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International Journal of Modern Trends in Engineering and Research

www.ijmter.com e-ISSN No.:2349-9745, Date: 28-30 April, 2016

@IJMTER-2016, All rights Reserved 1040

Modification of Grub Screw and Cam Plate for Reduction of Failure in PMC threading machine

Sujoy Deb Barma1, Ravi Kumar2, Atul Kashyap3, Donel Patel4, A. Y. Chaudhari5

UG Stu. Mechanical Engineering Department1, 2, 3, 4 MET’s BKC IOE, Nashik [email protected]

Mechanical Engineering Department5 MET’s BKC IOE, Nashik, [email protected] –––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– Abstract- In today’s age, high complex and invested machines need to be properly examined or maintained in order to increase or maximize their availability. The prime motive of the PMC clamping unit is to clamp or unclamp the API pipes in the industry for threading operation, but it comes along with failure of the bolt or grub screw due to the shear stress acting on it for many reasons . The purpose of this study is to find the cause for failure of the bolt using analytical analysis and bring up alternatives so that the failure of the components can be eliminated or reduced to a greater extent. We can achieve the objective, if we can reverse the operation of clamping of pipes through jaws corresponding to the push and pull of the hydraulic cylinder, then we can increase the maximum allowable stress of the grub screw to reduce failing. Keywords: - PMC machine, Clamping Unit, Shear Stress, Grub Screw.

I. INTRODUCTION

Modern Industries uses high level of automation with complex machines. The function of automation is to achieve higher production rate with better quality. Therefore machines must remain in operating condition in order to achieve the desired result or goal [1]. The API section of steel industry produces the steel pipes used in the petroleum industry worldwide. The PMC machine is an extremely expensive machine comprising of different linkage system, hydraulic cylinders and pistons that is primarily used by the industry for threading purpose. This project mainly focuses on the analysis of the root causes of failures of the clamping unit and modifications made into it to reduce the machine downtime. The failures are observed in the connection of the extension rod and the grub screw due to multiple reasons. The ultimate load carrying capacity of a connection will be governed by one of many possible failure modes including; bearing, end pull-out, net section fracture, bolt shear, block shear rupture, etc. Failure may be single load yielding or more commonly cyclic load fatigue fracture & is closely related to the design. Fatigue failure caused due to the action of shear stress in direction perpendicular to the area of the bolt leads to the breakage of the welded connection of the extension rod and the grub screw (bolt) [2]. In this study all these stresses are being analytically analyzed so that feasible modifications can be made to reduce the cyclic failures to an extent

II. PMC THREADING MACHINE

Threading is the process of creating a screw thread. There are many methods of generating threads, including subtractive methods, deformative or transformative methods, additive methods and combinations thereof. PMC threading machine is one of such expensive machine which carry out the process of threading in the industry on the large API steel pipes. It comprises of different linkage system, hydraulic cylinders and pistons working together in the complex machining process. The

International Journal of Modern Trends in Engineering and Research (IJMTER) Volume 3, Issue 4, [April 2016] Special Issue of ICRTET’2016


clamping unit of this machine comprises mainly cam plate, grub screw, hydraulic cylinder, jaws for clamping the pipe. Different linking mechanisms as shown in fig1 are used to transmit the motion of cam roller to the jaws for clamping the pipes.

Figure 1: PMC Threading Machine CAM PLATE

Figure 2: CAM Plate Figure 3: Grub Screw In threading machine, cam plate is one of the main component of the clamping unit which comprises of two slots in which cam roller rolls and the linking system transmit the reciprocating motion of the connecting rod to the linear motion of the jaw.

GRUB SCREW

In threading machine, fig. 3 shows the grub screw. Grub screw is the extension part of the connecting rod which is in contact with the cam plate. The bolt or grub screw has external threads which mesh with the internal threads of the holes of the cam plate. The hydraulic cylinder which exerts tensile force on the cam plate results into the shearing stress leads to failure of the screw.

GRUB SCREW

CLAMPING JAWS

HYDRAULIC CYLINDER

EXTENSION ROD

CAM PLATE



III. TENSILE LOAD CORRESPONDING TO CLAMPING OF PIPE

Figure 4: Cam Plate in Original Position Force calculations

We know that the hydraulic cylinder exerts the tensile force on the grub screw, so considering the pressure of the hydraulic system to be 5Mpa and the dimensions of the hydraulic cylinder, we find out the hydraulic force on the bolt

Hydraulic Force (Tensile)

KN3.31 14555415 )45(100

41P 22

Tensile stress on the cross sectional area of the bolt by hydraulic cylinder

Mpa

AF

6.158)798.15(

)410003.31(

15.798d 31.3KNF

2

Shear stress at thread root

nbP

1 Where b = Width of the thread section at the root.

HYDRAULIC CYLINDER

GRUB SCREW IN TENSILE LOAD

CLAMPING JAWS



1 = ଷଵ.ଷଵ ଵହ.ଽଶ.ହସଽ

=27.6 MPa

From Peterson Stress concentration Factors for whit worth threads, Ktg = 3.85 . . . .(stress concentration factor with the nominal stress based on gross area)

Ktgnom max =27.6 3.85 =106.26MPa

Thus , the maximum allowable shear stress in the bolt due the interference of the external threads of the grub screw and the internal threads of the cam plate if the clamping of the pipes through the jaws is acquired when hydraulic cylinder pulls the cam plate is 106.26 MPa.

IV. COMPRESSION LOAD CORRESPONDING TO CLAMPING OF PIPES

Figure 5: Cam plate in Reversed Position

Force calculation

Hydraulic force (external)

=4

1001 2P =39.25kN

Shear stress at thread root

nbP

2 Where b=Width of the thread section at the root.

2 = ଶଽ.ଶହ ଵ ଵହ.ଽ ଶ.ହସ ଽ

=34.6Mpa

From Peterson Stress concentration Factors for whit worth threads,

GRUB SCREW IN COMPRESSIVE LOAD

REVERSED CAM PLATE



Ktg=3.85 . . . (stress concentration factor with the nominal stress based on gross area)

Ktgnom max =34.6 3.85 =133.24 MPa

Thus, the maximum allowable shear stress in the bolt due the interference of the external threads of the grub screw and the internal threads of the cam plate if the clamping of the pipes through the jaws is acquired when hydraulic cylinder pushes the cam plate is 133.24 MPa. ACTUAL SHEAR STRESS OF BOLT Now we need to find out the actual shear stress on the grub screw (bolt) due to the misalignment of the plate, so we consider the deflection of bolt as 0.1 mm and calculate the force on the bolt perpendicular to the cross sectional area of the bolt. Material: En24- Hardness=26-30HRC, Tensile strength=850-1000N/mm2, Yield stress=680 N/mm2

Deflection AEPL

L=length of the bolt=32mm, Bolt diameter=19mm

A= Area of bolt=4

2d =4192 =283.528 mm2

E= Modulus of Elasticity=200GPa =0.1 mm

177.205kNΝ 177205P 1000200528.283

321.0

P

2N/mm625528.283

177205

AP

Thus we can notice that actual shear stress on the bolt (625 units) is just less than the yield stress of the bolt material (680).

CONCLUSION

From the above result, we have noticed that actual shear stress on the bolt (625 units) is just less than the yield stress of the bolt material (680) so by reversing the cam plate we can increase the maximum allowable shear stress of the bolt and also avoid the point load scenario of the bolt. Due to which the fatigue failure in grub screw and cam plate is reduce and also machine downtime is reduced.

REFERENCES

[1] A. Di Benedetto and A. Vinciguerra, “Kinematic Analysis of Plate Cam Profiles Not Analytically”, ASME Journal,

vol. 104, Issue 1, 34-38 (2009) [2] J. D. Chougule, R. G. Todkar, “Failure Analysis of Blister Packaging Machine Cam Shaft”, IOSR Journal of

Mechanical and Civil Engineering (IOSR-JMCE) ISSN(e) : 2278-1684, ISSN(p) : 2320–334X, PP : 07-14 [3] V. B. Bhandari, “Design of Machine Elements”, Tata McGraw-Hill Education, 2010.

modification of grub screw and cam plate for reduction of · pdf fileinternational j ournal of...

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