JPH0149773B2 - - Google Patents

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 particularly to a method for recasting and hardening the surface of a cylinder in a piston reciprocating internal combustion engine.

BACKGROUND 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 a TIG torch. In particular, in the case of cylinder blocks, the advantage of recasting and hardening is the use of cost-effective basic materials (for example, layered gray cast iron).
Despite the use of , the wear resistance of the cylinder surface can be increased to about 1000HV10.

Problems to be Solved by the Invention However, the known methods still pose a big problem when actually performing recast hardening.
On the one hand, especially since the cylinder block cannot be preheated due to its large mass and due to the risk of distortion, significantly high voltages have to be applied to the surface area to be hardened during recasting, and such voltages In extreme cases, this results in peeling of the hardened layer.

Furthermore, recasting may in some cases lead to a significant deterioration of the surface morphology of the already formed cylinder once again, and the necessary reworking is extremely costly and time-consuming due to the high hardness of the surface and requires tools such as (honing head) service life is reduced. In addition, when partially recasting and hardening the cylinder surface, it is difficult to obtain uniform and dimensionally uniform cylindricity, and this is because the degree of surface grinding performed by the tool corresponds to the different surface hardness. This is because they become different.

It is an object of the present invention to provide a recast hardening method which makes it possible to produce cylinders which are extremely wear resistant, have low stresses and require only modest rework.

Means for Solving the Problems In order to solve the above-mentioned conventional drawbacks, the present invention has the following features:
A direct quenching 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, the method comprising: (a) as an energy source; (b) the TIG torch is operated at a specified pulse frequency with a periodically varying energy density, and (c) the pulse frequency and feed rate of the TIG torch are sequentially adjusted to locally melt and form a scale. Adjust the segments so that they overlap by 20% to 90%, preferably about 60%.

A method for recasting and hardening the surface of a carbon-containing cast iron cylinder is provided.

Operation In the above configuration, the use of one or more TIG torches first reduces equipment costs 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 mass production using TIG torches.

The constant pulsation of the energy density of the TIG torch allows an effective segmentation of the hardening trajectory, which significantly reduces the surface voltage and completely eliminates hardening distortions without the conventional disadvantageous consequences during operation. bring. The hardening track contains approximately 2 to 6 segments per cm, which are scaly as intended due to the pulsation recasting operation. 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, relatively compressive stresses occur anyway in the cylinder jacket.

Repeated melting in the recast zone further causes secondary cementite separation in the texture, which reaches a hardness of 850 to 950 HV10 without problems.

What was further revealed was that the overlapping of the segments in the recasting region resulted in excellent smoothness and morphological stability of the hardened region;
This only requires a modest and benign rework, such as by honing.

Further 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 sufficient hardening depth, while lower values of the pulsating current result in local sedation and cooling of the molten metal. What is important in this case is that during changes in current intensity (including at the beginning and end of quenching)
Second, it is important not to create bubbles that would cause fine craters or bulges in the molten metal. The distribution of segment divisions in the quenching trajectory can be optimized by adjusting the TIG torch pulse frequency and torch feed rate.

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. For many types of internal combustion engines, it is sufficient to protect only the hardened raceway by a hardened raceway.

According to claim 6, electrochemical honing followed by mechanical abrasion is carried out after recast hardening. This exposes the martensite/graphite region, especially around the hardened track, through holes.
Enhanced oil retention or optimum lubrication of the sliding partners of the piston-to-cylinder surface is achieved here.

Embodiment Hereinafter, an embodiment of the present invention will be described based on the accompanying drawings.

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

The hardened track 6 is produced by local melting of the layer close to the cylinder surface and subsequent rapid resolidification, with the formation of a ledebrite structure in the immediate recast zone 8, while in the still heat-affected surrounding area. No. 10 has a martensitic structure.

As shown in FIG. 2, the hardening track 6 is formed by a TIG torch 12. At this time, the corresponding surface of the cylinder 4 is inert gas 1 between the cylinder 4 and the tungsten electrode 14 connected to the power source.
Local melting is caused by an arc 16 formed within the 8. Details of a TIG torch of this type can be found, for example, from the West German patent application P3339447.4 by the same applicant. The TIG torch 12 is moved toward the cylinder 4 in the direction of arrow 20 in FIG. 2 at a feed rate of 1.5 mm/sec.
It is moved forward along a quenching track 6 that is made at equal intervals.

The current intensity, which determines the energy density of the arc 16, ie amperes 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, and this current is then pulsed in a square pattern between 15 A and 80 A at a frequency of 1 Hz. Current interruption for TIG torch 12 is again at point A
is carried out at a current intensity lower value of 15A. As a result,
In the hardening trajectory 6 created by the pulsation of the current intensity, a scale-like overlap of about 60 to 70% of the individual segments 22 occurs, and the hardness is about 350 to 70%.
Reaching 950HV10.

After recast hardening, the cylinder 4 is subjected to electrochemical honing and subsequent mechanical friction coating. At this time, the unevenness of the hardened track 6 is removed, and the martensite/graphite structure in the peripheral region 10 is exposed. Electrochemical honing and mechanical friction coating, West German patent application if required
It can be carried out according to the embodiment disclosed in P3119847.3.

Effects of the Invention As described above, according to the recast hardening method of the present invention, recast hardening is performed by using a TIG torch and operating it with pulsating energy density while moving, so it is cost effective. This is advantageous and has the excellent effect that the hardened parts are not peeled or cracked and require only a small amount of post-treatment.

[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 of the present invention, and Fig. 2 is an enlarged detailed view of the Z section of Fig. 1 showing the middle of recasting and hardening work using a TIG torch. , FIG. 3 is a graph showing the relationship between TIG torch current intensity and pulse frequency. 4...Cylinder, 6...Hardened orbit, 12...
TIG torch, 22...segment.

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 one or more mainly circular hardening trajectories, followed by solidification of ledebrite. , (a) a TIG torch 12 is used as an energy source, (b) the TIG torch 12 is operated at a specified pulse frequency with a periodically varying energy density, and (c) the pulse frequency and feed rate of the TIG torch 12 are , 20% to 90%, preferably about 60 scaly segments 22, which are successively locally melted and formed.
A method for recasting and hardening the surface of a carbon-containing cast iron cylinder, which is characterized by adjusting the surface so that they overlap by %. 2 The current intensity of TIG torch 12 is from 10A to 100A,
2. A method according to claim 1, characterized in that the current is pulsated preferably between 15A and 80A. 3. Method according to claim 1 or 2, characterized in that the conduction of the TIG torch 12 is started and interrupted at a lower value of the pulsating current intensity. 4 The pulse frequency of TIG torch 12 is 3Hz or less,
Preferably it is 1 Hz and the feed rate is 0.4 to 4.
4. A method according to any one of claims 1 to 3, characterized in that the rate is mm/s, preferably 1.5 mm/s. 5. Each cylinder 4 is provided with a single circular hardened track 6, which hardened track 6 is located at the point of change of direction of motion of the piston ring installed in the cylinder 4. The method according to any of paragraph 4. 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.