JP3505792B2 - Engine cylinder block - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an engine cylinder block.
Tsu on click.

[0002]

2. Description of the Related Art When a surface hardening treatment is applied to a metal work, the residual stress caused by cold working up to that point, the temperature change at the time of quenching, the thermal stress due to the temperature difference of each part of the work, the transformation due to transformation It is known that stress and the like are overlapped with each other to cause quenching deformation in the metal work.

On the other hand, as means for preventing the above-mentioned quenching deformation, there are known methods such as proper pretreatment (annealing), prevention of uneven burning, and constrained quenching. Japanese Examined Patent Publication No. 4-21732 describes an example of constrained quenching. That is, the method described in this publication cools the outer peripheral surface of the cylindrical work with cooling water and hardens the both ends of the cylindrical work at the time of quenching the surface of the inner peripheral surface of the cylindrical work with a flange. The inner peripheral surface of the work is heated from one end to the other end by the induction heating coil while being restrained so as not to be deformed by ellipse.

[0004]

However, according to the above-mentioned constraint quenching, although the quenching deformation is reduced, the deformation may gradually progress due to the effect of residual stress after the constraint is released. . For example, when the inner peripheral surface of each cylinder bore of the cylinder block a of the water-cooled multi-cylinder engine shown in FIG. 16 is hardened, the cylinders b arranged in a line
As shown by the arrow, the contraction in the cylinder row direction is small, but it contracts relatively in the direction orthogonal to the cylinder row direction, and each bore deforms into an elliptical shape long in the cylinder row direction. It is difficult to reliably prevent deformation. Further, in the case of the cylinder bore, it is usual to quench only the upper part located on the combustion chamber side . As a result, as shown in FIG. 17 , only the inner diameter of the upper part of the cylinder b becomes small due to the contraction, Straightness is low.

When such a deformation occurs, it is difficult to obtain the roundness and straightness of the bore by the subsequent honing process, and when only the upper part of the cylinder largely contracts as described above, the honing is performed. Becomes extremely difficult.

[0006]

Means for Solving the Problems and its effect] The present inventor has repeated studies and experiments for the above problems, engine
The reason why the above-mentioned shrinkage deformation occurs in the cylinder block is that the shape is not isotropic.
In other words, there is a part with high rigidity and a part with low rigidity, and there is little shrinkage deformation in the part with high rigidity, and shrinkage deformation tends to increase in the part with low rigidity, and the degree of hardening depends on the ease with which this shrinkage deformation occurs. The inventors have found that the entire cylinder block can be deformed evenly if adjusted, and have completed the present invention. Hereinafter, the invention according to each claim for solving the above problems will be described.

<Invention of Claim 1> The present invention relates to a cylinder block of an engine,
Multiple cylinders in series and these series
Water jacket formed to surround all
And the inner peripheral surface of the bore of each of the above cylinders has a patchy portion.
It is hardened, and the inner surface of the bore is
Mottled quenching part of the surface facing in the direction orthogonal to the solder row
Area has a spot-like quenching on the surface facing in the cylinder row direction
It is characterized by being smaller than the area of the part.

The area of the mottled quenching portion is large.
Adjusted according to size (area) or distribution density of quenching spots
can do.

< Invention of Claim 2> This invention is a cylinder block of an engine,
Multiple cylinders in series and these series
Water jacket formed to surround all
And the inner peripheral surface of the bore of each of the above cylinders has a patchy portion.
It is hardened, and the inner surface of the bore is
Mottled quenching part of the surface facing in the direction orthogonal to the solder row
The quench hardened layer depth of the
It should be shallower than the depth of the quench hardened layer in the spot-like quenching part.
Is characterized by.

-Operation-In a water-cooled in-line multi-cylinder engine having a plurality of cylinders connected in a row, or a water-cooled V-type engine in which a plurality of cylinders of each bank are connected in a row, each cylinder is a cylinder row. Although the rigidity in the direction is high and the shrinkage in the direction due to quenching is small, the rigidity in the direction orthogonal to the cylinder row direction is low and the shrinkage in the direction due to quenching tends to be large .

On the other hand, in each of the first and second aspects of the invention, among the inner peripheral surface of the bore of each cylinder, the cylinder row
Direction perpendicular to (directions in which shrinkage due to quenching tends to increase)
The surface that faces the
In all, the area of the spot-like quenching part is small (claim
1) or because the quench hardened layer is shallow (claim
2), shrinkage in the direction orthogonal to the cylinder row due to the quenching
Deformation is less than in the cylinder row direction,
The roundness of will be secured.

That is, the entire cylinder block
When a large amount of
Cylinder even without quenching
Roundness is secured, and subsequent honing processing is easy
Become.

Since the quenching portions are arranged in a patchy shape, it means that quenching heating can be performed locally. Therefore, a high energy heating device is not required,
It is advantageous in reducing the quenching cost.

[0014] In addition, the phase Tonariru surface lower portion of the hardness between the hardened plaque becomes oil passage, since the oil passage is that spread continuously throughout the cylinder peripheral surface, throughout the entire cylinder It is advantageous in supplying oil.

Cylinder block cylinders are preferred.
The wall thickness of the part facing in the direction orthogonal to the row direction is
Shaped so that it is thicker than the thickness of the part facing in the row direction.
Is being done.

That is, the thickened part is that.
Suppresses shrinkage deformation due to quenching due to increased rigidity
be able to. In addition, the rigidity is increased and the shrinkage deformation
To be suppressed means that the degree of quenching is low.
Hardened layer
Even if the depth is shallow)
It means that it is possible to
It is advantageous in increasing the surface hardness of the lock. Furthermore, the thickness
Being formed in the flesh means that the above-mentioned shrinkage deformation occurs.
However, this means that a large processing cost can be obtained.
Later processing becomes easier. And it ’s made thick
Since it is only the region where the above-mentioned contraction deformation is likely to occur,
The weight of the entire dublock does not increase excessively.

Preferably, the cylinder row direction of the cylinders
The outer peripheral surface of the portion facing in the diameter direction orthogonal to
Connects to the outer wall that forms the water jacket of the dablock.
That is, a rib to be connected is provided.

Therefore, the rib causes the shrinkage deformation.
Shrinkage deformation due to quenching due to increased rigidity
Is less. Also, like the case of changing the thickness of the tip,
Less decrease in quenching degree in the above-mentioned areas where shrinkage deformation is likely to occur
Can be made into a cylinder cylinder by quenching
It is advantageous in increasing the surface hardness of the lock.

[0019]

Therefore, according to the present invention,
The inner surface of the bore is partially quenched in a patchy manner, and each
Out of the inner peripheral surface of the cylinder bore, orthogonal to the cylinder row
The surface facing in the direction of the cylinder is
In all, the area of the spot-like quenching part is small (claim
1) or because the quench hardened layer is shallow (claim
2), the circularity of each cylinder is ensured, and the subsequent Horni
Easier to process and a large energy heating device
Is not necessary, which is advantageous in reducing quenching costs.
In addition, it is effective in supplying oil throughout the cylinder.
Be profitable.

[0020]

Embodiments of the present invention will be described below with reference to the drawings.

<Embodiment 1> -Regarding Metal Work-FIG. 1 shows a cylinder block 1 of a water-cooled in-line 4-cylinder engine as a metal work. This cylinder block 1
Includes four cylinders 2 connected to each other and a water jacket 3 formed so as to surround all of the cylinders 2 connected to each other, and the inner peripheral surface of each cylinder 2 is quenched. This quenching is shown in FIG.
As shown by expanding the inner peripheral surface of the
4b and 4c are partial quenches that are scattered vertically and horizontally at a constant pitch, and the degree of quenching differs depending on the location of the inner peripheral surface of the cylinder 2.

That is, in FIGS. 1 and 2, A is an inner peripheral surface portion facing in the cylinder row direction, B is an inner peripheral surface portion facing in the direction orthogonal to the cylinder row direction, and the inner peripheral surface portion A
In the inner peripheral surface portion B, a small quenching unevenness 4c is formed. A quenching spot 4b having a size is formed. Regarding the depths of the quench-hardened layers of these quenching spots 4a, 4b, 4c, the quenching spot 4a is deepest and the quenching spot 4c is shallowest. Therefore, in the case of this example, the degree of quenching of each inner peripheral surface portion of the cylinder 2 is different from each other depending on the area of the quenching unevenness and the depth of the quench hardening layer.

-Quenching device- Fig. 3 shows a quenching treatment device for the cylinder block 1, and high frequency heating is used for the quenching. In the figure, 11 is a water tank for containing the cylinder block 1,
Reference numeral 12 is an induction heating coil for quenching and heating the cylinder block 11 in the water tank 11, and 13 is a pump for circulating water W between the water tank 11 and an external reservoir tank 14.

The bottom of the water tank 11 is inclined. Inside the water tank 11, a work table 15 for mounting the cylinder block 1 in an inclined state, a work receiver 16 for supporting the cylinder block 1 in an inclined state, and Cylinder block 1
Work cover 1 that covers the lower part of the machine (the part that is not quenched)
7 is provided. In addition, in order to circulate water, a water supply channel 18 is provided from the reservoir tank 14 to the upper part of the water tank 11.
And a drainage channel 19 extends from the bottom of the water tank 11 to the reservoir tank 14. The water supply passage 18 is provided with the pump 13 and the drainage passage 19 is provided with a drainage propeller 20.

A branch passage 18a is branched from a portion of the water supply passage 18 downstream of the pump 13, and the branch passage 18a penetrates the lower wall of the water tank 11 and the work cover 17 so that the nozzle at the tip thereof is placed on the work. It faces the upper surface of the table 15 from the side. Further, a foreign matter discharge hole 21 for discharging dust and other foreign matter G is formed at the lower end of the work receiver 16, and a foreign matter discharge pipe 22 extends to the outside from the lowest portion of the inclined bottom surface of the water tank 11. The drainage channel 19 is connected to a downstream portion of the propeller 20. Drainage channel 19
A filter 27 for removing the foreign matter is provided at the connection between the and the reservoir tank.

The induction heating coil 12 corresponds to the water tank 11
A support device 23 extending upward is supported by a cylinder device 24 so as to be able to move up and down. This induction heating coil 12
4 is formed by alternately arranging coil portions 25 and insulator portions 26 as shown in FIG. 4, and adjacent coil portions 25 are connected in series by lead wires 25a. There is. The energizing cable is connected to the adjacent coil portions 25, 25 which are not connected by the lead wire.

FIG. 5 shows an energization control means for the induction heating coil 12, in which reference numeral 28 denotes an oscillator.
29 is a transformer and 30 is a frequency control means. A high-frequency current having a frequency set by the control means 30 is obtained from the three-phase alternating current by the oscillator 28, and the induction heating coil 12 is energized via the transformer 29 to obtain a magnetic flux whose strength changes.

-Quenching- At the time of quenching, the cylinder block 1 having an as-cast structure (pearlite structure) is placed in the water tank 11, and the induction heating coil 12 is placed in the cylinder bore of the cylinder block 1 while circulating the water W. After the insertion, the induction heating coil 12 is energized to pass an induction current through the cylinder 2 to locally heat the cylinder 2 from the inner peripheral surface. in this case,
The portion of the cylinder 2 facing each coil portion 25 is strongly heated by the change in the magnetic flux generated around each coil portion 25 of the induction heating coil 12 and passing through the cylinder 2. Therefore, the quenching portion is formed in a spot-like shape on the inner peripheral surface of the cylinder 2. In the case of the embodiment, the quenching spots 4a, 4b, 4c are formed by appropriately setting the circumferential lengths of the coil portions 25 and the insulator portions 26 to be different from each other.

Then, the high frequency heating is intermittently carried out while gradually shifting the heating position by the induction heating coil 12 downward from the upper end of the cylinder 2, and then the upper inner peripheral surface of the cylinder 2 is The above quenching spots 4a-
4c are formed at intervals in the vertical direction. In this case, since high-frequency heating is performed in circulating water, local heating and rapid cooling are smoothly performed, and desired quenching spots are formed.

Therefore, when the cylinder 2 before quenching is formed into a substantially circular shape, the amount of contraction and movement of the inner peripheral surface of the cylinder 2 to the inside due to quenching is high in the inner peripheral surface portion. Since the degree of quenching at A is high and the degree of quenching at the inner peripheral surface portion B having low rigidity is low, the degree of quenching is substantially the same over the entire circumference, and the roundness is not greatly impaired.

Further, as shown in FIG. 6, a lid 10 is provided on the upper surface of the induction heating coil 12 to prevent water from passing through the central hole of the coil 12. Therefore, the water supplied to the upper portion of the water tank 11 vigorously flows through the gap between the inner peripheral surface of the cylinder 2 and the outer peripheral surface of the induction heating coil 12 as indicated by the arrow, and the inner peripheral surface of the cylinder 2 is heated by high frequency. Even if bubbles K are generated, the bubbles K are immediately removed by this water flow. This is advantageous in enhancing the quenching effect of water because the bubbles K remain attached to the inner circumferential surface of the cylinder 2 and hinder the rapid cooling of the inner circumferential surface of the cylinder 2 by its heat insulating effect.

Further, as shown in FIG. 7, the nozzle at the tip of the branch passage 18a is for removing the foreign matter G on the upper surface of the work mounting table 15 before mounting the cylinder block 1 by applying a water stream. Yes, this allows cylinder block 1
Can be placed on the work placing table 15 without displacement.
The foreign matter G is discharged to the foreign matter discharge pipe 22 and further removed by the filter 27 due to the inclined bottom surface of the water tank 11 and the influence of the flow of water toward the foreign matter discharge pipe 22.

In the above embodiment, each coil portion 25 of the induction heating coil 12 is connected by the lead wire 25a. However, by connecting an independent lead wire for each coil portion and controlling the current flowing through each coil portion. The degree of quenching by the coil portions may be different from each other.

-Regarding Honing- (Problem) In the cylinder block 1 obtained by the above quenching treatment, only the upper portion of the cylinder 2 is hardened by quenching.
The lower portion of the cylinder 2 has a relatively low hardness. When honing the inner peripheral surface of the cylinder 2 as described above, if the grindstone is stroked over the entire length of the cylinder 2, the hardness of the upper portion is high and it is difficult to grind, so it is difficult to secure the desired shape accuracy.

On the other hand, by honing only the upper part of high hardness, the inner peripheral surface of the cylinder 2 is stepped so that the upper part has a larger diameter, and then the entire cylinder length is honed. It may be processed.

However, even in such a case, for example, when only a high-hardness upper portion is processed by a short grindstone, the upper portion itself is distorted by the quenching treatment, so that the machining axis of the honing tool is not fixed and the circularity is round. As the height decreases, the position of the bore may shift. Further, in that case, the stroke of the grindstone is shortened, which means that the distance that the grindstone is guided by the cylinder 2 is also short, and the honing tool is likely to tilt and it is difficult to secure the roundness and straightness. Become. On the other hand, it is conceivable to use a long grindstone, but only a part of the grindstone processes the high hardness upper portion, which causes uneven wear of the grindstone.

(Honing process (1) of the embodiment) In this honing process (1), the lower part of the cylinder 2 which has not been subjected to quenching treatment and therefore has less distortion is used as a guide.
It is characterized in that the quenching-processed upper part is subjected to honing with a short grindstone and a short stroke. After that, the entire length of the cylinder 2 is honed.

That is, as shown in FIGS. 8 and 9, in the honing tool 31 used for this honing, the grindstones 33 are arranged on the upper part of the tool head 32 at regular intervals in the circumferential direction. Guide members 34 are arranged below the tool head 32 at regular intervals in the circumferential direction. The grindstone 33 is for performing a honing process by stroking the quenching process portion 2a of the cylinder 2 that has been subjected to the quenching process, and the guide member 34 is used for the quenching process of the cylinder 2 in the honing process. It slides on the non-quenched portion 2b which has not been treated.

Therefore, the grindstone 33 itself advances and retreats only in the high hardness quenching treatment portion 2a of the cylinder 2 with a short stroke, but the advancement and retreat is guided to the non-quenching treatment portion 2b of the cylinder 2 with less distortion. Honing Tool 3
The machining axis of No. 1 is prevented from shifting, which is advantageous for ensuring roundness and straightness.

(Honing Processing (2) of the Embodiment) This honing processing (2) is characterized in that two kinds of grindstones 35 and 36 are arranged vertically as shown in FIG. 10 to perform honing processing. .

That is, in the figure, 37 is a grindstone holder attached to the tool head, and the upper part of the grindstone holder 37 is mainly slid on the hardened upper part of the cylinder 2 for machining. A grindstone for high hardness 35 to be performed is attached, and a grindstone for low hardness 36 for sliding the grindstone holder 37 to slide the lower hardened part of the cylinder 2 which has not been subjected to the quenching treatment. Is attached. A CBN (cubic boron nitride) grindstone or a WA (white fused alumina) grindstone is suitable as the high hardness grindstone 35, and a diamond grindstone or a GC (green silicon carbide) grindstone is suitable as the low hardness grindstone. Is.

Therefore, in the case of this example, the high hardness upper part of the cylinder 2 is honed by the high hardness grindstone 25 and the low hardness lower part is honed by the low hardness grindstone 36, so that each stroke is short. In addition, the inner peripheral surface of the cylinder 2 can be simultaneously ground over the entire length without causing uneven wear of the grindstone and inclination of the machining axis, and high roundness and straightness can be obtained. Become.

Example 2 This example is shown in FIGS. 11 and 12, and is an example in which the cylinder 42 of the cylinder block 41 as a metal work is formed with a thick portion that is easily contracted and deformed by quenching. is there. That is, the upper portion of the cylinder 42, which is subjected to the quenching treatment, is the portion 4 facing in the direction orthogonal to the cylinder row direction.
The wall thickness of 2b is formed to be thicker than the wall thickness of the portion 42a facing in the cylinder row direction. Then, the cylinder 42 of such a cylinder block 41 is subjected to the same quenching treatment so as to form the quenching unevenness having different areas as in the first embodiment.

Therefore, in the case of the present example, since the rigidity of the thickened portion 42b becomes higher, the shrinkage deformation due to the quenching can be suppressed without making the quenching degree so low. Therefore, it is possible to suppress irregular shrinkage deformation while increasing the surface hardness of the work by quenching. Moreover, since the portion 42b is thick, a large machining allowance can be taken even if the shrinkage deformation occurs, and the subsequent machining becomes easy. Furthermore, since only the portion that is easily thickened is likely to be thickly formed, the weight of the entire cylinder block 41 does not increase excessively.

<Third Embodiment> This embodiment is shown in FIGS. 13 and 14, in which a rib 54 is provided in a portion of the cylinder block 51, which is a metal work, which is easily contracted and deformed by the quenching treatment of the cylinder 52. It is characterized by being

That is, the ribs 54 connect the outer peripheral surface of the portion 52b of the cylinder 52 which is diametrically opposed to the cylinder row direction and is orthogonal to the cylinder row direction, and the outer wall 51a forming the water jacket 53 of the cylinder block 51. Is provided in the cylinder 52 to increase the rigidity of the portion 52b of the cylinder 52 in the deformation direction. And
The cylinder 52 of such a cylinder block 51 is subjected to the same quenching treatment so as to form quenching spots having different areas as in the first embodiment. The ribs 54 can be formed by providing through holes in the jacket core when the cylinder block 51 is cast.

Therefore, in the case of this example, the portion 52b facing in the direction orthogonal to the cylinder row direction of the cylinder 52.
Tries to shrink inward by quenching,
The rib 54 opposes the deformation and prevents the excessive contraction deformation. Therefore, also in the case of this example, as in the case of Example 2, even if the degree of quenching is not so low, the shrinkage deformation due to the quenching can be suppressed, and while increasing the surface hardness of the work by quenching, It is possible to suppress irregular shrinkage deformation. Furthermore, the rib 54 because those are provided only on a part of the cylinder 52, it has a name that the weight of the entire cylinder block 51 is excessively increased.

< Others> If the work shape before quenching is previously deformed in the opposite direction to the shrinkage deformation direction in consideration of shrinkage deformation due to quenching, shrinkage deformation to a predetermined shape by quenching can be performed. In order to improve the dimensional accuracy of the work,
Alternatively, it is a suitable means for simplifying the subsequent machining.

For example, as shown in the example of the cylinder block 71 in FIG. 15 , the upper portion of the cylinder 72 is formed into an elliptical shape that is long in the direction orthogonal to the cylinder row direction, and then the inner peripheral surface of the cylinder 72 is formed. After quenching, the shape of the obtained cylinder 72 does not greatly deviate from the originally planned roundness and straightness.

Therefore, if such a technique is applied to each of the above-described embodiments, it is possible to prevent the dimensional accuracy from deviating without making the quenching degree partially different.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a cylinder block according to a first embodiment.

FIG. 2 is a development view showing quenching spots on the inner peripheral surface of the cylinder of the same example.

FIG. 3 is a sectional view showing a quenching apparatus of the same example.

FIG. 4 is a plan view showing an induction heating coil of the same example.

FIG. 5 is a block diagram showing an energization control unit of the induction heating coil of the same example.

FIG. 6 is a partial cross-sectional perspective view showing the relationship between the induction heating coil and the cylinder of the same example.

FIG. 7 is a cross-sectional view showing a work placement table and a foreign matter removal nozzle of the quenching device.

FIG. 8 is a side view showing the honing tool of the same example.

FIG. 9 is a plan view of the honing tool.

FIG. 10 is a side view showing another grindstone for honing and a grindstone holder of the same example.

FIG. 11 is a cross-sectional view showing a cylinder block according to a second embodiment.

FIG. 12 is a vertical sectional view of the cylinder block of the same example.

FIG. 13 is a cross-sectional view showing a cylinder block according to a third embodiment.

FIG. 14 is a vertical sectional view of the cylinder block of the same example.

FIG. 15 is a plan view showing another cylinder block .

FIG. 16 is a plan view showing a quenching deformation of a conventional cylinder block.

FIG. 17 is a vertical sectional view showing quenching deformation of a conventional cylinder block.

[Explanation of symbols]

1, 41, 51, 61,71 cylinder block 2, 42, 52, 62,72 cylinders 3,53 Water jacket 4a, 4b, 4c Quenching spots A cylinder inner peripheral surface B Cylinder inner surface 11 aquarium 12 induction heating coil 13 pumps 14 Reservoir tank 15 Work stand 16 Work receiving 17 Work cover 18 waterways 19 drainage 20 Propeller for drainage 21 Foreign object discharge hole 22 Foreign object discharge pipe 23 Support arm 24 cylinder device 25 insulator 26 Protrusion 27 filters 28 oscillators 29 transformer 30 frequency control means 31 Honing Tool 32 tool head 33 whetstone 34 Guide member 35,36 grindstone 37 grindstone holder

─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yukio Hamamoto No. 3 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture Mazda Co., Ltd. (72) Inventor Hisashi Kajikawa No. 3 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda (72) Inventor Norimasa Nagato, No. 3 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda Co., Ltd. (72) No. 3 Shinchi, Fuchu-machi, Aki-gun, Hiroshima Mazda Co., Ltd. (72) Iwao Yamashita, Inventor Iwao Yamashita, No. 3 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Mazda Co., Ltd. (56) References JP 61-8454 (JP, A) JP 5-17815 (JP, A) ) Actual Kaihei 3-106346 (JP, U) JP-B-62-54363 (JP, B1) (58) Fields investigated (Int.Cl. ⁷ , DB name) C21D 9 / 00-9 / 44,9 / 50 C21D 1/02-1/84

Claims (2)

(57) [Claims] 1. A plurality of cylinders connected to each other, and this cylinder.
Are formed so as to surround all of the connected cylinders.
Equipped with a water jacket, and the inner peripheral surface of the bore of each cylinder is partially quenched
Of the inner surface of the bore , and in a direction orthogonal to the cylinder row.
The area of the mottled quenching part of the facing surface is in the cylinder row direction.
Is smaller than the area of the spot-like quenching part of the surface facing the
Cylinder block of engine characterized by and . 2. A plurality of cylinders connected to each other, and
Are formed so as to surround all of the connected cylinders.
Equipped with a water jacket, and the inner peripheral surface of the bore of each cylinder is partially quenched
Of the inner surface of the bore , and in a direction orthogonal to the cylinder row.
The depth of the quench-hardened layer in the variegated quenching portion of the facing surface is
Quenching the spot-like quenching part of the surface facing the binder row direction
The engine system is characterized by being shallow compared to the depth of the hardened layer.
Linda block .