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Dry January
Monday, 11 April 2016 00:00

A new drying system from Harter is bringing impressive results

Time was when bulk material had to be transferred, often in a roundabout way, from a barrel to a centrifuge to be spun dry. Today, with sufficient amounts of dry air routed appropriately, small hardware can be dried in barrels in a gentle way involving no or only minimal interval movement of the items being dried. Duplex barrel drying with barrels in vertical or horizontal array has long since been realized, too. The resulting drying quality is high.

Drying system manufacturer Harter of Stiefenhofen, Germany, has learned that the drying operation constitutes a bottleneck in the overall process of many plating companies. The plating process has to be interrupted and bulk material manually transferred to centrifuges. The drying results are not always satisfactory with the material often left incompletely dry. Also, centrifuge drying deteriorates surfaces and sometimes compromises corrosion protection. There is a simple reason why barrel drying produced unsatisfactory results in the past: It was common practice to just blow hot air onto the barrels. There was no sufficient air flow, no forced air routing, and environmental conditions were not maintained as required. This is no longer state-of-the-art. Today, many examples show that comfortable in-line bulk material drying is possible.

Two components to success
The German company Harter manufactured its first barrel dryer almost 15 years ago. Harter purpose devised a heat pump based condensation drying system which, through physical action, quickly absorbs humidity on the surfaces of items to be dried, thus drying these items. This alone does not suffice to accomplish the extremely difficult task of drying inside the barrel. The second critical factor is appropriate air routing using the so-called half-shell technique. Dry air must be passed exactly to the place where humidity is to be absorbed, that is through the custom perforation into the barrel and out again. Air, by its very nature, follows the path of least resistance. To force it to follow the appropriate path is one of the two requisites for success. A perfect combination of these two components, only, ensures successful static in-barrel drying.

Static centrifugal drying
Barrel drying development started as early as in 1996. A Swiss company manufacturing fasteners of various sizes and geometries had launched a pioneering project. Bolts and screws were galvanized in the existing barrel line and then transferred to so-called centrifugal baskets for drying. The items were centrifuged in eight stations simultaneously at that time. After this operation, the fasteners were completely dry but corrosion protection was inadequate. Also, some of the fastener surfaces were scratched. The goal was to eliminate rejections and deterioration. Today, there are four stations where fasteners are dried without being moved. Targeted routing of extremely dry air has replaced centrifugal movement. The drying stations could not be installed in-line due to space restrictions. This is why the operator chose to retain its procedure – unloading from the barrel and loading into the basket – while investing into new baskets and drying stations.

A solution for each individual barrel
Much has happened ever since – both the technology has been advanced, and the number of barrel dryers installed has risen to well above one hundred. The first barrel dryer proper was installed with Duscher Galvanotechnik of St. Florian am Inn, Austria, in 1999. And there have been duplex barrel applications, for example with plating company IMO Oberflächentechnik of Königsbach, Germany. Their barrel dryers had not worked satisfactorily. Following successful trial tests of small hardware for use in the electronics industry Harter installed condensation dryers in all IMO fully automatic bulk material processing lines – duplex barrel type with barrels in horizontal array. Today, their material is statically dried within the specified cycle time. The drying trough and the built-in half-shell provision is always customized to comply with the customer’s existing barrel technology. Also, the drying trough has an automatic cover system to prevent air from escaping to the production area and to minimize energy loss.

Duplex barrel line drying
The internationally operating RUAG Technology of Altdorf, Switzerland, now Impreglon Coatings AG, wanted to increase the output of their plating line in 2010. Their process lines were also interrupted at that time. Bulk material was loaded in centrifuges and dried using hot air. RUAG were no longer willing to accept the extra time and handling effort plus the quality impact of deteriorated surfaces. The customer’s requirement was to integrate drying into the existing duplex barrel line. This project was a new, major engineering challenge for Harter. And its successful realisation was another milestone in Harter’s development. Today, RUAG dry bulk items at cycle times of six to ten minutes as appropriate for the type of material. The plating line cycle time is 15 min. With 9.5 kW rating, the Airgenex dehumidification module attached to the dryer does not only provide low energy operation but also high quality drying results.

Combined barrel/rack drying
There are exceptional applications where a customer requires a combined system for barrel and rack drying. An example is AHC Oberflächentechnik of Weiterstadt, Germany. The operator’s mandatory requirement was to have effective drying in their vertically arranged duplex barrels while, at the same time, allowing optional rack drying in the drying chamber. The half-shell technology had to be customized to meet this requirement. The two barrels have individual half-shells which move aside before the barrels are removed to make way for another barrel or a rack to be inserted.

Drying in the clock and watch industry
Drying in so-called Vibarrel baskets by STS Industrie S.A. of Yvonand, Switzerland, is a novel development. These baskets, when subjected to vibration, induce in the load a constant movement about the barrel axis. Today, several customers plate and dry hardware inside Vibarrel® baskets. Centrifuging has become obsolete. This ensures gain in time, better quality and process reliability. On top of this, Harter developed a special air routing system which automatically adjusts to the size of the Vibarrel® baskets. This way, dissimilar size baskets may be loaded in a single dryer without air loss incurred. Vibarrel baskets are primarily used in the Swiss clock and watch industry. The low temperature, gentle and stainless drying of highly sensitive smallest parts, such as case and electronic hardware, is an enormous process improvement for the clock and watch industry.

Trial testing brings success
Problems with often existing dryers tend to repeat themselves: process interruption, manual handling, unsatisfactory drying results, deterioration and rejections. Harter's solution approach is also always the same. Drying of bulk material with high water loads is a particularly difficult task. The parameters for successful drying must therefore be determined in Harter's in-house pilot plant station. The customer’s most delicate products are normally used for trial testing. This ensures that the solution found can be safely applied to the operator’s whole portfolio. Local conditions, cycle times and barrel properties are reflected in the layout and design of the new barrel drying system. “We always design a special forced air routing system for each individual application“, says Norbert Fessler, managing director of Harter. “A lot of know-how and twenty-five years of dryer engineering experience is put in this effort.“

Extremely dry air
The dryer has always attached a so-called Airgenex dehumidification module providing the appropriate environmental conditions inside the drying chamber. The module supplies the extremely dry air which contributes to the success of the process. The Harter named “heat pump base condensation drying” is a process capable of drying any kind of solid at low temperatures between 20 °C and 90 °C as appropriate for the specific application. For barrel drying, 75 °C maximum is used in order not to impair the life of the plastic barrels. Drying is effected by passing extremely dry and, thus, unsaturated air over the items to be dried to absorb humidity. In a downstream dehumidification module, the air is stripped of the humidity it carries. The humidity is condensed and the condensate drained off. Subsequently, the cooled air is reheated and recirculated. The loop is closed. This makes the drying cycle almost emission free. The dehumidification module, which controls the environmental conditions inside the dryer, is attached to the drying station. It does not matter if batch or continuous drying is used. This drying system may be adjusted to bulk, barrel or rack dryers, and to belt or chamber dryers as well. Also, products to be dried may be of any make or material.