Low pressure / temp plastic molding - Page 1
Forum section: electronics / general

author: DTJ
author_rank: Super Contributor
timestamp: January 19, 2017, 03:06:43 am
content: I keep coming back to looking at low pressure desktop plastic injection molding systems for electronics.There's systems like Macromelt that are used to over-mold low MP plastic onto PCBs and wire assemblies, stuff like this:https://www.google.com.au/search?q=macromelt&safe=off&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiCjqStm83RAhXKKZQKHV61AsoQ_AUICCgB&biw=1920&bih=939This is a quick overview of the process:http://www.loctite.co.uk/uke/content_data/230400_macromelt_molding_EN_FINAL.pdfThere are parts available on eBay/Aliexpress for building your own bench-top molding unit as well as fully assembled units for around Australian$1000.The more commercial machines are more costly.Has anyone here actually used this stuff?I'm thinking of using it to over mold a PCB that's connected to the end of a cable and is used submerged in water as a sensor. They'd be made in batches of 20 or so every few months.Will it seal and will it last?

author: technotronix
author_rank: Regular Contributor
timestamp: January 19, 2017, 05:18:36 am
content: I don't have much experience with this parts, but I think It provides superior sealing.

author: mrpackethead
author_rank: Super Contributor
timestamp: January 19, 2017, 05:22:08 am
content: I have used it extensively. And continue to use it extensively..If you are doing anythign bigger than a few grams of plastic then you will need to have a serious machine. those benchtop machines just will end up being fustrating for you.The stuff also shrinks after it cools, so you really need to consider htat.I

author: dimbmw
author_rank: Regular Contributor
timestamp: January 19, 2017, 10:55:11 am
content: Quote from: DTJ on January 19, 2017, 03:06:43 amThere is no good adhesion between the cable and the material unfortunately, so it will not work.

author: mrpackethead
author_rank: Super Contributor
timestamp: January 19, 2017, 06:02:21 pm
content: Quote from: dimbmw on January 19, 2017, 10:55:11 amMacromelt was used to protect components used on the tools at deep water horizon. Some 5000' under water. With the right design you can absolutely acehive a very good seal.

author: dimbmw
author_rank: Regular Contributor
timestamp: January 19, 2017, 07:14:53 pm
content: Quote from: mrpackethead on January 19, 2017, 06:02:21 pmI own a low pressure molding machine , and i asked this specific question to the machine's manufacturer. Their reply was discouraging - there is no good enough adhesion between the material and the cable's sheath. The water tightness should be ensured by something else. I guess that is what you are reffering as a "right design". But if you know how to do it by low pressure molding only - I am all ears, please educate me.

author: mrpackethead
author_rank: Super Contributor
timestamp: January 19, 2017, 07:28:00 pm
content: Quote from: dimbmw on January 19, 2017, 07:14:53 pmWhich machine do you have.. We have two, a optimel 2000, and a frakenstein that was made by converting a Boy 25 injection moulder.. Seriously the frankenstein works so much better particullary with larger shots..What material are you using? We typically use OM648 and recently TC50.You have to design the die set so when the macromelt cools it shrinks onto the cable. The shrink for 648 is around 1.5% It shrinks on more that tight enough. If you are really concerned there are 'primers' that you can apply as well.. ( Chemlok 485 with Curative 44 from Lord )

author: dimbmw
author_rank: Regular Contributor
timestamp: January 19, 2017, 08:16:17 pm
content: Quote from: mrpackethead on January 19, 2017, 07:28:00 pmWe have one of the lpms's machines. Not sure about the resin, some of the henkel's technomelt resins. We are only overmolding USBs with it.The shrinking idea does not look promising. It may be tight enough when there is no pressure (drop of water etc), but to withstand , let's say, 10 bars (100 m under water) is a different story.

author: DTJ
author_rank: Super Contributor
timestamp: January 20, 2017, 12:51:39 am
content: Thanks for all the replies guys. From what you've said it looks like it could work well though I might need more than a entry level or prototype machine as the injected volume is reasonably large at 16cc.That probably means the set up cost would be out of my reach. Looks like I'll stick with potting in epoxy for now. I might keep an eye on ebay / gumtree. There was a small system for sale in Victoria / NSW a few months back for what seemed a reasonable price but it looks like it sold.Again - thanks for the replies it's really useful to hear from folk who have worked with this stuff.

author: mrpackethead
author_rank: Super Contributor
timestamp: January 20, 2017, 08:24:34 am
content: Quote from: dimbmw on January 19, 2017, 08:16:17 pmIts works at 5000'. the equipment that was used on Deep Water Horizon was protected used macromelt. Its all in your design. I use it on parts that are 2-3m submerged and some have been running for 2 years without issue. I've got thousands of cable assemblys that are made with 648 and they lie around in the weather..It works for us.

author: mrpackethead
author_rank: Super Contributor
timestamp: January 20, 2017, 08:33:01 am
content: Quote from: DTJ on January 20, 2017, 12:51:39 amThe biggest issue you have to overcome is being able to get enough material into the die set quick enough so that it does'tn start to harden before you've got it filled.. We have water heating in our die set, so its at about 70C, which really helps. I've also got what can only been described as 'redicouly' large gates.. I'm pushing two cavitys of 54cm each.At 16cc you might just get away with it.QuoteProbalby painful but we can offer a overmoulding service out of New Zealand if its of interest to you. (http://synapco.co.nz/low-pressure-moulding/)

author: janekm
author_rank: Unknown
timestamp: January 20, 2017, 11:05:40 am
content: Quote from: DTJ on January 19, 2017, 03:06:43 amI'm curious what search terms you used to find that? I haven't been able to find those parts (at least not within China) and I can't quite figure out why, you'd think it'd be a common enough thing (but I could get a second hand 15T vertical injection molding machine for around $1000... tempting but it would take up quite some space!).

author: mrpackethead
author_rank: Super Contributor
timestamp: January 20, 2017, 06:28:16 pm
content: Quote from: janekm on January 20, 2017, 11:05:40 amYou need to add a bit to it to make it useable to be an overmoulding machine.. You need a melt tank and a pump to pump the molten plastic but its a very doable project. Its what the guys did here.. a boy 25 conversion.

author: DTJ
author_rank: Super Contributor
timestamp: January 21, 2017, 04:49:15 am
content: Quote from: mrpackethead on January 20, 2017, 08:33:01 amThanks but probably not viable as each unit has about 6kg of bulky cabling associated with it. Interesting website.

author: mrpackethead
author_rank: Super Contributor
timestamp: January 21, 2017, 05:10:21 am
content: There is a crowd in Melbourne... i just cant' remember the name at the moment.

author: DTJ
author_rank: Super Contributor
timestamp: January 21, 2017, 05:14:05 am
content: Quote from: janekm on January 20, 2017, 11:05:40 amI've found a variety of heating bands on eBay,http://www.ebay.com.au/sch/i.html?_odkw=plastic+molding+machine&_sac=1&_osacat=170769&_from=R40&_trksid=p2045573.m570.l1313.TR0.TRC0.H0.Xplastic+injection+machine.TRS0&_nkw=plastic+injection+machine&_sacat=170769On Aliexpress I found a number of small desktop machines that looked like a drill press arrangement. They had a melt tank in the centre, pneumatic cylinder at the top and the mold at the bottom. I've spend some time looking and cannot find them again. Some of them had temp controllers, some didn't. Aliexpress is frustrating!They were like this:http://www.techkits.com/There is a highly recommended (by others) book on how to DIY a machine by a guy called Vince Gingery.http://gingerybooks.com/Other interesting links:http://www.scorchworks.com/Injection_molding/injection_molding.htmlhttp://benchtopmold.com/index.phphttp://makezine.com/projects/make-41-tinkering-toys/diy-injection-molding/http://rick.sparber.org/Articles/gpi.pdfI think DIY is do-able but keeping quality up might be an issue.

author: DTJ
author_rank: Super Contributor
timestamp: January 21, 2017, 05:15:29 am
content: Quote from: mrpackethead on January 21, 2017, 05:10:21 amTarapath?www.lowpressuremoulding.com.au

author: Kean
author_rank: Unknown
timestamp: January 21, 2017, 05:29:26 am
content: And if in Sydney, I believe Clarke & Severn Electronics can also help with cable overmoudinghttp://www.clarke.com.au/cable_assembly.htmlI've bought parts and equipment from them, but not used their cable services

author: mrpackethead
author_rank: Super Contributor
timestamp: January 21, 2017, 05:47:07 am
content: Quote from: DTJ on January 21, 2017, 05:15:29 amYup thats the guys.. WHat i like about synapco is that they are actuyally really plastics guys. And they really understand plastics. Rather than a cable /. electronics place that has added it as an extra. It seems simple ( and it is ) untill you want to do somethign a bit out there.

author: DTJ
author_rank: Super Contributor
timestamp: January 21, 2017, 08:54:34 am
content: Yes I think production tools is Tarapath's core business.

author: richardlawson1489
author_rank: Regular Contributor
timestamp: January 21, 2017, 01:14:28 pm
content: Which machine are you using currently? Are you thinking to get new updated machine?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: January 21, 2017, 08:49:58 pm
content: Quote from: janekm on January 20, 2017, 11:05:40 amBear in mind that Ebay doesn't show search results for items not shown as shipping to your country - some sellers who will ship overseas set this as default but say in their listings they will ship international if you contact them. This seems particularly common for larger items from the USA.This site is a useful way of finding these international listings :http://www.geo-ship.com/

author: Niklas
author_rank: Frequent Contributor
timestamp: January 22, 2017, 01:30:10 am
content: Penetration of water through plastics could be an issue long term, especially for low power analog electronics like sensors.Select a wire insulation material with good adhesion to Macromelt.Avoid overmolding of connectors. You will be surprised how good penetration the molten plastic has, even inside crimped terminals.Do not assume that the overmolding will provide a firm mechanical support if used above 70'C. There is a reason why the name ends with -melt.Check chemical compatibility if the overmolded sensor is going to be submerged into other liquids than water.

author: mrpackethead
author_rank: Super Contributor
timestamp: January 22, 2017, 08:23:33 pm
content: Quote from: Niklas on January 22, 2017, 01:30:10 am- I've had Macromelt underwater for more than 24 months continuous.. ( at about 2meters ) and as yet it has not failed. I wont' say it wont', but i'd be quite suprized.-Overmoulding connectors is quite doable provided you do it properly andDESIGNfor it. Please see example above.- The plastic is a polyamide. It has good chemical resistance to most common things, other than acids which will eat it.

author: Niklas
author_rank: Frequent Contributor
timestamp: January 23, 2017, 06:58:23 am
content: Quote from: mrpackethead on January 22, 2017, 08:23:33 pmIt all depends on the application, but sensors are typically low power and their output signal can be affected by currents in the microamps range. For instance moisture acting as a resistor in parallel with an NTC or a capacitive sensor. We are currently working on a new project where a high performance engineering plastics is considered as an option for the housing material instead of stainless steel. One of the main concerns is the long term reliability due to water absorption and permeability. Expected service lifetime of the product is more than 10 years, submerged into a water based liquid, operating between -40'C and +85'C, 24/7.Not all PCB connectors, actually very few, are made for either potting or overmolding. Take a standard wire-to-board connector with a pin header inserted into a connector housing with crimped terminals, horizontal assembly with complete overmolding/potting. You will then have 3 entry points: where the wire enters, through the hole for the latch and where the pin is inserted. The result is, most likely, a connector where even the volume between the pin and the terminal is filled with potting/overmolding material. There is also another possible entry point for liquid intrusion, and that is where the wires from the connector exits the overmolding. If the adhesion between overmolding material and the wire jacket is not complete, also considering thermal expansion and possible annealing, then capillary force can cause a leakage.Take the same kind of connector, but with vertical assembly and only the pin header overmolded to a point well above the plastic part that holds the pins together. Here you need excellent adhesion to the metal pins to avoid leakage due to capillary force. If the connector is shrouded, then the adhesion demand also applies to the plastic material. As we are talking about a complete overmolding, we can assume no pumping effect from an enclosed gas volume (ideal gas law).Our customers have a long list of chemicals that our product should withstand. Even if the product is used with a waterbased liquid, it should still withstand some abuse by a clumpsy end user, without any major impact. It all depends on the application, but it is very easy to just focus on the main purpose and to forget about the small details.

author: JohnSL
author_rank: Regular Contributor
timestamp: January 23, 2017, 04:33:28 pm
content: Quote from: mrpackethead on January 19, 2017, 05:22:08 amWhat are the problems with benchtop machines? I have a lot of experience with benchtop machines, although only using polystyrene. I've done some over molding and it worked well. Also, in case anyone is interested in designing injection molds, I recently started a video series on just that:-- John

author: mrpackethead
author_rank: Super Contributor
timestamp: January 23, 2017, 06:02:35 pm
content: Quote from: JohnSL on January 23, 2017, 04:33:28 pmWhat are the problems with benchtop machines?The polyamide cools quick enough that unless your fill time is short you'll get voids forming and or weld fronts.. On the part i showed you above we have a gate that is massive in comparison to more typical Injection moulded parts... Its 3mm deep and 70m long

author: Sonny_a67
author_rank: Newbie
timestamp: February 07, 2017, 09:50:17 am
content: Hi guys, very interesting discussion! I thought I post my here instead of creating a new thread since it's very related.I have designed a board which should eventually be molded between two underwater sea cables and could potentially go down to the depths of 5000m!I was wondering if anyone has a suggestion as for what type of molding method, material, etc. I should consider and perhaps if someone knows a prototyping house which could do this type of stuff!Thank you in advance!

author: mrpackethead
author_rank: Super Contributor
timestamp: February 07, 2017, 06:29:40 pm
content: at 5000meters the pressure will be well down.I know that some of the macromelt products were used on teh deep water horizon recovery, the water was 1600m deep there. I'd suggest that this however is a very specialist topic and that the number of folks doing deep-sea cable joins are few.. But Cable joining is being done everyday, so its just a matter of finding who does it.

author: Kean
author_rank: Unknown
timestamp: February 07, 2017, 07:55:31 pm
content: Check outhttp://www.ronallum.com/who worked on the Deepsea Challenger and other projects

author: mrpackethead
author_rank: Super Contributor
timestamp: February 08, 2017, 08:40:39 am
content: deep for me is a couple of meters!