1. Field of the Invention
The invention generally relates to apparatus for abrasive blasting and is specifically directed to a silencer system for reducing noise during blowdown operation.
2. Discussion of the Prior Art
Blast pot system are well known in the abrasive blasting industry wherein particulate abrasives are released under pressure against various surfaces in surface preparation applications. It has long been important to depressurize the pressure vessel or blast pot during times of non-use, for periodically replenishing the abrasive material in the vessel or for routine maintenance. The depressurization of blast pots involves first shutting down the system pressure and then releasing the pressure in the vessel through a port commonly referred to as a blowdown port. Typically, this generates a high volume of air and creates with it a loud noise lever, sometimes as high as 127 dB or higher at 100 psig, which is typical during the initial blowdown procedure.
While it is not necessary to reduce this noise level, it is desirable to do so. In addition, particularly when the blast pot is full of particulate abrasive matter during blowdown, the exhausted air contains abrasive particles which can be destructive.
It is, therefore, desirable to reduce the level of noise and contain the destructive flow of particulate matter during blowdown.
Several systems have been designed to provide noise control. One design utilizes a small cylindrical porous element with external wire mesh reinforcement. All of which are encased in a metal housing with two slotted exhaust ports located 180 degrees from each other. The element can be replaced or cleaned by removing a pipe plug at the end. While this design does suppress noise, the porous element can accumulate dust and “clog”. In addition, the design is such that the abrasive particles that are entrained in the airstream will rebound off the pipe plug and destructively strike the element. In addition, because of the flow of the destructive particles this design inherently has a short life span in use. In order to prolong life, daily cleaning is require, which is not realistic in the working environment. As a result, end users will usually remove the system once it is damaged. A further drawback to this system is that the slotted port on the side of the housing will direct exhaust air and fugitive particles horizontally. This could blow dust and particles onto anyone near the exhaust.
In another system, the airflow is exhausted through a large porous (small pores) element encased by perforated metal. This design offers decent noise suppression with good airflow. However, the design can trap dust and quickly become more restrictive.
Other examples offer the similar styles that place a porous type element or mesh in the direct or rebound path of the exhaust compressed air near the expansion point.
The subject invention is directed to an air blast depressurizing system that will provide safer, less destructive, and quieter “blowdown” for depressurizing the blast pot or vessel in abrasive blasting operations. The silencer system of the invention comprises a two stage blowdown system that will allow thru-flow exhaust. The first stage is an expansion chamber sufficiently sized to act as an acoustic filter for octave band above a certain point. This acoustic chamber is created by significantly reducing port upstream and downstream of the acoustic volume. The ratio of the expansion volume diameter to the port diameter is typically in the range of 5:2 or more. The second stage is a through flow silencer or muffler subsystem which is also an expansion chamber and is constructed of specially perforated metal surrounded by porous material which by is an acoustic absorbing material. Both chambers serve to reduce and suppress the untreated exhaust noise. Wear is addressed through the double expansion. First is through the expansion chamber with restrictors upstream and downstream of the volume. These restrictors are sized to reduce the air flow and minimize entrained abrasive particles while causing a minimal increase in blowdown times. Second is through a specially designed muffler. This muffler is sized to expand and slow the compressed airflow. At the exhaust end of the muffler is a removable urethane lined pipe cap to resist the impact wear and minimize the rebound energy of striking particles. Exhaust slots divert the exhaust air horizontally towards the inside of the exhaust shroud which further reduces the particle velocity and diverts the exhaust flow safely downward.
In its broadest sense, the silencer system of the subject invention includes an initial restrictor in communication with a blast pot vessel. The restrictor controls the flow of pressurized air from the vessel into a first expansion chamber. The outlet of the expansion chamber is in communication with a reducer, which typically includes an opening about the same size as the restrictor. Thus air entering and exhausting from expansion chamber is not further pressurized. Typically, the reducer outlet is in communication with a shut-off valve, which may be manually controlled or automatic, as will be described herein. It should also be noted that the shut-off valve may be upstream or downstream of the reducer as a matter of choice. The outlet of the reducer/shut-off valve is introduced into a muffler system, which includes an exhaust path and, where desired, a deflector for absorbing and/or deflecting abrasive particles which may be evacuated from the blast pot during blowdown.
As diagrammatically illustrated in
A typical blast pot system is shown
In order to assure complete depressurization, the blowdown procedure is followed. Initially, the supply pressure to the blast pot is shut down. This will close the supply pressure in the pop-up valve line 32 and permit the pop-up valve 34 to drop to the open position shown in
Prior to opening the blaster, the blowdown procedure is next followed. Specifically, the shutoff valve 16 (
The restrictor 10 is in communication with an expansion chamber 12, which is in line with the reducer 14. The expansion chamber provides an initial silencing function. The reducer 14 typically has an inside diameter 40 which is similar to or larger than the inside diameter 38 of the restrictor to maintain pressure equalization as the air passes through the expansion chamber. The flow from the reducer 14 is in line with the muffler assembly 18. The air passes through the muffler body 47 and the exhaust port(s) 20. Where desired, a urethane deflector, or the like, 22 may be inserted into the airflow to capture and/or deflect stray abrasive particles which may be in the air flow.
The system of
In the example shown in
It should be noted that the design of the shut off valve is a matter of choice, for both the manual and the automated version of the system, and well within the purview of those who are skilled in the art.
The blowdown silencer system to the subject invention is a two stage blowdown system that will allow “thru-flow” exhaust. The first stage is provided by the expansion chamber 12 sufficiently sized to act as an acoustic filter for octave band above a certain point. This acoustic chamber is created by significantly reducing port of the acoustic volume upstream via the restrictor 10 and downstream via the reducer 14. As better shown in
Typically, during blowdown some of the abrasive in the blast pot will be exhausted with the escaping air through restrictor 10. The wear caused by this is addressed through the double expansion provided by the expansion chamber 12 and the muffler 18. First is through the expansion chamber with restrictors upstream and downstream of the volume. These restrictors are sized to reduce the air flow and minimize entrained abrasive particles while causing a minimal increase in blowdown times. Second is through the muffler system. The muffler chamber 50 is sized to expand and slow the compressed airflow passing through the reducer. At exhaust end 52 of the muffler is a removable urethane lined insert of deflector 22 in the muffler cap 54 to resist the impact wear and minimize the rebound energy of striking particles. Exhaust slots 56 divert the exhaust air horizontally towards the inside of the exhaust shroud 58 which further reduces the particle velocity and diverts the exhaust flow safely downward through the exhaust ports 20.
As best shown in
In the embodiment of
The reducer insert 14 is placed inside the flex conduit 44. It will be understood by those who are skilled in the art that the flex conduit 42 may be replaced by a rigid conduit when the manual shut-off mechanism 16A is used, or for other applications where the shut-off does not require pinching the conduit to a closed position.
The flex conduit 44 is connected to the muffler intake end cap 70 for directing the air flow into the interior chamber 50 of the second expansion chamber or muffler subsystem 18. In one embodiment, the outer wall 74 of the muffler 18 is a rigid, closed tube, as shown in
A detailed exploded view of the muffler subassembly 18 is shown in
The silencer system of the subject invention provides apparatus for reducing the noise level of the blowdown operation as well as capturing and/or redirecting abrasive particles which may be in the airstream. In some cases, the noise level of 127 dB at the blowdown outlet of the vessel has been reduced to 120 dB at the outlet of the first expansion chamber 12 and less than 110 dB at the outlet ports 20 of the muffler subassembly.
While certain features and embodiments of the invention have been described in detail herein, it should be understood that the invention encompasses all modifications and enhancements within the scope and spirit of the following claims.
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Number | Date | Country | |
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20120202407 A1 | Aug 2012 | US |