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Surface treatment methods for commonly used plastic molds

The commonly used surface treatment methods for plastic molds include nitriding, electroplating, sun marking, and sandblasting. Nitriding and electroplating are methods to improve the lifespan of molds, while sun marking and sandblasting are decorative methods for mold surfaces.

1、 Nitridation

Contact person: Mr. Tang 13825769150

Chlorination is divided into nitriding and nitrocarburizing. The biggest advantage of this process is the low heat treatment temperature (usually 500-600), small deformation after heat treatment, and the formation of a hard nitride layer, which improves the wear resistance of the mold

And improved anti bite ability. The corrosion resistance, heat resistance, and fatigue strength of the mold have been greatly improved.
    1. Nitriding: nitriding methods are divided into gas nitriding, liquid nitriding, solid nitriding, ion chlorination, etc. At present, we are more commonly used in gas nitriding, which is to pass nitrogen (NH3) into about 550? In the furnace, nitrogen obtained by the decomposition of ammonia gas seeps into the steel. The nitriding time is long, the shallow layer is generally about 0.015-0.02mm per hour, and the deep nitriding speed is about 0.0050.015mm per hour. In high-alloy steel, due to the high content of alloying elements, the nitrogen diffusion rate is low, and the nitriding rate will be lower than the above data. The time of gas nitriding (the workpiece is less than 300X300X50mm) is generally 8-9 hours, the depth of the penetration layer is between 0.1-0.2mm, the surface hardness after nitriding is between HV850-1200 (HRC65-72), and the surface color is bright.
    2. Nitrocarburizing: that is, what we call soft nitriding, also known as liquid nitrogen. The nitrocarburizing temperature is slightly higher than the nitriding temperature, which has no great influence on the hardness of the infiltration layer. It will not increase the brittleness of the permeability layer, but it can increase the diffusion speed. Nitrocarburizing generally uses about 570 is good, and low carbon steel can be nitrocarburizing above 600 to obtain a thicker compound layer. In the first 3 hours of nitrocarburizing, the penetration depth increases the fastest, and after more than 6 hours, the penetration depth does not increase significantly, so the time of nitrocarburizing is generally not more than 6 hours. The depth of the nitriding layer is generally

0.05-0.100mm, and the surface hardness is HV1000(RC68 or more). Some requirements for nitriding materials: dark gray.

(1) At the nitriding temperature, as long as the material does not undergo annealing, it can be nitrided.
(2) Metals with relatively high chromium content (such as 420, S136, 2083, M300) can not be used for gas nitrogen (because the gas containing too much chromium is difficult to penetrate into the steel). (1) There will be some "swelling" phenomenon on the surface of the workpiece after nitriding, which is the formation of a thin (0.02-0.03mm) white layer on the surface of the workpiece, and relatively soft,
This layer must be polished off before the workpiece can be restored to its original size, and the hardness after removing this layer is also the hardest.
(2) For some thin-walled, sharp corners and threaded places, appropriate protection should be given during nitriding to prevent cracking.
(1) During the processing of the workpiece, if it has been burned and welded, it must be told to the thermal treatment plant when sending nitriding to facilitate its local tempering treatment, otherwise the hardness of the workpiece after nitriding is uneven, and it is easy to crack or collapse. (2) When the workpiece is nitrided due to improper use. When the edge collapse or other reasons need to burn welding, if the large area, it must be returned to the thermal treatment plant for denitrification treatment (heating to more than 800), then welding, and then nitridation after processing (note: it may cause the hardness of the entire workpiece to change). If it is local welding, there are
two methods, one is to polish the nitriding layer to burn welding, the other is to locally heat and burn red after denitrification and then burn welding.

2. Electroplating

The purpose of electroplating is to prevent corrosion, improve the surface hardness and wear resistance of the mold, resist scratches and bite, facilitate demolding, and increase the lifespan of the mold. The commonly used method currently is nickel plating. The coating is approximately 0.025mm. Especially useful for plastic materials with acidic gas decomposition, such as PVC, POM, etc. Electroplated coatings are relatively sensitive to impact, and if they are subjected to impact for a day, they will fall off.

The difference between electroplating and nitriding :1. Electroplating changes the size of the mold cavity surface, while nitriding does not change the surface size of the mold cavity; 2. The plating layer needs continuous driving maintenance, while the nitriding layer does not need maintenance.

(3) Sun pattern and sandblasting

Sun pattern is a decorative pattern surface formed by using the principle of a photographic substrate and the use of chemical corrosion methods to corrode different patterns to the surface of the workpiece. Sandblasting is a mechanical method, which is a surface decoration method formed by spraying sand particles evenly at high speed and high pressure on the surface of the workpiece.
The relationship between the two and nitriding :
The common method is that the nitriding should be carried out after sunning or sandblasting, so that the grain depth of the surface of the material will not be different. If nitriding is performed first, then drying
grain or sandblasting is performed. It will cause different textures to form on the surface of the same product.

Contact: Mr. Tang 13825769150