Steel belt conveyors have been used for food processing for the best part of a century. Their first appearance in a continuously operating bake oven was in 1925; the 1930s saw the introduction of perforated steel belts on drying lines; and applications for this extraordinarily versatile medium expanded further still in the 1950s when they began to be used in contact freezers and on fish and meat cutting lines.
Wherever a product needs to be transported through a processing environment, hot or cold, dry or humid, steel provides an effective solution. It is a material with remarkable properties, capable of operating in temperatures as low as -80 deg C or as high as 750 deg C. On the one hand, it is extremely strong and resistant to damage, on the other, it is also incredibly flexible, undergoing constant changes in stress as it passes around the drums of a conveyor thousands of times a day, often undergoing a similar number of cooling and heating cycles at the same time. This repeats day after day, week after week, for 20 years or more, and still the steel belt endures.
These incredible properties are also reflected in the fact that the steel belt is far less susceptible to damage than other conveyor materials, which in turn means considerably less downtime lost to repair work or the installation of replacement belts.
If problems do occur, a steel belt can soon be returned to perfect working order. Small areas can be cut out and replaced, edge cracks welded and repaired, deformations flattened, and welds ground to a perfect finish. These jobs can be carried out either by the belt manufacturer’s own service teams or by in-house engineers equipped with tools specifically designed for the purpose. Either way, all but the most serious damages can soon be repaired and production resumed.
This longevity leads to a highly attractive return on investment, one that has helped secure the continuing popularity of the steel belt as a processing medium in the face of competition from other technologies with a lower initial investment cost.
But there are other reasons why food processors choose to invest in steel conveyor belts in preference to lower cost alternatives: product quality, process hygiene and production efficiency. For the purpose of this article, we will look at these benefits in respect to three food processing applications: baking, conveying and cooling/solidification.
Bake Oven Belts
The thermal properties of a steel belt make it ideal for conveying products through bake ovens, where temperatures can reach as high as 400 deg C. The belt remains flat and stable, provides excellent thermal conductivity for good baking performance and consistent product quality, and delivers clean product release, ensuring an achievement of high standards for product quality.
But perhaps most important of all, especially in recent years, is the solid form of the steel belt. This means it can be used for an array of baked goods that simply cannot be produced on anything other than a solid surface, such as the American-style cookies that can now be found on supermarket shelves all over the world.
As these products use real butter, and often chocolate chips too, they need to be baked on a surface without any holes, eliminating the risk of melted product dripping and causing a fi re, or simply drying out. The excellent heat transfer and thermal conductivity of the solid steel belt enables the delivery of the desirable combination of a crisp base yet rich, buttery cookie.
Such is the growth in demand for real butter cookies that a number of large players in the industry have converted existing wire mesh lines to run on steel belts. While this is not quite as straightforward as simply swapping out one type of belt for another (the conveyor components also need replacing), it is far more economical—and faster—than having to invest in completely new lines.
Changing global appetites also mean that many manufacturers are now looking at how to increase productivity, both in terms of the variety that can be produced on one line, as well as sheer volume. In both cases, there is a strong argument for steel belt technologies.
Looking at versatility first, one option could be to invest in a perforated steel belt. Available in a range of patterns, perforated belts provide a ‘universal’ solution with the ability to bake products usually associated with either mesh or solid belts. They are also extremely resistant to stretching and deformation, and require less heating energy than either solid or mesh belts.
In terms of volume, steel belts can be run faster than other conveyor types but this is not always a solution. The challenge many manufacturers face today is how to increase production without having to relocate or expand existing premises. One way is by using a wider oven.
For many years the maximum width of a single bake oven belt was 1,250 mm but advances in production technologies have seen this increase to 1,500 mm. Where wider ovens are required (e.g. for pizza or pies), it is possible to create bake oven belts as wide 3,600 mm by longitudinal welding. And yes, perforated belts can be produced in multiple widths too.
A key consideration for all food processing sectors, bakery included, is hygiene, and this is another area where steel belts offer considerable advantages. Put simply, the lack of hidden gaps, recesses or crevices mean steel belts are easier to clean than other conveying materials.
On bake oven belts, this is important as burnt carbon residues will eventually affect the taste and appearance of the product, not to mention the threat posed to human health by the likely presence of acrylamide, a potentially carcinogenic chemical.
In the meat processing sector, hygiene is equally important and again, the ‘cleanability’ of the steel belt makes it the first choice for many processors.
Businesses operating in this industry have to comply with stringent regulations in terms of health, hygiene and safety so every stage of the process—handling, boning, trimming, cutting—must be designed to minimise any risk of bacteria build up. And as a component that comes into direct contact with raw meat, the conveyor belt is a key factor in this.
Stainless steel is a corrosion-resistant material and this means there is no risk of a reaction with or contamination of the foodstuff being processed. It is also a material that can be cleaned and disinfected via many different methods: hot water, pressure, brushes, detergents, chemicals or any combination of these, ensuring the highest standards of hygiene.
This superior cleanability has been confirmed by research carried out by Finnish food laboratory VTT Expert Services Limited, which found that risk of bacterial build-up can be reduced simply by upgrading to a stainless steel conveyor.
Scientists at the laboratory looked at the ‘cleanability’ of three basic conveyor types used in meat processing— stainless steel, solid plastic and plastic slats—and concluded that: “stainless steel is more cleanable than the two different plastic surfaces tested according to the culturing results. The difference is more significant for damaged surfaces.”
Cleanliness is not just a health and hygiene matter either; it also impacts costs. Besides the low water consumption and reduced cost of cleaning chemicals or detergents (as much as 25 percent less) for steel belts, the ease with which a solid steel belt can be cleaned also means less downtime.
Belts used in meat processing also have to be able to resist materials like blood, fatty acids and salt, and often operate in conditions of high humidity and varying temperatures. Again, the properties of stainless steel make it ideally suited to environments such as these where the working life of other materials could soon be compromised.
Cooling And Solidification
The third area to look at in respect of the suitability of steel belts for food processing is the controlled cooling, casting and solidification of products such as caramel, chocolate and hard melt candy, nougat, nut brittle and more.
In this process, the product is applied onto the cooling belt in molten form. Different feed methods deliver different product forms: a wire feeder can be used to create a flat, sheet-type product that is then broken up into flakes at the discharge end; a stripformer will deliver strips that can be cut to length; and a drop depositor can be used to produce pastilles.
As the product is transported along the process line, the heat of the melt is transferred to cooling air that is blown onto the product and also to the belt itself. Another method suitable for products not sensitive to humidity, sees the heat transferred to cooling water sprayed against the underside of the belt. Either way, the excellent thermal conductivity of the belt delivers fast, controlled solidification and the solidified product is discharged cleanly at the end of the system.
The applications described are only three examples of how steel belts—carbon and stainless steel, solid and perforated— are used across the food processing industry. They can also be found in freezing systems, where their superb conductivity helps deliver reduced freezing times, high product quality and low energy consumption, and in drying, steaming, cooking and finishing systems too.
In each of these areas, and others, the unique properties and qualities of the steel belt continue to deliver a convincing argument to original equipment manufacturers (OEMs) and end-users alike. It is also entirely possible that new applications are still waiting to be discovered.