BMC is an abbreviation of Bulk Molding Compound in English, Chinese name is Bulk Molding Compound (also called: unsaturated polyester glass fiber reinforced Bulk Molding Compound) by the liquid resin, low shrinkage agent, crosslinking agent, initiator, filler, short-cut glass fiber flakes and other components of the physical mixture of the complex, in the temperature and pressure conditions, the crosslinking of unsaturated polyester and styrene, polymerization reaction occurs. Under temperature and pressure, the unsaturated polyester and styrene are cross-linked and cured by polymerization reaction. Its excellent mechanical properties and excellent electrical properties, and heat resistance and good processing properties are widely used in electrical appliances, instrumentation, automobile manufacturing, aviation, transportation, construction industries.
Formulation system
1. Unsaturated polyester resin: with smc/bmc special resin, mainly m-phenyl up, impact resistance, corrosion resistance, arc resistance, suitable for the production of block or anisotropic products
2. Crosslinking agent; with monomer styrene, the amount of up30% ~ 40%, depending on the content of double bonds in the unsaturated polyester and the proportion of trans double bonds and cis double bonds, high proportion of crosslinking monomers, can get a more complete curing
3. The initiator with high temperature curing agent, tert-butyl peroxybenzoate (TBPB) belongs to the commonly used high temperature curing agent, liquid decomposition temperature of 104 degrees molding temperature of 135 to 160 degrees.
4. Low shrinkage agent commonly used thermoplastic resins, the use of heat expansion to offset up the molding contraction. Generally, the shrinkage rate of the products should be controlled at 0.1~0.3%, so the dosage should be strictly controlled.
5. Reinforcement materials: generally used coupling processed 6 ~ 12mm long short fibers 6 flame retardant using Al2O3.3H2O-based, adding a small amount of new phosphorus-containing flame retardant, hydrated alumina also plays the role of filler 7. Fillers can reduce the cost of improving the electrical properties and flame retardancy. Calcium carbonate is the longest used filler with good overall performance, generally in the form of fine, micropowder after coupling treatment and then added.
BMC process
1. Pay attention to the sequence of adding materials. Mixed in z-type kneading machine, kneading machine has a heating device, whether the mixing is uniform can be observed color paste or carbon coloring uniformly appropriate, about 15 ~ 18 minutes
2. Short-cut glass fiber to join the last, early to join a large number of broken fibers, affecting the strength of the
3. BMC material must be stored at a low temperature, generally at 10 degrees Celsius, the temperature is high, the unsaturated resin is easy to cross-linking and curing, and then processing molding difficulties.
4. Molding temperature: 140 degrees or so, the upper and lower mold temperature 5 ~ 10 degrees, molding pressure 7mpa or so, holding time 40 ~ 80s/mm
Industrial diagnosis
1. Product cracking: product cracking problem is common, especially in winter low temperature conditions. The so-called cracking refers to the products by internal stress, external impact or environmental conditions and other impacts on the surface or internal cracks.
2. Solution; specifically from the raw materials, proportion and process to solve.
2.1 Selection and processing of raw materials
1) Resin is the matrix of bmc, unsaturated polyester resin, vinyl ester, phenolic resin, melamine, etc. Resin is the product curing, with the fundamental strength. Therefore, the use of smc/bmc special resin, is a m-phenylene type resin, m-phenylene resin than the o-phenylene type of high viscosity, so in addition to the resin itself shrinkage is small, can accept more crosslinking monomers, so that the density of the density increases, shrinkage rate decreases
(2) add composite low shrinkage agent; unsaturated polyester resin curing contraction rate of up to 5 ~ 8%, add a variety of filler shrinkage is still more than 3%, products generally shrinkage rate of more than 0.4% to crack, so add thermoplastic resins, the use of thermoplastic resins to eliminate thermal expansion of the curing contraction of the parts. pmma, ps add and monomer styrene mixing and dissolution of the better, the addition of pmma The finish is better. Product shrinkage can be controlled at 0.1~0.3%.
(3) filler, flame retardant, glass fiber; glass fiber length – generally 6 ~ 12mm, sometimes to meet the high mechanical properties to 25mm; in order to meet the requirements of molding fluidity, to 3mm. glass fiber content is usually 15% ~ 20%; for high-performance products, to 25%. BMC glass fiber content is lower than the SMC, you can add more filler, so the cost is lower in order to make inorganic filler. Lower in order to make the inorganic filler, flame retardant, glass fiber and resin have a chemical combination between the general use of silane coupling agent treatment before mixing, commonly used KH-560, KH-570 effect is good to join the solids are fine, micronized materials, such as heavy calcium carbonate with micronized grade, particle size 1 ~ 10um (equivalent to 1250 mesh)
2.2 BMC proportioning requirements Bmc base resin, the amount can not be less than 20%, its amount of initiator related to the amount of crosslinking agent basically do not have to additionally add the amount of crosslinking agent in the resin content accounted for 35%, in addition to the amount of low shrinkage agent to join also depends on the amount of resin. The use of high-temperature curing agent TBPB, filler and flame retardant (aluminum hydroxide) to join the total amount of about 50% is more appropriate, is twice as much as the resin, too much to join the strength of the structure is damaged, easy to crack!
2.3 Production process conditions
(1) mixing, first of all, when mixing the material to be mixed evenly, the powder first add a small specific gravity, and then add a large specific gravity, the liquid is mixed first and then added, the initiator is the last to be added, the thickener should be added before the resin paste and polystyrene kneading. Glass fiber is added in batches
(2) molding process conditions: molding process parameters directly affect the product good or bad. Usually with the increase of molding pressure, shrinkage decreases. Mold temperature is too high will form a surface fusion line, the material is not uniform, the internal stress is different, easy to crack. Holding pressure for an appropriate extension of time is conducive to the prevention of cracking of the parts.
(3) preheating insulation system: low temperature parts are easy to crack. Therefore, the material should be preheated
Post time: Jun-10-2025
