JP7709352B2 - Corrugated cladding and composite pipes - Google Patents

Description

The present invention relates to a corrugated cladding tube that is placed over a flexible inner tube suitable for transporting fluids, and to a composite tube that includes an inner tube and a corrugated cladding tube.

A corrugated cladding pipe with alternating peaks and valleys is known as a flexible cladding pipe for protecting a flexible pipe (inner pipe) for hot and cold water supply. This corrugated cladding pipe is easily stretched in the axial direction of the pipe because the inner pipe needs to be exposed when connecting the inner pipe to a joint.

In the corrugated cladding tubes of Patent Documents 1 to 3, retaining protrusions that protrude radially inward from the valleys are arranged at equal intervals in the tube axial direction, and the tips of these retaining protrusions restrict the lateral movement of the inner tube, holding the inner tube concentric with the tube axis of the corrugated cladding tube. This forms an air insulating layer between the corrugated cladding tube and the inner tube, improving heat retention.

JP 2021-41539 A JP 2021-138140 A JP 2021-139500 A

The inventors performed a simulation using analysis software on the thermal insulation of the corrugated cladding pipe. The composite pipe is equipped with an inner pipe made of a cross-linked polyethylene pipe with a nominal diameter of 13 mm, and a corrugated cladding pipe made of a foamed polyethylene pipe with an outer diameter of 30.5 mm and a wall thickness of 0.5 mm. Assuming a situation in which the ambient temperature is 5°C and water with a temperature of 42°C is stationary in the inner pipe, the decrease in water temperature after 30 minutes was analyzed. As a result of the analysis, the water temperature decreased to 20°C when the inner pipe is concentric with the corrugated cladding pipe or eccentric within 1 mm. Based on this temperature, it was found that the temperature decreased further by 2 to 3°C when eccentric by 3 mm, and further by 7°C when the inner pipe comes into contact with the valley of the corrugated cladding pipe. Thus, in order to improve the thermal insulation of the corrugated cladding pipe, it is important to avoid contact between the inner pipe and the valley of the corrugated cladding pipe.

When the composite tube is in a straight line, the retaining protrusions of the corrugated cladding tube hold the inner tube substantially concentric with the corrugated cladding tube, so that heat retention can be achieved. However, in harsh configurations, i.e. when bent at the minimum bending radius, it is not guaranteed that heat retention can be achieved by avoiding contact between the inner tube and the valleys of the corrugated cladding tube. None of Patent Documents 1 to 3 teaches heat retention from this perspective.

In order to solve the above problems, the present invention provides a corrugated covering pipe for covering a flexible inner pipe, comprising annular peaks and annular valleys alternately arranged in the pipe axial direction, and a plurality of retaining protrusions arranged at equal intervals in the pipe axial direction and spaced apart in the circumferential direction, wherein the retaining protrusions protrude radially inward beyond the valleys and hold the inner pipe substantially concentrically with the pipe axis with their tips, and the spacing between the retaining protrusions in the pipe axial direction is shorter than the limit value at which the inner pipe comes into contact with the valleys when it is assumed that the inner pipe is bent with a minimum bending radius.
According to this configuration, even in a situation where the inner pipe is bent at the minimum bending radius, the retaining protrusions can prevent contact between the inner pipe and the valley portion of the corrugated cladding pipe, thereby maintaining heat retention.

In the first aspect, when the interval between the holding projections in the tube axial direction is D and the minimum bending radius is R, the following formula is satisfied.
D≦πR/4
In the first aspect, preferably, the interval D between the holding projections in the tube axial direction satisfies the following formula:
D≧πR/8
In the first embodiment, within the range of sizes and materials of inner pipes used in normal houses, etc., the interval between the holding projections in the pipe axial direction is 534 mm or less.

In a second aspect, which sets stricter conditions than the first aspect, when the spacing between the retaining protrusions in the tube axial direction is D, the minimum bending radius is R, and the protruding height of the retaining protrusions from the valley portion is H, the following formula is satisfied.
D≦πR・ASIN{(H/2R) ^0.5 }/45
In the second aspect, preferably, the interval D between the holding projections in the tube axial direction satisfies the following formula:
D≧πR・ASIN{(H/2R) ^0.5 }/90
In the second embodiment, within the range of sizes and materials of inner pipes used in ordinary houses, etc., the installation interval in the axial direction of the holding projections of the covering pipe is 142.9 mm or less.

The tip of the holding protrusion forms a concave curve when viewed from the tube axial direction. This allows the tip of the holding protrusion to contact the outer periphery of the inner tube without slipping, so the inner tube can be held in place well.

Another aspect of the present invention is a composite pipe that includes a flexible inner pipe and the corrugated cladding pipe that covers the inner pipe.

According to the present invention, the heat retention function of the corrugated cladding tube can be maintained even when the inner tube is bent at the minimum bending radius.

1 is a side view showing a cross section of only the upper half of a composite pipe including a corrugated cladding pipe according to a first embodiment of the present invention. FIG. FIG. 2 is an enlarged side view showing a main part of FIG. 1 with only the upper half thereof being cross-sectional; FIG. 3 is a cross-sectional view taken along the line III-III in FIG. 2 . FIG. 13 is a schematic diagram showing a state in which an inner tube is bent at a minimum bending radius to explain a first calculation method for determining the axial spacing of holding protrusions of a corrugated cladding tube. FIG. 11 is a schematic diagram showing a state in which an inner tube is bent at a minimum bending radius to explain a second calculation method for determining the axial spacing of holding protrusions of a corrugated cladding tube. 3A and 3B are views showing modified examples of the holding protrusions.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, a composite pipe 1 includes a flexible inner pipe 10 and a flexible corrugated sheathing pipe 20 (corrugated pipe) that covers the inner pipe 10. The composite pipe 1 is used, for example, as a pipe for supplying cold water or hot water. The inside of the inner pipe 10 forms a fluid passage through which fluids such as water and hot water pass.

The inner tube 10 is formed with a constant circular cross section over its entire length and is flexible. The inner tube 10 can be a cross-linked polyethylene (PE-X) pipe, a polybutene (PB) pipe, a polyethylene (PE) pipe, a heat-resistant polyethylene (PE-RT) pipe, or a resin pipe containing two or more of these resins. It is also possible to use a metal-reinforced resin pipe containing at least one of the above resins and a metal. The above are examples, and there are no particular restrictions on the material of the inner tube 10 as long as it can ensure the required performance such as flexibility and fluid flowability.

The corrugated cladding pipe 20 is made of a single-layered resin pipe, and may be a polyethylene (PE) pipe, a cross-linked polyethylene (PE-X) pipe, a polybutene (PB) pipe, a heat-resistant polyethylene (PE-RT) pipe, or a resin pipe containing two or more of these resins. The flexibility of the cladding pipe 20 may be improved by foaming. In this case, it is preferable to use polyethylene (PE) as the main component and to have a low foaming ratio of 1.05 to 4 times. The above is an example, and there is no particular restriction on the material of the corrugated cladding pipe 20 as long as it can ensure the required performance such as flexibility and protection for the inner pipe 10.

As shown in Figures 1 and 2, the corrugated cladding tube 20 has a corrugated cross section formed by alternating annular peaks 21 and annular valleys 22 in the axial direction of the tube. As shown in Figure 2, the peaks 21 are short cylindrical with a constant diameter, and the cross section of the valleys 22 is U-shaped or V-shaped.

The corrugated cladding tube 20 further has retaining protrusions 23 that are distributed in the tube axial direction and circumferential direction and are independent of each other. Specifically, four retaining protrusions 23 are formed at equal intervals D in the tube axial direction and at equal circumferential intervals. The retaining protrusions 23 protrude radially inward beyond the valley portions 22, and their tips 230 contact the outer periphery of the inner tube 10 or face it at a small distance, thereby holding the inner tube 10 substantially concentric with the tube axis of the corrugated cladding tube 20.

The corrugated cladding tube 20 can suppress flapping of the inner tube 10 and reduce noise by holding the inner tube 10 concentrically with the retaining protrusions 23. In addition, the insulating air layer formed between the corrugated cladding tube 20 and the inner tube 10 can improve heat retention. The retaining protrusions 23 are distributed in the axial direction of the tube, so they do not affect the expansion and contraction in the axial direction of the tube. The retaining protrusions 23 are distributed in the circumferential direction, so the risk of structures getting caught can be reduced.

When the composite pipe 1 is in a straight state, the air insulation layer between the inner pipe 10 and the corrugated cladding pipe 20 provides optimal heat retention. However, if the axial spacing of the retaining protrusions 23 is long, the inner pipe 10 may come into contact with the valleys 22 of the corrugated cladding pipe 20, particularly the valleys 22 located in the center between the retaining protrusions 23, when the composite pipe 1 is bent, potentially reducing the heat retention function. Therefore, we determine the upper limit of the axial spacing of the retaining protrusions 23, i.e., the spacing at which the inner pipe 10 does not come into contact with the valleys of the corrugated cladding pipe 20 even when the composite pipe 1 is bent at the minimum bending radius.

<First Calculation Method>
Hereinafter, a first calculation method for determining the upper limit of the interval between the retaining protrusions 23 will be described with reference to Fig. 4. Since the composite pipe 1 is usually bent at an angle of 90° or less, the most severe bending condition, that is, the inner pipe 10 is bent at a minimum bending radius R and a bending angle of 90°, is assumed. In Fig. 4, the corrugated cladding pipe 20 is shown in schematic form. That is, the circumscribing circle 22A of the valley portion 22 located on the inside of the curve and the inscribing circle 22B of the valley portion 22 located on the outside of the curve are shown, and the retaining protrusions 23 protruding from the valley portion 22 are shown as short straight lines. The corrugated cladding pipe 20 is held by a fastener to the building structure and maintained in the above-mentioned bent state, and the inner pipe 10 is not held.

4, when the retaining protrusions 23 are provided at angular intervals of 90°, the inner tube 10 is most likely to come into contact with the valley portion 22 of the cladding tube 20 at the center position between the retaining protrusions 23 (a position 45° away from the retaining protrusions 23) as shown by the dashed lines in the figure. Therefore, by locating the retaining protrusions 23 at this intermediate position, it is more likely that contact between the retaining protrusions 23 and the valley portion 22 can be avoided. The interval Do between the retaining protrusions 23 at this time is set as the upper limit value.
The distance Do can be expressed by the following formula.
Do=2πR(45/360)...(1)
By rearranging the above formula (1), the following formula is obtained.
Do=πR/4...(2)
If the spacing D of the holding projections 23 is set to be equal to or less than the spacing Do, it is highly possible to reliably avoid contact between the inner tube 10 and the valley portions 22, and a high heat retention function can be achieved.

In Fig. 4, if the retaining protrusions 23 are also arranged at an angle of 45°, contact between the inner pipe 10 and the valley portion 22 of the corrugated cladding pipe 20 can be more reliably avoided, and the radial distance between the inner pipe 10 and the valley portion 22 between the retaining protrusions 23 can be prevented from narrowing. The distance between the retaining protrusions 23 in this case is given by the formula Do/2. The distance obtained by this calculation can also be used as the lower limit for reducing the number of retaining protrusions 23 and reducing contact between the retaining protrusions 23 and the inner pipe 10. In this case, the distance D can be expressed by the following formula.
D≧πR/8 (3)

Here is a concrete example. When a cross-linked polyethylene pipe, polybutene pipe, or metal-reinforced resin pipe is used as the inner pipe 10, the wall thickness increases as the size increases, making it difficult to bend the pipe raw. However, when used for end piping in residential or hotel rooms and toilets, the nominal diameter of the inner pipe 10 is 10 mm to 25 mm, and the pipe is placed in a raw bent state.

Different sizes and materials of the inner tube 10 have different minimum bend radii.
For example, when the inner pipe 10 is a cross-linked polyethylene pipe, the minimum bending radius is as follows.
Nominal diameter 10mm, outer diameter 13mm...minimum bending radius 150mm
Nominal diameter 13mm, outer diameter 17mm...minimum bending radius 150mm
Nominal diameter 16mm, outer diameter 21.5mm...minimum bending radius 200mm
Nominal diameter 20mm, outer diameter 27mm...minimum bending radius 300mm
Nominal diameter 25mm, outer diameter 34mm...minimum bending radius 350mm

Furthermore, when the inner pipe 10 is a polybutene pipe, the minimum bending radius is as follows.
Nominal diameter 10mm, outer diameter 13mm...minimum bending radius 130mm
Nominal diameter 13mm, outer diameter 17mm...minimum bending radius 170mm
Nominal diameter 16mm, outer diameter 22mm...minimum bending radius 220mm
Nominal diameter 20mm, outer diameter 27mm...minimum bending radius 270mm
Nominal diameter 25mm, outer diameter 34mm, minimum bending radius 680mm

In the above example, the minimum bending radius is largest when the inner pipe 10 is a polybutene pipe with a nominal diameter of 25 mm and an outer diameter of 34 mm (the outer diameter of the corrugated cladding pipe 20 is 52 mm), and the minimum bending radius R of the inner pipe 10 is 680 mm. When this minimum bending radius R = 680 mm is substituted into the above formula (2), the spacing D of the retaining protrusions 13 becomes 534 mm or less.

The smallest minimum bending radius is when the inner pipe 10 is a polybutene pipe with a nominal diameter of 10 mm and an outer diameter of 13 mm, and the minimum bending radius R is 130 mm. When this minimum bending radius R = 130 mm is substituted into the above formula (2), the spacing D of the retaining protrusions 13 becomes 102 mm or less.

<Second Calculation Method>
Next, a second calculation method for determining the upper limit of the interval between the holding projections 23 will be described with reference to FIG. 5. The second calculation method assumes stricter conditions than the first calculation method. FIG. 5 is a schematic diagram of the cladding tube 1 when the inner tube 10 is bent at the minimum bending radius. As in FIG. 4, the circumscribing circle 22A and the inscribing circle 22B of the valley portion 22 are illustrated for the corrugated cladding tube 20, and the holding projection 23 protruding from the valley portion 22 is illustrated as a short straight line. The worst situation that cannot actually occur is assumed. That is, the inner tube 10 forms a straight pipe shape between the two holding projections 23, 23 and is in contact with the valley portion 22. This straight inner tube 10 is indicated by the symbol 10'. The point of contact between the straight inner tube 10' and the circumscribing circle 22A of the valley portion 22 is indicated by the symbol P in the figure. Also, the displacement amount from the ideal shape in which the inner tube 10 is bent concentrically with the corrugated cladding tube 20 at the minimum bending radius to the above-mentioned straight shape is indicated by the symbol H'. The amount of displacement H' is equal to the protruding height H of the holding projection 23 from the valley portion 22. The minimum bending radius (the radius of the inscribed circle of the curved inner pipe 10) is indicated by R.

In order to obtain the calculation formula, a straight line of length L is defined in Fig. 5. This straight line is a line that connects the tip of the holding protrusion 23 with the contact point P. The triangle defined by this straight line of length L, a short straight line representing the displacement amount H', and another straight line is defined as a "small triangle." The angle between the straight line of length L and the other straight line is defined as Θ.
Furthermore, a triangle defined by a line connecting the center of the radius of curvature of the composite pipe 1 and the tangent point P, a line of length L, and another line (a line having the length of the minimum bending radius R and including the retaining protrusion 23) is defined as a "large triangle." In the "large triangle," the angle between the line connecting the center of the radius of curvature and the tangent point P and the other line (the angle between the tangent point P and the retaining protrusion 23) is 2Θ. The angle between the retaining protrusions 23 arranged on both sides of the tangent point P is 4Θ.

For the "small triangle" of FIG.
tanΘ=H'/L=H/L...(4)
For the "big triangle" the following formula holds:
sin2Θ=L/R...(5)
The following formula can be derived from (4) and (5) above.
L=H/tanΘ=Rsin2Θ...(6)
Further rewriting, we obtain the following formula:
tanΘ・sin2Θ=H/R...(7)
Here, by substituting tan Θ = sin Θ/cos Θ and sin 2 Θ = 2 sin Θ · cos Θ into equation (7), we obtain the following equation.
(sinΘ) ² = H/2R...(8)
From equation (8), Θ can be expressed as follows:
Θ=ASIN{(H/2R) ^0.5 }...(9)

As described above, the angular interval of the holding protrusions 23 can be expressed as 4Θ, and when this is expressed as a distance, the upper limit distance Dc at which the inner tube 10 contacts the valley portion 22 of the cladding tube 20 can be expressed by the following formula.
Dc=2πR・(4Θ/360)=πRΘ/45...(10)
By substituting the above-mentioned formula (9) into formula (10), the following formula is obtained.
Dc=πR・ASIN{(H/2R) ^0.5 }/45...(11)
In order to prevent the inner tube 10 from contacting the valley portion 22 of the cladding tube 20, it is necessary to set the interval D of the holding projections 23 to the above upper limit interval Dc or less. This is expressed by the following formula.
D≦πR・ASIN{(H/2R) ^0.5 }/45...(12)

5, if the holding protrusions 23 are also disposed at the contact point P, contact between the inner pipe 10 and the valley portion 22 of the corrugated cladding pipe 20 can be more reliably avoided, and narrowing of the radial interval between the inner pipe 10 and the valley portion 22 between the holding protrusions 23 can be suppressed. The interval between the holding protrusions 23 in this case is 1/2 of the equation (10), and can be expressed by the following equation.
Dc'=πR・ASIN{(H/2R) ^0.5 }/90...(13)

The distance D calculated by formula (13) can be used as an upper limit when the contact conditions are made stricter, but it can also be used as a lower limit for reducing the number of the retaining projections 23 and the contact between the retaining projections 23 and the inner tube 10. In the latter case, the distance D can be expressed by the following formula.
D≧πR・ASIN{(H/2R) ^0.5 }/90...(14)

A specific example will be given. In the sizes and materials given above, the largest upper limit spacing Dc is for an inner pipe 10 of a polybutene pipe with a nominal diameter of 25 mm and an outer diameter of 34 mm. In this case, the inner diameter of the corrugated cladding pipe 20 (excluding the retaining protrusions 23) is 42.5 mm, the retaining protrusion height H = 3.75 mm, and the minimum bending radius R = 680 mm. Substituting the retaining protrusion height H and the minimum bending radius R into equation (11) for calculation, the upper limit spacing Dc of the retaining protrusions 23 is 142.9 mm.

The smallest upper limit spacing Dc is for an inner pipe 10 that is a polybutene pipe with a nominal diameter of 10 mm and an outer diameter of 13 mm. In this case, the inner diameter of the corrugated cladding pipe 20 is 22.5 mm, the protrusion height H = 4.25 mm, and the minimum bending radius R = 130 mm. When the retaining protrusion height H and the minimum bending radius R are substituted into equation (11) and calculated, the upper limit spacing Dc of the retaining protrusions 23 is 66.7 mm. The lower limit spacing Dc' calculated by equation (13) for this size is 33.3 mm.

As shown in FIG. 6, the shape of the tip 230 of the holding protrusion 23 as viewed from the tube axial direction may be an arc (concave curve) shape that corresponds to the inner tube 10. In this case, the inner tube 10 can be held more stably.

The present invention is not limited to the above embodiment, and various configurations can be adopted within the scope of the spirit of the present invention. For example, the axial dimension of the retaining protrusion may be greater than or equal to the groove width of the valley portion.

The present invention can be applied to, for example, water and hot water supply pipes.

1 Compound pipe 10 Inner pipe 20 Covering pipe 21 Peak portion 22 Valley portion 23 Holding protrusion D Distance between holding protrusions R Minimum bending radius H Height of holding protrusion from valley portion

Claims (9)

A corrugated cladding tube covering a flexible inner tube,
annular peaks and valleys alternately arranged in a tube axial direction;
A plurality of holding projections arranged at equal intervals in the tube axial direction and spaced apart in the circumferential direction;
Equipped with
the retaining projection protrudes radially inward from the valley portion and retains the inner tube substantially concentrically with the tube axis by a tip thereof;
a distance between the retaining projections in an axial direction of the inner tube being shorter than a limit value at which the inner tube comes into contact with the valley portion when the inner tube is bent with a minimum bending radius. 2. The corrugated cladding tube according to claim 1, wherein the following formula is satisfied, where D is an axial interval between the holding projections and R is the minimum bending radius:
D≦πR/4 3. The corrugated cladding tube according to claim 2, wherein the axial distance D between the holding projections satisfies the following formula:
D≧πR/8 The corrugated cladding tube according to claim 2, characterized in that the spacing between the retaining protrusions in the tube axial direction is 534 mm or less. 2. The corrugated cladding tube according to claim 1, characterized in that the following formula is satisfied, where D is a distance between the holding protrusions in the tube axial direction, R is a minimum bending radius, and H is a protruding height of the holding protrusions from the valley portion.
D≦πR・ASIN{(H/2R) ^0.5 }/45 6. The corrugated cladding tube according to claim 5, wherein the axial distance D between the holding projections satisfies the following formula:
D≧πR・ASIN{(H/2R) ^0.5 }/90 6. The corrugated cladding tube according to claim 5, wherein the intervals between the holding projections of the cladding tube in the axial direction of the tube are 142.9 mm or less. A corrugated cladding tube according to any one of claims 1 to 7, characterized in that the tip of the retaining protrusion forms a concave curve when viewed from the tube axial direction. A composite pipe comprising a flexible inner pipe and a corrugated cladding pipe according to any one of claims 1 to 8 that covers the inner pipe.