Modification Of High Precision Tube Roller Mill Tool For Higher Production

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1 Modification Of High Precision Tube Roller Mill Tool For Higher Production B.Shirish 1, B.Mahasenadhipathi 2 and S.S.Das 3 1 PG Student, Department of Mechanical Engineering, Sreenidhi Institute of Science & Technology, Hyderabad, Telangana-State, INDIA. 2 Supervisor, Asst Professor, Department of Mechanical Engineering, Sreenidhi Institute of Science & Technology, Hyderabad, Telangana-State, INDIA. 3 Nuclear Fuel Complex, Hyderabad, Telangana-State, INDIA ABSTRACT Modification of high precision tube rolls (HPTR) mill tools increases the accuracy of pilgering process. Pilgering tools are used for tube reduction process where the outer diameter and the thickness of a tube are simultaneously reduced between roller and a fixed mandrel. This paper aims to develop a model of HPTR mill tool (support-plate) for the pilgering of Zr 4 and stainless steel tubes production. It also examines the effects of support-plate tapers in the pilgering process [1]. In the modified supportplate, 8-front tapers and 1-back taper has been used. The pilgering process in HPTR mills is fully depends on the design of support-plate tapering [3]. In the HPTR pilgering process the tube reduction is takes places in eight-step by using tapers of support-plate and 1-back taper for tube relief. From this modification it is observed that the product has smooth surface finish without cracks and the significant increases in production is also observed. Keywords: HPTR-mill, CRTM, Pilgermill, Stainless steel, Support-plate 1. INTRODUCTION Cold pilger mill is a process to reduce outer diameter and wall thickness at a time with compressive force. In pilgering process outer diameter is controlled by rollers and the wall thickness by a mandrel. This process initially developed in the 1950s for manufacture of tubes with ultrathin walls and this process is exclusively used all over the world for the manufacture of fuel clad tubes and structural requirements for nuclear reactors [1]. Cold pilger mills were classified into two types: 1.1 Cold roller tube mill (CRTM) CRTM is an earlier milling process, the tools of CRTM was grooved dies (75 VMR) and tapered mandrel [2]. In CRTM milling process saddle holds the grooved dies and forces the two dies over the tube material. The mandrel is tapered and maintains the tube inside diameter while the grooved dies reduce the outside diameter. In this cycling process, the incoming tube is fed into the dies and over the mandrel. The drawbacks of CRTM milling process was mill speed is just strokes/min due to this reason production ratio is very less. The main advantage of CRTM milling process it easily handles large diameter tubes. 1.2 High precision tube roller (HPTR) HPTR milling process is upgraded model. HPTR design was based on some of the principles of earlier rolling mills like CRTM. The high-precision tube roller mill process is a fast, economical way to achieve extreme reductions in diameter and wall thickness of tubes. The most common models of HPTR are , 30-60, 15-30, 8-15, in that model is a larger machine which uses four rolls to handle large tubes and 8-15 model is a small machine which uses three rolls to handle small tubes and it has capable of reducing tubes diameters from 8 to 15 millimeters. The tools of HPTR milling machine is different from CRTM milling machine, instead of grooved dies and tapered mandrel it have support-plates with tapers, rollers and straight mandrel is used in HPTR mill machine. The drawbacks of HPTR mill machine, it handle only small diameter tubes but it have many advantages when compared with CRTM like high machine speed strokes/min, high production rate, dimension accuracy. HPTR tool design was based on some of the principles of earlier rolling mills like CRTM [4]. This HPTR milling process depends on the support-plate tapers and roller design to reduce tube cross-section up to 90 percent. In HPTR milling process support-plate guides rollers for tube reduction and it takes places in eight-step by using tapers of support-plate and 1-back taper for tube relief. The tapper step on support-plate governs the production rates, precision and surface finish of the ultra thin tubes. Volume 2, Issue 9, September 2014 Page 49

2 2. DESIGN OF SUPPORT PLATE 2.1 Modification of Taper length height and angle In HPTR pilgering mill process the height of taper is obtained by using below formula [2]. x= (tan θ * ) + 4 Where, tan θ = x= ( ) + 4 (mm) ---- (1) Figure 1 Design of support plate Table 1 Mofification of support plate tapers Length Step Back taper zero Last 2.2 Measurement of taper angle using sine-bar Sine-bar is used in conjunction with slip gauges for precise angular measurement. Sine-bar is used either to measure angle very accurately or face locating any work to a given angle. Formula for taper angle: Sin θ = θ = --- (2) Here, length 0f sine-bar is 200 mm. 2.3 Calculation for tube reduction thickness: By using below equation we can easily calculate the tube reduction thickness of tubes in HPTR pilgering mill process. (Mm) ---- (3) Volume 2, Issue 9, September 2014 Page 50

IPASJ International Journal of Mechanical Engineering (IIJME) ISSN 2321-6441 Volume 2, Issue 9, September 2014 2.

5 Production rate Production rate ----- (5) 2.

3 IPASJ International Journal of Mechanical Engineering (IIJME) ISSN Volume 2, Issue 9, September Formula for elongation The below equation is used to calculate length of tube elongation in HPTR pilger mill (4) Elongation = = Production rate Production rate (5) 2.6 3D-Model in uni-graphics Figure 3 support-plate modeling The 3D-model was designed in uni-graphics software by using modified values of taper height and angle from table[4]. The tool model is designed in CAD software before going for manufacturing process because we check the output model and if we have any changes in model design we correct it before going for manufacture process. 3. MANUFACTURING OF SUPPORT-PLATE Figure 4 Support-plate 8-11 model Table 2 Material composition COMPONENT : Support-Plate 8-11 Model MATERIAL : H11 tool steel Carbon, C Manganese, Mn Silicon, Si Volume 2, Issue 9, September Page 51

4 Chromium, Cr Nickel, Ni 0.3 Molybdenum, Mo Vanadium, V Copper, Cu 0.25 Phosphorous, P 0.03 Iron, Fe balance Table 3 manufacture process of support plate is explained step by step in below table S.NO TYPE OF OPERATION TYPE OF MACHINE AFTER OPERATION (mm) 1 Raw material Cutting machine 45*26*430 2 Sizing Milling machine 41.5*23.5*430 3 Slot Milling machine 18.5*13 4 Parting (cutting) Amda cutting machine 41.5*23.5*215 5 Length maintaining Milling machine 211 mm (length) 6 Back-taper Grinding machine 0.7 degree taper 7 M8 tapping Radial drilling 8* Heat treatment Furnace (850 c) Measured HRC 9 Grinding Surface grinding machine Tapers 10 Chamfering Cylindrical grinding machine 1*45 degree 11 Polishing Grinding machine 1*45 degree 12 Inspection micrometer 40*22* Engraving Coding Supporting Plates are used to guide the rollers in the cassette housing of pilger mill process and also to reduce the OD of the tube. The following are the manufacturing process of supporting plates: 1. Raw Material: For manufacturing supporting plates, we use H11 material. Composition of H11 is 0.9%C, 1.0%Si, 5.2%Cr, 1.3%Mo, and 0.4% V. 2. Part Cutting: In milling machine, the material is cut with width, thickness and right angles of size 430 mm into two pieces of about 211 mm. 3. Slotting: Before slotting the length of the material is 430 mm, height of the material is mm, width of the material is mm. and then slot is made from to 18.5 mm is done on the supporting plate using the milling machine. Cutting: And then cutting of material into two pieces that individual length is maintained as 211 mm. 4. Length Maintaining: Using milling machine, the plate length is maintained to 211 mm. Back Taper: By using grinding machine, 1 back taper can be removed using fixtures, slip gauge height will be 4 mm. 5. M8 Tapping: The tapping is done by using drilling machine. 6. Heat Treatment: The support plates are kept in the electric furnace to the temperature of C. After the hardening, the material is covered with carbon and acts as excessive brittle in nature, to reduce the brittleness, the tempering process for the supporting plates having hardness of HRC at the temperature of C is done. 7. Grinding Process: After heat treatment, the grinding process is done for better surface finish of the supporting plates. In this process, mm of material is removed with the wheel speed of 1600 rpm. at a cutting speed of m/s. 8. Tapering: By using surface grinding machine, supporting plates are tapered to required dimensions using slip gauges and sine bar of length 200mm with a speed of 1600 rpm. 9. Slots Finishing: Using milling machine, slots of the supporting plates are offered smooth finish. 10. Polishing: The chamber corners of the support plates are polished using surface grinding machine. 11. Inspection: After completing all the manufacturing process of support plates, they are sent to inspection. Volume 2, Issue 9, September 2014 Page 52

5 12. Dispatch: Now the final product is ready to be used in the pilger mill process 4. RESULT AND DISCUSSIONS The below values of taper-height and taper-angle for modified support-plate was arranged in tabular column. It is calculated by using the equations from section[2]. Table 4 Calculation of tube reduction and tapers height (Before modification of support-plate) No.of.step Tube thickness reduction Reduction difference Slip gauge height mm Taper angle Taper length (mm) Back-Taper Last taper Table 5 Calculation of tube reduction and tapers height (After modifications of support-plate) No.of.step Tube thickness Reduction difference Slip gauge height mm Taper angle Taper length (mm) reduction Back-Taper Last taper Volume 2, Issue 9, September 2014 Page 53

6 Graph 1: No.of.steps vs Tube thickness reduction The graph 1 describes varation of tube thickness reduction at various steps of pilgering operation for both 7-steps and 8-steps. It is clear that reduction through 8-steps enable for smooth reduction in tube thickness compared to that of 7- steps. Graph 2: No.of.step vs reduction difference Graph 3: Reduction difference From the graph 2 it is inferred that pilgering in 8-steps achieved gradual reduction difference when compared to that of Volume 2, Issue 9, September 2014 Page 54

7 7-steps. However from point 4 the tube reduction difference becomes equal for 7 and 8 steps. The above tables and graphs it clearly show the difference between the original model and modified model of HPTR tool. It is observed that tube reduction takes place gradually in 8-steps with high machine speed strokes/min and we can create ultrathin tubes with high production rate when compared with previous HPTR tool. Graph 4: Deformation Zone 5. CONCLUSION Graph 5: Strain Intensity In this paper the HPTR tool (High precision tube roll) is designed and manufactured. Uni-graphics software is used for modeling. The main modification on the HPTR tool (Support-plate) is the reduction of taper height and angles, which reduces production time drastically. An analytical model is also developed in this paper to realize the fact that improves production rate. After modeling the tool is manufactured and installed in the mill. We can create ultra thin-walled tubes with high accuracy and also increases in production rate are also observed by implementing the modified developed model in HPTR mill. It is clear that reduction through 8-steps enable for smooth reduction in tube thickness compared Volume 2, Issue 9, September 2014 Page 55

8 to that of 7-steps. pilgering in 8-steps achieved gradual reduction difference when compared to that of 7-steps. However from point 4 the tube reduction difference becomes equal for 7 and 8 steps. 6. NOMENCLATURE Notation tgα s X Full form Inlet outer diameter pitch point Outer diameter shell Outlet outer dia Inlet thickness Outlet wall thickness Mandrel cylindrical zone Wall thickness out Distance between shell and mandrel Length of wall reducing Elongation ratio Wall elongation ratio Elongation Taper angle Difference between out coming thickness to required thickness Gauge length Slip gauge height required Step length Inlet tube thickness (mm) Available thickness at the step X (mm) Current step-1 S Total number of steps (mm) Thickness ratio = I.G O.G WT In going dia of tube Outgoing dia of tube Wall thickness of tube 7. REFERENCES [1] Sms-Meer group product unit seamless tube plants, Germany. [2] Mannesmann-Meer, West-Germany. [3] Tpj - The Tube & Pipe Journal July/August 2011 [4] H. Stinnertz, "Cold Pilger Tool Design: Prevention of Product Defects," in proceedings from conference sponsored by ASM, [5] Design and calculations of cold pilfer mill tools, written by Glen Stapleton. Volume 2, Issue 9, September 2014 Page 56

[6] B. Avitzur, Handbook of Metal-Forming Processes. [7] A publication of the fabrications and manufacturers association (thefabrication.com). [8] FPO -IP Research & Communities (FreePatentsOnline.

9 [6] B. Avitzur, Handbook of Metal-Forming Processes. [7] A publication of the fabrications and manufacturers association (thefabrication.com). [8] FPO -IP Research & Communities (FreePatentsOnline.com) United States patent document. [9] Manufacturing technology by george e. Dieter Author Shirish Bakki, I recived the B.Tech degree in Mechanical Engineering from JNTU-Hyderabad University in 2012 and perusing M.Tech final year in Mechanical Engineering (CAD/CAM) from Sreenidhi inistitute of science and technology, Hyderabad, JNTUH university, Telangana-State, India. Volume 2, Issue 9, September 2014 Page 57

Drawing. Fig. 1 Drawing

Drawing. Fig. 1 Drawing Drawing Drawing is a metalworking process which uses tensile forces to stretch metal. It is broken up into two types: sheet metal drawing and wire, bar, and tube drawing. The specific definition for sheet