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Guest woli

Material Commonly Used For

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Guest woli

Hi!

 

I'm trying to figure out which material is commonly used for the softer portion of co-molded parts like scissor and knife handles.

 

I would guess some kind of Thermoplastic Elastomer, possibly Santoprene, but would like a bit of backup on the issue.

 

Any help appreciated.

 

Oli

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Hi!

 

I'm trying to figure out which material is commonly used for the softer portion of co-molded parts like scissor and knife handles.

 

I would guess some kind of Thermoplastic Elastomer, possibly Santoprene, but would like a bit of backup on the issue.

 

Any help appreciated.

 

Oli

 

Your guess is correct - TPE, Santoprene being a commonly used brand of polymer.

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Guest Buff

Only certain modified grades of Exxon Mobil Santoprene will bond with ABS, PC, ASAL and these have much lower UV resistance. You can get much better bond with PP, HDPE without loosing the UV stability. You could talc fill to 40% to regain stiffness.

 

Another material I've found to be good is Alpha Gary Evopreenw Super G

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Guest woli

Buff, great input! Unfortunately I've only been permitted to modify the existing design with the soft inner. The handles, as they stand, are made from ABS although I'm not overly sure why this decision was made.

 

But either way it's only a preliminary specification so TPE is good enough for now.

 

Thanks for the heads up for when it gets down to business though!

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Guest woli

Hi,

 

So finally the scissor redesign project gets the go-ahead!

 

The brief is focused around slight manipulation of the existing product shape and new colour palette, but mainly around the addition of a soft inner portion to the handles. As these are kids scissors, and the existing shape is none too exciting I was considering adding shape to the join between the handle body material and the TPE.

 

Can anyone offer any advice on difficulties we may face with manufacture/tool making if the join line is too complex?

 

I wasn't thinking anywhere near as complex as this offering from Fiskars

 

5in-Softgrip-R-Kids-Scissors-Blunt_product_main.png

 

Something simple like a wavy join or a basic recurring pattern. I would guess that the more complex the design, the higher the tooling cost, or is it not really an issue?

 

Any help or a friendly point to a good resource would be greatly appreciated.

 

Oli

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Guest Buff

On ABS, Santoprene 8211-55B100 would be a good starting point

 

Try to keep both the substrate (ABS) and the overmould as tick as possible ), at least 1,5mm thick minimum recomended.

 

The engineering design intent should be to keep as much heat as possible into both the substrate and the overmould.

 

Keep the junction between the overmould and substrate thick. DON'T feather it out.

 

Best to keep the shut off on a differant surface (not flush) to help prevent flashing (i.e. let the overmould stand proud if possible).

 

The further the gate is away from the TPE the less it will stick so keep the gate close to areas that have to stick the best.

 

The tool cost won't (shouldn't) be much differant because of the wavyness.

 

Tey to design the overmould so it mechanically interlock with the ABS part, such as allowing the TPE to flow from one side to the other to form internal rivets.

 

Have the first shot cavity in the regions of the overmould bonding, SPI-D3 grti blast finish. This will create a whetting surface and help break down the surface tension in the TPE, helping to achive a better bond

 

If the tool is being made in overseas, check if its an export tool or non-export tool. non-export mean the tool will be built pretty much as cheap as possible.

 

This can cary with it some sizable risk in repatability of your parts.

 

Make sure whoever is 'building your tool' is actually building your tool and isn't just sub-contracting it to another cheaper toolmaker.

 

Get a comprehensive tool drawing BEFORE you sign off for manufacture.

 

Get progress reports weekly with pictures.

 

You have to make sure that the tool being built is the same as the one you agree too in the drawings. sometimes toolmakers change their mind about how to do the tool and 'forget' to tell you about it.

 

You'll get better results with a 2K tool than you would with insert overmoulding.

 

Sorry if I'm telling you how to suck eggs.

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