Sprue bush? 2

[cpretty]

What are the benefits of using a sprue bush when fabricating a die for plastic injection molding? Cold runner applications only of course.

We are debating the pros and cons of machining the sprue bush directly into the FH bolster rather than using a sprue bush. We are a molder and toolmaker combined so need to weigh up the benefits on both sides of the fence.

Construction this way saves a small amount of machining time, and elimates alignment issues etc. We have long nozzles on our machines that can reach through the backplate on all but the biggest tools. We have a large number of historical tools that do not have sprue bushes and have no real problems with them.

Off the shelf sprue bushes often have a hardened radii for the nozzle, but the comment is that this area is rarely damaged/worn.

What are other peoples thoughts and experiences on this?



Craig Pretty
Tru-Design Plastics

 

[patprimmer]

It gives you the ability to select steel and heat treatment that is best for this part.

It increases potential to easily repair damage to this area.

It provides the flexibility to more easily match the mould to different machines and nozzles.

It allows you to reduce the size more easily at a later date if you decide that is beneficial (I know, unlikely).

Regards
Pat
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[dpackard]

It can cut into the solid mold base. However, you are missing the benefits mentioned by patprimmer. If you put it in the solid just leave room to put in a manufactured one later as opposed to welding the plates to make any repairs. True the Nozzle seat rarely sees damage; abrasive/corrosive material can quickly wear out the diameter of the sprue in plain steel mold bases. We always use one because we find it easier to machine a c'bored hole for a bushing rather than to machine the spherical radius and tapered hole. And it can be easily replaced.

 

[cpretty]

I have just had 3 notifications of new posts on this thread but nothing is up on the forum. Any ideas why they have all dissappeared?

So far there has been nothing but helpfull responses. Can't imagine three getting red flagged before I get to see them.

Craig Pretty
Tru-Design Plastics

 

[MacGyverS2000]

c,

Someone spammed the forums with the sole intent to distribute links to their plastics company. That's a no-no, and I doubt the info would have served a useful purpose anyway. the offending posts have been removed.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[patprimmer]

I for one red flagged the spammer who hit a number of posts and threads.

I think it was a Chinese toolmaker

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[cpretty]

Cheers for the insight, and the good response. I thought there may have been something odd going on, as the two of the three responders were people that usually provide helpful insight.

We have now started tooling with sprue bushes. After further investigation in house it would appear no-one ever talks to each other.

Die-setters don't like them in solid as it can get in the way of the heater bands. A pity when looking over your shoulder reveiwing tool designs they don't even bring it up. This place has been making tools on and off with no sprue bushes for 20 years, and no-one had ever brought it up as an issue until I asked some very pointed questions.

Craig Pretty
Tru-Design Plastics