Preface
The development of society, especially the rapid development of modern industry, poses more and more challenges to the lost foam casting technology. Although the design of the lost foam casting open line has reached the requirements of general customers, the open line is subject to certain restrictions in the case of mass production, short production cycle, limited labor, continuous casting, and less casting equipment. The automatic production line of lost foam casting breaks various restrictions on the basis of making up for various defects of the open line. Our company has successively designed, manufactured, and put into normal production. There are more than a dozen lost foam casting automated production lines. This article introduces the design requirements and related content of the lost foam casting automated production line as follows:
1. Determine the production specification requirements of the automated production line.
According to the size specifications of the castings produced by the user, the size of the sand box is designed, the product production program calculation is carried out, and the overall layout of the production line is carried out according to the workshop situation. That is, calculate the weight of the casting every hour every day. So as to calculate the hourly sand processing capacity of the production line. Choose a reasonable lost foam sand processing system.
Calculation of production specifications:
1. First, calculate the production program (calculated according to the number of pieces produced per year for each type of casting);
2. Make process analysis based on casting drawings.
3. According to the production program and the domestic average production quota, combined with the specific conditions of the factory, determine the rejection rate of castings, the rejection rate of modeling and mold making.
4. Determine the size of the sand box and the number of castings on each box.
5. Calculate the model specifications, technical parameters and quantity of the molding department, vacuum system, and sand processing system.
6. Select the layout form of the casting production line, calculate the production cycle of the production line, etc.
2. Sand processing system of the fully automated production line of lost foam casting
1. The amount of sand processed by lost foam casting must meet the needs of the production program. By calculating the reasonable sand processing capacity, our company has developed: 5t/h, 10t/h, 20t/h, 30t/h, 40t/h, 50t/h, 60t/h and larger 120t/h h sand processing line.
2. The technical specifications and parameters of each equipment in the sand processing system must meet the requirements of sand processing capacity.
3. The functions of the lost foam sand processing system meet the following requirements:
⑴ Falling sand screening.
Sieving two-stage screening, the first-stage screening is used to screen out debris larger than φ5 in the falling sand of the overturning box by the vibrating conveyor screen; the second-stage stratified linear vibrating screen screens the unsuitable fine particles larger than 10 meshes and smaller than 100 meshes. Sand and debris increase the air permeability of sand.
⑵Wind separation and magnetic separation functions.
The winnowing machine relies on its own adjustment to make the dry hot sand fall in the form of a flow curtain, and the classification of sand and dust depends on
Regulating valve, adjust the size of the air volume to control. The permanent magnetic separation drum separates sand and iron.
The dry sand after magnetic separation falls into the connecting equipment of the next process, and the iron bean flash from the magnetic separation, etc.
Flow into the waste bin. Dust enters the dust removal system from the dust removal port of the winnowing machine.
⑶Using two-stage used sand cooling method, which can ensure the continuous production and operation of the assembly line.
The cooling problem of hot sand is a technical problem that needs to be considered in the composition and design of the lost foam casting production line, and it is also the key to whether the production line can be designed and produced. According to the slow cooling rate of hot sand in lost foam production, this system adopts the secondary used sand cooling method. When the sand falls, the temperature of the sand is cooled from 500°C to below 50°C through this step. The cooling process usually adopts the first-stage water-cooled boiling cooling bed for cooling, and the second-stage cooling by the sand temperature regulator. The cooling method of boiling cooling bed includes heat exchange between water and hot sand, and heat exchange between air and hot sand. The heat exchange efficiency of hot sand in a boiling state is several times higher than that in a static state. Therefore, the cooling effect of this machine is better than other kinds of cooling devices, and it is accepted by the majority of users. At the same time of heat exchange, the dust in the boiling dry sand is drawn into the dust collector along with the hot air formed by the heat exchange, which greatly reduces the dust content of the cooled dry sand, maintains good air permeability of the dry sand, and realizes cooling , The dual purpose of dust removal. The sand temperature regulator realizes the function of adjusting the sand temperature by the peristaltic contact between the sand and the circulating water pipe. Suitable for assembly line automatic production.
⑷Sand conveying link
When sand is transported, the sand temperature is very high when the sand is shaken out. The vibration conveyor and chain bucket elevator can ensure the sand transportation under high temperature, and the use performance is good. The cooled sand can be transported between height and horizontal distance by using belt elevator and belt conveyor.
⑸Control of production line
The control of the production line adopts PLC automatic control. The control methods are controlled by analog screen, touch screen and industrial computer respectively.
⑹Dust removal system
Lost foam casting is a new green and environmentally friendly process in the 21st century. The dust removal system of the lost foam sand processing production line should select equipment according to the sand processing capacity and the production line. By calculating the dust removal air volume of the sand processing system, the power of the dust collector fan is selected according to the calculated air volume. Complete the design of the dust removal system pipeline, and each dust point is equipped with an air volume regulating valve to control the reasonable air volume of each pipeline.
3. The sand box operation of the automatic production line of lost foam casting
The operation of the sand box of the automatic production line of lost foam casting is fully automated. The special sand box runs on a roller table or track, and is realized by a hydraulic box pushing machine, an electric transition trolley, and a fully automatic hydraulic box turning machine. The running time of the sand box is consistent with the production line beat. The operation cycle is automatically controlled by the touch screen to realize the requirements of fully automated operation of the sand box. The layout of the entire sand box running line is smooth and concise.
Four, vacuum negative pressure system
The molding and pouring process of lost foam casting is usually carried out under vacuum conditions, and a closed system is composed of a special sand box and a negative pressure system.
Vacuum pump is the most basic equipment in vacuum lost foam casting. The vacuum negative pressure system is composed of a vacuum pump, a wet dust collector, a pressure tank, a steam-water separator, a water tank and pipeline accessories.
The principle of choosing a vacuum pump is to pump a large amount of air, but the vacuum degree it can achieve is not high. When determining the pumping capacity of the vacuum pump in actual production, the following factors can be considered:
⑴The size of the casting casting;
⑵The cast metal material;
⑶The size of the sand box and the number of sand boxes used for simultaneous pouring.
Relevant literature points out that the power consumption of the "FV" method vacuum pump can be calculated as follows:
W=kn(V1+β.m.Q)
In the formula, W----motor power of vacuum pump (kw)
k----2-6(kw/m³)
n----Number of sand boxes
V1---Volume of sand box (m³)
β---Safety factor (take β=3-10)
m----the mass of the lost pattern in each sand box (kg)
Q---- is the air volume of polystyrene foam (m³/kg)
The sealing plastic film must be protected from burning when pouring, otherwise the vacuum degree of the mold will be significantly reduced.
Application of vacuum negative pressure connection in automatic line. The automatic line adopts fixed vacuum docking machine, automatic or mobile vacuum docking machine to complete vacuum docking and pumping negative pressure.
5. The molding department of the fully automated production line of lost foam casting
The molding department of the automatic line can be broken down into several stations. That is, bottom sand tapping, white mold placement, sand tapping, bedding mold, sand capping, and sprue cup placement.
There are three commonly used sand adding methods in lost foam casting: artificial sand adding by hose, sand adding with spiral feed and sand adding by rain. Our company adopts rain-drenching sanding in the automatic line modeling. The rain-drench sand adding mainly depends on adjusting the relative position of the moving plate and the static plate in the porous gate to change the size of the cross-sectional area of the sand leakage hole, and then change the size of the "sand rain" (that is, change the sand adding speed). This kind of sand adding method has uniform sand adding and high efficiency, and is suitable for use on automatic assembly lines. It is also one of the most widely used sand adding methods at present.
Vibration is tight. Since lost foam casting uses binder-free dry sand to fill the model, it usually only needs to use vibration to achieve compaction. Vibration compaction table is one of the key equipment in lost foam casting.
Determine the specifications of the vibrating table in the production line. First, the lost foam casting process is formulated according to the overall dimensions of the casting workpiece. So as to determine the specifications of the sand box. Choose the appropriate tapping table size from the sand box size. By calculating the weight of the sand box and the sand to determine the rated bearing capacity of the vibrating table, the size of the exciting force and the power of the vibrating motor. At present, the vibration compaction equipment used by our company is a frequency conversion three-dimensional vibration compaction table. The high-frequency vibration motor is used for three-dimensional micro-vibration and compaction. The three-dimensional vibrating table has different vibration modes. According to the parts of different shapes, the different vibration modes are adjusted through stepless frequency conversion. Make the dry sand quickly reach all parts of the shape and form sufficient compactness. Ensure that castings with clear contours and precise dimensions are obtained after pouring.
Six, the advantages of the fully automated production line of lost foam casting
1. The production line adopts fully automatic control, which shortens the production cycle and has high production efficiency.
2. High degree of automation, simple operation, reduce labor intensity and save labor. Compared with the lost foam open line, the automatic line has lower labor intensity and is more labor-saving; for example, only 3 people are used in the production and modeling department of a single shift of 5000t/year; only 5 people are used in the production and modeling department of a single shift of 10000t/year, and female operators are used It can meet the requirements, solve the labor shortage, and reduce labor costs.
3. The process technology is easy to master, and the production management is convenient.
The lost foam automatic production line is a technological innovation based on the open line. Its appearance is an inevitable trend for the foundry enterprises to develop from the initial lost foam production line to the automated assembly line control. Our company will carry out technological innovation on the existing basis, continue to improve existing equipment, develop new equipment, and further improve the automation of the lost foam casting automatic production line, and continue to make progress and work hard to meet the needs of different customers.