Control of dimensional accuracy before thread plating

Many rod end joint bearing products are threaded, and most of their surfaces are coated with anti-corrosion and decoration. How to ensure the thread size after plating is a difficult problem in the production process. In the long-term production practice, I have mastered some experience in the control of thread plating size, and I will summarize it here.

Many rod end joint bearing products are threaded, and most of their surfaces are coated with anti-corrosion and decoration. How to ensure the thread size after plating is a difficult problem in the production process. In the long-term production practice, some experience in thread plating size control has been mastered and summarized and summarized here.

1 Influence of plating on thread geometry parameters Assuming that the thickness of the coating is evenly distributed on the thread, the effect of the coating on the diameter of the thread is as shown (external thread, taking the common tooth angle 60 as an example), where: T It is the diameter of the thread before plating; d1 is the diameter of the thread after plating; it is the thickness of the plating layer; Ad is the unilateral amount of the diameter of the thread after plating.

The total amount of the thread diameter after plating is: d1 - d means that the diameter of the thread is 4 times the thickness of the coating.

By the same token, after the internal thread is plated, the diameter reduction is also four times the thickness of the coating.

In the case where the protruding portion of the part is prone to excessive concentration of the electric power line, the so-called 2 is generated. Therefore, it must be considered when formulating the electroplating effect schematic plating process.

2 Dimensional control before thread plating In order to make the dimensions of the threaded parts after plating, the following methods can be used.

Appropriate reduction of the thickness of the plating layer under conditions permitting corrosion resistance can reduce the influence of the thickness of the plating layer on the fit size.

Under the conditions of the performance of the parts, the process of pickling and chemical polishing is used to process the parts in advance, and the thickness of the parts to be plated is reserved to ensure that the size of the parts after plating is within the requirements of the drawings.

Adequate plating thickness dimensions are reserved during part machining.

Use a base material with better corrosion resistance to reduce the thickness of the coating, or use a high corrosion resistance coating (the same protection performance can be achieved at a lower coating thickness) to ensure the dimensional accuracy of the part.

In the actual production process, there are two common methods to make the surface of the part close to the size margin of the coating, that is, sufficient thickness of the coating is reserved in the chemical size polishing and machining process, which will be described in detail below.

2.1 Chemical Size Polishing Chemical size polishing is a process in which a metal product is subjected to regular dissolution in a specific solution to achieve a specified size. In the chemical polishing process, the dissolution speed of the thread tip portion is greater than the dissolution speed of the thread slope and the root portion, and the coating distribution of the tooth tip portion after plating is relatively thick, which is beneficial to correct the tooth tip geometry after plating. Chemical polishing can smooth the rough surface, which is beneficial to improve the smoothness of the coating, reduce the porosity and improve the corrosion resistance. 11 Chemical polishing can also play the role of derusting. The chemical size polishing operation is relatively simple, the production efficiency is high, and it can be integrated with the plating operation. It is only necessary to add a chemical polishing tank and a cleaning tank to the original equipment.

It is recommended to use the following formula 111:% (volume fraction)/min. In the production, the dissolution time can be calculated according to the thickness of the part to be plated, and verified by the production test, which can effectively control the plating quality of the thread.

2.2 Preserving sufficient plating thickness during machining process To solve the problem of dimensional matching after plating with parts that meet the requirements, the product design and process department must negotiate the size of the pre-plating process, and the thickness of the coating and the deviation of the plating size should be reserved in advance. It should be particularly noted that the thickness of the coating should also be considered in consideration of the uneven thickness of the coating due to the shape of the part.

Due to the thickness and uniformity of the coating, components that cause tolerance problems are not well controlled, the most common of which are threaded parts and fasteners. When the threaded part is plated, as previously mentioned, the thickness of the burr and valley of the thread is not the same. Therefore, the main reason for the matching obstacle after the thread is electroplated is the angular deformation of the tooth caused by the uneven thickness of the plating layer, and the second is the problem that the thickness of the plating layer is thick.

In the actual production process, the above two methods are often combined, and an effective operating procedure must be mastered to ensure the quality of the plating of the threads.

3 The thickness of the coating specifies that the thickness of the coating that can be accommodated by a common thread depends on the pitch and the position of the thread tolerance band.

―85 threaded fastener plating layer 21 selected in the table.

The minimum thickness of the plating layer: the plating layer must reach a certain thickness before it has application value. It can be measured according to the national salt spray test standard GB/T10125 artificial atmosphere corrosion test salt spray test. The general control is determined in detail.

4 actual precision control For the internal thread, the commonly used grade accuracy is H grade. Under normal circumstances, the plating thickness of the thread part is relatively thin due to the shielding effect of the internal thread during plating, if the actual contour of the internal thread is not the maximum In the case of a solid tooth type, the H-level tolerance can accommodate a part of the coating thickness, that is to say the maximum physical shape of the plated internal thread without the actual tolerance of the H-level tolerance will not affect its screwing. Therefore, the H-level tolerance can meet the requirements of the general industry. That is to say, when the standard fastener surface needs to be plated, the H-stage plug gauge is used before plating, and the H-stage plug gauge is also used after plating.

For internal threaded fasteners with special requirements, due to the limitation of processing methods and testing methods, high-grade plug gauges are generally used to detect and control the dimensional accuracy before thread plating, while controlling the thickness of the coating to avoid excessive plating. It affects the dimensional accuracy.

There are many methods for forming external threads, such as twisting, rolling, reaming and turning. The thread size and machining tolerance are relatively easy to control. Considering the influence of the plating on the geometric parameters of the thread, the dimensional control criteria before plating are as follows: Diameter = d2min - 4X minimum plating thickness maximum diameter = dmax - 2X maximum plating thickness minimum large diameter = dmin - 2X minimum plating thickness thread diameter = d1 - 2X maximum coating thickness diameter.

Mm, the pre-plating size is calculated as follows: 015 = 8.824 In the actual production process, in order to simplify the problem, easy to produce and test control, generally only the method of controlling the diameter of the thread can be used.

5 Conclusion After long-term production practice, reasonable control of the pre-plating size control methods and guidelines can better control the quality of thread plating, especially fine thread and some difficult to plate the thread can be moved during the relocation of Shenyang Machine Tool Group Reaching smoldering liquid and cooling water zero discharge 卯石刚S宿新天2, Fan Shuangxi 2 Wang Wei 2 (1. Shenyang Machine Tool Co., Ltd., Shenyang Shenyang 1100252 Baoding Jinneng Heat Exchange Equipment Co., Ltd., Baoding 071000, Hebei) The cooling water is closed-loop cooling, achieving the zero-emission target of heat treatment quenching medium and cooling water, while ensuring the quality of the heat-treated workpiece, improving the production efficiency, reducing the amount of repair, and achieving the expected energy-saving and emission-reducing effect.

In 2006, Shenyang Machine Tool was relocated and reorganized. At the same time, the former heat treatment workshop of Shenyang First Machine Tool Plant, Shenyang CNC Machine Tool Plant and Zhongjie Radial Drilling Machine Factory was reorganized. In the relocation plan, the proposed goal is to implement a comprehensive new process for process layout, equipment, power supply, quenching medium and cooling water system based on the principles of energy saving, consumption reduction and environmental protection.

According to the targets of emission reduction and consumption reduction, the new plant first selected 27 air coolers produced by Baoding Jinneng Heat Exchange Equipment Co., Ltd., which comprehensively cooled the heat treatment equipment and closed the circulating cooling of the quenching medium to achieve zero discharge of heat treatment quenching liquid and cooling water. The goal. Mainly used for air cooler cooling equipment: 8 bed quenching machines (maximum 200kW), 10 high-frequency quenching machines (maximum 200kW), 1 French box multi-purpose furnace (26kW), gas carburizing furnace (100kW) 2 sets, 3 gas nitriding furnaces, 1 3t brine quenching tank, 10t quenching water tank and quenching oil tank, and 7m well type quenching water tank.

The air coolers that have been in use since 2007 have maintained their performance so far, effectively ensuring the smooth completion of production tasks. The quenching oil air cooler is placed outdoors, the quenching liquid (power circulating water) cooler is placed indoors, used in all weather in summer and winter, and the failure rate is low, especially the brine tank cooling ensures continuous salt furnace quenching, and the quenching liquid water temperature is lower than 40 C. It guarantees the quality of continuous production and heat treatment of the workpiece, and the use of air coolers brings obvious economic and social benefits.

The air cooler has been promoted and applied in Shenyang. The large state-owned enterprises such as Northern Heavy Industry and Shengu Group have adopted the equipment after the relocation. The private heat treatment enterprises such as Shuangma Heat Treatment Plant have also used the air cooler. With unanimous praise.

1 quenching medium and cooling water process analysis 1.1 original quenching medium cooling condition The original use situation is: all equipment cooling water, quenching water are directly discharged, the temperature of the quenching liquid in the brine quenching tank rises, affecting the normal production, only It can be cooled by adding tap water, the cost of salt water discharge is high (5t salt per month), and the waste is very large; there is no cooling equipment in the oil tank, and the high temperature oil can only be used after natural cooling, which seriously restricts production.

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