JPS6284239A - Friction type blade assembly - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a grill assembly for use in ventilation systems.

Conventional grills generally include a rectangular metal frame and a plurality of parallel transverse blades rotatably mounted to the frame. The blades are generally frictionally fixed in a particular angular position relative to the frame and airflow.

Some examples of such typical grills are disclosed in U.S. Pat. No. 4,103,601. Conventional devices for obtaining a tight friction fit between a blade and a frame may have one of two drawbacks. Firstly, the air ducts (conduits) used e.g.
If the length of the blades increases, such as when the blades become wider, the frictional torque becomes insufficient to withstand the pressure of the air flowing through the duct or the torque exerted on the blades. Second, the cost of manufacturing and installing equipment to obtain a proper friction fit is high.

It would therefore be desirable to provide a grill blade assembly that provides a tight friction fit and is simple and inexpensive to manufacture and install.

The present invention is a friction blade assembly for a grill for use in conjunction with a ventilation system, the assembly having a pair of spaced apart, parallel thermoplastic support bars 8, each having a The bars extend on one side at right angles and in mutual alignment. the assembly comprises a plurality of coplanar impact bars, each impact bar having a uniformly shaped outer surface having a generally cylindrical profile and integrally molded as part of the support bar; further comprising a plurality of blades disposed between the bars, each blade defining first and second ends and having a uniform cross-sectional shape and dimension along the longitudinal direction; defining a generally streamlined tube, the tube defining a first edge, a second edge and an interior space, the interior space at the first edge being about 27 mm;
It has a substantially circular cross section over an arc of 0°, and the diameter of the circular cross section is 0.05 to 0.1 m larger than the diameter of the impact rod.
m (0,002 to 0.004 inches), and the blades are respectively connected to the impact frame by inserting the impact rod into the interior space with a first edge of the blade. A friction fit between each impact frame and each blade is obtained by rotatably mounted on the blades.
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One object of the invention is to provide a device with reduced diameter blades to achieve a friction fit between the blades and the frame of a ventilation grille, reducing the thickness of the blades and maximizing the open area to the air flow. It's about giving.

Another object of the present invention is to provide a ceremonial blade assembly that is inexpensive and easy to manufacture and install.

Hereinafter, preferred embodiments of the present invention will be described with reference to the attached page 0.

Referring to the first factor and FIG.
A representative grill assembly (18) is shown including two. Grille Frame +121 is patented in U.S. Patent No. 4,103,
Exemplary frame members (161) may be joined at the corners in any conventional manner, as shown in FIGS. 1-5 of the '601 issue.
A recess is defined within which the blade assembly can be supported. Preferably, such a depression αgJl
-1 The cross-sectional shape may be trapezoidal or may have another shape. The blade assembly includes a plurality of rotatable, laterally parallel air deflection blades Q51. The angular position of each blade a9 during operation is fixed with respect to the frame member αe.

From the direction shown by arrow A at the entrance to grill assembly H to the direction shown by arrow B at the exit of grill assembly QQI
The direction of the airflow in the I56 direction is changed by the blade (15). The angle through which the air is deflected is generally less than 20''.

The third factor is reference element 6, and the friction type blade assembly u41 is g
ti6 and second thermoplastic support bars (20, 24)
including. The first support bar (4) defines an axis C208), which axis defines a longitudinal axis. Further, the support bar 4 has an axis M
It defines a plurality of coplanar abutment frames (20b) extending substantially perpendicularly to one side of L and integrally molded with the axis <20a). Each abutment frame (20b) defines a uniformly shaped outer surface with a generally cylindrical profile (see FIGS. 6 and 7). Each impact frame (20b) has approximately the same length and diameter as the other impact frames (20b). Each collision frame (20b) defines a tapered free end (20C) with a 6° free end C2OC.
) is conveniently conical, but other shapes are also acceptable.

The support bar may further define a longitudinal axial extension (20d) that facilitates positioning the friction blade assembly (14J) within the grill frame member.
Can be used for The bar prisoner is in the collision frame (20b
) can define a surface (2Of) where it connects to the axis (20a).

In another embodiment, the collision frame (20b) is the collision frame (20b).
20b) can define a groove device (20e) extending along the surface of the blade d!1 (see FIG. 8).
Cleaning, painting or any other treatment on the 9 or blade assembly may be effective. During operations of this type, fluid may accumulate inside the blade (19). When the blade assembly I is later subjected to heat, such fluid may evaporate and become pressurized. Pressure may cause damage to blade assembly α4.Groove device (20
e), the fluid and steam can flow inside the blade 7)s
It will not come off and cause any damage.

The shaft (20a) and the extension (20d) are part of the frame member a.
It may be convenient to give it a trapezoidal cross section so that it can be joined in a dovetail manner to the recess α of e (see Fig. 6), or it may be convenient to give it a trapezoidal cross section so that it can be joined in a dovetail manner to the recess α of e, or if it seems to fit snugly with the recess 0, other shapes may be used. The shaft (20a) has sufficient thickness so that the surface (2Of) extends outside the recess. With this configuration, the receiver that keeps the end of the blade u4 from coming into contact with the frame member tte can work from the surface (20f) by facing it. In addition, when cleaning, painting, or disposing of the blade assembly α, liquid can escape unobstructed by the frame member (16).

The blade (the second end of the IQ is the 20th thermoplastic support bar 04) is rotatably mounted. The second support bar (2 pulls) is substantially equal to the first support bar (a).
Define. The abutment part (24b) is inserted into the space (22a) at the second end of each blade (19).
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Multiple blades (1!19 or thermoplastic support bars (2)
It is rotatably installed during the installation. Each blade 0
9 defines first and second ends and has a uniform cross-sectional shape and dimensions along its length; each blade a9 is slotted to define a generally streamlined tube; ,6
゜The shape of each blade is almost flat or curved),
Or it may be of any shape known to those skilled in the art.

Each blade Q has a first edge (15a) and a second edge (15a).
b) and defining an internal space (2). First edge (1
The inner surface of 5a) defines a space part <22a),
The portion (22a) has a substantially circular cross-section over an arc of approximately 27 (1').
) 0.05~0.1 stop (0,002~0.
004 inches) is desirable. The blade haze may define at least one outer surface groove (FIG. 4, 23a) along its length.

Such an external groove (23a) is an internal ridge (23b)
f form. Grooves (23a) and ridges (23b) like this
) formation gives additional stiffness and strength to the blade haze.

Blade Q! The part of space (sha) at the same end of 9 (
22a), the blade t1 [
] is rotatably attached to the contact portion (20b, 24b).

The relative diameters of the portion (Z2a) and the contact portion and the portion (22a)
) Q] 270" arc ensures that the first edge (
15a) Make it work. The fifth factor is a close-up view of the end of blade Q51 that is about to fit onto the impact portion. The dotted line diagram shows the position of the blade (1510) when the impact portion is fully inserted into the blade 09.

Blade TT! 19 are mounted and adjusted so that each defines an angle about the axis at which the air is to be deflected.

The width of the blade (18), ie the distance between the first edge (15a) and the second edge (15b), corresponds approximately to the spacing of the abutments. The small width is 12.4 to 25.7 dragons (0,490
-1.010 inches). In rare cases, the blade (19) may be rotated to a vertical position, so that the friction torque that causes the grille assembly α (3F may be closed) to approximately this extreme level.
In order to be sufficient to withstand the torque created by the air pressure in the space, the diameter of the abutting portion should be 0.05-0. ) is desirable. More extreme conditions must be met when using a blade wider than 25.4 mm (1.0 in.);
Additional frictional forces can be generated by reducing the diameter of a) or by increasing the diameter of the abutment. The width of the blade 09 used in conjunction with an abutment of a particular diameter must be such that sufficient spring-like tightening against the blade (19) or the abutment remains in effect. limited by the fact that

The diameter of the impact part is used for the blade (19)! It is limited both by the thickness of the material used in the grille (16) and the amount of free area required to allow air to flow through the grille (18). The maximum free area for air to flow through the grille aQ is obtained when the blades 0!5) are oriented parallel to the airflow entering the grille aql. When blade a9 is in such an angular position as Ql, the air is not deflected by blade a9 and there is no change in the direction of the airflow. When the blade haze is tilted relative to the frame haze, the area of the grille Ql available to the airflow is smaller. It is also possible that airflow is restricted below a predetermined acceptable level.

If the diameter of the impact rod is too large, the blade will be too thick. In this case, even if the blades (151) are parallel to the airflow, the thickness of the blades may result in insufficient airflow through the grille (A).Thus, thinner blades may be used. Therefore, the diameter of the impact rod must be small enough to provide a satisfactory airflow even at the required angular orientation of the blade (19).

The area used for airflow through the grille is the area of the blade Q.
It is further reduced by the thickness of the material used to form 9. The thickness of this material must be sufficient for the blade (19) to be easily fabricated and to tighten well around the impact rod. Therefore, the combination of the diameter of the impingement rod and the material thickness must define an overall thickness of the blade that will flow a sufficient amount of air through the grille (IQ) at the required angular orientation of the blade cod.

It is desirable that the relationship between the diameter of the impact rod, the thickness of the blade material, and the area of the grille is expressed by the following formula: However,! = Ni blade length d; diameter of impact rod t = Ni blade material thickness A = grill area n = number of blades If a longer blade is used, the torque due to the larger air pressure ζ will be applied to the blade V). By increasing the length of the impact rod, the generated friction torque can be increased. Therefore, in order to counteract the pneumatic torque, a longer impact rod may be used. Preferably, the blade length is 61cr
n (24 inches) or less, and the length of the impact rod is less than or equal to 25.4i+i+ (1,0 inches), excluding the length of the truncated conical end.

Blade Q! 9 g: $ Support bar (20,2
4) provides support during that time. The open friction of the blade (19) and its associated impact rod (20b, 24b) is sufficient to prevent rotation of the blade a9 from the predetermined required angular displacement It-) relative to the frame αe. Furthermore, the friction is not so great as to prevent the angular position from being adjusted or changed by hand or the like as necessary. Furthermore, the friction is not large enough to impair the ease of assembling the friction type blade assembly I.

In use, the friction blade assembly α4 is inserted into the grill frame α. This is a support bar (20°24
) by sliding it into the recess α frame of the frame member aυ. The grill assembly is then installed into the desired duct or opening. The angular direction of the T6 blade 9 relative to the grill α can be adjusted to the desired position by hand. The frictional blade assembly I thus operates to deflect the airflow as required.

There are several factors that have contributed to the success of this invention. First, the material of the present invention and the surface finish of the material can be selected and treated to provide suitable frictional resistance against pneumatic torque. Thermoplastic polyester (support bar gloss.

24] and the rolled aluminum sheet metal (for blade 15) have a clean surface finish, have a sufficient coefficient of static friction against each other, and provide an acceptable amount of frictional resistance. The material was found to be suitable for It is desirable that the thermoplastic polyester contains 2 to 30% glass fiber component for durability and strength. POCAN B Sai -4225 or g4
A material such as POCAN B $F 4225 or =4235 has a coefficient of static friction of 0.11 against a lapped copper coating.
~0.13. The coefficient of static friction of aluminum against mild steel is 0.5 to 0.7. Because both thermoplastic polyester and aluminum are inexpensive, 1 strong, tenacious, durable, corrosion resistant, and lightweight, the frictional blade assembly according to the present invention has similar properties 7a-1 assembly B and layering. is easy. Other blade materials such as sheet steel, plastic or nylon may also be used.

Second. The shape and internal space of the impact rods (20b, 24b) (
The cylindrical portion (22a) provides the maximum amount of surface area for generating frictional forces. Thirdly, the impact rod (20b).

24b) and the part (22a) of the space (the diameter of the impact rod (zob) is 0 than the diameter of the part (22a)
．． 05~0.1mm (0,002~0.004 inch)
However, it is also important to create sufficient frictional force for ease of assembly and long life. m4, the arc of the circular portion (22a) extending over approximately 270° also forms the first edge (15a) of the blade a.
This is important because it can act like a spring on the impact rod (2ob, 24b). This provides sufficient radial force.

A corresponding frictional force is created between the impact rod and the inner surface of the first edge (15a). Fifth, the relationship between the diameter d of the impact rod (20b) and the width of the blade a9 is the distance M between the impact rods.
'a--It is important to adjust the required frictional force and maintain an appropriate grill maximum free area when changing. Sixth, the relationship between impact rod length and blade length can be used in adjusting the required frictional force when using different blade lengths. Seventh, the relationship between the impact rod diameter and the material thickness of the blade (19) is important for adjusting the strength of the spring-like action of the blade a5 on the impact rod (2ob, z4b). Eighth, the ratio between the maximum free area of the grill and the overall area of the grill is important to ensure sufficient airflow through the grill Q[1] when positioning the blade Q9 in the required angular orientation.

Referring to another embodiment shown in No. 90 and No. 1 O, the blade (one angular position) for the frame mackerel can be permanently fixed. Such an embodiment is advantageous for use in return air grills. be.

The first edge (15a) of the blade a-shaped has first and second thermoplastic support bars (20, 24), as in the previous embodiment illustrated in FIG. installed on
,ru. In the embodiments of Figures 9■ and 1O.

The second edge (15b) of the blade haze is attached to third and fourth thermoplastic support bars (26, 28), respectively. Advantageously, the support bars (26, 28) have substantially the same shape as the support bars (20, 24).

Like the bars (20, 24), the bars (26, 28) have shafts,
Defining a shaft extension and an impact rod.

The inner surface of the second edge (15b) of each blade (I9) defines a portion (22b) of the interior space, said portion approximately 2
It has a nearly circular cross section over an arc of 70@. As in the case of the first edge (15a), the diameter of said circular cross section is 0.05-0.
．． It is advantageous to reduce the diameter by 1 mm (0.002 to 0.004 inch). This relationship between 28) and the diameter of the impact rod ensures that the second edge (15b) never oscillates relative to the impact rod and allows the use of standard components. Advantageously, all support bars (20, 24, 26, 28) are of substantially the same shape. The first edge support bar (20, 24)
) and the second edge support bar (26, 28), the manufacturing cost is lower than that in the case where the second edge support bar (26, 28) is different. force) force <2
, 28) M does not necessarily have to be the same shape as the bar (20, 24) at all points. The two bars (26, 28) have a shape similar to the bars (20, 24), and the impact rods of the bars (26, 28) have dimensions that allow them to be inserted into the portion (22b) of the internal space (2z). and the blade (19) or bar (20, 24)
) is sufficient to prevent rotation around the impact rod.

Frame member ae defines a second recess within which the bar (26, 28) is supported. As in the case of the recess a barrel, the cross section of the recess (7) is preferably trapezoidal in order to provide a dovetail connection of the axes of the bars (26, 28).

In order to define a particular angle at which the blade (I51) should be directed, the impact rods of the bars (26, 28) are connected to the impact rods (20b, 2
4b). selected n,
Therefore, the axial extension of the bars (26, 28) would have to be truncated.

In another embodiment, it is also possible to use a support bar C'4) of the thread 2, which defines an impact bar, which serves only as a pivot axis for the blade a9. In such an embodiment, the first bar slender blade (19) is sufficient to hold it at the required angle. The second bar 24) is a blade tt
! It does not help prevent rotation of 9.

All of the above factors allow the fabrication of grills of specific dimensions and capacities that meet many requirements.

The quality of the blade assembly is maintained at a low cost, durable, and simple to manufacture and mount. Frictional blade assemblies can thus be ordered and manufactured as needed, and can also be conveniently stocked by stacking blades and frame members to standard lengths. The blade is economically formed from rolled cedar strip aluminum with a 6.degree. By using a blade with a straight end in a blade assembly according to the present invention, the difficult and expensive process of cutting and notching the hollow roll-formed blade blank can be avoided. Additionally, cutting the blade and assembling the blade assembly and grill can be automated to reduce the amount of manual labor. This automated assembly procedure speeds up production and allows for faster response to orders.

Another embodiment of the blade cross section is shown in FIG. two spaced apart portions n5 extending from a semi-cylindrical portion r1;
A blade assembly is shown having side members (34, 34) that are shaped. The central portions (36, 36) of the side portions are narrowed so that the free edge of one side wall is folded over the other side wall.

The foregoing is a description of preferred embodiments of the invention, given by way of example only. The present invention has not been described, and has some specific features.
However, the present invention is not limited to the above, and various modifications can be made within the scope of the claims set forth above.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway perspective view of one embodiment of the present invention when used in a whole grill assembly, FIG. 2 is a cross-sectional view taken along line 2-2 in FIG. 1, and the third factor is Disassembly of the friction-type blade oil assembly according to the present invention. 4th Q is a sectional view of an embodiment of the air deflection blade, and FIG. A close-up perspective view of FIG. 6 is 6- in FIG.
6 is a sectional view taken along line 6, FIG. 7 is a sectional view taken along line 7-7 of FIG.
The cause is a plan view of an alternative embodiment of the present invention, FIG.
A sectional view taken along line 9-9 in the figure. Fig. 11 shows the cross section U01O of another embodiment...
・Grill assembly 12...Grill frame 14...Blade assembly 15...
Curved blade 15a...first edge 15b.
...Second edge 16...Frame member 1
8...Indentation...Support bar
20a...shaft 20b...impingement rod 2
2... Internal space 23a... Groove
23b...ridge 24...support bar
211a... Shaft 24b... Impact rod

Claims (1)

Claims: (1) A friction-type blade assembly for a grill used in conjunction with a ventilation system: each defining an axis defining a longitudinal axis and substantially on one side of the axis; first and second thermoplastic support bars having a plurality of perpendicularly extending coplanar impact bars, each of said impact bars having a uniform generally cylindrical shape of approximately the same length; a support bar having outer surfaces of approximately equal diameter, said impact bars being integrally formed as part of said support bar, said impact bars being arranged in spaced apart parallel relationship such that said impact bars face each other; positioned between the bars, each defining a first and second end and an upper and lower side, defining a generally streamlined tube having a uniform longitudinal cross-sectional shape and dimensions; a plurality of blades, the tube defining a first edge, a second edge and an interior space and formed from a one-piece sheet metal of relatively thin material, the sheet metal being folded to form one edge; is fixed to the underside of the other, and the interior space at the first edge has a generally circular cross-section over an arc of about 270°, the diameter of the circular cross-section being less than the diameter of the impact rod. 0.05~0
．． 1 mm (0.002 to 0.004 inch) smaller, and the first ends of the blades are respectively reduced by inserting the impingement rod into the interior space at the first edge of the tube. rotatably mounted on the impingement rod, thereby providing a frictional fit between the impingement rod and each of the blades, such that the blades resist frictional resistance against the first and second bars. a frictional blade assembly capable of being rotated and further defining a longitudinal rib system formed opposite each other along the longitudinal direction of each of said sides. 2. The friction blade assembly of claim 1, wherein the second thermoplastic support bar is substantially the same as the first support bar. (3) The friction blade assembly of claim 2, wherein the blade has a width greater than 12.4 mm (0.490 inches) and less than 25.7 mm (1.010 inches). (4) each impact bar defines a tapered free end;
A friction type blade assembly according to claim (3). (5) The length of the blade is 610 mm (24 inches)
or less, and the length of the impact rod, excluding the length of the tapered free end, is 25.4 mm (1.0 inch) or less, according to claim (4). blade assembly. 6. The frictional blade assembly of claim 5, wherein the thermoplastic support bar defines an axial extension extending from the axial axis. (7) Claim No. 6, wherein the thermoplastic material is a thermoplastic polyester containing 20 to 30% glass fiber.
) The friction type blade assembly described in item 2. (8) The friction type blade assembly according to claim (7), wherein the blade is roll-formed from aluminum sheet metal. (9) The friction type blade assembly according to claim (8), wherein the diameter of the impact rod and the thickness of the aluminum have the following relationship with respect to the overall area of the grill: 0.15 <(l(d+2t)(n+1))/A<0.4
where l=blade length d=impingement rod diameter t=blade material thickness A=grill area n=number of blades (10) said rib arrangement extends along the longitudinal direction of said blade on both sides; A friction blade assembly according to claim 1, including at least one outer groove and inner ridge formation, the formations on opposite sides defining a space therebetween. (11) The surface of each of the impact bars defines a groove arrangement extending along the surface.
Friction type blade assembly as described in section. (12) The friction blade assembly of claim (6), wherein the extrusion of the shaft defines a trapezoidal cross section. 13. The friction blade assembly of claim 4, wherein the tapered free end defines a frustoconical shape. (14) the interior space at the second edge of the blade has a generally circular cross-section over an arc of about 270 degrees and includes third and fourth thermoplastic support bars; and each of the fourth bars has a plurality of coplanar impingement bars defining an axis defining a longitudinal axis and extending substantially perpendicularly to one side of the axis; Each of the impact bars of the fourth bar is inserted into the interior space at the second edge of the respective blade at the first end of the blade, and each of the impact bars of the fourth bar is inserted into the interior space at the second edge of the respective blade. A frictional blade assembly according to claim 1, wherein the frictional blade assembly is inserted at the second end of the blade into the internal space at the second edge of the respective blade. (15) Each of the impingement rods of the third and fourth bars defines a circular cross-section, the diameter of the circular cross-sectional portion of the interior space at the second edge of the blade being 0.
Claim 14 having a diameter greater by 0.05 to 0.1 mm (0.002 to 0.004 inch)
Friction type blade assembly as described in section. (16) Claim No. 15, wherein the second, third and fourth bars have substantially the same shape as the first bar.
Friction type blade assembly as described in section. (17) A grill assembly for use in conjunction with a ventilation system and including a friction blade assembly and a grill frame arrangement, each defining an axis defining a longitudinal axis and having a substantially first and second thermoplastic support bars having a plurality of coplanar impact rods extending at right angles to each other, each of said impact rods having a uniform cylindrical shape of approximately the same length; of approximately equal diameter with smooth outer surfaces and defining a tapered free end, said impingement bars being integrally formed as part of said support bar such that said impingement bars face each other. support bars arranged in spaced apart parallel relationship;
a generally streamlined tube disposed between the bars, each defining first and second ends and upper and lower sides, having a uniform longitudinal cross-sectional shape and dimensions; defining a plurality of blades, the tube defining a first edge, a second edge and an interior space and formed from a unitary sheet metal of relatively thin material, the sheet metal being folded to form one plate; an edge is fixed to the lower side of the other, and the first
The internal space at the edge of the bar has a generally circular cross-section over an arc of about 270°, the diameter of the circular cross-section being 0.05-0.1 mm (0.002-0.0 mm) smaller than the diameter of the impact bar.
．． 0.004 inch) smaller than the first
The first ends of the blades are each rotatably attached to the impact rod by inserting the impact rod into the internal space at the edge of the impact rod, thereby connecting the impact rod and the respective blade. a frictional fit is obtained between the blades so that the blades can be rotated against frictional resistance relative to the first and second bars, and further opposite each other along the longitudinal direction of each side. A grill assembly comprising: a blade defining a longitudinal rib arrangement formed by the blade assembly; (18) Claim 17, wherein the second thermoplastic support bar has substantially the same shape as the first support bar.
The grill assembly described in section. (19) the frame device defines a first recess configured to receive the frictional blade assembly;
A grill assembly according to claim (18). (20) The shaft and the first recess define a trapezoidal cross section, whereby the support bar can be dovetailed to the first recess.
) The grill assembly described in section 2. (21) The grill of claim 20, wherein the shaft extends outwardly of the recess, thereby defining a gap between the blade and the grill frame device. assembly. (22) the interior space at the second edge of the blade has a generally circular cross-section over an arc of about 270 degrees and includes third and fourth thermoplastic support bars; Each of the fourth bars has a plurality of coplanar impact bars defining an axis defining a longitudinal axis and extending substantially perpendicularly to one side of the axis; Each of the impact rods is inserted at the first end of the blade into the interior space at the second edge of the respective blade, and each of the impact rods of the fourth bar is inserted into the interior space at the second edge of the respective blade. 18. A grille assembly as claimed in claim 17, wherein the grille assembly is inserted into the interior space at the second edge of the respective blade at the second end of the grille. (23) the frame device defines first and second recesses, the first recess being adapted to receive the first and second support bars, and the second recess defining the first and second recesses; 23. A grille assembly as claimed in claim 22, adapted to receive third and fourth support bars. (24) the second, third and fourth support bars have substantially the same shape as the first support bar;
24. The grill assembly of claim 23, wherein the and second recesses define a trapezoidal cross-section such that the support bar is tabtailed to the first and second recesses. (25) A blade for use in a ventilation grill comprising a thermoplastic support bar having a plurality of coplanar cylindrical impact bars defining first and second ends and extending longitudinally defining a generally streamlined tube of uniform cross-sectional shape and dimensions along the length of the tube, the tube defining a first edge, a second edge and an interior space, and formed from a unitary sheet metal of relatively thin material. molded, the sheet metal is folded so that one sheet edge is secured to the underside of the other, and the interior space at the first edge has a generally circular cross-section over an arc of about 270°; The diameter of the circular cross section is 0.0 smaller than the diameter of the impact rod.
the first edge of the blade by inserting the impingement rod into the interior space at the first edge of the tube by 5-0.1 mm (0.002-0.004 inch).
are adapted to be rotatably attached to said impact rod, thereby providing a frictional fit between said impact rod and said blade, and further to be attached to each other along the longitudinal direction of each said side surface. Blades defining opposingly formed longitudinal rib systems.