|
|
Silveys' Plastic Consulting
Notes, thoughts, ramblings |
|
| November/2008
Vol 2 No 11 |
|
|
Greetings!
Hallo!! I trust this finds all doing great, the election in the states are over, the economy well I don't know what to call it but only to look forward to what it can bring. Personally I feel there are many opportunities out there and it is only a matter of capitalizing on them. On the life side of things we got out on the motorcycle the other week before the rains and had a great ride up around St. Helens and down the Gorge. Sunny but cool, the leaves were changing and roads were open. Had some openings on the river for salmon this last week, but with October being dry as it was water flow may not be there yet though November is trying to make up for it. I'll be down in the San Francisco area at the end of the month, what with Thanksgiving and a list of things to do at mom's house, so any who are in that area please note, most of the travel expense is already paid for. We continue with color this time but looking at the effect it has on shrinkage and part performance. Once we had cracking in an ABS part colored white, seems it was related back to particle size and shape of the TiO2 used to make the part white. Anyway thanks for the time, comments as always welcome. TA- Steven Don't forget the achives: http://archive.constantcontact.com/fs034/1101663388820/archive/1102138661635.html silveysplastics@aol.com
360-882-3183
|
| Colorants continued |
| Shrinkage effects via coloring of materials
by Steven Silvey |
Definition: Shrinkage 1; the fractional difference in corresponding dimensions between a mold cavity and the molding made in the cavity, both molding and cavity being at room temperature when measured. 2 reduction or contraction /depreciation.
Any additive well influences shrinkage in a material, and colorants are no different. When using color it is best to understand what is happening to part size, functionality and quality via the pigments added. This is not only what you think is going on but if a supplier changes sources, or you change sources within your organization and than have issues. Documentation in this aspect is critical.
In the case of Semi crystalline polymers such as PE, PP, Nylon, etc. the degree of crystallinity has an effect on shrinkage and ultimately part size. It should be noted here that in published literature from various material suppliers that lowering mold temperature tends to increase part size in semi-crystalline materials. Basically what is happening is that we are changing the degree of crystallinity in the polymer making it more amorphous and less crystalline. (A paper unto itself at some point)
Colorant may affect the shrinkage. The degree depends on the following: chemistry of colorant, particle size of the colorant, particle shape of colorant and pigment concentration.
Understand and remember that colorants are divided into organic and inorganic, further is the fact that many organic pigments influence shrinkage by becoming a nucleating agent within the material / polymer matrix. It has been found that inorganic pigments do not have this effect. They perform the function of becoming nuclei that initiate crystal growth. It is not only the crystallization rate that is influenced but also the morphology and thus the mechanical properties of the end product. The mechanicals that can change for example would be that tensile strength may go up in a highly crystalline polymer. The addition of organic pigment will affect the degree of crystallinity and starting temperature of the crystalline growth.
Particle shape of the colorant can play an effect also, in that if the pigment is round it will be uniform in how it spreads about in the incorporation into the polymer. If the pigment is of a flat plate, or elongated it may aligned itself in the direction of flow and thus have an adverse effect on the finished part size both in shrinkage rates, non-uniform and physical structure of the part, cracks easier, elongates differently.
Particle size can play an effect in the amount of nuclei we provide. This being the fact that a smaller size has more surface area total and is disperse throughout the structure where as a larger size are fewer in number.
The most interesting effect of nucleation is that it is a surface effect. What is meant by this is that the surface of the pigment acts as the nuclei, and if we were to change the surface by coating it with a wax it eliminate the effect of nucleation due to the colorant additive. The concern here is that in processing we do not separate the wax from the pigment. This may happen by high shear rates in either the mixing via screw rotation or shear created in the injection or extrusion of the product.
An example of nucleation is a housing used to hold a gear train. For years it was manufactured out of Acetal with a blue pigment. As modification were made to end use functionality multi version were created but all using the same plates, and so to differentiate the units it was decided to make the plates in various colors. The processor molded all at the same conditions and upon assembly it was found that they were all various sizes, meaning the blue were still good, but the other colors were different than the blue. The nucleating effect was both greater and lesser than the current blue color.
The end result was that machine conditions had to be changed for each color processed to assure correct part size for fit and function.
SLS
360-882-3183
|
| What we do |
| Some of what we do if you don't see ask!! |
|
1- Troubleshooting: assisting in the processing
a. At your plant,
b. Over the phone, internet, Skype, MS Messenger
2- Plant Audits,
3- Training / education programs.
4- Mold optimizations / new mold trials
5- Other services
a. program management
b. material development ( oversee with external assistance)
c. testing of materials (oversee with external sources)
d. BTI MeltFlipperŽ ( distributor for)
e. Expert witness
MeltFlipperŽ, is the registered trade mark of the Beaumont Technologies, Inc
Missed an issue check out the archives:
http://archive.constantcontact.com/fs034/1101663388820/archive/1102138661635.html
|
| Distribution |
|
BeaumontTechnologies,Inc.  2103 East 10th Street Erie, PA 16511 Telephone 814-899-6390 Fax 814-899-7117 www.beaumontinc.com Optimize your processing with balanced fill and uniformity... call for information |
|
|
|
Steven Silvey
Silveys' Plastic Consulting
PO BOX 5216, Vancouver, WA 98668-5216
360-882-3183, cell 360-606-1156, Fax 360-882-3184
|
 |
|
|
|
|
|
