The world’s first fully automated production line to produce 1kg silver blanks (Ag 999) has been commissioned.   

As a result of the extremely high demand for silver investment products throughout the “COVID-period”, a new production concept has been introduced.

The production of investment coins and similar silver products do contain typically numerus steps, such as: melting, casting a strip, milling the strip, rolling the strip, annealing the strip, fine rolling the strip, blanking, rimming the blanks, annealing the blanks (softening), surface finishing the blanks, coining the blanks and finally packaging the coins!

In the mint industry around the world, it is very common that all these steps are not connected to each other. This offers some flexibility in the production of different silver products. On the other hand, a direct connection between the different production steps provides a continuous flow and, more importantly, a consistent level of quality.

In the described concept, the automation starts with a silver coil from which the blanks are cut out (blanking). The melting/ casting is always excluded from the automation due to its environmental impact (heat and dirt).

Concept: The blanking line is connected via signal exchange and transport belt to a loading system to feed the furnace. The 1kg blanks can be positioned next to each other on the stainless-steel belt of the furnace. The duration through the furnace is approximately 20 minutes in a protected atmosphere. 

At the exit of the furnace, it is important that the parts are smoothly transferred onto a belt to allow the blanks to enter the surface finishing at the entrance. 

This is where the newly developed technology comes in:  

A so called throughfeed vibrator allows a surface finishing time of the blanks between 12 and 18 minutes. The design of this surface finishing machine is unique. The 18-meter-long throughfeed vibrator is designed as a spiral concept. The three spirals, polyurethane coated from the inside, are positioned on top of each other with a clearance of about 200mm. 

The vibration is generated by a high performance unbalance motor located at the centre of the machine, creating an amplitude between 3,5mm and 6mm. This amplitude is the actuator to rotate the surface finishing media inwards. It also pushes the media and the blanks upwards towards the separation area, where the surface finishing media and the silver blanks are separated from each other. Every 30 seconds, a blank enters the finishing line - keeping their distance and never damaging each other. Thanks to the spiral design of the finishing machine, the media is fed back by gravity towards the entrance of the throughfeed vibrator.

The blanks will be vibrated smoothly onto the Teflon screens. Teflon prevents the blanks from being scratched.

The finishing cycle is one of the most important production steps within the manufacturing line. Vibration as the mechanical act, water plus chemistry and the surface finishing media need to be harmonised. The hammering of the media on the surface of the blanks hardens the surface in a micron layer, whereby the deionised water and the chemicals ensure the required cleanliness and preparation prior to the hammering step. 

The surface finishing media has the biggest impact on the required finishing results. Stainless steel media is very well known to finishing experts – not chosen in this application. 

CHD media – “Ceramic High Definition” - is the only media performing well. The media shows a density of up to 5kg per litre, heavy enough to handle the heavy silver blanks. The media mix of 75% 3.3mm diameter balls and 25% 5x8mm Satellites  – 3,800kg as a permanent load within the throughfeed vibratory machine.

After the blanks have been surface finished for about 15 minutes, they leave the stepless separation section and enter the rinsing area. This area is designed in a way that the blanks will only touch the transfer area on their edges, eliminating any risk of damage. 

DI-water rinse and air flushes pre-dry the blanks before they enter the textile drying process. This method has long been valued in the mint industry and has also been adapted for this new development.

A pocket cloth design of the textiles cover the drying area, heated up to 80 degrees Celsius to remove any micro-moisture from the blanks. This is the final step before a robot picks up the blanks and places up to 500 pieces onto a Teflon pallet. 

Up to five pallets can be stored before the storage area requires attention from an operator. The operator will locate one of those pallets next to a coining press. It is essential to coin the blanks within a specific period of time to prevent any environmental influences from changing the perfect surface quality of the blanks.

This concept adds on to a series of automated processes developed by Spaleck Oberflächentechnik GmbH & Co. KG Germany for the mint industry!

Contributing Editor MFN andSales Director, Spaleck 

Oberflächentechnik GmbH

Germany

Tel. +49.1621.382853 

E-mail: thomas@mfn.li