JPS5949168B2 - Method for manufacturing non-circular tubes and formwork used therein - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a method of manufacturing a pipe by tightening a material using centrifugal force, such as a Huyum pipe (centrifugal force reinforced concrete pipe), and a formwork used therein. Specifically, the present invention relates to a method for casting a non-circular tube having a circular cross-sectional shape and a non-circular portion by centrifugal molding, and a formwork thereof.

A centrifugal reinforced concrete pipe, also known as a Huum pipe, is made by pouring fresh concrete into a cylindrical formwork in which reinforcing bars have been assembled and arranged in advance, and then rotating this formwork a with a rotating wheel as shown in Figure 1. The centrifugal force generated by the rotation compacts and shapes the concrete c.

Therefore, all of them have a hollow circular cross section and can be formed into pipes with high material density, and are used in a wide range of areas such as water supply and sewerage, agricultural waterways, and industrial waterways.

However, the biggest problem with such a pipe with a circular cross section is that the flow velocity decreases significantly as the flow rate decreases.

That is, in a pipe with a circular cross section, when the flow rate decreases, the contact area between the water and the pipe wall becomes larger than the cross-sectional area of the flowing water, so the flow velocity rapidly decreases due to the influence of frictional resistance on the pipe wall.

This point becomes particularly serious as the pipe diameter increases; in a wide-diameter pipe, when the flow rate decreases, the water depth becomes extremely shallow, and the contact area increases significantly compared to the cross-sectional area of the flowing water.

Therefore, in order to overcome the drawbacks of tubes with circular cross sections, tubes with special cross sections have been devised.

An example is a tube with an oval cross section, which has a special shape at the bottom that is different from a circular cross section so that the contact area does not increase relative to the flowing water cross section even when the flow rate decreases. .

However, a problem with such non-circular pipes is the manufacturing method (casting method).

That is, if a non-circular pipe is cast using the centrifugal forming method described above, the material in a plastic state will be shifted to a position far from the center of rotation, making it impossible to form a pipe of the desired shape.

For this reason, non-circular pipes have been compacted by methods other than those described above, such as vibration compaction.

However, this method cannot apply a steady stress in the radial direction of the pipe during pouring, so it is not possible to obtain sufficient density not only in the radial direction but also in the hoop direction. It has the disadvantage of inferior properties.

The present invention was made as a result of studies in view of the above conventional problems, and its primary purpose is to provide a method for easily centrifugally forming even non-circular pipes, and furthermore, to provide a formwork for use in this method. This is the second purpose.

That is, in the method according to the present invention, a gap corresponding to the wall thickness of the tube is formed between the outer frame and the inner frame in the portion corresponding to the non-circular portion of the tube, and a gap corresponding to the wall thickness of the tube is formed in the portion corresponding to the circular portion of the tube. forming a circular hollow material input port corresponding to the input port, and rotating the outer frame and the inner frame integrally about the central axis of the circular portion while inputting the material in a neutral state from the input port;
The first object is achieved by forming a layer of the above-mentioned material inside the outer frame, curing and hardening it, and then casting a non-circular pipe.

Further, in the formwork according to the present invention, the inner surface shape of the outer frame corresponds to the outer surface shape of the pipe to be poured, and the outer surface shape of the inner frame is made to correspond to the inner surface shape of the non-circular portion of the pipe, and a circular surface having a diameter equal to the inner diameter of the circular portion, an inner frame being disposed inside the outer frame, and a non-circular surface of the inner frame facing the non-circular portion of the outer frame to form a gap therebetween; The circular surface of the inner frame faces the circular part of the outer frame, a material input port is formed between them, and the outer frame and inner frame are fixed to each other in this state.
This aims to achieve the second objective mentioned above.

Hereinafter, this invention will be explained in detail based on the drawings.

1 to 3 show an example in which the present invention is applied to the manufacture of a concrete pipe having a so-called oval cross section.

As shown in these drawings, the formwork according to the present invention includes an outer frame 10,
Inner frame 20 and means for integrally fixing them, e.g.
It consists of 30 lunges.

The outer frame 10 has an internal cross-sectional shape corresponding to the external shape of the pipe A to be cast (in the case shown, a so-called oval cross section), and this internal cross-sectional shape corresponds to the external shape of the pipe A to be cast, as shown in FIG. In the case of a so-called A-shaped pipe, which has a uniform cross-sectional shape in the axial direction, the cross-sectional shape is uniform in the axial direction, and the cross-sectional shape changes in the axial direction, as shown in Figure 4. In the case of a so-called B-shaped tube, the cross-sectional shape changes continuously in the axial direction.

In the illustrated outer frame 10, a fixed radius R+T from a fixed central axis O is set at the joint 18.14 (where T is the wall thickness of the pipe to be cast).

same as below.

) and a non-circular portion 12 having an inner surface that does not have a constant radius of curvature. It is from the opposite side.

On the other hand, the inner frame 20 has a cross-sectional outer shape consisting of a non-circular portion 22 corresponding to the inner surface shape of the non-circular portion C of the tube, and a circular surface 21 having a radius R equal to the inner diameter of the circular portion B of the inner tube A. The illustrated non-circular surface 22 is formed from a plurality of curved surfaces with various radii of curvature.

In the curved pipe shown in FIG. 4, a step is provided on the inner periphery of the end surface of the pipe A, but in this case, the inner frame 20 has a uniform cross-sectional shape in the axial direction from the viewpoint of drawing operations, etc., which will be described later. , a collar 31 as a core is extended from the flange 30,
It is appropriate to use this as an inner mold to form the step.

To assemble this formwork, first, as shown in Figure 2, the outer frame 1
The circular part 11 and the non-circular part 12 of 0 are joined at the joint 13.14 and fixed with bolts, nuts, etc., thereby assembling a cylindrical body having an inner surface corresponding to the outer shape of the pipe A to be cast. .

The number of joints, that is, the parts where the outer frame 10 is divided, is usually two, but if the shape of the pipe is complex, this may be three or more. Sometimes things are in one place.

Furthermore, this assembled outer frame 10 is fixed between two or more flanges 30.

Next, insert the inner frame 20 into this outer frame 10 and connect the joint 28.
．． This inner frame 20 is fixed to the flange 30 via 33.

In this way, the outer frame 10 and the inner frame 20 are firmly fixed. At this time, the non-circular surface 22 of the inner frame 20 is made to face the non-circular part 12 of the outer frame 10, and the wall thickness of the pipe A is A gap corresponding to T is formed, and the circular part 21 of the inner frame 20 is made to face the circular part 11 of the outer frame 10, and a circular hollow material input port 15 corresponding to the inner diameter of the circular part B of the pipe A is provided between the gaps. Form.

Note that in many cases, pre-assembled reinforcing bars are inserted inside the outer frame 10.

The formwork assembled in this way is rotated around the central axis C of the circular part B of the pipe A by feeding neutral materials such as fresh concrete, ductile, asbestos, and plastics through the material input port 3. do.

Then, the material first gathers at the farthest position from the central axis C, which is the center of rotation (lowest part in Figure 2), and then gradually fills the gap between the outer frame 10 and the inner frame 20, where a certain amount of material When this is filled, the material also wraps around the circular part 11 side of the outer frame 10, and finally a uniform layer of material corresponding to the shape of the tube A is formed.

In this state, the formwork is initially rotated at a low speed, and then the speed is increased to medium and high speeds, so that the material is gradually compacted and excess water contained in the material is removed.

The rotation is performed using the flange 3 as shown in the figure as a means of fixing the formwork.
9 is used, a rotary wheel S is applied to the flange 30 to rotate it, but in addition to the method using such a friction wheel, a method of directly applying rotation to the formwork may also be adopted.

In addition, in this invention, since the formwork and tube A are not circular, an imbalance occurs with respect to the center axis C, which is the center of rotation.
In this regard, dynamic balance is adjusted by attaching balance weights 16 and 16 at appropriate positions.

Once the material is sufficiently compacted by such rotation, it is cured and hardened, but before this, the inner frame 20 is pulled out in its longitudinal direction as shown by the dotted chain line in FIGS. 3 and 4. and disassemble it.

However, this is a disassembly method when the inner frame 20 is formed as one piece, and if the inner frame 20 is divided along diagonal lines in FIG. 2, it can also be disassembled after curing.

Curing is usually accelerated at a temperature of around 60'C, and after curing, the outer frame 10 is disassembled to obtain the non-circular tube A.

When the egg-shaped concrete pipe manufactured by the method according to the present invention was compared with the same type of pipe manufactured by the conventional vibration casting method, both the density and strength of the material were extremely good.

In particular, the upper layer in actual use is said to be subject to high internal pressure.
The non-circular part C at the bottom of the figure has excellent strength, and in that sense, its mechanical properties are comparable to conventional circular tubes formed by centrifugal molding.
Or maybe even more.

As described above, according to the method of the present invention, a tube with excellent mechanical properties can be manufactured by centrifugal molding of a non-circular tube, which has been considered difficult in the past.

Further, according to the formwork according to the present invention, pipes of complicated shapes can be centrifugally formed with simple operations, and there is an advantage that the number of operations does not increase compared to the conventional casting method using vibration.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing a conventional method for centrifugally forming circular tubes, FIG. 2 is a longitudinal sectional front view showing an embodiment of a mold according to the present invention, and FIGS. 3 and 4 are illustrations of tubes of different shapes. FIG. 10... Outer frame, 11... Circular part of outer frame, 12...
Non-circular part of outer frame, 15... Input port, 20... Inner frame,
21...Circular part of the inner frame, 22...Non-circular part of the inner frame,
30...Flange as a fixing means, A...Pipe, B
...Circular part of the pipe, C...Non-circular part of the pipe

Claims (1)

[Scope of Claims] 1. A method for manufacturing a non-circular tube having circular and non-circular sections in the cross-sectional shape of the inner and outer surfaces, respectively, in which a tube is disposed between the outer frame and the inner frame in the portion corresponding to the non-circular section of the tube. A gap corresponding to the wall thickness of the tube is formed, and a circular hollow material input port corresponding to the inner diameter of the circular portion of the tube is formed in a portion corresponding to the circular portion of the tube, and a material in a plastic state is inputted from this input port. The outer frame and the inner frame are integrally rotated about the central axis of the circular portion, a layer of the material is formed inside the outer frame, and this is cured and hardened to cast a non-circular pipe. A method for manufacturing a non-circular tube, characterized in that: 2. The manufacturing method according to claim 1, wherein the inner frame is pulled out from inside the outer frame in the longitudinal direction before the material is cured. 3 In a formwork consisting of an outer frame, an inner frame, and fixing means for integrally fixing these, the inner surface shape of the outer frame is made to correspond to the outer surface shape of the pipe to be cast, and the outer surface shape of the inner frame is made to correspond to the outer surface shape of the pipe to be cast. It is formed from a non-circular surface corresponding to the inner surface shape of the non-circular portion and a circular surface having a diameter equal to the inner diameter of the circular portion of the tube, the inner frame is arranged inside the outer frame, and the non-circular surface of the inner frame is arranged outside. The non-circular portion of the frame is faced to form a gap therebetween, the circular surface of the inner frame is faced to the circular portion of the outer frame and a material input port is formed therebetween;
In this state, the outer frame and inner frame are fixed to each other to form a non-circular pipe casting form. 4. The formwork according to claim 3, wherein the inner frame has a uniform cross section along its longitudinal direction.