Like any other industries, the suppliers of mass finishing equipment are constantly striving to improve their products to make them more economical and environmentally more sustainable. This is partially achieved by digitization, the use of sophisticated electronic controls, but also by creative new equipment designs. In this article, we highlight a success story, where a supplier of mass finishing equipment was able to improve the energy efficiency of its rotary vibratory driers by utilizing an innovative new heating system. Compared with traditional vibratory drying equipment, the new driers require an up-to-70% lower energy input and reach their operating temperatures in half the time. All this results in significant annual cost savings of thousands, even tens of thousands, of Euros and makes the drying operations considerably more efficient.

Drying of the finished work pieces – an essential part of mass finishing operations

With a few exceptions, for example, dry polishing, most mass finishing applications are “wet” processes, requiring the continuous addition of water and suitable chemical compounds. Since the finished work pieces are coming out of the machine in wet condition, they must undergo an intensive drying operation. This prevents premature oxidation/corrosion and facilitates downstream manufacturing operations, storage or shipping of the work pieces.

The most common drying methods are utilizing hot air or special drying media that is heated to a certain temperature. In hot air driers, the work pieces are exposed to a flow of hot air, which blows away the moisture from the work piece surface and evaporates it. In driers with drying media, the work pieces are embedded in the media that is heated to a temperature of 45 to 60°C. This absorbs the water from the work pieces and, since the media are heated, the absorbed moisture evaporates.

Rotary vibratory driers are, by far, the most popular drying systems in mass finishing operations: They consist of a round processing bowl, a vibratory motor placed in the center of the processing bowl, and a heating system. For the drying operation, the bowl is filled with drying media and the wet work pieces that come from the finishing machine. The vibratory motor induces a spiral movement of the media/work piece mass. The constant rubbing between media and work pieces causes the media to absorb the moisture from the work piece surface.

Drying is not cheap!

Obviously, these drying systems, be it by hot air or with drying media, demand a lot of energy. For example, depending on the machine size, hot air belt driers have a total installed power between 26 and 77 kW, of which nearly 90% are required for heating and distributing the air. 

The total installed power in larger traditional rotary vibratory driers can be up to 27. 5 kW with the heating power alone accounting for up to 20 kW.

At an average price per kWh of around 0.40 Euro (2023 price level in Germany) the annual drying costs in mass finishing operations amount to thousands, even tens of thousands, of Euros.

New heating system cuts the costs for heating energy by up to 70%

In light of the drastically increased price for electric energy and growing demands for environmental sustainability, it is not surprising that the suppliers of mass finishing equipment are looking for ways to make the drying operations more efficient and less costly. By developing an innovative new heating system for rotary vibratory driers, a leading manufacturer of mass finishing equipment is not only able to make the drying operation faster, but also to reduce energy consumption for heating the drying media by up to 70%.

To date, this manufacturer places heating spirals in the non-vibrating machine base. For a good reason: By attaching them to the bottom of the processing bowl, they will be exposed to the intense vibration in the processing bowl, thus creating the risk of premature failure. However, placing the heating unit in the machine base means that it is relatively far from the drying media in the processing bowl. This “indirect” heating arrangement causes substantial heat loss, resulting in a fairly long heat-up phase and substantial energy input to achieve and maintain the required operating temperature of the drying media of 45 to 60°C.

Innovative heating block replaces the heating spirals

To resolve this problem of “indirect” heat transfer, the manufacturer develops a clever system of electrical heating blocks that can be firmly bolted to the underside of the processing bowl. Since the blocks are now firmly attached, they absorb the vibration, no matter how intensive it might be. This revolutionary design allowed to place the heat source at where it is needed, namely the processing bowl, and completely eliminates the risk of premature failure.

This switch from “indirect” to “direct” transfer of the generated heat to the drying media has amazing results. Not only could the installed heating power be substantially reduced. At the same time, the heat-up period could be reduced from about 60 to 30 minutes, and the maximum temperature of the drying media could be increased by nearly 20%. The shorter heat-up period increases the productive time of the drier, and the lower energy requirements result in substantial energy savings.

The energy savings at a glance!

For a comparison of the heating energy requirements between the old and new designs, we choose a mid-sized rotary drier with a processing bowl that holds 290 liters of drying media and work pieces.

Our calculations consider that the heating system does not have to be “on” all the time. Actually, it is intermittently switched on and off to maintain the specified operating temperature. While during the heat-up phase, the heating system is continuously switched on, during the actual drying operation, it must only be switched on 50%. Therefore, the average “on” time amounts to about 55% of the actual run time.

The above shows impressively, how a clever design change in a standard machine can save thousands in costs and can make an invaluable contribution towards environmental sustainability.

Other developments in the field of work piece drying

The same equipment supplier develops other drying systems with a goal of saving energy and making the drying process more efficient. For example, in the field of coin blank finishing, the blanks must be polished and dried before they can be coined. For this demanding task, the company develops a hot air drying system based on heat pump technology.

After the blanks are polished, they undergo a drying operation that must ensure that they are absolutely free of dust and stains, are not discolored and are not damaged in the form of scratches.

This is achieved with a hot air drying method utilizing heat pump technology. The air from the drying unit, saturated with moisture, is guided through a heat pump-based condensation system, where the moisture is removed from the air. The now dry and unsaturated air is then returned to the drying unit.

With this solution, the energy requirements for the drying operation could be reduced by up to 70%, another significant contribution towards cost saving and environmental sustainability.

by Eugen Holzknecht 

Contributing Editor MFN and

Rösler Oberflächentechnik GmbH

E-mail: holzknecht.usa@gmail.com