Can surface treatment be performed for custom black PVC?
No, because PVC is a kind of plastic. First, we need to be clear that surface treatment can only be performed for only metal CNC machining materials, such as cooper, iron, stainless-steel, aluminum, titanium, carbon steel, alloy steel and zinc. PVC is not one of them, so surface treatment for CNC machining cannot be performed.
Copper, iron, zinc, stainless-steel, aluminum, titanium, carbon steel, alloy steel, ABS, nylon, and makrolon.
Composition of PVC
PVC, short for Polyvinyl Chloride, is a polymer which is polymerized by vinyl chloride monomers with an initiator like peroxide or azoic compound or under the action of both light and heat based on the free radical polymerization mechanism. Both vinyl chloride homopolymer and vinyl chloride copolymer can be called vinyl chloride resin.
PVC is made from white powder of amorphous structure, with lower degree of branching and a vitrifaction temperature of 77~90 ℃. PVC starts to decompose at about 170℃ and has poor light and heat stability. At over 100 ℃ or subjected to long-time direct exposure to strong sunlight, PVC decomposes and produces hydrogen chloride which automatically furthers the decomposition, and leads to color change as well as rapid decrease of physical and mechanical properties. Therefore, in actual application, a stabilizer must be applied to improve PVC’s light and heat stability.
The PVC from industrial production has a molecular weight of 50K – 110K which increases as the polymerization temperature decreases, without a definite melting point. It starts to soften at 80-85 ℃ and turns viscoelastic at 130 ℃, and starts to be viscous at 160-180 ℃. It features good mechanical property, about 60 MPa tensile strength, 5-10k J/m2 impact strength and excellent dielectric property.
Difficulties of CNC Machining for PVC and Cautions
PVC machining and metal machining are very different in terms of material molecule structure, material molecule activity in different environments, material hardness, heat resistance, and geometric stability. To reduce the possibility of defects as much as possible, Yijin Hardware reminds you that the following five points must be followed during CNC machining for PVC:
1.Because of poor thermal stability, the heat produced by long-term machining causes PVC to decompose and release the HCL gas which changes the color of polyvinyl chloride. Therefore, after machining, some parts made from PVC have their colors changed into gray. It is very possible that the failure of using reasonable cutting parameters and scientific cooling methods leads to overheat which causes decomposition. If such a case occurs and fails to be found in time or well handled, the customer will tend to think that the CNC cutting for Black PVC was not performed based on the requirements of the drawing.
2.Black PVC is a kind of plastic with poor thermal stability and shock resistance during CNC machining compared to common plastic POM. Because of possible embrittlement during machining, it is important to use dedicated cutting tools featuring sufficient sharpness and higher ease of cutting residue removal. Otherwise, the possibility of cracks, pits, and chipping off on the part is pretty high after machining. It is like cutting the same piece of bean curd with a knife that is very sharp or a knife that is not that sharp. Which will produce better effects and better appearances? How about 10 pieces or even 100 pieces? If failing to be removed from the cutter in time during machining, the residues will be sintered into a block which sticks to the cutter and hinders normal cutting, and this causes high temperature to the cutter. In a serious case, the cutter will collapse or break.
3.Reasonable cutting parameters are used to achieve large cutting amount but low feed speed as much as possible. This is good for plastic residue removal and prevents cutter collapse or break due to failure of timely residue removal. Air cooling or water cooling can be used, and the cooling pipe should be aimed at the cutter for continuous washing as so for temperature decrease when the part is being machined.
4.The dedicated fixture is used and good part protection is performed. This part is made from plastics with lower hardness than metals and needs multiple times of clamping, so reasonable clamping surfaces and clamping forces need to be considered during clamping. Otherwise, the part may be knocked off due to poor clamping stability or its surface may be damaged by over clamping.
5.A machined custom black PCV part has much more flashes and burrs, which in normal. Compared to most CNC machining materials, PVC requires more time for flash and burr treatment and has a higher possibility of scratch occurrences, so more care is needed. Improper treatment of flashes and burrs will directly affect part assembly and product use, and even hurt the user.
PVC has many colors, and the common ones are red, yellow, brown, and black. Because of PVC’s chemical characteristics, the PVC coloring pigment should be checked as to whether it reacts with the PVC or other components of a PVC product. Due to transference resistance and heat resistance of the pigment itself, some components of the colorant may induce degradation of the resin.
Some colorants may react with the degradation product from PVC resin. For example, because of poor acid resistance, during PVC coloring, ultramarine pigments will react with the hydrogen chloride from PVC decomposition, leading to color loss. Therefore, as far as PVC is concerned, the characteristics of the resin used and related auxiliaries should be considered.
Where can I purchase this CNC milling part of black PVC?
This is certainly one of the key questions. As you can see, this is a custom CNC milling part that you can purchase from Yijin Hardware. Besides, if you need more precision custom CNC milling services or custom CNC turning services, contact Yijin Hardware. As a top custom CNC machined parts manufacturer, Yijin Hardware provides its customers the best custom CNC machining services and the greatest custom CNC machining parts.
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