The world is undergoing a significant increase in its industrialized food processing, and this has entailed a close examination of all aspects of modern hygienic food processing. This involves more investment in machinery and while factory owners may only consider saving of time, space and money and the wish to increase output to serve a wider market, there is another consideration, which is the increased risk of food-borne illnesses and the sometimes unbearably high costs of rectifying this post facto.
There are many systems used to eliminate or reduce the risks of contamination which begin with the raw materials from the farm and field and continue throughout the process until packing. Some risks can be eliminated once and for all, such as small stones and insects washed out of a vegetable harvest but there are far more dangerous forms of contamination further down the line before packing, including inside the factory.
WHY DO WE DISCUSS CONVEYOR BELTS?
What are the most sensitive parts of a factory and thus most under scrutiny during an audit? Factory floors and drains, the use of stainless steel for machines and many other things. One big issue is the only plastic machine component normally and routinely in contact with all food types: conveyor belts.
Conveyor belts help avoid handling of product but in terms of direct contact with food they are a hygienic nightmare and harbor more bacteria than any other processing tool or machine in the factory. Plastic does not disinfect as easily as stainless steel and they are therefore a particular concern of auditors and an easy point on which to fail an audit. Plastic is more prone to degrade and can be damaged by product, by movement around the conveyor pulleys and by the cleaning chemicals. There are two traditional plastic belts types: “Ply” and “Modular” and one new hygienic type, “Thermoplastic”, also called “Homogeneous”.
Ply belts are a textile/fabric belt with a coat of polymer (e.g. Rubber, PVC, PU) for protection. They are the cheapest and most widely used belt in industry but are the least hygienic belts for food. From the first use they absorb and promote bacteria as the textile is exposed at the edges and underneath and they were not designed for use in any humid application. Ply belts also have the shortest working life due to the joint which is either a weak vulcanized area or an unhygienic mechanical fastener. Ply belts soak up water, oil, fats, and food fragments into the fabric and the plastic. The belt is porous all over and the plastic layer also delaminates easily, depositing undetectable belt fragments into the food. Many are marketed as food grade PU belts – this requires vigilance from the end user.
Sometimes belts need features (fabrications), such as cleats (flights) to move product up a steep angle or guides to control belt movement. When these are fabricated on ply belts, they are weak and break easily which wastes all the labor and material costs used in producing them.
These are versatile belts that can even work in a spiral. They are ideal in logistics and bottling lines and are constructed from plates or links with pins joining them. These pieces are made from very hard plastic moldings. Modular belts were, perhaps unfortunately, introduced into the processing of food as a simple system for machine builders but they also pass on all responsibility for maintenance and changeover of parts to the factory; a nice bonus for modular belt producers who then resell the parts again and again.
They have many disadvantages for a food processor, firstly the cost of cleaning. Modular belts have over 30% more surface area to clean due to the contours and thickness. They are also very costly to clean – food particles, water and oily fats get into the joints and decompose. Quality departments who check on the bottom of modular belts or in between the joints will always find bacteria. A food processor may spend 60% more on cleaning modular belts: water, chemicals, and manpower (which also means time wasted that could be used for production). This extreme addition to daily running costs affects what is now known as ‘cost of ownership’. This is the true cost of running a factory factoring all resources expended on production.
Modular belts are inflexible, and breakages or attrition can be frequent in some applications like frozen food or where there is impact. Links can also break easily by accident. Maintenance departments order spare parts as needed with no financial restraint – once a belt is installed, the conveyor must keep working, pouring good money in after bad.
Finally, modular belts are expensive and their heavy weight per square meter means that conveyor systems that use them must often be heavier and more robust. This in turn means that the conveyor itself is more expensive and has more parts to clean.
Belts made from extruded thermoplastic elastomer (usually PU) not by hot rolling or molding. This process gives the following advantages:
1. Non-porous, dense material which is flexible
2. No ply textile or fibers to soak-up and harbor bacteria
3. No finger joint – solid edges are butt welded – gives many times the lifetime compared to ply belts
4. No links and pins like modular – less to clean and less to break
5. Strong fabricated features
6. Tears can be repaired
7. Ultra-hygienic – clean in much less time and at a fraction of the cost. Compatible with all auditing demands
8. Lightweight compared to modular – lighter, cheaper conveyors with smaller motors are possible
9. All food types can be handled with the only significant restriction being very hot.
Auditors are key figures in companies targeting national or international markets. They are trained by accredited organizations and their reports are relied on by food importers, major supermarket chains and multinational companies seeking to source ingredients. The most up to date document by an international organization on conveyor belts is the EHEDG Guideline 43. EHEDG is a voluntary organization which has, since the early 1990s, published guidelines on many topics with the aim of outlining what a food processor should do in every aspect of factory design in order to comply with the best hygienic practice – the principle is called Hygienic Design (HD). HD says that a factory should be designed hygienically to begin with rather than leave a processor trying to manage the problems and ensure the product is safe by rules and regulations in systems like ISO. The HD concept eliminates many of the problems that management systems struggle to contain and thus lets a producer spend on design rather than on solving problems arising from poor choices of machinery and layout.
The belt which comes into contact with food, is maybe more than half of the story but the conveyor also requires cleaning and another advantage of using a belt like Volta Super Drive© or Mini Super Drive© is to reduce the amount of conveyor parts, the weight and cost of the conveyor and the overall economy. These belts have a central extruded row of teeth integral to the belt and this is used to track the belt thus preventing one of the main causes of belt failure, which is when the belt runs off to one side (off- tracking). Some examples of this in practice are shown below. Every conveyor should adopt HD principles regardless of belt type. There are some guidelines with regards to stainless steel, surface quality, welding, folding bends, hygienic feet, and sensors but the key is to reduce the points at which food will be trapped anywhere on the conveyor structure. Such points are referred to as ‘dirt traps’ two words which summarize well the prevailing modern attitude to unhygienic processed food.
EHEDG Guideline 43, 2016
Clive Silverman studied in the UK and Israel and has over 30 years industrial experience in implementing technologies on four continents. He and is currently working from the Head Office of Volta Belting Technology in Israel. He sat on the committee that formulated EHEDG Guideline 43 and a co-author of the chapter on conveyor belts in the ensuing EHEDG Hygienic Design Handbook 2nd Edition. He is married and has 3 daughters and 4 grandchildren.