Sticking Sprue

[Josue]

Hi:
we will receive a new tool (over molding polyester on a PBT case), unfortunatly the mold its not running Ok, actually mold maker apply mold release every 10 shots on the sprue to avoid sticking,, they say they already use a teflon coat on this area, but not good results,, what do you think could cause this sticking issue?,, some time also the full part was sticking, but they add a knock block, but the sprue continue sticking on the fixed side,,

I dont have experience with this resin, even the mold its not here, but, What do you recommend for this issue,, the mold maker think this is cause by the resin characteristic ,, this mold its very simple, just one cavity,,

any suggest will be appreciate

Resin Brand : Vyloshot
Type: Thermoplastic Polyester resin

I attach a picture,

[rickbatey]

Normally you'd add undercuts to the moving half but not sure that works for you. I'd measure the steel temp of the bushing as it may be getting too hot allowing the spruce to pull. I also can't tell how well the bushing has been polished. It may have cutter marks or pitting in the steel. I also hate the look of the sprue at the interface with the nozzle tip. They may be using the wrong type, radius, or orifice size on the tip. Make sure the tip and bushing are properly fitting and the nozzle centered on the bushing. You may have to run sprue break to stop the sprue from sticking.
Rick.

[Jendalf]

Hi Josue,
change the tool construction - the sprue is too long and seems not polished well.

First try to polish sprue channel to high level
and second shorten or avoid the sprue completely.

J.

[moldingppm]

Agree with above...
Try with a sprue break first, if this works for you, your issue is within the nozzle. Change the tip and try without a break, see if anything changes.

The biggest thing I can see to be an issue is the sprue itself. It looks to have a poor surface finish. This more than likely is why it's sticking. Have the bushing polished and see if that fairs any results.

Can you post a better picture of the sprue? This will help us diagnose it better.

Mitchell

[Josue]

Agree with above...
Try with a sprue break first, if this works for you, your issue is within the nozzle. Change the tip and try without a break, see if anything changes.

The biggest thing I can see to be an issue is the sprue itself. It looks to have a poor surface finish. This more than likely is why it's sticking. Have the bushing polished and see if that fairs any results.

Can you post a better picture of the sprue? This will help us diagnose it better.

Mitchell


Well, sorry, this poor surface that shows the sprue, its becasue was near to stick, actually its good polish finish,, I attach 2 pictures with 2 diferent size of sprue lenght,, short and long,, both are sticking, the shorter version its better, but any way the best rate its 20~25 shots and then start to sticking, so, supplier already try sprue brake, but still not working,, I will review next countermeasure,,, I suggest to reduce packing and hold time, any way sticking sprue,,,

Best regards

[rickbatey]

How soft is the over mold? Soft resins will form a vacuum seal to high polished mold steels. Vapor honing or draw polishing with a coarser compound can help the sprue release from the bushing. Also monitor the actual steel temp of the bushing because too hot OR cold; it'll stick!
Rick.

[stevenchengcn]

Hi Josue,
change the tool construction - the sprue is too long and seems not polished well.

First try to polish sprue channel to high level
and second shorten or avoid the sprue completely.

J.

I couldn't agree any more,the same problem occured here,too long and thin sprue,some circle undercut on inner surface.
shorten the sprue bush(lathe a hole on the cavity side) and change a good quality shorter sprue,in fact the sprue quality also is a big problem.

[Sammy101]

Josue,

We also experienced this problem, I bet most of us I believe.
Considering the appearance of your product, first try o check the channel as they mentioned for the uneven surface or misaligned plates, if you are not using sprue bushing and the channel is cut-out through the plates itself. Second, looking at the product with the product you attached, the sprue tip is somehow large requiring larger force to detached it from the IMM nozzle. If this is the issue, try to purchase sprue cut-off plates (conical shaped thin plates with small hole) which helps in our case.

Sammy