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Practice of hanging tools for surface treatment
In electroplating production, hanging tools are indispensable tools.Its function is to fix the parts, connect the electrodes, so that the current is evenly transmitted to the parts for electroplating.Therefore, reasonable selection of hanging tools is of great significance to ensure coating quality, improve production efficiency and reduce labor intensity.
The basic principles for designing the hanger are:sufficient mechanical strength and good electrical conductivity; Parts and hangers should be in firm contact and convenient loading and unloading; In addition, we should strive for light weight, small size, durability and proper loading capacity.
1.The type and form of hanging tools
The type and form of hanging tools for electroplating are determined according to the shape of parts, technical requirements of plating, electroplating process and equipment size.There are also differences between automatic lines and manual electroplating hangers.
General electroplating factories and workshops are equipped with general hanging tools suitable for various common parts and special hanging tools designed and manufactured only for certain parts.
There are many types and forms of universal hanging tools, which are suitable for various processes and parts.
Special hangers can be divided into two situations:one is special hangers designed and manufactured for mass production of parts; The other is a special hanging tool designed and manufactured according to the complex geometric shape and special technological requirements of parts.
(1)Basic types of universal hangers
Universal hangers are suitable for a variety of parts and processes.For example, when anodizing aluminum parts, hanging tools made of aluminum or aluminum alloy should be used.Contact parts (hooks, clamping teeth) should have elasticity to clamp parts and prevent the anodic oxidation from continuing due to the formation of non-conductive oxide film with the contact parts when the contact is loose.
(A) Suspended hook hanger; (B) Clamping, elastic hook hanger.
(2) Special Hanging Tool
This paper introduces only a few special hanging tools designed and manufactured according to the geometric shape of parts and special technological requirements.
1.Bipolar inner hole plating fixture
2.Chromium plating fixture
The electrolyte used in chromium plating has poor dispersion ability, and the current density used in chromium plating is relatively high.Therefore, the requirements for hanging fixture are strict, so a reasonable fixture must be designed and manufactured according to the technological characteristics and the specific shape of parts.The following points should be paid attention to when designing and manufacturing chrome-plated hanger:
1) The selected hanger material should be stable and insoluble in chromic acid.
2) The conductive part of the fixture shall have sufficient cross-sectional area and shall not generate heat.
3) The fixture structure is connected by welding, and the conductive copper hook should be bent into a right angle shape.
4) Fixture and parts should be in contact with threads as far as possible.
5) The cathode and anode of the inner hole chrome plating fixture must be separated from each other.Use insulating block (hard plastic plate or plexiglass) instead of protecting cathode.
6) The non-working face of the fixture should be insulated to reduce current consumption.
(7) The location where the parts are mounted, the gas discharge should be the easiest.On the premise of ensuring applicability, the hanging device should be as light, simple, universal and convenient for loading and unloading as possible.
Several commonly used chrome-plated hangers
Ⅰ-parts; II-Hangers; III-Mounting state.
(a) Hanger 1-upper protective cathode for chrome plating of bolt parts; 2-PVC tape insulation.
(b) Hanger 1-lower protective cathode for chrome plated parts with internal threads at both ends; 2-Protect the cathode.
(c) Chrome-plated hanger for inner hole of large parts 1-upper insulating block; 2-Lower insulating block; 3-Lower insulating cap (when threaded at the lower end of the part); 4-Auxiliary anode.
(3) Hanging tool for electroplating small parts
Small parts can be electroplated by barrel plating.Hanging basket can be used as electroplating tool when barrel plating is carried out unconditionally.The skeleton of the hanging basket is brass or iron wire, and wire mesh is used at the bottom and around it.The size of the mesh is based on the fact that the parts do not leak out of the hole.A slightly larger hole is beneficial to obtain a uniform coating.In order to improve the coating quality and increase the deposition rate, the drilled plastic plate can be used instead of the surrounding metal mesh.
(4) Hanging tool for chemical treatment
Hanging tool or hanging basket can be used for phosphating and oxidation of steel parts, and hanging basket is used as far as possible for general parts.Under the condition of lifting equipment, the hanging basket can be larger to improve production efficiency.All hanging tools are made of steel.Copper and brass are not used to ensure the film quality.
Hangers and baskets used in pickling are easily damaged, and materials with good corrosion resistance should be selected.
2.Structure of hanger
The structure of hanger generally consists of five parts:hook, lifting rod, main rod, support rod and hook
(1) Hook
Hook is the connecting structure between hanger and pole, which transmits current to hanger and parts during electroplating.Therefore, it must be made of materials with good conductivity.Hook and pole should keep a large contact surface and good contact state to ensure the smooth passage of current.The hook should bear the weight of the hanger and the plating part, so it is required to have sufficient mechanical strength.Hook and main rod are usually made of the same material, which can be made into one or made separately.Hanging tools and hooks made of steel or aluminum alloy are generally copper and brass, and the connection mode can be riveted and welded.
2) Lifting rod, main rod and supporting rod
1.The lifting rod is located at the upper part of the main rod and perpendicular to the main rod, and is connected with the main rod by welding.When the hanging tool is suspended in the plating bath, the position of the lifting rod should be about 80mm higher than the liquid level.
2.The main rod supports the weight of the whole hanger and the hung parts, and transmits current to each support rod and part through the main rod.The main rod is generally made of brass rods of4 ~ 6mm.
(iii) Hooks
Hooks are generally welded to struts and sometimes to main rods for hanging or clamping parts.Its materials are generally steel wire and phosphor bronze wire.
The distribution density of hooks on the hanger should be appropriate.Most surfaces or important surfaces of the parts on the hanger should face the anode and avoid the phenomenon of pressing and stacking.Generally, the spacing between small and medium-sized plating parts is 15 ~ 30mm, and the spacing of cup-shaped plating parts is generally 1% of the diameter
.5 times.According to the different connection modes between hooks and plating parts, hooks are divided into two forms:hanging type and clamping type.
1).Suspended hook plating and hook generally adopt free suspension method.After the parts are hung, they can move without falling off, and the contact points can be changed when shaking the hanging tool.This kind of hook is easy to load and unload, and the marks on the plating parts are not obvious
2).The connection between the plating parts of the clamping hook and the hook depends on elastic contact.Generally, it is used in bright electroplating, chromium plating and other occasions or when a large current density is adopted.It uses the elasticity of the hook to clamp a certain part of the part, and relies on the contact pressure to make it conduct electricity well.The strength of elasticity is determined by the material, wire diameter, wire length, plate width and plate thickness used by the hook.
No matter which way the parts are hung, the gas generated during electroplating should be discharged smoothly, so as to avoid the gas accumulating in a certain part to form an" air bag" and affect the coating quality.For example, when blind holes and concave parts are hung, their mouths should be slightly inclined upward, and plastic parts should be contacted with hooks by multiple contacts.In a word, the form of the hook and the way of hanging depend on the shape of the part and the electroplating process conditions

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