Truck Cylinder Trunnion Water Glass Investment Casting

Product Introduction

Investment Casting Process
Truck cylinder trunnion water glass investment casting has the characteristics of high dimensional accuracy, low surface roughness, and can be used without or with little processing. It is an advanced casting process with little or no cutting processing. It is a metal close-cut, clean Forming process; therefore investment casting is also called "lost wax casting", "precision casting" and "precision casting". Investment casting is widely used in aerospace, weapons, machinery, electronics, petroleum, chemical industry, energy, transportation, light industry, textiles, medical equipment and gifts, etc., and is used in all walks of life in the sky, on land and underwater; it is It is an important basic industry for the development of the national economy and the realization of the "Chinese Dream".
Due to the complexity of the investment casting process and the many influencing factors, most of the production is manual and difficult to control; therefore, the scrap rate of investment castings is relatively high. According to incomplete statistics, the scrap rate is about 10%, and the scrap rate of individual defects The rate is even higher; and the quality of the castings is very unstable. Solving investment casting defects is one of the main tasks of investment casting workers. To do this job well, you need to: master the necessary knowledge of investment casting; be familiar with the methods of defect analysis of investment castings; and use common tools for defect analysis of investment castings.

Process Characteristics Of Investment Casting
(1) Castings have high dimensional accuracy (CT4-6 level), low surface roughness (Ra1.6-3.2µm), and complex shapes;
(2) The casting has thin walls (0.5mm), light weight (several grams), narrow slots, fine holes, and can produce exquisite patterns;
(3) It can replace complex structural parts such as assemblies and welded parts, reducing the weight and machining allowance of the parts;
(4) It can precision cast complex castings of various alloys, such as engine blades and other high-temperature alloy castings;
(5) There is no limit on the production batch size, it can be single piece or batch.
 

Eight Processes Prone To Defects
1. Customer needs
(1) When customers have new needs, parts drawings should be provided first;
(2) Based on the part drawings provided by the customer, the foundry company requires its designers to design the investment casting process after signing the contract, including analyzing the processability of the investment casting structure, determining the process plan and process parameters, such as machining allowances , casting holes, process holes, process ribs and process bosses, etc.; select the datum plane of investment castings; design the gating system for investment casting feeding; and draw process drawings or casting drawings. The technical conditions should be marked on the designed casting drawing, such as: general technical conditions, special technical conditions, or special technical conditions for casting acceptance; heat treatment method (usually normalizing and annealing) and hardness; whether casting defects are allowed, and what is allowed What is the extent; whether welding repair is allowed and which locations are allowed; residual amount of the inner gate; unmarked casting fillet, slope, etc. On casting drawings, the size and machining allowance of the casting are generally marked, but the dimensional tolerance and surface roughness of the parts are not marked;
Remember: Casting drawings must be signed and confirmed by the customer.
(3) For new castings, before signing a contract, the company must conduct an extremely important and easily overlooked contract review; the contract can only be signed after passing the contract review;
(4) The purpose and function of contract review:
The first is to clarify customer requirements: identify and fully understand customer requirements; new products should obtain their various technical, quality and other special requirements; as well as laws, regulations and environmental protection requirements related to new products;
The second is the internal relevant departments: the engineering technology department reviews the technical requirements of new products; the purchasing department reviews the supply capacity of raw materials required for products; the production department reviews product quantity and delivery time; the quality department reviews product quality inspection and testing capabilities; The Finance Department reviews the legality, completeness and economics of the contract; the general manager or his authorized person signs the contract/order (the content of the review should be different as the functions of the relevant departments of each enterprise are different);
The third is to achieve customer satisfaction: provide customer-satisfied castings that meet customer requirements in a timely manner.
2. Pressure design and manufacturing
Based on the casting drawings and combined with previous design data and experience, designers design the molding and track the manufacturing of the molding, so as to solve technical and quality problems in the manufacturing of the molding at any time. Profile design is one of the key processes to ensure the dimensional tolerance and surface roughness of castings.
3. Pressed wax mold
(1) New product: This is the first comprehensive inspection of the molding. Experienced designers can basically know the size of the casting after pouring by inspecting the size of the wax model, and make a preliminary judgment as to whether the molding needs to be modified?
(2) Normal products: focus on controlling the mold process and execution;
Although the performance of paraffin-stearic acid wax is poor, because paraffin-stearic acid wax is abundant in supply, cheap and can meet the quality requirements of general castings, many domestic investment casting companies still continue to use it. Paraffin - stearic acid wax material;
The main process parameters that affect the quality of the wax mold are: wax configuration, molding temperature and pressure during wax injection, filling time or filling speed, wax temperature, holding time, mold ejection time, cooling method and coolant temperature and cooling time, etc.
Currently, the wax mold is pressed at a low pressure of 0.2-0.5MPa, using a pneumatic wax press or manually. The temperature of the wax material during injection is 45-48°C; the pressing temperature is 18-25°C; the holding time ( (Adjust according to the size and wall thickness of the wax pattern) 3-5s; mold removal time (adjust according to the size and wall thickness of the wax pattern) 20-100s; release agent 10# transformer oil or turpentine.
4. Assemble welding wax mold
The wax mold assembly is welded in the process design, including the selection of the pouring system, pouring position and internal gate design content. Improper process design will result in batch and recurring waste of castings.
The wax molds are assembled and welded according to production needs and process design requirements. Note: Welding gaps must be avoided during assembly welding. It is easy for gaps to form during the shell making process, causing defects such as burrs and blisters in the castings.
5. Shell making
The shell making process directly affects the strength and air permeability of the mold shell, and the roughness of the inner surface of the mold shell. It is one of the special processes that affects the quality of castings; it is a key control process.
To control the shell-making process well, it is necessary to control the ratio and viscosity of the surface layer and reinforcement layer coatings, control the concentration, temperature, and hardening time of the hardening liquid, and control the surface layer, transition layer, and reinforcement layer shell powder ( sand) selection, etc.
Although the water glass shell has certain shortcomings in terms of high temperature performance, dimensional accuracy, surface roughness, etc.; however:
(1) The performance of water glass is relatively stable. Wet shell making and chemical hardening methods are used in production, which can quickly harden the shell and establish room temperature strength (wet strength). The production cycle is short, the production efficiency is high, and the production process is easy to control;
(2) Water glass is cheap, abundant, and easy to purchase;
(3) More importantly, the water glass shell making process can fully meet the quality requirements of ordinary investment castings and is suitable for mass production; therefore, most domestic investment foundries still use water glass shells.
For silica sol molded shells, the humidity, temperature and drying time of the drying chamber, as well as process parameters such as wind speed, must be strictly controlled.
6. Smelting and pouring
The smelting and pouring process directly affects the quality of castings. It is a special process that affects the quality of castings and is one of the key control processes. On the premise of ensuring strict implementation of the smelting process, it is necessary to control the temperature of the molten metal during pouring, the pouring speed, the shell temperature during pouring, etc.
Truck cylinder trunnion water glass investment casting is generally smelted in an induction furnace. The smelting process mainly generates eddy currents through electromagnetic induction, and relies on resistance heat to achieve melting and refining. Through deoxidation during the smelting process, the content of metal inclusions in the molten metal is reduced, floated and facilitated removal. When using precipitation deoxidation, pay attention to the order and amount of deoxidizer used to facilitate the deoxidation effect.
Induction furnace smelting has strict requirements on the charge. It generally requires accurate composition, cleanness, no oil, dryness and no rust.
7. Shot blasting and sand blasting
A thick oxide layer adheres to the surface of the cut casting, and some even adhere to sintered molding sand. Considering production efficiency and other aspects, shot blasting is easy to use and has high efficiency; however, it has an impact on the surface roughness of the casting. .
There is a very thin layer of oxide scale on the surface of the heat-treated casting, which is easy to be cleaned by sandblasting. Compared with shot blasting, the efficiency is lower, but it has less impact on the surface roughness of the casting.
8. Inspection
For new products, it is necessary to check whether the size and surface roughness of the casting meet the requirements according to the drawings? Then use this to determine whether the profile design needs to be modified? The castings that have passed the inspection will be sent to the customer for confirmation and signature, or it is called "seal sample". This is an extremely critical step and is one of the important basis for future acceptance of castings by both supply and demand parties.
For exported investment castings, in accordance with international practice, any defects visible to the naked eye are not allowed on the surface of the investment castings. A very small number of companies in the domestic aerospace and mechanical departments use high-quality wax materials with low shrinkage and high strength; under constant temperature conditions, they use higher pressure to press bright and precise wax models; they even use liquid pressed wax.
The shell is made of high-quality ethyl silicate and silica sol as binders, as well as high-quality refractory materials such as zircon powder, corundum, and quartz glass. Using high-pressure steam kettle dewaxing, rapid atmospheric or vacuum smelting and pouring, and high-pressure water or water sand cleaning processes, the resulting castings have high dimensional accuracy, CT4-CT6 level, low surface roughness Ra0.8-1.6µm, and internal Good quality castings.
In normal production, on the premise of ensuring strict implementation of the process, the dimensions of investment castings are only randomly inspected; the focus is to regularly inspect whether the dimensional accuracy of the molding has changed and whether it needs to be corrected?
With the commercialization, internationalization and competition of investment castings, the use of the latter two binders will become more and more widespread.
 

Detection Systems

Copper Silica Sol Investment Casting