DE1160259B - Cast parts made of aluminum or aluminum alloys are given a permanent high gloss by polishing and subsequent protective oxidation - Google Patents

Description

Technology is increasingly being used to produce castings from heavy and light metal Dimensions of the known die-casting processes. Castings that are produced in this way stand out mainly through great dimensional accuracy and a minimum of machining required, so that one such Can use parts as finished parts with almost no rework. Other advantages of this process lie in the fact that series up to over 100,000 pieces can be made from one mold and that it it is possible to produce large numbers in a very short time. So these procedures are on the whole seen very economically.

On the other hand, it is known that surfaces can be obtained on aluminum and suitable aluminum alloys by previous or mechanical polishing processes which are characterized by a particularly high reflection, which comes close to that of a silver mirror. In order to make the shine of such a surface durable, it is known to use anodic oxidation, in which a hard, firm, transparent and anti-corrosive protective layer preserves the shine. The use of such anodic oxidation processes is possible with aluminum and aluminum alloys of suitable composition if these are in the form of wrought material, sand or chill castings. In contrast, it has not previously been possible to produce such decorative, uniform and high-gloss surfaces in series on aluminum and aluminum alloys if these are available as die-cast pieces. In attempts to protect such high-gloss surfaces with anodic protective layers, it has been shown time and again with die castings that the corrosion protection provided by the anodic protective layer is present, but that the gloss, the uniformity of the appearance and the reflectivity after anodic oxidation are severely affected by cloudiness and streaking. Defects in anodized die castings made from an AlMg ₃ alloy have also been reported in the literature. After anodizing, these repeatedly show a stained, speckled appearance at the machined areas. In order to achieve a uniformly clean surface and color, special measures have been taken, which consist in pressing the pieces of thin metal above the liquidus line. These efforts to achieve a uniformly clean surface and color after the anodizing of pressed pieces are nowhere near the aim of the invention, printing

Protective oxidation with a permanent high gloss finish made of aluminum castings

or aluminum alloys

Applicant:

United Aluminum Works
Aktiengesellschaft, Bonn, Am Nordbahnhof

Dipl.-Ing. Wolfgang Nies, Grevenbroich (Ndrh.),
has been named as the inventor

To provide castings with a durable high gloss. Manufactured in conventional die-casting processes Objects whose surface has been polished and anodized to achieve a decorative effect are not yet on the market. The reasons for this lie in the nature of these usual ones Die casting process justified.

In this die-casting process, the gate has a relatively small cross-sectional area; the The speed of the metal flow is very high there and reaches up to 15 m / sec. One counts with it Filling times in the order of magnitude of a maximum of 0.2 seconds. The casting process proceeds as a result so that the liquid metal through the gate at high speed into the mold is sprayed and is extensively mixed with air, creating disruptive oxides and foam. The shape is filled - which is very important - not starting from the gate, but from the opposite one Side towards the bleed. With geometrically simple castings leads this already to the inevitable structural disturbances; Such disturbances become much more unpleasant then, if there are complicated shapes, the deflections and divisions of the filling metal beam force. Due to the small cross-sections in the gate, the metal solidifies very quickly there, and the emphasis can then no longer be placed on any metal parts that are still liquid or pasty in the mold act so that it can lead to the formation of cavities and sink marks.

309 770/364

As is known from practice and the literature, die-cast parts should be produced in the usual way Have wall thicknesses that are evenly up to 4 to 5 mm if possible and only in exceptional cases go beyond that. Thick walls are disadvantageous in the usual die-casting processes, since these in particular have an unfavorable effect on the compression of the castings. But also independently from the wall thickness, the usual die casting process parts with perfect Do not establish casting density. As a result, their mechanical and dynamic strength properties are also important impaired.

. With regard to the disadvantages for the castings produced by the usual die-casting processes exist, 'this process has been modified in such a way that a special die-casting process is used the die-casting molds are filled with molten metal by applying pressure from the bottom to the top and has now held the metal in the form until it solidifies under increased pressure.

It has now been shown that cast parts made of aluminum or aluminum alloys, which are produced by the molten metal in a known manner from bottom to top at a relatively low, depending on the respective cross-section of the gate amount to about 0.1 to 2 m / sec Filling speed is introduced into a permanent mold in a vortex-free manner and that subsequently a pressure of 100 to 20,000 kg / cm ^{2 is} exerted on the molten metal in the permanent mold until it solidifies, can be used for objects made by polishing and subsequent anodic oxidation according to known Process are to be provided with a permanent high gloss.

As a result of the use of a relatively very low face velocity during the whole Filling process, the metal is not mixed with air, so that the front surface of the metal when Filling process is not torn, so that the metal does not splash or spray or move during its movement flips over. The inevitable turbulence caused by the shape of the piece to be cast of the metal flow is due to the low inflow speed in the gate and all parts suppressed the shape if possible. The incoming metal pushes the air in front of it, and this is removed from the mold in a known manner, e.g. B. by molding, core pulls or air ducts.

The filling time of the mold is so short that it is just enough to fill it with sharp edges in all parts. After completion of the filling process, the still liquid metal through the gate z. B. by means of a piston, the aforementioned high pressure of 100 to 20,000 kg / cm ² , preferably 1000 to 5000 kg / cm ² , exerted until the metal has completely solidified. The pressure exerted on the metal during the filling process is extremely low and practically negligible.

Using this special die-casting process, die-castings are made from aluminum and suitable aluminum alloys, e.g. B. fittings, door, window and automobile fittings, manufactured, the surfaces of which can also be provided with a gloss by the known processes and which, through subsequent anodic oxidation, retain this luster practically indefinitely. These Pieces have higher values for electrical and thermal conductivity. Furthermore, the static and dynamic strength significantly improved. The structure becomes dense over the entire cross-section and is free from the deficiencies of the usual die-casting processes described above.

A door handle made of a wrought aluminum alloy was used as an example with 0.8% Mg, 0.4% Si and

ίο 0.035 ° / c Fe, remainder Al produced by the special die-casting process. A filling speed of 1.30 m / sec and a pressure of 1200 kg / cm ^{2 were maintained} until the metal solidified. The door handle produced in this way gave a surprisingly good surface gloss after polishing and anodic oxidation. The production of this door handle was not possible with the previously known Druokgußverfahren, because the handles produced in this way could be polished, but after the anodic oxidation had such a bad appearance that they were unusable for the intended purpose. On the other hand, the surface of this door handle, which is manufactured using the special die-casting process and subsequently polished and anodically oxidized, is comparable to objects that either consist of kneaded material or have been cast in sand or chill molds and surface-treated in the same way.

In addition, the example shows the interesting observation that not only aluminum casting alloys, but also wrought aluminum alloys are suitable for the production of castings by the special die-casting process, while in the Experts have not thought of using wrought alloys for cast workpieces. It is a matter of course for every person skilled in the art to use cast alloys for the production of castings to use. Cast alloys are known to differ from wrought alloys in that they have higher contents of additives, whereby a better castability of the metal is effected. on the other hand but this content of alloy components is the cause that the cast alloys in comparison to wrought alloys have a generally reduced glossiness. Since the special die-casting process now surprisingly also permits a wrought alloy To shed such die castings, there is the further advantage that the nature of the purer wrought alloys a further increase in gloss compared to the special die-casting process Allow castings made from cast alloys. It will thus be preferred Embodiment of the invention achieved a combination of advantages, which are achieved on the one hand by production of workpieces by means of casting per se and on the other hand especially in the achievement high surface quality according to the invention for the surface treatment of according to the special Die casting process produced castings are based on the use of wrought alloys.

Claims (3)

PATENT CLAIMS: 1. Use of castings made of aluminum or aluminum alloys, which thereby are made that the molten metal in a known manner from bottom to top at a relatively small one, depending from the respective cross-section of the gate about 0.1 to 2 m / sec filling speed is introduced into a permanent mold and that subsequently a pressure of 100 to 20,000 kg / cm ^{2 is} exerted on the molten metal in the permanent mold until it solidifies , for objects that are to be provided with a permanent high gloss by polishing and subsequent protective oxidation using known methods. 2. Use of castings according to claim 1 made of such aluminum alloys that have hitherto been used as Wrought material were used. 3. Use of cast parts according to claim 2 made of an aluminum alloy containing 0.8% magnesium, 0.4% silicon, 0.035% iron, the remainder aluminum. Considered publications:
German Patent No. 745 545;
French Patent No. 643,691;
ίο "Zeitschrift für Metallkunde", 1950, p.
to 109; Max Schenk, "Material aluminum and its anodic oxidation", 1948, pp. 845 to 848.