3、 The main body of SMC production equipment is divided into two parts: one is resin paste preparation equipment, which includes three processes: feeding, mixing and conveying. One part is production equipment, which includes pasting, roving cutting, impregnation and rolling. This part mainly introduces SMC production equipment. A complete SMC unit consists of 7 main parts, i.e. frame, conveying system, PE film supply device, scraper, fiberglass cutter, impregnation and compaction device, winding device, and 3 necessary auxiliary systems, i.e. fiberglass frame, resin paste preparation and feeding system, and electrostatic eliminator. The composition of SMC unit is shown in the following diagram. Typical photos of SMC unit are shown in the figure, and parameters of typical SMC unit are shown in the table. 1 - roving without twist; 2 - lower film unwinding; 3 - spreading roller; 4 - three roller cutter; 5 - lower resin scraper; 6 - upper resin scraper; 7 - spreading roller; 8 - upper film unwinding; 9 - frame; 10 - guide roller; 11 - impregnating compaction roller; 12 - traction roller; 13 - transmission device; 14 - drawing of winding device: SMC unit
Figure: photo of SMC unit
Table: typical SMC unit parameter No. parameter No. parameter No. parameter No. parameter No. parameter No. 01 product width 48 inches (1220mm) 05 product weight 1.6-6kg/m202 film width 52 inches (1321mm) 06 production speed 3-20m / min ± 2% 03 resin paste viscosity 12000-60000cps07 fiber cutting length 1 inch and 1 / 2 inch 04 fiber content 20-50% ± 2% 08 filler content 40% - 50% (a) rack Generally, it is welded with various sections (such as angle steel, channel steel, etc.) or connected with bolts. Its main function is to install the conveying system and various components. In order to prevent deformation under various static and dynamic loads, the frame should be rigid enough, and in the new structure design, there should always be spare space on the frame. (b) There are generally two types of conveying system, one is conveyor belt, the other is to use polyethylene (PE) film directly and play the role of conveyor belt. Special attention shall be paid to the control device of conveyor belt movement track in the design of the unit. (c) PE film supply device the PE film supply device shall ensure sufficient film supply in the production process, and ensure that the film can enter the upper paste area without wrinkles under the condition of adjustable tension. Generally, two sets of film supply devices are set in the unit, and each set can install two rolls of film at the same time, so that after one roll of film is used up, the other roll of spare film can be put into use immediately without any pause in the production process. (d) The scraper device is installed in the upper paste area of the unit, with two scraper devices. Its main function is to evenly apply a controllable amount of resin paste to the PE film as the film passes between the scraper and its bottom plate. The scraper shall be easy to adjust and the adjustment accuracy shall be high. The gap between the scraper and the base plate shall be uniform and the error shall be less than 0.05mm. In order to prevent the film from tearing caused by agglomerations or external impurities in the resin paste entering the scraping area, the scraper base plate or scraper can realize temporary instantaneous drop. In the design, the radius of blade should be as small as possible. (e) Glass fiber cutting in many earlier design units, the cutter is installed on another machine alone, when using glass fiber felt, the equipment can be produced without too much change. However, due to the reasons of price and performance, felt is rarely used as the reinforcement material of SMC, so most of the cutters are directly fixed on the main frame. The fiberglass is cut by a cutter. The cutter is a three roller structure, as shown in figure 43.178. The continuous glass fiber is led out from the yarn frame and enters between the pressing roller 5 and the rubber covered supporting roller 3 through the yarn traverse rod 2. Due to the traction of the two rollers, the fiber is led between the rotating supporting roller and the cutting roller 8 and cut into short cut glass fiber. 1 - continuous glass fiber; 2 - traverse rod; 3 - supporting roll; 4 - metal roll; 5 - pressure roll; 6 - blade; 7 - pressing block; 8 - cutting roll; 9 - metal roll figure: glass fiber three roll cutter for SMC unit
(f) Impregnation and compaction equipment impregnation and compaction equipment consists of a series of smooth rollers and grooved rollers, with piercing rollers added in some units. Their function is to realize the composite, impregnation, defoaming and compaction of SMC sheet. The use of groove roller can strengthen impregnation and avoid resin paste outflow under impregnation pressure. In the impregnation and compaction area, the pressure of various rollers can be pressurized by gas or liquid. The compaction roller at the end of the area can also adjust the sheet thickness. In SMC unit, soaking, defoaming and compaction are mainly realized by the bending, extension, compression and kneading of various rollers and sheets. In order to saturate the fiber with resin, drive out the bubbles and compact the sheet molding plastic to a uniform thickness, there are two kinds of impregnation and compaction structures in the unit, namely, the ring groove roller type with multiple rollers and the curved double belt type with conveyor belt, as shown in the figure and figure. Figure: roller impregnation unit
Figure: curved double belt impregnation unit
(g) The function of the winding device is to collect the impregnated SMC into rolls. For the experimental unit or small batch production unit, the double axis and double position winding device is generally used, which can realize the roll change in the production process. (2) The production process of SMC the preparation of SMC sheet is mainly composed of the following parts: (a) resin paste preparation and paste up process. There are three preparation methods of resin paste: a) batch mixing method. This method is to add various materials other than thickener into the reactor in proportion, and use them as a paste mixture. Add thickener before SMC unit. After the thickener is added, it is usually used up within 30 minutes. b) Batch mixing / continuous mixing process is characterized by two blending kettle systems. One is filled with unsaturated polyester resin, low shrinkage additive, initiator, release agent and filler, and the other is filled with resin, colorant and thickener. During production, the metering pump is used to mix through the mixer. c) The measurement, transportation and mixing of all liquid or solid in the formula of continuous mixing method are all mechanized and automatic. This system has high investment cost and is suitable for continuous mass production. (b) The purpose of the impregnation process is to impregnate the resin with fibers, expel bubbles and compress the sheets. For this reason, various types of rolls (smooth roll, groove roll, puncture roll and spiral roll) are arranged in SMC unit. When the sheet passes through the upper part, the lower part and the surrounding of these rollers, the impregnation is realized due to the bending and extension effect. (c) Thickening process and storage process when the SMC sheet is rolled up, it can only be used after a certain thickening time. If SMC sheet is stored at room temperature, it will take about 1-2 weeks. It takes 48 hours or 72 hours to thicken at 40 ℃. At present, some thickeners are added to SMC unit or some new thickeners are used. SMC can be pressed after being prepared into sheet. The storage period of sheet is related to the storage state and conditions. The storage period of SMC sheet is obviously affected by ambient temperature. Taking the sheet produced by Scott bard company in the UK as an example, its storage period is 3 months at 15 ℃ and 6 months at 2-3 ℃. The shelf life of the sheet is also related to the formulation. If polymerization inhibitor is added to the formula, the storage period will be longer. (3) SMC production process control as mentioned above, SMC is composed of a variety of components by special equipment. From the aspect of raw materials, it has organic materials and inorganic materials, solid materials and liquid materials, powder materials and fiber materials, and the system will produce various physical and chemical changes when the components are combined. In its production process, there are many factors, such as material factors, equipment factors, human factors and so on, which will affect the production process and the quality of the final product. Therefore, only by considering the overall quality management of sheet molding materials from the perspective of the whole production system, can we get a good and stable sheet molding material product. Generally speaking, the quality management of SMC manufacturing consists of two parts, i.e. raw material quality management and SMC production process management. (a) Quality management of raw materials raw materials for SMC production mainly include unsaturated polyester resin, low shrinkage additive, styrene monomer, filler, glass fiber, internal release agent, initiator, color paste, chemical thickener, etc. the items to be controlled are listed in the table. Table: main inspection indexes of raw materials for SMC
Serial number
Material name
Quality control index
01
resin
Color, viscosity, solid content, acid value, hydroxyl value, moisture content, 80 ℃ SPI curing characteristics, thickening performance
02
Low shrinkage additive
Solid content, acid value, viscosity, moisture content, relative molecular weight, shrinkage
03
Zinc stearate
Main component analysis, impurity content, total ash, soluble salt, melting point, fineness, apparent density and moisture content
04
Thickening agent
Purity, moisture content, thickener content and thickening performance
05
styrene
Color, purity, flash point, prepolymer content and impurity content
06
Initiator
Purity, active oxygen content, other peroxide content, curing characteristics
07
filler
Main component analysis, moisture content, average particle size, particle size distribution, oil absorption value, relative density, color, impurities
08
fibre
Strength, soakage agent content, Tex number, moisture content, banding, solubility, monofilament diameter, appearance, cutting and electrostatic properties
It should be emphasized that the items listed in the above table do not need to be tested item by item. In the whole SMC sheet production process, it is particularly necessary to strictly control the moisture content of the system, especially the moisture content of the raw material system. (b) SMC process quality management SMC production process includes the following steps: feeding, mixing, resin paste transportation and coating, fiber transportation and cutting, composite and impregnation, winding and metering, and aging. The follow-up is described in terms of SMC process control and quality control. a) SMC process control online gamma ray testing device continuously measures the thickness of SMC / BMC resin paste on the carrier film, keeps the thickness of SMC / BMC resin paste on the carrier film consistent (in the width direction, the SMC paste distribution is uniform without deviation), and keeps the glass fiber distribution uniform and stable glass fiber content (2%); Measure the weight of unit area SMC at different positions in the width direction of SMC by cutting SMC and weighing; measure the weight of unit area SMC at the beginning of production, in the middle of production process and at the end of production (a method to control the thickness uniformity of SMC); The viscosity and temperature of the resin paste shall be tested when replacing the resin and using the new batch of fillers; SMC shall be stored in a constant and controlled environment, i.e. a higher temperature curing chamber (such as 28 ℃) and a lower temperature storage chamber (such as 18 ℃); In order to control the viscosity growth of SMC / BMC paste, it is necessary to store the sample of SMC / BMC resin paste in the SMC / BMC curing chamber, and measure the thickening of SMC / BMC resin paste by using the Brinell viscometer according to the regulations; when adding raw materials such as resin, filler, assistant and magnesia paste, the adding amount should be accurate. b) SMC quality test Test the reactivity of SMC with exothermic test equipment. If there is no reactivity tester, measure the temperature change curve with time during the plate forming process through thermocouple; measure the shrinkage of the plate; test the consistency (plasticity) of SMC with plasticizer. This method is very suitable for the production monitoring of SMC with the same formula. If the fiber used in the production changes, test the knot