JPS5856662B2 - Camshaft casting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for casting camshafts for automobiles and other various internal combustion engines.

Traditionally, camshafts for various internal combustion engines have been cast using green sand molds, shell molds, or molds that combine green sand and shell molds. There are many disadvantages such as gas blowing, dimensional defects, etc., and there is a limit to the size of the cam that can be cast, and especially when cold metal is used, various defects are likely to occur. With shell molds, defects such as sand engraving and gas blowing are reduced compared to green sand molds, but dimensional defects due to deformation of the mold are likely to occur, so a large finishing allowance of 3 to 4 mm is required. There is.

In addition, methods for hardening the tip of the cam, which is the protruding part of the cam provided on the camshaft, include placing a cold metal on the mold surface corresponding to the tip of the cam, locally hardening the cam tip after casting, or hardening the tip of the cam after casting. There are methods such as rapidly heating the tip of the rear cam, remelting it, and then rapidly cooling it. However, with methods other than cooling, casting is relatively easy regardless of the type of mold, but heat treatment such as quenching is required after casting. This method requires a lot of finishing work as it requires re-processing after surface hardening, and the wear resistance of the cam due to such heat treatment is inferior to that using a chilled metal. The dimensional accuracy of camshafts using a cold metal is generally considered to be the most common method, but the dimensional accuracy of the camshaft using a cold metal is mainly due to differences in thermal conductivity depending on the location within the mold, and mold wall movement during solidification of the molten metal. Camshafts are affected by warping due to factors such as differences in location and shrinkage characteristics of molten metal.Therefore, traditionally, emphasis has been placed on countermeasures for warpage when casting camshafts.For example, when casting camshafts, During molding, the upper and lower molds are sufficiently filled, and after the molds are dismantled, the camshaft is left standing on a flattened sand bed for a specified period of time. The disadvantage is that sufficient results are not obtained for the removal of

The present invention was completed with the aim of providing a method for casting camshafts that does not have the above-mentioned drawbacks. That is, the bulk density of a high-pressure molding mold made of green sand is approximately 1.459/c♂, whereas the bulk density of a high-pressure molding mold made of green sand is approximately 1.459/c♂, whereas the bulk density of a high-pressure molding mold made of green sand is approximately 1.459/c♂, whereas a vacuum molding mold is Focusing on the fact that the mold is quite large at approximately 1.679 yl, we created a camshaft with fewer defects such as sand traps and less warpage by using a vacuum mold with a cooling metal placed at the position corresponding to the tip of the cam. The illustrated embodiment will be described in detail below.

As shown in FIG. 1, 1 is a model for a vacuum molding mold, which is provided with a vacuum chamber 3 that communicates with a vacuum source (not shown) via a connecting pipe 2, and has a product model 4 for a required camshaft attached to its upper surface. The product model 4 includes a shaft horizontal part 5 corresponding to the shaft of the product camshaft, a bearing model part 6 corresponding to the bearing, a cam model part 7 corresponding to the cam, and an axis of the shaft horizontal part 5 from one end. It consists of a ventilation hole model part 8 which is provided protruding in the direction, and a sprue model 9 is placed parallel to the product model 4 at a slight interval on the model plate 1 on the side of the product model 4. The sprue model 9 is connected to the shaft horizontal part 5 or the bearing model part 6 of the product model 4 by a plurality of weir models 9'. When the product model 4 and the sprue model 9 placed parallel to the product model 4 face upward, the longitudinal direction of the product model 4 and the sprue model 9 placed parallel to it are the vertical direction, and each weir model 9' is aligned with the axis of the product model 4. It has an inclined shape with the side connected to the horizontal part 5 or the bearing model part 6 slightly above the side connected to the sprue model 9, and is arranged approximately parallel to the model plate 1 at an appropriate interval. , and the position where the lowest weir model 9' is connected to the product model 4 is the shaft horizontal mold part 5 or the bearing model part 6 slightly above the lower end of the product model 4, and the model plate 1 and the product model 4. The surfaces of the sprue model 9 and the like are communicated with the vacuum chamber 3 through an appropriate number of suction pores 10, so that a suction action is exerted on each surface by the vacuum action applied to the vacuum chamber 3. The model plate 1 is placed horizontally on a vibration table (not shown), and as shown in FIG. Depending on the source, connecting pipe 2, decompression chamber 3,
A suction action is exerted on the surfaces of the model plate 1, product model 4, etc. through the suction pores 10, and then a flexible shielding member 12 such as a heat-softened synthetic resin film is inserted into the cooling plate 11. A mold coating material is applied to each surface of the shielding member 12 as necessary. Next, a molding flask 13 for vacuum molding is placed on the model plate 1, and the molding material is applied to the shielding member 12. A filler 14 such as dry sand is put into the formed space, the bulk density of the filler 14 is increased by vibration of a vibration table, and the filler 14 on the upper surface of the flask 13 is scraped off to level it. After covering the upper surface of the filler 14 with a flexible member 15, a depressurizing effect is applied to a depressurizing chamber 16 provided on the outer periphery of the flask 13 via a connecting pipe 17 communicating with a vacuum source (not shown). The shielding member 12, the flask 13, and the flexible member 15 are connected to the decompression chamber 16 by a perforated pipe 18 disposed inside the flask 13 and whose surface is covered with a wire mesh or the like.
The air in the filler 14 in the space surrounded by the filler 14 is sucked into a reduced pressure state, and the filler 14 is solidified by external pressure applied via the flexible member 15 to perform vacuum molding.

Next, by releasing the decompression effect in the decompression chamber 3 of the model plate 1 and introducing outside air, the shielding member 12 is released from the close contact with the model plate 1 containing the product model 4, etc., and the model plate 1 is released from the mold. For example, as shown in FIG. 3, the mold surface 19 covered with the shielding member 12 has a shaft recess 4 corresponding to the shaft of the camshaft, a bearing recess 21 corresponding to the bearing. A product mold part 24 consisting of a cam recess 22 corresponding to a cam and a vent recess 23 for communication with the outside, a sprue 25 and a weir 26 are molded, and a cooling metal is installed at a position corresponding to the cam tip side of the cam recess 22. The vacuum molding mold 27 holding the mold 11 is molded and held within the flask 13.

When the vacuum molding mold 27 is of a vertical type with the vent recess 23 facing upward as shown in FIG. Therefore, the product mold part 24 and the sprue 25 of the vacuum forming mold 27 are parallel to each other in the longitudinal direction, and each base 26 is slightly inclined upward to connect the sprue 25 and the product mold part 2.
The lowermost weir 26 is positioned so as to communicate with the shaft recess 20 or bearing recess 21 located slightly above the lower end of the product mold part 24. .

This vacuum molding mold 27 is molded with the other vacuum molding mold that has been vacuum molded by the same operation and holds a cooling metal at a position corresponding to the cam tip side of the cam recess, to form a vertical split type vertical mold. If you pour the metal from sprue 25 as a completed mold,
The molten metal is first poured into each base 2 of the product mold section 24 from the lowest weir 26.
The molten metal flows into the lowermost area divided by 6 by a dropping method, and after the lowermost area is filled with molten metal, the molten metal flows from the weir 26 located at the next upper side to the uppermost area of the lowermost area. The molten metal flows into the area in the same way, and thereafter the molten metal flows in the same way from the succeeding weir 3 located above, so that the product mold part 24 has the lower area of the small area divided by each base 26. The molten metal is sequentially poured in by the dropping method and is filled from below in a kind of push-up method, and the distance that the molten metal travels by dropping in the product mold section 24 is shortened. The flying distance of the generated gas and unburned matter of the shielding member 12 is also shortened, and the phenomenon of the tip of the hot metal splattering and forming hot water balls due to the good running of the molten metal, which is a characteristic of the vacuum molding mold, is eliminated, and the phenomenon of hot water balls caused by hot water balls is eliminated. without causing defects, and
The above-mentioned gas is actively sucked and removed toward the filling material 14, which is being subjected to a vacuum suction action, and the unburned matter in the shielding member 12 is also penetrated into the filling material 14 in a molten state, thereby preventing the cooling, which had many defects in the past. Even on the cam tip side where the pad 11 is located, no gas defects or sand particles occur, and by using a vacuum molding mold with high bulk density, a sound camshaft with less warpage is cast as a whole.

After solidifying the molten metal by pouring the metal, the depressurization acting on the filler 14 is released and the mold is released, and the sprue 25 is opened.
By removing the raised portions formed by the molten metal entering the bases 26 and the vent recesses 23, a cast 31 of the camshaft consisting of the shafts 28, 29, and cams 30 shown in FIG. 5 is obtained. .

Furthermore, by tilting the matched completed mold when pouring the metal, it is possible to further promote the escape effect of the gas generated by pouring the metal.

Note that the sprue 25 and weir 26 of the vacuum molding mold 27
In the result of pouring the finished mold into a horizontally split mold that is stacked vertically, a large amount of sand is generated, which is inappropriate for practical use. In the so-called simple push-up method in which molten metal flows in, does the shielding member 12 melt? Due to vaporization, gas defects and sand deposits occur on the lower cam tip side, and the ventilation recess 2
Even if various conditions such as the size of mold 3, the type and thickness of coating material and shielding member 120, the polishing condition of chiller 11, and pouring time are changed, the above-mentioned defects cannot be prevented. In the so-called simple dropping method in which the molten metal is poured from the top of the part 24, the molten metal runs smoothly, causing the tip to scatter and form molten beads, which cause a type of gas defect when the molten metal enters the molten metal. However, even if measures such as pouring the molten metal gently to prevent molten metal from forming or completing the pouring in a very short period of time, for example, about 7 seconds, the central part of the product mold 24 No gas defects were observed on the cam tip side that was hidden below the sides, but defects due to molten metal occurred on the cam tip side located at the top of the product mold section 24 in the late pouring stage, and therefore the pressure was reduced. When casting a camshaft using a mold, it is not possible to prevent the above-mentioned defects that occur on the cam tip side by a simple push-up method or a drop-in method.

As is clear from the above description, according to the present invention,
It is possible to cast a sound camshaft with little warpage and without any defects on the cam tip side that is hardened by cold metal, and therefore the finishing allowance is extremely small, making processing and other operations simple and easy. It has many advantages and is of great value to the industry.

Example: A camshaft with a length of about 1 m was cast by pouring molten cast iron equivalent to F'C30 and having a carbon equivalent of about 3.9 into a vacuum mold as shown in Fig. 4 at a temperature range of 1300 to 1400°C. As a result, there were no gas defects or sand particles on the cam tip side where the cold metal was located, and the warpage was very small, with the finishing allowance at the cam tip being within 0.5 to 0.9 mm. I was able to do this.

[Brief explanation of drawings]

The drawings show an embodiment of the method of the present invention, and Fig. 1 is a partially cutaway side view of a model plate for vacuum molding of a camshaft, and Fig. 2 is a side view of a model plate with a chiller placed on it and a shielding member attached. FIG. 3 is a vertical side view of the vacuum molding mold in a released state, and FIG. 4 is a front view of the vacuum molding mold shown as a vertical mold. FIG. 5 is a front view of a camshaft cast by the method of the present invention. 11... Cold metal, 12... Shielding member,
19...Mold surface, 22...Cam recess, 2
, 4... Product mold section, 25... Sprue,
26... Weir, 27... Vacuum molding mold.

Claims (1)

[Claims] 1. A vacuum molding mold in which a product mold part and a sprue are vertically formed in parallel on a mold surface covered with a shielding member is molded to form a vertical mold, and a shaft rotation part or a bearing recess of the product mold part of the vacuum molding mold is formed. The product mold is connected to the sprue by a plurality of weirs that are slightly inclined upward, and the lowest weir is connected to the shaft part or bearing recess slightly above the lower end of the product mold part. A method for casting a camshaft, characterized in that a chilled metal is held at a position corresponding to the cam tip side of a cam recess in the camshaft and poured.