JPH0413459A - Centrifugal casting method - Google Patents

Abstract

PURPOSE:To well absorb some errors, flexures, etc., in a pressing direction and to assure stable press-fitting by inserting and fixing a core into the diametrally expanding part in a cylindrical mold and casting a prescribed molten metal while rotating the mold at a high speed, then integrally correcting the annular projection on the inner peripheral surface after solidification. CONSTITUTION:A core 3 is inserted into a pouring cup of the cylindrical mold 1 and after a band 4 is fixed to a prescribed position by means of pins 5, the molten metal M is poured into the mold while the mold is rotated at a high speed. While the molten metal M is pressed to the inside wall, the molten metal runs spirally through the top of a skin layer 2 of resin coated sand and arrives at the other end from which the molten metal arrives at an annular hollow part and fills this hollow part on progression of the casting, thus casting-in the exposed toric surface 33 and outer peripheral surface 34 of the core by coming into contact with these surfaces. The toric is applied with the high heat of the molten metal pressed thereto and the exposed parts of the front surface and side faces begin to melt. The boundaries melt to each other and attain the integrally fused state to the unidentifiable extent at the time the molten metal solidifies. The skin layer 2 and the sand part of the core 3 collapse by receiving the heat in the mold which stops rotating after the solidification. The cast pipe having the prescribed outside diameter and the projecting line 75 provided projectingly from the inside diameter D to the inside remains.

Description

DETAILED DESCRIPTION OF THE INVENTION 'Industrial Application Field' The present invention relates to a centrifugal casting method for producing cast iron 'Q' having an expanded diameter of 5 [-1 parts.

[Prior Art] Centrifugal casting has traditionally been used to manufacture cast iron pipes, which are the mainstay of water pipes.

FIG. 8 shows an outline of the method, in which a thin skin layer 2a made of sintered resin-coated sand is attached to the inner peripheral surface of a cylindrical mold 1a,
For the enlarged diameter socket part, the inner peripheral surface of the mold is retracted to form the outer surface of the enlarged diameter part, and the core 3a is inserted into this part, and the annular band 4a is fitted into the mold entrance and the pin is inserted. Lock at 5a. The mold 1a prepared in this way is placed on two sets of support rollers 6a, and when a metal bath mma (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. After solidification, both the skin layer on the inner circumferential surface of the mold and the core collapse due to the heat, and the cast iron pipe with the socket is removed from the mold.

By the way, since ancient times, cast iron pipes have been manufactured using the centrifugal casting method.
In particular, ductile cast iron pipes are highly valued for their corrosion resistance, portability, and compressive strength, and are mostly used for underground water, sewage, and gas pipes, but recently it has become increasingly difficult to lay pipes. This has become an important issue.

Pipelines are usually buried underground under roads, so in the past, they were excavated from the ground to create a trench of the desired depth, inserting cast iron pipes into the trench, connecting them together, and then backfilling the trench to its original appearance. However, traffic stagnation during this period has become increasingly severe, and new measures have been required.

The non-excavation propulsion method is a pipe installation method that has rapidly become popular as an alternative to this.A starting shaft is dug, and cast iron pipes 7a are horizontally pressed into the ground through this shaft. , insert the next pipe into the receiving lower 1a (expanded diameter part) and lower 3a.
(straight part) is fitted and press-fitted from the rear end of the next pipe, and the state is shown in Fig. 9.

[Problem to be solved by the invention] The main method is the installation method of cast iron pipes or the propulsion method, and also the so-called pipe-in-pipe method, in which a new pipe is inserted into the old pipe when upgrading an existing pipe. When the method of moving forward by pushing from the rear became popular, new requirements emerged that differed from the conventional excavation method for cast iron pipes.

That is, as is clear from FIG. 9, the horizontal pressing force from the jacking etc. from the rear end of the subsequent pipe is concentrated at the deepest part 72a of the socket 71a of the cast iron pipe 7a, and is applied to the tip 74a of the insertion lower 3a of the rear pipe. Only the metal touch, excluding the mortar lining 76a on the inner surface, becomes the pressure receiving surface.

This pressing force is strong, and the longer the pipe line is, the more weight is transmitted from the rear. However, as shown in the figure, the contact area between the deepest part 72a and the tip 74a is small, so there may be some misalignment or If there is any bending required by the pressure receiving surface, the pressure receiving surface may become extremely narrow and the concentrated load may become too large, or there may even be concerns that the pressure receiving surface may come off.

Therefore, in the past, there was a restriction on the length between the starting shaft and the destination shaft, and it was necessary to limit the length of the laying work that could be done at one time within a range that could absorb some errors.

Of course, it is possible to consider a method of fitting a steel ring into the deepest part of the socket in order to increase the pressure receiving surface, but it must be said that this is far from a complete solution to the problem.

In order to solve the problems mentioned above, the present invention aims to provide a centrifugal force casting method for cast iron pipes that forms a pressure receiving part particularly suitable for propulsion construction methods.

[Means for Solving the Problems] The centrifugal force casting method according to the present invention provides that when molding a core with the inner circumferential surface of the socket portion reversed, the outer diameter is set at a desired position of the core. A steel ring with an inner diameter smaller than that of the planned straight section of the cast iron pipe is embedded and formed, and the core is inserted into the expanded diameter section of the cylindrical mold and fixed, and the mold is moved at high speed. The above problem was solved by casting a predetermined molten metal while rotating, and integrally modifying the annular protrusion on the inner circumferential surface after solidification.

[Operation/Example] The operation of the present invention will be explained with reference to FIGS. 1 to 4 showing examples.

FIG. 1 shows an embodiment of the core 3 in the present application, in which the sand @ 3 is supported by an annular band 4 and molded with highly disintegrable sand.
1 and a steel ring 32 bonded to both ends thereof. The outer diameter of the ring 32 is equal to the sand layer 31, and the inner diameter d is set smaller than the inner diameter of the planned cast iron pipe 7.

FIG. 2 Insert the core 3 into the socket of the cylindrical mold 1, lock the hand 4 with the pin 5 and fix it in a predetermined position, and then rotate the mold at high speed to pour the molten metal M. We are keeping a close eye on the state of injection using known means. The molten metal M receives centrifugal force from one end of the mold and is pressed against the inner wall while running in a spiral over the resin coated sand skin @2 until it reaches the other end, expanding the diameter of the core and mold. It reaches the annular hollow part formed as a part, fills this hollow part as the casting progresses, and comes into contact with the exposed annular surface 33 and outer circumferential surface 34 of the core, thereby enclosing it. Since the ring rotates violently together with the mold, it changes relative to the molten metal being pressed, and the exposed parts of the front and sides begin to melt due to the high heat that is applied to it, and when the molten metal solidifies, The interface or melting reaches a state of integral melting to the extent that it cannot be identified.

This effect naturally arises from the volume of the ring and the sensible heat held by the molten metal. After solidification, the sand in the skin layer 2 and core 3 will receive heat in the mold that has stopped rotating. The tube collapses, leaving behind a cast tube with a predetermined outer diameter and a protrusion 75 protruding inward from the inner diameter.

This state is shown in FIG.

Figure 4 shows the state in which the centrifugal cast iron pipe manufactured according to this embodiment is applied to the propulsion method. , to ensure smooth progress of construction by fully absorbing slight deviations, fluctuations, and bends during construction.

Fig. 5 shows an example in which steps are added to the sand molded part of the core 3 to embed the ring from three sides, so that the positioning of the steel ring can be more accurately fixed, and the projection after casting can be made more precisely. This has the unique effect of improving the dimensional accuracy of the strips.

In addition, FIG. 6A 2nd hole and FIG. 7 show different embodiments of the ring 32, and in FIG. Groove 35 and 36 respectively near z [! ], and a step is cut to increase the contact surface with the molten metal, so that the welding is more firmly secured.

[Effects of the Invention] Since the present invention has the above-described configuration, it can effectively absorb some errors in the suppression direction, bending, etc. during the propulsion method, and can perform stable press-fitting. Therefore, even if the distance between the starting shaft and the arriving shaft is long, the total amount of errors that occur can be sufficiently compensated for, which has the effect of significantly reducing the time and cost of the installation work.

An integrally provided circumferential protrusion is much stronger than a ring interposed as a separate member, and even if the area increase effect is the same, it has clearly superior material strength.

[Brief explanation of the drawing]

Fig. 1 is a vertical sectional view of a core in an embodiment of the present invention, Figs. 2 and 3 are vertical sectional views showing the effects at each stage of manufacturing, and Fig. 4 is a casting molded using the method of the present invention. 5 is a vertical sectional view showing another embodiment of the core, FIG. 6 A is a plan view and a front view showing another embodiment of the ring, FIG. 7 is a plan view showing yet another circular ring embodiment, FIG. 8 is a vertical sectional view showing a conventional centrifugal casting method, and FIG. 9 is a vertical sectional view illustrating how a conventional cast iron pipe is used. 1... Mold, 3... Core, 7...
...Cast iron pipe 31...Sand layer, 32...Circle, 33...Front surface 34...Outer peripheral surface, 3
5.36...Notch groove 71...Socket, 72...Deepest part, 73...Lower insertion 4
...Tip, 75-...Protrusion, d...
... Core outer diameter D ... Cast iron pipe straight inner diameter

Claims (2)

[Claims] (1) In the centrifugal casting method for manufacturing cast iron pipes that have a socket with an enlarged diameter at one end, when molding a core with the inner peripheral surface of the socket reversed, the outside diameter is placed at the desired position of the core. is equal to the outer diameter of the core and whose inner diameter is smaller than the inner diameter of the planned straight section of the cast iron pipe. , a centrifugal force casting method characterized by casting a predetermined molten metal while rotating a mold at high speed, and after solidifying, annular protrusions are integrally provided on the inner peripheral surface. (2) The centrifugal casting method according to claim (1), characterized in that a large number of notched grooves are provided on the outer peripheral surface or exposed front surface of the ring.