Can anybody tell me how to calculate the cooling channel diameter in injection mold & on which factors it depends?

Hi Ranjit. Good morning.
I advise you a good book for moulds. "The Mould Design Guide". Peter Jones (Smithers Rapra)

Hi Ranjit , Good Evening,
not an easy task , it depends upon mould cavity and core surface area,material shot temperature , ambient temperature and mould material heat dissappation rate and cooling fluid temperatureand flow rate and mould mounting vertical or horizontal and moulding machine parameter--do not get confused , it easier to copy the nearest similar mould and copy similar or read books or use analysis software , thanks and regards

There is nothing more important to a mold then the cooling unfortunately this is usually the last item to be designed in the tool. Everything else take priority; ejection, slide, lifters, cavity combinations, inserts, part design, and so on are all features that need to be taken into consideration when designing cooling channels.
One of the biggest issue I’ve seen is that tool shops live in the past meaning “ I’ve been putting water in a tool like this for 50 years” which means no one thinks much about it. Without giving out our specification the biggest issue I see is that they use to small of water lines over and over we see 8mm water lines being used and this is way too small.
We’ve spent days designing water circuits making sure there balance and there enough of them so that we get the proper flow.
This subject is so big that there is no simple answer it’s very complicated because of all the factors involved, you can have the best design tool in the world but if your plants delivery system is bad then you’re in trouble.

Dears thanks for your valuable suggestions, but how to specify these factors & z there any relation with thermal conductivity of H-13, p-20,stavax...

All steels transfer heat at a different rate H-13 is one of the poor one’s due to it’s hardness. The rule of thumb is the harder the steel the worse it transfer heat. Copper is one of the best but a tool would never hold up if you used it. The solution is to balance the steel with the material your trying to run. If it’s a high abrasive material like Glass filled materials then you need to go with the harder steel. You can also go with P-20 and have them Dyna Blued which bring up the hardness to around 45-55Rc. The other choose is to us special steel in your tool that allow better heat transfer things like Mold Max when used as an insert can work great, but keep in mind that you must have a water line in the insert or it’s not going to work and will be worse than the original steel. Bottom line is you never get anythign for free you will sacrifice one for the other it's just a matter of what your goal is.

Respected Ranjit-- you really have to worry and calculate -- if your component -- is transparent , material is highly shrikable , if the component has a abrubt parting line , if the component has a glossy "A" class surface and is non painted component used in a sub/ or part of a assembly or directly used as product, has abrubt section , has large radius in corners , esp thickness section varies at the cornes or section , ribs ,.
Have mentioned some points where proper cooling must be there .
The machine should have a consistent shot (feedback loop required ) and good temperature controll and and good optimised time of cycle wrt to mould and mould cooling flluid , and raw material also.
Please do not worry , just see if you can what the old moulds have been designed or analysis if component is of crtical few points which i have mentioned in the above , and it depend how much variation from the first good {acceptable } component to the most variable component {on the boundryline of acceptance or non acceptance } , you may have to study the process parameters and readjust or analysis this simulation with a good simulation software -- so dont worry, checkout by thumb rule. ie most easiest way but may turn out diffucult if not experienced.

What happens if your old tools aren't done right then you’re just going to copy bad to bad. The issue isn't whether or not they have high shrink ability or not all material will shrink and that's a factor’s build into your tooling. The issue you need to worry about is indifferencial shrinkage meaning the part shrinks at different rates throughout the part and that’s due to part design. The problem is you need to be very aware of your parts design so that when designing your water circuits that you can take into consideration those areas of concern. The goal should be to get the coldest part possible off the tool the goal should be uniform temperature distribution across the entire part, we shoot for +/- 15c from one end of the part to the other. If you can accomplish that your will minimize your indifferencial shrinkage. The other huge factor is using MFA if you understand and can use MFA then your way ahead of the game.

we were taking it as 10 mm in Igtr there is also a concept that if you can reduce the temperature of water about 10 deg c the entire mould cycle time comes down drastically as the only scope of reducing time is in the cooling time.

Respected Ranjit, copy the correct working moulds if possible --as tom sir says it differential rate of shrinkage of component (desingned) . Now you have to decide -- whether the component is astectic or functional important. And tom sir rightly say some problem can be visuallised by MFA ( i am not experienced). But by thumb rule-- wt of component -- + wt of runner + wt of riser +wt of Sprue.-- calculate for the plastic material amount of energy required to maintain the liquid temp for or before shot-- on the mould side energy calculation , by specfic heat of material (mould) , component temp -- and assuming the cooling side to be ambient. and then see( after calculation) how much will be temperature of surface , and check with material manufacturer how much temperature difference is allowed and esp to the points where i mentioned earlier. Points to remember are 60 to 70% of heat is trying to go in antigaravitational direction rest of the heat will be go in to the other perpendicaluar direction and some hot spot will be there as i mentioned before (all points)-- you have to visualise this by ur thumb rule calcuations. Hope your worry is over.
Now your got 5to 7 stand points---One energy balance calculations (above mentioned) and second from good working similar mould , third is from MFA software analysis , fourth is from other Validation of proceess by ANother Analysis software and FINALLY FIFTH- YOUR JUDGEMENT AND PECEVIERIENCE AND YOUR DESIGN INSTINCT. AND SIXTTH (IMPORTANT) RAW MATERIAL MANUFACTURERs comment or analysis of data properties OF RAW MATERIAL (PLASTIC ) BEING USED .
Multinationals require some analysis software base validation
thats all from me ( though i am not so experienced )-- sheetal amnaji

For me 10mm water lines are not very good the problem is that when you stack up all the connection that you will have fittings less then 10mm and once you put in one diameter less then 10mm then the whole circuit is compromised. Again water temperature isn’t as important as you may think one of the biggest issues will be that the mold and water lines will sweat and that water tends to fall into the mold. Also remember heat dissipates at 90 degree angles that’s way when you get into corners you will have such a huge problem the inside corner has all the heat and the outside of the corner is much less, the result is clam shelling or warpage. If you really want to see what’s going on with your part then buy a thermal imagine camera, Flir is one of the biggest names but there are other companies. I’ve been using one for years and trust me this is the only way to really see what your tool is doing or how good or bad your mold is performing. The parts will tell you everything you need to know about how well you design your tool.