SYSTEM FOR IMPROVED POWDER COATING OF DUCT FITTINGS

AND PROCESS FOR SAME

FIELD OF THE INVENTION

The present invention relates to a system for an improved powder coating of duct

fittings and a process for powder coating of duct fittings using the said system.

PRIOR ART

The existing technique for the application of powder coating to the internal walls of a duct fitting

involves the following steps:

Stepl: Duct fittings are placed inside an oven for pre-heating to the desired temperature suitable for

the application of powder coating.

Step 2: After the pre-heating phase has ended, the duct fittings are removed from the oven for the

application of powder coating via conventional electrostatic spraying method.

Step 3: The duct fittings are then returned to the oven to allow baking and curing of the powder

coating.

Steps 2 and 3 above are repeated for each subsequent layer of powder coating applied and the duct

fittings need to be removed repeatedly from the oven for the powder coating process resulting in

long processing times and low production output efficiency.

PROBLEMS TO BE SOLVED BY THE INVENTION

Practitioners of the existing technique described above face the following problems:

1) Uneven powder coating as subsequent coatings are harder to apply due to

electrostaticity of powder coat.

2) Inefficient use of powder coating, as the spraying is carried out in an

open confined area.

3) Heat loss due to opening and closing of oven, resulting in higher energy

costs and more energy consumption in order to raise the oven's temperature every

time the duct fitting is placed back into the oven.

4) Long processing time due to movement in and out of the oven, application of

powder coating and baking and curing taking place in sequenced steps.

In the existing technique, the duct fitting is held stationary and the spray head

has to be rotated along the longitudinal axis of the duct to ensure the powder is evenly

sprayed onto the internal walls of the duct. The application of a rotary spray with forward and

backward movement fulfilling the above requirement would no doubt be uneven and inefficient.

The inventors have studied the problems and propose placing the duct fitting in a

purpose-made oven to heat the duct fitting and which is continuously rotated so as

to facilitate the application of powder coating onto the internal walls of the duct fitting

and then for curing of powder coating.

It is therefore desirable to have a system which can apply one or more layers of

powder coating onto the internal walls of a duct fitting to obtain a more uniform

and improved coating finish and effective thickness without repeated movements in and out

of an oven. It is also desirable for such a system to reduce loss of heat

energy and powder coating and reduce production time for powder coating a duct

fitting. These and other subsidiary objects of the invention would be apparent from a

reading of the description of the embodiments of the invention.

MEANS FOR SOLVING THE PROBLEM

A first object of the invention is a system for improved powder coating of

the internal walls of a duct fitting, the duct fitting having a first and

second end, the system comprising:-

an oven, the oven comprising a base and a removable top insulated cover

with an oven cavity formed therein;

duct attachment means;

a drive mechanism;

heating means; and

an automatic powder coating sprayer;

wherein the first end and second end of the duct fitting is attached to each

end of the oven by the attachment means and placed within the oven cavity,

the automatic powder coating sprayer applying a first powder coating to the

internal walls of the said duct fitting, which is continuously rotated by the

drive mechanism, so that a first powder coating is applied evenly throughout the

internal walls of the said duct fitting, while being heated continuously by the

heating means, so that the first powder coating is baked and cured, followed by

application and heating of additional layers of powder coating to the internal walls

of the duct fitting, so that the each additional layer of powder coating is baked

and cured, until the duct fitting has one or more layers of powder coating

resulting in an improved powder coating for the duct fitting.

Preferably the system has an oven comprising of base and a top insulated

cover forming an oven cavity wherein the top insulated cover is removable to

allow the duct fitting to be placed onto the base of the oven, said duct

fitting secured within the oven cavity by the duct attachment means.

Preferably, the system has a drive mechanism consisting of an electric motor,

clamp down wheel and at least two traction wheels, for rotation of the duct fitting,

the first and second end of which are attached to the duct attachment means.

Preferably the system has duct attachment means which consisting of a collar

for each end of the duct fitting, to secure the duct fitting within the cavity

where the temperature is more even and also act to cut off powder coating from

reaching the top insulated cover and base of the oven and the external surface of the

duct.

Alternatively, the system has duct attachment means which consist of a grip

for each end of the duct fitting, to secure the duct fitting onto the oven.

Preferably, the system has heating means consisting of a plurality of electrical

elements in the oven.

Alternatively, the system has heating means consisting of a plurality of gas

burners in the oven.

Preferably the system has a PLC controller to control the drive mechanism, to start

and control movement of the automatic powder coating sprayer and to regulate

the baking and curing temperature throughout the application, baking and curing of

powder coatings on the internal walls of the duct fittings.

Preferably the baking temperature of the oven is from 250 ⁰ C to 350 ⁰ C.

Preferably the curing temperature range of the oven is from 270 ⁰ C to

300 ⁰ C.

Preferably, the controller has a plurality of temperature sensors which turns on or turns off the

electric heaters to regulate the baking and curing temperature range and by releasing or

keeping heat within the oven and also to improve the circulation of heat within

the oven.

Preferably, the system has a plurality of hot flue gas inlets and outlets wherein

at slow starting temperature, the temperature sensors will sense the oven

temperature is below the baking and curing temperature range, the controller

will open the inlet flue gas damper and close the outlet flue gas damper to

raise the temperature in the oven and if the oven temperature is over the

baking and curing temperature range, the controller will open the inlet flue gas

damper and close the outlet flue gas damper to lower the temperature in the

oven.

Preferably the system further comprises a high temperature fan and hot air/gas suction

duct for re-circulation of hot air from within the oven and back into the

ends of the oven so that all parts of the oven can be maintained at an

even baking and curing temperature range.

Preferably, the system has an automatic powder coating sprayer having a spray

head, said sprayer mounted on a set of guide rails, laid parallel to the

horizontal axis of the duct fitting, the spray head movable by the electric motor

of the drive mechanism, along the length of the internal walls of the duct fitting

to spray powder coating onto the entire internal walls of the duct fitting.

Preferably, the system has an automatic powder coating sprayer which will be

activated by the controller and move into the internal of the duct to perform

spraying of powder coating when the temperature of the oven is within the

baking temperature range.

Preferably the system further comprising an oven frame and a pulley system to

open the oven for monitoring of the duct fitting and for mounting the duct attachment

means.

Preferably the oven frame has an adjustable fixing bracket on the oven frame,

said adjustable fitting bracket fitted with clamp down wheel.

Preferably the pulley system is fitted to the oven frame and consists of fixed

pulleys, with steel cables attached at one end to the clamp down wheels and at

the other end attached to a counter weight block.

Preferably the rotation speed of the duct fittings is from 6 rpm to 1440

rpm.

A second object of the invention is for an improved powder coating

process for the internal walls of a duct fitting, using the system for

improved powder coating of the internal walls of a duct fitting, comprising

these steps :-

attaching a first and second end of the duct fitting to duct attachment

means;

loading and enclosing the duct fitting complete with the end attachments in an

oven cavity of an oven;

using the heating means to heat the duct fitting until the temperature

reaches baking temperature range;

whereupon the automatic powder coating sprayer will move into the

oven and along the horizontal axis of the internal wall of the duct fitting;

said drive mechanism rotating the duct fitting so that the sprayer will

spray a first layer of powder coating evenly onto all areas of the internal

wall of the duct fitting;

said powder coating being heated continuously by the heating means so

that the first layer of powder coating is baked and cured, followed by application and

heating of additional layers of powder coating to the internal walls of the duct

fitting, so that each additional layer of powder coating is baked and cured, until

the duct fitting has one or more layers of powder coating resulting in an

improved powder coating for the duct fitting.

Preferably the process further comprise a step of

clamping the duct attachment means to the duct fitting, said duct

attachment means held by an adjustable fixing bracket on the oven frame,

said adjustable fitting bracket fitted with clamp down wheel so that when the

duct fitting is rotated, said clamp down wheel will position the rotation of the

duct attachment means so that the duct fitting is rotated along the same axis.

Preferably the process comprise the additional steps of

controlling the heat inside the oven cavity to ensure a consistent and

stable operating environment for the powder coating process, while the powder

coating is baked and cured to form a first layer on the internal walls of

the duct fitting, followed by additional layers of powder coating, by turning on or turning

off the electrical power supply to one or more of the electrical heater elements or by regulating

the hot flue gas supply and exhaust, depending on the size of the oven,

opening the inlet flue gas damper and closing the flue gas outlet damper

when the temperature is below the baking and curing range,

closing the inlet flue gas damper and opening the flue gas outlet damper

when the temperature is over the baking and curing range, and

re-circulating the hot air or flue gas during the entire heating, baking and curing

process.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a side view showing the construction of essential parts of an example of a system for

powder coating a duct fitting according to an embodiment of the present invention.

Fig. 2 is a front view of the same system.

EMBODIMENTS OF THE INVENTION

The present invention will now be described in detail with reference to the accompanying drawings

showing the preferred embodiment.

Fig. 1 is a side view showing the construction of essential parts of an example of a system

for powder coating of a duct fitting. Fig. 2 is a front view of the same

system. The system has an oven frame (4) to which an oven (5) is attached.

The oven (5) comprises a removable top insulated cover (7) and a base piece (13)

which forms an oven cavity (14) where the duct fitting (8) is loaded. The duct fitting is not

limited to a straight configuration. This system also includes a drive mechanism that rotates the

duct fitting (8) inside the oven cavity (14) along its longitudinal axis and an automatic sprayer

(20) that performs the spraying of powder coating onto the internal walls of the duct fitting (8)

which is placed inside the oven cavity (14). The drive mechanism also have the capability to

rotate duct fitting of curved and angled configurations. The automatic sprayer (20) includes the spray

head (15) which travels into and out of the oven cavity (14).

The drive mechanism includes the duct attachment piece (9) that is fastened to the duct fitting (8)

to facilitate rotation. One end of this duct attachment piece (9) extends from the side of the

oven (5) into the oven cavity (14). As shown in Fig. 1, there are two duct attachment pieces (9).

The first and second duct attachment pieces (9) extend from the opposite sides of the oven

(5) into the oven cavity (14). The spray head (15) of the automatic sprayer (20) moves pass the

end of the first duct attachment (9) into the interior of the duct fitting (8) within the

oven cavity (14). Mounted onto the oven frame (4) are traction wheels (11) and clamp-down wheels

(6) whose axes are aligned in parallel to the longitudinal axis of the duct attachment pieces (9). The

external circumferential surfaces of the traction wheels (11) and clamp-down wheels (6) are in

contact with the external circumferential surfaces of the duct attachment pieces (9). There is a total

of one pair of traction wheels (11) whose axes are aligned on the same horizontal plane. These

traction wheels (11) are located at the bottom of the duct attachment pieces (9) and in contact with

the external circumferential surfaces of the duct attachment pieces (9), supporting them above.

The traction wheels (11) are coupled to the drive mechanism. The drive mechanism's electric

motor (19) is mounted onto the oven frame (4) and this electric motor's (19) output gear shaft is

wound with a chain-link (17). The electric motor (19) is coupled to the traction wheel (11) through

the chain-link (17). The fixing wheel for chain-link (16) mounted on the oven frame (4) serves to

tighten the chain-link (17) such that the electric motor (19) can drive the traction wheels (11) via the

chain-link (17) which in turn allows the traction wheels (11) to rotate the duct attachment pieces (9)

through frictional forces.

Inside the oven (5), electric heating elements (12) are fitted inside the oven cavity (14) to facilitate

heating and these electric heating elements (12) are connected to the control panel (18). The control

panel (18), which is mounted on the oven frame (4), controls the switching on and off of electric

heating elements (12) and also dynamically adjusts the power output of electric heating element (12)

to achieve the desired oven temperature. For bigger ovens, hot flue gas from LPG/LNG burner is

used for heating instead of electric heating elements. In this case, the control of oven temperature

is also by control panel. The control will close the inlet flue gas damper (29) on the inlet flue gas

duct (24) and open the outlet flue gas damper (30) on the exhaust flue gas duct (25) when the oven

temperature is too high. When the oven temperature is too low, the control panel will open the inlet

flue gas damper (29) and close the outlet flue gas damper (30). In both electric heating and flue gas

heating, the oven cavity (14) temperature is made more even by circulating the hot air or flue gas

through a hot air/gas suction duct (26) through a high temperature fan (23) and blow back the hot

air/gas back into the oven through the hot air/gas return duct (27). The temperature inside the oven

cavity (14) can be controlled within 500°C but based on actual implementation, the characteristics of

the powder coating material has limited the oven cavity (14) temperature to 350°C. The oven (5)

includes the base piece (13) of the oven and the top insulated cover (7) of the oven.

The process for an improved powder coating for the internal wall of a duct

fitting involves these main steps:

Step 1 : Load the duct fitting into the oven, mounting the duct fitting onto the oven with

the first end and second end of the duct fitting attached to the first and

second duct attachment pieces. The duct attachment pieces rests on the traction

wheels. The rotational speed is then set. The duct fitting is therefore rotating

inside the oven, with the turning of the traction wheels, which is driven by the

electric motor (19). At the same time, the clamp-down wheels will hold the duct

attachment piece in place. The duct fitting is then heated up as it rotates along its

longitudinal axis.

Step 2: While allowing the continuously heated duct fitting to remain rotating inside the oven,

the automatic sprayer is moved along or parallel to the longitudinal axis of the

interior of the duct fitting. The automatic sprayer applies the powder coating by spraying

onto the internal wall of the duct fitting.

Step 3: After the completion of the spraying process, the duct fitting is allowed to remain inside the

oven for the dwell time to elapse so that the powder coating could bake and cure.

For the application of subsequent powder coats, Step 2 is repeated after the completion of Step 3 and

this process is iterated depending on the number of coats to be applied. At the end of the entire

coating process, the duct fitting is removed from the oven for cooling down.

When performing Step 2, the rotational speed of the duct fitting is adjustable within the range from 6

- 1440 rpm to ensure that powder is evenly sprayed onto the internal wall of the duct fittings.

Depending on the size of the oven, the temperature control is achieved by a PLC controller

switching on/off the electrical heater elements or by PLC controller to regulate the hot flue gas

supply and exhaust.

Before carrying out Step 1 , the top insulated cover of the oven (7) needs to be lifted up to allow the

duct fitting (8) to be loaded onto the oven (5), after which the top insulated cover of the oven (7)

is lowered down and closed. Both ends of the duct fitting (8) are fastened with the duct attachment

piece (9). The electric heating element (12) can then be switched on to heat up the oven cavity (14).

The electric heating elements (12) are installed inside the base piece of the oven (13) and these

electric heating elements (12) are located close to the duct fitting (8). When the electric heating

elements (12) heats up the oven cavity (14), the duct fitting (8) is rotated by the duct attachment

pieces (9) and as a result the duct fitting (8) is evenly heated up. When the temperature within the

oven cavity (14) reaches the desired set-point value, the spray head (15) of the automatic sprayer

(20) is activated to move into the duct fitting (8). The spray head (15) then begins to perform

spraying of the powder coating onto the internal walls of the duct fitting (8). hi the process of the

spraying, the duct fitting (8) remains rotated by the duct attachment pieces (9) and results in the

powder being evenly coated onto the internal walls of the duct fitting (8). While the spray head

(15) is performing the spraying process, the automatic sprayer (20) needs to move along or parallel

to the longitudinal axis of the duct fitting (8). To facilitate this, a set of guide rails for the automatic

sprayer (21) are installed aligned in parallel to the longitudinal axis of the duct attachment piece (9).

The automatic sprayer (20) is mounted onto these guide rails (21) and as the automatic sprayer

(20) moves along the guide rails (21) driven by the mechanised screw (22), the spray head (15)

moves along or parallel to the duct fitting's (8) longitudinal axis into the interior of the duct fitting

(8).

To prevent the displacement and misalignment of the duct attachment pieces (9) while they are in

rotation, the clamp-down wheels (6) are fitted to press down on the external circumferential surfaces

of the duct attachment pieces (9). As shown on Fig. 2, fixing brackets for the clamp-down wheels

(10) are fitted on the oven frame (4) to both sides of the duct attachment pieces (9) and the

clamp-down wheels (6) are fitted to these fixing brackets (10).

Fixed pulleys (1) are fitted to the oven frame (4) and these are fitted with steel cables (2). One end of

these steel cables (2) is attached to the fixing brackets for the clamp-down wheels (6) while the other

end is attached to the counterweight block (3). As a result of the traction effect in the steel cables (2),

the position of clamp-down wheels (6) can be adjusted to suit the different dimension of the duct

attachment pieces (9), and consequently different diameters of duct fittings can be fitted

into the oven.

Before powder coating is applied, the internal wall of the duct fitting is first heated up with the

duct fitting rotating on its longitudinal axis. After the spraying of powder coating onto the internal

wall of the duct fitting is completed, it shall remain rotated and heated inside the oven to allow for

the dwell time to elapse so that the powder coating could be baked and cured.

The system for a duct fitting with improved powder coating includes the supporting frame

of the oven and the main body of the oven. The main body of the oven is an enclosure that

could accommodate the duct fitting and it includes all parts of the rotational drive mechanism that

rotates the duct fitting on its longitudinal axis and the automatic sprayer that performs the

spraying of powder coating onto the duct fitting's internal walls.

The automatic sprayer mentioned herein consists of a spray gun head that moves into and

out of the oven along its longitudinal axis while the rotational drive mechanism includes the

customized duct attachment pieces that are fastened to the duct fitting such that one end of each

duct attachment piece is extended into the oven. Fitted to the oven frame are traction wheels and

clamp-down wheels whose axes are oriented in parallel to that of the duct attachment pieces. The

external circumferential surfaces of the traction wheels and the clamp-down wheels are in contact

with the external circumferential surfaces of the duct attachment pieces. The traction wheel is

coupled to the power drive mechanism which consisted of an electric motor mounted on the oven

frame that is coupled to the traction wheel by a chain-link that is wound onto its output gear shaft.

At the end of each duct attachment piece, there is an adjustable fixing bracket on the oven frame

from which the clamp-down wheel is attached. At the top of the oven frame, there is a pulley system

that consisted of steel cables with one end attached to the clamp-down wheel fixing bracket and the

other end attached to a counterweight block.

Mounted on the oven frame is a pair of traction wheels whose axes are aligned on the same

horizontal plane. These traction wheels are located below the duct attachment pieces and in contact

with the latter's external circumferential surfaces, supporting them above.

Each end of the attachment piece is covered by an insulated cap. On the cap nearer to the spray

gun is an opening for the sprayer to access into the inner part of the duct.

When compared to existing processing techniques, the invention described above has several merits

as detailed below:

In the course of actual implementation, with the duct attachment pieces fastened to the duct fitting

and the entire assembly placed inside the oven, the duct fitting will rotate together with the

attachment pieces during operation. While the automatic sprayer performs the spraying of powder

coating onto the internal walls of the duct fitting, the fact that the duct fitting still remains inside

the continuously heated oven enclosure will ensure that a consistent and stable operating

environment so that the powder coating process is maintained. This also meant that spraying and

curing can be completed in a single step without the hassle of bringing the duct fitting into and out

of the oven repeatedly, cutting down on processing time and improving the production output

efficiency.

Heating of the oven can be done by means of electric heaters installed within the chamber of the

oven, i.e., the space formed by the outside of the duct fitting, the attachment pieces and the oven

body. However for bigger ducts, a bigger oven is required and consequently the heat needed for

baking and curing is by introducing hot flue gas from burning of LPG or LNG.

As the spraying process is performed while the duct fitting is rotating, the internal wall of the duct

fitting is evenly powder coated thus improving the quality of the coated product.

The rotation of the duct fitting also enables the temperature to be more even. In addition, a

recirculation system will suck hot air/hot gas from the chamber of the oven and blow back to the 2

ends of the oven.

In the configuration described above, it is found rotating a duct fitting is simpler to attain instead of

a rotational mechanism to be fitted onto the spray gun head. The inventor has greatly simplified the

design and installation of this customized powder coating equipment.

Although an embodiment of the invention have been described, it should be apparent, however,

that various modifications, rearrangements, substitutions alterations and adaptations to those

embodiments may occur to persons skilled in the art with the attainment of some or all of the

advantages of the present invention. Accordingly, it should be clearly understood that the present

invention is not intended to be limited by the particular features and structures hereinbefore

described and depicted in the accompanying drawings. It is therefore intended to cover all such

modifications, alterations and adaptations without departing from the scope and spirit of the present

invention as defined by the appended claims.

ADVANTAGEOUS EFFECTS OF THE INVENTION

The use of a continuously heated oven throughout the stages of the powder coating

process will ensure that a consistent and stable operating environment so that spraying and

curing can be completed in a single step without the hassle of bringing the duct fitting into and

out of the oven repeatedly, cutting down on processing time and improving production output

efficiency.

As the spraying process is performed while the duct fitting is rotating, the internal wall of the duct

fitting is evenly powder coated thus improving the quality of the coated product.

The spraying of layers of powder coating onto the internal walls of a duct fitting

while enclosed inside the continuously heated oven would also reduce energy

consumption and powder coating since the duct fitting remains inside the oven throughout

the process.