Thermoplastic laminate duct

A duct formed of a thermoplastic material is lightweight, strong, flame and smoke resistant, and non-toxic. The duct is formed from a flat laminate and does not require a specialized, disposable mandrel for supporting conventional thermoset plies. Preferably, the duct is formed from a preform, which is cut according to the desired shape and size of the duct so that trimming after the duct has been formed is not required. Additionally, features such as holes and spud locations can be provided by cutting or marking the preform before forming the duct. Each duct can be formed of multiple articulated segments that are joined by connectors.

BACKGROUND OF THE INVENTION

1) Field of the Invention

The present invention relates to ducts and, more specifically, to ducts formed of thermoplastic laminates and preforms and methods for forming such ducts.

2) Description of Related Art

Ducts provide transport passageways for a wide variety of applications. For example, tubular ducts are widely used for air flow in aircraft environmental control systems. Similarly, ducts provide passageways for transporting gases for heating and ventilation in other vehicles and in buildings. Water distribution systems, hydraulic systems, and other fluid networks also often use ducts for fluid transport. In addition, solid materials, for example, in particulate form can be delivered through ducts. Ducts for the foregoing and other applications can be formed of metals, plastics, ceramics, composites, and other materials.

One conventional aircraft environmental control system utilizes a network of ducts to provide air for heating, cooling, ventilation, filtering, humidity control, and/or pressure control of the cabin. In this conventional system, the ducts are formed of a composite material that includes a thermoset matrix that impregnates, and is reinforced by, a reinforcing material such as Kevlar®, registered trademark of E. I. du Pont de Nemours and Company. The thermoset matrix is typically formed of an epoxy or polyester resin, which hardens when it is subjected to heat and pressure. Ducts formed of this composite material are generally strong and lightweight, as required in many aircraft applications. However, the manufacturing process can be complicated, lengthy, and expensive, especially for specially shaped ducts such as curved ducts and ducts that include a spud or attached fitting, a bead, a bell or flared portion, a conical section, or another contour. For example, curved ducts are conventionally formed around a disposable plaster mandrel. The plaster mandrel is formed in a specially shaped rotatable tool that acts as a mold to form the plaster mandrel according to the desired shape of the duct. First, a cavity of the tool is partially filled with uncured plaster, and the tool is rotated so that the plaster coats an inner surface of the tool cavity. When the plaster is partially cured to form the mandrel, the tool is stopped and opened so that the plaster mandrel can be removed and placed in an oven for subsequent curing. The mandrel is then treated with a sealant, cured again, and treated with a release agent. Plies of fabric, such as Kevlar®, preimpregnated with the thermoset material are cut and draped over the mandrel, often by hand, and a heat gun is used to mold the plies to the shape of mandrel. The mandrel is placed in a vacuum bag, which is fitted with one or more valves, and air is evacuated from the bag through the valves so that the bag urges the plies against the mandrel and consolidates the plies while heat is applied to cure the plies and form the duct. When the plies are cured, the vacuum bag is removed and the plaster mandrel is broken and removed from the duct. The duct is cleaned and trimmed to the desired dimensional characteristics. A jig that corresponds to the desired shape of the duct is often used for trimming the duct and for accurately locating additional features on the duct such as holes, spuds, brackets, and the like. Further processing is sometimes necessary for adding a bead or bell so that one or both ends of the duct can be secured and sealed to another duct. Typically, a bead is formed by adding additional material, thus adding weight to the duct. Insulation can also be added to the inside and/or outside of the duct.

The manufacturing process for such reinforced thermoset ducts is complicated, time consuming, and expensive. The rotatable tool used to mold the plaster mandrel is specially sized and shaped for creating a duct of specific dimensions, so numerous such tools must be produced and maintained for manufacturing different ducts. The plaster mandrel is formed and destroyed during the manufacture of one duct, requiring time for curing and resulting in plaster that typically must be removed or destroyed as waste. Additionally, the preimpregnated plies change shape while being cured and consolidated and therefore typically must be trimmed after curing to achieve the desired dimensions. The jigs required for trimming and for locating the proper positions for features such as holes and spuds are also typically used for only a duct of particular dimensions, so numerous jigs are required if different ducts are to be formed. Like the rotatable tools used for forming the mandrels, the jigs require time and expense for manufacture, storage, and maintenance.

Additionally, ducts formed of common thermoset epoxies do not perform well in certain flammability, smoke, and toxicity tests, and the use of such materials can be unacceptable if performance requirements are strict. For example, changes in environmental laws or proposed changes to performance requirements mandated by the Federal Aviation Administration would prevent the use of ducts formed from some thermoset composites in certain aircraft environmental control system applications.

Thus, there exists a need for an improved duct and method of forming a duct that reduces complexity and increases cost efficiency. Preferably, the method should not require the formation of a special rotatable tool and plaster mandrel for each duct or special hand tool for hand lay-up. The duct should be compatible with efficient methods for forming beads and bells and for locating other features, preferably without the use of an expensive jig that is duct-specific. Additionally, the duct should be lightweight and strong and should meet strict flammability, smoke, and toxicity standards.

SUMMARY OF THE INVENTION

The present invention provides a duct formed of a thermoplastic laminate and an associated preform and method. The duct is lightweight, strong, and performs well in flammability, smoke, and toxicity tests. The duct is formed by configuring a flat laminate and does not require a disposable plaster mandrel for supporting plies, a duct-specific rotatable tool for forming such a mandrel, or a special hand lay-up tool. Locations for features such as holes and spuds can be determined before the duct is formed from the laminate. Additionally, the duct can be formed to provide beads and bells without the addition of material.

In one embodiment, the present invention provides an articulated thermoplastic laminate duct that includes a plurality of duct segments, which are formed of thermoplastic laminate, for example, a composite material that includes a thermoplastic matrix such as polyetherimide or polyphenol sulfide and a reinforcing material such as fabric or fibers formed of an aramid, carbon, or glass. First and second duct segments are connected to define a continuous passage therein, for example, by a flexible connector between ends of the duct segments, which are otherwise offset with a longitudinal axis of the first duct segment being angled relative to a longitudinal axis of the second duct segment. According to one aspect of the invention, the flexible connector defines first and second elongate portions which are partially enclosed. Each portion defines an opening for receiving the end of a respective duct segment, and the portions are connected so that the openings are generally outwardly opposed to each other.

The present invention also provides a thermoplastic laminate preform for manufacturing a duct segment of an articulated duct. The preform includes a flat sheet of thermoplastic laminate that defines a flat geometric pattern corresponding to the desired shape of the duct segment so that the sheet can be configured to generally define the desired shape of the duct segment, which defines a passage. The sheet can be formed of a composite material that includes a thermoplastic matrix such as polyetherimide or polyphenol sulfide, and a reinforcing material such as an aramid, carbon, or glass. Construction data can be disposed on the perform, including a duct segment identification mark, an orientation mark, a radial alignment mark, a spud location mark, a detail location mark, and/or a cuff location mark. According to one aspect of the invention, the flat geometric pattern is at least partially defined by a sinusoidal curve and/or arc that is based on a number of duct segments required to form the articulated duct, a curvature of the articulated duct, a diameter of an inlet of the articulated duct, a diameter of the outlet of the articulated duct, a bend radius of the duct segment, a desired location for the seam of the duct segment, a seam overlap, and a desired deformation of the inlet and outlet of the articulated duct.

The present invention also provides methods of forming a thermoplastic laminate preform and duct. The preform, which generally corresponds to a desired shape of a first duct segment, can be formed by impregnating a reinforcement material with thermoplastic to form a flat sheet, determining a flat geometric pattern that generally corresponds to the desired shape of the first duct segment, and cutting the sheet according to the flat geometric pattern. Preferably, the geometric pattern is determined such that the duct segment is consolidated to the desired shape of the first duct segment without trimming the segment after consolidation. For example, the dimensions of the flat geometric pattern can be calculated at least partially according to a sinusoidal curve and/or arc based on a number of duct segments for an articulated duct, a curvature of the articulated duct, a diameter of an inlet of the articulated duct, a diameter of the outlet of the articulated duct, a bend radius of the first duct segment, a desired seam location, a seam overlap, and desired deformations of the inlet and outlet of the duct. The duct is formed by configuring the perform to approximate the desired shape of the first duct segment, which defines a passage, and consolidating the preform to form the first duct segment. According to one aspect of the invention, the methods also include marking the sheet with construction data such as a duct identification mark, an orientation mark, a radial alignment mark, a spud location mark, a detail location mark, and/or a cuff location mark. According to another aspect, the first duct segment is connected to at least a second duct segment so that the passage defined by the first duct segment is fluidly connected to a passage defined by the second duct passage. For example, the ducts segments can be connected by joining a flexible connector to opposing ends of the duct segments. The first duct segment can be connected to the second duct segment such that longitudinal axes of the duct segments are angled relative to one another and the segments in combination at least partially form an articulated duct.

DETAILED DESCRIPTION OF THE INVENTION

Referring now toFIG. 1, there is shown an articulate duct10according to one embodiment of the present invention. The duct10is formed of straight duct segments20, four in this embodiment, which are connected by connectors80such that the duct segments20define a continuous passage12extending from an inlet14to an outlet16. The duct10can be used in numerous applications including, but not limited to, environmental control systems of aerospace vehicles, in which air is delivered through the passage12of the duct10to provide heating, cooling, ventilation, filtering, humidity control, and/or pressurization to an aircraft cabin. The inlet14and outlet16of the duct10can be connected to other ducts or other devices such as heaters, air conditioners, ventilators, filters, compressors, and the like. The duct segments20are connected so that a longitudinal axis of each duct segment20is configured at an angle relative to the longitudinal axis of the adjoining duct segment(s)20. Thus, the duct10defines an articulated shape and the inlet14and outlet16are angled relative to one another. Alternatively, the duct segments20can be connected to form a straight duct10.

The ducts segments20are formed of a thermoplastic laminate. Thermoplastic materials are characterized by a transition to a plastic state when heated above a glass transition temperature and a return to a non-plastic state when cooled to a temperature below the glass transition temperature. For example, the duct segments20can be formed of polyetherimide (PEI) or polyphenol sulfide (PPS), both of which can be thermoplastic. Thermoplastic PEI, available under the trade name Ultem®, a registered trademark of General Electric Company, typically becomes plastic at temperatures above about 417° F. According to one embodiment of the present invention, each segment20is formed of a composite material that includes a matrix of thermoplastic PEI that is reinforced with a reinforcing material such as a fabric or fibers of carbon, glass, or an aramid fabric such as Kevlar®. Fabrics of these and other reinforcing materials can be prepared by various methods as are known in the art. For example, numerous types of chopped fiber and weave patterns can be used, including a 0/90 degree crowfoot fiber weave. Alternatively, the segments20can be formed of other thermoplastic materials, which can be reinforced by other reinforcing materials, or can include no reinforcing materials.

For clarity of reference, there are illustrated inFIG. 2several dimensions of the duct10. As shown, the inlet14of the duct10has first diameter D1and the outlet16has a second diameter D2. The diameters D1, D2can be different, but as shown in the embodiment ofFIG. 2, the diameters D1, D2are equal and hereinafter referred to similarly as the diameter D. Each duct segment20defines a first segment width W1and a second segment width W2. In the illustrated embodiment, the second segment width W2of each duct segment20is longer than the first segment width W1, and the duct segments20are configured so that the duct10is articulated about a duct center18. The articulation of the duct10depends on an angle σ between adjoining duct segments20. The angle σ is measured between adjoining duct segments20at the outermost portion of the duct segments, i.e., where the second segment width W2occurs. However, the angle σ can alternatively be measured elsewhere, for example, between the longitudinal axes of adjoining duct segments20. An angle B is equal to the sum of the individual angles σ of the duct segments20. Thus, the angle B is the total articulation of the duct10. A bend radius R is measured as the distance between the duct center18and the outermost portion of the duct segments20, though the bend radius R can also be measured elsewhere, for example, between the center18and the longitudinal axes of the duct segments20.

A preform60for forming one of the duct segments20is shown inFIG. 3. The preform60is formed from a flat sheet58formed of a thermoplastic laminate, as shown inFIG. 4. The preform60defines first and second ends62,64and first and second side edges66,68. The preform60is configured to form one of the duct segments20by bending the preform60so that the first and second side edges66,68are brought together. The preform60can be bent in a circular cross section or another shape such as a square, rectangle, triangle, ellipse, and the like. The first and second side edges66,68are joined to form a seam26so that the duct segment20defines a closed polygonal cross section defining the passage12. Preferably, one of the first or second side edges66,68overlays a portion of the other edge66,68by a distance designated as a seam overlap LOLas shown inFIG. 2. An angular location S of the seams26can be staggered on the duct10.

The preform60can be bent and configured manually or by an automated machine. Methods of configuring a preform are provided in U.S. application Ser. No. 10/215,815, titled “Preforming Thermoplastic Ducts,” filed concurrently herewith, the entirety of which is incorporated herein by reference. Preferably, the portion of the duct segment20at the seam26is consolidated and joined using glue, heat, or other joining methods. Joining is typically achieved by applying heat and pressure to the edges66,68to form the seam26. As the thermoplastic material of the duct segment20is heated above its glass transition temperature, the material becomes plastic and the pressure consolidates and joins the overlapped material tat makes up the seam overlap LOL. Joining can be performed by manual or automated methods, for example, as described in U.S. application ser. No. 10/215,833, titled “Consolidation Joining of Thermoplastic Laminate Ducts,” filed concurrently herewith, the entirety of which is incorporated herein by reference.

The shape of the preform60is determined by projecting the desired shape of the duct segment20onto the flat laminate sheet58. For example, the duct segments20shown inFIGS. 1 and 2can be formed from preforms60as shown inFIG. 4. The preform60shown inFIG. 3can also be used to form the duct segments20ofFIGS. 1 and 2, though the symmetrical preform60ofFIG. 3would result in a duct segment20with the seam26located at the narrowest section of the duct segment20, i.e., the radially innermost portion of the duct10relative to the duct center18. Thus, each duct segment20can be formed from preforms60of different shapes, and the shape of the preform60can be modified to affect the angular seam location S for each duct segment20. In the embodiment illustrated inFIG. 2, the seams26are staggered so that the seam26of each duct segment20is located at an angular position S that is 180° away from the seams26of the adjoining duct segments20.

Preferably, at least one of the first and second ends62,64of each preform60are curved as shown inFIG. 3so that the first end62of one of the duct segments20can be engaged with and connected to the second end64of another one of the duct segments20without a gap between the duct segments20. According to one embodiment of the invention, at least one of the first and second ends62,64of each preform60is at least partially defined by a sinusoidal curve that is based on the following characteristics of the duct10and duct segments20: a number N of duct segments20connected to form the duct10, the angle B of articulation of the duct10, the duct diameter D, the bend radius R, the desired angular position S for the seam26of each of the duct segments20, the seam overlap LOL, and a desired deformation of the inlet and/or outlet16of the duct10. Possible deformations that can be formed in the duct segment20include bells and beads, as described below. For example, in one embodiment, the diameter D of the duct10is uniform throughout, and a length L of each preform60, measured as the distance between the first and second side edges66,68is equal to
D×π+LOL
where π is an irrational constant approximately equal to 3.1415. The first segment width W1is equal to

2⁢(R-D2)×sin⁡(B2⁢N),
and the second segment width W2is equal to

2⁢(R+D2)×sin⁡(B2⁢N).
When the diameters D1, D2are the same, i.e., equal to the diameter D, the curved first and second ends62,64are symmetric as shown inFIGS. 3 and 4, and one end62,64is described by the function

f⁡(x)=±D⁢⁢sin⁡(B2⁢N)⁡[R±0.5⁢⁢sin⁡(360⁢xD⁢⁢π+S)]
where the desired angular seam location S is expressed as an angle, the variable x is defined along the length L of the duct segment, and the function f(x) is measured perpendicular to the variable x. As shown inFIG. 4, multiple preforms60can be formed from a single thermoplastic laminate sheet58, and the preforms60can be configured in a nested arrangement on the sheet58to minimize wasted material.

There is shown inFIG. 5the flexible connector80that is used to connect the duct segments20to form the duct10according to one embodiment of the present invention. The flexible connector80is an elongate member, which defines first and second partially enclosed portions82,84that define first and second openings86,88respectively for receiving one of the ends62,64of one of the duct segments20. The first and second openings86,88are generally outwardly opposed to one another such that the duct segments20attached to the connector80extend therefrom in generally opposing directions. In the embodiment shown inFIG. 5, the connector80defines an elongate web90from which extend first and second flanges92,94that form the partially enclosed portions82,84. Either or both of the flanges92,94can define gaps96that increase the flexibility of the connector80. The gaps96can also extend through the web90, as illustrated by an alternative connector80aillustrated inFIG. 6, which provides separate webs90afor supporting individual flange tabs92a. Preferably, the connector80is attached to a duct segment20such that the first partially enclosed portion82receives one of the ends62,64of the duct segment20through the first opening86, and such that the gaps96are directed radially inward, or toward the passage12of the duct10, as shown inFIG. 7. Another alternative connector80bis shown inFIG. 8. The connector80bdefines two connected elongate tubes97,98each of which defines one of the openings86,88and one of the partially enclosed portions82,84.FIG. 9illustrates two duct segments20that are connected via a connector80. Preferably, the connector80holds the two segments20together and also hermetically seals the passage12of the duct10. The connector80can be glued in place. Alternatively, the connector80and/or the duct segments20can be heated until at least partially plasticized and consolidated to join the connector80to the duct segments20. Consolidation can be performed by pressing the connector80against the duct segments20manually or using an automated mechanism.

The connector80can define a uniform cross-sectional shape along its length, as shown inFIGS. 5–9, or the cross-sectional shape can vary along the length of the connector80, for example, to better accommodate the articulated configuration of the duct segments20joined by the connector80. The connector80shown inFIGS. 9A–9Dis elliptical to correspond to the shape of ends62,64of the two cylindrical duct segments20, as shown inFIG. 9D. The first and second flanges92,94of the connector80do not define gaps96, but the flanges92,94are angled relative to the web90. Further, the flanges92,94are non-uniform along the connector80. Specifically, the flanges92,94are perpendicular to the web90at one or more locations along the connector80, as shown inFIG. 9B, and vary from the perpendicular configuration by an angle A along the length of the connector80. For example, the angle A can vary to a maximum of B/2N as shown inFIG. 9C. Thus, the partially enclosed portions82,84define the angle A therebetween, and the angle A varies along the connector80such that the connector80is configured to receive the ends62,64of the duct segments20, which meet at an oblique angle, which can be equal to the angle A, as shown inFIG. 20to form the articulated duct10.

Preferably, the preform60is formed of a thermoplastic laminate that can be formed and consolidated uniformly and predictably so that features that are desired to be located at specific positions on the duct segment20can first be located on the preform60and, as the preform60is configured to form the duct segment20, the features are moved to the desired positions. For example,FIG. 10illustrates a layout of the preform60on the thermoplastic laminate sheet58. The perimeter of the preform60is demarcated by a line69, along which the preform60can be cut from the sheet58. The preform60includes spud holes70for attaching spuds71, or fittings, to the duct segment20, as shown inFIG. 11. The spuds71can be connected to the duct segment20by heating one or both of the spud71and the duct segment20and pressing the spud71into the spud hole70. Adhesives, mechanical fasteners such as screws, bolts, clips, or rivets, and other joining devices or methods can be also be used to fasten the spuds71to the duct segment20. Preferably, the spud holes70are bores defined by the preform60before the preform60is formed into the duct segment20, but the location of the spud holes70can alternatively be marked on the preform60and formed by drilling the duct segment20after the preform60has been formed into the duct segment20. Spud location marks72and/or spud orientation marks73are used to identify each spud hole70and/or indicate the desired position and orientation of the spud71. The spud location marks72can show part of the outline of the spud71that is to be connected to the duct segment20, e.g., the corners, so that the spud71can be quickly and accurately positioned on the duct segment20, preferably without the use of a special jig. If there is more than one orientation of the spud71in which the spud71corresponds to the location marks72, and a particular orientation of the spud71on the duct segment20is desired, the orientation marks73can also be provided. For example, each spud orientation mark73can include an arrow, as shown inFIG. 10, which indicates the desired directional orientation of the spud71that is to be connected to the duct segment20.

The preform60can include other holes and/or marks for additional features, such as detail holes74and detail marks75for receiving detail devices. The detail holes and marks74,75are similar to the spud holes70, location marks72, and orientation marks73. For example, two detail holes74can be provided for receiving bolts or other fasteners for connecting a bracket (not shown) or other detail device to the duct segment20. The detail marks75provide an easily identifiable indicator of the desired placement and orientation of the detail device, simplifying the assembly and installation of the duct segments20and the duct10. Duct orientation marks76can be used to indicate the desired orientation of the duct segment20or the duct10. For example, the duct orientation marks76can include an arrow that indicates which end62,64of the duct segment20should be connected to another duct segment20to form the duct10. The duct orientation marks76can also indicate the location of the inlet14and/or outlet16of the duct10formed from the duct segment20and, therefore, how the duct10should be positioned during installation in a duct system. Angular alignment marks77indicate the desired angular alignment of the duct segment20, for example, relative to a corresponding mark on another duct segment20. Thus, an operator assembling two duct segments20can align the angular alignment marks77on the duct segments20to achieve the correct angular alignment therebetween. Cuff marks78located near the side edges66,68of the preform60identify the location or length of a cuff79of the preform60or duct segment20, i.e., the portion of the preform60or duct segment20that is used to join the duct segment20to another duct segment20. For example, each cuff mark78can include a line parallel to the ends62,64of the duct segment20that indicates how much of the duct segment20should be inserted into another duct segment20for joining thereto. A seam overlap line69acan also be provided on the preform60to indicate the extent to which the side edges66,68should be overlapped to form the seam26, i.e., the length of the seam overlap LOL.

It is appreciated that holes, marks, and other details can be provided on the preform60for locating detail devices other than spuds, brackets, and cuffs. For example, the preform60can be marked with lines or other marks to indicate the position of features that are to be formed subsequently in the duct segment20, such as the desired location for a bell or bead for facilitating the connection of the duct segment20to another segment20or other device.FIG. 12illustrates the duct segment20in which a bead50has been formed. Beads formed on conventional ducts formed of thermoset materials are typically formed by adding plies to the duct to build up the bead shape. The bead50of the present invention can be formed by such a build-up process, but preferably the bead50is formed by heating the thermoplast duct segment20to a temperature at which it becomes plastic and urging a tool against the duct segment20to deform the duct segment radially outward and form the bead50. A discussion regarding the formation of duct features such as bells and beads is provided in U.S. application Ser. No. 10/215,780, titled “Post-Forming of Thermoplastic Ducts,” filed concurrently herewith, the entirety of which is incorporated by reference. The bead50, which extends radially outward, can be used to connect the duct segment20to another segment20or other device by inserting the beaded segment20into the other segment20or device. The formation of the bead50can also result in a recess51on the inner surface of the duct segment20. The recess51can be used to receive the bead50of another duct segment20for connecting the duct segments20. The calculated length L and/or widths W1, W2of the preform60can be adjusted for the formation of a bead50, bell, or other feature, which may affect the overall dimensions of the duct segment20. Additionally, marks can be provided for identifying the duct segment20or the duct10. For example, identifier marks (not shown) can be provided for indicating a model number, serial number, material type, and the like. One or all of the marks can correspond to data provided in manufacturing or assembly drawings.

The preform60can be cut from the sheet58using an automated oscillating knife, rotating blade, waterjet, scissors, or other cutting devices, and the holes70,74can be drilled or cut using a drill, punch, or other such devices. The lines and marks69,69a,72,73,75,76,77,78can be formed before, during, or after the preform60is cut from the sheet58. For example, in one embodiment, a numerically controlled ultrasonic knife with a pen capability is used to cut the preform60and form the lines and marks69,69a,72,73,75,76,77,78while the preform60is still flat.

According to one embodiment of the present invention, the duct10is formed by first forming the preform60from a flat sheet of thermoplastic laminate. The preform60is marked with construction data such as the preform demarcation lines69, the spud holes70, the spud location marks72, the spud orientation marks73, the detail holes74, the detail marks75, the orientation marks76, the angular alignment marks77, the cuff marks78, the seam overlap line69a, and the identification marks. Preferably, the preform60is cut according to a flat geometric pattern that generally corresponds to the desired shape of the duct segment20so that the preform60can be configured and consolidated to form the desired shape of the duct segment20without trimming the duct segment20after forming. For example, the preform60is cut along the demarcation lines69, and the spud holes70and detail holes74are drilled in the preform60. The preform60is configured, consolidated, and connected to one or more other duct segments20to form the continuous passage12therethrough using the elongate flexible connector80. Preferably, the duct segments20are connected such that a longitudinal axis of each duct segment20is angled relative to a longitudinal axis of the duct segment(s) that are connected thereto, and the duct segments20form an articulated duct10. The marks72,73,75,76,77,78can be used as guides during construction, for example, when connecting the duct segments20to one another or when connecting spuds71or other devices to the duct segments20.