FORM 2
THE PATENTS ACT 1970
(39 of 1970)
&
The Patent Rules, 2003
Complete Specification
(See section 10 and rule 13)
An Apparatus And A Method For Induction Hardening Of Crankshafts
Bharat Forge Limited
An Indian company registered under the Indian Companies Act, 1956. Mundhwa, Pune - 411036, Maharashtra, India
The following specification particularly describes the invention and the manner in which it is to be performed.

Field of Invention
The present invention relates to a method and apparatus for induction hardening. Particularly the present invention relates to the method and apparatus for induction hardening to avoid defects during induction hardening of a crankshaft.
Background of Invention
Crankshaft is one of the most critical components used in an IC engine. The crankshaft in conjunction with the cylinder, piston, and connecting rod converts the linear motion of the piston, generated during the fuel burning in the cylinder, to the rotational motion.
The performance of the crankshaft in service depends on many different aspects right from its material and geometry to the different manufacturing steps used in its production. Every manufacturing step provides certain characteristic property to the crankshaft which helps in extending its service life.
During the internal combustion cycle of an IC engine, the power generated by combustion of fuel in the cylinder is transmitted to the crankshaft through the piston and the connecting rod. This leads to bending and torsional fatigue loads being produced on the crankshaft. The fatigue loading may lead to generation and development of cracks on the surface. The cracks may travel deeper into the crankshaft body ultimately leading to fatigue failure of the crankshaft.

One way to avoid fatigue crack generation is to increase the hardness of the material. But, at higher hardness, the fracture toughness of the material also reduces, whereby the cracks develop and travel down to the core of the crankshaft resulting in a failure that can be catastrophic in nature.
In order to avoid this, induction hardening process is used which increases the surface hardness of the crankshaft’s Pins and Journals (where the fatigue crack initiation happens) while keeping its core tough.
The induction hardening process works on electromagnetic induction principle where an alternating magnetic field is produced by an induction coil which produces eddy currents in the surface of the component thereby heating up the surface. Once the surface is adequately heated, the component is quenched in water, oil or polymer which leads to hardening of the surface due to formation of martensite in the surface layer. This is followed by a tempering operation which gives the final microstructure of tempered martensite on the surface layer of the component.
Typically the induction hardening process consists of following steps:
1. Cleaning of crankshaft: The crankshaft is cleaned using a cleaning cloth or any other medium to remove loose burr/ chips / oil if any.
2. Placement of crankshaft: Place the crankshaft in Induction hardening machine on pre loaders.

3. Fixing of crankshaft: Fix the crankshaft in chucks at both front end or flange end and rear end or tail end.
4. Selection of induction hardening program: Select the specific recipe for the crankshaft to be hardened. Cross check recipe for Power, Heat time, quench time, quench flow and energy values.
5. Inductor placement: Place the Inductors/ Induction heating coil as per hardening sequence.
6. Process start: Start hardening one diameter at a time as per hardening sequence.
7. Process monitoring: Monitor Energy input and quenching parameters for every diameter.
The amount of heat required to be induced in the surface of the pin or journal of the crankshaft depends on the size, geometry and case depth requirement of the crankshaft. Greater the size and case depth requirement of the crankshaft, greater the amount of heat required for the hardening process. The heat is typically induced through electric power supply to the inductor. In case of very large crankshafts, such as those used in locomotive or ship engines, or power generators, the required case depth is very large. Due to the very large size of the crankshaft and case depth requirement, very high amount of eddy currents have to be induced in the pins and journals which generates high amount of heat in surface layer.

The heat produced during induction hardening also gets dissipated through conduction into the region (counterweights, webs etc.) adjoining the pins and journals of the crankshaft. If the mass of the adjoining region (i.e. counterweights, webs etc.) is not sufficient (due to thin webs or counterweight) to dissipate the transferred heat or if the mass of the adjoining region i.e. counterweight is not available on the crankshaft, it may lead to overheating of the regions adjoining to pins and journals. This kind of overheating may lead to defects (refer to Figure 4A) like localized surface melting, cracks, heat checks etc. However, even the smallest reduction in heat induced during induction hardening to avoid these problems could lead to undesirably low case depth and thus, faulty products.
Thus, there exists a room for advancement over the existing technology in that an innovative and cost effective method of induction hardening has to be designed to overcome the drawbacks of the current induction hardening methods.
Objects of invention
Some of the objects of the present disclosure which at least one embodiment herein satisfies are as follows:
It is an object of the present invention to provide an induction hardening method for crankshafts.

It is another object of the present invention to provide an induction hardening method which avoids the problem of overheating (see Figure 1A) of the regions adjoining to pins and journals of a crankshaft during the induction hardening process.
It is another object of the present invention to provide an induction hardening method which reduces the defective parts generated during this process.
It is yet another object of the present invention to provide a cost effective induction hardening method which avoids the problem of overheating of the areas adjoining to pins and journals (see Figure 1A) of a crankshaft during the induction hardening process.
It is still another object of the present invention to provide an induction hardening method which does not increase the cycle time of process while avoiding the problem of overheating of the areas adjoining to pins and journals of a crankshaft during the induction hardening process.
Other objects and advantages of the present disclosure will be more apparent from the following description which is not intended to limit the scope of the present disclosure.

Brief description of accompanying drawings
Figure 1 shows a typical crankshaft.
Figure 1A shows over-heating of the surface during conventional induction hardening.
Figure 1B shows the uniform distribution of heat caused by the invention.
Figure 2A shows the Journal Side half of the apparatus used to avoid the overheating of the surfaces adjoining to the pins and journals.
Figure 2B shows the Pin Side half of the apparatus used to avoid the overheating of the surfaces adjoining to the pins and journals.
Figure 3 shows the apparatus assembled on a crankshaft and cross section S-S taken through the crankshaft.
Figures 4A shows defects produced by conventional induction hardening methods.
Figures 4B shows defect free surfaces produced with the method of induction hardening of the invention.

List Of Parts:
1. Pin 7. Internal shape of journal-side
2. Journal 10 half of heat sink adapter
3. Tail 8. Pin-side half of the heat sink
4. Flange adapter
5. Web 9. Internal shape of pin-side
6. Journal-side half of heat sink half of heat sink adapter adapter 15 A. Heat sink adapter
Summary of invention
The present invention is related to a method of induction hardening. The invention is directed to overcome the various drawbacks of the conventional methods of induction hardening of crankshaft.
The present invention provides an induction hardening method which avoids the overheating of the region adjoining to the area being induction hardened when heat accumulation capacity of these adjoining regions is not adequate, thus avoiding defects (see Figures 4A and 4B) like localized surface melting, cracks, heat checks etc. Further, the present invention achieves this without any expensive or complex changes to the induction hardening equipment or its software programming.

The invented method provides an innovative apparatus which is fixed on the crankshaft in the region adjoining to area being induction hardened. This apparatus remains affixed to the crankshaft during the induction hardening process and acts as a heat sink for conducting a part of heat from the induction hardening zone to the adjoining region. Without this apparatus, the heat will entirely be transferred to the adjoining regions only (see Figures 1A and 1B). This helps in conducting a part of heat away from the adjoining region thus, avoiding any overheating of the adjoining region.
Description of the invention
The present invention discloses an apparatus for and a method of induction hardening of crankshaft which avoids defects like localized surface melting, cracks, heat checks etc. due to overheating of the areas adjoining the regions being induction hardened.
Normally, in a crankshaft all the barrels/cylinders are induction hardened; the barrels being the pins, journals, tail and flange.
Figure 1 shows a typical crankshaft used in an internal combustion engine. The crankshaft shown in Figure 1 is an 8 cylinder crankshaft which can be used in any kind of application ranging from automobile engine, locomotive engine, power generator, marine engine etc. Although further description will be given with

reference to this crankshaft, the various embodiment of this invention are equally applicable to all the other type of crankshafts also.
A crankshaft basically has following main geometric features:
1. Barrels/cylinders – this consist of pins (1) which is assembled with the connecting rod, journals (2) which are assembled with the engine block, a tail (3) and a flange (4) both of which are at the extreme end of the crankshaft.
2. Webs (5) – The webs are adjacent to every pin and journal as shown in the Figure 1. The webs (5) may be with or without integral counterweight. In the second case the counterweights are made separately and joined with webs using joining method like welding or bolting.
All the barrels of a crankshaft are induction hardened to increase the fatigue strength of the crankshaft. During the induction hardening process, a semicircular inductor is used to induce the required eddy currents in each barrel. Sometimes, only one barrel is induction hardened at a time and in some other cases multiple barrels can be induction hardened at the same time.
During induction hardening, the surface of a barrel is heated to a temperature which is above the recrystallization temperature of steel – the material typically used to make crankshafts. The inherent characteristics of the process lead to

heating of only the surface of the barrel. This is then immediately quenched to produce martensite on the surface of the barrel.
During the heating of the barrels in the process, the heat generated at the barrels is transferred through conduction to the regions (webs and counterweights) adjoining to the barrels. The webs with or without counterweight which are connected to barrels act as a heat sink and thus, the heat gets accumulated and distributed in whole of the mass of the webs. Due to this distribution of heat energy in the web through conduction, the temperature of the surface of web in immediate vicinity or contact with the barrel does not heat up to that extent where surface melting or other defect will occur.
Sometimes the shape of the web is such that its mass is small. Due to small mass, the heat conducted from the induction hardened barrel is not redistributed properly in the web. In absence of this heat sink effect of the web, the surface just adjacent to the barrel heats up significantly (see figure 1A). The temperature of the surface increases above the recrystallization temperature and sometimes even reaches close to the melting point of the steel. Due to this, after quenching, this area shows cracks, melting marks or heat checks (see Figure 4A).
To avoid this overheating of the adjacent regions, the power of induction hardening process cannot be reduced as this will reduce the case depth of the surface hardened layer. Thus, to avoid overheating, an apparatus has been

designed which, when fitted on the web (5) adjacent to the barrel being hardened, acts as a heat sink and dissipates part of the heat away from the region of the web (5) adjacent to barrels. Heat sink adapters can be used on one side or both sides of the barrel being induction hardened depending on the shape and size of the webs i.e. whether the web is capable of dissipating enough heat to avoid overheating or not.
The heat sink adapter (A) is made in two parts. Of these, the journal-side half (6) is the heat extractor, which actually extracts heat from the component, whereas the pin-side half (8) simply facilitates mounting of the heat sink adapter (A) on the web (5). Mounting of the heat sink adapter (A) on the web (5) is done using nut and bolts or any other fastening arrangement.
Figure 2A shows the journal-side half (6) of apparatus (heat sink adapter - A) which acts as a heat sink during induction hardening. The internal shape (7) of the journal-side half (6) of the apparatus is made same as the external shape of the web (5) adjacent to the barrel being hardened. Figure 2B shows the pin-side half (8) of the apparatus (heat sink adapter - A).
Thus, in the invented process of induction hardening disclosed here, the heat sink adapters (6, 8) are first fitted on the webs (5) adjacent to the barrels being induction hardened. After the fitment of the adapters (A) on the crankshaft web (5), the crankshaft is taken up for induction hardening. During the induction

hardening process, the adapter (A) remains affixed to the webs (5). Surface melting is avoided by providing means for absorbing/ extracting/ dissipating part of heat transferred towards the regions adjacent to barrels being induction hardened. This part of heat is absorbed/ dissipated by providing extra mass in the form of the adapter (A) which works as a heat sink.
Figure 3 shows how the heat sink adapter (A) having two halves (6, 8) is fixed to the web (5). The heat sink adapter (A) does the extraction of heat from the web (5) i.e. it acts as a heat sink. Hence, the shape of journal-side half (6) of the adapter (A) preferably matches exactly with the corresponding shape of the web (5). On the other hand heat extraction is not required on the pin-side of the web as overheating does not occur there. Thus, shape of the pin-side half (8) of the adapter (A) is unrelated to the corresponding shape of the web (5) and made only for the purpose of fixing the adapter on (5). In another embodiment, the internal shape (9) of the pin-side half (8) of said heat sink adapter (A) is made same as the external shape of said web (5) on which it is mounted.
The induction hardening process of invention consists of following steps:
1. Cleaning of crankshaft: The crankshaft is cleaned using a cleaning cloth or any other medium to remove loose burr/ chips / oil if any.
2. Assembly of the heat sink adapter: Next the heat sink adapter (A) is assembled on the crankshaft using following process steps:
2A- Put Heat sink adapter (A) on web between Journal and Pin.

2B- Tighten the adapter till it sits properly on web (5) surface
2C- Ensure no gap between journal-side half (6) of said heat sink adapter
(A) and the external shape or surface of web (5).
3. Placement of crankshaft: Place the crankshaft assembled with heat sink adapter (A) in Induction hardening machine on pre loaders.
4. Fixing of crankshaft: Fix the crankshaft with heat sink adapter (A) in chucks at both front (flange side) and rear (tail side) end.
5. Selection of induction hardening program: Select the specific recipe for the crankshaft to be hardened. Cross check recipe for Power, Heat time, quench time, quench flow and energy values.
6. Inductor placement: Place the Inductors/ Induction heating coil as per hardening sequence.
7. Process start: Start hardening one diameter at a time as per hardening sequence.
8. Process monitoring: Monitor Energy input and quenching parameters for every diameter.
The benefits of this invention are as follows:
1. The use of the heat sink adapter (A) during induction hardening does not allow the area adjacent to barrel to overheat by acting as a heat sink. The problem of overheating of parts and non-uniform distribution of heat are overcome by the present invention. This is clearly visible from the colour photographic images shared in Figure 1B.

2. By avoiding this overheating, defects like heat checks, localized surface melting and cracks formed during induction hardening are completely avoided. This is evident from the photographic images of the products treated with the method of invention shown in Figure 4B.
3. The step of mounting of the heat sink adaptors on the webs / counterweights before the induction hardening process, which helps in avoiding the overheating of the region is a truly low cost solution which does not require any costly changes in the induction hardening equipment or its programming.
4. The time required for assembling the Adapter (A) and mounting it on the web (5) is very less and it can be done offline. Thus, this invention does not add any extra cycle time to the process.

We Claim:
1. An apparatus for induction hardening of crankshafts, said crankshaft having barrels in the form of pins (1), journals (2) a tail (3) and a flange (4), and webs (5) provided adjacent to every pin and journal, characterized in that said apparatus comprising a heat sink adapter (A) to be mounted on said web (5) adjacent to the barrels being induction hardened, said heat sink adapter (A) consisting of a journal-side half (6) and a pin-side half (8), wherein said mounting of said heat sink adapter (A) on said web (5) is done using nut and bolts or any other fastening arrangement.
2. The apparatus as claimed in claim 1, wherein the internal shape (7) of the journal-side half (6) of said heat sink adapter (A) is made same as the external shape of said web (5) on which it is mounted.
3. The apparatus as claimed in claims 1 to 2, wherein internal shape (9) of the pin-side half (8) of said heat sink adapter (A) is unrelated to the corresponding shape of the web (5) on which it is mounted.
4. The apparatus as claimed in claim 1, wherein the internal shape (9) of the pin-side half (8) of said heat sink adapter (A) is made same as the external shape of said web (5) on which it is mounted.
5. The apparatus as claimed in claims 1 to 4, wherein said heat sink adapters (A) are provided on one side or both sides of the barrel being induction hardened.
6. A method of induction hardening of crankshafts said crankshaft having barrels in the form of pins (1), journals (2) a tail (3) and a flange (4), and

webs (5) provided adjacent to every pin and journal, characterized in that said method comprises the steps of
a. cleaning said crankshaft to remove loose burr or chips or oil;
b. mounting a heat sink adapter (A) on said web (5) adjacent to the
barrels being induction hardened, said heat sink adapter (A) consisting
of a journal-side half (6) and a pin-side half (8), and ensuring there is
no gap between said journal-side half (6) of said heat sink adapter (A)
and the external shape or surface of said web (5);
c. placing said crankshaft with said heat sink adapter (A) mounted on it
in an induction hardening machine on pre-loaders;
d. securely fixing said crankshaft inside said induction hardening
machine on chucks at its front and rear ends;
e. carrying out hardening in accordance with a pre-determined sequence.
7. The method as claimed in claim 6, wherein the internal shape (7) of the journal-side half (6) of said adapter (A) is made same as the external shape of said web (5) on which it is mounted.
8. The method as claimed in claims 6 to 7, wherein internal shape (9) of the pin-side half (8) of said adapter (A) is unrelated to the corresponding shape of the web (5) on which it is mounted.
9. The method as claimed in claim 6 to 7, wherein the internal shape (9) of the pin-side half (8) of said heat sink adapter (A) is made same as the external shape of said web (5) on which it is mounted.

10. The method as claimed in claim 6 to 9, wherein said heat sink adapters (A) are provided on one side or both sides of the barrel being induction hardened.
11. The method as claimed in claims 6 to 10, wherein said mounting of said journal-side half (6) and said pin-side half (8) of said heat sink adapter (A) on said web (5) is done using nut and bolts or any other fastening arrangement.