JPS60245725A - Recasting quenching process for carbon-containing cast iron cylinder surface - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for recasting and hardening the surface of a cylinder made of carbon-containing cast iron, and more particularly to a method for recasting and hardening the surface of a cylinder in a piston reciprocating internal combustion engine.

2. Description of the Related Art It has already been proposed to recast and harden the cylinder surface of a piston reciprocating internal combustion engine in order to improve its wear resistance.

The energy source used in this case is an electron beam gun or a laser beam gun or TIG). In particular, in the case of cylinder blocks, the advantages resulting from surface hardening are that despite the use of cost-effective basic materials (e.g. layered gray cast iron), approximately 1000 HVIO
The wear resistance of the cylinder surface can be increased up to

Problems to be Solved by the Invention However, with the known methods, there are still major problems when actually performing recast hardening.

On the one hand, cylinder blocks in particular cannot be preheated due to their large mass and due to the risk of distortion, so during recasting significantly high voltages have to be applied to the surface area to be hardened, and such In extreme cases, the voltage can cause delamination of the hardened layer.

In some cases, the surface morphology of the already formed cylinder deteriorates significantly again, and the necessary reworking is extremely costly and time-consuming due to the high hardness of the surface and requires tools such as The service life of the honing head (honing head) is reduced. In addition, when the cylinder surface is partially recast and hardened, it is difficult to obtain uniform and dimensionally uniform cylindricity, and this is because the degree of surface grinding performed by the tool may result in different surface hardness. This is because they differ accordingly.

The object of the invention is to provide a recast and hardening process which allows cylinders to be produced which are extremely wear resistant, have low stresses and require only a small amount of rework.

Means for Solving the Problems In order to overcome the above-mentioned conventional drawbacks, the present invention provides a method in which the surface of a cylinder made of carbon-containing cast iron is locally melted by an energy source along one or more mainly circular quenching trajectories. , followed by ledebrite solidification, in which a) a TIG torch is used as the energy source, b) the TIG torch is operated at a specified pulse frequency with a periodically varying energy density, and c)
)TIG)-CH pulse frequency and feed rate are adjusted so that the scale-like segments that are successively locally melted overlap each other by 20% to 90%, preferably about 60%. We provide a method for recasting and hardening the surface of carbon-containing cast iron cylinders.

OPERATION In the above configuration, the use of one or more TIG torches first reduces equipment cost compared to electron beam guns or laser beam guns. Furthermore, the cylinder recasting process is more advantageous in terms of accessibility, production control and production monitoring, especially in the case of large-volume main seats using TIG chips.

The constant pulsation of the energy density of the TIG )-chi allows an effective segmentation of the hardening trajectory, which is accompanied by a significant reduction in surface voltage and a complete reduction of hardening distortions without the conventional disadvantageous consequences during operation. bring about removal. The hardening track contains about 2 to 6 segments per cm, and these are continuous scales intended for pulsation recasting operations. Experiments have shown that these segmented hardened tracks are never prone to crack formation or spalling. Moreover, in the case of use in internal combustion engines, due to the relatively high temperature of the cylinder surface, compressive stresses occur relatively primarily in the cylinder jacket anyway.

Repeated melting of the recast zone further causes secondary cementite separation in the texture, which is unproblematic from 850 to 9.
A hardness of 50HVIO is reached.

Furthermore, it has become clear that the overlap of the segments in the recasting area results in excellent smoothness and morphological stability of the hardened area, which allows for slight and problem-free reworking such as honing. Just need it.

Other suitable and advantageous processing features are evident from the features of claims 2 to 4. Upper values of the current intensity, on the one hand, ensure a sufficient depth of melting, ie a sufficient hardening depth, while lower values of the pulsating current result in local sedation and cooling of the molten metal. In this case, it is important that when the current intensity changes (including at the beginning and end of quenching), bubbles that cause fine craters and bulges in the molten metal are not generated. The distribution of segment divisions in the quenching trajectory can be optimized by adjusting the pulse frequency of the TIG torch and the torch feeding speed.

The features of claim 5 relate to a particularly cost-effective method for hardening the cylinder surfaces of reciprocating piston internal combustion engines, which allows short cycle times in series production. As is generally known, in the cylinder of an internal combustion engine, the upper movement direction change point of the upper piston ring, which is closest to the combustion chamber, is the part of the cylinder surface that is subject to the most wear, so only this part is hardened. Track protection is sufficient for many types of internal combustion engines.

According to claim 6, stain vapor chemical honing followed by mechanical friction machining is carried out after recast hardening. This opens up and exposes the martensitic/graphite structure around the hardened raceway, where enhanced oil retention or optimum lubrication of the nullide partner on the piston-to-cylinder surface is achieved.

Example Hereinafter, one embodiment of the present invention will be described based on the accompanying drawings.

In Fig. 1, there are a plurality of cylinders (4) in a cylinder block (2) of a multi-cylinder internal combustion engine made of layered gray cast iron.
) are arranged, and these are usually machined to almost finished dimensions. In each cylinder (4), the cylinder (
An annular hardened track (6) is formed at the upper movement redirection point of the upper piston ring closest to the combustion chamber of each of the pistons (not shown) sliding in 4).

The hardened track (6) is produced by local melting of the layer close to the cylinder surface and subsequent rapid resolidification, with a ledebrite structure forming in the immediate recast zone (8), while In addition, the surrounding area −〇〇 affected by heat becomes a martensitic structure.

As shown in Figure 2, the quenching track (6) is TIG
- formed by Chi@. At this time, the corresponding surface of the cylinder (4) is connected to the tungsten electrode 04) connected to the power source.
The inert gas is locally melted by an arc θQ formed in the inert gas α stage between the inert gas and the cylinder (4). Details of a TIG torch of this type can be found, for example, from the four-day patent application P3339447.4 by the same applicant. The TIG torch 02 beam is moved forward at a feed rate of 5 mm/sec in the direction of the arrow (4) in FIG. 2 along a hardening track (6) made at equal intervals relative to the cylinder (4).

The current intensity determining the energy density of the arc Qfj, ie ampere A at time t, is shown in the graph of FIG.

The current injection at point (E) takes place at a lower value of the current intensity 15 A, which current is subsequently increased to 15 A and 8 OA at a frequency of IHz.
pulsating in a square pattern between.

Current interruption for TIG )-CH (2) is again at point (A)
at a current strength lower value of 15A. As a result, in the hardening trajectory (6) created by the pulsation of current intensity,
A scaly overlap of about 60 to 70% of the individual segments occurs, and the hardness reaches about 350 to 950 HV10.

After recast hardening, the cylinder (4) is subjected to electrochemical honing followed by mechanical friction coating. At this time, slight irregularities on the hardened track (6) are removed,
The martensite/graphite structure of the peripheral region 00 is exposed.

Electrochemical honing and mechanical friction coating can optionally be carried out according to the embodiment disclosed in West German patent application P3119847.3.

Effects of the Invention As described above, according to the recasting and hardening method of the present invention,
Since recast hardening is performed by using a 1'IG )-chi while moving it and operating it with pulsating energy density, it is advantageous in terms of cost, and it does not cause peeling or cracking in the hardened parts. It has the excellent effect of requiring only a small amount of post-processing.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a cylinder block of an internal combustion engine having a cylinder surface hardened by the method according to the present invention;
Figure 2 is an enlarged detailed view of part 7 of Figure 1 showing the process of recasting and hardening using a TIG torch, and Figure 3 is a TIG torch.
FIG. (4)...Cylinder, (6)...Quenched orbit, 0z
...TIG) -chi, ■...Segment agent Yoshihiro Morimoto Figure 1 4----- ShiD7ta. l-quenched track envy

Claims (1)

[Scope of Claims] 1. A recast hardening method in which the surface of a cylinder made of carbon-containing cast iron is locally melted by an energy source along a mainly circular hardening trajectory or paths, followed by solidification of ledebrite. a) a TIG)-chi (2) is used as the energy source, b) the TIG torch (2) is operated at a specified valve frequency with a synchronously varying energy density, and c) a TIG)-chi (2) ) pulse frequency and feed rate are
A method for recasting and hardening the surface of a cylinder made of carbon-containing cast iron, characterized in that the four scale-like segments that are sequentially and locally melted are adjusted to have a 20% to 90%, preferably about 60% electric fit. 2. Current intensity of TIG torch (2) is 100 from IOA
A. 2. A method according to claim 1, characterized in that the current is pulsated preferably between 15 A and 8 OA. 3. Method according to claim 1, characterized in that the conduction initiation and interruption of the TIG)-chi (6) takes place at a lower value of the pulsating current intensity. 4. The pulse frequency of TIG)-CH (2) is 3Hz or less,
Preferably, IHz is 9, and the feeding speed is 0.4 to 4πm.
4. A method according to any one of claims 1 to 3, characterized in that the rate is 15 fights/second, preferably 15 fights/second. 5. Single circular hardened track (6) for each cylinder (4)
Claims 1 to 4 are characterized in that the hardened raceway (6) is located at a turning point in the direction of movement of a piston ring fitted in the cylinder (4).
The method described in any of the paragraphs. 6. Process according to any one of claims 1 to 5, characterized in that the cylinder (4) is subsequently subjected to electrochemical honing and optionally mechanical abrasion.