Adhesive for bonding in automotive applications

[Ratty]

Hello everyone, my first posting on this site! I'm hoping you may be able to help me...

I am designing a proximity sensor for use in an agricultural application. It is to be fitted outside the passenger cabin and must operate within fairly standard automotive specifications with the addition of:

Resistance to checmicals includes 20% aqueous mix of liquid lime and 7.5% NPK Fertiliser. Temperature specification is -40 deg C to +135 deg C and the sensor must be resistant to water ingress to IPx6 or better.

The eletronics in the sensor are contained in a plastic housing, material is syndiotactic polystyrene (sold under the name of Questra), and will be sealed by a lid of the same material. I was going to ultrasonic weld this joint, but we've run into process problems. Ultrasonic welding doesn't provide the exact location I need, so I'm looking into a field new to me - adhesives!

I've tried a couple of adhesive manufacturer's here in the UK, but both have shied away with little explanation. Does anyone have any advice on possible adhesives, suppliers or why the two I have tried want nothing to do with the idea?

 

[smitacowper]

Dear Ratty,
Do you want only bonding between the plastic housing and lid or also you want complete sealing/potting of the housing for protecting electronics of the sensor.

Anyway i had come across similar kind of application where the sensor was used in the ships and submirines for temperature readings. Here RTV silicon sealant from Company named Henkel Loctite did the function of bonding and sealing. I suggest you contact HENKEL LOCTITE (Adhesice manufacturer) for this.

Any further help, let us know.
mohan

 

[Ratty]

Mohan,

Thank you for your advice. I have contacted Henkel Locktite already regarding the application, and, although several of their products appear to be able to give me the joint I want (when you look at their datasheets on the internet), they declined to offer any help. I'm of the opinion that there must be an environmental specification I need to meet that they are scared off by.

The joint I am looking for is going to fix the lid to the housing. A single part encapsulant will be used to seal and protect the internal electronics, but the joint does need to provide a seal, due to the presence of lime in many fertilisers and the corrosive effect that this will have on a stainless steel spring inside the housing.

This is one solution I am looking at, the other is aimed at addressing the ultrasonic welding processing issues.

nick (ratty)