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Vol. 13
September Issue
Year 2012
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Articles


in Vol. 13 - September Issue - Year 2012
Dry Vibro-Finishing Processes, Vibrodry



Orbital machine RWO-D-330 Vibrodry version, complete with soundproof cover and suction connector


Brass handles and zamac fashion accessories smoothed with Vibrodry process


Zamac locks and belt cursors smoothed with Vibrodry process


QF30NL5 media inside working bowl for mass finishing of wood articles


Wooden knife hilts, from top left to bottom right: raw, Vibrodry smoothed, vibro-waxed after varnishing

Metal surfaces mass finishing, also known as tumble finishing and vibro-finishing, is going through a very interesting renovation phase.

There are at least two keys to understand this phase: strongly reduced environmental impact and decisive process cost reductions.

This phase has at least two main characteristics: an innovative finishing media (i.e.: abrasive chip) called QF and a series of processes called Vibrodry, both patented (patent pending – I).

In order to see how one can get there, let’s start with the results: the strongly reduced environmental impact and the decisive process cost reductions mentioned above.

The first step was made thanks to the new technology offered by abrasive chips or even the finishing media called QF.

This kind of media, whose complete name is "Quattrofinish", counts with a heterogeneous series of media, including some dry-finishing versions.

Furthermore, it is also important to point out that, among the products designed for dry applications, some media are especially suitable for metal surface finishing whereas others are especially suitable for wood, plastic or softer material surface finishing.

Based on the type of application required, the new metal or wood abrasive media of the QF series can perform finishing processes by themselves, thanks to the balance between density, elasticity and abrasiveness, or, especially as far as metal surfaces are concerned, in combination with additive compounds.

Dry processes with QF media have more advantages than limits. Let’s start analyzing the limitations to deliver proper and transparent information:

Safety – ATEX policy verification

Dry-finishing processes with specific metal alloys (Aluminum, Magnesium) can be considered part of ATEX policies, which regulate environments at risk of explosion.

As much as one felt deep excitement in finding "positive" finishing results, deep respect and attention was paid to the safety issue. This is why this kind of application in some environments was put on hold.

There are always three main causes linked to each other that can determine an explosion, the so called fire triangle:

• Combustible (in this case, metal powder at certain concentrations);
• Combustive agent (e.g. air and oxygen, during the suction phase of the process);
• Sparkle (it could be, e.g., electrostatic power or a small sparkle caused by the metal friction, which only lasts a few milliseconds but is enough to trigger an explosion);

Very accurate tests carried out in the workshops on very common applications, transformed from classic processes (wet) into experimental processes (dry), have produced variable powder concentrations.

They were thoroughly compared to the ATEX policy information where the following levels are highlighted – for the sake of example:

Lower explosive limit (LEL)

Aluminum (LEL medium): 45mg/l = 0,045gr/l = 0,045gr/dm3

The conclusion is, when not sure about the safety of the procedure, avoid using dry processes for metal finishing with aluminum and magnesium alloys.

Alternatively it is suggested it is still as innovative and competitive as Microfluid processes.

Application on zamac and brass

Brass, but especially zamac, can undergo dry vibro-finishing processes Vibrodry – just like martensitic and austenitic steel, bronze, titan and other kinds of metals, as long as they respect the above-mentioned limits.

Application on wood and polymers

With a particular variation especially studied for material that is softer than metals, such as wood or plastic, Vibrodry processes can make soft and smooth surfaces that will be impregnated and/or varnished at a later point.

As far as wood articles are concerned, interesting results have been achieved with hilts of cutlery, furniture knobs, holding rings for curtains and the like, whereas as far as the polymers are concerned, there are even more application possibilities, varying from decorations to technical articles.

These processes can act together with the QF media producing the desired result as well as the wished finishing level. Vibrodry processes are in fact based on the addition of abrasive compounds into the working vibrating bowl as the parts are being loaded into the bowl. Because of their dosage, these compounds can keep working for a set amount of time, and then they are suctioned for the final phase, just before the end of the cycle and the machine is turned off (or the parts are automatically offloaded). This technique reduces to a minimum the suction phase and therefore limits considerably the power consumption.

This Vibrodry process generates interesting applications for the final user, which one can summarize as follows:

Efficiency of the process

Comparing a classic process to a Vibrodry process, the same results can be reached in half the time. In most cases, with similar times, surfaces polished through Vibrodry processes can result slightly better, that is to say they result in smoother and thinner surfaces (e.g. a zamac buckle, using the same time a wet process would take, can result in a lighter product and of course is free from micro-signs and oxidation, as it never touches any water).

Basically, the difference between the use of these processes and the traditional ones is not the time, which is about the same, but the fact that these new techniques do not need the use of water.

Dust reduction

Dusts generated during metal scraping or treatment as well as dusts coming from abrasive media and compounds used in the finishing processes are sucked by a custom-sized dust-reducing device.

An interesting and innovative feature of this process is that it is studied to make progress over time and to engage the suction phase just for a small fraction of the total process time, achieving interesting reductions of power costs. On the other hand, other kinds of processes (such as wood polishing process, just to name one) maintain constantly active suction and consume a great deal of power.

Residual waste reduction

Residual waste (dust) coming from media consumption is very low, which determines, at the end of the day, lower disposal costs.

Residual dust reduction

In most cases, residual dust on the parts is really irrelevant and therefore the parts can go directly, for instance, to the plating lines – some operational limits can be found in case of peculiar shapes, with micro-holes, very long and small blind holes, arabesque-decorated motives and the like.

Reduction of the "below measure"

The frequencies on which traditional media wear off normally cause relevant selection problems, that can be remarkably decreased with the use of the new long-lasting QF media.

Transport and stocking costs reduction

With a consumption rate 10 times lower than usual, one can certainly foresee a pollution reduction, due to the lower number of transportations, and of course also a reduction of the costs. As a consequence, stocking costs will also decrease.

Summary

To summarize: no more waste water treatment-related problems; limited polluting residual emission.

It is also possible to evaluate the possibility to adapt existing plants with maximum ratio costs/benefits.

How to evaluate the feasibility of a process

Rollwasch® Italiana S.p.a. test room and its workshops are the fastest way to make a preliminary evaluation, without costs or engagement.




Author: Paolo Redaelli
For Information:
Rollwasch® Italiana S.p.a.
Via San Carlo, 21
20847 Albiate (MB), Italy
Tel. +39.0362.930334
Fax +39.0362.931440
E-mail: info@rollwasch.it
www.rollwasch.it