GB2498136A - Controlling spray booth ventilation - Google Patents

Abstract

A method of controlling airflow in a spray booth is disclosed. The method includes controlling input air handling equipment to provide a first predetermined airflow (108, figure 7) into the air input region, the predetermined airflow having a desired volumetric flow rate (110, figure 7), and controlling a plurality of air extraction units, so as to produce predetermined airflow velocity temperature distribution and predetermined air flow distribution in a work space. The method may comprise receiving measurement signals relating to airflow velocity and temperature, comparing these to desirable quantities and controlling heating and air extraction means accordingly.

Description

SPRAY BOOTHS

The present invention relates to spray booths.

BACKGROUND OF THE INVENTION

A spray booth is a structure that provides a ventilated, air filtered and temperature controlled S environment in which spraying activities such as painting and powder coating can take place. A spray booth is necessary for the safe execution of such activities, since the sprayed materials include solvents and particulate material that must not enter the atmosphere in large quantities. The particulate material that does not stick to the article being sprayed must be removed from the spraying area to ensure safe working conditions, and to manage environmental impact.

A spray booth also provides a controlled supply of filtered air that aids the spraying process and leads to higher quality finishes. In addition, it is necessary to heat sprayed materials in order to dry them (in a process known as baking), and the spray booth provides a controlled temperature environment in which such baking can be undertaken.

Spray booths are used in the wind turbine industry during the painting and finishing processes for sections of wind turbine towers. Since the tower sections can be many metres in length, the booth tends to be a long, relatively narrow design.

By way of example and explanation, one known tower spray booth is illustrated in Figure 1 of the accompanying drawings. The spray booth 1 comprises a roof portion 10 from which first and second end portions 12, 14 and first and second side portions 13, 15 extend to the ground, thereby forming a closed chamber, or work space, in which spraying can be carried out. The first end portion incorporates a closable access way (not shown for clarity) through which the tower sections (or other items to be sprayed) can enter and exit the work space.

A plenum 16 is formed adjacent an end region of the roof portion 10 by the provision of a filter element 18 substantially parallel to, and spaced from the inner surface of the end region of the roof portion 10. The plenum 16 may extend any desired distance along the roof portion 10 from the first end 12 to wars the second end 14 of the booth 1. The filter element 18 may extend across the whole of the roof portion 10, as illustrated, or may be provided across only a limited width. As will be described in more detail below, an input airflow 20 is supplied into the plenum 16, after which it passes through the filter 18 and forms an incoming air flow 22. Ideally the air flow 22 is uniform across the width of the booth.

The airflow 21 passes along the booth 1, and forms an outgoing air flow 24. This outgoing airflow 24 passes through an outgoing filter 23, into an extraction region 22, which provides an extracted airflow 42.

The input airflow 20 is provided by air handling equipment, such as that shown for illustrative purposes in Figure 2 of the accompanying drawings. The air handling equipment 26 of Figure 2 comprises input ducting 30 which guides air 28 into the equipment from the atmosphere. Afan unit 32 is provided for drawing in the air 28, and for moving the air via ducting 34 to a heater 36 which operates to heat the air to a desired temperature. The temperature controlled air 20 is then provided to the plenum 16 of the spray booth 1 via ducting 38.

Air extraction from the booth 1 is provided by air extraction equipment 40, such as that shown for illustrative purposes in Figure 3 of the accompanying drawings. The outgoing airflow 24 is drawn through ducting 44 by an extraction fan unit 46. The airflow passes through a further filtration unit 50 before exiting to atmosphere as the extracted airflow 42 via further ducting 52.

Figures 4 and 5 of the accompanying drawings illustrate plan and side views respectively of the booth 1 of Figure 1, showing the airflow therein. Air 20 is provided into the plenum 16 from which is exits as a filtered uniform airflow 21. The airflow 21 travels along the length of the booth 1 from the plenum 16 towards the second end 14 of the booth 1, forming a uniform outgoing airflow 24. The airflow 24 passes through the exit filter 23, and into the extraction region 22 for exit from the booth as an extracted airflow 42.

The spray booth 1 of Figure 1 and the air handling equipment 26, 40 of Figures 2 and 3 has been described by way of example and illustration only, and it will be readily appreciated that the design and construction of a spray booth can vary. For example, the input and output air handling equipment can be combined to reduce the number of fan units and reduce the heating requirements by using recirculation of air.

It will also be appreciated that the principles of the spray booth described above can be applied to a booth for the spraying of aircraft, or other large items other than wind turbine tower sections. Naturally, the specific design requirements of each application will determine the size and specification of the spray booth and the equipment, but the principles remain the same as for the booth described above.

Existing spray booth designs suitable for providing spraying environments for large items, particularly long items, suffer from a drawback that drying of the sprayed coating can take a significant amount of time due to the cooling characteristics of the airfiows provided.

It is, therefore, desirable to provide a solution to such drawbacks.

SUMMARY OF THE INVENTION

According to the present invention, there is provided a method for controlling a spray booth for providing a controlled environment for spraying of material, the spray booth comprising a work space having a longitudinal axis and a substantially planar floor, a first end portion, an air input region adjacent the first end portion, which air input region is arranged for introduction of a substantially uniform air flow into the work space, substantially parallel to the longitudinal axis of the work space, a second end portion, spaced from the first end portion, the second end portion defining therein an air extraction aperture, the air extraction aperture being arranged for extraction of air out of the work space, and an air extraction area external to the work space, and arranged for extraction of air through the air extraction aperture, the air extraction aperture being provided by a plurality of separate air extraction apertures, each of which has an associated air extraction area, and an associated air extraction unit operable to extract air from the aperture concerned, and including a filter element, for filtering air being extracted through the air extraction aperture concerned, the method comprising controlling input air handling equipment to provide a first predetermined airflow into the air input ducting, the predetermined airflow having a desired volumetric flow rate, and controlling the plurality of air extraction units, so as to produce predetermined airflow velocity temperature distribution and predetermined airflow distribution in the work space.

Such a method may further comprise controlling a heater unit for pioviding the air flow at the desired temperature.

Such a method may further comprise obtaining measurements indicative of at least one airflow velocity in the booth, and generating control signals for the air extraction units in dependence upon such measurements.

Generating such control signals for the air extraction units may comprise retrieving stored working parameters, comparing such retrieved working parameters with received measurements, and generating the control signals in dependence upon the result of such a comparison.

BRIEF DESCRIPTION OF THE DRAWINGS

S Figure 1 illustrates a known spray booth; Figures 2 and 3 illustrate known air handling equipment for the spray booth of Figure 1 Figures 4 and 5 illustrate plan and side views respectively of the booth of Figure 1, showing airflow therein; Figure 6 illustrates a plan view of a spray booth; Figure 7 illustrates an end view of a spray booth; Figure 8 is a schematic block diagram of a control; Figure 9 shows a schematic block diagram of a controller of the system of Figure 8; and Figure 10 is a flowchart of steps in a method embodying the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figure 6 illustrates a plan view of a spray booth 100, which is similar construction to the booth described above. A roof portion (not shown), first and second end portions 102 and 104, and first and second side portions 103 and 105 form an enclosed work space 111. A plenum 106 is provided adjacent one end region of the roof portion, and serves to direct an incoming airflow 110 into and along the length of the booth 100. Extraction area 120/121/122 is provided into which air from the work space 111 is drawn, through an exit filter 124/125/126. The extracted air is exhausted from the booth as exhaust airflows 130/131/132 into an output zone 128 to be expelled from the booth as airflow 135. This uniform airflow 110 is provided as described above during the spraying operation, and provides a filtered air stream that removes overspray away from the object being sprayed.

Figure 7 shows a side view of the booth 100 of Figure 6. The rear wall 104 of the workspace is inclined at angle ci to the vertical. In addition, the extraction filter provided in the wall 104 is divided into a number of separate sections. In the example shown in Figure 7, the filter is divided into first second and third filter sections 124, 125 and 126. The filter sections are arranged one above the other, and, in this embodiment extend across the width of the booth 100. Each filter section has an associated extraction area 120, 121, 122 into which extracted air is drawn. The extracted airflows 130, 131, 132 are then combined in an extraction zone 128 before expulsion from the booth as airflow 135. Each extraction area 120, 121, 122 has associated air extraction equipment, such as that described above, for extracting air form the area concerned.

It will be appreciated that the filter may be divided into any number of horizontal and/or vertical sections, and each may have an associated extraction area. Alternatively, sections may share extraction areas.

The splitting of the rear filter into a number of sections 124, 125, 126 and the setting of those filter sections at an angle off vertical results in a controllable airflow velocity profile across the booth 100. If the same airflow is extracted from each of the filter sections 124, 125, 126 then the angle at which the filter sections are set will determine the airflow profile in the booth 100. In the example shown in Figure 7, the first (lower) filter section 124 is positioned closest to the air inlet plenum 106 with the third (upper) filter section being furthest away from the plenum 106. This arrangement results in a lower airflow 112 along the floor of the booth 100 being faster than an intermediate airflow 113. The intermediate airflow 113 is itself faster than an upper airflow 114.

This airflow velocity profile can be further controlled by making use of individual control of the extraction areas 120, 121, 122. For example, the airflow extraction through the first extraction area 120 can be set to a higher level than that for the second and third extraction areas 121 and 122. In such a way the velocity of the lower airflow 112 can be increased relative to respective velocities of the intermediate and upper airflows. The lower extracted airflow 130 is then ata higher rate than the intermediate extracted airflow 131 and the upper extract airflow 132.

It is desirable to control the respective velocities and flow rates in such a manner, since during a spraying operation, overspray particulate material tends to accumulate towards the floor of the booth, since it falls due to gravity. Although the airflow in the booth is designed to retain this particulate material in the air so that it can be removed from the work space, it will tend to accumulate in the lower parts of the booth. Accordingly, it is desirable to increase the airflow, both in terms of velocity and volume flow rate, at the lower levels of the booth.

There are some further advantages of the division of the filter into a number of separate sections. Firstly, such division allows the filter sections to be replaced at different time intervals. For example, the lower filter section may require changing relatively frequently, for example monthly, due to the higher levels of particulate material with which it must deal.

The intermediate and upper filter sections may then need changing less frequently, for example six monthly and annually respectively. Division of the filter into separate sections enables more economic provision of filter assemblies, since the separate sections can be replaced at appropriate intervals, rather than at the shortest interval defined for the lower part of the filter.

Secondly, the division of the filter allows the upper airflow, which, as described above, is less contaminated with particulate material, to be recirculated into the incoming airflow supplied to the plenum, and hence to the booth. This recirculation cuts the amount of heat energy required for heating the incoming airflow, since the recirculated air is already at or near the desired temperature. Such a reduction in the heating requirement can substantially lower the cost of running the booth.

Figure 8 shows a schematic block diagram of a control system. The control system includes a controller 150 to which are connected a temperature measurement unit 152, and an airflow measurement unit 156.

The temperature measurement unit 152 receives signals indicative of temperature of the input airflow 153, and in positions in the booth 154, 155. These signals are provided by temperature sensors, and can be provided using wired or wireless data transfer techniques.

Figure 8 shows that the temperature measurement unit 152 receives such signals from two booth positions POS1 and POS2, but it will be appreciated that temperature measurement signals can be received from appropriate sensors at any number of positions in the booth.

The airflow measurement unit 156 receives signals indicative of air flow rates of the input air flow 153, and at selected positions 158, 159. These signals are provided by airflow sensors, and can be provided using wired or wireless data transfer techniques. Figure 10 shows that the airflow measurement unit 156 receives such signals from two sensors P051 and POS2, but it will be appreciated that any number of sensors may be provided in the booth 100.

The controller 150 receives these measurement signals, either by receiving transmissions from the temperature and airflow measurement unit 152 and 156, or by polling those units at regular or other intervals. For example, the controller may poll the measurement unit 152 and 156 when the booth is moved from a spraying mode of operation to a drying (or baking) mode of operation, in order to obtain current measurements on which to base control of the airflow and temperature.

One possible example of the controller 15001 Figure 8 is shown in schematic form in Figure 9, and comprises a processor 160, an input interface 162, an output interface 164, a storage device 166, and a user interface 168. The processor 160 is connected to receive measurement signals from the measurement unit 152 and 156 of Figure 8, via the input interface 162. The processor is connected to output control signals to the booth equipment via the output interface 164. The interface standards used by the input interface 162 and the output interface 164 are chosen to be suitable for the sensors and controlled equipment, and may be wired or wireless in nature. The processor 160 is operable to store and access data in the storage device 166. The user interface 168 provides user access to the controller 160 and may be a direct interface, or may be a remote interface. The controller may be combined with an overall booth control system, or may be provided by such a system. The control scheme embodying the present invention may be implemented in software, hardware, or a combination of the two.

An example operation of the controller 150 will now be described with reference to the flowchart of a method embodying the present invention shown in Figure 10, as well as to the block diagrams of Figure 8 and 9. The processor 160 receives (step 200) measurement signals from the measurement units 152 and 156 via the input interface 162. The processor retrieves (step 202) working parameter information from the storage device 166. The working parameter information is set by the user or by the commissioner of the booth, and relates to the desired temperature distribution and airflow requirements of the booth in any given mode of operation of the booth.

The processor 160 compares (step 204) the retrieved working parameters with the received measurement signals, and generates (step 206) control signals from the results of the comparison. The control signals are the output (step 208) to the relevant equipment via the output interface 164. In one embodiment, the control signal relating to temperature is used to control a heater unit which heats the incoming airflow.

The control signals are used to control the airflow extraction equipment for each of the extraction areas 120, 121, 122, to provide the desired velocity profile across the booth 100.

The control system is thereby able to control the airflow rate and temperature, so as to produce a desired temperature and air flow distribution.

Although aspects of the invention have been described with reference to the embodiments shown in the accompanying drawings, it is to be understood that the invention is not limited to the precise embodiment shown and that various changes and modifications may be effected without further inventive skill and effort.

Claims (1)

1. <claim-text>CLAIMS: A method for controlling a spray booth for providing a controlled environment for spraying of material, the booth comprising a substantially planar floor for supporting an object to be sprayed, a roof portion located substantially above, and spaced apart from, the floor, a first end portion which extends from a first end region of the roof portion to the floor, a second end portion which extends from a second end region of the roof to the floor and which is spaced apart from the first end portion, the second end portion defining therein an air extraction aperture, first and second side portions which extend from the roof portion to the floor and from the first end portion to the second end portion, the roof portion, floor, first and second end portions and first and second side portions thereby defining a work space therebetween, the air extraction aperture being arranged for extraction ot air out of the workspace, and the workspace having a longitudinal axis which extends substantially parallel to the floor, an air input region adjacent the first end portion, which air input region is arranged for introduction of a substantially uniform air flow into the work space, substantially parallel to the longitudinal axis of the work space, and an air extraction area external to the workspace, and arranged for extraction of air through the air extraction aperture, the air extraction aperture being provided by a plurality of separate air extraction apertures, each of which has an associated air extraction area, wherein each air extraction aperture has associated air extraction equipment operable to extract air from the aperture concerned at a respective rate, and wherein each air extraction aperture includes a filter element, for filtering air being extracted through the air extraction aperture concerned, the method comprising: controlling input air handling equipment to provide a first predetermined airflow into the air input region, the predetermined airflow having a desired volumetric flow rate; and controlling the plurality of air extraction units, so as to produce predetermined airflow velocity temperature distribution and predetermined airflow distribution in the work space.</claim-text> <claim-text>2. A method as claimed in claim 10, further comprising controlling a heater unit for providing the air flow at the desired temperature.</claim-text> <claim-text>3. A method as claimed in claim 10 or 11, further comprising obtaining measurements indicative of at least one airflow velocity in the booth, and generating control signals for the air extraction units in dependence upon such measurements.</claim-text> <claim-text>4. A method as claimed in 11, wherein generating control signals for the air extraction units comprises retrieving stored working parameters, comparing such retrieved working parameters with received measurements, and generating the control signals in dependence upon the result of such a comparison.</claim-text> <claim-text>5. A method as claimed in any one of claims 10 to 13, further comprising causing at least a portion of extracted air to be recirculated to the air input region.</claim-text> <claim-text>6. A method for controlling a spray booth substantially as hereinbefore described with reference to, and as shown in, Figure 10 of the accompanying drawings.</claim-text>