditions while ensuring that unwanted contaminants are not released into the process line. Some of the most significant threats to seal degradation are process media, clean-in-place (CIP) or sterilization-in-place (SIP) procedures, and faults with installation.
From oils and acids through to salts and sugars, a hygienic seal in a food or beverage process application needs to be able to withstand a diverse range of challenges with chemical compatibility. Continuous contact with the food or beverage product itself – or its constituent ingredients – can be a source of seal damage, and subsequent process contamination. Alongside the chemical nature of the process media, there may also be considerations on the temperature and pressure of the process lines. If an engineer has confidence in a sealing component to handle several different chemical challenges without damage or compromised sealing performance, the process lines can run uninterrupted for longer periods, improving productivity and efficiency.
Some types of seal material can be significantly damaged by the aggressive chemicals used in CIP and SIP cleaning procedures. While the use of these powerful chemicals is vitally important in killing sources of microbial contamination after process runs, the chemicals are at risk of clashing with the sealing components with irreparable damage to the structural integrity of the seal. The chemicals used in CIP attack many elastomeric seals, causing swelling, leaching, loss of mechanical strength, embrittlement and ultimately failure. The potential exists for fragments of the seal to break away into the process media.
Exposure to steam (typically 120°C to 135°C) in SIP causes many elastomers to soften and lose mechanical strength, extruding into the pipeline. This thinning of the gasket reduces the compressive load and potentially can result in leaks, as well as bug traps where the seal protrudes into the pipeline.
By taking the time to select a sealing material with the properties to resist the thermal and chemical demands of the cleaning method, the risk of seal failure and subsequent product contamination can be kept as low as possible.
Oversights during the original installation of the sealing component can impact the resilience of the seal, and cause proneness to damage. If the seal has been positioned inaccurately, or if the seal has been superficially damaged during installation – however imperceptibly – this leaves sealing weaknesses, which might be exposed through the thermal and chemical pressures of the application. A simpler sealing system, or more comprehensive training, can help to negate these effects.
Standards & regulations
Standards are important for consistency in all industries, but for ensuring the safety of products intended for human consumption, it is imperative that every required guideline and certification is followed meticulously. Many industrial material grades are well suited to sealing oil, gas, seawater and other notably aggressive media, but would not be appropriate for the food or beverage processing industries. There are some key internationally recognized standards in place concerning leachable and potentially harmful constituents, which if not in place could put consumer health at risk.
The Food and Drug Administration (FDA) is the U.S. federal agency responsible for ensuring that foods and beverages are safe, wholesome and sanitary; human and veterinary drugs, biological products and medical devices are safe, and effective and cosmetics are safe.
CFR21.177.2600 describes the relevant regulations for “rubber articles intended for repeated use.” Paragraphs A – D detail the requirements for dry foods, paragraphs E and F detail the requirements for aqueous and fatty foods.
3-A Sanitary Standards Inc. is an organization in the United States that formulates sanitary standards and practices for the design, fabrication, installation and cleaning of equipment in the food and pharmaceutical process industries.
Standard 18-03 (“Multiple-Use Rubber and Rubber-Like Materials Used as Product Contact Surfaces in Dairy Equipment”) describes requirements for food quality materials that are suitable for steam sterilization, acid and alkali cleaning solutions and chlorine sanitizing agents.
European Parliamentary Council
The European Parliament has installed a series of regulatory guidelines concerning food contact materials, which apply across all European Union member states. The principle of the directive is that materials should be sufficiently inert to prevent transfer of substances into food in quantities that might be large enough to endanger human health.
Annex I of EC1935-2004 lists 17 groups of materials, which may be covered, including rubbers and silicones, while instructing on proper tracking and labeling systems for any food contact components. EC 2023/2006 concerns general good manufacturing practice for materials and articles intended to come into contact with food.
Materials approved for drinking water applications must satisfy the requirement of BS 6920 for the Water Regulations Advisory Scheme (WRAS).
The testing regime for WRAS approval is different than FDA testing, in that it tests the “Suitability of non-metallic products for use in contact with water intended for human consumption with regard to their effect on the quality of the water.” The test ensures sealing materials do not promote the propagation of bacteria or affect the color, appearance and taste of drinking water.
Importance of material choice
From a sealing engineer’s point of view, the implementation of an effective hygienic seal begins with the right choice of material. An effective food industry sealing material needs to demonstrate a broad chemical compatibility profile, compatible with virtually all process media and able to withstand cleaning regimes and sterilization practices including solvents, steams and amines. Mechanical and thermal resistance is required, with an operating temperature range between -60°C and 327°C. Full manufacturing traceability of the material – with certification to BS EN ISO 10204 – would also be advantageous.
FFKM (perfluoroelastomer) offers the gold standard for chemical resistance together with high-temperature performance. Effectively a rubber form of FFKM, PTFE (polytetrafluoroethylene) seals have demonstrable benefits in food and beverage process lines, including:
- Reduced process contamination
- Reduced equipment downtime
- Increased seal lifetime
- Extended equipment planned maintenance intervals
Beyond the base sealing material choice, the sealing solution market has a good range of innovative products to offer improved hygienic qualities. One example is the development of metal-detectable elastomeric sealing components designed to ensure the earliest possible detection of process contamination by rubber parts. Some metal-detectable brands can be detected by metal detection and X-ray equipment in fragments as small as 2 millimeters (mm). Considering this, it is more desirable to prevent contamination in the first-place instance – contamination events are often very costly, with investigation, scrapped product, clean-down and replacement of seals and gaskets as required.
Special considerations for shaft sealing in food process equipment
Many food production processes depend heavily on large mixing and blending equipment. Applications are varied, from powder blenders for protein shakes to steam mixers for cooking ready meals. There is a huge range of rotary blade, plough and paddle mixers and blenders available to blend, dry, cook and homogenize.
The size of the plant and processing duties alter the magnitude of issues experienced but there are several typical issues that they have in common.
Unlike high-speed rotary pumps, which are typically well balanced with minimal shaft run-out, many mixing and blending process equipment types inherently suffer from run-out and eccentric shaft movement.
Furthermore, the length of the shaft means that span between the supporting bearings can often be significant – leading to shaft deflection.
Also, due to thermal cycling and subsequent thermal expansion and contraction during operation, the seal and bearing arrangement must be able to allow and compensate for this. The process media needn’t be heated for this to occur. The shearing motion of the mixing and blending process can create sufficient heat as to cause thermal expansion of the shaft.
These characteristics can be exacerbated with the addition of powders, solids, liquids and slurries creating additional torsional and shock loads on the shaft.
The use of shaft contact seals can further complicate matters, whereby the seal running surface is in contact with, and runs against the shaft, causing friction. The friction generated has several potentially detrimental effects, including:
- The seal can wear down the shaft, leading to shaft damage requiring expensive repair or replacement
- The seal contact face experiences wear, leading to seal failure and replacement
- Worn sealing materials can migrate into the process media, resulting in process contamination
- The frictional heat generated can damage the process media
Some solutions could involve the application of a wear sleeve to the shaft, using seals with a lower friction coefficient or adding a cooling lubricant to the seal area. However, these solutions can add layers of cost and complexity, and the use of cooling media is not always advisable in a hygienic production environment.
Particularly with larger mixers and blenders, seal maintenance and replacement can be challenging. The decoupling, removal and reassembly of the shaft, bearings and drive after takes valuable time and resources. Therefore, what can be done to optimize the performance of sealing solutions on food process shafts?
Select a seal that can handle shaft runout – Many seals can be compacted and deformed by eccentric shaft motion, creating a potential leak path. Some split mechanical shaft seals can allow up to 6 mm shaft runout as standard.
Take away the dynamic contact with the shaft to prevent friction and heating in the sealing area and wearing of the shaft. Choosing a dynamic face seal, in which the sealing face (the stator) remains static and a dynamic sealing face (the rotor) rotates with the shaft, can help to achieve this.
Simplify the seal repair and replacement process by choosing a split seal design requiring no major machine disassembly, saving time and resources and getting your process line operational much more quickly.
Sealing consultancy – Is it worth it?
A trusted sealing supplier able to provide technical support and associated food and beverage approvals, certifications and traceability is an option that provides valuable peace of mind. Not only does it give confidence that the sealing materials have been selected with appropriate standards and legislation in mind, but also expert support in selecting the most appropriate option for any given process line application can be vital to the long-term efficiency and safety of plant equipment.
A complete sealing consultancy service could cover food and beverage process operations from single-seal components to a total overhaul of a sealing system. Experienced sealing specialists would be involved from the outset, from initial concept specification and development through to installation and training for engineers and operatives. In this way, working with sealing specialists to secure food and beverage process lines against avoidable contamination can be seen as an important investment in the safety of your consumers.
Russ Pimblett is the business development manager at FTL Technology, specializing in sealing solutions for food process equipment, using extensive mechanical engineering experience to find innovative solutions for varied industrial problems.