JPH11190057A - Manhole molding form for invertible monolithic molding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To freely set a projection-type mounting position in a step position and, at the same time, to enable the setting of mounting positions of projection- type both ends mounted also to the bottom type variably within specific range when the molding of a manhole main body and an invert simultaneously are formed together as a unit by incorporating an invert molding projection-type into a manhole molding form. SOLUTION: Invert molding projection-types 6 having various kinds of shapes are selectively arranged to the bottom type 4, and the bottom type 4 is set in the circumferential optional rotating position of an inside type 3 for a step 35 position of the inside type 3. Each of the projection-types 6 is constituted of a drum type 60 of a flexible columnar body in the shape of an approximately semi-circular cross section and mounting pipe types 61 connected to both end faces of the drum type 60 in a state to extend from the circumferential edge of the bottom type 4, and a mounting position to the drum type 60 of one of the mounting pipe types 61 is moved and adjusted by proper quantity along the circumferential direction of the bottom type 4 and can be fixed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mold for forming a manhole having a bottom, and more particularly, to a manhole formed integrally with an invert, wherein the bottom is inverted at the same time as the main body is formed and at an appropriate curvature. The present invention relates to a molding form.

[0002]

Assumptions of the Invention Usually, manholes are composed of an entrance layer, an intermediate layer,
And a precast concrete body is formed for each layer of the bottom layer, and these are laminated and buried underground. In the bottom manhole structure, an installation port for piping for sewage distribution is opened on the bottom side wall, and a gutter-like flow path having a substantially semicircular cross section connecting the two installation ports is further provided on the bottom inner surface. ("Invert").

[0003] Each of the mounting ports is formed in accordance with the specification of the mounting position according to the condition of the sewage pipe at the construction site.
Therefore, the invert connecting these is not necessarily formed in a straight line, but is formed in various curved lines.
Furthermore, in such a manhole structure, since the step position for elevating and lowering is integrally formed in advance, even if it is a linear invert, only the bottom manhole structure is axially rotated in accordance with the direction of the sewer pipe. Correspondence was not possible due to the step position of the upper manhole structure.

[0004] Specifically, the specification of pipe installation to the bottom manhole structure includes sections of the intersection angle between the inflow and outflow pipes, and sections of the positional relationship of the installation port with respect to the step position (invert direction). However, a variety of specifications were required.

[0005]

2. Description of the Related Art As shown in FIG. 9, most of the conventional invert formations are based on the above-mentioned current situation, and as shown in FIG. A construction method has been adopted in which the component a is installed, and thereafter, the bottom inner surface is filled with a mortar b to a predetermined thickness, and an invert d of various shapes is formed manually by an operator c.

[0006] As shown in FIG. 10, there has been a method of using an invert-molding formwork e for the purpose of streamlining by eliminating the manual work of the worker c. Further, as shown in FIG. 11, a bottomed manhole structure a with or without a bottom
And the bottom body f in which the invert d has been previously molded at the factory
Has been used as a separate body, and these are combined on site to combine them.

[0007]

However, in the above-described on-site construction, the manual construction method involves not only the complicated and dangerous work in the manhole, but also the finish quality varies depending on the worker. There were challenges. Also,
The construction method using the invert molding form e has a disadvantage that the connection between the invert d and the mounting opening g is not smooth. The molding of the invert d by casting in place requires not only the work waiting time until the mortar b hardens, but also the work efficiency is poor, and the integration between the molding mortar b and the manhole body is poor, so that integration is difficult. However, there has been a problem that cracks and peeling are apt to occur due to long-term use.

Further, as shown in FIG. 11, a construction method of separately constructing the bottom body f and assembling and combining the bottom body f is to avoid the step h attached to the inner surface of the manhole body a. I have to put the body f
In addition, extremely complicated work is required, for example, it has to be adjusted so that the mounting opening g and the invert d are continuous inside. Further, in order to integrate the bottom body f and the manhole main body a, further on-site work such as filling the gap with a grout material such as mortar is required, and there is a problem that work efficiency is poor.

Therefore, the present invention has been made by focusing on the above-mentioned problems, and by incorporating a convex for invert molding into a manhole molding mold, the invert is formed together with the molding of the manhole body. The mounting position of the convex mold can be freely set with respect to the step position, and the mounting positions of both ends of the convex mold mounted on the bottom mold can be changed within a predetermined range. It is an object of the present invention to provide a manhole molding formwork that can be set in one direction and that can be inverted and integrally molded.

[0010]

Means for Solving the Problems In order to achieve the above-mentioned object, an invertable and integrally formed manhole molding form according to the present invention is constituted as follows.

A cylindrical inner mold which is provided on a pedestal and has a step portion and is configured to be moldable, and a substantially disk-shaped bottom mold fitted so as to cover an upper end opening of the inner mold. And a cylindrical outer mold that is arranged so as to surround the outer peripheral side surface of the bottom mold and the inner mold at a constant interval, and is configured to be moldable. The upper surface is provided with a convex for invert molding which is passed between the edges in a straight line or a curved line, and the positional relationship of the convex with respect to the step position of the inner die is set at an arbitrary rotational position in the inner die circumferential direction. It is characterized by being set and fitted to the inner mold.

In the above-mentioned convex mold for invert molding, a trunk mold having a substantially semi-circular cross-sectional shape and having a straight or curved columnar body and having a flat side detachably attached to the upper surface of the bottom mold, and a peripheral edge of the bottom mold. A cylindrical mounting pipe type that is connected to both end faces of the body mold in a continuous state in an extended state, and the connection position of one of the mounting pipe types to the body mold is appropriately determined from the periphery of the bottom mold. Characterized in that it is located closer to the center of the length.

[0013] Further, as a next configuration, a cylindrical inner mold which is provided on a base, has a step portion and is configured to be moldable, and is fitted so as to cover an upper end opening of the inner mold. A manhole composed of a substantially disk-shaped bottom mold, and a cylindrical outer mold arranged so as to surround the outer peripheral side surfaces of the bottom mold and the inner mold at regular intervals, and configured to be moldable. In the forming mold, the bottom mold is provided with a convex shape for invert molding in which the periphery is linearly or curvilinearly passed between the peripheral edges and at least an intermediate portion is formed of a flexible body, and one end of the convex shape. It is characterized in that the side or both ends can be moved and fixed by an appropriate amount along the circumferential direction of the bottom mold and fixed.

In the above-mentioned manhole molding form of the freely-invertable integral molding, the bottom mold is set such that the positional relationship of the convex mold with respect to the step portion of the inner mold is set at an arbitrary rotational position in the circumferential direction of the inner mold. It is characterized by being fitted to.

In the above-mentioned convex mold for invert molding, a trunk mold which is formed of a straight or curved flexible columnar body having a substantially semicircular cross section and which is detachably attached to the upper surface of the bottom mold with a flat surface, A cylindrical mounting pipe type that is continuously connected to both end faces of the body die in a state of extending from the mold periphery, and in one of the mounting pipe types, the connection position to the body die is a bottom type. It is characterized by being located at a position closer to the center of an appropriate length than the peripheral edge, and capable of being fixed by being moved by an appropriate amount along the circumferential direction and being attached to the peripheral edge of the bottom mold.

In mounting the bottom die on the inner die, the bottom die is mounted via a disk-shaped setting plate fitted into a fixed position on the upper end surface of the inner die, and the bottom die rotates about the center of the setting plate. It is characterized in that it can be fixed at an appropriate rotational position as an axis.

[0017] Further, the present invention is characterized in that a slope is formed on the upper surface of the bottom mold to which the convex is attached, from the mounting position of the convex toward the periphery of the bottom.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described in detail with reference to the drawings. FIG.
FIG. 2 is an exploded perspective view showing the entirety of the manhole forming form of the present embodiment, FIG. 2 is a longitudinal sectional view of the manhole forming form of the present embodiment, and FIG. FIG. 4 is an exploded perspective view of a convex mold attached to a bottom mold according to the present embodiment.

The manhole forming form 1 includes a base 2 for installation.
A cylindrical inner mold 3 mounted and held on a pedestal 2;
A disk-shaped bottom mold 4 placed and held on the upper surface of
And an outer mold 5 arranged so as to surround the outer peripheral side surface of the inner mold 3 at a constant interval.

Since the basic structure is the same as that of the conventional bottom manhole structure and the forming mold, detailed description of the prior art which is not a feature of the present invention will be omitted.

The inner die 3 has a cylindrical shape which is open upward and is constituted by a mold split body divided into four parts. The inner mold 3 is divided by a movable means 37 and is contracted. The movable means 37 is composed of two sliding members 37b screwed to operation rods 37a having spirals formed in opposite directions from the center to both ends, respectively, and the facing mold body 31 (the left and right mold bodies in FIGS. 2 and 3). Body) via a link rod 37c. The two sliding members 37b are moved toward or away from each other according to the axial rotation direction of the operation rod 37a, and the mold body 31 linked to the two slide members 37b is connected to the hinge 37d connected to the rear mold body 32 (on the drawing). It moves in the opening or closing direction as a rotation axis. After the opposing mold bodies 31 are closed and contracted, the inner mold 3 is compacted by moving the front mold body 33 (on the drawing) to the center. On the side wall surface of the mold split 33 in front of the inner mold 3, a concave portion 34 for forming the support portion of the step 35 is formed.

A fitting receiving portion 36 having a fitting opening 36a that is open upward is attached to the inside of the upper end face of each mold body of the inner mold 3. This is for positioning and fitting and holding the setting plate 7 (described later).

The bottom die 4 is formed in a substantially disk shape whose outer peripheral shape coincides with the outer peripheral shape of the inner die 3, and the inner die 3 is provided via a disk-shaped setting plate 7 having the same outer peripheral shape. (FIG. 3).

The disc-shaped bottom mold 4 is composed of an upper plate 40, a lower plate 41 spaced apart from the upper plate 40, and a peripheral side plate 42 which integrates the outer peripheral edges thereof. An adjustment hole 40a for mounting a body die 60 constituting the convex die 6 (described later) is formed in a predetermined position (appropriate depending on the shape of the body die 60) in the upper surface plate 40. In the case of adopting the configuration according to claim 3 or later, the adjustment hole 40a is an arc-shaped long hole. Further, the upper surface plate 40 is formed with a downward slope (θ) from the mounting position of the convex mold 6 toward the peripheral edge (FIG. 2).

The lower plate 41 is provided with a mounting hole 41a including a position corresponding to the adjusting hole 40a, and a bolt receiving hole 41 for mounting the setting plate 7 (described later).
b has been established.

On the lower surface of the setting plate 7 to which the bottom mold 4 is attached, fitting projections 70 for fitting with the fitting receiving portions 36 of the inner mold 3 are arranged at corresponding positions. With this fitting, the positioning and setting and holding of the setting plate 7 with respect to the inner mold 3 are performed.

On the surface near the center of the setting plate 7, the center (C)
A concentric guide groove 71 having a circular arc shape is formed in one round. As a result, the setting plate 7 and the bottom mold 4 are attached by using the bolt 72 having the guide groove 71 penetrated from below.
This is performed by screwing into a bolt receiving hole 41b formed in the lower surface plate 41. By setting the fastening position of the bolt 72 to an appropriate position of the guide groove 71, the position of the bottom mold 4 with respect to the setting plate 7 (or with respect to the inner mold 3) can be changed.
An arbitrary angle (α) rotated at the center (C) (coincident with the center of the setting plate 7) can be set. As a result, as shown in FIG. 6A, the convex mold 6 attached to the upper surface of the bottom mold 4 by a method described later is at an arbitrary angle (α) with respect to the step 35 attached to the inner mold 3. Can be set.

Next, the convex mold 6 attached to the upper surface of the bottom mold 4 has a barrel mold 60 for defining the groove shape of the invert.
And a fitting tube die 61 for forming a fitting entrance 80 at the end of the pipe 9 into the bottom layer manhole structure 8.

The body mold 60 has a columnar shape (so-called kamaboko shape) having a substantially semicircular cross section in the transverse direction, and a flat lower surface (in the drawing) of the upper mold plate 40 of the bottom mold 4. It can be attached to any position. As shown in FIG. 6, the shape of the body mold 60 is formed from a straight line to various curved shapes when the top plate 40 is viewed from a plane. That is, FIG.
To (D), both ends of the body mold 60 and the upper plate 4
Angle between 0 and the center (C) (or open angle in both end directions)
(Β) is appropriately set in the range of 180 ° to 90 °. In addition, as the material of the body mold 60, an appropriate material such as a metal, a hard rubber, a resin, or the like is selected, but in the configuration of claim 3 or later, a material having flexibility is selected.

The method of mounting the body mold 60 is as follows. The adjusting hole 40 of the upper surface plate 40 is inserted through the mounting hole 41a of the lower surface plate 41 into the embedded nut 60a for screwing the bolt embedded on the lower surface side.
a, and a plurality of fastening bolts 60b are screwed and fastened.

The mounting pipe mold 61 is formed in a bottomed cylindrical shape conforming to the outer shape of the inflow / outflow pipe, and a substantially lower half on the bottom side is formed in the bottom mold 4.
Bottom contact portion 61a adapted to abut against the peripheral side plate 42, and a trunk type abutment portion 61 adapted to abut approximately the upper half to both ends of the trunk die 60.
b. The body die contact portion 61b has a cover 61c formed on the bottom die 4 extended with a step. The cover 61c is formed by one (the right side in the drawing) mounting pipe die 61 being the other. It is formed longer than the mounting tube type 61.

As shown in FIG. 5, this is achieved by forming an escape area 81 into the bottom surface (invert) of the bottom manhole structure 8 while keeping the opening of the fitting port 80 on the bottom surface of the bottom manhole structure 8 as shown in FIG. After moving the pipe 9A attached to 8 to the escape area 81 (arrow Sa), laying the next pipe 9B connected thereto at a predetermined position, move the pipe 9A in the direction of the pipe 9B (arrow Sb). This is for connecting the ends.

The method of attaching the convex mold 6 to the bottom mold 4 is performed as follows. First, the both end surfaces of the body mold 60 and the body mold contact portion 61
After being connected to the upper side plate 40 at a predetermined position, the shorter mounting pipe die 61 of the covering portion 61c is fastened and fixed to the peripheral side plate 42 by the mounting bolts 61d. Is mounted as described above. Next, the bottom die contact portion 61a of the longer mounting tube die 61 of the covering portion 61c is fastened and fixed to the peripheral side plate 42 of the bottom die 4 with mounting bolts 61d.

Here, in the case of adopting the configuration of claim 3 or later, a long hole 61e in the circumferential direction is formed in the bottom die contact portion 61a of the mounting pipe die 61 having the longer covering portion 61c. This long hole 6
1e, one end side of the flexible body mold 60 is attached to the attachment pipe 61
At the same time, it is moved in the left-right circumferential direction to adjust the curvature of the trunk mold 60. In the present embodiment, the movement angle amount of the end of the barrel die 60 is set so that the deflection angle (γ) with respect to the center (C) of the bottom die 4 is within a range of ± 5 degrees (FIG. 7).

The structure of the bottom mold 4 with respect to the inner mold 3 described above,
In combination with the configuration of the convex mold 6 with respect to the bottom mold 4, the shape of the convex mold 6 can be set to an appropriate shape from a linear shape to a right-angle curved shape, and further, the mounting position of the bottom mold 4 to the inner mold 3. Is rotated by an arbitrary angle, the positional relationship of the convex mold 6 with respect to the position of the step 35 can be freely set. In the present embodiment, the opening angle (β) in the both ends direction of the convex mold 6 is set to 9
Bottom mold 4 attached at 10 ° intervals from 0 ° to 180 °
Are prepared, and a desired bottom mold 4 is installed and molded according to the specifications at the site.

As shown in FIGS. 6 (A) to 6 (D), the configuration of claim 3 and subsequent figures is based on the fact that the amount of movement angle of the mounting pipe mold 61 is determined by the deflection angle (γ) with respect to the center (C). ) Is within the range of ± 5 degrees, 90
Open angle (β) continuously changed from degrees to 180 degrees
Can be obtained.

Next, the outer mold 5 includes the bottom mold 4 and the inner mold 3.
It is arranged to surround the outer peripheral side with a certain interval,
At the time of assembling, it has a cylindrical shape with an open top, and at the time of disassembly, it is divided vertically and divided into two semi-circular curved shapes. The thickness of the bottom side manhole structure 8 determines the thickness of the cylindrical side surface, while the thickness of the bottom surface is determined by the horizontal position between the upper surface plate 40 of the bottom mold 4 and the upper end opening edge of the outer mold 5. Is determined by the difference between

[0038] The mold moving is performed by a conventional method such as moving on a rail (not shown) provided on a pedestal, or lifting and moving each mold by a crane or hoist (not shown). This is done by the technology.

With the above-described configuration, the state before the concrete casting of the manhole forming form 1 of the present embodiment is such that the bottom mold 4 is positioned upward as shown in the vertical sectional view of FIG. It is placed and held on the pedestal 2 in this state. And inner mold 3
Concrete is poured into and poured into the casting space 10 defined by the outer mold 5 and the casting space.

Next, the mold is released from the manhole forming form 1.
Is lifted up by a crane or the like, and the pedestal 2 is turned upside down so that the pedestal 2 is turned upside down and placed on the floor again. Here, the pedestal 2 and the outer mold 5 are disassembled and removed. The inner die 3 is rotated when the operation rod 37a is rotated to move the movable means 37 to move each mold body inward, and is removed when the inner mold 3 is contracted. Finally, the mounting pipe mold 61 is released from being attached to the bottom mold 4 and is detached in both directions, and the setting plate 7, the bottom mold 4, and the trunk mold 60 in the state of being attached to the bottom mold 4 are: Lift it up and take it out to complete.

As shown in FIG. 8, the bottom-layer manhole structure 8 formed to be adapted to the specifications at the site is transported to the construction site and installed, without any additional work on the bottom surface.
Scheduled piping is performed, and thereafter, as in the conventional construction, the intermediate layer manhole structure i and the entrance layer manhole structure j are sequentially stacked on the upper portion to build the structure.

[0042]

[Effect] The present invention is configured as described above,
The configuration of the bottom mold for the inner mold and the configuration of the convex mold for the bottom mold are combined, and the shape of the convex mold is changed from linear to right-angled curved,
It can be set to an appropriate shape, and by rotating the mounting position of the bottom die to the inner die by an arbitrary angle, there is an effect that the positional relationship of the convex shape to the step position can be set freely.

Further, according to a third aspect of the present invention,
By making the end of the convex shape adjustable along the periphery of the bottom mold with a predetermined deflection angle (γ) with respect to the center of the bottom mold, a continuously changed opening angle (β) can be obtained.

As described above, according to the manhole forming mold of the present invention, it is possible to omit the cumbersome and poor work quality on-site work conventionally performed, and to adapt it to the piping specifications of the work site. The bottom manhole structure can be manufactured as a precast concrete product at the factory, which enables extremely reliable and durable construction work, shortens the construction period, and reduces construction costs. It has a remarkable effect that also contributes to the reduction of

[Brief description of the drawings]

FIG. 1 is an exploded perspective view showing the entire manhole forming form of the present embodiment.

FIG. 2 is a longitudinal sectional view of the manhole forming form of the present embodiment.

FIG. 3 is an exploded perspective view of an inner mold and a bottom mold according to the present embodiment.

FIG. 4 is an exploded perspective view of a convex type attached to a bottom die according to the present embodiment.

FIG. 5 is a partially cutaway perspective view illustrating an example of pipe installation to a bottom manhole structure formed according to the present embodiment.

FIG. 6 is an explanatory plan view showing an example of the positional relationship between the inner frame, the bottom mold, and the convex mold according to the present embodiment.

FIG. 7 is an explanatory plan view showing an example of a positional relationship among the inner frame, the bottom mold, and the protrusion according to the present embodiment.

FIG. 8 is a partially cutaway perspective view showing a manhole construction example using a bottom manhole structure formed according to the present embodiment.

FIG. 9 is an explanatory perspective view showing a conventional construction example.

FIG. 10 is an explanatory perspective view showing a conventional construction example.

FIG. 11 is an explanatory perspective view showing a conventional construction example.

[Explanation of symbols]

 DESCRIPTION OF REFERENCE NUMERALS 1 Manhole forming form 10 ・ Casting space 2 Pedestal 3 Inner die 31 ・ (Opposite) mold split body 32 ・ (Back) split mold body 33 ・ (Front) split mold body 34 ・ (Step support part forming) ) Recess 35 ・ step 36 ・ fitting receiving portion 36a ・ ・ fitting opening 37 ・ movable means 37a ・ ・ operation rod 37b ・ ・ sliding member 37c ・ ・ link rod 37d ・ ・ hinge 4 bottom mold 40 ・ top plate 40a ・・ Adjustment hole 41 ・ Bottom plate 41a ・ ・ Mounting hole 41b ・ ・ Bolt receiving hole 42 ・ Peripheral plate 5 Outer die 6 Convex 60 ・ Body die 60a ・ ・ Embedded nut 60b ・ ・ Tightening bolt 60c ・ ・ Connection bolt 61 ・Mounting tube type 61a Bottom contact portion 61b Trunk contact portion 61c Covering portion 61d Mounting bolt 61e Slot 7 Setting plate (bottom type) 70 Fitting protrusion 71 Guide groove 72 ・ Bolt Bottom layer manhole structure 80, fitting hole 81 and relief zones 9 pipe 9A-pipe (first) 9B-pipe (second)

Claims (7)

[Claims] 1. A cylindrical inner mold which is provided on a pedestal and has a step portion and is configured to be moldable, and a substantially disk-shaped bottom fitted so as to cover an upper end opening of the inner mold. A manhole molding form comprising: a mold; and a cylindrical outer mold that is arranged so as to surround an outer peripheral side surface of the bottom mold and the inner mold at a constant interval, and is configured to be moldable. The bottom mold is provided with a convex mold for invert molding with the periphery between the edges being linearly or curvedly arranged on the upper surface thereof, and the positional relationship of the convex mold with respect to the step position of the inner mold can be freely rotated in the circumferential direction of the inner mold. An invertable integrally molded manhole-molding form, which is set at a position and fitted to an inner mold. 2. A convex mold for invert molding, comprising: a trunk mold having a substantially semicircular cross-sectional shape and formed of a linear or curved columnar body and having a flat surface detachably attached to a bottom mold upper surface; And a cylindrical mounting pipe type that is connected to both end faces of the body die in a continuous state in a state where the mounting die extends from the bottom die peripheral edge. The manhole forming formwork according to claim 1, wherein the manhole forming form is formed at a position close to an appropriate length center. 3. A cylindrical inner mold which is provided on a pedestal and has a step portion and is configured to be moldable, and a substantially disk-shaped bottom fitted so as to cover an upper end opening of the inner mold. A manhole molding form comprising: a mold; and a cylindrical outer mold that is arranged so as to surround an outer peripheral side surface of the bottom mold and the inner mold at a constant interval, and is configured to be moldable. The bottom mold is provided with a convex for invert molding which is formed in a straight line or a curved shape between the peripheral edges on its upper surface and has at least an intermediate portion formed of a flexible material, and one end or both ends of the convex are formed on the bottom. An invertable integrally molded manhole molding form, which can be moved and fixed by an appropriate amount along the circumferential direction of the mold. 4. The manhole-molding formwork of claim 3, wherein the bottom mold is configured such that the position of the convex mold with respect to the step portion of the inner mold is adjusted by rotating the inner mold in the circumferential direction of the inner mold. An invertable integrally molded manhole-molding form, which is set at a position and fitted to an inner mold. 5. A convex mold for invert molding, comprising: a trunk mold formed of a straight or curved flexible columnar body having a substantially semicircular cross-section and having a flat surface detachably attached to an upper surface of a bottom mold; And a cylindrical mounting pipe type that is connected to both end faces of the body die continuously in a state of extending from the periphery of the bottom die. 4. A position closer to the center of a suitable length from the mold periphery, and the position of attachment to the bottom mold periphery can be fixed by moving an appropriate amount along the circumferential direction. 4
The manhole molding form of the invertable integral molding described in the above. 6. A method of mounting a bottom mold on an inner mold, wherein the bottom mold is attached via a disc-shaped setting plate fitted into a fixed position on an upper end surface of the inner mold, and the bottom mold has a center of the setting plate and a rotation axis. 6. The manhole molding form of claim 1, wherein the manhole molding is capable of being fixed at an appropriate rotational position. 7. A method according to claim 1, wherein a downward slope is formed from the mounting position of the convex toward the periphery of the bottom on the upper surface of the bottom having the convex. 6. A manhole-molded formwork according to claim 6, which is integrally molded with an invert.