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The control of the size accuracy before the thread electroplating
Auther: Pubdate:2018-05-08

Many rod end joint bearing products have threaded structure, which mostly use electroplating to carry out anticorrosion and decoration. It is a difficult problem in the production process to ensure that the size of the thread after electroplating is qualified. In the long term production practice, we have gained some experience in the dimension control of thread plating.
1 the effect of electroplating on the geometric parameters of the thread assumes that the thickness of the coating is evenly distributed on the thread, and the effect of the coating on the diameter of the thread is shown (external thread, with the common tooth angle 60 as an example), in which T is the middle diameter of the pre electroplating thread; D1 is the middle diameter of the electroplating thread; the thickness of the electroplating layer; Ad is the post thread of the electroplating. The single side of the middle diameter.
After plating, the total diameter of the thread is D1 - D, that is to say, the large diameter of the thread is 4 times the thickness of the coating.
Similarly, after internal thread plating, the reduction in diameter is 4 times the thickness of the coating.
Due to the excessive concentration of power lines in the prominent parts of the parts, the so-called 2 shows. Therefore, it must be considered when working out the electrical tip effect schematic drawing process.
2 thread size control before plating, in order to make the thread parts qualified after plating, the following ways can be adopted.
Under the condition of permissible corrosion resistance, the effect of coating thickness on the size of the coating can be reduced by reducing the thickness of the coating properly.
Under the condition of permissible part performance, the process of pickling and chemical polishing is used, the parts are treated in advance. The thickness of the parts is needed to keep the parts in order to ensure the size of the parts after the plating.
Adequate thickness of the plating is reserved in the machining process of the parts.
A better corrosion resistance matrix material is selected to reduce the thickness of the coating or select the high corrosion resistance coating (the same protective performance can be achieved under the condition of lower coating thickness) to ensure the dimension precision of the parts.
In the actual production process, there are 2 commonly used methods to make the surface of the part close to the size margin which is close to the coating. That is, the size of the coating thickness is reserved in the process of chemical size polishing and mechanical processing. The following is explained in detail.
2.1 chemical size polishing, chemical size polishing is a processing method for making metal products in specified solution through regular dissolution to achieve the required size. In the process of chemical polishing, the dissolution rate of the tip of the threaded tooth is greater than that of the helical surface and the root of the tooth. It is compensated by the thicker distribution of the coating on the tip of the teeth after electroplating, which is beneficial to the correction of the geometry of the tooth tip after the electroplating. Chemical polishing can make the rough surface leveled, improve the smoothness of the coating, reduce the porosity and improve the corrosion resistance by 11. Chemical polishing can also play a role in rust removal. The chemical size polishing operation is simple, the production efficiency is high, and it can be connected with the electroplating operation. Only a chemical polishing tank and a cleaning groove can be added to the original equipment.
It is suggested that the 111:% (volume fraction) /min of the following formula is used, and the dissolution time can be calculated according to the thickness of the coating needed in the production, and it can be verified and summarized by the production test. The quality of the thread can be effectively controlled.
2.2 in the process of mechanical processing, enough coating thickness is reserved to solve the problem of size fit after plating. It is necessary to consult with the product design and process department to negotiate the pre plating process size of the parts, and to reserve the thickness of the coating and the coating size deviation in advance. We should pay special attention to the problem of uneven thickness of the coating due to the different shape of the parts when the thickness is reserved.
Due to poor control of coating thickness and uniformity, parts with tolerance problems are the most common ones, such as threaded parts and fasteners.  When the threaded parts are electroplated, the thickness of the tip of the thread and the coating thickness of the bottom are different. Therefore, after thread plating, the main reason for the matching obstacle is the tooth form deformation caused by the uneven thickness of the coating, followed by the thickness of the coating.
In the actual production process, the above 2 methods are often combined, and a set of effective operation procedures must be mastered to ensure the quality of the thread plating.
3 the thickness of the coating stipulates that the thickness of the coating that can be accommodated by the ordinary thread depends on the pitch and the location of the thread tolerance zone.
The 85 thread fastener is selected in the 21 form of electroplating.
The minimum thickness of electroless plating: the electroless coating must be of a certain thickness to be applied. It can be measured by the salt fog test of the GB/T10125 artificial atmosphere corrosion test, according to the national salt spray test standard, and the general control is determined in 3.
4 actual precision control for internal thread, generally commonly used grade precision is H grade, usually in the case of electroplating, because of the shielding effect of internal thread, the thickness of the thread part of the coating is relatively thin, if the actual outline of the internal thread is not the maximum solid tooth profile, the H class tolerance can hold a part of the coating thickness. That is to say, the maximum solid tooth shape that does not exceed the H grade tolerance after internal thread plating will not affect its screwing property. So H tolerance can meet the requirements of the general industry, that is, when the surface of the standard fastener needs electroplating, the H gauge is used before plating, and the H gauge is also checked after plating.
For the internal thread fasteners with special requirements, due to the limitation of processing methods and testing methods, a high grade gauge is generally used to detect and control the dimensional accuracy before the thread electroplating, and control the thickness of the coating to avoid the size accuracy due to the thickness of the coating.
External thread
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