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  • Barrier Style Terminal Blocks

    Discussion in 'Plastic moulding' started by McBain, Jul 28, 2020.

    1. McBain

      McBain New Member

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      I am looking for information on manufacturing double row barrier style terminal blocks. I imagine that they have been manufactured using an injection molding process to embed the threads (or studs) into the dielectric material. I have a situation where the style terminal block used is no longer available (obsolete) and we have been unable to locate anyone to manufacture again. I could design a block from FR4 or FR5 and use female threaded inserts (or studs) but past experience has not been good with getting users to maintain the low torque required during install. If anyone has any recommendations for installing female threads (or studs) into FR4 (or FR5) or knows exactly how barrier style terminal blocks are manufactured (like what female threads / studs are used, or do you know a supplier for them), I would appreciate any help. TIA
      terminal block.png
       
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    3. Simon Rafferty

      Simon Rafferty Member

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      How many of these do you need to manufacture? It makes a difference to the best method.
      If the volume is small (less than say 100), 3D Printing might be an option. More than that, injection moulding is the best option - but the cost of the mould tooling is likely to be in the $1000 to $10,000 range. Fine if you want to make millions - otherwise expensive.

      A third half-way solution is to cast in Polyurethane, which can be bought as a two part mix. (There are many alternatives to PU which work the same way) Mix the two parts, pour into a mould and wait for it to cure. The mould can be made out of Silicone. Recently, I've 3D Printed a positive blank then used this to make a Silicone mould. Each Silicone mould is good for about 50 parts before the surface finish degrades. There are many PU Moulding companies who would do this for you. The tooling cost is lower than Injection Moulding, but the material & labour cost is higher. This works well for medium scale manufacture (100 to 10,000).

      My approach for all of these would be to use CNC Buss Bars (Brass?) with the threads cut in those. (For smaller volumes, the Buss Bars could be laser cut and the threads tapped manually.)

      One option would be for the buss bar to slide into a groove in the plastic housing. The housing would have two pockets, one below each screw. When the screws are screwed through the buss bar, the threads extend into the pockets, preventing the Buss bar from sliding out of the housing.

      Threaded inserts or even plain nuts could work. Generally the approach is to insert them from behind into a pilot bored hole, so in the event of over-tightening, it is compressing the plastic between the nut & the buss bar, rather than trying to tear the insert out of the plastic.

      Pressing a nut into a Hexagonal pocket is often used in 3D Printed parts to give a strong thread.
       
    4. McBain

      McBain New Member

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      Thank you for the reply Simon. I am looking for roughly 100 terminal blocks so injection molding isn't practical. I did talk to our additive manufacturing expert, but we looked at it from the perspective of is there a material that has the electrical properties we need, that could be used to 3D print the terminal board. He couldn't come up with anything. It never crossed my mind about printing a blank and using a silicone mold. Over the weekend I drew up a couple of options using FR4 and brass inserts. I toyed with the idea of installing the inserts from the bottom to increase pullout torque, but with the small form factor of the 43TB18 terminal board and the overhead clearance in the box, I didn't think it was a good option. I like the brass buss bar idea you have, I think I can eliminate the terminal plate with that concept.
       
    5. Simon Rafferty

      Simon Rafferty Member

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      Glad to be able to help!

      FR4 is going to be difficult to mould in Silicone - IIRC it needs high pressure. However, you could use a Polyimide Resin which has similar thermal, dilectric & flame retardant properties. Although it's mechanical properties are different - I doubt these would matter too much in this application.
       

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