Increased quality and productivity

Walter Sonntag

The companies belonging to the Dentaurum group offer a range of more than 5,000 different products. Their tried-and-tested range of orthodontic products includes bracket systems, braces, wires and wire elements, space correction screws and various instruments and equipment. The group’s dental range is based on the balanced interaction of optimally coordinated investments, cast metals, materials and equipment. Dentaurum has developed spe-cial titanium-casting systems and dental laser devices for further processing biocompatible base materials such as pure titanium.

Increasing production, safeguarding quality, broadening the product range to 15 formulations from the original two and – last but not least – optimizing workplace conditions were the main goals of the partnership with AZO. “Our plan was that the plant should ease our operating staff’s workload and protect their health, as well as ensure consistent quality through documentation of the production processes,” explained Peter Ohnmacht, Senior Director and Head of Technology and Production in the Chemical Division at Dentaurum.

The tough requirements involved called for a complex system with simultaneous automation of the raw materials and micro-ingredients (Fig.1 and 2). Reaction ingredients and coloring matter more than anything else in Dentaurum’s case. To protect the health of all personnel and simultaneously ensure product quality, an enclosed system which operates free of dust and contamination was constructed. The project was not without serious challenges. The available space was relatively small. The huge product demand dictated that the new production system should begin operation as soon as possible with absolutely no downtime.

The production of investments requires large quantities of various fillers (e.g. quartz powder). In 1978 AZO equipment automated the feeding of fillers, to relieve the staff of the tedious task of moving approximately 68,000 sacks per year from the storage facilities to the production line. Owing to the highly hygroscopic nature of these fillers, the six mild-steel silos used for storing them, each with a capacity of 45 m3, were given a high-quality coating of epoxy resin and built in a shell form, in order to permit their insta-llation in an enclosed room (Fig. 3). Two further silos were added in 1988 as a result of increased demand. When the plant was enlarged in 1997, the initial silos looked as good as new, despite almost 20 years of continuous operation. 30 to 40 t of raw materials are delivered in bulk trucks and emptied into the silos. Each batch is subjected to a receiving inspection in the company’s laboratory, as a means of assuring quality. The respective materials are only released for storage if their quality meets Dentaurum’s high standards, in accordance with the supplier’s documentation. They are subsequently tested for particle distribution, moisture content, pourability and powder density. Element and compound analyses are also conducted. If any quality deficiencies are discovered during these extensive material tests, it is possible to empty the silo again by means of the conveyor scale and to fill the raw material in question into big bags for return to the supplier.

All bulk ingredients need to be conveyed at a high throughput rate. A conveyor scale with a multi-port valve was installed, to ensure an efficient and economical feeding process. This allows high-precision delivery of individual ingredients from the large indoor silos to the mixer. Any impurities and agglomerates are automatically removed by a centrifugal screener, which is integrated into the material flow. The weighing and dosing accuracy achieved with the chosen equipment not only met, but also surpassed, the stringent requirements set by Dentaurum when working with a batch of 2,000 kg (Fig. 4).

The large variety of alloys used in the field of dental technology calls for a multitude of different investment compounds. Each alloy has its own characteristics that influence the way in which it is processed. The contraction which occurs when metals cool down, for example, must be offset by a corresponding expansion of the investment by precisely the same factor.The high quality and large variety of investment compounds (currently at least five different formulations) manufactured by Dentaurum necessitate the use of additional raw materials and extremely diverse additives. In many cases, this involves reaction ingredients that must be combined with particular care and accuracy.

Depending on the supplier and the quantity involved, the requisite raw materials and micro-components (approx. 300 t/year) are delivered either in big bags or in sacks. In order to integrate these into the automation process, AZO installed 10 additional indoor silos in the new plant. These have a diameter and capacity of 800 mm and 1 m3, 1100 mm and 2 m3 or 1600 mm and 5 m3 respectively, according to the throughput.

The advantages are impressive:

l In-house transport is reduced to a minimum.

l The workload has been significantly reduced and time saved.

l 40 to 50 fewer pallet slots are needed in the high-bay warehouse.

l Hygroscopic materials no longer have to be transported across the yard and exposed to outdoor elements.

l The time-consuming check-in and check-out of raw materials in the warehouse is no longer necessary.

Since big bags have become established as an economical transport medium, a separate big-bag filling station was installed for transferring materials into either the large warehouse silos or the smaller day silos. Materials delivered in sacks are transferred dust-free to the day silos via a special sack-filling station. An integrated empty-sack compressor simplifies disposal.

In order to ensure careful, dust-free feeding of the silos, a vacuum conveyor facility was installed and used as a collective feeding system. All the silos are equipped with generously dimensioned filters, an efficient vibrating silo discharge and metering screws with coarse/fine adjustment to facilitate consistent, uniform dosing. An additional safety filter fitted upstream of the vacuum generator guarantees virtually dust-free operation, thereby fulfilling the requirements of the German Clean Air Code (TA-Luft), which specifies that powdery or dusty emissions should not exceed a 10 mg/m3 limit. Since the ingredients involved are highly abrasive, a slow-moving, pneumatic conveyor system with abrasion-resistant bends was installed.

The reaction ingredients required for the respective production processes are delivered to the mixer via a special conveyor scale (capacity: 50 kg), multi-port valve and electro-magnetic weighing device. A special big-bag filler station installed directly at the mixer enables optimum flexibility for feeding pre-weighed quantities. This in turn permits optimum flexibility during the production process.The high level of formulation flexibility within extremely narrow tolerances ensures that Dentaurum’s investments achieve a very high level of dimensional accuracy, extremely smooth surfaces and optimum temperature and expansion behavior – in each case precisely matched to the appropriate dental metal alloy (Fig. 5).

Depending on the terms of reference, the investments can be admixed with other additives or possibly dyes. The operator can weigh these supplementary ingredients to the nearest gram on a compact platform scale and deliver them directly into the mixer via a filling hopper.

The integrated process control and graphics system enables optimum production planning; orders can be entered in advance and called up on schedule. Data relating to the storage location, materials and formulations as well as formula allocations and material inventories is checked and if necessary updated via the master data management facility.

The operator in the central control station can switch between a general overview and five detail views according to current requirements.

These clearly structured color graphics show the contents of the various silos as well as the complete mixer feeding operation. Color coding enables the operator to identify at a glance which functions are active or in-active. At the same time, all the actual and desired values for the entire mixing process can be monitored. An integrated error-indication system enables rapid localization of, and appropriate reactions to, any faults which might arise.

Since production operations take place on two floors within the building, an additional visualization system is installed on the lower floor where the mixer is located. It is provided for monitoring purposes only, however. Process intervention is restricted to the authorized operator in the central control station via a password.

A production history is maintained in the batch record under the heading “Production specification”. This simplifies lot tracing as well as customer documentation and formulation certificates.

The actual material consumption per production order can be accurately determined on the basis of the order statement. The current levels can be read out at any time, thus enabling material planning in good time. This prevents production downtime caused by a lack of raw materials. The daily, monthly and annual throughputs can be calculated by the statement management system. This represents a crucial advantage as far as planning and economic analyses are concerned.

The automated feeding system developed by AZO for Dentaurum has more than fulfilled all specifications and expectations. The space available for the project was put to optimum use. The quality, capacity and flexibility of production operations were all improved. Above all, the system has improved workplace conditions, thereby enhancing staff morale. “One particularly positive aspect was that we were able to continue production without any downtimes whatsoever and thus managed to meet all our deadlines“ added Peter Ohnmacht. “Our users – the dental laboratories – testify to the consistently high quality of our products. This customer satisfaction gives us the incentive to improve even further. We therefore see our new automated feeding system, with its state-of-the-art process control technology, literally as an investment in the future.”

AZO

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Further information cpp 200