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1、Definition of SMC sheet molding compound：
SMC composite material is an abbreviation for sheet molding compound in English, which stands for sheet molding compound. It is a high-quality reinforced composite new material and also an energy-saving and environmentally friendly high-tech product encouraged by the country for development. Domestically known as unsaturated resin glass fiber reinforced sheet molding compound, the main raw materials consist of GF (special yarn), UP (unsaturated resin), low shrinkage additives, MD (filler), and various additives. Processed by a dedicated SMC production line unit, the sheet material is covered with polyethylene film on both sides. Thickness 2.5mm -6mm, width 1000mm, packaged in whole rolls or boxes.
2、Definition of BMC bulk molding compound：
BMC (DMC) material is an abbreviation for Bulk (Dough) molding compounds, also known as bulk molding compounds in Chinese. BMC is a semi dry process molding intermediate material for manufacturing glass fiber reinforced thermosetting products. It consists of GF (short cut glass fiber), UP (unsaturated resin), MD (filler calcium carbonate), low shrinkage/low profile additives, initiators, internal release agents, mineral fillers, etc., which are pre mixed into a paste. Thickening agents, coloring agents, etc. are then added and stirred in a dedicated material kettle for thickening process, ultimately forming a clustered intermediate material.
3、Characteristics and Applications of SMC Sheet Molding Materials：
SMC sheet molding compound is formed by high-temperature one-time compression molding, which has high mechanical strength, light material weight, corrosion resistance, long service life, high insulation strength, arc resistance, flame retardancy, good sealing performance, and flexible product design. It is easy to scale production and has the advantages of safety and beauty. Its mechanical properties can be comparable to some metal materials. The products manufactured by it have the advantages of good rigidity, deformation resistance, and a wide range of operating temperatures. It has all-weather protection function and can meet the needs of various harsh environments and places in outdoor engineering projects, overcoming the defects of easy corrosion, short service life, and poor thermal insulation performance of outdoor metal equipment enclosures. Widely used in fields such as telecommunications, electricity, automobiles, aviation, railways, and rail transit.
4、Characteristics and Applications of BMC Bulk Molding Materials：
BMC bulk molding materials have good physical, electrical, mechanical, heat resistance, and chemical corrosion resistance, and are suitable for various molding processes to meet the performance requirements of various products. Therefore, its application is very extensive, for example, it can be used to produce mechanical parts such as transmission components, intake pipes, valve covers, bumpers, etc; It has also been widely used in aviation, construction, furniture, and other fields that require earthquake resistance, flame retardancy, aesthetics, and durability; In the traditional field of electrical appliances, its use is becoming increasingly widespread.
5、SMC sheet molding compound usage instructions：
1. It is recommended to store in a cool place at 20 ± 5 ℃, away from light and heat. The packaging should not be damaged during the storage period.
2. Seal the material packaging and remove the load-bearing film on both sides of the sheet before entering the mold to avoid contamination from external impurities. Once opened, please use it as soon as possible. If it is no longer used within 24 hours, it must be sealed again.
3. Please use within the shelf life. The shelf life of different grades of SMC may vary, and the general storage period is one month from the date of production. Please consult our company for further information.
4. Please read the Product Safety Data Sheet (MSDS) carefully before use.
6、Introduction to SMC sheet molding plastic molding process for molded products：
Process principle: After a certain amount of SMC molding material is loaded into the mold, the SMC molding material plasticizes, flows, and fills the mold cavity at a certain temperature and pressure. At the same time, the SMB molding material undergoes cross-linking and agglomeration reactions, forming a three-dimensional structure to obtain the expected product. Throughout the entire pressing process, processes such as pressurization, shaping, and insulation rely on the closure of the heated mold.
Under the conditions of heating, pressure, and insulation, the molded material undergoes the following stages of changes.
1. The first stage is the heat plasticization of SMC molding material, which flows and fills the mold cavity to obtain the required shape of the product.
2. The second stage is the crosslinking reaction between resin and crosslinking monomer, forming a partial network structure. The viscosity of SMC molding material increases, the flowability decreases, and it exhibits a certain degree of elasticity.
3. The third stage is the continuation of crosslinking reaction, where the copolymerization reaction between resin and crosslinking monomer becomes more complete, causing the SMC molding material to lose fluidity and significantly increase hardness.
7、Production process flow of SMC sheet molding plastic molded products：
Material preparation → Pressing → Demolding and shaping → Grinding → Inspection → Packaging and storage.
8、The impact of SM sheet molding plastics on the environment：
There is no environmental pollution problem in the production and molding of SMC sheets, which has been confirmed by environmental monitoring results of similar manufacturers at home and abroad. There is only a small amount of gas odor. Fully compliant with the national standard (TJ36-79), the workshop exhaust gas can be extracted and discharged at high altitude. The production process does not require water, and there is no sewage treatment problem. The noise of SMC sheet production line and molding machine is much lower than that of general metal cutting machine tools. So SMC sheet molding compound is a new environmentally friendly material in the 21st century.
9、SMC product performance：
| Serial Number | Indicator Name | unit | Indicator value | ||||||
| TC-4331 | TC-4333 | TC-4335 | TC-4341 | TC-4343 | TC-4345 | TC-4347 | |||
| general use | Wear-resistant type | Mechanical performance ordinary type | High mechanical performance type | Electrical type | High mechanical and electrical type | Corrosion resistant type | |||
| 1 | density | g/cm3 | 1.75--1.95 | ||||||
| 2 | Water absorption | mg | ≤20 | ||||||
| 3 | Moulding shrinkage | % | ≤0.30 | ≤0.15 | ≤0.30 | ≤0.15 | ≤0.15 | ≤0.30 | ≤0.15 |
| 4 | Heat distortion temperature | ℃ | ≥220 | ≥240 | ≥220 | ||||
| 5 | Charpy impact strength | KJ/M | ≥45 | ≥60 | ≥120 | ≥75 | ≥60 | ≥120 | ≥60 |
| 6 | bending strength | MPa | ≥135 | ≥150 | ≥200 | ≥170 | ≥150 | ≥200 | ≥150 |
| 7 | insulation resistance | Ω | ≥1.0x1012 | ---- | ≥1.0x1013 | ---- | |||
| 8 | electric strength | MV/m | ≥11.0 | ≥12.0 | ---- | ||||
| 9 | Dielectric loss factor | MH2 | ≤0.015 | ---- | ≤0.015 | ---- | |||
| 10 | relative dielectric constant | MH2 | ≤4.8 | ≤4.8 | ---- | ||||
| 11 | Arc Resistance | - | ≥180 | ≥180 | ---- | ||||
| 12 | proof tracking index（PTI） | V | ≥600 | ≥600 | ---- | ||||
| 13 | flame resistance | S | FV0 | ---- | |||||
| 14 | Long term heat-resistant temperature index | ℃ | 155 | 130 | 155 | ||||
10、Defects and Countermeasures of SMC Forming Method：
| Defects | reason | Countermeasures |
Poor Filling SMC cannot reach the corners | Insufficient supply quantity | 1. Increase the supply quantity 2. As the wall thickness changes, the loading amount increases 3. Even if the wall thickness always changes significantly, the loading amount and loading area should be increased according to the different surface areas |
| Due to the high temperature of the mold, the material coagulates before the flow is completed | 1. Reduce temperature 2. Accelerate the mold closing speed | |
| Due to slow mold closing speed, the adhesive will solidify before the mold closing is completed | 1. Accelerate the final mold closing speed, or shorten the time between feeding and mold closing completion 2. Reduce mold temperature | |
| Insufficient molding pressure | 1. Increase pressure and enhance the fluidity of SMC 2. Preheating | |
| The gap between the cutting edges is either completely or partially too large, or due to the short stroke of the mold, there is a lot of material flowing out, which cannot guarantee internal pressure, resulting in insufficient local material | 1. Reasonably change the gap 2. Extend the journey | |
| SMC has arrived, but there is poor filling on the way | Insufficient liquidity of SMC | 1. Preheat beforehand 2. Adopting SMC without excessive viscosity increase 3. Re study SMC raw materials |
| Insufficient materials | Increase supply quantity | |
| Air bubbles or blind holes occur due to incomplete air removal, forming an air storage box | 1. Change the shape of the material (driven out of the air by the flow of SMC) 2. Re study the mold and change the design 3. Slow down the mold closing speed and increase the pressure | |
| bubble | The air has not been completely expelled | 1. Study the formation of additives to exhaust the air 2. Reduce the feeding area |
| Due to high mold temperature, volatile components are generated in the resin | 1. Reduce temperature 2. Study the measures to eliminate volatile matter before gel | |
| Due to the short curing time, the interior has not yet solidified, resulting in bubbles caused by volatile components or interlayer peeling after demolding | Extend the curing time (especially when forming thick parts) | |
| fold | No uniform flow occurs, resulting in wrinkling of the felt in SMC | 1. Improve the cutting section to effectively apply pressure to the molded product 2. Change the shape of the additive 3. Reduce the pressurization speed |
| Poor luster | Low mold temperature | Raise the temperature (extend the curing time) to make the mold temperature uniform |
| Poor surface of mold | Chromium plating on metal molds | |
| Insufficient feeding amount | Increase feeding weight and area, increase molding pressure, and reduce shear edge clearance | |
| Uneven solidification shrinkage | Check the temperature relationship between the upper and lower molds | |
| pollution | Due to the adhesion of metal micro powder on the friction mold to the molded product | Hard chrome plating |
| SMC pollution | Be careful not to mix in foreign objects and use SMC with caution | |
| shrinkage cavity | Curing shrinkage of resin | Using low shrinkage resin |
| Originating from the shape of ribs or platforms | Change the shape of the ribs or platform on the inner surface | |
| Poor feeding shape | Change the shape of the feeding material. For molded products with unevenness or significant thickness changes, the feeding shape should ensure that the time for SMC to flow to the shear edge is the same in every aspect | |
| illiquidity | Adopting SMC with good liquidity | |
| ripple | SMC's flow is too good | Reduce flow |
| Small feeding area | Increase the feeding area | |
| Sudden change in feeding thickness | Change the shape of the additive | |
| SMC gel in flow | Check the mold temperature and closing speed | |
| Uneven pressure | Adjust the cutting edge and increase the amount of material added in advance in areas where surface pressure is not easily formed | |
| Flow mark | The large gap between the cutting edges causes material flow | Correct the cutting edge, reduce the gap, and extend the stroke |
| Low molding temperature | Raise the molding temperature | |
| The feeding area is small, and directionality occurs when the fiberglass flows | Increase the feeding area and reduce flow | |
| Product warping | The curing shrinkage of resin is large | Use low shrinkage resin |
| Large temperature difference in mold | Reduce temperature difference | |
| illiquid | ||
| Difficulty in demolding | Low mold temperature | Raise the mold temperature |
| Short curing time | Extend curing time | |
| The surface of the mold is not good | Polishing mold | |
| Mold not applicable | Using silicon or wax release agents | |
| Poor curing caused by air or styrene evaporation trapped on the surface of the mold, resulting in local adhesion to the mold | Using New SMC: Improving Feeding Methods |
11、Defects and Countermeasures of BMC Molding Method：
| 缺 陷 | 原 因 | 对 策 |
| poor filling | No deflation, it may be due to air accumulation The mold temperature is too high, and gel is formed before the mold cavity is filled with materials Due to slow injection speed, the material solidifies before flowing Insufficient material supply The gap between the molds is too large | vacuum forming Design pores Install ejector pins on the mold and also serve as air holes Slow injection speed Reduce mold temperature Increase injection speed Check the measurement situation Transforming molds |
| bubble | Excessive temperature causes styrene gas to evaporate Short curing time, slow internal curing Low mold temperature, poor curing | Reduce mold temperature Extend curing time Raise the mold temperature Increase PE powder |
| Die Adhesion | The surface of the mold is not good back taper Low mold temperature, poor curing The product expands due to heat There is oil and other substances on the new mold | Grinding and repairing molds Transforming molds Raise the mold temperature Extend curing time Pay attention to temperature difference Consider the ejector device again Use materials with lower thermal expansion coefficients instead Completely wipe off the oil and apply the external release agent thoroughly |
| buckling | Due to posterior contraction Due to improper fiber configuration direction | Readjust the cooling process Readjust product design Using cooling fixtures Adjust the nozzle position again Injection compression molding |
| Confluence pattern | Two or more material streams are not mixed due to sales, holes, etc Confluence pattern at the tip | Vacuum forming, equipped with ventilation ports Connect the holes with thin flying edges Significant changes in the position of the injection port |
| Poor luster | Insufficient solidification Insufficient pressure The surface of the mold is not only Uneven temperature | Improve mold quality Extend curing time Increase pressure Grinding mold Improve temperature distribution |
| color change | After the mold is closed, the air accumulated inside the mold is compressed, and the temperature rises, causing thermal decomposition | Vacuum forming, opening air holes Reduce mold temperature Slow injection speed |
| crack | The protruding part is damaged The fiber streamline bends at the confluence pattern Injection pressure too high Due to shrinkage and cracking | Increase the number of top out sales Make the position of the ejector pin suitable Adjust the action of the ejector plate Grinding mold Extended curing time, sufficient curing, change of nozzle position Vacuum forming, open energy vent Reduce injection pressure Use PE powder instead Refer to the item of poor demolding |