CLIAMS:We Claim,

1. A method of manufacturing aluminium tubes for telescopic mast comprising following steps:

a) manufacturing porthole extruded aluminium tubes from billets formed by an aluminium alloy;

b) cold drawing the extruded aluminium tubes at a room temperature to improve mechanical properties and to achieve required dimensional tolerance in said extruded aluminium tubes,

c) straightening the cold drawn aluminium tubes at a room temperature to remove stress generated during step b),

d) carrying out artificial age hardening treatment to further improve the mechanical strength in straightened aluminium tubes.

2. The method of manufacturing aluminium tubes for telescopic mast as claimed in claim 1, wherein the mechanical properties include tensile strength and percentage elongation; and wherein the dimensional tolerance includes H11 tolerance on internal diameter of the aluminium tubes.

3. The method of manufacturing aluminium tubes for telescopic mast as claimed in claim 1, wherein, optionally after step c) and before step d), solution treatment with water quenching process is carried out for imparting improvement and consistency in mechanical properties of aluminium tubes.

4. The method of manufacturing aluminium tubes for telescopic mast as claimed in claim 1, wherein the step c) is carried out by hyperbolic 6 roll machine.

5. The method of manufacturing aluminium tubes for telescopic mast as claimed in claim 1, wherein the step d) is carried out at 165 to 170 ?C for a soaking time of 3 to 6 hours.

6. The method of manufacturing aluminium tubes for telescopic mast as claimed in claim 1 or 5, wherein the temperature and soaking time are varied according to dimension and thickness of the aluminium tubes.

Dated 13th January, 2014
,TagSPECI:FORM 2
THE PATENT ACT 1970
(39 of 1970)
&
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
1. TITLE OF THE INVENTION: A METHOD OF MANUFACTURING ALUMINIUM TUBES FOR TELESCOPIC MAST

2. APPLICANT:
(a) NAME : Siddhi Engineers
(b) NATIONALITY : Indian
(c) ADDRESS : “Siddhi house”,
6, Vikrunj Society,
Near Vidyanagar School,
Usmanpura, Ahmedabad-380014
3. PREMABLE TO THE DESCRIPTION
PROVISIONAL

The following specification describes the invention. þ COMPLETE

The following specification particularly describes the invention and the manner in which it is to be performed.

Field of the invention

The present invention relates to a method of manufacturing aluminium tubes and more particularly it relates to a method of manufacturing aluminium tubes for telescopic mast utilized in variety of applications such as mobile radar system, bomb disposal process, search light mast and cleaning up of places where it is very difficult to reach.

Back ground and prior art of the invention
Telescopic masts that are used for variety of application such as telescopic assembly are formed by inserting about 3 to 7 different sizes of aluminium tubes into one another to ensure that the very small assembly has to be carried to the field. For example, in the field for radar application, the mast is erected at the height in the range of 3 to 20 meters through pneumatic or hydraulic arrangement so that radar or other communication device may be attached at the top of the telescopic mast. The telescopic mast can also be utilised for several applications such as bomb disposal unit while the human being remains at a fairly large distance from a bomb or objectionable item. To have above mentioned utilization, the material used for manufacturing the tubes for telescopic mast should have better mechanical properties like light weight, high tensile strength, better proof stress and very close dimension tolerances.
For this purpose, aluminium is most advantageous suitable and advisable metal because of its high electric conductivity, non magnetic, high heat conduction, light weight, excellent ductility, malleability and easy continuous extrusion. Moreover, the aluminium is strongest metal compared to other metals considering weight to strength ratio. For example, 1 Kg of aluminium gives more strength than 1 kg of steel or any other metal. Furthermore, a considerably maximum tensile strength be expected for aluminium, though not as high as that of iron and it is possible to obtain a tube that can withstand a considerably high pressure. Although aluminium has excellent properties, pure aluminium doesn’t have a high tensile strength. However, the addition of alloying elements can increase the strength properties of aluminium and produce an alloy with properties tailored to particular applications. Hence, aluminium alloys have been widely used particularly for application where strength requirement are fairly high and weight of the aluminium tube is to be fairly low to meet the field application needs. However, for telescopic mast, tensile strength of aluminium alloy should be fairly high enough so that it can elongate up to large distance without any breakage.
Hence, hot extrusion process is carried out to achieve required tensile strength and other mechanical properties. In this method, as billets are heated at high temperature, the surface finish and accuracy of the parts get affected during this process. Also, at this step, friction and wear at a die metal interface increases that result into reduction in tensile strength of resultant aluminium tubes. However, in the application where erection of length of 15, or more, meters is required, the resultant aluminium tube must have good tensile strength so that it remains stationary without bending due to wind load or such other load. Also, H11 tolerance is also necessary on internal diameter of tube. Also, during extrusion, dimension tolerance achieved is fairly wide which is not suitable for telescopic mast. Hence, to overcome limitation of the extrusion process, cold drawing process is successively conducted for better surface finishing and achieving close dimension tolerance (H11 tolerance).
Conventionally, various methods for manufacturing of cold drawn aluminium products are available. For example, in US 5342459, a method for producing cold worked aluminium products from aluminium alloy is disclosed. In this process, extruded aluminium products such as wire, rod and bar are cold drawn for reduction in size of the aluminium products and then aluminium products are subjected to artificial age hardening to strengthen it. But the resultant aluminium products obtained by this process haven’t sufficient tensile strength and better dimension control suitable for manufacturing of telescopic mast. Moreover, indirect extrusion is employed in this process. In indirect extrusion, also known as backwards extrusion, the billets and container move together while the die is stationary. The die is held in place by a "stem" which has to be longer than the container length. The maximum length of the extrusion is ultimately dictated by the column strength of the stem. Because the billets move with the container the frictional forces are eliminated. This leads to 25 to 30% reduction of friction, which allows for extruding larger billets, increasing speed, and an increased ability to extrude smaller cross section. Although above described method has an advantageous feature, still it leaves the scope for solving various problems. During indirect extrusion, impurities and defects on the surface of the billets affect the surface of the extrusion. These defects may ruin the resultant products. Hence, in order to get around this, the billets may be wire brushed, machined or chemically cleaned before being used. This process isn't as versatile as direct extrusions because the cross-sectional area is limited by the maximum size of the stem.
Hence, to overcome above mentioned problems, it is desperately needed to invent a method of manufacturing aluminium tubes for telescopic mast which is not subjected to aforesaid problems so that the finally obtained aluminium tubes has desired mechanical properties and high level tolerance that is suitable for using in telescopic mast for radar application and the like.
Object of the invention

The main object of present invention is to provide a method of manufacturing aluminium tubes suitable for telescopic mast application.

Another object of present invention is to provide an aluminium alloy having excellent ductility, suitable tensile strength and proof stress for manufacturing aluminium tubes for telescopic mast.

Yet another object of the present invention is to provide a method of manufacturing aluminium tubes for telescopic mast in which there is a provision for providing desired mechanical properties and close dimensional tolerance for the resultant aluminium tubes.

Further object of present invention is to provide a method of manufacturing aluminium tubes for telescopic mast that can be erected up to 15, or more meters, without get buckling due to head load or wind load.

Summary of the Invention

The present invention relates to a method for manufacturing of aluminium tubes for telescopic mast in which primarily billets, formed from an aluminium alloy, are subjected to a porthole extrusion process. The porthole extruded aluminium tubes are further cold drawn for reducing the cross sectional area of the tubes which results into to increase in tensile strength, achieving H11 tolerance, improving percentage elongation and achieving better grains orientation. Successively, the tubes are then straightened on straightening machine to relieve the stress generated during cold drawing process. Subsequently, the artificial age hardening is carried out at about 165? centigrade with a view to achieve the required mechanical properties and dimensional tolerance in resultant products (aluminium tubes) for telescopic mast.

Detail description of the invention

Before explaining the present invention in detail, it is to be understood that the invention is not limited in its application to the details of the construction and arrangement of parts illustrated in the accompany drawings. The invention is capable of other embodiments, as depicted in different figures as described above and of being practiced or carried out in a variety of ways. It is to be understood that the phraseology and terminology employed herein is for the purpose of description and not of limitation.

In the method for manufacturing aluminium tubes for telescopic mast, primarily porthole extruded aluminium tubes are manufactured from billets formed from aluminium alloy. The aluminium alloy contains magnesium 0.4 to 1.2%, silicon 0.6 to 1.3%, manganese 0.4 to 1%, ferrous 0.6% max., copper 0.1% max, zinc 0.2% max, titanium 0.1% max and chromium 0.25% max, the balance substantially aluminium and incidental elements and impurities. The aluminium alloy has best machining properties so that the assembly joint can be suitably mounted after machining each end of the aluminium tube. The alloy also has better drawability while combining high mechanical strength so that a very close dimension tolerance can be achieved at internal diameter as well as thickness. To make shape of material suitable for further processing, the alloy is solidified into working stock such as a 14 to 15 inch to 22 inch or larger diameter size by continuous casting or semi continuous casting into shape suitable for extrusion.

After said extrusion, the mechanical properties like tensile strength of the aluminium tubes should be achieved 230 MPa minimum and also percentage elongation should be achieved 17% Minimum. However, these mechanical properties are not sufficient for forming aluminium tubes for telescopic mast. Further, during extrusion, the level of dimensional tolerance achieved is also fairly wider. Hence to counter these issues, the extruded aluminium tubes are subsequently cold drawn at room temperature. This cold drawing process serves to reduce cross section area of the aluminium tubes with better surface finish and also for achieve close dimensional tolerance (H11 tolerance) on internal diameter. In cold drawing process, required area reduction is achieved after successive drawing passes and tensile strength of the aluminium tubes can be elevated to a level of 250-300 MPa. But during this process, percentage elongation is reduced to about 4-12% with reference to extruded aluminium tubes.
During the cold drawing process, the stress is developed in the aluminium tubes. Hence, to relieve the stress, the cold drawn aluminium tubes are straightened on hyperbolic 6 rolls machine. This process is done with tubes inputs from one end and if required the tubes direction is reversed to again pass through the straightening machine with a view to make sure that straightness achieved is exceptionally good to extent of about 1/1500. During this process, better dimension control can also be achieved so that it can be erected up to 15 to 20 meters without getting bend due to wind load or such other load in rough terrains. But during cold drawing, ductility of aluminium tubes is reduced due to which breakage or damages in the resultant products often generates.
Hence, eventually heat treatment process is carried out by artificial age hardening process to generate fine grains in the recrystallization thereby ensuring tensile strength along with ductility of aluminium tubes can be effectively recovered. In artificial age hardening process, the aluminium tubes are heated at about 165? to 170? centigrade for soaking time of about 3 to 6 hours, the time generally depends upon the dimension and thickness of the tubes, after which tensile strength is achieved minimum 295 MPa and percentage elongation is elevated to a level of 7 to 15% with reference to cold drawn aluminium tubes. The resultant aluminium tubes obtained by the foregoing method having higher strength along with higher ductility than conven¬tional aluminium tubes are substantially suitable for telescopic mast.

In case when, after extrusion, 150-230 MPa tensile strength of extruded aluminium tubes is achieved below 230 MPa, i.e. in the range of 150-230 MPa, an alternate process root is carried out to achieve desirable mechanical properties in resultant products. In this root, cold drawing process is carried out in the same manner as described above to achieve tensile strength in the range of 175-350 MPa and to reduce elongation in the level of 4-15%. Subsequently, straightening process is carried out in same manner as described above to relieve stress developed during cold drawing. After straightening, an additional process of solution treatment with water quenching is carried out for bringing improvements and consistency on mechanical properties of the resultant products (aluminium tubes). After that age hardening process is carried out in same manner as described above. At the end of the process carried by this root, tensile strength of the aluminium tubes is achieved to a level of 295-375 MPa and elongation is achieved up to 7-15%.

The invention is illustrated more in details in the following example. The example describes and demonstrates embodiments within the scope of the present invention. This example is given solely for the purpose of illustration and is not to be construed as limitations of the present invention, as many variations thereof are possible without departing from spirit and scope.

Example 1:
1) Primarily, for manufacturing aluminium tubes for telescopic mast, porthole extruded aluminium tubes of 62 mm outer diameter and 4.5 mm thickness having tensile strength of 254 MPa and percentage elongation up to 17.40% were manufactured from billets of suitable aluminium alloy.

2) The extruded aluminium tubes were then cold drawn at room temperature during by reducing the cross section area and thickness of the aluminium tubes from 62 mm to 52 mm and 4.5 mm to 3.7 mm respectively, H11 tolerance on internal diameter and tensile strength 278 MPa of aluminium tube is achieved. However, during this process, elongation is moved down to 6.80%.

3) After that, the cold drawn aluminium tubes were straightened on hyperbolic straightening machine to achieve straightening up to 1/1500 (maximum 1mm deflection of tubes in length of 1500 mm) in two or more passes.

4) The straightened aluminium tubes were then subjected to artificial age hardening process at 170 ?C temperature for soaking time of 6 hours to impart the tensile strength of straightened aluminum tubes up to 309 MPa. During this process the elongation is elevated from 6.8% to 9.3%.

Table – I

Sequence Of Process Tensile strength (MPa) Improvement in
% elongation Internal diameter tolerance (mm)
After Extrusion 254 17.40 +0.3
After Cold Drawing 278 6.80 +0.16
-0.00
After Age hardening 309 9.30 +0.16
-0.00

Example 2:
1) Primarily, for manufacturing aluminium tubes for telescopic mast, porthole extruded aluminium tubes having tensile strength of 216 MPa and percentage elongation up to 15.6 were manufactured from billets of suitable aluminium alloy.
2) The extruded aluminium tubes were then cold drawn at room temperature during by reducing the cross section area and thickness of the aluminium tubes, H11 tolerance on internal diameter and tensile strength of 245 MPa of aluminium tubes is achieved. However, during this process, elongation is moved down to 5.60%.

3) After that, the cold drawn aluminium tubes were straightened on hyperbolic straightening machine to achieve straightening up to 1/1500 (maximum 1mm deflection of tubes in length of 1500 mm) in two or more passes.

4) The straightened aluminium tubes were then subjected to solution treatment followed by water quenching at 515? temperature for imparting improvement and consistency in aluminium tubes.

5) The tubes were then subjected to age hardening process at 170 ?C temperature for soaking time of 6 hours to impart the tensile strength of straightened aluminum tubes up to 317 MPa. During this process, the elongation is elevated from 5.6% to 8.90%.

Table – II

Sequence Of Process Tensile strength (MPa) Improvement in
% elongation Internal diameter tolerance
(mm)
After Extrusion 216 15.60 +0.3
After Cold Drawing 245 5.60 +0.16
-0.00
After Age hardening 317 8.90 +0.16
-0.00

Observation:
The manufactured aluminium tubes by method according to present invention have ultimate standards of mechanical properties for telescopic mast.
While various embodiments of the present invention have been described in details, it is apparent that modification and adaptation of those embodiments will occur to those skilled in the art. It is expressly understood, however, that such modifications and adaptations are within the spirit and scope of the present invention as set forth in the following claims.