“Quality and appearance” – cleaning before coating

For 100 years now, Montblanc stands for the highest quality, the best craftsmanship and tradition. The manufacturer of fine writing instruments, watches, leather articles, women’s jewelry, accessories and eyewear has always attached great importance to quality control and cleanliness at its headquarters and production facility in Hamburg. For the cleaning of finest polishing residues, which sometimes remain in the smallest engravings, a new parts cleaning machine was purchased, which is convincing in terms of ease of maintenance, operating costs and cleaning quality.

As a manufacturer of the most exclusive products, which stand for quality, tradition and high craftsmanship, the appearance is of utmost importance in addition to function and durability. Cleaning before electroplating has therefore always been an important part of the production process at Montblanc. The expansion of capacities made it necessary to procure a new cleaning machine for the parts soiled with polishing paste prior to electroplating.

With this challenge, Montblanc approached several cleaning equipment manufacturers. The cleaning specialist Karl Roll in Mühlacker was finally able to convince Montblanc with its concept: In several cleaning trials with different cleaning media in Roll’s technical center, the process and system parameters were optimized. The cleaning quality in the trials was at a level that could not be achieved either with the existing competitor’s hydrocarbon cleaning system or in trials with other manufacturers. However, it was not only the optimal test results, but also the high-quality plant technology, the minimal operating costs due to the heat recovery system and the ease of maintenance, together with a visit to a Roll reference customer, that convinced the company Montblanc.

In order to guarantee the cleaning of the polishing pastes on the one hand and to be able to meet the high throughput requirements in the given confined space conditions on the other, Roll decided to develop a hydrocarbon plant system with two working chambers. The cleaning agent is a hydrocarbon mixture that was specially adapted to Montblanc’s requirements. Due to the safety-related design of the plant and the fact that it operates under vacuum, explosion protection is not required. Since the plant realization in 2002, the parts, which used to be cleaned in two shifts, can be cleaned in a 1-shift operation without any problems.

Non-ferrous metal parts such as brass points, nickel silver clips and cap sleeves, as well as gold nibs are cleaned. These are cleaned in the plant after shaping and polishing and then forwarded for galvanic finishing. The contaminations mostly polishing paste are on the surface of the parts as well as in the smallest engravings. The polishing paste has partially dried on the surface.

70 different washing programs

Depending on the parts loaded and the degree of contamination, the specific programs are selected via a flexible, modern PLC control system with plain text display. Currently, around 90% set goods and 10% basket goods are cleaned with 70 different programs. Depending on the sensitivity of the workpiece surfaces, jacketed or non-jacketed fabric racks with or without lids are used.

The first working chamber is loaded with the goods via the automatic loading and unloading device. After locking the working chamber, checking the door seals and evacuating the working chamber to approx. 100 mbar, the first work step is pre-cleaning. The solvent is flooded from the storage tank 1 into the first working chamber and pumped in a circuit at a temperature of approx. 65 °C. The solvent is then pumped into the second working chamber. Flooding always takes place via the filtration unit (70 µm), so that the solvent is continuously freed from solid particles and treated. Due to the increased temperature and the resulting turbulence, the paste residues are detached from the part surface. Depending on the program selected, ultrasonic cleaning can also be carried out after or instead of flooding. Once this process is completed, the working chamber is emptied via a filtration device back into the storage tank 1.

Single ultrasonic oscillator specifically aligned for the goods

Now the post-cleaning process begins. Fresh solvent is flooded from the storage tank 2 into the first working chamber. In order to be able to optimally remove the remaining firmly adhering contaminations, both working chambers are equipped all around with individual ultrasonic elements which are specifically aligned to the goods to be cleaned. Once post-cleaning is complete and the solvent has been pumped back into the storage tank 2 via a second filtration device (50 µm), the final cleaning step, vapor degreasing, begins. In this process, the hot solvent vapor is fed into the working chamber where it condenses on the part surface. This washes off any residual impurities that may still be present. Subsequent drying takes place at approx. 1 mbar. This vacuum is achieved by the powerful two-stage pumping station. After completion of the drying process, the baskets with the parts are taken out of the chamber again via the unloading device and can be removed at the end of the unloading roller conveyor. One program cycle takes between 12 min and 25 min. Even persistent, dried polishing pastes can be completely removed from the surface of the parts. During the entire process sequence in the first working chamber, cleaning and drying takes place simultaneously in the second working chamber, possibly with a different selected program for the next batch. In a continuous plant operation the number of batches to be treated in one hour is doubled.

Quality is everything!

The parts must be clean and may not be damaged. Therefore, a visual quality control with a magnifying glass takes place directly after cleaning. Here, attention is paid to any drying and pigment residues, as well as deformations etc. A further inspection of the parts and the end products takes place via the central quality control at Montblanc.

External vacuum distillation for automatic oil discharge

The cleaning system is supplemented by a bypass vacuum distillation unit. This provides 120 l/h of distillate to treat the solvent simultaneously to the normal plant operation. The oil and solids content in the steam generator is thus kept at a low level and the maintenance intervals for draining and cleaning the steam generator are considerably extended. Furthermore, the additional treatment ensures a high-quality solvent and constant process parameters during plant operation. From the plant’s steam generator, the solvent-oil mixture is continuously fed to the external vacuum distillation unit and distilled at a pressure of approx. 50 mbar. The solvent evaporates at this pressure and the oil accumulates in the boiling sump. When an oil content of approx. 80% is reached, the supply from the plant’s steam generator is interrupted and the pressure is further reduced. With a simultaneous increase in temperature, the boiling sump is thickened. The remaining waste oil with a low solvent content is automatically emptied into a waste solvent barrel. With this system, the plant can be operated for up to 12 months before it is necessary to empty and clean the steam generator.

Low operating costs due to heat recovery

The integrated heat recovery system ensures a reduction in energy requirements and thus also in operating costs. The energy required for distillate generation in the system simultaneously provides indirect heating for the two storage tanks. In this way, the energy loss due to the goods throughput can be compensated. The steam is fed through the storage tanks via heating coils. The solvent in the storage tanks absorbs the thermal energy and cools the heating coils in the process. The steam that condenses in the heating coils as a result is fed back into the storage tanks as solvent distillate via a water separator. This eliminates the additional energy consumption of the cooling system otherwise required to condense the vapor.

The plant also proves to be very easy to maintain and repair thanks to the well thought-out and generous arrangement of the individual components, explains Mr. Briewig, the plant supervisor. For example, the distillation plant is designed with a flanged heater, which is indirectly heated electrically via steam. This heating has the advantage that the steam tube can be easily removed for cleaning if necessary. Another advantage compared to the usual bottom surface heaters of some competitors is that a caking of contaminations on the vessel bottom and thus the deterioration of the heat transfer – which would result in an increase in energy consumption – is not given with this design.

The system and the external vacuum distillation unit have been running to Montblanc’s complete satisfaction since commissioning. This is due not only to the durable plant technology and the good service provided by Roll, but also to the conducive care and maintenance provided by the plant operator.

(With kind permission of Karl Roll GmbH & Co KG, Reinigungssysteme, Kanalstrasse 30, D – 75417 Mühlacker-Enzberg)