JPH0818120B2 - Centrifugal casting - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a centrifugal casting method for producing a cast iron pipe having an expanded diameter receiving portion.

[Prior Art] Conventionally, a centrifugal casting method has been adopted to manufacture a cast iron pipe which occupies a mainstream of a water pipe. Fig. 8 shows its outline. A thin skin layer 2a made by sintering resin-coated sand is attached to the inner peripheral surface of a cylindrical mold 1a, and the inner peripheral surface of the mold retreats for the expanded mouth part. While forming the outer surface of the expanded diameter portion, the core 3a is inserted into this portion, the annular band 4a is fitted into the die inlet and locked by the pin 5a. The mold 1a prepared in this way is placed on the double support rollers 6a, and when the molten metal Ma (mostly ductile cast iron) is injected while rotating at high speed, the molten metal is pressed against the inner peripheral surface of the mold by centrifugal force. Since it solidifies while being cooled, both the skin and the core on the inner peripheral surface of the mold are destroyed by heat after the solidification, and the cast iron pipe having the receiving port is extracted from the mold.

By the way, for a long time, cast iron pipes manufactured by centrifugal casting,
In particular, ductile cast iron pipes are highly evaluated for their corrosion resistance, vibration resistance, compressive strength, etc. and are mostly used for underground water pipes, sewage, gas pipes, etc. It has become an important issue.

Pipes are usually buried underground, so in the past they were excavated from the ground to form grooves of the desired depth, cast iron pipes were inserted into them to connect them, and then they were backfilled to their original form. But,
The stagnation of traffic during this period has intensified, and we have been forced to take new measures.

The non-excavation propulsion method is a pipe laying method that has rapidly spread as a counter-measure, and a starting pit is dug down, a cast iron pipe 7a is injected horizontally into the ground from this pit, and if one is press-fitted. The insertion opening 73a (straight portion) of the next tube is fitted into the receiving opening 71a (expanded portion) and press-fitted from the rear end of the next tube, which is shown in FIG.

[Problems to be solved by the invention] The main method of laying cast iron pipes is the propulsion method, and when renewing existing pipes, the so-called pipe-in-pipe system is used to fit the new pipe into the old pipe. When the number of construction methods that move forward by pressing from occupy becomes large, new requirements differ from those of the conventional cast iron pipe of the excavation method.

That is, as is clear from FIG. 9, the succeeding pipe receives a horizontal pressing force from the rear end by a jack or the like, and the receiving portion of the cast iron pipe 7a.
The deepest part 72a of 71a must be intensively received from the tip 74a of the insertion port 73a of the rear tube, and only the metal touch except the mortar lining 76a on the inner surface serves as the pressure receiving surface.

This pressing force is strong, and transmission from the rear is weighted as the length of the conduit increases, while the contact area between the deepest part 72a and the tip 74a is small as shown in the figure, so some deviation or conduit If there is a required bending, the pressure receiving surface becomes extremely narrow and the concentrated load becomes too large, or in some cases, the pressure receiving surface may come off.

Therefore, conventionally, there was a restriction on the length between the start pit and the arrival pit, and the length of the laying work that could be done at one time had to be kept within a range where some errors could be absorbed. Of course, in order to increase the pressure receiving surface, a method of fitting a steel ring into the deepest part of the receiving port may be considered, but the work of fitting another member at the actual installation site is troublesome, and the work due to forgetting to insert it It cannot be said that there is no possibility of mistakes, and it is far from complete resolution of the problem. Among the manufacturing methods of centrifugal cast iron pipe, as a conventional technique of inserting a deformed core into a mold to form a deformed inlet shape, there is a utility model No. 64-54952. It does not give any suggestion to solve the problem as the cast iron pipe for the propulsion method. Further, there is a conventional technique disclosed in Japanese Patent Laid-Open No. 122242/1975 related to improvement of a rolling roller manufactured by double casting in a mold as shown in FIG. This is the casting of the rolling roller, after casting the primary molten metal for the outer shell into the rotating mold and solidifying a part or all of it, then the secondary molten metal for the shaft core, which is another material, is subsequently cast. Although it is a double casting that is integrated by pouring, the casting for the outer shell must be stopped at a thickness that ends outside the diameter of the neck, unless the primary molten metal overflows from the sleeve parts at both ends. The hard material will penetrate even to the part, which will ruin the intended double structure. However, in reality, there is an extremely strong demand for further increasing the wall thickness of the rolling body of the rolling roller, and it has been a great challenge for the manufacturer to meet this demand. In order to solve the problem in this conventional technique, a ring-shaped metal plate 32 having an inner diameter smaller than the neck diameter is provided in the neck portion of the rotary mold 1a.
It is claimed that by installing a in advance, the outer shell layer could be formed thick without being limited to the neck diameter. However, the point of this prior art is that the casting of the molten metal is divided into the primary casting and the secondary casting, and the function of forming a dike in the die is to prevent the molten metal from spilling during the primary casting. It is in the point imposed on the metal plate and is unrelated to the solution of the problem to be solved by the present invention, and after the molten metal is solidified, this ring is driven into the boundary between the body and the neck of the rolling roller. It induces a new task that may become a negative factor equivalent to a wedge.

An object of the present invention is to provide a centrifugal casting method for cast iron pipes which forms a pressure receiving portion particularly suitable for the propulsion method in order to solve the above problems.

[Means for Solving the Problem] In the centrifugal casting method according to the present invention, a core 3 to be mounted in the mold 1 to form a step or a curved surface of the receiving portion 71 of the cast iron pipe 7.
In forming, a cast iron pipe receiving part 71 is a steel annular body having a rear surface 30 that forms a pressure receiving surface 72 that contacts the step of the deepest part, and a front surface 33 that faces the molten metal to be cast, The diameter is equal to the maximum inner diameter M of the step, the inner diameter d is smaller than the expected inner diameter D of the straight portion of the cast iron pipe 7, and the front surface 33 is provided with a circular ring 32 having a large number of notched grooves 35. The sand layer 31 buried in the position is hardened and molded, and the core 3 is charged and fixed to the expanded diameter part of the cylindrical diameter mold 1 and the mold 1 is rotated at a high speed to melt a predetermined molten metal. The above problems were solved by casting and forming an enlarged and robust pressure-receiving surface integrally including an annular protrusion 75 in the deepest portion of the receiving portion after solidification.

As still another aspect, the annular ring 32 is replaced with a notch groove formed in the front surface 33, and a large number of notch grooves are provided on the outer peripheral surface 34 thereof.
The structure in which 36 is engraved may be used.

[Operation / Embodiment] The operation of the present invention will be described with reference to FIGS. 1 to 4 showing an embodiment.

FIG. 1 shows an embodiment of a core 3 in the present application, which is a sand layer supported by an annular band 4 and formed of sand having good collapsibility
31 and a steel ring 32 adhered to both ends thereof.
The outer diameter of the annular ring 32 is equal to the maximum inner diameter M of the pressure receiving surface 72 at the deepest receiving end of the centrifugal cast iron pipe 7, and the inner diameter d is set to be larger than the inner diameter of the straight pipe portion of the cast iron pipe to be planned. There is.

FIG. 2 shows that the core 3 is inserted into the receiving portion of the cylindrical mold 1.
The state in which the band 4 is locked by the pin 5 and fixed at a predetermined position and then the metal melt M is injected by a known means while rotating the mold at a high speed is seen through. The molten metal M spirally ran through the skin layer 2 of the resin coated sand while reaching the other end while being pressed against the inner wall by receiving centrifugal force from one end of the mold, and was formed by the core and the enlarged diameter part of the mold. It reaches the annular hollow portion, fills this hollow portion as the casting progresses, contacts the exposed front surface 33 and outer peripheral surface 34 of the ring of the core, and wraps around.
Since the annulus rotates violently with the mold, the high heat is applied while it relatively moves with the molten metal to be pressed, the exposed portions of the front and side surfaces begin to melt, and when the molten metal solidifies, the boundary The molten metal reaches an integrated state to the extent that the surfaces melt and cannot be distinguished. Further, since a large number of notched grooves 35 or 36 are formed on the front surface 33 of the ring facing the inflow direction of the molten metal or the outer peripheral surface 34 thereof, the contact area with the molten metal is doubled. The welding action at the surface is further enhanced, and the molecular exchange that promotes integration at the interface progresses extremely actively.

This action is inevitably caused by the volume of the ring and the sensible heat of the molten metal. In the end, after solidification, the sand parts of the skin layer 2 and the core 3 receive the heat in the mold that has stopped rotating. Ridge 75 that collapsed due to the maximum inner diameter M and the inner diameter D of the cast iron pipe protruding into the pipe.
A centrifugal cast iron pipe having a pressure receiving surface 72 having a solid stepped portion which is enlarged as a deepest portion appears. This state is shown in FIG. A large number of notched grooves cut into the front surface 33 and the outer peripheral surface 34 of the ring are solidified after the solidification, and the surface is integrally welded to the base material, and also has a locking shape that meshes with or interlocks with the base material. Therefore, when the external force is applied horizontally to the rear surface 30 (pressure receiving surface) and immediately before, the function of receiving the whole by the firmly engaged engaging surface and integrally backing up is strengthened.

FIG. 4 shows a state where the centrifugal cast iron pipe manufactured by this embodiment is applied to the propulsion method, and the pressure receiving surface 72 of the receiving port of the cast iron pipe 7 has a step area much wider than the conventional one. As a result, it is possible to ensure smooth progress of the construction by sufficiently absorbing some deviations, fluctuations and bends during construction.

FIG. 5 shows an embodiment, in which the sand molding portion of the core 3 is stepped to embed the ring from the three side surfaces, the steel ring is positioned more accurately, and the protrusion after casting is improved. It has a unique effect of improving the dimensional accuracy of the strip.

6A and 6B and FIG. 7 show different embodiments of the notch groove formed in the ring 32. In FIGS. 6A and 6B, on the front surface 33 of the ring, and in FIG. A large number of notched grooves 35, 36 are respectively provided in the surface 34 to make a step, and the contact surface with the molten metal is increased, so that the welding is performed more firmly and integrally.

[Advantages of the Invention] Since the invention of the present application has the configuration as described above, it is possible to well absorb some errors in the pressing direction during the propulsion method, bending, etc., and perform stable press-fitting. Therefore, even if the distance between the start pit and the arrival pit is long, it is possible to sufficiently deal with the total error that occurs, which has the effect of significantly reducing the time and cost of the laying work.

The integrally-provided ridge is much stronger than the ring interposed as a separate member, and has a material force that clearly exceeds the effect of increasing the area evenly. Also,
In the prior art shown in FIG. 10, there is a concern that an uncertain weak point may be induced in the portion where the shear stress is concentrated in the product in use. The symmetrical difference that the positive factor is large, on the contrary, is expected to have the advantage of increasing the cooling rate of the mouth and being effective for the miniaturization of the tissue, and rather, the effect linked to the strengthening of the pressure receiving surface is double derived. Appears.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a core of an embodiment of the present invention, FIGS. 2 and 3 are vertical cross-sectional views showing the action at each stage of manufacturing, and FIG. 4 is a casting in which the method of the present invention is carried out. FIG. 5 is a vertical sectional view showing another embodiment of the core, and FIGS. 6A and 6B are plan views and front views showing another embodiment of the ring. FIG. 7 is a plan view showing still another embodiment of the annular ring, FIG. 8 is a vertical cross-sectional view showing a conventional centrifugal casting method, and FIG. 9 is a vertical cross-sectional view explaining the usage of a conventional cast iron pipe. FIG. 10 is a vertical sectional view showing another conventional technique (a).
And the front view of the product (b). 1 ... Mold, 3 ... Core, 7 ... Cast iron pipe, 30 ... Rear surface 31 ... Sand layer, 32 ... Ring, 33 ... Front surface 34 ... Outer peripheral surface, 35, 36 ... Notch Groove 71 …… Receptacle, 72 …… Pressure receiving surface, 73 …… Insertion 74 …… Tip, 75 …… Ridge, d …… Core outer diameter D …… Cast iron pipe straight inner diameter

Claims (2)

[Claims] 1. In a centrifugal casting method for producing a cast iron pipe having an expanded receiving end portion at one end, it is mounted in a mold 1 for forming a step or a curved surface of the receiving end portion 71 of the cast iron pipe 7. When molding the core 3, the pressure receiving surface is the step at the deepest part of the cast iron pipe receiving portion 71.
The rear side 30 forming 72 and the front side facing the molten metal to be cast
33 is a steel annular body including 33, the outer diameter of which is equal to the maximum inner diameter M of the step, the inner diameter d is smaller than the inner diameter D of the straight portion of the cast iron pipe 7 to be planned, and a large number of them are provided on the front surface 33. An annular ring 32 having a notch groove 35 formed therein is formed by hardening a sand layer 31 embedded at a predetermined position, and the core 3 is inserted into a diameter-expanded portion of a cylindrical-diameter die 1. After fixing, casting a predetermined molten metal while rotating the die 1 at a high speed to form an enlarged and robust pressure receiving surface that integrally includes the annular projection 75 at the deepest portion of the receiving portion after solidification. Characteristic centrifugal force casting method. 2. The ring ring 32 according to claim 1, wherein the annular ring 32 has a plurality of cutout grooves 36 formed on the outer peripheral surface 34 thereof instead of the cutout grooves formed in the front surface 33. Centrifugal casting.