|Title of Invention||
HIGH-TEMPERATURE LUBRICANT AND ITS USE
|Abstract||High-temperature lubricant for the lubrication of two areally touching heated metal objects that execute a relative movement vis-à-vis to one another, in particular steel objects, containing alkali phosphate, wherein the lubricant, based on its solids content, consists of at least 80 wt.-% of at least one alkali orthophosphate, wherein the lubricant has a melting temperature above the maximum working temperature of the heated metal objects, but at least above 600°C.|
|Full Text||High-temperature lubricant and its use
The invention relates to high-temperature lubricants for the lubrication of two areally
touching heated metal objects that execute a relative movement vis-à-vis each other.
For example, in the production of seamless steel or non-ferrous metal pipes, it is
important to intensively lubricate the tools, in particular the mandrel rods in order that
they have the highest possible lives. The surfaces of the mandrel rods are to be
uniform and smooth in order to ensure a uniform material flow of the metal to be
The quality of the inner pipe surfaces depends on the surface quality of the mandrel
rods. If the inner surface of the pipes is rough or rippled or even has damage that is
attributable to the quality of the mandrels, there is a high discard rate. Efforts have
therefore already been made in the past to increase the lives of mandrel rods by
applying lubricants to them.
Organic lubricants used in the thermoforming of metals, such as fats, oils or soaps,
proved unsuitable at high temperatures. To improve the lubricant properties, graphite
was therefore used as an essential constituent of the lubricant in DE-PS 4 300 464 or
EP-PS 0 554 822. In particular in conjunction with inorganic salts such as for example
borates or phosphates, graphite has good separation and lubrication properties.
Disadvantageous however is the tendency of graphite to contribute at high
temperatures to carbonizations of the workpiece surfaces, here the pipe surfaces. Tool
and workpiece can also become welded together pointwise. The result of both effects
is a high tool wear and a high discard rate of the workpieces.
To avoid this negative effect of graphite, salt mixtures have already been used as
high-temperature lubricants which melt at the working temperatures at which they are
used as lubricants and ensure good lubricant properties in the liquid state. Such salt
mixtures are known from EP-OS 0 829 528, which for improvement also contain a
gas-forming additive. According to column 3, lines 41 to 48 of this document, an
advantage of these lubricants is that they already begin to melt at 200 to 250°C and
are present as clear melts as of 500°C. As a result good lubricant properties are
already to be ensured at low temperatures.
With such lubricants that are present as melts at working temperatures, scale that has
formed and so-called secondary scale is firmly stuck to the tool, as a result of which
the surfaces of the tool, such as the mandrel rod, becomes correspondingly rough. As
mentioned above, this results for its part in roughness of the inner surfaces of the .
pipes. At the same time the flow behaviour of the metallic material on the mandrel
rods is disrupted, which manifests itself when measuring the current consumption
between the individual roll grooves.
The object of the invention is thus to obtain a high-temperature lubricant to which no
graphite need be added and which reduces the discard rates compared with a use of
known lubricants. In particular, with the help of the new lubricants the services lives
of mandrel bars in the production of metal pipes are to be increased and the quality of
the inner pipe surfaces improved.
This object is achieved according to the invention with high-temperature lubricants
for the lubrication of two areally touching heated metal objects that execute a relative
movement vis-a-vis each other in that the lubricant comprises at least 80 wt.-% of at
least one alkali orthophosphate and has a melting temperature above the maximum
working temperature of the heated metal objects.
Although it is known to add alkali phosphate to graphite-free mandrel-bar lubricants.,
the alkali phosphates in such lubricants account for only a relatively small percentage
and are mixed with other salts such that the lubricant is present in melted, i.e. liquid,
state at the working temperatures.
The high-temperature lubricants according to the invention can be used wherever two
areally touching metal objects execute a relative movement vis-a-vis each other at
high temperatures. These are for example friction bearings with which high
temperatures can occur. Preferably however the lubricants according to the invention
are used where the areally touching metal objects are a tool on the one hand and a
workpiece on the other. .The lubricants are quite particularly suitable for the
lubrication of mandrel bars in the production of seamless metal pipes.
In principle, the inventive concept is suitable for the lubrication of any metal objects,
but is particularly suitable for the machining of steel objects, in particular as
mentioned above for the production of seamless steel pipes in which the mandrel bars
are lubricated with the lubricant according to the invention. However this is not
intended to exclude the use of the lubricants according to the invention for example
for the production of pipes from non-ferrous metals, aluminium or similar.
Here, by maximum working temperatures is meant the highest temperature occurring
on the lubricated contact surface, as this could melt the lubricant if the melting
temperature of the lubricant were lower than it, which is to be avoided. When
machining workpieces with a tool, as a rule the workpiece will have the higher
temperature and the tool the lower temperature, as in the case of the use of mandrel
bars in the production of metal pipes. The maximum working temperature above
which the melting temperature of the lubricant is to lie is in this case the temperature
of the hotter metal object, i.e. the workpiece.
Expediently the high-temperature lubricant according to the invention is present in the
form of an aqucous solution. This is applied for example to the mandrel bars during
pipe production or elsewhere and, after the water has evaporated, forms a fine
separation and lubricant film that is extremely abrasion-resistant when used. As the
lubricant does not melt due to its high melting temperature when used, scale is
prevented by the lubricant from becoming fixed on the mandrel bar surface or other
tool surface. After drying, the lubricant is present in the form of very fine particles
that fill all the surface roughnesses of the tool surface and thus smooth this surface,
which is transmitted to the workpiece surface. The separation film formed also
promotes the material flow on the workpiece surface of the metal to be formed and
therefore has the character of an excellent lubricating film.
The high-temperature lubricant according to the invention is particularly suitable in
the case of the Assel rolling process with the "free mandrel bar" technique and in the
case of the rotary forge process. Clear advantages with regard to the surface quality,
the life of the mandrels and the exertion of force between the roll stands are also
achieved with continuous rolling, e.g. according to the "semi-floating" principle.
With the lubricants according to the invention, clear, high-percentage solutions can be
easily prepared that are to be applied to the mandrels by means of airless pumps and
nozzles. Atomization is also possible using air, so-called binary nozzles, or similar.
Naturally, the lubricant can also be applied in powder form.
The melting temperature of the lubricant according to the invention is expediently at
least 10°C above the maximum working temperature that was defined above.
The lubricant is to consist largely of one or more alkali orthophosphates, the alkali
orthophosphale content being expediently at least 95 wt.-%. If several alkali
orthophosphates are used, care is to be taken that the melting temperature is above the
maximum working temperature with such mixtures also.
Up to a maximum 20 wt.-%, preferably up to a maximum 5 wt.-% of the lubricant can
consist of other substances, which can optionally also include small quantities of
graphite, which as a rule however is not preferred.
The expediently used alkali orthophosphates are trisodium orthophosphatc with a
melting temperature of 1583°C, tripotassium orthophosphatc with a melting
temperature of 1340°C and trilithium orthophosphale with a melting temperature of
857°C. Trisodium orthophosphatc and tripotassium orthophosphatc are preferred, in
particular the latter. Provided the melting temperature of the lubricant remains high
enough, other phosphates can also be added in smaller quantities.
It has been shown that with the addition of small quantities of alkali aluminate and/or
alkali zincate, the fineness of the lubricant particles, and thus the adhesion of the
lubricant to the metal surface, is improved. It is thus preferred to add to the lubricant,
in each case in a quantity of at most 5 wt.-%. preferably 0.2 to 3 wt.-%, at least one
alkali aluminate and/or at least one alkali zincate. As mentioned, the superfine
particles of the lubricant settle in all depressions of the surface and in so doing seal
them, with the result that the scale cannot settle in these depressions. The lubricating
action can therefore also be described as smoothing.
The actual melting temperature of the lubricant according to the invention depends on
the maximum working temperature when using the lubricant and thus on the condition
of the areally touching heated metal objects. Thus the melting temperature of the
lubricant can be relatively low if it is to he used to produce pipes from non-ferrous
metal or aluminium, as relatively low working temperatures are employed with these
metallic materials. When machining steel, a lubricant with much higher melting
temperatures must be used, these in turn depending on whether chrome nickel steels
with working temperatures of approximately 1050 to 1100°C or steels with higher
working temperatures are used. When lubricating tools for steel workpieces, such as
for example when lubricating mandrel rods for producing steel pipes, the melting
temperature is expediently above 1100°C, preferably above 1200°C. When lubricating
tools for the machining of non-ferrous metals, the melting temperatures can be for
example 600 or 650°C.
Taking account of the technical teaching according to the invention, lubricants with
different melting temperatures are expediently prepared, which is to be easily
achieved by varying the ingredients and the quantities of the mixture. The appropriate
lubricant, the melting temperature of which is known, can then be selected for each
The following examples serve to further explain the invention.
On an Assel rolling mill with free mandrel rod, a mixture of 99 wt.-% tripotassium
orthophosphate and 1 wt.-% sodium zincate (each relative to the solids content of the
lubricant) was poured as 10% aqueous solution into the tank that served to cool the
rods alter the rolling process had ended. The temperature of the bath and mandrel rod
was 80 to 90°C. After the Assel mandrel was dried, it was coated with a white
lubricant film. Light- to medium-alloyed steels were rolled with the Assel rolling mill.
The lives of the Assel mandrels were able to be increased by 25% compared with
Assel mandrels lubricated with a known lubricant. The surface-roughness
measurements of the inner surface of the finished pipes that were used for antifriction
bearings showed a reduction from 22 µm to 10 µm.
In a tube-piercing bench unit, the mandrels with a diameter of 130 mm were treated
by spraying-on of a 20% lubricant solution comprising 98 wt.-% tripotassium
orthophosphate and 2 wt.-% sodium aluminate (both relative to the solids content of
the lubricant). The mandrels had a temperature of 450°C. A white coherent lubricant
layer was produced. Medium- to high-alloyed steels were rolled. The impact force
between the roll stands was reduced by 35% compared with conventional lubricants.
The durability of the mandrels increased by 20%. The inner surface of the pipes was
clearly smoother than when using the known lubricants. The quality test showed a
reduction in the discard rate from 4 to less than 1 %.
1. High-temperature lubricant for the lubrication of two areally
touching heated metal objects that execute a relative movement
vis-a-vis to one another, in particular steel objects, containing
alkali phosphate, wherein the lubricant , based on its solids
content, consists of at least 80 wt-% of at least one alkali
orthophosphate, wherein the lubricant has a melting temperature
above the maximum working temperature of the heated metal
objects, but at least above 600°C.
2. High-temperature lubricant as claimed in claim 1, wherein it has a
melting temperature at least 10°C above the maximum working
3. High-temperature lubricant as claimed in claim 1 or 2, wherein at
least 95 wt-% of the lubricant consists of at least one alkali
4. High-temperature lubricant as claimed in one of claims 1 to 3,
wherein it has a melting temperature above 1100°C, preferably
5. High-temperature lubricant as claimed in one of claims 1 to 4,
wherein as alkali orthophosphate, it contains at least one trialkali
phosphate, preferably trisodium, tripotassium or trilithium
orthophosphate, in particular trialuminium orthophosphate.
6. High-temperature lubricant as claimed in one of claims 1 to 5,
wherein it also contains, in each case in a quantity of at most 5 wt.-
%, preferably in a quantity of 0.2 to 3 wt.-% at least one alkali
aluminate and/or at least one alkali zincate.
7. High-temperature lubricant as claimed in one of claims 1 to 6,
wherein it is present in the form of an aqueous solution.
8. Method for the lubrication of mandrel rods in the production of
seamless metal pipes, wherein a high-temperature lubricant as
claimed in one of the claims 1 to 7 is applied.
High-temperature lubricant for the lubrication of two areally touching heated
metal objects that execute a relative movement vis-à-vis to one another, in
particular steel objects, containing alkali phosphate, wherein the lubricant,
based on its solids content, consists of at least 80 wt.-% of at least one alkali
orthophosphate, wherein the lubricant has a melting temperature above the
maximum working temperature of the heated metal objects, but at least
723-kolnp-2004-granted-reply to examination report.pdf
723-kolnp-2004-granted-translated copy of priority document.pdf
|Indian Patent Application Number||723/KOLNP/2004|
|PG Journal Number||02/2009|
|Date of Filing||28-May-2004|
|Name of Patentee||CHEMISCHE FABRIK BUDENHEIM KG|
|Applicant Address||RHEINSTR. 27, 55257 BUDENHEIM|
|PCT International Classification Number||C10M 173/02|
|PCT International Application Number||PCT/DE02/03772|
|PCT International Filing date||2002-10-04|