FASTENINGS & ADHESIVES FEATURE


Balancing is required for various types of applications. Up until now, the predominate way to balance an object was through subtractive methods, like machining and lasering. However, a new additive balancing technology for rotating parts has been developed which consists of high-precision unbalance measurement, precise dispensing and very fast curing of specially formulated balancing compounds based on adhesives. Dr. Manfred Bobertag, managing partner, Präzisionsmaschinenbau Bobertag, and Dr. Karl Bitzer, head of product management, DELO Industrial Adhesives, explain


A BALANCING ACT B


alancing is not only required for fitting new tyres, it is also necessary for most


applications that include rotating components – like electric motors, fans, blowers, pumps or turbines. When an unbalance is improved, it enhances the quality of the device by reducing vibrations and loads, while enabling higher rotational speeds, lower noise volumes and a longer lifetime. Balancing ensures, for example, that a hand


drill has little vibration; noise from a dentist’s drill is dampened; and the ability of a fan to run at low noise levels. Regardless of the industry – automotive,


aerospace, medical technology or mechanical engineering – balancing demands the highest precision. As unbalance forces increase as the square of the rotational speed, a doubling of the rotational speed means that balancing must be performed four times as well. Balancing performed in serial operations is


usually subtractive, meaning excess material is removed from the object being balanced. In this type of process, sacrificial material must always be available so that it can be partially removed as needed to balance. In contrast, additive balancing is more material-efficient, involving the exact amount of material required to balance a unit.


HIGH-TECH ADHESIVES A completely new additive balancing process, based on the use of adhesives as balancing compounds, has recently been developed. In the past, attempts to correct unbalances


with two-component epoxy resin did not meet demands, and was a slow, inaccurate, process that did not reproduce well. The process is based on an entirely different


approach suitable for industrial serial processes that require maximum accuracies without the removal of material from the workpiece. With minimum possible correction accuracies as low as 0.1mg, residual unbalances of 1mg*mm, as required by the optical industry, can be achieved. Due to its excellent process reliability, this additive approach is also ideal for use in small fans that have medium unbalances of 50 to 100 mg*mm. This is possible because unbalances can now be measured much more precisely than before. A


speed and volumetric accuracy, the application of the adhesive, which can be performed in one or two balance planes, is performed using a non-contact jetting method. The balancing compounds cure completely under high-intensity UV light within a few seconds before a control measurement verifies the result. The balancing is usually completed following a correction step. Depending on the required cycle time, the


dispensing and curing can be performed in either the measurement station or a separate station. Since process steps run simultaneously, this technique can also be used for extremely high quantities and is scalable from small-batch to large-scale production.


WEIGHING UP THE DIFFERENCES Besides technical issues, it is important that, no matter what process is chosen, it is cost-effective for industrial applications. If the cost of the three balancing methods – machining, lasering and bonding – are considered, machining usually has the lowest investment costs. On the other hand, the resulting tool costs, dust and chip removal, as well as time required for tool change, can incur ongoing operating costs. Lasering initially incurs the highest


investment costs. However, it offers the lowest operating costs, which is a good option for high-volume applications. The investment costs for bonding usually


ranges somewhere between the two other processes of machining and lasering. Operating costs are incurred by adhesive as a consumable,


/ DESIGNSOLUTIONS


Balancing fans with adhesive


calculation of the required position and the amount of the balancing compound that will be needed to bring the unit into balance is performed. Once the number is determined, a light-curing adhesive is used for correction. This adhesive should have a high density, so that the required mass per adhesive droplet only requires little volume. Due to its high


amounting to 0.03g of adhesive per unit for typical components. From a controlling perspective,


when deciding on any one of these three processes, annual production volumes and the


size of the application should be taken into consideration. In the high-end segment, technical advantages are usually more influential in the decision making process than whether the solution is economical. Machining offers a lasting solution. However,


it requires excess material, produces chips and is expensive because of probing problems. Lasering represents a precise process, but is a subtractive solution. An additive process is a good solution.


Jetting of balancing compounds requires no sacrificial material and offers the highest precision, where subtractive processes are often prohibited for certain assemblies to protect the bearings against dirt.


THINK OBJECTIVELY Users need to set aside their preconceived objections to all three processes – for example, if bonding will hold, machining is antiquated, lasering will cause fine dust pollution. Users should instead objectively consider their advantages and disadvantages, calculate their economic efficiency, and perform preliminary tests on them. Short cycle times, freedom from chips and


the precise control of mass correction are excellent reasons to consider the new additive balancing process.


DELO Industrial Adhesives www.delo-adhesives.com/en/


DESIGN SOLUTIONS | FEBRUARY 2021 11


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52