How to look after them and when should they be changed?
When does a print head need replacing?
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Printheads come in all shapes and sizes and types they also come with a manufactures warranty which can vary from one month to one year depending on the type of printer and who the manufacturer is. Given they are an expensive item to replace. It is very important that some time be taken to look after them. Daily use will lead to build up of overspray this will vary depending on the head height being used, this build up in conjunction with the media type being used and the environment will attract particles to the surface of the head.
All printers give the capability to carry out head maintenance this should be done on a daily basis using a mild solvent /Flush and lint free swabs. Take time not only to clean the surface but also the edges. When printers are not being used on a regular basis it can take some time to bring the heads back to an acceptable level especially in the case of solvent and UV inks. If at all possible try and run some simple test prints which require all colours everyday or perhaps some prints for internal use.
If the printer is not going to be used for a week or so it is best to flush heads through and leave flush in the heads. If this cannot be done then soak some lint free cloth with a mild solvent and place on the capping station prior to capping if possible, if this is not possible then clamping the capping station tubes and placing some mild solvent on the actual caps prior to capping the heads should help. The figure shows normal bulldog clips but clamps of all sorts are available.
Both thermal and piezo heads do wear in the case of the thermal heads the heating element may fail as these are being switched on and off hundreds of thousands of times. In the case of the piezo head the crystal characteristics will change over a period of time both of these actions will cause the quality to deteriorate. There are other factors such as media debris and the environment that can cause quality issues, which is why it is important to carry out the manufactures daily / monthly preventative maintenance by doing this when quality issues arise it helps diagnose where the problem lies.
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Head height adjustment is also key in getting quality output, depending on the material and printer being used the closer you can get the head to the media the better. This cuts down both deflection and banding, you obviously have to be aware and make allowances for the media thickness to avoid any head strike. Some manufacturer have automatic head height facilities and others just have fixed settings, but it is always worth finding out the best height that can be used for a given media.
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Problems occurring with Print heads drying up and causing blockages to the nozzles, this does not necessarily mean installing a new print head which is costly and may sometimes be unnecessary to do. An easy fix and solution to this problem is detailed below:
With the carriage locked in home position and the heads capped.
Take a clean syringe, and fill it with a clean solvent solution.
Attach a male adapter to a syringe, (used to connect the pump tubing), as this fits perfectly into the top of a new damper.
Carefully remove the damper from the troubled print head, with the syringe attached to the new damper push onto the manifold on top of the print head. Gently push the plunger on the syringe, until you can see the blockage clearing from the print head through the tubing that connects to the pumps. Be careful not to apply too much pressure there are filters in the actual head and to much pressure can cause issues. The same thing can be done by connecting the tubing from the syringe directly onto the manifold this should only been done once you have experience of doing this.
Do this until the solvent becomes clear going through the tubing of the pump. It can sometimes take a couple attempts. If the solvent goes through to the pump tube you can be sure that the manifold, head, capping station and pump are clear of any blockage. If after a couple of attempts nothing is happening you need to isolate where the actual blockage maybe. This can only be done with the heads disengaged from the capping station. Once the head is uncapped ensure the printer is switched off and the power lead is removed this mainly applies to the large format printers and not the Grand format. This is to avoid any possibility of causing problems to a main board if you disturb ribbon cables that plug into the print head.
Move the carriage to a comfortable position to work on and place lint free material under the print head to catch the solvent. With the damper removed attach the syringe to the print head and gently push you should feel no resistance and the solvent should jet out of the bottom of the head. Look at the base of the head whilst doing this and you should see a nice curtain of solvent from all the nozzles. If this is good move onto the capping station.
On the capping station, disconnect the tube at the pump end place some lint free material on the bottom of the tube and using a pipette place some solvent on the cap after a short time this should drain away. If it drains away move onto the pump.
Place the syringe onto the pump tube and gently push this should push the solvent through to the waste bottle.
When doing this always complete the process as quick as you can and never walk away and come back. Because the carriage is not capped leaving it uncapped for a long time could cause other heads to dry up and become blocked. Also if you are unsure of any of the above process do not attempt it, get an engineer to check it for you.
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When does a print head need replacing?
Below is a nozzle test print that we are probably only two aware off, if this is the case after trying to recover the head(s) then the only thing to do is to replace the head.
After a while a print head may become blocked by paper debris or solidified/dried ink. And you notice your printing quality is suffering or the printer fails to print at all, and the above has not help it may be time to change your print head. On some printers it is very easy to change a print head on others it is not so easy. There are quite a few items to be removed to gain access to the print heads, precautions have to be taken against static and you should not remove any heads unless the mains lead is removed after power down simply switching of from the control panel is not enough. Unless you are familiar with these it is best left to engineers who know what they are doing.
There are always mechanical, electronic and electrical adjustments to carry out when fitting a head.
Mechanical – This is always obvious and when taking a print head out the least amount of disturbance on removal makes it easy to adjust when using the appropriate test file.
Electronic – This adjustment is used to line all the heads together given the mechanical adjustment is correct. It moves the firing up or down usually using the black as reference.
Electrically – This is the voltage that is applied to the head to force out the droplets on grand format printers it is normally as a voltage reference which is adjusted by a potentiometer on a head board, however on large format it is by entering a head rank number which not only sets the voltage but various other items such as drop size, firing rate etc. It is on these units it becomes difficult to determine which numbers actually change the voltage, because the crystal characteristics change by increasing the voltage you can sometimes improve the quality but changing the numbers randomly can cause problems like nozzle drop out and deflection. These heads are manufactured with the head rank for optimum quality for a given printer and should therefore be replaced when quality starts to fall away normally with blocked nozzles that cannot be cleaned, leading to deflection or no output.