Manufacturing of Stuffing Box

TEAM DETAILS

GYANENDRA AWASTHI (13135043)

ANKIT SAXENA (13135019)

NITIN KUMAR (13135059)

MUKUT KUMAR MEENA (13135057)

RAHUL KUMAR (13135063)

ASHOK KUMAR MEENA (13135026)

CONTENTS

1. BRIEF INTRODUCTION

2. MATERIAL SELECTION

3. DESIGN AND APPLICATIONS OF STUFFING BOX

4. MANUFACTURING PROCESSES

Casting Machining Consolidation

5. DEFECTS OBSERVED

A stuffing box is an assembly which is used to prevent leakage of fluid, such as water or steam, between sliding or turning parts of machine elements, specifically a rotating or reciprocating shaft.

A Stuffing box assembly satisfies two requirements; preventing any leakage of steam out of the

cylinder and at the same time allowing free movement of

shaft.

BRIEF ABOUT STUFFING BOX

The Stuffing Box is a cylindrical space in the pump casing surrounding the shaft.

Packing is the material in the form of rings or strands that is placed in the stuffing box to form a seal to control the rate of leakage around the shaft.

Packing is then held in place and compressed by the ‘Gland’ to give a leak-tight seal.

MATERIAL SELECTION

Stuffing box and Gland are made up of Cast Iron due to its following properties:

Good casting properties Good machinability Good wear resistance Low notch sensitivity excellent vibrational damping characteristics

.

The space around the piston is filled with asbestos-fibre packing because its fibrous nature makes it a good absorber of both leaking fluids as well as lubricants. Also, it is chemically inert, can sustain high temperatures and halt the spread of fire.

Studs and nuts are made of Mild Steel due to its better ability to resist tensile failure.

Variety in designs of stuffing box has increased significantly as processes and the pumps used have evolved but purpose is same i.e. “ SHAFT SEAL”.

Dimensions used

DESIGN OF STUFFING BOX

MODELLING IN CATIA

APPLICATIONS

BOAT PROPELLER -

Here, Stuffing box is used to prevent “WATER LEAKAGE”.

HOW it works??.....stuffing box prevents sea water from entering the boat's hull.

AUTOMOBILE-

Here, Stuffing box is used to prevent “GAS LEAKAGE”.

HOW it works??.....gas coming out of piston arrangement is prevented.

STEAM ENGINE-

In a steam engine, where the piston rod reciprocates through the cylinder cover, a stuffing box provided in the cylinder cover prevents the leakage of steam from the cylinder.

MANUFACTURING PROCESSES INVOLVED

CASTING MACHINING CONSOLIDATION

Stuffing box assembly is made by green sand casting process.

Green sand composition is… 70-85% silica sand (SiO2) 10-12% bonding material e.g., clay etc. 3-6% water

Casting is the preferred method to manufacture stuffing box because it has a quite complex shape.

Green sand casting is quite economical.

CASTING

1.Mold cavity is produced having the desired shape and size of the part- Dimensional allowance for cast iron is 0.8% -1.0% .

2.Melting and Pouring of metal- Metal is melted at elevated temperature and poured into the mold at a proper rate to ensure that erosion and defects are minimized.

3. Solidification- Liquid metal is allowed to solidify under controlled conditions to obtain desirable mechanical properties.

Steps involved in casting

4.Mold removal- The casting is removed by breaking away the sand mold.

STEPS INVOLVED

HARDNESS 47.1 – 54.4HRCULTIMATE TENSILE STRENGTH

345 – 689MPa

Typical values of some mechanical properties of casting made up of cast iron

DEFECTS OBSERVED1. BLOW HOLES : It is a fairly large, well-rounded cavity produced It is occurred by the gases which displace the molten metal at the cope surface.Blows. Usually occur on a convex casting surface and can be avoided by having a proper venting and adequate permeability . A controlled content of moisture and volatile constituents in the sand mix also helps in avoiding the blowholes.

This contains very small holes uniformly dispersed throughout the casting. It arises when there is a decrease in gas solubility during solidification. : .

2.POROSITY :

3. CORE SHIFT : A misalignment between two halves of a mould give rise to a defective casting , as shown in fig. accordingly ,this defect is called a mould shift or a core shift.

Core shift observed: 1mm

4. SCAR : A shallow blow, usually found on a flat casting surface , is referred to as scar.

5.PIN HOLES : these are nothing but tiny holes, and occur either at or just below the casting surface . Normally, these are found in large numbers and are almost uniformly distributed in the entire casting surface

MACHINING Post casting operations: Excess material has to be removed along parting lines.The casting also requires to be grinded to ensure a good surface finish.

Drilling: For hard metals(C.I.), drilling is to be done slowly and

steadily. But, soft metals(Al) will require a faster speed because the metal shaving may melt if machined too slowly. Even with soft metals too high speeds are avoided.

Since we have drilled metric fine threads, so we used drill of 8.5mm diameter size for drilling the holes and producing threads of size M10*1.5.

THREADING We used hand taps for threading. 1. At first we used Tapered tap because, each turn of this tap will remove only a small part of material and the threads will be cut gradually. This reduces the stress on the tap, which is important because taps are brittle and it's not uncommon to break one while tapping. Also TAPER TAPS have a lead of 7-10 threads at 5 degrees per side. This taper lead distributes the cutting force over a large area, and the taper shape helps the thread to start. They can therefore be used to start a thread prior to use of second or bottom leads, or for through holes.

Alignment of taps to holes should be done properly because misalignment of taps may cause breakage of taps as well as improper threading.

Started tapping the hole with the tapered tap and then used the bottoming tap.

Two bolts of size (M10×1.5) were used for joining the stuffing box with the gland.

2.After this we used Bottoming tap-.for  forming the last few threads which were not formed by tapered tap due to its tapered size. These TAPS have a chamfer (lead) of 1–2 threads, the angle of the lead being around 18 degrees per side. They are used to produce threads close to the bottom of blind holes.

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