Joining Processes: Riveting, Soldering and Brazing
Overview
Joining processes are fundamental skills for an ITI Fitter. Riveting creates permanent mechanical joints using metal pins called rivets, used in structural and boiler work. Soldering and brazing are thermal joining methods using filler metals at different temperature ranges. Soldering works below 450°C while brazing works above 450°C. These processes differ in joint strength, filler material, and application. Understanding tools, defects, and safety precautions for each process is essential for NCVT Semester 2 examinations.
Typed Notes
Riveting — Types, Tools and Procedure
Riveting is a permanent mechanical joining process. A rivet is a metal pin with a preformed head. The shank is inserted through drilled holes and the tail is hammered to form a closing head. Main rivet head types: snap (round) head — most common in boilers; countersunk head — used where flush surface is needed; pan head — used in structural work; flat head — used in light sheet work. Tools used: rivet set, snap, dolly, and ball-peen hammer. Lap joint overlaps two plates; butt joint uses cover plates. Caulking and fullering make joints leak-proof.
Soldering — Process, Materials and Defects
Soldering joins metals using a filler (solder) melted below 450°C. Common solder is 60% tin + 40% lead (melting point ~183°C). Flux removes oxides and improves wetting — zinc chloride (active flux) for metals, resin/rosin (non-corrosive) for electronics. Tools: soldering iron (copper bit heated by gas or electric), tinning brush, flux pot. Procedure: clean surface → apply flux → heat joint → apply solder → cool. Defects: dry joint (dull appearance, weak), cold joint (insufficient heat), excess solder, flux residue. Used in electrical wiring, plumbing, and tin work.
Brazing — Process, Filler and Applications
Brazing joins metals with filler melted above 450°C but below base metal melting point. Common filler: brass spelter (copper 50% + zinc 50%) or silver brazing alloy. Flux used: borax powder or paste, which prevents oxidation. Heat source: oxy-acetylene torch or furnace. Procedure: clean joint → apply borax flux → heat base metal to red heat → apply filler rod — filler flows by capillary action. Joint gap should be 0.05–0.2 mm for best capillary flow. Brazing gives stronger joints than soldering. Used in carbide tool tips, bicycle frames, refrigeration copper pipes.
Defects, Safety and Comparison
Riveting defects: rivet not centred, cracked head, loose rivet, tilted shank. Soldering defects: dry joint, cold joint, blowholes. Brazing defects: porosity, incomplete fusion, flux inclusion. Safety in riveting: wear goggles, use proper dolly support. Safety in soldering/brazing: ensure ventilation (flux fumes are toxic), wear gloves, keep fire extinguisher nearby. Key comparison — Soldering: temp <450°C, weak joint, low-cost filler; Brazing: temp 450–900°C, stronger joint, costlier filler; Riveting: no heat needed for cold riveting, strongest permanent mechanical joint for structural use.
Topics & Sub-topics
Har topic ke saath sub-topics aur example — chapter ka complete coverage.
01Riveting
- Types of rivet heads: snap, countersunk, pan, flat
- Types of riveted joints: lap joint, butt joint (single/double cover plate)
- Rivet materials: mild steel, copper, aluminium
- Riveting tools: ball-peen hammer, rivet set, snap, dolly
In a boiler drum, snap-head rivets of 20 mm diameter are used; pitch = 3 × 20 = 60 mm and margin = 1.5 × 20 = 30 mm from plate edge.
02Soldering
- Solder composition: 60% tin + 40% lead, melting point ~183°C
- Flux types: zinc chloride (active) for metals; rosin/resin for electronics
- Soldering tools: copper-bit soldering iron, tinning brush
- Common defects: dry joint, cold joint, excess solder
In electrical panel wiring, a 25W electric soldering iron with rosin flux is used to join copper wires — resin flux prevents corrosion on PCB.
03Brazing
- Filler metals: brass spelter (Cu 50% + Zn 50%), silver alloy
- Flux: borax powder or paste prevents oxidation above 450°C
- Heat source: oxy-acetylene torch; joint gap 0.05–0.2 mm for capillary action
- Applications: carbide tips on cutting tools, refrigeration copper pipes
A tungsten carbide tip is brazed onto an HSS tool shank using silver brazing alloy at ~700°C with borax flux and oxy-acetylene flame.
04Joint Design and Efficiency
- Lap joint: simplest, one plate overlaps another
- Butt joint: plates end-to-end with single or double cover plates
- Joint efficiency = (strength of joint ÷ strength of solid plate) × 100
- Caulking and fullering: make riveted joints pressure-tight
A single-riveted lap joint with 16 mm rivets has efficiency approximately 60–70%; double-riveted lap joint improves efficiency to about 80%.
05Defects and Safety
- Riveting defects: loose rivet, tilted shank, cracked head, off-centre rivet
- Soldering defects: dry joint (dull/grainy), cold joint, flux residue
- Brazing defects: porosity, incomplete fusion, flux entrapment
- Safety: goggles for riveting; ventilation + gloves for soldering/brazing fumes
A dry solder joint on a motor starter terminal caused intermittent failure — identified by dull grey appearance instead of shiny surface, re-soldered with proper heat.
Key Concepts
Revision ke liye ek nazar — exam se pehle yahi padhna hai.
- 01Riveting: permanent joint; rivet materials — mild steel, copper, aluminium; lap joint and butt joint are two main types
- 02Soldering filler: tin-lead alloy (60% tin, 40% lead); flux used is zinc chloride or resin; working temperature below 450°C
- 03Brazing filler: brass (copper-zinc alloy) or silver alloy; flux used is borax; working temperature 450°C–900°C
- 04Rivet head types: snap/round head (most common), countersunk, pan head, flat head — snap head used in boilers
- 05Pitch of rivet = 3 × diameter of rivet (standard formula); margin = 1.5 × diameter of rivet
Questions & Solutions
Pehle khud try karo — phir solution kholo. Yahi tariqa topper banata hai.
What is the standard formula for the pitch of a rivet, and why is it important?
Differentiate between soldering and brazing with respect to temperature and filler material.
Name four types of rivet heads and state where each is used.
What is a 'dry joint' in soldering and how can it be identified and prevented?
Explain the role of flux in soldering and brazing, and name the flux used in each process.
Riveting, soldering, and brazing are three key joining processes in the ITI Fitter trade. Riveting gives permanent mechanical joints using snap, countersunk, or pan head rivets. Soldering uses tin-lead filler below 450°C with zinc chloride or resin flux. Brazing uses brass or silver filler above 450°C with borax flux. Knowing temperatures, filler materials, flux types, defects, and tools is critical for NCVT Semester 2 exam success.
Chapter-end quiz
4 MCQsOption tap karo — turant pata chalega sahi ya galat, explanation ke saath.
Q1.What is the melting point range of common tin-lead solder (60% Sn + 40% Pb)?
Q2.Which flux is used in brazing to prevent oxidation at high temperatures?
Q3.In a riveted joint, what is the correct margin (edge distance) for a rivet of 18 mm diameter?
Q4.Which rivet head type is most commonly used in boiler construction?
Mark karo — dashboard par progress dikhega.