Note: Descriptions are shown in the official language in which they were submitted.
~0E39411
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The present inven-tion relates to a ~lethod for extruding
I metallic objects through a die, and more specifically to a
¦ method which provides for an improved surface quality of the
produc-t when extruded at elevated temperatures.
DESCRIPTION OF THE PRIOR ART
In the hydrostatic extrusion of metallic billets in
extrusion presses, the billet is surrounded by a pressure medium,
I and this pressure medium causes the billet to be pressed out
through the clie portion of the press in order to form a rod,
tube or wireshaped product. If the extrusion is carried out
at an elevated temperature, e.g., if the billets are preheated
¦ pri~r to extrusion, a lubricant layer i5 normally applied to
to the surface of the billet to aid in the extrusion processing
~ and to reduce the surface imperfections in the extruded product
¦ caused by contact with the die opening. Typical lubricants
applied to billets in such circumstances are stearatesO such
Il as zinc stearate and sodium stearate, highly viscous mineral
I oil, and a finely divided soft inoryanic material such as
¦ chalk, talcum, graphite, molybdenum disulphide and soft metals.
When the billet extrusion is carried out at room
temperature, i.e., the billet is not preheated prior to
extrusion, processing lubricants can also be'applied to the
¦ surface of ~he billet so a~ to maintain a lubricating film
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between the billet and the die (or forming tool3 during the
extrusion step. Indeed, beeswax has been previously used in
such circumstances as a lubricant when the billets are made of
,1 aluminum or aluminum alloys. However~ i-t has been recognized
~I that beeswax cannot be used as a lubricant when the billet is
extruded at an elevated temperature.
It is an object of the present invention to provide a
¦ method for extruding metallic billets, specifically billets made
Il of aluminum or aluminum alloys, at elevated temperatures through
~i a die opening wherein the surface of the extruded product has
i less surface imperfections due to cladding and galling created
¦as the billet passes through the die opening than has been
previously obtainable.
~I SUMMARY OF THE INVENTION l I
¦1 According to the present invention, extruded aluminum or
aluminum alloy products are formed which have reduced surface
¦imperfections as a result of the application to the surfaces of-
Ithe aluminum or aluminum alloy billets, prior to
¦¦extrusion, of a lubricating layer o polyethylene wax.
¦I The inventive technique has particular application to
extrusion processes wherein the billets pass through dies ¦
~(forming tools) which result in the cross-sections of the billets
being reduced by more than 50 to I. ¦
¦¦ Thus, in accordance with one embodiment of the present
¦ invention, thè aluminum or aluminum alloy billet is coated with
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the polyethylene wax lubricant, heated to a temperature of ~bove
, 130 C., and then hydrostatically pressea through the die opening
!l in a suitable forming tool. At this elevated temperature, the
polyethylene waxes will indeed melt; however, and most surpris-
5 1¦ ingly, it has been found that they will retain their ability tolubricate the passage of the billet through the die opening in
' the forming tool.
In accordance with another embodiment of the present
~ invention, the polyethylene wax-coated billet is heated to at
least 200 C. prior to passage thr.ough the die opening in the
forming tool. The advantage of this embodiment resides in the
fact that the required pressure needed to press the billet through
the die opening-in the forming tool is reduced and the cross
sectional reduction-in the size o~ the billet can be increased.
1l It has been found that the polyethylene.waxes used as lubricants
¦ in accordance with the present invention ~unction quite well at
above 200 C., and even up to 400 C., which temperatures are far
above the melting points o~ available polyethylene waxes.
l The polyethylene waxes used as the lu~ricating agents
¦ in accordance with the present invention comprise polyethylenes
having molecular weights.between 2,000 and 15,000. Particularly,
preferred polyethylene waxes include polyethylenes having molecula
¦ weights exceeding 5,000. Minor~amounts of straight and branched ~;
~ chain hydrocarbons having molecular weights of up to 1,500 ..
I may be optionally added o the poly-thylenes to form the wax.
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The aluminum alloys which can be used to form the billets in the
¦1 method of the invention con~ist~ of at lea~t 855~ by weight of aluminium
Il and at mo~t 15% by wei~ht of alloyin~ material~. For example, one .
Il suitable alloy may comprise 5,5% by weight copper, 0.5% by
5, weight lead, 0.5% by weight bismuth, with the remainder being
aluminum (AA 2011 ) ~ Another suitable alloy may comprise 4O5%
~¦ by weight copper, 1.5% by weight magnesium, 0.6% by weight
¦ manganese with the remainder being aluminum (AA 2024). Another
! suitable alloy may comprise 5.2% by weight of magnesium, 0.1% by
I weight of magnanese, 0.1% by weight chromium, with the remainder
being aluminum (AA 5056). other suitable alloys may comprise
the following constituents as follows: 0.7% by weight magnesium,
0.4% by weight silicon, with the remainder being aluminum (AA
¦l 6063); 1.0% by weight magnesium, 0.6% by weight silicon, 0.25%
¦1l. by weight copper, 0~25% by weight chromium, with the remainder ¦
being aluminum (AA 6061); 5.5% by we.ight zinc, 2~5% by weight
magnesium, 1~5% by weight copper, 0.3% by weight chromium,
I with the remainder being aluminum (AA 7075); and 6.8% by weight
¦I zinc, 2.7% by weight magnesium, 2~0% by weight copper, 0.3% by
~I weight chromium, with the remainder being aluminum (AA 7178).
¦, The polyethylene wax can be applied to the surface of
the billet by first dissolving the polyethylene wax in a
¦~ suitable solvent (e.g. white spirit) and then either penciL
Il coating or spraying tbe solution onto the billet which has been
warmed to about 100- C. or, alternati~cly, by ir~ersing =he
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, warm~d billet in solution containing the polye-thylene. Once the ~
~I solvent has been allowed to evaporate by equilibriation with the ¦
surrounding atmosphere, a suitable thin film o the polyethylene
~I wax will be leEt on the billet surface.
, The novel features of the presen-t invention will now be
explained and better understood by reference to the accompanying
Il Figure and the following discussion.
I DESCRIPTION OF THE FIGURE
...
The Figure shows a cross-sectional side view of an
extrusion device, supported on a suitable press table and
containing an extrudable meetallic billet, in accordance with
the present invention.
DESCRIPTIO~ OF THE PREFERRED EMBODIMENTS
I As shown in the Figure, on-top of a press table 1 is
15 l¦ positioned a cylinder 3 within which an operating piston 2 is
! positioned or reclprocating movement. -These structures are all ¦
- ¦¦ located within a hydraulic press (no-t shown) which includes a
cylinder with-a piston or operating piston 2. Resting on the -
~ top of table 1 and inside of cylinder 3 is a die support 5
1~l with-central hQle 12, which itself supports a die 4 with opening
11. The table 1 has a hole 13 which has a larger diameter than
hole 12, and which is positioned directly beneath hole 12 !
Between piston 2 and die 4 is a mandrel 6 having a conical upper
Il portion 7, a mandrel holder plate 8 with a recess9 or the
l~ mandrel (the top of the recess 9 being shaped in a corresponding
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fashion to the shape of upper conlcal portion 7 of the mandrel)
l~ and a support tube 10 for the mandrel holder plate. The support
~I tube 10 is supported by the die 4 and functions to hold the
¦¦ mandrel 6 in its correct position. ;;
¦i In operation, a billet 14 oE aluminum or an aluminum
¦ alloy (for example an alloy containing 5.5% by weight of zinc,
¦ 2.5% by weight magnesium, 1.5% by weight copper, 0.3/O by weight
chromium, with the remainder aluminum (AA 7075))is inserted into ~ ;
l the cylinder (the billet having a cylindrical shape and having
an axiai hole lS therethrough for the mandrel 6). The mandrel
and mandrel holder plate is then properly inserted into the - ~
cylinder 3. A pressure medium 16, such as castor oil, lS ~ :
poured into the cylinder such that it fills the space above and
then, by flow through holes 17, below the mandrel holder plate 8. ;;~
Piston 2 i5 p~sitioned to extend into cylinder 3 and by movement ;
downwardly causes pressure build up on billet 14. In this
regard, the pressure medium is retained within~the cylinder aue
to the use of seals 20 and 21 which are respectively arranged
between the die support and the cylinder, and between the
piston and the cylinder. Once a suitable pressure build up is
~ achieved, i.e., between 500 and l500 MPa, and due to the fact ;
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¦ that the lower portion 18 oE billet 14 is shaped in a corres-
¦ ponding fashion to the inlet cone 19 of the die 4, the billet
¦I will be extruded through opening 11 in die 4.
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` Before the billet 14 is placed in the extrusion device,
I however, it is coated with a polyethylene wax and heated to at
least 200 C. in accordance with the present inven-tion.
I More specifically, the billet 14 can be first cleaned by
1~ both washing and trichloroe-thylene and then blasting with steel
shot (e.g., steel shot havlng a grain size of 0.7-0,8 mm);
heated to about 100 c.,-pencil coated with a hot (120 C.)
solu-tion of polyethylene wax solution (e.g., solution comprising
jj 15 parts by weight of a polyethylene wax having a melting point
of between 120 C. and 130 C. and a molecular weight of the
major part thereof of 9,000 (and identified as PA l90 by
Fabwerke Hoechst AG) and 85 parts by weight white spirit solvent);l
¦ allowed to equilibriate with the surrounding atmosphere such that¦
' the white spirit solvent evaporates, leaving a thin film of
I polyethylene wax on the surface o~ the billet; and heated to a
¦ temperature of240 C,
I -Actually, as the billet passes through the nozzle in the
¦¦ die, the billet temperature will rise to about 350-600 C.
Of course the billet is to be extruded into the shape of
20 1l rod or wireshaped product according to the invention, the design ;
¦ of the press is not quite the same as shown in the Figure; it is
¦1 simpler since neither the mandrel or mandrel holder plate is
Il needed.
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While there has been shown and described what is
¦ considered to be the preferred embodiment of the present .
invention, it will be obvious to those skilled in the art that
~ various changes and modifications may be made therein without ;-
5 1l departing from the invention as defined in the appended claims.
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