MFN Trainer Column
in Vol. 14 - March Issue - Year 2013
Degreasing Additive Improves The Process Reliability Of Blasting Processes
Worn out blade from operating mix with too much fines
Left: oily origin metal surface, middle: blasted but still oily surface, right: blasted and de-oiled surface
MFN Trainer Thorsten Evert - training on site
A well known weakness
Contrary to widespread opinion, shot peening is not a simple, coarse and dirty process.
Conventional shot peening is also not a process for the degreasing of metallic surfaces.
Quite the opposite, shot peening is a complex process in which - according to the definition of task - it is necessary to consider inter-related details of different importance at different positions.
For example the contamination of the blasting shot; which is the actual tool, by oils, greases, oily substances or oil-like substances must be avoided.
If this prerequisite is not, or not sufficiently observed this results in a chain reaction of damaging influences and effects on the shot peening or blast cleaning process itself and its results.
Users of blasting systems are fundamentally aware of this.
Metal blasting shot and the objects to be blasted are both metal surfaces. The shot peening process entails permanent contact between both of these. A very intensive exchange of embedded oils and greases is therefore possible between the objects blasted and the blasting shot. The fatal result is, initially, the homogeneous distribution of these interfering substances over the entire process, as with an infection.
This results in the contamination of the blasting shot, the object subjected to blasting, the shot-blast system and, not in the least, the filter media and filter systems.
Oily dust particles are transported by the dust extraction in the blasting room and the separator to the filter media of the filter system. The filter is intended to serve the purpose of separating dust particles, such as abraded metal, shattered grain, contamination, rust or scales, from the air and ultimately eliminating these from the process.
However, oil and grease also cause dust accumulation here, with the filter media. The sticky particles are no longer separated on passing through the purification stage of the filter, such as by an air pulse, and gradually and increasingly clog the filter media.
This in turn reduces the air flow velocity in the cross-current of the air flow separator. The separation capacity of the separator continuously drops. The fraction of dust and undersized grains in the operating mixture rises constantly.
The blasting intensity is reduced, in spite of constant energy consumption.
The roughness height of the shot-blasted surfaces is lowered.
The degree of cold work is permanently reduced.
Significant increase of wearing on machine parts.
These changes for the worse occur gradually and uncontrollably.
The process reliability can then no longer be maintained.
A simple solution
The described serious defects can be eliminated easily.
A new supplementary process with the use of a degreasing additive can be easily integrated in the existing blasting process. The additive can be poured directly into the return flow of the blasting media. Then it is permanently mixed with the media on the transport, in the hopper and during the blasting process. It is immediately effective and, within a short time following admixture, a significantly better free flow capacity and therefore an improved peening result will be clearly evident.
The additive is comprised of microscopically tiny thin platelets, which position themselves on the oil wetting of metal surfaces of the abrasive and the work pieces. Due to the comparatively very high force of adhesion, oils and greases are immediately virtually torn away from the metal surfaces and bound to the surfaces of the additive particles. As a result of the blasting effect, the additive particles, with oil and grease adhering to them, are removed from all metal surfaces and transported out of the system by air flow. The additive particles are practically completely removed from blasting process by the air flow separator and the dust extraction.� In the follow-on filter system, the now no-longer sticky dust particles are then separated, and can be disposed of with the normal filter dust.
The use of an additive in shot peening processes immensely simplifies these and enables very effective improvements. The cost savings which can be achieved and the possibilities of quality improvement make the additive process an interesting alternative and/or supplement to conventional wet-chemical purification processes in connection with shot peening processes. Many possibilities are now available for improving the blasting process reliability itself and even for integrating the purification step into this process of surface treatment.
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