Surface finishes for compression molds
A discussion started in & continuing through 2017
Q. We are compression molding a special thermoset material into .375 thick wafers having an internal straight tooth spline form that is blind on one side. The parts stick to the mold's tooth form insert and chips the sharp outside corners on ejecting. The tooth surface is finished to 35/40 RMS and TiN coated. The finish may be the problem, but I would appreciate help on specifying a finish which will enhance ejecting and how to accomplish it on the inserts. The mold release is not the problem. Can anyone help?Terry Voss
- Milwaukee, Wisconsin USA
A. Being more familiar with chrome plating than TiN, I would suggest you consider chrome plating these mold inserts. Chromium plating offers the lowest coefficient of friction of any metal, and I think it's worth investigating whether chrome plating these inserts will make the problem instantly go away.
Ted Mooney, P.E.
Pine Beach, New Jersey
Checking mold cavity for presence of chrome plating(2005)
Q. We have a mold for automobile component with ABS material. My Question is the mould cavity insert is made of P20 steel and looks like chrome plated but the tool maker says that it is not plated and only polishing is done on the cavity.
Please tell me how to check whether the cavity is plated or not.
Schefenacker Motherson Limited - Chennai, Tamilnadu, India
A. If you have a plating thickness gauge, check for thickness;
or sprinkle a few drops of water on the die, the highly polished surface will stain overnight and the chrome will not.
Bangalore, Karnataka, India
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Chrome plated molds are getting damaged(2007)
Q. We are producing oil seals and o ring. we are facing some problems in rubber compound(after amadeya42)and mould damage during process. we are doing some plating process like chrome plating. I think titanium nitride is also suitable for us. give some suggestions and information regarding this problems.Mohan [last name deleted for privacy by Editor]
R & D - Chennai, India
A. I think you need to speak to local mold coaters and figure out exactly what is wrong, Mohan. Switching your technology is certainly possible and may even be advantageous, but you must very clearly define your situation before you will know whether the new technology offers theoretical advantages. To switch technologies because of day-to-day operational problems almost never works because the new technology will also have maintenance and education requirements. Good luck.
Ted Mooney, P.E.
Pine Beach, New Jersey
A. I agree with Ted. You need to identify the problem to be able to solve it. Chrome is very hard and oxidation resistant but it is dissolved in halides, so if you are molding resins with chlorides or fluorides it will be a terrible choice (better w/o it). Also, chrome is almost always microcracked, so it does not offer a good barrier against corrosion. Try high phosphorous electroless nickel, 0.001-002" thick.Guillermo Marrufo
Monterrey, NL, Mexico
November 28, 2017
Q. Dear sir,
I am a manufacturer of plastic items. The mould are usually chrome plated and then buffed to bring a shiny glass like finish on the product as it is natural in colour. The plastic material I use is polystyrene . Even after chrome plating there are a few scratches appearing on the product which is not acceptable. What can be done to avoid these scratch marks on the product?
- Chennai, tamil nadu / India
December 26, 2017
A. Hello Ashish,
A lot of possibilities...did you try using a thicker Cr coating and then doing a light grind in lieu of buffing? I assume the scratches are in the same location on one defective part same as another. If the scratches are random you might want to think about mold release agents instead.
Feather Hollow Eng.
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