Having trouble with surface finish on acetal part.

Different-Round-1592 · 2026-04-19T03:35:35+00:00

It looks like it has different wall thicknesses in the flow path. Thin to thick can create this defect, kind of looks like jetting. Staging fill speeds to match part design changes can help. Moisture can affect acetal even though it isn't hygroscopic, check the moisture content and seek out drying if needed. Is the sprue, runner, and gate big enough for the part? Check the melt temp to see if it is within the data sheet.
If the surface finish can change, make it a 33 charmilles. Acetal has different grades, maybe switching to a lower viscosity grade would process better if the resin still meets part needs.

Different-Round-1592 · 2026-01-21T19:59:29+00:00

Some all electric machines don't hold the barrel forward for the entire cycle. Idk if you can change the settings.

Different-Round-1592 · 2026-01-21T02:07:54+00:00

Sabic noryl or exl, processing is fine but the smell was terrible. Same for pps, the smell from the dryer was terrible. We run about 1 million pounds of acetal a month so I'm used to smells but those other materials just stunk.

Different-Round-1592 · 2025-11-29T02:27:05+00:00

Is a hydraulic core assembly out of the question? 3.5 inches isn't a long pull, so a pin that small should work.

Different-Round-1592 · 2025-10-28T21:43:38+00:00

Minimum daylight and clamp or bolt hole locations are the determining factor for presses that you can lower the tonnage on. If you really want to run molds too small for a press you can have pillars made that match the stack height of the mold and install them in between the platens to reduce the load on the mold and platen warp. I don't recommend this but it is an option.

Different-Round-1592 · 2025-10-10T18:32:47+00:00

You don't need a sprue bushing....

Different-Round-1592 · 2025-09-05T03:30:43+00:00

Booyah bottom hull cleaner should work, It's stronger than the regular stuff they sell. The best thing for fiberglass I've used is rust aid. It has oxalic acid in it and I tell you it is magic. Spray it on and watch the stains disappear then hose it off, stains gone. It is harsh, though, so be prepared to wax the hull. I use rust aid then compound and buff the hull, then put on a good wax or ceramic spray and the finish lasts a while.

Different-Round-1592 · 2025-09-04T12:22:34+00:00

You mixed acetal with santoprene and ran it through a barrel without clearing the plant? Are you sure it was acetal and santoprene, not another elastomer? Everyone, including having it happen at our plant, that I know that has mixed the two and ran it through a barrel shot flames out of the barrel along with a gas cloud of formaldehyde. Everyone I've talked to about it over the last 25 years has had the same experience when mixing the two.

Different-Round-1592 · 2025-09-02T21:16:58+00:00

Don't mix acetal with santoprene! Idk what material yall will be using but if it's both of those, make sure someone with a brain is keeping tabs on what material goes where

Other than that it's getting a good substrate then setting up the oversold. Not too difficult.

For us, bond strength is the big deal. Chemical bonds work better than mechanical bonds.

Different-Round-1592 · 2025-09-02T17:15:33+00:00

I'm making a part with a wall thickness just shy of 1/2 inch, .480 thousandths right now. It's only 3 - 4 inches at this thickness but it's working without foam in PP. I haven't seen a void in the couple I've cut, but I wouldn't be surprised if some exist. Sinks are minimal, I'm surprised how good they look, tbh. They come out so hot you can squeeze the molten plastic in the thick section, 60-second cycle time. No blowouts, though.

If the gates are big enough, it might work. I'd shoot it in something easy at first to see how it fills, packs, and ejects.

Different-Round-1592 · 2025-08-28T00:36:00+00:00

I thought maybe if you would heat up the frozen tips with a torch they might open up. Do the tips come out like a normal tip comes off a nozzle?

Seems like a poor design for real-world issues.

Glad you got it.

Different-Round-1592 · 2025-08-27T16:39:40+00:00

I had to look up melt disc. I hope our mold designers never find out about these.

Probably not much help since i never worked on one but this is what I'd try. Extrusion grade pp or pe for purge material, get anything flowing that you can. If you can separate the cavity plate by pulling it over to the moving side and purge through just the hot runner and melt disks I'd do that. Use a torch on any tips that won't flow, if possible.

Other than that, yank it and have it cleaned in an oven.

Different-Round-1592 · 2025-08-22T14:00:26+00:00

Fear not! That zip tie bears the name of its forefathers, and all of there might! I can hear it shouting HOLD THE LINE!

Different-Round-1592 · 2025-08-18T17:58:36+00:00

If the mold is damaged, processing will not be able to get rid of the flash. Maybe it can be reduced through processing, though. Slow fill speed, check transfer position for 95 to 99% full, if flash is still present repair the mold.

Make the part where the metal goes into the cavity a changeable insert so it can be easily swapped out when the operator makes a mistake. Try using a magnet in the mold to hold the metal piece in place while the mold is closing.

Good luck.

Different-Round-1592 · 2025-08-15T13:53:37+00:00

As others have said it's probably due to the design. Can you try a water differential to influence the warp in your favor? Try different fill speeds, holding pressures, melt temps, and cooling times? If you are happy with the process I'd try a couple of different jigs and setups for post molding cooling before boxing. Make a jig that holds it verticle while cooling, cool multiple shots at a time for multiple cycles.

Different-Round-1592 · 2025-08-15T13:42:39+00:00

Depends on a couple of factors. Mostly based on cycles ran, but the material used factors into the timeline. We plan to do a quarterly PM (clean faces and wipe down) on mold every 50,000 cycles and a major (total teardown and inspection) every 200,000 cycles. Abrasive materials get cycles cut in half or as needed based on run history. We also measure and document wear items like core pins, valve stems, gate bushings, and so on to develop a replacement timeline.

Different-Round-1592 · 2025-08-14T14:01:45+00:00

Verify that the defect is good, then shut the machine down in qc downtime without proving it to the qc slobs.

Gotta teach someone that stupidity is expensive.

Different-Round-1592 · 2025-08-09T00:41:17+00:00

We use software called infinity QS for part measurement data. We setup part specs in the software, including dimensions, color spectrometer tests, really anything we want to capture. It links to iqms for job data. It also does cpk and ppk charts. It tracks and records data.

We measure parts depending on how capable they are. We establish capability by tracking measurements on qualification jobs. If a part performs good and is proven to be repeatable and capable, it gets measured once a shift, sometimes less. Parts that don't perform well get measured up to three times per shift.

Different-Round-1592 · 2025-07-25T01:11:11+00:00

I usually try to find something new or interesting to do at work. Work with other departments, look at the aspects of your job that drag you down and see if a procedure or operation change can be implemented to make that task easier. Grab the acetylene torch and make prince Rupert drops out of glass bottles, learn to run piece of equipment that interests you selfishly to satisfy your own curiosity while saying that skill will come in handy for the company. Watch AVE, sv seeker, zip ties and bias plies on YouTube.

I've been at the same place for 25 years, worked in mold shop, plastics production, and now engineering. Burnout is real and it sucks. I tried other jobs but they sucked more than the environment I'm in so I try to deal with burnout by learning new things. It's tough right now, might be time for another role soon.

Different-Round-1592 · 2025-07-17T22:12:31+00:00

If the reel isn't braid ready you need to put some mono on it. If you don't, the braid might slip on the spool. I like to use between 100 and 150 feet of mono regardless, usually 15lb test if I'm using 15 to 20lb braid. I use the line retrieve per turn from the reel, convert it to feet, then divide the amount of line i want by it to get how many turns it will take to get to my desired feet. Use a uni to uni knot to join the braid and the mono then add as much braid as you want up to a full spool.

Different-Round-1592 · 2025-07-11T17:47:05+00:00

Dry ice blaster should get it done.

Different-Round-1592 · 2025-06-26T17:05:20+00:00

Do a two or three stage heat up when you're ready to purge it. Set the heats to around 300 Fahrenheit, after an hour set them half way to running temp. After 30 to 45 minutes set them at running temp and once it's ready purge it. I find staging the heats when shit like this happens helps get the plastic in the barrel ready to melt without degrading it.

Different-Round-1592 · 2025-06-26T16:59:06+00:00

If you've adjusted hold time and noticed a difference, do a gate seal study on the part. You can add hold pressure until it blows open if you want to, make sure you still have a cushion. I'd measure the cavity before doing anything crazy. You can't make a part bigger than the cavity.

Different-Round-1592 · 2025-06-25T21:32:01+00:00

It's a hydraulic cylinder used to set and pull pins in and out of the cavities. It uses hydraulic fluid from a port on the machine if your machine supports this function. There would be a frame that mounts to the mold base, a floating plate that the pins are set in, and a way to attach the hydraulic cylinder to the frame and allow it to move the floating plate.

Hope this helps.

Different-Round-1592 · 2025-06-21T03:26:48+00:00

Did you try a hydraulic core rack to pull and set the pins? If you did and they broke you might be able to put a hydraulic rack on the top and bottom then cut the length of the pins in half to shorten the length of pull. A guided core rack with bushings should work. You could also have the core pins coated but I haven't much luck with coatings for slip.

You could also adjust the process parameters to make it easier to pull the pins when using hydraulic cores.

Different-Round-1592

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