This week I mainly practiced in the EPS / EPP workshop of the production department to understand the process of EPS / EPP molding. A qualified packaging designer can put ideas into practice only after he is familiar with the production process; on the contrary, the design on paper will definitely encounter problems in the subsequent production process, which can not meet customers' timely delivery, Cost control, fine quality, etc., then this design must fail.
EPS molding involves the selection of raw materials, piping technology and mold technology, and is finally reflected in such aspects as molding technology. Our EPS molding is divided into the following steps in turn: pre-issue → mold → molding → finishing → drying → packaging → storage.
The pre-processed raw material beads (BSF raw materials) are softened when heated in the pre-machine barrel by steam above 90 ° C, the foaming agent is volatilized and escaped, and the volume of the particles is expanded to the required ratio or weight. Within the allowable foaming speed, the foaming ratio required for the subsequent cushioning design is obtained by adjusting the pre-emergence temperature, steam pressure, and feed amount. We can produce the required expansion ratio, which is the EPS raw material of the specified weight, according to the needs of customers.
The foam particles that have just been sent are softened and have no elasticity due to the evaporation of the foaming agent and the condensation of the remaining foaming agent. Therefore, there must be sufficient time for air to enter the micropores inside the foam to make the internal and external pressures balanced and flexible It usually takes about 4 hours. The round-cooking process is completed in a round-cooked warehouse made of mesh anti-static gauze to disperse the adhered foam particles and eliminate the static electricity that naturally accumulates when the foams are rubbed.
Depending on the molding machine (mainly other performance parameters such as clamping size) and the needs of the product, the EPS molds are also different. In order to realize the standardization and serialization of the mold, facilitate the assembly and disassembly of the mold, reduce the processing volume, and improve the productivity, the mold is divided into two parts, the mold base and the cavity.
The installation of the mold and the replacement of the cavity are solidified into standard actions. Our molding machines are all-in-one machines. The height of the die frame is adapted to the needs of different products. Generally, it is made into a series of several specific specifications. Therefore, the back of the die is equipped with different height support frames.
2. The cavity is composed of a concave mold, a convex mold face plate and a back plate. When the mold is replaced, the cavity only needs to be replaced, which will be very convenient during manufacturing and use. (1) Due to the different working tables of different forming machines, a reasonable choice needs to be made according to the size of the product. (2) The collection shape of the cavity is directly related to the shape of the product. Fix it on the mold base with screws. After the position of the back plate and the panel is adjusted, install the feeding gun and ejector. All possible gaps are installed. Sealing ring for subsequent evacuation process. After the female mold and the male mold are installed, the mold is locked, and the air pipe, the material pipe connected to the mold end are connected, and the machine is ready for production.
3. After the mold is installed in the mold loading area, it is installed on the machine, connected to the water pipe, material pipe and gas pipe at the end of the molding machine, and the concave mold and the convex mold are opened, and the trial molding process can be performed.
Control the length of heating and water cooling time according to different product specifications, sizes, thicknesses and other factors; in general processing and molding, water cooling time accounts for half of the total cycle time of processing and molding; steam, cooling water and compressed air supply conditions are to ensure the product The basis of good demoulding, good maturity, surface smoothness and shortening the molding cycle. The experienced equipment maintenance master will adjust the corresponding parameters according to product characteristics to quickly reach the best molding state.
The key to EPS heating
1. Low pressure must be used for penetration, and high pressure is used for ordinary heating (different high pressure can be set according to the characteristics of the raw materials and the mold);
2. Before the penetration, exhaust must be performed, that is, the two steam valves and the drainage valve are all opened, and the air and water in the raw material and the mold cavity are exhausted by steam. This step can be appropriately adjusted according to the mold temperature. Generally, 1 ～ 2S;
3. The requirements for steam must be dry, without water or boiling water
Otherwise: 1) the penetration time will be long (equivalent to boiling the mold with hot water); 2) the mold is extremely corrosive (equivalent to punching the mold with hot water with pressure)
Reasons for steam with water: the water level of the heat storage tank may be too high or the steam with boiler water;
For EPS molding, you can choose different penetration methods according to the molded product: when the general cavity is relatively large and the punch is simple, you can choose one penetration, that is, one-way penetration, so the molding time can be greatly reduced. The penetrating pressure selects the low pressure region.
The key in EPS molding:
1, the situation of the material gun (insufficient feed, increased waste, low efficiency); therefore, the material gun often needs to be overhauled in daily mold maintenance;
2. Eliminate air leakage and water leakage (energy consumption, efficiency, machine corrosion);
3, vacuum degree inspection (poor vacuum degree, not easy to vaporize, the product is easy to swell);
4. Pressure check (including pressure check of feed and various controllers);
Finishing requires preliminary quality screening of the molded product. Moisture adheres to the surface of the product that is released from the mold. At the same time, the steam of the product foam condenses into water and must be evaporated to dry. Large shrinkage force will be generated, and higher magnification products may shrink in thin-walled parts. Therefore, the molded EPS products need to be placed in the baking room for curing in time.
The temperature of the drying room is generally 50 ℃ ~ 60 ℃, the drying time is generally 4 hours at this temperature, the hardness and strength of the product will increase after drying.