1. TMC ( Techno Material Corp.)
What Happened in Diesel Engines
Valve Train Parts : Severe/Abnormal Wear at Cam/Tappet
Power Train Parts : Severe/Abnormal Wear at Piston Ring/liner
TMC ( Techno Material Corp.)

2. TMC ( Techno Material Corp.)
Heavy Duty Diesel-Engine Exhaust Gas Regulation
EURO1(1992)
EURO2(1996)
EURO3(2000)
EURO4(2005)
Cam: Induction H Tappet: Hard Metal
Ring: Cr-Ceramic Liner: High Alloy Cast
Cam: Induction H Tappet: ? Ceramic
Ring : ? Cr-Diamond Liner: ? Laser Steel
Cam: Induction H Tappet : Chilled Cast
Ring: Cr Plating Liner: High P-Cast
KOREA(2004)
KOREA(2006)
KOREA(2000)
70Kg/mm^2
160Kg/mm^2
Stress: ?
It is a Chance of Technologies Advance.
TMC ( Techno Material Corp.)

3. TMC ( Techno Material Corp.)
Cam and Tappet Movement in Valve Train System
Contact between Cam and Tappet
Line contact, Rolling with sliding
Crowned surface of tappet (for uniform wear)
Lubrication
Cam Base Area : Hydrodynamic lubrication
Cam Nose Area : Boundary lubrication
# Nose ± 20° , Max. contact stress, Lubrication film failure
 Severe wear occurs
Hertzian Contact Stress
σmax ∝ [P/WR(1/E1+1/E2)] ½
W = Cam width R = Cam radius
P = Max. load σmax =Max. Contact Stress
E1/E2 = Young’s modulus of Cam/Tappet
It's the valve train system in OHV type diesel engine.
Valve, Rocker Arm, push-rod , Tappet and cam.
Valve is open and close by cam rotating movement. so cam profile and length of valve train system will be maintained during engine life.
Here, cam and tappet have a line contact and rolling with sliding movement.
It's lubrication condition is a Hydrodynamic lubrication at cam base area
Boundry lubrication at cam nose area,
Sometimes metal metal contact occured at those cam nose area, during that times two solid body have a herts contact stress Sigma max , This sigma max are fuction of load, materials young's modulus, and geometrical factor
In our case, chilled iron tappet and Induction hardening steel cam, hertz stress is over 60 kg/mm^2
TMC ( Techno Material Corp.)

4. TMC ( Techno Material Corp.)
Valve Train System, OHV Type Diesel Engine
Diesel engines, it's has a 2 tribiological main issuses
The one is Piston Ring & Cylinder Liner Wear and Failure Mainly by scuffing or adhesion.
It is give rise to PM and NOx increase and output decrease.
The other one is Cam/Tappet Wear and failure By scuffing and pitting
It's give rise to severe noise and some cases engine stop. And also PM and NOx increase and output decrease.
So to solve these problem, so many studies performed at engine maker. Among those trials, surface treatments is the powerful solutions, I think.
In the case of piston ring : composite plating(Cr-Ceramic),or Nitriding is a typical examples, And In the case of tappet, hard metal or ceramic bonding to cam contact surface,
In this case, I'll present about the devlopements of hard metal bonding steel tappet.
Valve timing control
Profile of Cam nose will be maintained during engine life
Wear of Cam and Tappet  Timing Changed  Imperfect Burning
PM and NOx increase in exhaust gas
If severe wear occurrs in cam and tappet  Engine Fails
TMC ( Techno Material Corp.)

5. TMC ( Techno Material Corp.)
A case of failure - Tappet Pitting and Cam Scuffing
Here is a case of wear failure, Chilled cast Iron tappet pitting and induction hardening cam scuffing.
It's the pitting of tappet, and cross section's microstructure. white structure is carbide and base is a martensite.
those pitting originated from subsurface crack, and it's crack is formed due to excess Hertz stress and material's defects.
Also this is a case of cam scuffing, and cross sections of scuffing occured surface
We can see the white layer, it's means dull layer to etching, extreamly heat change and material transfer occured, by adhesion.
Below this white area we can see the Plastic deformation occured layer.
These scuffing and pitting to raise excess wear of each parts rapidly.And finally engine noise increase and engine stop.
Our Developed engines have higher hertz contact stress before. so in the case of Induction hardened cam used, chilled iron tappet have a problem. so we developed hard metal tappet.
Next present is a characteristics of chilled iron tappet and developed hard metal tappet
High Hertzian Contact Stress
Adhesion of mating materials
TMC ( Techno Material Corp.)

6. TMC ( Techno Material Corp.)
Newly Designed Hard metal tappet - Characteristics I
Simple Process
Low Sintering Temperature for WC Tip (1450 =>1050°C)
Direct Bonding of As-Received WC tip and Machined Body
High Bonding Strength
Vacuum Atmosphere
High Wettability to Steel
Formation of Diffusion Layer
- Main composition : WC with Binder Alloy
WC size : Average 1~5m
Hardness : Above HRA 85
Bending strength : Average 100 kgf/mm^2 (TRS)
Young’s modulus : 43,000 kg/mm^2
Thermal conductivity : 0.17 cal/cm sec C (75W/mK)
Thermal expansion coefficient : 6 x 10-6/ C
TMC ( Techno Material Corp.)

7. TMC ( Techno Material Corp.)
Mass Production
 Technical Alliance with the T.M.C, High Technology possession enterprise
 There’s no Quality Problems in mass production of Hard Metal tappet for 5 years
▶CUSTOMER & SPECIFICATION OF ENGINE
▶ SUPPLY RECORD OF HARD METAL TAPPET(T.M.C)
Conclusion.
To test the performance of a newly developed hard metal tappet compared
with conventionally chilled iron tappet,
We performed wear test, mortoring test, engine dynamo test, and field test
The test results show that
the wear characteristics of hard metal tappet, such as scuffing, pitting and
friction coefficient, are much better than those of conventionally chilled iron
tappet.
Therefore, the commercial use of the newly developed hard metal tappet
is possible. Furthermore, the re-use of the newly developed hard metal tappet will be possible.
TMC ( Techno Material Corp.)

8. TMC ( Techno Material Corp.)
Wear Test - Scuffing
Line contact, Reciprocal sliding with rolling.
Scuffing occur
No Scuffing
Wear test is performed by roll and adaptor.
This adaptor move reciprocal sliding with rolling movement.
Moving Roller specimen is a cam material with induction hardened.
Fixed specimen made by tappet material, taken from each hard metal and chilled iron tappet.
To compare and evalute scuffing, we defiend scuffing time, It's rapidly increse of friction coefflicient.so longer scuffing time is better scuffing characteristics.
Also we compare the friction coefficient, surely lower friction coefficient is better, in this case
Next is the results
Measure the rapid increase time of friction coefficient  scuffing time
TMC ( Techno Material Corp.)

9. TMC ( Techno Material Corp.)
Wear Test - Results
 Hard metal tappet have a longer scuffing time than Fe-alloy tappet
 3 of 5 case of hard metal tappet have not scuffing during test
Here is the results of wear test.
1st scuffing time, as you see, Hard metal tappet have a longer scuffing time than chilled iron tappet, Ans 3 of 5 case of hard metal tappet have not seen scuffing during test time 9 hours.
Also friction coefficient of hard metal tappet is lower than chilled iron tapptet's friction coefficient. In this case surface roughness Rmax or Ra of each tappet is same.
Hard metal tappet have a smaller friction coefficient than Fe-alloy tappet
Hard metal tappet have a better anti-scuffing characteristics than Fe-alloy tappet
TMC ( Techno Material Corp.)

10. TMC ( Techno Material Corp.)
Rig Test(Motoring) - Pitting
- Part test of engine, driven by electrical motor
- Performed 500 hours, at 2200 crankshaft RPM
- Contact stress of cam and tappet is higher than in a real engine
- 6 Fe-alloy tappets and 6 hard metal tappets are tested.
And next, We performed rig test to compare the piting characteristics.
Rig test euipment is a 6 cylinder engine used. Rig test is a Parts test of engine, drive by electrical motor
- Performed 500 hours, at 2200 crankshaft RPM
- Contact pressure increase By increasing valve spring force.
at exhaust port cam tappet contact load is 262.9kg (30% increase than field engine)
-> It's the chilled tappet's Pitting induced conditions.
At the case of rig test crankshaft balance weight adjusting is needed.
There is no piston, connecting rods, so take the dummy weight at Crankshaft
- 6 chilled iron tappets and 6 hard metal tappets were tested.
- Fe alloy Tappets have pitting & all of them have not shown crowned shape
- Hard Metal tappets have no pitting & remain crowned shape
TMC ( Techno Material Corp.)

11. TMC ( Techno Material Corp.)
Dynamo Test & Field Test
To test the Reliability of Engine parts
 Engine Dynamo Test : 1,000 hour, 2200 RPM
- Fe alloy tappets have pitting (2 of 6) & Not scuffing
- Hard metal tappets have no pitting and no scuffing
 Field Test : 100,000km
- Bus and Truck mounting, Only hard metal tappet test.
- No pitting and No scuffing
- Crowned shape of tappet is remained.
- The surface of Tappet and cam were fine-polished.
- It means that it is possible to use the tappets again.
To test the reliability of hard metal tappet , we perforemd engine dynamo test and field test.
Engine dynamo test were performed with chilled iron tappet, A test condition was like this, valve spring force is same as real engines.
The pittng found at chiled iron tappet,
Field engine test were performed with Bus and Truck. Only hard metal tappets were tested. There'e no pitting and other wear problem.
Also Tappet and cam surfaces were fine polished. Value of Sufface roughness Rmax is 0.4 ㎛ to 0.1 ㎛ It’s means, Re-use of tappet and cam possible
- There’s no wear problem after applying in the field for nearly 5 years
TMC ( Techno Material Corp.)

12. TMC ( Techno Material Corp.)
Reliability of Tappet Bonding
Ultrasonic test of bonded parts
 Last 3 years, mass production of Hard Metal tappet, There’s no apart of bonded part .
 Quality assurance system of tappet produced, it has a reliabilities
TMC ( Techno Material Corp.)