Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Graphite – coal – or elemental carbon
Reexamination Certificate
1999-09-09
2001-01-23
Howard, Jacqueline V. (Department: 1764)
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Graphite, coal, or elemental carbon
C508S126000, C508S127000, C508S129000
Reexamination Certificate
active
06177386
ABSTRACT:
Lubricants which are used in the hot forming of metals have long been known. Such lubricants are composed, for example, of mixtures of graphite and mineral oil. Such mixtures decompose at normal temperatures of use of from 1100 to 1300° C. and thus produce a serious impact on the environment.
Lubricants which are used for lubricating the so-called mandrel rods during manufacturing of seamless pipes, have to satisfy particular criteria and are therefore composed of graphite and mixtures of substances which produce these particular properties. DE-B-2 350 716 describes a high-temperature lubricant of 10 to 90% graphite, 2 to 60% alkene polymer or copolymer, 0.2 to 8% suspension agent and 2 to 40% film stabiliser. EP-A-0 554 822 describes a lubricant which contains, in addition to graphite, one or more clay minerals of the bentonite class, as well as polysaccharide and a non-ionic tenside.
By and large, in addition to graphite, the lubricants known up until now contain organic, and thus decomposing, substances and/or additions, which seriously pollute the waste water occurring later, for example by sediment formation, and thus represent serious damage to the environment.
The object of the invention is thus to obtain a lubricant which can be used in particular as a mandrel lubricant, which, in addition to graphite, essentially contains where possible no organic substances carbonising at low temperatures at all, and is as little environmentally harmful with respect to waste water pollution as possible.
In accordance with the invention, this object is solved with a lubricant with a content of 75 to 90% by weight graphite, which is characterised in that it contains 1 to 10% by weight phosphates.
The advantage of the lubricants according to the invention compared to those of the prior art, in particular compared to mandrel lubricants, is in that they need not contain any organic substances, and preferably contain absolutely no organic substances, so the graphite is the only decomposing component. They thus preferably contain exclusively inorganic substances. Graphite, which is suitable for the main lubricating effect of such lubricants, is composed of pure carbon which, at the high temperatures of use, burns in an oxygen containing environment, wherein carbon dioxide is produced which creates a gas buffer on which the separation of the pipe and mandrel rod is principally based.
The other contents of the lubricant have the object of creating an even lubricant film, producing rapid drying of the lubricant film, and preventing damage to the mandrel rod and respectively to the internal surface of the pipe. These objects are primarily solved in accordance with the invention by means of the phosphates which, at the high temperatures of use, form a low-viscosity, reactive molten mass which is able to dissolve scale and similar pollutants and thereby prevent the harmful effects thereof.
The lubricants according to the invention preferably contain 85 to 90% by weight graphite and advantageously 3 to 5% by weight phosphates.
It is particularly advantageous to use a phosphate mixture of tetrasodium diphosphate, primary zinc orthophosphate, primary manganese orthophosphate, disodium dihydrogen diphosphate and potassium polyphosphate as phosphates in the lubricant according to the invention. This phosphate mixture advantageously contains 25 to 50, preferably 33 to 43% by weight tetrasodium diphosphate, 1 to 20, preferably 3 to 11% by weight primary zinc orthophosphate, 0.5 to 20, preferably 1 to 10% by weight primary manganese orthophosphate, 2 to 25, preferably 5 to 15% by weight disodium dihydrogen diphosphate and 8 to 35, preferably 15 to 25% by weight potassium polyphosphate. A phosphate mixture well suited for this purpose contains approximately 38% by weight tetrasodium diphosphate, approximately 7% by weight primary zinc orthophosphate, approximately 5% by weight primary manganese orthophosphate, approximately 10% by weight disodium dihydrogen diphosphate and approximately 20% by weight potassium polyphosphate.
Advantageously, the phosphate mixture added as the phosphates to the lubricant additionally contains 5 to 25, preferably 10 to 20% by weight boric acid and/or 0.5 to 15, preferably 1 to 10% by weight hydroxyl apatite. The well suited phosphate mixture described hereinabove advantageously contains approximately 15% by weight boric acid and approximately 5% by weight hydroxyl apatite.
In addition to the 1 to 10% by weight phosphates, in particular the preferred phosphate mixture described hereinabove, and the 95 to 90% by weight graphite, the lubricant according to the invention advantageously also contains 1 to 4, preferably 2 to 2.5% by weight alkali silicate, in particular sodium disilicate, and/or 1 to 10, preferably 4 to 6% bentonite, preferably commercially available bentonite 34 with a 6 m
2
/g BET surface area, and/or 0.5 to 1, preferably 0.7 to 0.9% by weight silico-phosphate, which intensify the action of the phosphate mixture described hereinabove. The latterly described percentages relate to the total weight of solids of the lubricant according to the invention, while the percentages of the phosphate mixture including those of the boric acid and the hydroxyl apatite relate only to the total weight of the solids of the phosphate mixture alone.
Any graphite, natural or synthetic graphite normally used for lubricants, advantageously one with a high crystallinity and an ash content of less than 5%, can be used as the graphite. A sodium silicate with a SiO
2
:Na
2
O ratio of 2 is advantageously used as the sodium silicate. The silico-phosphate used advantageously contains approximately 22% SiO
2
and approximately 54% P
2
O
5
.
The mandrel lubricants according to the invention are preferably used as aqueous suspensions with a solids content of 20 to 40% by weight, preferably 25 to 35% by weight. The application of the lubricant takes place in the normal manner, by spraying the suspension onto the mandrel rod after it has left the cooling bath, and is again transported to the rolling process
Advantageously, the lubricants according to the invention can additionally contain normal solid lubricants such, as calcium fluoride, cryolite, antimony trioxide, molybdenum sulphide, zinc pyrophosphate, boron nitride or iron (III) pyrophosphate.
The unexpected effectiveness of the lubricant additives and respectively the lubricants according to the invention were tested in a large number of experiments and trials. By applying a lubricant according to the invention onto the mandrel, sticking no longer occurred, and up to 50 units could be rolled by one mandrel. In contrast to this, there was frequent wastage when, previously, high-alloy steel was perforated by cross-rolling using a mandrel, as it was often impossible to remove the mandrel seized in the pipe. Even when it was possible, the wear on the mandrel was so great that on average only 3.8 units could be rolled with one mandrel.
Even with the so-called reciprocating rolling of austenitic pipes from pre-bored units, considerable advantages are produced with the lubricant according to the invention. The technical process is that a long, initially cold mandrel of a uniform thickness is inserted into a previously perforated, red-hot loop. Said mandrel is now conducted, together with the loop, in a reciprocating motion, that is to say alternately forward and backwards again, through the pilger rolling mill. Here, with the aid of eccentrically-shaped rollers, a kind of rolling and forging process is carried out, which step by step forms a seamless pipe from the loop, which pipe is then rolled over the whole length of the pilger mandrel. Pipes of a considerable length are produced in this way. The mandrel, which in the meantime has also become red-hot must then be withdrawn from said pipe. According to the prior art, this was often not possible at all, so the completed pipe had to be welded down from the mandrel and therefore destroyed. When the separation was at all successful, the separation pressure required was very high, on average 200 atm
Chemische Fabrik Budenheim Rudolf A. Oetker
Dunn Michael L.
Howard Jacqueline V.
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