Patent Application
20140220370
This innovative process represents the continuation and solving of technical problems derived from the processing of the new pre-tube to form a standardized commercial tube in accordance with patent application 1935-2011 and PCT/CL2012/00013.
As was indicated previously, the traditional process generally commences with the melting of material with which cylinders, commonly known as “billets” (technical term), are cast in a range of 9.8 cm (3.5 inches) and 25.4 cm (10 inches) o more. Then these billets are heated at high temperatures to later be extruded in a high pressure press, or perforated and lengthened by means of mechanical systems whose result is what is known in the industry as “pre-tube” which, as we pointed out, will be referred to in this specification as “old pre-tube”. This old pre-tube has a length that is predetermined by the size and weight of the billet. In the industry, the weight of the billet currently oscillates between 75 and 400 kilos, which restricts the size of the old pre-tube because it must be limited to the capacity of the extrusion press or the perforators.
Once the old pre-tube is formed, it passes through a series of wiredrawing processes that consist, basically, of stretching and reducing the thickness of its walls by using traction to pass it through:
Both are shown in
In other words, the old system consists of passing a tube through a die or hollow plate whose hole has walls of tungsten carbide of a diameter smaller than the mentioned tube. The tube is threaded through said hole (after reducing its diameter at one end) and a plug or metallic cylinder with a diameter somewhat larger than the hole in the sheet is placed within the pre-tube. Thus, when traction is applied to the tube, the mentioned plug is pushed by the tube, locks and permits the reduction of the thickness of the wall while passing through the die, as shown in
The production process of this invention consists of unifying in a three-stage production line to obtain a standardized tube that is equivalent to one eighth of the process of the traditional line. These can be seen in
The stages of this online production process will be described below:
The continuous vertical casting process is a process that was created in the nineteen seventies for the exclusive manufacture of oxygen free high conductivity (OFHC) wire rod.
During the month of May 2008, a failed casting occurred in one of these machines at Madeco that produced a continuous hollow wire rod. This continuous hollow wire rod, after multiple breakthroughs and tests, finally became the origin of patent application 1935-2011 and application PCT/CL2012/00013.
From that moment and to this date, different ways have been tried to obtain tubes from this type of casting machine. It has been possible to standardize the casting process in a pre-tube of 38×2.5 mm.
With regard to the operation of the casting machine, following is a description of the melting process and initiation of the casting.
An automatic loading machine feeds copper cathodes into the smelting furnace, where the melted metal is maintained at a temperature of 1160±5° C. covered with a layer of graphite in flakes to partially avoid its oxidation.
Prior to starting the casting process, a special cooler is set up with a graphite matrix, a kaowool cup, a graphite cup and a mortar, all shown in
The casting process is started with the insertion of a steel tube (“fishing rod”) with a piece of perforated steel on the tip (
These new pre-tubes have two special characteristics that distinguish them from the old pre-tubes and that interfere with their reduction to marketable sizes. These are:
With the invention described in this process we have successfully resolved all the above-mentioned problems.
The materiality of the tube comprises a metal and/or a non metal, a metal alloy, metal compound, metal-ceramic alloy, ceramic or a polymer, preferably copper.
One object of this patent is the sequence of additional steps required to ensure that the new pre-tube (just taken from the continuous vertical casting machine) can end up being a marketable product.
Another object of this patent is to obtain a tube in which the type of grain required for its application can be selected, which includes a tube with a minimum or no degree of oxidation.
Some characteristics of the tube, preferably of copper, obtained with the process that will be described below, are: that it has grains whose formation is homogeneous, preferably equiaxial, with an average grain size in the range of 0.025 mm to 0.050 mm, preferably of 0.040 mm.
Moreover, chemically the copper tube has a sulfur concentration range of 2 ppm-12 ppm, preferably 6.6 ppm and an oxygen concentration range of 5 ppm-12 ppm, preferably 10.5 ppm.
With regard to the process proposed in this invention, the sequence of steps required will be indicated.
As was commented with regard to the old system, the wiredrawing process consists, basically, of stretching and reducing the thickness of the walls of a tube by using traction to pass the tube through a tungsten carbide die with a plug or chuck or mandrel inside it until the desired result is achieved. There are different ways in which to execute the wiredrawing process, as shown in
The type of wiredrawing for the new pre-tubes originating from the continuous vertical casting is the floating plug type indicated in
The new pre-tube is received from the continuous casting with measurements of 38.00×2.50 mm +/−5%. It is then taken to the wiredrawing sector where a double wiredrawing process is carried out thanks to the joining and synchronization of two wiredrawing machines that work in tandem.
The material is prepared before starting the wiredrawing process. The new pre-tube is brought close to the jig borer where it is lubricated on the inside, a tungsten carbide plug is inserted (
The mechanical properties of the tube are recovered in this process (a re-crystallization of the tube takes place).
Without this step it would be impossible to control the pre-tube's fragility in the wiredrawing process as the structural arrangement that it has enables the appearance of micro-fissures, as was said, disorderly and large size grains, and their attendant rapid oxidation that produces their breakage in the wiredrawing process due to the emanation of free oxide particles. The wiredrawing process cannot be carried out satisfactorily without solving those problems.
The material received from the wiredrawers is inserted manually into the inlet guides of the furnace (
To start the process, the inside of the new pre-tube is purged with a noble gas, preferably nitrogen. It then enters a chamber where a solvent, such as turpentine, is applied to the exterior of the tube to remove the lubricant and other elements that affect the process such as dust, shavings or stains, among others. The tube then enters a furnace where induction coils are used to heat the metal. This furnace works at a maximum speed of preferably 40 meters/minute and a maximum current intensity of 5000 Amp. Subsequently the tube passes through a cooling chamber where the temperature of the metal is reduced to room temperature, to finally roll the tube inside a basket. Protective wax is applied during the passage to that zone.
The zone of the furnace and cooling chamber are constantly saturated with the same purged noble gas, preferably nitrogen.
The final product is a tube with an equiaxial grain structure having an average size of 0.040 mm. Also, as it is worked in an inert environment this avoids the forming of oxidation on the tube's surface, therefore the final product complies with the characteristics identified commercially.
Once the process is known, these are the principal advantages that the tube manufacturing process using continuous vertical casting has versus the traditional procedures:
Comparatively, the tube itself, obtained via the process described in this invention, is very different to the products in the processes of the prior state of the art.
These physical characteristics can be analyzed on the basis of the following table II:
From an analysis of Table II it is clear that grain distribution for the process of this invention is highly homogeneous, which reduces the speed of oxidation and deterioration of the tube. The rest of the tests are part of the state of the art where non homogenous grains and/or macrograins are obtained with large spaces where the oxygen penetrates and increases the variability in their distribution generating numerous spaces, thus making oxygen penetration easier.
The combination of grain size and hardness provide better mechanical properties for tube production to the end consumer.
Finally, the pre-tube is presented in the penultimate line, which corresponds to the development closest to this invention and the last line of the table corresponds to the innovative system with the application of this patent.
As an example of application, we shall bear in mind the manufacture of a nominal % inch standard tube for the construction industry.
Once 1300-1500 kilograms of the new pre-tube have been melted and cast through the continuous vertical casting, these are taken to the wiredrawing process section for a first and second wiredrawing in two wiredrawing machines working synchronously until a tube with a diameter of preferably 30.00'1.44 mm is reached.
The product of these wiredrawing machines is accumulated in a basket as shown in
After being annealed, the material is processed in a circular wiredrawer giving a single wiredrawing undercut, and finally, the finishing undercut in the straight wiredrawers.
Comparatively, in the traditional process for the same nominal % inch tube for the construction industry, mentioned in the previous example, the flowchart of this process can be appreciated in
Once the initial reduction is carried out on the banks and a tube is produced that has a diameter close to the one desired, the tube passes to a wiredrawing process in rollers using circular wiredrawing machines. These have the same function as the banks but with smaller diameters and longer tubes. Once the desired diameter and thickness have been reached, the tube is cut in the lengths required commercially.
All this in accordance with the description in the comparison indicated in Table I attached previously.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/CL2013/000007 | 2/4/2013 | WO | 00 | 6/26/2013 |
