The chiller, which is usually called "laser water tank", is not only used to cool down the laser source, but also serves as the cooling system of the laser cutting/welding/cleaning head.
Following is the knowledge of working principle, daily maintenance and precautions related to water chiller.
01
Why does laser equipment need a chiller?
The main working principle of laser equipment is to convert electrical energy into light energy, for the conversion is not 100%, so when a part of the electrical energy is converted into light energy, the other part is converted into heat energy; in addition, the operation of the equipment and the friction of the metal will also cause the laser welding/cutting/cleaning head to generate a lot of heat.
Heat energy stays inside the laser and welding/cutting/cleaning head, which can affect the processing effect at least, or damage the internal components at worst. Everyone knows that the cost of lasers and welding/cutting/cleaning heads is high, and the repair and replacement after damage are also very expensive. Therefore, the use of water cooling can reduce the loss rate of equipment and reduce maintenance costs.
02
How does the chiller work?
Water chiller is a cooling water device that can provide constant temperature, constant flow, and constant pressure. Water chillers are divided into two types: air-cooled chillers and water-type chillers. Water-type chillers are common in laser processing. The machine is also the model to be discussed in this article. Common laser equipment chillers can provide two cooling media with stable temperature, one uses low-temperature coolant to cool down the laser, and the other uses normal temperature coolant to cool the welding/cutting/cleaning head.
Schematic diagram of water cooler
03
How can we maintain the chiller daily?
The first is routine inspection. Every other week, check whether the water level of the cooler meets the requirements, and check once a month whether the water quality of the water cooler has changed (color, smell, impurities, etc.). The second is regular replacement and cleaning, you can refer to the following replacement and cleaning cycle.
Filter cleaning cycle: according to the water quality, check once a week whether the filter is blocked (laser water inlet filter, water cooler filter), the laser water inlet filter is in the laser water inlet Y-shaped mouth.
Laser water inlet filter
Remove the water cooler filter
Dust filter cleaning cycle and cleaning steps: The dust filter is on both sides of the water cooler, and the dust filter is easy to remove. When there is a lot of dust, the cleaning frequency can be increased. Remove the dust screen and use an air spray gun to remove the dust on the dust screen. For oily dirt, please clean it with a neutral detergent. Before reinstalling the dust screen, rinse and dry it.
Chiller Dust Filter
Filter element replacement cycle: Check whether the filter element of the water cooler is polluted, and the filter element of the water cooler needs to be replaced once every six months at most (according to the actual model, some have no filter element).
Cooling water replacement cycle: replace the cooling water according to the water quality, and the cooling water needs to be replaced once every 3 months at most. The water tank of the water chiller is not sealed. Long-term exposure to the dusty environment, dust, metal filings and bacteria enter the cold water to cause water deterioration, and produce insoluble water substances that adhere to the inner wall of the laser waterway, thereby blocking the waterway and causing water flow. Decreases the cooling effect. If this happens, drain all the deteriorated cooling water in time and replace it with new cooling water.
Contaminated filters, filter elements and laser waterways
04
How to choose the correct cooling water?
Cooling water chooses distilled water and deionized water. The reason for choosing these two kinds of water is that distilled water or deionized water is not easy to produce scale during the circulating heating process. It is strictly forbidden to use bottled pure water and tap water.
Distilled and deionized water
05
How to replace the cooling water?
Procedure for replacing cooling water
1. Disconnect the equipment power supply and water cooler power supply. 2. Drain the water in the water cooler and laser, clean the water tank and drain the water.
3. Clean the water filter and filter element of the water cooler (some water coolers do not have a filter element, please consult the water cooler manufacturer for specific conditions) and the filter of the laser water inlet. 4. Install the filter screen and filter element.
5. Inject distilled water into the water cooler to reach the standard liquid level.
6. Turn on the water cooler to circulate the water, check the liquid level display of the water cooler, and add distilled water if the liquid level drops. Note: To prevent the growth of bacteria and algae, 10% alcohol can be added to the cooling water.
06
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What else needs special attention in the daily maintenance of the chiller?
When the ambient temperature is 0 degrees or below, it is recommended that users add antifreeze to the cooling water of the laser. After adding antifreeze, the freezing point of the water can be lowered so that the cooling water does not freeze.
Antifreeze cannot be used for a long time: any antifreeze cannot completely replace plasma water, and antifreeze has certain weak corrosion and can only be used for a short period of time. Long-term use will cause damage to the laser and cutting head optics, causing unnecessary losses. After winter, the pipeline must be cleaned with distilled or deionized water, especially the filter screen of the water cooler, the filter element and the filter element of the laser water inlet, and the distilled water or deionized water should be used as the cooling liquid.
If the machine is shut down for a long time, such as the Spring Festival shutdown or before the laser is transported, the cooling water in the chiller must be drained, and the residual water in the equipment including the laser and the chiller must be blown out with compressed air to prevent internal icing or water leakage from causing device damage.
Drain the cooling water in the chiller
Prerequisite Libraries
The Arduino sketch is attached. You will need the following libraries installed in order to compile and use it:
I recommend building a small circuit and sketch to test each component before building the larger circuit, just in case something has changed and you need a different library.
The Sketch File
If you wish to use my sketch as-is, it is attached to this step as Thermostat.ino. It should work with your Arduino Uno (or clone) without changes if you followed my circuit.
How it works...
The thermostat is fairly simple, and not unlike the thermostat you use to control the temperature in your home. The LCD displays the current water temperature in Fahrenheit and Celsius on the first line, and the current setting on the second line. Whenever the water temperature is above the setting, the pump and chiller are turned on. When the temperature drops 1.75 F° below the setting, the chiller, pump, and fans will all shut off until the temperature again rises above the setting.
Input Lockout
Because of the difficult of getting a clean signal from the Arduino Interrupt Pins (maybe this is a problem with my old over-used Arduino Uno? Or maybe it is because of noise from the rest of the circuit), I have added a "Setting Lock" feature. In order to change the thermostat setting you must hold down both the UP and DOWN buttons for 1 second. When this has been detected, the LCD will display the message "----UNLOCKED----" on the top line and " Enter Temp: " on the second line for 3/4 of a second. While unlocked, the UP and DOWN buttons may be used to increase or lower the thermostat setting. If no buttons are pressed for 10 seconds, the input lockout is reinstated. If both buttons are pressed and held simultaneously again for 1 second the lock is also reinstated, but be warned that it can be difficult to press both buttons simultaneously without bounces causing the temperature setting to increase or decrease by one or two. For that reason you may prefer to just let the system re-lock on its own by leaving the buttons untouched for 10 seconds.
Reading the Temperature
Please read through the sketch for all of the details on how the code works. Here I will only highlight portions of it. In particular, the TemperatureModule class utilizes the OneWire 2 library to read the temperature from the DS18B20 in the IP65 Digital Waterproof Temperature Probe. The TemperatureModule class is based on code in the DS18x20_Temperature, OneWire 2 example sketch. It offers only two methods: Initialize() and ReadTemperatureF(). Initialize() must be called before ReadTemperatureF is called for the first time. ReadTemperatureF will return the temperature in Fahrenheit and will fill in a passed variable with the temperature in Celsius. An instance of TemperatureModule is declared on line 171 of the sketch, after the definition of the class:
You will also notice g_lcd on line 172 - an instance of LiquidCrystal_I2C. Both of these global objects utilize macros defined at the top of the file. These macros also define each Arduino PIN used by the sketch:
Setup
Lines 1 through 3 include the libraries used by this sketch. On line 3 you will see the include of EEPROM.h. This will be used during setup, and after the thermostat setting is adjusted to save the temperature in the Arduino's EEPROM so that it is remembered across power resets. The temperature is stored as a single byte and allowed temperature settings go from 35°F to 85°F. This seems to be a reasonable range for our purposes and by using a single byte to store the value things are simplified.
The setup() function of the sketch will first set a couple of global variables used to debounce our push button switches. After this it will set the Pin Mode for each pin we will use (lines 255 through 260):
On line 261, we set the Chiller to the Off state, and on line 263 through 269 the temperature setting is read from the EEPROM and set to 56°F if the current value is out of range. Lines 271 through 273 initialize the I2C LCD library and because it takes about a second to initialize the TemperatureModule, the message "Initializing...." is displayed on the LCD until the temperature sensor is detected (lines 278 through 280). An additional 1 second wait is forced on line 281 -- this seems to be required by the OneWire library for properly reading the temperature sensor.
With everything else initialized we attach Interrupt 0 to the BumpSettingsUp function on line 283, and Interrupt 1 to BumpSettingsDown on line 284 and enable interrupts (line 285).
The BumpSettingsUp and BumpSettingsDown functions check to see if the input is locked. If it is not, they will increase or decrease g_uiTemperatureSetting, as long as the interrupt (triggered by a push) satisfies the time requirements to not qualify as a switch bounce. These two functions also ensure the setting stays between 35 and 85 degrees.
Not shown here is BumpSettingsDown() which is identical to BumpSettingsUp except that it drops the value in g_uiTemperatureSettings. There are also a few other functions used as helpers such as OutputLCDLine() which will display a string on line one or two of the LCD. The function TurnCoolingOnOrOff shown below is used to set all 4 relays to the ON or OFF position and to record whether things are ON or OFF in g_bCooling:
The function ToggleInputMode is called when both buttons are held down for one second, or after 10 seconds of no buttons being pressed while input is unlocked. As you can see it records a new setting in the EEPROM slot 0:
This double-button press check is done by the helper function CheckLockUnlock():
All of this leads to the main loop:
In this first half, there is a check to see if the user is unlocking input. If 10 seconds has passed since a button has pressed, while input is unlocked, the code on lines 373 through 379 will ensure that the lock is reinstated.
On line 383 the current thermostat setting is displayed on the second line of the LCD, and on line 387 the current temperature is read from the thermometer. It is then displayed on the first line of the LCD, on line 397. Because the thermostat setting was converted to a float on line 385 a simple comparison can be done to see if the Chiller needs to be turned on:
If the current temperature is above the thermostat setting the Chiller is always turned on (line 406). Otherwise we check to see if the temperature is 1.75 degrees below the setting and if so the Chiller is turned off.
On line 418 a one second delay occurs to provide time for the thermometer to be read properly again and the loop is reentered.
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