LIBRARY

Wear
basics
Hardfacing
basics
Forming
Methods
Joining
Methods
Conversion
Tables
Types of wear

Major types of wear include:

• Metal-to-metal wear

Wear resulting from contact between two metal surfaces.

• Abrasive wear

Abrasive wear is the main wear mechanism in industrial equipment.
It can be defined as the progressive loss of material from a surface by the mechanical action of external elements (abrasive particles) in contact with the surface.

• Environmental wear

Corrosion and elevated temperatures can combine with the abrasive wear mechanisms  to exacerbate the wear of a component.

Metal to metal wear

Metal to metal wear can be subdivided to the following categories:

1.Adhesive or sliding wear:
In sliding wear, friction occurs between two surfaces which are in intimate contact. [Img.1]

2.Impact wear:
In impact wear, parts encounter repeated impact which can cause brittle fracture or gross plastic deformation. [Img.2]

3.Rolling wear:
In rolling wear, contact stresses are often high and wear occurs by a fatigue mechanism. [Img.3]

Abrasive wear

Abrasive wear wear can be subdivided to the following categories:

1.Erosion:
In erosive wear, parts encounter high velocity fluids (liquids or gaseous) with or without solid particles. The two major types of erosion experienced are:
• Solid particle erosion: Wear of a part by the action of solid particles impinging on the surface. [Img.4]
• Liquid droplet and cavitation erosion: Wear of a part by the action of liquid droplets or bubbles on the surface. [Img.4]

2.Low stress (scratching) abrasion:
In low stress abrasion, the abrasive particles, which are usually small and unconstrained, scratch the surface continuously to cause wear. The particles are not fractured or ground up during service. [Img.5]

3.High stress (grinding) abrasion:
In high stress abrasion, the abrasive particles, which are initially small (rocks < 50mm in diameter), are fractured or ground-up during service. [Img.6]

4.Gouging abrasion:
In gouging abrasion, the abrasive particles, which are usually large (rocks > 50mm in diameter), gouge or groove the surface during service. [Img.7]

Approaching wear problems

The aim is to provide the best solution to the specific wear problem at hand by selecting a build-up or hardsurfacing alloy. This solution is usually arrived at by considering a combination of factors including; past experience, a knowledge of the wear types experienced, a knowledge of welding alloy wear performance and verification through practical tests. While selecting a wear solution for a particular application, one has to keep in mind that equipment components/ parts are subjected to more than one set of wear conditions – with wear modes differing from one component to another and from one application to another.

What is hardfacing

“Hardfacing is the process of depositing, by one of various welding techniques, a layer or layers of metal of specific properties on certain areas of metal parts that are exposed to wear”.

By expanding this definition a little further, it can be seen that hardfacing has more to offer than most other wear prevention treatments:

1. It is performed by welding. Thus it is part of a well established practice with which people are familiar. There are very few new skills to be learned and in the vast majority of cases, existing equipment can be employed.
2. A layer or layers of metal can be deposited. This means that hardfacing provides protection in depth. It can be applied in a thickness required to give long lasting protection.
3. Metal of specific properties is deposited. There are a wide variety of deposit types available, each specifically designed to withstand certain forms of wear and service conditions.
4. Hardfacing is applied only to specific areas of metal parts that are exposed to wear. There is often no need to protect the entire surface of a component from wear. Hardfacing can be applied selectively and in different thicknesses to suit the exact requirements of a piece of equipment, thereby proving a most economical way of combating wear.

According to the American Welding Society, “hard surfacing” or hardfacing is defined as; “The deposition of filler metal on a metal surface to obtain the desired properties and/or dimensions”, the desired properties being those that will resist abrasion, heat and corrosion.

A further definition of hardfacing is: “The application of hard, wear-resistant material to the surface of a component by welding, spraying or allied welding process for the main purpose of reducing wear or loss of metal by abrasion, impact, erosion, galling and cavitation” .It also applies where corrosion and elevated temperatures are present with one or more of the above service conditions.

Hardfacing is a particular form of surfacing that excludes the application of materials primarily for corrosion prevention or resistance to high temperature scaling or the application of low hardness, low friction over-lays to prevent galling -eg. bronze surfacing. It also excludes the hardening of surfaces solely by heat treatments such as flame hardening, or nitriding.

A wide range of CeraMetal wire products and electrodes are available for the three main types of hardfacing applications carried out in industry;

1. Build-up or rebuilding applications.
2. Hard surfacing or overlay applications.
3. Both build-up and overlay applications.

Why is hardfacing important

1.Hardfacing extends the life of worn components and equipment:
Build-up or hard surfacing can extend the life of a component by as much as 250% compared to that of a new or non hardfaced component.

2.Hardfacing increases the operating efficiency of equipment by reducing downtime: Hardfaced components last longer, because fewer shutdowns or stoppages and therefore increase the operating efficiency of the equipment.

3.Hardfacing reduces overall costs:
The cost of refurbishing a worn component is typically 50 -75% of the cost of a new component.

4.Hardfaced parts can be manufactured from cheaper base metals:
A part which is hard surfaced before use can often be manufactured from a cheaper base metal than one which is not designed to be hard surfaced before use.

5.Hardfacing minimises the inventory of spare parts:
If worn parts are usually refurbished there is no need to keep high stock holdings.

Rolling machine
Bending machine

Hardfacing Internally
Small Radius

Hardfacing Externally
Small Radius

Hardfacing Internally
Large Radius

Hardfacing Externally
Large Radius

Forming with hardfacing internally

Forming with hardfacing internally reduces the crack width. Under certain circumstances forming can lead to breakage. Care should be taken to avoid breakage & detachment.

Forming with hardfacing externally

Forming with hardfacing externally increases the crack width. Large cracks can be corrected by welding using matching consumables.

Indicative bending radii *
Popular Plate Sections (base plate + hardfacing)Hardfacing Internally
Rmin
Hardfacing Externally
Rmin
3+390140
5+3100180
6+4113190
8+5150280
10+5175290
10+10350350

* These values are only indicative and greatly depend on the hardfacing type and on the bending method used.

Corner joints
Wearplate joints
Other arrangements
Typical insert ring arrangements
Typical stud arrangements
Flange joints
Joining sequence
Comparison of Hardness Scales
Vickers hardness
(diamond pyramid)
H.V. 30 kg load
Brinell
(steel ball HB)
3000 kg load
Rockwell hardness
(direct reading test)
HRc
Approx. Tensile
Strength MPa
10095-327
120115-393
140135-455
160150-527
180170-598
200190-658
220210-723
24023020780
26025024850
28026527923
30028530972
320305321041
340320341102
360340371166
380360391231
400380411290
420395431355
440415451417
460435461481
480450481546
500470491610
520485511674
540505521739
560520531802
580535541868
600520551922
620535561984
640550572015
660565582069
680580592108
700590602150
72560561-
75061562-
80062564-
85064066-
900-67-
950-68-
1000-69-
1100-71-
1200-72-
Common Welding Conversion Data
Electrode Sizes Pack Weights Pack Weights Lengths 
Imperial UnitMetric UnitImperial UnitMetric UnitMetric UnitImperial UnitImperial UnitMetric Unit
.025”0.6mm1lb.45kg1kg2.20lb2”50.8mm
.030”0.8mm2lb.91kg2.5kg5.50lb4”101.6mm
.035”0.9mm5lb2.27kg5kg11.02lb6”152.4mm
.040”1.0mm10lb4.54kg10kg22.05lb8”203.4mm
.045”1.2mm16lb7.26kg15kg33.07lb10”254mm
.052”1.3mm20lb9.07kg17kg37.48lb12”304.8mm
1/16”1.6mm25lb11.34kg25kg55.11lb14”355.6mm
5/64”2.0mm30lb13.61kg30kg66.14lb15”381mm
3/32”2.4mm33lb14.97kg50kg110.23lb16”406.4mm
7/64”2.8mm40lb18.14kg60kg132.27lb17”431.8mm
.120”3.0mm45lb21.77kg70kg154.32lb18”457.2mm
1/8”3.2mm50lb22.68kg100kg220.46lb20”508mm
5/32”4.0mm250lb113.40kg250kg551.15lb22”558.8mm
3/16” 4.8mm400lb181.44kg300kg661.37lb26”660.4mm
7/32” 5.6mm500lb226.80kg500kg1102.29lb30”762mm
1/4” 6.4mm600lb272.16kg810kg1785.71lb36”914.4mm
5/16” 8.0mm700lb317.52kg918kg2023.81lb39”990.6mm
3/8” 9.5mm1000lb453.60kg1000kg2204.58lb40”1016mm
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