JPS5891351A - Crankcase for engine - Google Patents

Abstract

PURPOSE:To increase the hardness of the inner surface thereof, make a cylinder liner unnecessary and reduce the cost of manufacturing by a method wherein the surface of the inner wall of the bore of the crankcase of the engine is treated by ionic nitriding after the casting thereof. CONSTITUTION:The crankcase is cast by the material of FC25, consisting of 3% of carbon, 2.1% of silicon, 0.7% of mangan and the balance of iron, and the inner surface of the bore thereof is machined. Subsequently, the crankcase is washed by hot-water, then dried, whole surface thereof except the inner wall surface of the bore is masked by soft steel plates, the crank case is transferred into the furnace of the device of the ionic nitriding treatment, and a negative potential is charged to the crankcase while a plus potential is charged to the wall of the furnace to effect the ionic nitriding treatment. As a result, the layer of chemical composition consisting of Fe-N is formed with the depth of 2.5-5.0mu from the surface thereof, thereafter, the layer of diffusion of nitrogen is formed. Accordingly, a range, in which the hardness is HV500 or more, is arrived at the depth of 20mu from the inner surface of the bore and thereby making the cylinder liner unnecessary.

Description

[Detailed Description of the Invention] Conventionally, a special cast iron cylinder liner was press-fitted into the crankcase bore in order to improve the wear resistance and scuff resistance of the inner wall of the engine crankcase bore, but the number of parts increased by 9. Also, the press-fitting work was complicated.

The inventor of the present invention has conducted various studies to solve the above problems, and as a result, sufficient hardness of the inner wall surface of the bore can be obtained by ion-electrifying the inner wall of the bore of the crankcase.

In addition, it was possible to obtain a crankcase with good workability, low cost, and almost no thermal deformation of the crankcase due to the low processing temperature.

An embodiment of the present invention will be specifically described below.

First, C:3. achi, 8i: 2.1%, ・Ms
: The crankcase was cast from Fe12 material consisting of 0.7% and the rest.

Machine the inner bore surface. Next, the crankcase was washed with hot water, dried, and masked with a mild steel plate except for the inner wall surface of the bore.
This crankcase is placed in the furnace of an ion nitriding treatment equipment, and a negative potential is applied to the crankcase.

A potential of 10°C was applied to the furnace wall, and ion nitriding was performed under the following conditions.

Processing conditions Processing temperature Hssob Processing time: 5 hours Voltage: 5oov Current: 40 people Gas pressure in the furnace: 2 Torr Atmosphere gas: Ha, N* Gas flow rate: 3 to 5 hooks IN And after the ion nitriding process, in the furnace Cool and remove masking.

When we examine the inner surface of the crankcase bore that has been subjected to the ion nitriding treatment, we can see that it is
A compound layer a made of Fe--N is formed at a depth of ~50 mm, followed by a nitrogen diffusion layer.

When the hardness of the inner surface of the bore is examined, as shown in FIG. 3, in the compound layer a, the diffusion layer extends to a depth of 12 mm and has a hardness of Hv 375 or more.

By the way, the inner surface of the crankcase bore is scraped off by about 10% by the piston string during use, but the hardness of the inner surface of the bore reaches a depth of 20 (HV500 or higher), so it has sufficient durability. Therefore, a cylinder liner is not required and costs can be reduced.

゛Again. The crankcase is only heated up to 550 degrees Celsius, and since the temperature is generated by applied voltage and current, no heating furnace is required and the cost is low.

Furthermore, unlike nitriding using salt or gas, it is non-polluting and does not discharge waste water. Furthermore, since the nitrogen potential is high, a nitride layer can be formed in a short time. Since the gas pressure in the furnace is about 1/100 of atmospheric pressure, gas consumption is extremely small. Further, since the process is performed in a vacuum, post-processing and post-processing are not required.

In addition, as shown in FIG. 2, since nitrogen does not cover the graphite, the graphite provides wear resistance and the graphite forms an oil residue, resulting in good lubricity.

In the above example, the furnace temperature was 550°C, but since ion nitriding is generally performed at 590 to 350°C,
In the present invention as well, it is acceptable as long as it is within the above range.

In addition, although Fe12 material was used in the above embodiment, 1
For example, C: 25-3.8%, Si: ], 5-2
．． 8chi.

MN: 1.0% or less, P: 0.15% or less, S: 0. I
Ochi or less, Ni: 0.3-0%, Cr: 0.3-0%,
Mo: 9NS1) 020~0chi, F%a+: 0.1~θ%, Pongee: θ
, 10 to 0 degrees of gray cast iron or vermicular cast iron.

[Brief explanation of drawings]

Claims (1)

[Claims] An engine crankcase characterized by ion electrification of the inner wall surface of the bore after casting.