blow hole

[srinu2804]

hello ever y one,
we running 160cc of 7 cavity mold on a 45 tonnage IBM (injection blow molding)m/c with marlex hdpe (HHM 5502BN)material. The problem i face is blow hole bottles on 6th and 5th cavity. Blow holes botles of 6th and 5th cavity are coming in one station only and not in remaining two stations. i changed the core rods of those cavities of that particular station but the problem is still coming ethier transperent or blow hole bottles.

processing temperature 190 to 230 temperature
mtc temperature (bottle body topand bottle base 95 degree)
mtc temperature (bottle body bottom 115 degree)
neck mtc temperature(75degree)

blow time of 14 seconds

can any one sugesst me the reasons for blow holes and transperent bottle .

thanking you all,
Regards
N.satya srinivas
+91 9849135857

[Will Call]

I read your post several times and I'm have a problem understanding what your issue is. Not sure if you mean the blow pins aren't retracting, moving forward or a totally different problem.

Can you explain the problem another way then maybe I can help?

[srinu2804]

HELLO WILL CALL,
Thank you for reply.we are using injection blow molding process for the manufacture of HDPE BOTTLES. hole or transperent bottles are seen the base of the bottle. iam attaching few pics of tranperent botles for easy understanding.There are no blow pins in ibm process . Thanks in advanace for your reply

Image(214).jpg

Image(217).jpg

Image(214).jpg

[Will Call]

Although the pictures are a little blurry, it looks to me that the parison is either not centered in the mold or tooling not centered in the head causing one sode to be thin. during the parison drop, does the parison curl to one side?

[haf]

HI,
I suggest that you check the parison thickness, this should be uniform or might the thickness of paraison be thin (due to low swelling ratio) not enough to be stretched result in lack of resin and thin thickness results in more transparency.
Haf

[srinu2804]

hello every one,

let me clear you all one thing, there will be no parison in injection blow molding it is not extrusion blow molding process there are three stages in injection blow molding
1. preform is formed in one station where material is injected to injection mold in first station
2. it is blow in to bottles in second station
3. bottle will ejected in third station.

thanks to every one who tried to slove my problem.The solution which i got from you is not for injection blow molding process. i think you are not aware of injection blow molding process.

Regards
N.satya srinivas

[Will Call]

You're right....missed the "injection" part. But, it appears the problem is still due to an uneven wall thinkness. check the preform for a consistant wall. if it varies from part to part check the mold and make sure something hasn't come loose. Have you run production on this same tooling previously and not seen these problems or is this a new job that you've never run before?

[rickbatey]

Check the core for poor cooling/blockage. To me, it looks like heat stress due to a hot spot in the core. I have seen a similar issue in the past when the cooling plug/baffle inside the mold core broke, causing the water to not cascade down the entire core surface. A thermal image should prove the point. Perhaps you are not allowing enough cooling time? Are these the last two parts to be cooled?

[srinu2804]

Hello every one

Ithank you all ,for trying to help me. Mr.rickbatey we dont have water cooling system to core rods. since we are processing only HDPE material. the problem is seen in only station out of three station. the mold was manufactured in china. iam looking forward for your reply

Thanks and Regards
N.SATYA SRINIVAS

[rickbatey]

Then HOW are you cooling the cores? There has to at least be heat transfer to some cooling media; air, heat pipes, convection to water based cooling. Since you ony have the issue on one station, you should check the temp of the core and the ejected temp of the parts. Again, a thermal picture would help prove a (low or no) heat transfer issue, quickly.

[srinu2804]

hello every one

Thanks to the reply rickbatey. the core rods get cool by air only.It was not the first time we are running this mold . the problem frequently comes during production. can you just me different type of mould tempearture circuit to injection mold so that i can try on it. actually we have given one mtc to neck and second mtc to body topand bottle base . and the third mtc to body bottom .


I WISH YOU ALL A VERY HAPPY NEW YEAR

REGARDS,
N.SATYA SRINIVAS

[Bader]

Hello Satya..

After reading this thread twice, here is my two cents!

I noticed you are using HDPE Marlex 5502. Right?
This material is strictly for "extrusion blow molding" any may not work well for your process (injection blow molding).
But having said that, you mentioned the problem is only on cavity 5 and 6.

You need to find out if the problem is at the injection or at the blow station.
To do that, i suggest you STOP the machine just after injection process and take-off all the preforms from the cores and inspect them thoroughly.
If all is well at injection, the problem definitely lies in the blowing station.

If it is not a material issue, it is (most probably) a temperature related issue PROVIDED you have been running this product before on the same machine, with the same material with the same molds...without any problems !

Bader

[Wiseco]

As you said it start to happen recently, I would check nozzles for those cavities. Check if they are not damage or plugged by something (metal chip...)

If those cavities are filled last, the preform have not enough time to be conditionned to the mold temp, so the bottom is too hot compare to the rest so it will lift easier, which will stretch more the melt. But as it happen on one station only... it's a bit strange.

First, try switching station for these core rods for these cavities and see if the problem follow. If so, your core rods have something. If core rods have a seperate neck ring, check if they are in position. If they've slipped, the bottom of the preform will be thinner.

One question, does your core rods are chromed?

[satya0104]

hello wiseco ,

can you tell, the recomended value for chorme plating to core rods?

[Wiseco]

A flash chrome is enough.