The Danish company Tvilum is one of the largest manufacturers of flat-pack furniture for self-assembly, and sells eight million pieces of furniture a year all over the world through various furniture retail chains. In its highly automated production plants, Tvilum places great importance on process safety and economic efficiency. This is one reason why Tvilum has converted the vacuum supply for two of its palletising robots at its main plant to Busch’s Mink claw vacuum technology. Palletising flat packages has thus become trouble-free, and operating costs have been drastically reduced.
Tvilum was founded in 1965 as a family business. After various mergers, it now belongs to a Danish investor group comprising Viking Trading, Kristiansen Properties and CEO Torben Porsholdt. Today, Tvilum manufactures flat-pack furniture in various styles and designs and sells them worldwide through various furniture retail chains. Tvilum’s headquarters and main plant are in Faarvang, Denmark, with 450 employees. The remaining 700 employees work in two further production plants in Denmark and Poland.
At the main plant in Faarvang, the furniture parts packed in flat packages are palletised by two robots and prepared for shipping in a fully automatic process. Using both robots (Fig. 1), the flat packages are held by vacuum via suction cups and stacked on pallets.
One of the two robots palletising flat packages
In order to generate the necessary holding force, a dry-running rotary vane vacuum pump with a pumping speed of 140m3/hr was mounted on each of the two identical robots. However, these did not provide the required holding force, with the result that packages fell off several times a day, causing the system to come to a standstill and requiring manual intervention by the staff. This also often resulted in material damage.
Peter Larsen, a maintenance technician, tried to make the automated handling process safer and added an additional rotary vane vacuum pump to each robot. These each had a pumping speed of 70m3/hr. As a result, the system became more reliable and the number of furniture packages that fell was reduced.
Another problem, however, was the noise of the rotary vane vacuum pumps. The vacuum pumps were positioned directly next to the robots and their noise level also affected nearby workstations. Peter tried to enclose the vacuum pumps, but this did not prove successful because the heat radiation from the vacuum pumps caused heat to build up inside the enclosure.
He then placed the vacuum pumps in a separate room and connected them to the robots via a pipeline. This solved the problem with noise and heat radiation in the packaging room – or at least, moved it elsewhere. What remained was the elaborate and costly service work. Twice a year, the vacuum pumps were serviced and the vanes had to be replaced.
The rotary vane vacuum pumps used were what are known as dry-running pumps. With this type of vacuum pump, the rotating vanes in the pump casing are subject to high levels of wear because they grind directly along the inside wall of the casing. The vanes containing graphite have a certain self-lubricating capacity, which slows down the wear somewhat, but cannot prevent it. As these vanes wear, there is also a loss of performance in terms of pumping speed and vacuum performance.
Contact with Busch Vacuum Solutions was established at a trade show, where Busch presented a Mink claw vacuum pump that was adjustable via a frequency converter.
As a result, Peter took a closer look at this type of vacuum technology. He believed it had several advantages.
Mink vacuum pumps compress the air completely contact-free. This means that the moving parts inside the vacuum pump do not come in contact with each other. In turn, this means that there is no wear that can adversely affect performance. The contact-free compression principle also has the advantage that it is extremely energy-efficient and requires less power than a dry-running rotary vane vacuum pump.
Peter saw an additional advantage in the fact that Mink claw vacuum pumps are infinitely variable in the range between 10-60Hz via a frequency converter. This allows a preset vacuum level to be accurately maintained, and thus ensures a consistently high holding force regardless of the size of the package, or whether leaks in the suction cup suck in more or less ‘leak air’.
Centralised vacuum supply with two Mink claw vacuum pumps
Peter was convinced by Mink claw vacuum technology, and was given advice by vacuum experts from Busch Vacuum Solution. They recommended a vacuum system consisting of two Mink claw vacuum pumps (Fig. 2), each with a pumping speed of 140m3/hr and connected in parallel with a demand-driven control system.
They were installed in a separate room in January 2019 and connected to the two robots via a pipeline. Immediately after starting to use them, it became apparent to Peter that Mink claw vacuum pumps run much more quietly than dry-running rotary vane vacuum pumps.
After one year in operation (January 2020), he can also state with reassurance that not a single package fell to the ground during this period due to insufficient holding force. In addition, the maintenance effort is minimal compared to the rotary vane vacuum pumps. The gear oil is only changed once a year, just as a precaution. Since Mink claw vacuum pumps have no wearing parts, the costs for their replacement or purchase are completely eliminated.
Another positive effect was the energy savings, which Peter estimates to be more than -50%. Whereas four rotary vane vacuum pumps with two 4kW motors and two 2.4kW motors were previously installed, the two Mink claw vacuum pumps each require 3.5kW for 50Hz operation. Since they are controlled according to demand, full power is not usually required – meaning that energy consumption is even lower than in the calculation (Fig. 3).
Calculation of the energy savings based on the nominal motor rating. The often considerably lower rotational speed of the vacuum pumps and the resulting lower power consumption are not taken into account. The omission of compressed air generation for the ejectors that were previously in operation on the insertion devices is also not taken into account
Peter thus had another idea to save energy. He had previously used ejectors to generate vacuum on four insertion devices for package erectors. These devices insert the individual package sheets into the package erectors (Fig. 4). The compressed air required by the ejectors for vacuum generation was supplied by a compressor.
One of four insertion devices that are also supplied with vacuum by the two Mink claw vacuum pumps
The ejectors were removed, and all four package erectors were also connected to the Busch vacuum system. The system has enough reserves that it also supplies these package erectors with vacuum, and the previously used compressor is no longer needed, which again has a positive effect on the energy balance.
Inspired by these successes in optimising process safety during packaging and the enormous energy savings, Peter is confident that he will be able to implement further optimisation measures in his company using Mink claw vacuum technology.
www.buschvacuum.com
www.tvilum.com
Images: Busch Vacuum Solutions
