Painting
Content
Automatic Painting System
Abstract
The aim of this project is to minimize the processes and production cost in a
spray line. The painting operation is the bottleneck point in modular furniture industries.
For minimize the wastage of the paint by avoiding overspray painting on the article and
improved the quality of the coating by using work study methodology and RTA method.
Both are widely used to produce articles as per customer’s demands. The sequencing is
an important factor in powder coating industries. For resolved the sequencing problem in
favour of minimizing the total cost and keeping uniform usage of each part and cost
model is presented. To get best alternative between work study and RTA method, a
comparison is done, concerning sequencing problem. This investigation suggests best
sequence of the process and method. It gives continued consumption of parts as well as
reducing cycle time which helps for higher production and cost saving.
Introduction
A paint spraying system has a conveyor line for carrying different sized
workpieces through a spray booth past a plurality of sprayers. Each sprayer is selectively
operated in accordance with a program element carried by the conveyor in conjunction
with each workpiece to be operated upon. Operation of the sprayers is controlled by a
series of timers each designed so that, when conditioned and activated, it will operate the
selected sprayer for a different predetermined period of time. The workpieces are
arranged on the conveyor in different series whereby the workpieces in each series are to
be sprayed for the same period of time. Program elements are arranged on either end of
each series so as to selectively condition and de-condition the timer that operates the
sprayer for the desired period. Additional program elements are mounted on the conveyor
next to each workpiece to 'be sprayed for selectively activating the conditioned timer and
sprayer.
This project relates to manufacturing systems of the type wherein manufacturing
operations are selectively performed on workpieces automatically under program control
as the workpieces are carried through a work station by a conveyor.
In the past, many manufacturing systems have been devised for automating portions or all
of a production line wherein workpieces are moved by some form of a conveyor through
a work station. At the work station, a manufacturing operation is performed on each work
piece and this operation may range from the simple task of repetitively performing the
same operation on identical workpieces, as each one passes through the station, to the
more complex tasks of performing different operations on different sized workpieces for
different periods of time as they pass through the work station. Prior art systems for the
control of the latter type of operations have been relatively elaborate, complex and costly,
and one of the main objects of the invention is to provide a simple, inexpensive system
for automatically and selectively performing timed operations on different workpieces.
Another object of the project is to provide a simple means for controlling an operating
unit which performs a manufacturing operation on a workpiece as it is conveyed by the
operating unit, the means being capable not only of performing the operations on certain
ones of the articles while not performing it on other articles, but also of performing
operations on different articles for different periods of time.
While the invention in its broad aspects is applicable to manufacturing systems in
general, it is especially advantageous when used in a system, such as a spraying line,
wherein a coating material is applied to each article and the article is then passed through
an oven to dry the coating. Thus, another object of the invention is to provide a system
for controlling the spraying of a material on articles carried by a conveyor wherein the
control system is unaffected by any clogging or accumulation of coating material
particles and wherein it includes control elements carried by the conveyor, which
elements are unaffected by the heat as they pass through the drying oven.
Why you need spray booth ?
LAW : There is a statutory requirement under the Factories Act that adequate ventilation
be
installed
wherever
spray
painting
is
carried
out.
SAFETY : Spraying paint may involve fire risk from both solvent and overspray
deposits.
A
spray
booth
is
essential
to
dispose
off
both.
POLLUTION : The air exhausted from the paint shop must be clean of paint as much
possible. Only an efficient spray booth will ensure this and prevent pollution from the
atmosphere.
QUALITY OF WORK :To remove dry-over spray effectively, thus eliminating its
settling,on.wet painted components.
The Development Process
“A product development process is a sequence of steps or activities which an enterprise
employs to conceive, design and commercialize a product. Many of these steps and
activities are intellectual and organizational rather than physical.”
Development process in some basic steps and the model is shown in figure 2.1.
SystemConcept
Planning
Level
Development
Testing and
Productio
n
Refinement
Ramp-Up
Detail Design
Design
Figure 2.1. A product development process by Ulrich & Eppinger.
First is the planning phase where market segments, business goal and constraints are
defined. When a new project is going to start and a new product will be developed it is
very important to get a general overview and decide where to start, what has to be done
and how much time it will take. The output from this phase is a mission statement.
One of the most important part of the product development process for a designer is the
concept development phase. The customer needs are identified, several alternative
concepts are generated and further development for one or more of the concepts is done
in this phase.
The system-level design is where the architecture and functional specifications of the
product are defined. The output of this phase is a geometric layout and a preliminary
process flow diagram according .
Detail design is what follows the system-level phase. Type of material, final
geometry and a detailed specification of all parts are defined in this phase.
The testing and refinement phase is where tests are made on performance, life and
reality. If some changes in the design has to be done this is where those are made.
In the final phase, production ramp-up, the product is going to an early
production and the entire production system is started to get operated.
A. GENERAL DESCRIPTION
Automatic spray painting machines can be designed to coat almost any type of product
regardless of shape, size, color or material. The basic design of these machines will
conform to one of the following type motions, excluding minor changes which may be
used to suit the particular product.
Types of spray painting systems
Horizontal Reciprocating Machine
This coats flat objects such as steel plate, plywood, etc., which can be carried on a laydown conveyor under the spray gun. The motion of a horizontal reciprocating machine,
together with the movement of the conveyor, may be described as a series of ‘W’s”. The
spray guns are fixed at right angles to the surface of the product. When using one spray
gun with a 6 inch spray pattern, the product will move 3 inches for every stroke of the
machine. For a more uniform coat, an overlap is provided to cover the previous stroke
using one half of the effective portion of the spray pattern of the previous strokes. The
spray gun moves six inches past the product and is turned off. The gun is turned on six
inches before starting the next stroke. Triggering the gun helps to keep the fluid nozzle
clean. Recommended for up to 25 feet per minute conveyor speeds.
Vertical Reciprocating Machines
Designed to produce a vertical stroke, these machines are normally used in conjunction
with overhead conveyor systems, but can be adapted to other types. The design of these
machines and controls axe determined by the size, shape, type of material being sprayed,
production requirements and budget allowed by the customer.
Rotary Spray Machines
These do the same basic operation as a horizontal reciprocating machine, but are able to
operate at higher conveyor speeds. The machine rotates at about 20 RPM and the spray
pattern coverage in conjunction with the conveyor, covers the object with a series of
overlapping arcs-the flatter the arc, the more unform the coating. Four arm rotary spray
machines are recommended for up to 50 feet per minute. Eight arm rotary spray machines
are recommended for any conveyor speed over 50 feet per minute. A limitation of this
machine is that it cannot handle abrasive materials because of the rotary seals it uses.
Spindle Machines
An automatic spraying system consisting of exhaust system, conveyor (chain on edge
type) and spray gun controls with the exception of loading and unloading portion
(*optional equipment). Most types of products coated with this machine conform to
spherical or cylindrical shapes. Square shapes require two rotational units. The object is
placed on a specially designed work holder and rotated or spun in fort of one or more
spray guns. For a fine uniform finish the product must be rotated at least a minimum of
two revolutions in the front of each spray gun.
Depending upon the shape and size of the product, the minimum spacing of the work
holder is normally every other pin; greater spacing between work holders can be as
desired.
The spindle conveyor chain is available in l%, 2, or 3 inch pitch, depending on
requirements. Conveyor path can be arranged to suit the individual needs.
Robots
Robots axe spraying machines that virtually duplicate complex human hand, wrist,
and arm motions. They are computer-controlled for production line spraying and offer
particular advantages in hazardous areas, and where the work is repetitive. Robots can be
powered either electrically or hydraulically and are well suited for precision work.
Short Stroke Reciprocating Spray Machines
Sometimes called oscillators, SSRM normally oscillate over a range of 1 to 24 inches
with adjustment capability in 1-inch increments. They can be oriented for either vertical
or horizontal motion.
Automatic Spray Machines for Mouldings
Used in the finishing operation of flat and profiled mouldings, either continuously or
inte4ttently for strip lengths in any combination. Capable of high production speeds (up
to 36,000 ft. per hr.) these machines can be mounted with up to four spray heads, each
individually controlled. Spray booths usually are not required since exhaust systems are
integral with the machine.
CONSIDERATIONS IN SELECTING A PIECE OF AUTOMATIC SPRAY
EQUIPMENT
1. Size and configuration of product.
2. Conveyor speed-maximum and minimum.
3. Production requirements (to include future plans).
4. Film build and finish required.
5. Types of spray guns being used.
6. Method of material atomization (airless or conventional).
7. Types of spray systems: hot spraying, electrostatic, circulating or dead end.
8. Type of conveyor.
9. Conveyor size.
10. Spray booth size.
11. Spray booth type-waterwash or dry type.
E. OPERATION
1. Material is supplied to the automatic spray machines by standard pressure tanks or
pumps for conventional applications, and airless high pressure pumps for airless
spraying, or where production warrants, the circulating system is used for supply. 2. The
spray guns cover the product with a spray pattern which is perpendicular to the surface.
Triggering the spray guns at the end of each stroke, overlapping at the same rate, and
maintaining the proper spraying distance produces the required uniformity of the coating.
F. LIMITATION
1. The size and configuration of the object to be coated.
2. The film thickness required in one pass through the machine.
3. Cost of the equipment must be justified in material savings, production increase and/or
product uniformity in one or two years.
G. TRANSFER DEVICESIPICK-AND-PLACE UNITS
When automatic transfer of parts is required from one conveyor to another, e.g. spindle
conveyor to belt conveyor or over under conveyor to belt conveyor.
H. CONTROLS
The controls that are available on these automatic spray machines can be either
semiautomatic or fully automatic. The controls can be designed to have the ability to
identify the shape and size of the product and coat only its surface area with minimum
overspray. Automatic color changing units are available to change from one color to
another. Skip spray devices are available in order to prevent spray guns from operating
when there is no product present on the conveyor. A special device which has the ability
to carry out skip spray function, is a pin memory ring mounted singly or in a series. The
memory ring is connected to a parasitic drive which powers and moves the memory ring
in direct relation to the conveyor speed. Each ring is connected to. a sensing device
mounted along the conveyor. This may be a switch or a photo cell. As the part passes the
sensing station, a signal is given to the timer unit. This signal energizes a solenoid which
extends a number of pins in the rotating ring. For example if each one of the 100 pins
could have a memory assignment of 4 inches across the product, the ring would retain
this information for a distance up to 400 inches. By varing the memory assignment or
using additional rings longer distances can be obtained. The pins, moving in time with the
conveyor, advance to an output switch mounted in the unit. The switch is activated by the
pins, and in turn, sends a signal to activate the spray gun. While this has been taking
place, the part has been moving on the conveyor until it is in spraying position at the
same time the spray gun is activated. This type of control permits us to spray when the
part is in position; and we can determine the approximate shape of the part, and reducing
waste and maintenance.
If more sophisticated control methods are required, computer controlled (PLC) machines
are also available.
I. DOES YOUR PRODUCTION WARRANT AUTOMATION?
1. High production rates.
2. Similarity of products.
3. Same type of material being used.
4. Uniformity and quality finish required.
J. PURCHASE OF EQUIPMENT
There is limited catalog information available on automatic systems since each unit is
designed for standard components to meet the requirements of each particular operation.
Each automatic machine is assembled on an individual order basis to meet the particular
specifications of the customer.
Automatic Test Panel Spray UnitA programmable machine used to spray panels for laboratory use in determining number
of coats, color, speed of application, etc.
I.
OVERALL STRUCTURE SCHEME
The construction of the automatic wall painting robot consists of two
main parts. They are
1 Mobile Platform
.
• Frame Stand
• PMDC Motor
• Spur Gears
• Control Unit
2.Spray gun mount
• Inductive proximity sensor
• Flow control valve
• Spray gun
1.Frame Stand
II.PMDC motor
Chain gear are designed and made to give motion to conveyor . PMDC motor is a
combination of 2 mechanical technologies to perform their tasks,A combination electric
motor and worm gear reduction provides power to the chain gear.
Motor and Gear reduction:
It takes a lot of force to accelerate the conveyor in leanear motion across the spray
gun soquickly. In order to generate this type of force, a worm gear is used on the output of
a smallelectric motor.The worm gear reduction can multiply the torque of the motor by
about 50 times, whileslowing the output of the electric motor by 50 times as well. The
output of the gear reduction operates a chain gear that moves the conveyor.
POWERING THE MOTOR
Voltage
The standard voltage requirement for the wiper motor is 12 volts DC. The electrical
system in a running automobile usually puts out between 13 and 13.5 volts, so it's
safe to say the motor can handle up to 13.5 volts with no problem.
Current
The minimum required current for the motor is 1.6 amps at 70 rpm, 0.9 amps at 41
rpm (and 4 amps if you elect to run it at 106 rpm see note on the next page). These
current ratings are for the motor spinning with no load. As you add mechanical load,
these numbers can increase dramatically, doubling or even tripling under a heavy
load. (When account when selecting a power supply. Since the motor will only use what it
needs when it comes to current, it's best to provide a source with a higher current rating
than you think you might need.
TORQUE REQUIRED
T = Torque =? Nm
P = Power = 17 watt
N₁ = at low speed = 60 rpm
N₂ = at high speed = 120 rpm
CASE 1:
The force exerted on the piston must be =(� × � )
T = (P) ÷ (2ΠN₁)
T = (17×60) ÷ (2×Π×60)
T = 2.78 Nm
CASE 2:
T = (P×60) ÷ (2ΠN₂)
T = (17×60) ÷ (2×Π×120)
T = 1.35 Nm
The torque obtained will be maximum at the lower speeds. Hence the same
is adopted.
IV. Control Unit
The 555IC used in the controller unit is astable multivibrator. The 555 unit is used to control the
PMDC motors and the movement of spray gun fitted on the conveyor belt. 555 unit is provided
with the 5V signal and as soon as the supply is ON, LCD gets initialized. The controller sets to setting
mode and the moving and painting time are given as input to the 555IC circuit. The 555 controls
the rotation of DC motor based on the time given in order to control conveyor belt move- ment.
When proximity sensor receives the signal, the conveyor belt movement. When IR receiver receives
the signal, the conveyor belt stop and the spray gun goes to ON condition and if the conveyor belt
ON, the spray gun goes to OFF condition. It contains relays for the control of forward movement of
the PMDC motors. When the 555 receives the signals from proximity sensor, it will be taking a
decision to operate the machine. This pulse signal received from proximity sensor circuit when
there is any object.
VI. Proximity sensor
Proximity Sensors
Proximity Sensors are available in models using high-frequency oscillation to detect
ferrous and non-ferrous metal objects and in capacitive models to detect non-metal objects.
Models are available with environment resistance, heat resistance, resistance to chemicals,
and resistance to water.
Operating Principles
Detection Principle of Inductive Proximity Sensors
Inductive Proximity Sensors detect magnetic loss due to eddy currents that are generated on a
conductive surface by an external magnetic field. An AC magnetic field is generated on the detection
coil, and changes in the impedance due to eddy currents generated on a metallic object are detected.
Other methods include Aluminum-detecting Sensors, which detect the phase component of the
frequency, and All-metal Sensors, which use a working coil to detect only the changed component of
the impedance. There are also Pulse-response Sensors, which generate an eddy current in pulses and
detect the time change in the eddy current with the voltage induced in the coil.
<Qualitative Explanation>
The sensing object and Sensor form what appears to be a transformer-like relationship.
The transformer-like coupling condition is replaced by impedance changes due to eddy-current
losses.
The impedance changes can be viewed as changes in the resistance that is inserted in series with the
sensing object. (This does not actually occur, but thinking of it this way makes it easier to understand
qualitatively.)
Detection Principle of Capacitive Proximity Sensors
Capacitive Proximity Sensors detect changes in the capacitance between the sensing object and the
Sensor. The amount of capacitance varies depending on the size and distance of the sensing object.
An ordinary Capacitive Proximity Sensor is similar to a capacitor with two parallel plates, where the
capacity of the two plates is detected. One of the plates is the object being measured (with an
imaginary ground), and the other is the Sensor's sensing surface. The changes in the capacity
generated between these two poles are detected.
The objects that can be detected depend on their dielectric constant, but they include resin and water
in addition to metals.
Detection Principle of Magnetic Proximity Sensors
The reed end of the switch is operated by a magnet. When the reed switch is turned ON, the Sensor is
turned ON.
chain-on-edge conveyor
With the chain-on-edge of work piece and various angles of spray gun according to
work piece types, painting can reach any position without hidden angle. Continuous
chain-on-edge or single point chain-on-edge can be selected as desired. Also, stroke and
speed are adjustable. No painting performs when work piece is moving. Painting starts
only when work piece reaches to a fixed position.
Vertically hung products that have varying lengths can all be coated with the
same machine. Essentially, the machine is designed to operate with the longest
part. During operation with shorter work, the guns physically move through
the design stroke, but only trigger on as they pass through the work piece
length.
Many machine applications use two machines, one on either side of the
conveyor line for straight-through operations. This is usually done where the
work is more than several feet in length horizontally. If the work is shorter,
indexing 90° between machines permits spraying from one side of the
conveyor only. The advantage here is the requirement of only a single spray
booth.
Machine construction and design will vary depending on duty requirements
and cost considerations. However, all involve a carriage moving on a section
of tracks, rails or a tube of given length. This carriage can be moved in several
different ways.
One method is a continuously moving chain, which is supported by sprockets
at either end of the machine support frame. With a vertical machine, the lower
sprocket is motor driven at the desired speed. Attached to one side of the chain
is a sealed roller bearing that rides between a pair of vertical gibs or metal
blocks on the carriage. This arrangement pulls the carriage along the straightline travel. As the bearing goes around the sprocket at either end of the
machine, the carriage comes to a halt and the bearing changes position
between the gibs. Actually, the carriage decelerates to zero, and then
accelerates to gun speed in the time it takes for the bearing to travel the 180°
around the end sprockets. This mechanism is called a “scotch crosshead.”
There are several power options for use with machines employing crosshead
mechanisms. A continuously running, single-speed electric motor with a
variable-speed belt-reduction system driving one of the sprockets is the least
expensive. More expensive, although more versatile, are gear reduction drives
with variable-speed motors.
Machines that do not employ the crosshead can be driven by direction-
reversing DC motors with built-in programmable controllers. These machines
can move in one direction faster than in the other, or change speed during
travel in either direction. They can also be programmed for a number of
selectable stroke lengths. These machines are frequently referred to as “smart”
reciprocators.
With transverse machines, either vertical or horizontal, the work moves at
right angles to the machine stroke. As a result, the strip of paint applied to the
work with a single gun is never in a straight line. It is always angled to the left
or right depending on which way the conveyor is moving. The angle is a
function of conveyor speed as related to machine speed. To obtain a
continuous coating, the spray patterns must overlap approximately 50%. On a
vertical machine carrying a single spray gun with a 10-inch wide pattern, the
machine or gun speed must be about 10 times that of the conveyor. If two
guns were mounted and spaced so that their fixed spray patterns overlap by 20
inches, the machine speed could be reduced to about five times the conveyor
speed. Similarly, three guns would reduce machine speed to a third. Most long
stroke machines are mechanically limited to approximately 250 ft per minute
(FPM) and a specific carriage load which depends on machine construction.
The relationship between machine cycles (FPM divided by chain length) and
conveyor speed is given by:
Cycles x Spray Pattern Width = Conveyor F.P.M.
Besides DC motor drives, there are other machine movement options that do
not require a crosshead. Rotary hydraulic motors are used, which are reversed
at the top and bottom of the stroke. Control cams for the hydraulic actuators
permit selection of several preset stroke lengths. Work has also been done
with air-actuated long-stroke cylinders. Pneumatic and hydraulic power
options avoid the expense of explosion-proof motor housings and wiring
required with electric versions.
Spray guns on a long-stroke machine need not be positioned at a fixed
distance from the work. Where part width varies perpendicular to the
conveyor, the machine can be automatically moved to maintain proper gun-towork distance. In many instances it is desirable to follow a long-radius,
somewhat circular surface, such as the side of an automobile. In “contour”
machines of this nature, the gun array is attached to the vertically moving
carriage with a sliding arm mechanism. This permits horizontal movement of
the guns with respect to the painting surface. A swivel joint is included,
allowing the guns to be tilted approximately 30 degrees up or down. Guide
rollers attached to the gun array ride a cam surface that is shaped like the
surface to be sprayed. As the carriage moves in a straight line up and down,
the guns follow the cam. The guns contour and swivel to keep the guns
perpendicular to the work surface.
There are several long-stroke techniques employed that “toe” a gun array up at
the bottom of the stroke, or down at the top of the stroke. Guns at either end of
a horizontal array of four can be angled left or right at an appropriate degree,
and triggered to spray at an object’s leading or trailing edges. This can be
useful with rectangular “door” shaped objects that have several inches of
depth at right angles to conveyor travel. This could avoid the requirement for
a manual touch-up station.
Where product may be conveyed with a chain-on-edge (C.O.E.) machine,
vertical gun-moving machines may be used in conjunction with the C.O.E. for
unique coating applications. Coating the interior of rotating, upright pails four
at a time is an example. At a predetermined point, an array of four extension
guns positioned above and collinear with the axes of the pails, begins to move.
Moving with the pails, the guns descend to a predetermined depth. They begin
to spray and withdraw simultaneously. Spraying stops as the gun tips reach the
lip of the pail. As the guns clear the pail, the VGM (vertical gun mover)
moves the gun array back to the start position to pick up another set of four
pails.
The exterior of the pails can also be coated using the VGM. Four individual
spray guns can be attached and positioned to spray at each pail’s centerline
during the synchronized travel. When the extension guns are spraying and
withdrawing, the guns outside the pail on the centerline are also spraying and
moving upward, coating the part.
Another option for the pail’s exterior is the use of several stationary guns,
positioned so that their patterns overlap for uniformity. As the rotating pail
moves into range, the guns are triggered on, quickly coating the part.
Following VGMs, are overhead monorail conveyors as well as C.O.E. Washer
and dryer drums, or products of a similar nature, can be suspended from the
conveyor with their openings facing down. The automated VGM and gun
array, following the rotating drums, can move upward into the cavity and
spray during withdrawal.
System Features:
Heavy Duty 1 1/2” double pitch Chain-On-Edge Spindle Conveyor. Included
is PCT’s exclusive “V”- wheel and spindle assembly stabilizing guide
bearing design, electric gearmotor drive and manually adjusted chain
tensioner. Select continuous running, index cycling or both conveyor
operations with a variety of speed ranges. Positive engagement chain-type
powered product rotator with an electric explosion proof gearmotor, variable
frequency drive and chain tensioner. Optional adjustable spray gun mounting
bar available.
Chain-on-edge systems have been used successfully to apply liquid and
powder coatings for many years, but not many manufacturers know they
exist. They are called chain-on-edge because the system consists of a
continuous loop chain with pins or spindles that convey the parts to be
coated in and out of the spray area. The systems can be configured to have a
small footprint with high production rates.
The Process
The chain-on-edge conveyors work with your spray booth in an automated
process. The parts are loaded on a spindle, which moves the part into the
spray area and in front of the spray guns. The part is rotated for full coverage
and conveyed to the drying/oven section of the loop. The system has skip
spray sensors that can read whether a part is present and only sprays when
there is a part to be coated. The gun controls ensure that no coating is
wasted.
Depending on the size and shape of the part to be coated, the spacing of the
spindles can be easily adjusted to allow space for full rotation of the part.
The spindle chain can be sized to accommodate larger and heavier parts.
Liquid and Powder Coatings
The chain-on-edge systems works equally well for liquid or powder
coatings. The liquid coatings can be applied by automatic air spray, HVLP,
air-assisted airless or electrostatic guns. For powder coatings, you can use
electrostatic or tribo charge guns. The chain-on-edge systems most often
utilize a dry filter spray booth with high-efficiency Wave™ spray booth
filters.
The spray booth sidewalls will have an appropriately sized conveyor
opening.The parts can be conveyed through an in-line oven, which can be
convection, pre-heat, or a Halogen curing system.
The chain-on-edge systems are very flexible in layout and design and can
conform to your spray booth operation.
Advantages
Uniformity of the coating on the product.
Cutting down of product rejections.
Minimum human element.
Paint savings.
In most cases, production rates can be increased.
Eliminate skilled Painter or Operator
Deliver consistent quality of painting on product
Simple to operate
High productivity of Paint consumption
Finally cost per unit is lowest due to
Be of International quality
- Less space
- Less power
- Less manpower cost, paint consumption cost etc.
- Less rejection
Lastly
highly
Application
Widely applicable to production of,
Plastic Electronics
Hardware
economical
&
reliable
Sports Equipment
Household Appliances
Vacuum Coating Industries
Such as various types of high-yield, high-yield high-quality automation
can paint equipment.
JUSTIFICATION OF COST
Material savings.
Increased production.
Improved product quality.
Finish uniformity.
Labor savings.
Abstract
The aim of this project is to minimize the processes and production cost in a
spray line. The painting operation is the bottleneck point in modular furniture industries.
For minimize the wastage of the paint by avoiding overspray painting on the article and
improved the quality of the coating by using work study methodology and RTA method.
Both are widely used to produce articles as per customer’s demands. The sequencing is
an important factor in powder coating industries. For resolved the sequencing problem in
favour of minimizing the total cost and keeping uniform usage of each part and cost
model is presented. To get best alternative between work study and RTA method, a
comparison is done, concerning sequencing problem. This investigation suggests best
sequence of the process and method. It gives continued consumption of parts as well as
reducing cycle time which helps for higher production and cost saving.
Introduction
A paint spraying system has a conveyor line for carrying different sized
workpieces through a spray booth past a plurality of sprayers. Each sprayer is selectively
operated in accordance with a program element carried by the conveyor in conjunction
with each workpiece to be operated upon. Operation of the sprayers is controlled by a
series of timers each designed so that, when conditioned and activated, it will operate the
selected sprayer for a different predetermined period of time. The workpieces are
arranged on the conveyor in different series whereby the workpieces in each series are to
be sprayed for the same period of time. Program elements are arranged on either end of
each series so as to selectively condition and de-condition the timer that operates the
sprayer for the desired period. Additional program elements are mounted on the conveyor
next to each workpiece to 'be sprayed for selectively activating the conditioned timer and
sprayer.
This project relates to manufacturing systems of the type wherein manufacturing
operations are selectively performed on workpieces automatically under program control
as the workpieces are carried through a work station by a conveyor.
In the past, many manufacturing systems have been devised for automating portions or all
of a production line wherein workpieces are moved by some form of a conveyor through
a work station. At the work station, a manufacturing operation is performed on each work
piece and this operation may range from the simple task of repetitively performing the
same operation on identical workpieces, as each one passes through the station, to the
more complex tasks of performing different operations on different sized workpieces for
different periods of time as they pass through the work station. Prior art systems for the
control of the latter type of operations have been relatively elaborate, complex and costly,
and one of the main objects of the invention is to provide a simple, inexpensive system
for automatically and selectively performing timed operations on different workpieces.
Another object of the project is to provide a simple means for controlling an operating
unit which performs a manufacturing operation on a workpiece as it is conveyed by the
operating unit, the means being capable not only of performing the operations on certain
ones of the articles while not performing it on other articles, but also of performing
operations on different articles for different periods of time.
While the invention in its broad aspects is applicable to manufacturing systems in
general, it is especially advantageous when used in a system, such as a spraying line,
wherein a coating material is applied to each article and the article is then passed through
an oven to dry the coating. Thus, another object of the invention is to provide a system
for controlling the spraying of a material on articles carried by a conveyor wherein the
control system is unaffected by any clogging or accumulation of coating material
particles and wherein it includes control elements carried by the conveyor, which
elements are unaffected by the heat as they pass through the drying oven.
Why you need spray booth ?
LAW : There is a statutory requirement under the Factories Act that adequate ventilation
be
installed
wherever
spray
painting
is
carried
out.
SAFETY : Spraying paint may involve fire risk from both solvent and overspray
deposits.
A
spray
booth
is
essential
to
dispose
off
both.
POLLUTION : The air exhausted from the paint shop must be clean of paint as much
possible. Only an efficient spray booth will ensure this and prevent pollution from the
atmosphere.
QUALITY OF WORK :To remove dry-over spray effectively, thus eliminating its
settling,on.wet painted components.
The Development Process
“A product development process is a sequence of steps or activities which an enterprise
employs to conceive, design and commercialize a product. Many of these steps and
activities are intellectual and organizational rather than physical.”
Development process in some basic steps and the model is shown in figure 2.1.
SystemConcept
Planning
Level
Development
Testing and
Productio
n
Refinement
Ramp-Up
Detail Design
Design
Figure 2.1. A product development process by Ulrich & Eppinger.
First is the planning phase where market segments, business goal and constraints are
defined. When a new project is going to start and a new product will be developed it is
very important to get a general overview and decide where to start, what has to be done
and how much time it will take. The output from this phase is a mission statement.
One of the most important part of the product development process for a designer is the
concept development phase. The customer needs are identified, several alternative
concepts are generated and further development for one or more of the concepts is done
in this phase.
The system-level design is where the architecture and functional specifications of the
product are defined. The output of this phase is a geometric layout and a preliminary
process flow diagram according .
Detail design is what follows the system-level phase. Type of material, final
geometry and a detailed specification of all parts are defined in this phase.
The testing and refinement phase is where tests are made on performance, life and
reality. If some changes in the design has to be done this is where those are made.
In the final phase, production ramp-up, the product is going to an early
production and the entire production system is started to get operated.
A. GENERAL DESCRIPTION
Automatic spray painting machines can be designed to coat almost any type of product
regardless of shape, size, color or material. The basic design of these machines will
conform to one of the following type motions, excluding minor changes which may be
used to suit the particular product.
Types of spray painting systems
Horizontal Reciprocating Machine
This coats flat objects such as steel plate, plywood, etc., which can be carried on a laydown conveyor under the spray gun. The motion of a horizontal reciprocating machine,
together with the movement of the conveyor, may be described as a series of ‘W’s”. The
spray guns are fixed at right angles to the surface of the product. When using one spray
gun with a 6 inch spray pattern, the product will move 3 inches for every stroke of the
machine. For a more uniform coat, an overlap is provided to cover the previous stroke
using one half of the effective portion of the spray pattern of the previous strokes. The
spray gun moves six inches past the product and is turned off. The gun is turned on six
inches before starting the next stroke. Triggering the gun helps to keep the fluid nozzle
clean. Recommended for up to 25 feet per minute conveyor speeds.
Vertical Reciprocating Machines
Designed to produce a vertical stroke, these machines are normally used in conjunction
with overhead conveyor systems, but can be adapted to other types. The design of these
machines and controls axe determined by the size, shape, type of material being sprayed,
production requirements and budget allowed by the customer.
Rotary Spray Machines
These do the same basic operation as a horizontal reciprocating machine, but are able to
operate at higher conveyor speeds. The machine rotates at about 20 RPM and the spray
pattern coverage in conjunction with the conveyor, covers the object with a series of
overlapping arcs-the flatter the arc, the more unform the coating. Four arm rotary spray
machines are recommended for up to 50 feet per minute. Eight arm rotary spray machines
are recommended for any conveyor speed over 50 feet per minute. A limitation of this
machine is that it cannot handle abrasive materials because of the rotary seals it uses.
Spindle Machines
An automatic spraying system consisting of exhaust system, conveyor (chain on edge
type) and spray gun controls with the exception of loading and unloading portion
(*optional equipment). Most types of products coated with this machine conform to
spherical or cylindrical shapes. Square shapes require two rotational units. The object is
placed on a specially designed work holder and rotated or spun in fort of one or more
spray guns. For a fine uniform finish the product must be rotated at least a minimum of
two revolutions in the front of each spray gun.
Depending upon the shape and size of the product, the minimum spacing of the work
holder is normally every other pin; greater spacing between work holders can be as
desired.
The spindle conveyor chain is available in l%, 2, or 3 inch pitch, depending on
requirements. Conveyor path can be arranged to suit the individual needs.
Robots
Robots axe spraying machines that virtually duplicate complex human hand, wrist,
and arm motions. They are computer-controlled for production line spraying and offer
particular advantages in hazardous areas, and where the work is repetitive. Robots can be
powered either electrically or hydraulically and are well suited for precision work.
Short Stroke Reciprocating Spray Machines
Sometimes called oscillators, SSRM normally oscillate over a range of 1 to 24 inches
with adjustment capability in 1-inch increments. They can be oriented for either vertical
or horizontal motion.
Automatic Spray Machines for Mouldings
Used in the finishing operation of flat and profiled mouldings, either continuously or
inte4ttently for strip lengths in any combination. Capable of high production speeds (up
to 36,000 ft. per hr.) these machines can be mounted with up to four spray heads, each
individually controlled. Spray booths usually are not required since exhaust systems are
integral with the machine.
CONSIDERATIONS IN SELECTING A PIECE OF AUTOMATIC SPRAY
EQUIPMENT
1. Size and configuration of product.
2. Conveyor speed-maximum and minimum.
3. Production requirements (to include future plans).
4. Film build and finish required.
5. Types of spray guns being used.
6. Method of material atomization (airless or conventional).
7. Types of spray systems: hot spraying, electrostatic, circulating or dead end.
8. Type of conveyor.
9. Conveyor size.
10. Spray booth size.
11. Spray booth type-waterwash or dry type.
E. OPERATION
1. Material is supplied to the automatic spray machines by standard pressure tanks or
pumps for conventional applications, and airless high pressure pumps for airless
spraying, or where production warrants, the circulating system is used for supply. 2. The
spray guns cover the product with a spray pattern which is perpendicular to the surface.
Triggering the spray guns at the end of each stroke, overlapping at the same rate, and
maintaining the proper spraying distance produces the required uniformity of the coating.
F. LIMITATION
1. The size and configuration of the object to be coated.
2. The film thickness required in one pass through the machine.
3. Cost of the equipment must be justified in material savings, production increase and/or
product uniformity in one or two years.
G. TRANSFER DEVICESIPICK-AND-PLACE UNITS
When automatic transfer of parts is required from one conveyor to another, e.g. spindle
conveyor to belt conveyor or over under conveyor to belt conveyor.
H. CONTROLS
The controls that are available on these automatic spray machines can be either
semiautomatic or fully automatic. The controls can be designed to have the ability to
identify the shape and size of the product and coat only its surface area with minimum
overspray. Automatic color changing units are available to change from one color to
another. Skip spray devices are available in order to prevent spray guns from operating
when there is no product present on the conveyor. A special device which has the ability
to carry out skip spray function, is a pin memory ring mounted singly or in a series. The
memory ring is connected to a parasitic drive which powers and moves the memory ring
in direct relation to the conveyor speed. Each ring is connected to. a sensing device
mounted along the conveyor. This may be a switch or a photo cell. As the part passes the
sensing station, a signal is given to the timer unit. This signal energizes a solenoid which
extends a number of pins in the rotating ring. For example if each one of the 100 pins
could have a memory assignment of 4 inches across the product, the ring would retain
this information for a distance up to 400 inches. By varing the memory assignment or
using additional rings longer distances can be obtained. The pins, moving in time with the
conveyor, advance to an output switch mounted in the unit. The switch is activated by the
pins, and in turn, sends a signal to activate the spray gun. While this has been taking
place, the part has been moving on the conveyor until it is in spraying position at the
same time the spray gun is activated. This type of control permits us to spray when the
part is in position; and we can determine the approximate shape of the part, and reducing
waste and maintenance.
If more sophisticated control methods are required, computer controlled (PLC) machines
are also available.
I. DOES YOUR PRODUCTION WARRANT AUTOMATION?
1. High production rates.
2. Similarity of products.
3. Same type of material being used.
4. Uniformity and quality finish required.
J. PURCHASE OF EQUIPMENT
There is limited catalog information available on automatic systems since each unit is
designed for standard components to meet the requirements of each particular operation.
Each automatic machine is assembled on an individual order basis to meet the particular
specifications of the customer.
Automatic Test Panel Spray UnitA programmable machine used to spray panels for laboratory use in determining number
of coats, color, speed of application, etc.
I.
OVERALL STRUCTURE SCHEME
The construction of the automatic wall painting robot consists of two
main parts. They are
1 Mobile Platform
.
• Frame Stand
• PMDC Motor
• Spur Gears
• Control Unit
2.Spray gun mount
• Inductive proximity sensor
• Flow control valve
• Spray gun
1.Frame Stand
II.PMDC motor
Chain gear are designed and made to give motion to conveyor . PMDC motor is a
combination of 2 mechanical technologies to perform their tasks,A combination electric
motor and worm gear reduction provides power to the chain gear.
Motor and Gear reduction:
It takes a lot of force to accelerate the conveyor in leanear motion across the spray
gun soquickly. In order to generate this type of force, a worm gear is used on the output of
a smallelectric motor.The worm gear reduction can multiply the torque of the motor by
about 50 times, whileslowing the output of the electric motor by 50 times as well. The
output of the gear reduction operates a chain gear that moves the conveyor.
POWERING THE MOTOR
Voltage
The standard voltage requirement for the wiper motor is 12 volts DC. The electrical
system in a running automobile usually puts out between 13 and 13.5 volts, so it's
safe to say the motor can handle up to 13.5 volts with no problem.
Current
The minimum required current for the motor is 1.6 amps at 70 rpm, 0.9 amps at 41
rpm (and 4 amps if you elect to run it at 106 rpm see note on the next page). These
current ratings are for the motor spinning with no load. As you add mechanical load,
these numbers can increase dramatically, doubling or even tripling under a heavy
load. (When account when selecting a power supply. Since the motor will only use what it
needs when it comes to current, it's best to provide a source with a higher current rating
than you think you might need.
TORQUE REQUIRED
T = Torque =? Nm
P = Power = 17 watt
N₁ = at low speed = 60 rpm
N₂ = at high speed = 120 rpm
CASE 1:
The force exerted on the piston must be =(� × � )
T = (P) ÷ (2ΠN₁)
T = (17×60) ÷ (2×Π×60)
T = 2.78 Nm
CASE 2:
T = (P×60) ÷ (2ΠN₂)
T = (17×60) ÷ (2×Π×120)
T = 1.35 Nm
The torque obtained will be maximum at the lower speeds. Hence the same
is adopted.
IV. Control Unit
The 555IC used in the controller unit is astable multivibrator. The 555 unit is used to control the
PMDC motors and the movement of spray gun fitted on the conveyor belt. 555 unit is provided
with the 5V signal and as soon as the supply is ON, LCD gets initialized. The controller sets to setting
mode and the moving and painting time are given as input to the 555IC circuit. The 555 controls
the rotation of DC motor based on the time given in order to control conveyor belt move- ment.
When proximity sensor receives the signal, the conveyor belt movement. When IR receiver receives
the signal, the conveyor belt stop and the spray gun goes to ON condition and if the conveyor belt
ON, the spray gun goes to OFF condition. It contains relays for the control of forward movement of
the PMDC motors. When the 555 receives the signals from proximity sensor, it will be taking a
decision to operate the machine. This pulse signal received from proximity sensor circuit when
there is any object.
VI. Proximity sensor
Proximity Sensors
Proximity Sensors are available in models using high-frequency oscillation to detect
ferrous and non-ferrous metal objects and in capacitive models to detect non-metal objects.
Models are available with environment resistance, heat resistance, resistance to chemicals,
and resistance to water.
Operating Principles
Detection Principle of Inductive Proximity Sensors
Inductive Proximity Sensors detect magnetic loss due to eddy currents that are generated on a
conductive surface by an external magnetic field. An AC magnetic field is generated on the detection
coil, and changes in the impedance due to eddy currents generated on a metallic object are detected.
Other methods include Aluminum-detecting Sensors, which detect the phase component of the
frequency, and All-metal Sensors, which use a working coil to detect only the changed component of
the impedance. There are also Pulse-response Sensors, which generate an eddy current in pulses and
detect the time change in the eddy current with the voltage induced in the coil.
<Qualitative Explanation>
The sensing object and Sensor form what appears to be a transformer-like relationship.
The transformer-like coupling condition is replaced by impedance changes due to eddy-current
losses.
The impedance changes can be viewed as changes in the resistance that is inserted in series with the
sensing object. (This does not actually occur, but thinking of it this way makes it easier to understand
qualitatively.)
Detection Principle of Capacitive Proximity Sensors
Capacitive Proximity Sensors detect changes in the capacitance between the sensing object and the
Sensor. The amount of capacitance varies depending on the size and distance of the sensing object.
An ordinary Capacitive Proximity Sensor is similar to a capacitor with two parallel plates, where the
capacity of the two plates is detected. One of the plates is the object being measured (with an
imaginary ground), and the other is the Sensor's sensing surface. The changes in the capacity
generated between these two poles are detected.
The objects that can be detected depend on their dielectric constant, but they include resin and water
in addition to metals.
Detection Principle of Magnetic Proximity Sensors
The reed end of the switch is operated by a magnet. When the reed switch is turned ON, the Sensor is
turned ON.
chain-on-edge conveyor
With the chain-on-edge of work piece and various angles of spray gun according to
work piece types, painting can reach any position without hidden angle. Continuous
chain-on-edge or single point chain-on-edge can be selected as desired. Also, stroke and
speed are adjustable. No painting performs when work piece is moving. Painting starts
only when work piece reaches to a fixed position.
Vertically hung products that have varying lengths can all be coated with the
same machine. Essentially, the machine is designed to operate with the longest
part. During operation with shorter work, the guns physically move through
the design stroke, but only trigger on as they pass through the work piece
length.
Many machine applications use two machines, one on either side of the
conveyor line for straight-through operations. This is usually done where the
work is more than several feet in length horizontally. If the work is shorter,
indexing 90° between machines permits spraying from one side of the
conveyor only. The advantage here is the requirement of only a single spray
booth.
Machine construction and design will vary depending on duty requirements
and cost considerations. However, all involve a carriage moving on a section
of tracks, rails or a tube of given length. This carriage can be moved in several
different ways.
One method is a continuously moving chain, which is supported by sprockets
at either end of the machine support frame. With a vertical machine, the lower
sprocket is motor driven at the desired speed. Attached to one side of the chain
is a sealed roller bearing that rides between a pair of vertical gibs or metal
blocks on the carriage. This arrangement pulls the carriage along the straightline travel. As the bearing goes around the sprocket at either end of the
machine, the carriage comes to a halt and the bearing changes position
between the gibs. Actually, the carriage decelerates to zero, and then
accelerates to gun speed in the time it takes for the bearing to travel the 180°
around the end sprockets. This mechanism is called a “scotch crosshead.”
There are several power options for use with machines employing crosshead
mechanisms. A continuously running, single-speed electric motor with a
variable-speed belt-reduction system driving one of the sprockets is the least
expensive. More expensive, although more versatile, are gear reduction drives
with variable-speed motors.
Machines that do not employ the crosshead can be driven by direction-
reversing DC motors with built-in programmable controllers. These machines
can move in one direction faster than in the other, or change speed during
travel in either direction. They can also be programmed for a number of
selectable stroke lengths. These machines are frequently referred to as “smart”
reciprocators.
With transverse machines, either vertical or horizontal, the work moves at
right angles to the machine stroke. As a result, the strip of paint applied to the
work with a single gun is never in a straight line. It is always angled to the left
or right depending on which way the conveyor is moving. The angle is a
function of conveyor speed as related to machine speed. To obtain a
continuous coating, the spray patterns must overlap approximately 50%. On a
vertical machine carrying a single spray gun with a 10-inch wide pattern, the
machine or gun speed must be about 10 times that of the conveyor. If two
guns were mounted and spaced so that their fixed spray patterns overlap by 20
inches, the machine speed could be reduced to about five times the conveyor
speed. Similarly, three guns would reduce machine speed to a third. Most long
stroke machines are mechanically limited to approximately 250 ft per minute
(FPM) and a specific carriage load which depends on machine construction.
The relationship between machine cycles (FPM divided by chain length) and
conveyor speed is given by:
Cycles x Spray Pattern Width = Conveyor F.P.M.
Besides DC motor drives, there are other machine movement options that do
not require a crosshead. Rotary hydraulic motors are used, which are reversed
at the top and bottom of the stroke. Control cams for the hydraulic actuators
permit selection of several preset stroke lengths. Work has also been done
with air-actuated long-stroke cylinders. Pneumatic and hydraulic power
options avoid the expense of explosion-proof motor housings and wiring
required with electric versions.
Spray guns on a long-stroke machine need not be positioned at a fixed
distance from the work. Where part width varies perpendicular to the
conveyor, the machine can be automatically moved to maintain proper gun-towork distance. In many instances it is desirable to follow a long-radius,
somewhat circular surface, such as the side of an automobile. In “contour”
machines of this nature, the gun array is attached to the vertically moving
carriage with a sliding arm mechanism. This permits horizontal movement of
the guns with respect to the painting surface. A swivel joint is included,
allowing the guns to be tilted approximately 30 degrees up or down. Guide
rollers attached to the gun array ride a cam surface that is shaped like the
surface to be sprayed. As the carriage moves in a straight line up and down,
the guns follow the cam. The guns contour and swivel to keep the guns
perpendicular to the work surface.
There are several long-stroke techniques employed that “toe” a gun array up at
the bottom of the stroke, or down at the top of the stroke. Guns at either end of
a horizontal array of four can be angled left or right at an appropriate degree,
and triggered to spray at an object’s leading or trailing edges. This can be
useful with rectangular “door” shaped objects that have several inches of
depth at right angles to conveyor travel. This could avoid the requirement for
a manual touch-up station.
Where product may be conveyed with a chain-on-edge (C.O.E.) machine,
vertical gun-moving machines may be used in conjunction with the C.O.E. for
unique coating applications. Coating the interior of rotating, upright pails four
at a time is an example. At a predetermined point, an array of four extension
guns positioned above and collinear with the axes of the pails, begins to move.
Moving with the pails, the guns descend to a predetermined depth. They begin
to spray and withdraw simultaneously. Spraying stops as the gun tips reach the
lip of the pail. As the guns clear the pail, the VGM (vertical gun mover)
moves the gun array back to the start position to pick up another set of four
pails.
The exterior of the pails can also be coated using the VGM. Four individual
spray guns can be attached and positioned to spray at each pail’s centerline
during the synchronized travel. When the extension guns are spraying and
withdrawing, the guns outside the pail on the centerline are also spraying and
moving upward, coating the part.
Another option for the pail’s exterior is the use of several stationary guns,
positioned so that their patterns overlap for uniformity. As the rotating pail
moves into range, the guns are triggered on, quickly coating the part.
Following VGMs, are overhead monorail conveyors as well as C.O.E. Washer
and dryer drums, or products of a similar nature, can be suspended from the
conveyor with their openings facing down. The automated VGM and gun
array, following the rotating drums, can move upward into the cavity and
spray during withdrawal.
System Features:
Heavy Duty 1 1/2” double pitch Chain-On-Edge Spindle Conveyor. Included
is PCT’s exclusive “V”- wheel and spindle assembly stabilizing guide
bearing design, electric gearmotor drive and manually adjusted chain
tensioner. Select continuous running, index cycling or both conveyor
operations with a variety of speed ranges. Positive engagement chain-type
powered product rotator with an electric explosion proof gearmotor, variable
frequency drive and chain tensioner. Optional adjustable spray gun mounting
bar available.
Chain-on-edge systems have been used successfully to apply liquid and
powder coatings for many years, but not many manufacturers know they
exist. They are called chain-on-edge because the system consists of a
continuous loop chain with pins or spindles that convey the parts to be
coated in and out of the spray area. The systems can be configured to have a
small footprint with high production rates.
The Process
The chain-on-edge conveyors work with your spray booth in an automated
process. The parts are loaded on a spindle, which moves the part into the
spray area and in front of the spray guns. The part is rotated for full coverage
and conveyed to the drying/oven section of the loop. The system has skip
spray sensors that can read whether a part is present and only sprays when
there is a part to be coated. The gun controls ensure that no coating is
wasted.
Depending on the size and shape of the part to be coated, the spacing of the
spindles can be easily adjusted to allow space for full rotation of the part.
The spindle chain can be sized to accommodate larger and heavier parts.
Liquid and Powder Coatings
The chain-on-edge systems works equally well for liquid or powder
coatings. The liquid coatings can be applied by automatic air spray, HVLP,
air-assisted airless or electrostatic guns. For powder coatings, you can use
electrostatic or tribo charge guns. The chain-on-edge systems most often
utilize a dry filter spray booth with high-efficiency Wave™ spray booth
filters.
The spray booth sidewalls will have an appropriately sized conveyor
opening.The parts can be conveyed through an in-line oven, which can be
convection, pre-heat, or a Halogen curing system.
The chain-on-edge systems are very flexible in layout and design and can
conform to your spray booth operation.
Advantages
Uniformity of the coating on the product.
Cutting down of product rejections.
Minimum human element.
Paint savings.
In most cases, production rates can be increased.
Eliminate skilled Painter or Operator
Deliver consistent quality of painting on product
Simple to operate
High productivity of Paint consumption
Finally cost per unit is lowest due to
Be of International quality
- Less space
- Less power
- Less manpower cost, paint consumption cost etc.
- Less rejection
Lastly
highly
Application
Widely applicable to production of,
Plastic Electronics
Hardware
economical
&
reliable
Sports Equipment
Household Appliances
Vacuum Coating Industries
Such as various types of high-yield, high-yield high-quality automation
can paint equipment.
JUSTIFICATION OF COST
Material savings.
Increased production.
Improved product quality.
Finish uniformity.
Labor savings.
