Quote from: Niklas on January 22, , 01:30:10 amIt 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.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.
- 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 and DESIGN for 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.
It 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.
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Injection molding has a number of advantages. It minimises molding costs and is a highly repeatable way of producing plastic or elastomeric parts with high precision. Once set up, it can manufacture a large volume of parts per hour, from a wide range of different plastics plus other materials such as liquid silicone rubber.
Are you interested in learning more about low-pressure overmoulding molding techniques? Contact us today to secure an expert consultation!
However, like any manufacturing process, it does have some disadvantages, and if these prove significant to the success of your project, then you may be better off exploring alternative manufacturing technologies such as 3D printing or CNC machining.
In this blog, we will take you through the main advantages of injection molding and explore when it may be better for you to consider an alternative production method.
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