Molding (also known as press forming or compression molding) is a process in which a powdery, granular or fibrous plastic is placed in a mold cavity at a molding temperature, and then closed and pressurized to form and solidify it. Molding Can be used in thermosetting plastics, thermoplastics and rubber materials.
Molding is widely used in the following areas:
·Electrical: insulators, switch boxes, electrical equipment casings, insulation tools, wiring boards, etc.;
·Automobile: lamp cover, front and rear bumpers, battery brackets, engine insulation panels, etc.;
· Railway: vehicle window frame, bathroom components, seats, coffee table tops, compartment wall panels and roof panels;
·Construction: water tanks, bath products, door panels, septic tanks, building templates, etc.;
·Bathroom: bathtub, whole bathroom equipment, integrated hand basin, etc.;
· And other industrial and agricultural fields.
There are many varieties of molding materials, and the current market mainly uses BMC/DMC (bump molding compound) and SMC (sheet molding compound) molding materials.
2nd,Quality control of molding materials
1. Unsaturated polyester resin
(1) Easy to react with thickener to meet thickening requirements (mainly for SMC)
(2) Rapid curing and improved production efficiency
(3) High thermal strength, ensuring that the product is not damaged during demolding
(4) It has sufficient toughness and will not crack when some deformation occurs in the workpiece.
It is safe to store and operate; it does not decompose at room temperature; the prepared SMC has a long storage period and can be quickly decomposed and crosslinked when it reaches temperature; the price is cheap.
The amount of initiator needed to be controlled:
Excessive dosage: low molecular weight of the product, poor mechanical properties; too fast reaction rate, rapid curing and shrinkage of the resin, and easy cracking of the product.
If the amount is too small, the product will not cure enough.
3, polymerization inhibitor
Prevents unsaturated polyester resin from cross-linking polymerization at room temperature, extending shelf life
SMC requires high viscosity during press molding, storage and transportation (low viscosity is required when preparing SMC, impregnated fiber), and the viscosity is improved by thickener.
The viscosity change of the SMC from production to use is controlled by a thickener.
5, low shrinkage additives
Generally, the curing shrinkage of the polyester resin is 7% to 10%, and the shrinkage ratio can be greatly reduced after the addition of the low shrinkage additive, so that the shrinkage ratio is close to zero, and the surface of the SMC product can be made smooth and free from cracks.
Low shrinkage additives are thermoplastic polymers
6, inorganic filler
1. Reduce material costs
2. Improve product performance
Disadvantages: As the amount of filler added increases, the viscosity of the resin paste increases, which makes the batching and impregnation work difficult and the density increases.
7. Internal release agent
In the SMC molding process, the internal mold release agent must be used.
Internal mold release agent principle: The internal mold release agent is a compound whose melting point is slightly lower than the molding temperature.
Compatible with liquid resin, but incompatible with cured resin. Product thermoforming
When the release agent overflows from the inside to the interface where the molding material contacts the mold, it melts and forms an obstacle, prevents adhesion, and achieves the purpose of demolding.
Commonly used internal release agents:
Stearic acid, zinc stearate, calcium stearate, magnesium stearate
Melting point: 70°C 133°C 150°C 145°C
Dosage: 1~3% of the amount of resin
The most commonly used are chopped glass and felt, followed by asbestos fibers, hemp and other fibers.
General requirements: easy to cut, easy to disperse, good impregnation, high strength, etc.
NEWECO is one of the leading unsaturated polyester resin manufacturers and suppliers,widely used in automobiles, ships, rail transit, wind power generation, pipe cans, heat and corrosion protection, building materials, stone repair, sanitary ware, artificial stone and other industries. Suitable for hand lay-up, spray, pultrusion, winding, molding, vacuum introduction / RTM, casting and other molding processes. Xinyang Resin is committed to excellence and focuses on the application of composite materials to provide customers with comprehensive solutions.