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Re: Help With Injection Moulding Cooling
Quote:
Originally Posted by
Peter_1
Just joining this thread and not read everything thoroughly , if it's an open circuit, then probably you have also fungus and some sort of gelly inside the tubes.
The plastic granules are covered with some sort of white gliding powder. This gliding powder is mostly organic.
Due to the ideal warm temperatures, this powder 'transforms' to some sort of gelly and blocks strainers and tubes in heat exchangers.
I should also follow the advice of USIceman, never follow for 100% what someone is telling you. Take out a story or arguments what can be useful to solve the problem. If they don't give enough information, it's up to you to ask the proper questions.
This has nothing to do with the fact that he's your friend or that he's trying to screw you up. Your friend can think that these are the right values, these values can come from another, he's saying this to help you but believing everything for 100% is wrong.
Besides, your friend is not a refrigeration tech, it's up to you now to prove you are the right man on the right place and check what's really needed and then see what's already installed. You then can conclude if there's not enough capacity.
We install for such an application a 3 way mixing valve and VFD controlled pumps.
Peter
The client has expanded the operation from 12 injection moulding machines to 19. The new machines are larger capacity and the heat load has almost doubled.
The problem is more to do with scale build up and not so much algae or debris. Treatment of the water is not an option and strainers are also not going to stop scale build up.
The client, his production manager and the injection mould engineer are all insisting that these machines require a high pressure differential between the flow and return pipes to induce enough water flow though the mould tools. I am not going to argue with them, they have factories in many counties making medical items such as oxygen masks. Should I ignore their advice and install the more usual chilled water lop set up with either variable flow pumps or standard pumps and mixing valves and we don't get enough water flow, I think I might just get sued to bankruptcy!
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Re: Help With Injection Moulding Cooling
Quote:
Originally Posted by
Refrigerologist
Gary, I had already covered this in a previous post. We are aware of the lack of flow. This is the main reason for wishing to make the system a sealed and pressurized.
The heat exchangers are full of scale. There are no end plates and the only options are to carry out an acid clean.
At this point I see no evidence of scale build up, unless you are running a very low SST (high approach). What I see from the data given is a flow problem, not a scale problem.
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Re: Help With Injection Moulding Cooling
Quote:
Originally Posted by
Refrigerologist
RE: Flow ring
I had never seen a set up like this one. I have a drawing but unfortunately my scanner is busted!
So I will try to explain the flow:
1. The process pump pulls water from the cold tank, the water flows into the process chilled water ring main. This make a complete loop of its' own. There is no direct return water pipe from this ring main!
2. Water flows into each machine. The heated water flows into a process chilled water return ring main. This ring main is a complete loop of its' own, but has the addition of a pipe 'teed' into it, this pipe returns to the warm tank.
3. Installed between the flow ring main and return ring main is a pressure control valve. As each machine closes down and the pressure increases in the flow ring main, a spring controlled bypass valve opens and allows water from the flow ring main into the return ring main. The water is returned to to the warm tank.
4. The chilled water units are piped so that water from the warm tank is pumped through the chiller heat exchanger, is chilled, and returned to the cold tank.
This would probably make sense if, and only if, I knew what a ring main was. Not having a clue, the above makes no sense at all.
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Re: Help With Injection Moulding Cooling
i think i start to understand the set-up,but is it not possible to post a drawing of some kind,so we can make note's and idea's and send it back??? i think that everyone will understand it much better that way,and you can pick the best of choices.
Ice
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Re: Help With Injection Moulding Cooling
Quote:
Originally Posted by
Gary
At this point I see no evidence of scale build up, unless you are running a very low SST (high approach). What I see from the data given is a flow problem.
Gary you have not been on site! I have, the flow is next to nothing through the heat exchanger.
The tubes are probably clear and the scale has built up around the ends before water has a chance to enter the tubes. I have had this problem many times both on water cooled condensers and chilled water evaporators. Hence the low leaving water temperature and poor flow. You are confusing the issue!
Some of us do actually know what we are doing! i am asking for advice on what to do with an open system of unusual design. I was not here for debate on flow rates, capacities etc:D. The chillers are knackered. They are undersized, they are no longer required by the client. Could we please stick to the request for help in closing the system if that is possible?
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Re: Help With Injection Moulding Cooling
Quote:
Originally Posted by
Gary
This would probably make sense if, and only if, I knew what a ring main was. Not having a clue, the above makes no sense at all.
A ring main is a circuit that leaves and returns to the same place making a complete loop.
An example in UK wiring is for 13 amp socket outlets for appliances. A 3 core cable, (L,N & E) are connected into the distribution board. The live at the circuit breaker, the neutral at the neutral bar, and the earth at the earth bar. This cable is run from socket to socket, finally returning to the distribution board and connected in the identical points as above. This constitutes a ring main. Effectively 2, 3 core cables feeding all sockets and increasing the amount of amperage that may be pulled through a relatively small cable. For instance 32 amp@ 240v on a 2.5mm cable.
In this instance it is a 3" pipe completing a circuit with a pump teed in at one point.
I hope that makes sense:p:p
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Re: Help With Injection Moulding Cooling
Quote:
Originally Posted by
icecube51
i think i start to understand the set-up,but is it not possible to post a drawing of some kind,so we can make note's and idea's and send it back??? i think that everyone will understand it much better that way,and you can pick the best of choices.
Ice
Sorry, my scanner is broken so I cannot upload the schematic. I have tried to explain it as best I can, but it is hard to follow. I have not spoken with any body, and that includes companies who deal mainly with process cooling, who have come across this set up!
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Re: Help With Injection Moulding Cooling
Quote:
Originally Posted by
US Iceman
That in itself is a waste of energy. A better solution is use a VFD with a pressure transducer to slow the pump down when the pressure begins to rise.
The underlined section I question also. If you dump cold water back into the return side that can potentially lower the LMTD that might be available for the chiller.
One question: what is a flow ring?
Iceman, I could not agree more about the waste of energy, I would love to use variable flow, but if you look at my previous post, (after your one on this subject as I missed this one), the client is insisting that they need a high pressure differential for flow accross the tool heads. I have not heard of this requirement before, and nor has anyone I have spoken to. The installed pumps for the process side are not circulators but are 2 stage pressure pumps! Personally I feel the requirement may have been misunderstood by the original installer!
I think I may have to contact the injection machine manufacturer and confirm the actual worst case pressure loss for each machine tool. Then as per usual, if I install the correct pumps, there should be no problem other than back pressure which we can control with variable speed drive.
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Re: Help With Injection Moulding Cooling (For information)
Guys
I would like to make you aware of water problems that we face in Guernsey.
Domestic water in this area has a pH of about 7.1 to 7.6, slightly alkaline. It contains quite a lot of lime scale.
I have been on several sites where a 4" incoming cold water main serving a school, prison or large office has been almost blocked with scale build up. About 5 years ago we replaced a number of 4" valves that had only a 3/4" hole left in which to pass mains water. The dinner ladies at the shool had to fill every pot and pan they had with water, if lunch prep time coincided with the kids taking showers!
The local government plumbing department failed to find the problem in 2 years of trying. They assumed the valves were ok!
So from this you will see that scaling can and is a big problem even where cold water is concerned and especially where there is a continual replenishment of nutrient, lime scale, iron etc, in the water.
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Re: Help With Injection Moulding Cooling
Quote:
Originally Posted by Refrigerologist
...the client is insisting that they need a high pressure differential for flow across the tool heads.
That may be, if the molds are not designed for sufficient water flow to provide adequate cooling. Therefore, if the mold flow paths are restrictive then the only way to gain cooling is push more water through at higher supply pressure.
I have not seen this before on the projects I have worked on as all had single stage centrifugal pumps.
Is the water quality is as bad as you say, then a closed loop with treated water would be an immensely better solution.
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Re: Help With Injection Moulding Cooling
maybe consider "reverse osmosis" water?
and as i understand,is when the chilled water entering the mould machine,it become so hot that it would return instead of going forward,so you have to install or very heavy circulation pump or heavy duty pression pumps?
Ice
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Re: Help With Injection Moulding Cooling
I should do what the client is asking for, even it's an energy wasting system or a short sight vision.
Install more chillers, make a closed loop system of it and install some HP pumps (for example Grundfoss CR pumps) working parallel so that you have some redundancy or one VFD controlled and 2 full speeds. Hitachi has a VFD which can control this without additional electronics (up to 4 compressors or pumps).
Don't argue with your client any longer them, make that you earn money now.
Install an isolated tank of +/- 500 l with a centrifugal pump and let the chiller cool this reservoir.
Then a second loop with a 3 way bypass with the HP pumps to the molds.
There is circulating a schematic on this forum, I think from a Norwegian or Danish poster.
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Re: Help With Injection Moulding Cooling
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Re: Help With Injection Moulding Cooling
Quote:
Originally Posted by
Refrigerologist
Gary you have not been on site! I have, the flow is next to nothing through the heat exchanger.
The tubes are probably clear and the scale has built up around the ends before water has a chance to enter the tubes. I have had this problem many times both on water cooled condensers and chilled water evaporators. Hence the low leaving water temperature and poor flow. You are confusing the issue!
Some of us do actually know what we are doing!
Don't take it personally. There are other people watching and learning. They need to know which symptoms indicate flow problems (delta-T) as well as which symptoms indicate scale build-up/heat transfer problems (approach).
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Re: Help With Injection Moulding Cooling
Was thinking th same Gary.
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Re: Help With Injection Moulding Cooling
Let's see if I am visualizing this system correctly:
Warm return water flows from the processes to the return ring/loop, then from the opposite side of that return ring/loop to the warm tank. From the warm tank, the water flows through the chiller to be cooled, then through the cold tank to the supply ring/loop. From the opposite side of that supply ring/loop, the cold water flows to the processes.
The pump is between the warm tank and the chiller.
There is a spring loaded pressure relief bypass from the supply ring/loop to the return ring/loop.
Does that sound about right?
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Re: Help With Injection Moulding Cooling
Quote:
Originally Posted by
Peter_1
and install some HP pumps (for example Grundfoss CR pumps) working parallel so that you have some redundancy or one VFD controlled and 2 full speeds. Hitachi has a VFD which can control this without additional electronics (up to 4 compressors or pumps).
make sure they are strong enough to overcome the going pressure rate.:rolleyes:
Ice
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Re: Help With Injection Moulding Cooling
Quote:
Originally Posted by
Gary
Let's see if I am visualizing this system correctly:
Warm return water flows from the processes to the return ring/loop, then from that return ring/loop to the warm tank. From the warm tank, the water flows through the chiller to be cooled, then through the cold tank to the supply ring/loop. From that supply ring/loop, the cold water flows to the processes.
The pump is between the warm tank and the chiller.
There is a spring loaded pressure relief bypass from the cold ring/loop to the hot ring/loop.
Does that sound about right?
is there not going to be a chilled water tank needed?
Ice
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Re: Help With Injection Moulding Cooling
Quote:
Originally Posted by
icecube51
is there not going to be a chilled water tank needed?
Ice
I'm thinking that's the "cold tank".
On the other hand I may be entirely wrong in my understanding of how the system is piped?
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Re: Help With Injection Moulding Cooling
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Re: Help With Injection Moulding Cooling
From your description of the system it should be possible to close the system but is the existing ring (which I believe is acting as supply buffer tank/ low pressure header) big enough to take the new load and is it likely that all the injection circuits will be running at once.
The warm tank could pose more of a problem because if you upgrade the chillers then you`ll definately have to up the flow rate which will mean you might end up drawing off from the cold tank to maintain the warm tank under low load conditions.
I can see why it is designed as an open system and closing it without a complete redesign may prove to be..............interesting:D
It would be really helpful if you could draw up a schematic.
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Re: Help With Injection Moulding Cooling
Its making a little more sense now
I think if you look at just the chillers, cold tank and warm tank as being the primary circuit and close it as you would any normal chilled water circuit the the take off from the cold water tank must be big enough to compensate for no warm return from the process (might need a one way valve in it) work out if you need an expansion vessel on the warm tank and or invertor drive your pump feeding the chiller from the discharge to ensure your vol remains constant, depending on system characteristics the cold to warm take off might want to have a modulating valve on driven by cold tank pressure.
Hope that might put you on the right path. Its a bit difficult to say without seeing the system and shed loads of calcs.
Don`t forget that if youre going for vt on the process take offs then you need the temp diffs for the process water to size and select your valve arrangement.
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Re: Help With Injection Moulding Cooling
Hi Refrigerologist Only just picked up on your post, and have quickly scanned what has been said.
There are two points that do not seem to have been asked or questioned. Your existing chiller are likely to have shell and tube evaporators ? the new chillers you are looking at will have Plate type heatexchagers ?
The second item is are you keeping a primary loop through chillers and back to the buffer tank ?.
Providing the primary and secondary loop feed directly from the buffer tank you will not have any problems with a sealed system, as any imbalance is cancelled out within the buffertank. We have completed many such modifications over my 35 years in process cooling, with no problems.
Ensure New Pumps match design flow for new chillers as Plate type HeatX have greater PD across them from Shell and tube.
Flow to process should be from base of buffer tank, as should the return from chiller. Flow to chiller should be from top of buffer tank as should the return from process.
Hope this helps.
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Re: Help With Injection Moulding Cooling
Thanks for all the ideas and assistance.
I have since spoken with the guy who originally designed the system! He has told me that in order to ensure that the water temperature at each mould head remains constant, the chilled water loops are fed via pressure pumps and the flow pipe is a complete loop. The return water path is via each mould head unless the pressure increases to a point where the spring loaded pressure relief valve opens and allows water to flow directly to the return circuit.
He has advised us not close the system due to balancing problems.
We are going replace the existing plastic water tanks with GRP insulated tanks and install process chillers with shell & tube heat exchangers. We will be recommending water treatment of the ingoing make up water to help prevent scaling in the tubes.
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Re: Help With Injection Moulding Cooling
Quote:
Originally Posted by
Gary
Let's see if I am visualizing this system correctly:
Warm return water flows from the processes to the return ring/loop, then from the opposite side of that return ring/loop to the warm tank. From the warm tank, the water flows through the chiller to be cooled, then through the cold tank to the supply ring/loop. From the opposite side of that supply ring/loop, the cold water flows to the processes.
The pump is between the warm tank and the chiller.
There is a spring loaded pressure relief bypass from the supply ring/loop to the return ring/loop.
Does that sound about right?
Sorry for not replying earlier, but I have been on holiday in Ireland, and the Guiness has been good!
Yes, I think your despcription is about right. It may be a bit academic now as we have decided to keep with an open system but treat the make up water.
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Re: Help With Injection Moulding Cooling
Quote:
Originally Posted by
Peter_1
I should do what the client is asking for, even it's an energy wasting system or a short sight vision.
Install more chillers, make a closed loop system of it and install some HP pumps (for example Grundfoss CR pumps) working parallel so that you have some redundancy or one VFD controlled and 2 full speeds. Hitachi has a VFD which can control this without additional electronics (up to 4 compressors or pumps).
Don't argue with your client any longer them, make that you earn money now.
Install an isolated tank of +/- 500 l with a centrifugal pump and let the chiller cool this reservoir.
Then a second loop with a 3 way bypass with the HP pumps to the molds.
There is circulating a schematic on this forum, I think from a Norwegian or Danish poster.
I haven't been arguing with my client. What makes you think I have been? They asked if we could close the system. We said we could, every one I have spoken to says we can, now the client is no longer sure and does not understand fluid dynamics very well. So we have decided to leave it as an open system and treat the water instead. A far easier install, but actually more expensive as we must now use shell and tube heat exchangers in place of plate type.
Thanks for all the ideas and advice though!
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Re: Help With Injection Moulding Cooling
Hi Refrigerologist and guys,
Have just picked up on this thread and one thought has occurred to me....with reference to the supply loop.....
Although the supply ring is pressurised by the pressurisation pumps (which should be VSD controlled in this day and age) the water in the supply loop will surely have a temperature variation around it, as there is no mention of a circulator pump, and as you mentioned machines being turned off....will not the flow and thus temperature vary according to demand? Maybe this is not percieved as a problem?....perhaps the loop is only small?
You mention project costs are tight and funds limited....are there any goverment tax incentives on Guernsey for energy saving projects (as on the mainland)..?.(ie Enhanced capital Allowance)...just another thought!
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Re: Help With Injection Moulding Cooling
Quote:
Originally Posted by Refrigerologist
He has advised us not close the system due to balancing problems.
How will the system be closed if it has storage tanks in it? The tanks will most likely be open to atmosphere, but the piping would essentially be a closed loop (except hydraulically).
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Re: Help With Injection Moulding Cooling
Your initial major problem is the water quality, as in high calcium content, (hard water). I would definitly recommend converting to a closed loop water system, with high circuit flow rates and a high water chiller by-pass rate. In effect the chiller is trimming the loop temperature, and the low delta tee system water is doing the work. You must add to system a pressure compensation vessel on the primary pump circuit to handle the changes in system and elliminate pipe hammer, the heat exchangers at the moulding machines should have rapid response 3 way by-pass vavs. then you maintain a constant loop volume flow.
First thing to address in the obvious scaling problem in existing system. Ridlime is an excellent product, and eco friendly, add lots of flushing. Next is the problem with closed circuit water cooling systems is the water quality and PH control. Basically you have a perfect low voltage battery, as in dissimilar metals and temp variations and an electrylite (water), so PH and water conditions are important. Cathodic corrossion is un-cool and can send companies broke, because all of a sudden everythings is leaking water and the refrig system is full of water, result no production and huge repair and recovery costs.
Down the track a bit you should recommend a dry cooler with water additions to elleviate the chiller loads, depending on local ambient conditions and wet buld conditions.
magoo
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Re: Help With Injection Moulding Cooling
you will be best to use one buffer tank so that you are constantly mixing the water down through the chiller, otherwise it will be too high on the return to the chiller.
So basically buffer tank flow and return to the moulds then flow and return to the chiller.
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Re: Help With Injection Moulding Cooling UPDATE
Hi guys, an update is long overdue!
Thanks for the comments and advice.
The client has now gone out for a requote, and I am not hopeful of getting the job, but that could now be a blessing!
Anyway the contractor who has now quoted has chosen a plate heat exchanger system on the same open loop system, so I am expecting them to have some serious problems as the water is not treated and the old shell and tubes are fouled with scale deposits!
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Re: Help With Injection Moulding Cooling
You may be thankful you don't get the job. Loosing a job is bad enough. Getting a bad job can be even worse.;)