JP2012201072A - Duct - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a duct capable of obtaining a desired shape without increasing man-hours, reducing operation sound of a fan and suppressing excessive heating of the duct.SOLUTION: The duct (1) of this embodiment is the duct (1) molded by adding a foaming agent to a thermoplastic resin, and has a rib (2) to be in a projected shape in the view from the inner side of the duct (1) and to be in a recessed shape in the view from the outer side of the duct (1).

Description

  The present invention relates to a duct made of a thermoplastic resin used as an exhaust duct used in combination with a cooling fan such as a projector, and more particularly to a duct obtained by foaming a resin by blow molding to obtain a desired shape.

  Currently, a projector is used that modulates a light beam emitted from a light source device according to image information to form image light, and enlarges and projects the image light. In such a projector, the light source device and the like generate heat during projection. Therefore, using air taken from outside the case, cooling the light source device, etc., using a fan to remove heat from the light source device, etc. via the exhaust duct, and releasing the heated air to the outside of the projector Is adopted.

  However, in the exhaust system using the cooling fan, the sound generated by the fan motor is also emitted to the outside of the projector. Since projectors are often used in places with low background noise, the sound of fans can be a factor that hinders user concentration and causes discomfort.

  In order to reduce the noise emitted from the outlet of the exhaust duct, for example, Patent Document 1 proposes a method of arranging a sound absorbing material inside the duct, and Patent Document 2 uses a laser on the duct wall. A method of providing pores is proposed.

  On the other hand, the air exhausted after cooling the light source device or the like has a high temperature, and there is a problem that the exhaust duct and the casing are heated.

JP-A-11-117761 JP 2009-281166 A

  However, in Patent Document 1, a sound absorbing material is bonded to create a duct, and in Patent Document 2, a laser hole is formed after molding. Therefore, the number of processes increases in any method, and various materials are used. It is necessary to prepare, and the regulation of the shape is large.

  The present invention has been made in view of the above circumstances, and a duct capable of obtaining a desired shape without increasing the number of man-hours, reducing operating noise of the fan, and suppressing excessive heating of the duct. provide.

In order to achieve this object, the present invention has the following features.
The duct according to the present invention is
A duct formed by adding a foaming agent to a thermoplastic resin,
It has a rib having a convex shape when viewed from the inside of the duct and a concave shape when viewed from the outside of the duct.

  According to the present invention, a desired shape can be obtained without increasing the number of man-hours, the operating noise of the fan can be reduced, and excessive heating of the duct can be suppressed.

It is the schematic of the duct of this embodiment. FIG. 2 is a schematic cross-sectional view of a surface parallel to the flow direction of exhaust fluid in the duct shown in FIG. 1. FIG. 2 is a schematic cross-sectional view of a surface perpendicular to the flow direction of exhaust fluid in the duct shown in FIG. 1. It is an expansion schematic diagram of the rib cross section shown in FIG. It is the schematic which shows the example which has arrange | positioned the pin type rib, (a) is sectional drawing perpendicular | vertical to the duct flow path which passes through a rib, (b) is sectional drawing parallel to the duct flow path which passes through PL. is there. It is the schematic which shows the example which has arranged the partition type | mold rib, (a) is sectional drawing perpendicular | vertical to the duct flow path which passes through a rib, (b) is sectional drawing parallel to the duct flow path which passes through PL. is there. It is a figure which shows the sound pressure measurement result of a duct exit.

  Hereinafter, the exhaust duct 1 of the present embodiment will be described in detail with reference to the accompanying drawings.

  As shown in FIG. 1, the exhaust duct 1 of the present embodiment has a spiral rib 2 on the wall surface. As shown in FIGS. 2 and 3, the rib 2 has a concave outer wall. The inner wall of the duct has a convex shape.

  The noise of the fan motor is guided to the outside of the housing through the exhaust duct 1. At that time, the sound waves come into contact with the duct inner wall rib surface 2a of FIG. 2 of the exhaust duct 1, so that the frequency of sound wave reflection increases and the sound pressure is attenuated. Further, the sound reduction effect can be obtained by contacting the ribs 2 and refracting the sound waves that interfere with other sound waves and cancel each other.

  Forming the rib 2 so as to extend in a spiral shape has an effect of preventing an abrupt change in direction of the exhaust fluid passing through the duct internal passage 4 and suppressing an increase in ventilation resistance.

  With respect to the flow direction of the exhaust fluid, if the rib attachment angle 5 formed by the tangent line of the duct inner wall rib surface 2a and the duct inner wall surface 3a shown in FIG. Is preferably 45 ° or less, more preferably 40 ° or less. On the other hand, when the rib attachment angle 5 is excessively small, the number of reflections of sound waves in the flow path is not sufficiently generated. Therefore, the rib attachment angle 5 is preferably 10 ° or more, and more preferably 20 ° or more. In addition, as shown in FIG. 4, the rib attachment angle 5 is measured at a portion where the inclination is maximum.

  The rib height 6 shown in FIG. 2 also greatly affects the ventilation resistance and the sound pressure reduction effect. The limit of the rib height 6 varies depending on the required exhaust flow rate and the cross-sectional area of the duct flow path, but when the width of the flow path excluding the rib 2 is 1, the rib height 6 is 1/20. It is preferably in the range of ˜1 / 3, more preferably in the range of 1/7 to ¼. When the rib height 6 is increased, the airflow resistance is increased, and when the rib height 6 is decreased, a sufficient sound reduction effect cannot be obtained.

  The high-temperature air that is guided to the outside of the housing by the fan through the exhaust duct conducts heat when coming into contact with the inner wall of the duct, and thus the duct may become hot when the projector is used for a long time. The concave rib 2b formed on the duct outer wall surface 3b has an effect of increasing the contact area between the air 7 outside the duct flow path and the duct wall, and promoting heat radiation on the duct outer wall.

  After adding a foaming agent to a polyolefin-based resin and kneading with an extruder, the resin is stored in an accumulator, and after a predetermined amount of resin is stored, the piston is extruded to divide the parison. A foam blow molding method for obtaining a desired shape by attaching to a mold is generally known. The foaming agent may be an inorganic physical foaming agent such as air, nitrogen gas, carbon dioxide gas or water, an organic organic physical foaming agent such as butane or hexane, or an inorganic chemical foaming agent typified by sodium bicarbonate. Any one of organic chemical foaming agents such as azodicarbonamide and dinitrosopentamethylenetetramine is used.

  The exhaust duct 1 of this embodiment is created by foam blow molding. The wall of the duct manufactured by blow molding is transferred to the mold shape and gives an uneven shape similar to the inner and outer walls, so it is possible to easily form spiral ribs on the inner and outer walls of the duct. No need to create a process.

  Further, by using blow molding, a duct having not only a straight pipe shape but also a bent shape can be easily expressed. In addition, since the direction change of exhaust fluid arises in a bending part, ventilation resistance increases, but the sound reduction effect also increases.

  In addition, since foam pressure is low in foam blow molding, a higher foaming ratio can be obtained than in injection molding. By making the wall surface of the exhaust duct 1 into a foam, a high sound absorption effect can be obtained by vibration of bubbles contained in the wall.

  Furthermore, by arranging fine air bubbles in the duct wall, a large number of air layers are formed, and the temperature boundary layer increases, so the thermal conductivity of the entire wall is reduced and the temperature rise of the duct is suppressed. Can do.

  In order to obtain the above-described noise suppression effect and temperature rise suppression effect, the duct expansion ratio is preferably 1.5 times or more, and more preferably 2 times or more.

  The expansion ratio described here represents a value obtained by dividing the apparent specific gravity of the resin pellet as the base material by the apparent specific gravity of the molded product. For example, if the apparent specific gravity of the base resin is 1 and the apparent specific gravity of the molded product is 0.5, the expansion ratio is doubled.

  In a resin having the same expansion ratio, the heat insulation effect increases monotonically as the average diameter of bubbles scattered inside the duct wall decreases. However, if the bubble diameter is suppressed, it is difficult to obtain a product with a high expansion ratio. In view of this point, the average bubble diameter of the product is preferably 20 μm to 130 μm, more preferably 30 to 110 μm.

  In the sound absorption generated in the duct wall, the small diameter bubbles are effective in reducing the sound power level of high frequency sound, and the large diameter bubbles are effective in reducing the sound power level of low frequency sound. Foam blow molding is influenced by resin draw-down, pre-blow, etc., and forms non-uniform bubbles. Therefore, it can be expected to be effective for sound reduction over a wide frequency range.

  In blow molding, in particular, when blowing molten resin to a mold, blow air is generally blown into the parison. Bubbles that are crushed by the pressure of air and have an elliptical shape are formed on the cross section of the duct wall. There are many.

  In foam blow molding, when the parison is attached to the split mold, blow air is blown into the parison, and the resin is pressed by the pressure inside the parison. The parison has a minor axis, and since the parison is generally stretched by its own weight, the parison tends to have a major axis in the direction of gravity acceleration.

  Therefore, the above-mentioned bubble diameter appeared by cutting the surface perpendicular to the direction of movement of the exhaust fluid inside the duct with a sharp blade at two locations on the two wall surfaces facing each other at both ends of the duct and the central portion of the exhaust passage. A line segment indicating the duct wall thickness is drawn for the cross section, and the lengths of the line segments existing in the bubbles divided by the cell walls are measured for all the bubbles intersecting the line segment, and the average value is obtained. . The average value is calculated by dividing the sum of the segment lengths divided above by the number of bubbles.

  As shown in FIG. 3, the exhaust duct 1 has a parting line (PL) 11 formed at a corner 9 facing each other instead of a side 10 formed by a cross section of the duct perpendicular to the direction in which the exhaust fluid flows. Has been.

  With this shape, even if spiral ribs are arranged on almost all duct wall surfaces except the parting line 11, the product can be removed from the mold.

  As the type of resin, polypropylene, polyethylene, or polystyrene resin is preferred because of its high degree of freedom in duct shape and foamability, but polypropylene or polystyrene that has excellent heat resistance in applications where exhaust is expected to be particularly hot. It is desirable to use

  Moreover, in the range which does not reduce a foaming ratio remarkably, you may add compounding agents, such as a coloring material, an antibacterial material, and a flame retardant, in the range which does not reduce a foaming ratio remarkably.

  A rib shape other than a spiral may be employed. For example, a pin-shaped rib 81 (a plurality of rod-shaped protrusions protruding inside the duct) as shown in FIG. 5 or a screen-type rib 82 (a plurality of plate-like protrusions protruding inside the duct) as shown in FIG. 6 is adopted. You can also

  Next, examples of the above-described embodiment will be described. However, the following examples are a part of examples, and are not limited to the following examples.

<Measurement of noise using duct>
A speaker was attached to one end of the duct to generate random noise, a microphone was placed on the other end, and the sound pressure at the duct outlet was measured. In the test, the sound pressure of the speaker was fixed at 42 dB or 62 dB, and the sound absorption performance was compared by replacing the duct. It should be noted that the exhaust channel length is 125 mm, the wall thickness is 1.5 mm on average, the cross section perpendicular to the exhaust direction is rectangular, the long cross section is 80 mm, and the short cross section is 50 mm. Used as a piece.

Example 1
Polypropylene as a main raw material, rib height of about 20 mm, rib attachment angle of 40 ° spiral rib (rib that is formed from one end of the duct to the other end and makes one round around the duct), expansion ratio of 2.7 times The duct which is is produced by foam blow molding. This duct is mainly made of PP resin mainly composed of WB140 manufactured by BOREALIS. In the sound pressure measurement test using this duct, the overall value at the duct outlet when the sound source sound pressure was 42 dB was 35.1 dB, and the overall value at the duct outlet when the sound source sound pressure was 62 dB was 56.2 dB.

(Comparative Example 1)
A non-foamed duct having a spiral rib having the same shape as that of Example 1 and having a rib height of about 20 mm and a rib mounting angle of 40 °, mainly made of polypropylene, was formed by blow molding. This duct is mainly made of PP resin mainly composed of WB140 manufactured by BOREALIS. In the sound pressure measurement test using this duct, the overall value at the duct outlet when the sound source sound pressure was 42 dB was 39.3 dB, and the overall value at the duct outlet when the sound source sound pressure was 62 dB was 59.1 dB.

(Comparative Example 2)
A duct made of polypropylene as a main material and having no ribs and having an expansion ratio of 2.7 times was prepared by foam blow molding. This duct is mainly made of PP resin mainly composed of WB140 manufactured by BOREALIS. In the sound pressure measurement test using this duct, the overall value at the duct outlet when the sound source sound pressure was set to 42 dB was 40.3 dB, and the overall value at the duct outlet when the sound source sound pressure was set to 62 dB was 60.0 dB.

(Comparative Example 3)
A non-foamed duct having no ribs made mainly of polypropylene was produced by blow molding. This duct is mainly made of PP resin mainly composed of WB140 manufactured by BOREALIS. In the sound pressure measurement test using this duct, the overall value at the duct outlet when the sound source sound pressure was 42 dB was 40.9 dB, and the overall value at the duct outlet when the sound source sound pressure was 62 dB was 60.7 dB.

  It was confirmed that the overall value was attenuated by foaming the resin and arranging the ribs. It was also found that the sound pressure attenuation tendency between the ducts was the same even when the sound source sound pressure was changed.

  FIG. 7 shows the test results when the sound source sound pressure is set to 42 dB. From FIG. 7, it can be confirmed that the sound pressure drop due to foaming appears remarkably in the frequency region of 800 Hz or less. For example, at a frequency of 500 Hz, Example 1 using a foamed resin is 7.9 dB, and Comparative Example 1 using a non-foamed resin is 21.1 dB. A sound pressure reduction of 13.2 dB was confirmed by foaming.

  By foaming, countless cells are generated in the duct wall, and the cell wall vibrates under the influence of sound pressure. At this time, the energy of sound is absorbed by the internal friction of the cell wall and the elasticity of the cell wall, and it is expected that the sound pressure is reduced in the low frequency region.

  Moreover, as shown in FIG. 7, the sound pressure reduction by arrange | positioning a spiral rib was confirmed notably in the frequency area | region of 5000 Hz or more. For example, comparing the presence or absence of ribs at a frequency of 5000 Hz, Example 1 with ribs is 29.5 dB, Comparative Example 2 without ribs is 37.2 dB, and the ribs can reduce the sound pressure by 7.7 dB. confirmed.

  This is because the air layer exists behind the ribs, and the entire wall tends to vibrate, and when the sound wave collides with the ribs, the entire wall including the ribs vibrates, resulting in a loss of internal energy. However, it is considered that the sound pressure is attenuated.

  In the high frequency region, since the mass of the cell wall is dominant over the sound energy, it is expected that the vibration of the cell wall does not occur and the sound pressure is not reduced due to foaming.

  The above-described embodiments and examples are preferred embodiments and examples of the present invention, and the scope of the present invention is not limited only to the above-described embodiments and examples, and does not depart from the gist of the present invention. Implementation in a form in which various changes are made in the range is possible.

1 exhaust duct 2 rib 2a duct inner wall rib surface 2b duct outer wall rib surface 3 duct wall surface 3a duct inner wall surface 3b duct outer wall surface 4 duct inner channel 5 rib mounting angle 6 rib height 7 duct channel outer air 8 rib other than spiral Shape 81 Pin type ribs 82 Screen type ribs 9 Corners 10 Sides 11 Parting line

Claims (2)

A duct formed by adding a foaming agent to a thermoplastic resin,
A duct having a rib having a convex shape when viewed from the inside of the duct and a concave shape when viewed from the outside of the duct.   The duct according to claim 1, wherein the rib has a spiral shape extending in a flow path direction of the duct.

Images