POWDER MATELLURGY

BEARING MATERIALS

Supervised by :Dr. Abdullah Akpolat

Presentation By : Abdullah Hameed Khalaf

CONTENT

IntroductionA brief historyHow self lubrication worksMaterials used for self lubricationImportant requirements of a P/M bearing materialTypes of bearing materialsSecondary manufacturing OperationsAdvantages and disadvantagesDiscussion and Conclusion

2

BEARING MATERIALS Introduction

Powder Matellurgy may be defined as .” the process of manufacturing components from metal powder by compacting and sintering».Sintered-metal self-lubricating bearings, produced by Powder Metallurgy route are a unique P/M product and one of the large volume products made by P/M. They are economical, suitable for high-production rates and can be manufactured to precision tolerances. Sintered-metal self-lubricating bearings are widely used in home appliances, small motors, machine tools, aircraft and automobiles, business machines, farm and construction equipment .

3

A brief history

Self-lubricating bearings were the first PM components to be mass-produced. Since their introduction, in the beginning of the 1920’s , they represent by far the highest volume part output of in PM industry: every year billions of oil-impregnated PM bearings find their applications in mechanical and electromechanical devices, where sliding processes, especially rotary motions, are occurring.There are three types of self-lubricating plain bearings used today. Oil-filled sintered bronze bearings were first conceived in the 1930s, with self-lubricating metal-polymer bearings developed around 1950 and lubrication-free solid polymer bearings appearing in the 1960s.

4

BEARING MATERIALS

How self lubrication Works Products produced by powder metallurgy can be given any degree of desired porosity. It is achieved by controlling the size of particles, their distribution and pressure utilized for compaction. Porous self-lubricating bearing used generally consists of powders of bronze, copper, tin, iron, mixtures of copper and tin powder, iron and copper powders, all with or without graphite. After the sintering operation, these bearings are impregnated with oil or grease etc. So they do not need lubrication during workingComposite PM bearings represent another interesting solution: in this case solid lubricants are present in the structure, so that during sliding they form a film which minimises solid-solid friction and controls all tribological functions.

5

BEARING MATERIALS

The mode of functioning of PM porous bearings may be summarised as follows: when the shaft is at rest all the oil is retained in the pores and the load is sustained by direct metallic contact between the two surfaces. At the beginning of movement the direct metallic rubbing between bearing and journal with its high friction coefficient raises the temperature rapidly. As the expansion coefficient of the oil is higher than that of the alloys used for the bearings by an order of magnitude, the oil is pushed out of the pores and, as rotation continues and load and speed are kept within certain limits, it almost instantaneously forms a thin film, which prevents further metallic contact.

6

BEARING MATERIALS

Materials used for self lubricationBasic types of materials used in the manufacture P/M bearingapplications include:i) Bronze: This is the most common porous-bearing material with 90%

copper and 10% tin. Addition of graphite (1%) is also done. These bearings can be produced with a wide range of porosities.

These bearings have excellent wear resistance, ductility, and corrosion resistance. Ease of lubrication, low cost and ease of production gives this material a wide range of applications.

7

BEARING MATERIALS

ii) Leaded Bronzes: In this type of material, both tin and copper contents are lower in comparison to the bronzes.Lead content can go up to 1.6%. The main advantages of this material are its lower coefficient of friction, higher conformability then the 90-10 bronzes and good resistance to galling, which is advantageous in case the lubricant supply is interrupted.

8

BEARING MATERIALS

iii) Iron: Iron is used for low-cost bearings, widely used in automotive applications farm equipment, and machine tools. Copper (up to 10%) is added to iron powders for improving the compressive strength. These materials have a relatively low-limiting value of V in the PV ( Pressure velocity ) factor, but have high-oil-volume capacity because of the high porosity.iv) Leaded Iron: Addition of lead to iron improves speed capability and reduces cost.v) Aluminium: Aluminum is used in some applications as they provide cooler operating conditions, light weight, greater tolerance for misalignment and longer oil life than porous bronze or iron. The limiting PV value is 50,000, the same as that for porous bronze and porous iron bearings. 9

9

BEARING MATERIALS

Important requirements of a P/M bearing

material are:

(i )Good lubrication characteristics with minimum maintenance and long service life.

(ii )Adequate mechanical strength including fatigue strength over a range of temperatures.

(iii )Good wear characteristics.(iv )Good heat dissipation capacity

(v )Must not weld/seize with the mating parts shafts during service.

10

10

BEARING MATERIALS

Types of bearing materials

Most porous-metal bearings are made of either bronze or iron, with 10 to 35 vol% interconnected voids or porosity.In operation, lubricating oil stored in these pores feed the bearing surface through these interconnected pores, when the temperature increases during operation. Any oil, which is forced from the loaded zone of the bearing is later reabsorbed by the pores through capillary action.

11

BEARING MATERIALS

High porosity with a maximum amount of lubricating oil is used for high-speed light-load applications, such as fractional-horsepower motor bearings. A low-oil-content low-porosity material with high-graphite content is more cogent for oscillating and exchanges motions where it is difficult to build up an oil film.

12

BEARING MATERIALS

Dry bearings are made from metallic alloys or from fluoropolymer (Teflon). This bearing material is soft enough to handle interference fits with minimal stick-slip and a low coefficient of friction. Dry bearings are available with metal backing made of aluminium and bronze-steel.Features of oil-impregnated bearings include excellent self-lubrication properties, wide range of operating temperature ( -200 to 2500C), low-thermal expansion, no water absorption, and silent operation. The extended bearing life, even in severe environments with no need for external manual lubrication, reduced maintenance times and extended service life are other attractive advantages

13

BEARING MATERIALS

Performance of bearingsFor plain, dry-running bearings, it is often helpful to reference a Pressure-Velocity (PV) factor as a guide in determining bearing capability .

It should be understood that this factor is actually a variable which reflects the point where surface temperatures are at a maximum, but are still stable. The maximum PV established ranging PV continuous(60,000)

PV intermittent(150,000)

14

BEARING MATERIALS

The bearing material of the medium the content of graphite, the graphite content is 0.5% to 0.8%, such a material bearing used under heavy load and high-speed and normal abrasive conditions.The graphite content of more than 0.3% of the bearing operation is very calm. They tend to require less field refueling and in a slightly elevated temperature. They are often used for the working conditions for the oscillating or intermittent rotation.

15

BEARING MATERIALS

Secondary Manufacturing operations

P/M process flowchart

16

BEARING MATERIALS

Complementary Manufacturing Operations

17

BEARING MATERIALS

Picture of some self lubrication bearing product

18

BEARING MATERIALS

ImpregnationThe term used when oil or other fluid is permeated into the

pores of a sintered PM part• Common products are oil-impregnated bearings, gears, and

similar components• An alternative application is when parts are impregnated with

polymer resins that seep into the pore spaces in liquid form and then solidify to create a pressure tight part

19

BEARING MATERIALS

Resin impregnation is a method of sealing porous materials Without impacting on the function or dimensional

characteristics of the material . Impregnation is not only effective for preventing leaks, it is also

an excellent pre-treatment for surface finishes.

20

BEARING MATERIALS

MACHINING Sintered components can be sometimes machined when

a shape or tolerance not achievable by compacting is required. Sintering support all conventional machining operations turning, milling, drilling, threading, grinding, lapping, reaming, polishing, and so forth.

21

BEARING MATERIALS

DEBURRING Deburring is applied to remove burrs inherent to compacting

process. Burrs are removed either in bulk (tumbling, shot blasting, …), or on a unit basis (brushing, polishing, electrolytic deburring, …). Bulk deburring is sometimes used to provide an homogeneous surface aspect, or a very low roughness.

22

BEARING MATERIALS

CLEANING Cleaning operations are used to reduce or remove the

amount of pollutants, solid or liquid, that a part may contain. There are many techniques, depending on material, type of pollutant, and required specifications.

23

BEARING MATERIALS

STEAM TREATMENT This is a thermal cycle of controlled oxidation of a

steel, carried out in continuous furnaces with water steam. A magnetite layer coat is formed on the part surface and porosity. Its application on a component increases its compression strength, seals its porosity, and improves its environmental corrosion resistance.

24

BEARING MATERIALS

HEAT TREATMENTS A heat treatment is a thermal cycle that modifies the material

properties. They are typically applied to increase hardness and strength of the component. The main surface or core heat treatments are: quenching, case hardening, and carbonitriding. Induction hardening is used to increase hardness in a local area of the part. Other possible treatments are ion nitriding, oxynitrocarburizing, or annealing.

25

BEARING MATERIALS

COATING / PLATING It is a material deposition on the component surface, which

modifies the surface properties without changing the base metal chemical composition. Coatings are applied to fulfil functions under fatigue, wear, friction, or corrosion protection.

Sintered parts accept almost all conventional coatings, like zinc plating, chromium plating, nickel plating, phosphating, and other special coatings.JOINING

Sintered parts are prone to be joined to other sintered parts or to components made from other technologies. Typical joining techniques are welding, brazing, sinter-bonding, fitting, sticking, riveting, over-moulding, etc.

26

BEARING MATERIALS

Advantages and disadvantagesA self-lubricating sintered bearing is a metallic component

with high porosity (20-25% in volume), impregnated in a lubricant oil. The oil contained in the porosity provides a constant lubrication between bearing and shaft, so the system does not need any additional external lubricant. Self-lubrication allows this type of sliding bearing to work under hydrodynamic conditions, resulting in a very low friction coefficient.

27

BEARING MATERIALS

Self-lubricating sintered bearings have some advantages compared to other types of dry sliding bearings: - Reliability. The constant oil presence eliminates the risk of seizure, and allows the bearing to work during thousands of hours without wear. - Economy. Maintenance-free, no need for lubricants. - Performance. Able to work under loads of up to 10 MPa, and speeds up to 5 m/s. The maximum working PV is the range of 5 MPa·m/s . the dimensional precision is very high, and produces extremely low noise.

28

BEARING MATERIALS

Discussion and ConclusionA predıctable wear rate is extremely desirable for

maintenance of machineries. Users should selects a bearings manufacturer with the

ability to accurately calculate bushing lifetime in a specific application based on an extensive tribological test database.

presently, this technology is only available, self-lubricating bearings.

Self-lubricating bearings require less maintenance, perform better in dirty and high-heat environments, and handle higher load capacities than most traditional plastic or metal bearings.

29

BEARING MATERIALS

THANK YOU