Die coating pulsed spray system

Abstract

A die coating pulsed spray system for use in metal foundries having a spray gun 1 and a pulse actuator 2 for pulsed actuation of a spray gun fluid needle 3. A control system 10 may be provided having

Description

This invention relates to the application of coating onto metal casting dies in foundries. The invention increases the coating life through multi layered coating application, therefore increasing productivity, reducing scrap and improving profitability. Casting dies and molds require a barrier between molten metal and the die or the mold’s metallic surfaces. The barrier is made from high temperature ceramic materials and is applied as a layer of coating onto the die or mold surfaces. Barrier coatings function as an aid to molten metal flow, solidification and as an anti-soldering agent between the die and the molten metal being casted. Barrier coating thickness varies between 0.10mm to 0.25mm depending on the product being casted. Barrier coatings wear out on each cycle of casting and eventually must be renewed when worn beyond a workable standard. Coating renewal is a long and skill intensive process, and short coating life is costly in terms of production loss, skills and product quality. Barrier coatings are applied manually by using a spray gun or adopted paint spray gun. Compressed air is applied to transform liquid coating media into spray. A single pass of spray deposits a single layer of coating that easily wears off. Therefore, maximum layers are sought within the thickness limit of 0.10 - 0.25mm to increase the coating life, typically a maximum of three layers are possible. Another technique of achieving multiple coating layers is by small bursts or pulses of coating spray. However, it is impossible to maintain a uniform pulse pattern manually, causing uneven, non-compliant coating, leading to a high reject rate. Additionally, manual pulsing of conventional spray guns results in health and safety issues such as RSI (Repetitive Strain Injuries) for the operator. Trials were carried out with pulsed compressed air supply to the spray gun, however compressibility and expansion of air results in poor coating finish and cause “coating spatter” that leads to bad quality castings. In this invention, automatic reciprocating movement is applied on fluid needle 3 through an actuator to achieve accurate coating pulses. The invention “Die Coating Pulsed Spray System” applies coating with time adjustable pulses, without spray “spatter” defects and it is safe to use without Health and Safety concerns. The invention will now be described with reference to the accompanying drawings in which: Figure 1 shows a pulsed spray gun system with a pulse spray gun 1, connected to the control system 10, Figure 2 shows a pulsed spray gun, In figure 1, a pulse spray gun 1 is connected to the air flow sensor 15 on the control system 10 by means of compressed air hose 8. A pulse transmission line 7 is connected between pulse actuator 2 and pulse power source 13 with pneumatic tubes or a low voltage electrical cable. In figure 2, The pulse spray gun 1 is shown. It is equipped with a linear actuator 2 that is coupled to the fluid pin 3. An actuator can be a pneumatically operated cylinder or an electromechanical device such as electromagnetic solenoid, linear motor or a voice coil actuator. When actuator 2 is activated, it pulls the fluid needle to open position and coating spray starts, vice versa fluid needle closes when actuator 2 is deactivated and coating spray stops. The trigger 4 has two functions, partial trigger opens air flow to the spray nozzle 6 and the coating reservoir 9, full trigger opens the fluid pin 3 by manual action. Compressed air supply hose 14 connected to the air flow sensor’s 15 inlet port and outlet port is connected to the spray gun air supply port through a flexible hose 8. Spray gun air flow starts when trigger 4 is pulled partially for coating to be started, allowing compressed air to flow through the flow sensor 15, that sends air flow ON signals to the pulse control electronics to start pulse output to the actuator 2 to move. Pulse actuator movements then allow coating spray in pulsing pattern, pulse on-time and off-time is set by controls 11, 12. Up to 30 pulses per second can be adjusted. Stroke of the actuator 2 and fluid pin 3 is controlled by the adjustable stopper knob 5, this allows control of coating volume applied during each pulse. Coating volume also supplies fine or coarse coating applications. Actuator force is controlled by pneumatic regulator and lubricator 16 or by electronic pulse amplitude control. The actuator force control allows operator to override the pulse function by further pulling the trigger 4, therefore operator has full control on the pulsed or non-pulsed spray. The actuator force control also extends the fluid pin life. As a result of the system shown in figure 1, continuous pulsed coating is sprayed and deposited in layers onto a die surface for as long as spray gun trigger 4 is partially pulled. When spray gun trigger 4 is pulled fully, a continuous spray pattern is achieved.

Claims

1. The invention Die Coating Pulsed Spray System increases the coating life through multi layered coating application.

2. Die Coating Pulsed Spray System according to claim 1, in which multi layered coating is provided by automatic pulse actuator on the spray gun and the control system.

3. Die Coating Pulsed Spray System according to claim 1, in which coating layers are adjusted by pulses per second, from 0.5 up to 30 pulses per second can be adjusted.

4. According to claim 2, in which pulse control system is provided, a pneumatic, electromechanical or electromagnetic actuator can be used.

5. According to claim 2, in which pulse control system is provided, pulse spray gun can be operated in pulsed or non-pulsed function.

6. The Die Coating Pulsed Spray System in which actuator stroke is adjustable, coating volume can be adjusted for each layer.

7. According to claim 6, in which coating volume can be adjusted, fine or coarse coating can be applied.

8. The invention Die Coating Pulsed Spray System allows automatic pulse function on the spray gun, preventing repetitive strain injury to the operators.

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