Mold plastics have the characteristics of bright appearance, good dimensional accuracy, and high density and strength

SMC is a sheet-like molding material composed of short cut fiber rovings or glass fiber felt impregnated with unsaturated polyester resin, thickeners, initiators, crosslinking agents, low shrinkage additives, fillers, internal release agents, and coloring agents, and coated with polyethylene or polypropylene films on both sides to form a resin paste; DMC (or BMC) is an improved pre mixed bulk molding material that is sealed and stored in a sealed plastic bag before being opened and weighed.

(1) Insulators include various types such as needle insulators, butterfly insulators, suspension insulators, porcelain cross arms, rod insulators, and tension insulators. We use the compression molding method to produce high polymer composite insulators for voltage resistance, using FX-501 molding material and FX produced in the 482 workshop of Hangzhou Glass Factory; 501 molded plastic, which is a thermosetting plastic reinforced with short cut alkali free glass fibers and modified with polyvinyl butyral phenol aniline formaldehyde resin as a binder, is used to produce voltage resistant insulators. It has a layered umbrella shape with curved transitions between the umbrella layers to increase the climbing interval of the arc on the surface, reduce flashover, and improve insulation safety;

The shape is as follows:

(2) The components that move inside electrical appliances often exhibit arcs, and the function of arc extinguishing devices is to extinguish the arcs that occur when the contacts block the circuit. In this regard, due to its chemical properties, melamine formaldehyde resin is superior to phenolic resin and urea formaldehyde resin in terms of arc extinguishing function. Therefore, arc extinguishing plates are commonly limited by arc resistant BMC melamine molding materials. Alkali free glass fiber reinforced melamine molding materials have various functions such as arc extinguishing flame retardancy, insulation, high strength, heat resistance, water resistance, self extinguishing, mold resistance, and arc resistance, and are used for experiments. In this regard, different melamine molding materials have been repeatedly tested in the past (exported from Tianshan and Mianyang), but due to the strict requirements of the entire voltage resistance experiment, after being immersed in oil for 4 hours, the appearance cannot show a trace of exposed white (i.e. the surface resin is damaged). Although there were only a few that could meet the requirements in the experiment, the pass rate remained the same. Not high, it has not been successful in high-level pressure resistant equipment.

 

Compression molding (also known as confinement molding) is the process of placing loose plastic reinforced with fiber-reinforced resin into a mold cavity at a molding temperature, and applying appropriate pressure to the mold (closed mold) to shape and cure it.

In the use of electrical appliances, the molding material must have suitable and high insulation properties, ensure fluidity during construction, and attach great importance to its volatile matter. Once it is too low, molding will be difficult. During the molding process, according to the product shape and mold temperature reaching the specified value, separate selection point pressure, boost pressure, and full pressure will be successively applied. Feeding - mold closing - exhaust - curing - demolding

 

Pre impregnated tape for producing insulation rods

For products with strength requirements, it is generally expected to maintain the continuity of glass fibers, but the specific situation will be analyzed on a case by case basis.

The occupational qualification of insulation products for high voltage and ultra-high voltage is still relatively high. Unlike ordinary low voltage electrical appliances, high voltage transmission is used to reduce the cost of transmission. One of the equipment, a high voltage switch, is used. Once the blasting result is severe, it will cause a large-scale power outage; The material of the insulation rod and the sealing performance of the switch are the key points. Due to the wide impact and large scale of the problem, high-voltage insulation layer limited products (boards, pipes, rods) such as 3240 (boards) pull rods, 3840 rods, 3640 pipes, etc; Insulated pull rod (also known as insulated operating rod) is used to connect or disconnect equipment such as high-voltage barrier switches.

The resin system we used at that time was 2124 phenolic resin 6101 epoxy resin (E-44) (relevant solvents are required for bonding), and the reinforcing material was 0.14mm alkali free plain glass cloth for electrical use.

(1) Insulation laminated board is a whole composed of two or more layers of resin impregnated fibers or fabrics that are stacked and hot pressed together. In the early stage, a suitable part of the insulation rod was cut and processed from the 3240 insulation board to make high-voltage insulation rods. Therefore, the end face was simply layered or moisture entered to affect the insulation effect. The method we chose at that time was to cut the adhesive tape, roll it up one by one, and put it into a mold for hot pressing curing. It evolved from the 3240 insulation board and was limited one by one. Although the production power was not high, the quality was greatly improved, and the end face shape became a work shape. (See the implied photo for the end face)

 

(2) The fundamental process is to manufacture resin liquid by share; Glue application (glass cloth dipping)‐ Cutting glass adhesive tape (laminated pre formed)‐ Rolling/molding/laminating‐ Curing (according to the curing curve)‐ Cut open‐ Central Inspection‐ Drying (moisture) - Immersion insulation paint (1032 melamine alkyd impregnated insulation paint)‐ Drying‐ Final inspection.

 

(3) The fundamental process is to immerse the glass cloth in glue on a vertical glue machine, and glue it according to the demand (at a speed of 1.4± 0.5m/min). If the speed is fast, the glue content is high, and if it is slow, the opposite is true. It can be adjusted according to the measurement. After the glass cloth is semi cured by the glue machine, it is called glue cloth, which is now known as the fashionable prepreg (resin reaches stage B); I thought this was actually the same concept, but the difference is that the adhesive tape is produced and used by our factory, and its storage period is relatively short, while the shelf life of the prepreg is much longer (with strict low-temperature storage requirements).

(4) Raw materials: 0.14mm alkali free plain glass cloth, 6101 epoxy resin, 2124 phenolic resin. The vertical gluing machine and pipe rolling machine are controlled by the factory's machine repair workshop and are suitable and useful.

Epoxy resin with medium molecular weight is generally used for prepreg, which has good dielectric properties (with as low free chloride ions as possible), high strength, chemical corrosion resistance, good scale stability, and low water absorption rate;

In this resin system, epoxy resin and phenolic resin are curing agents for each other, and are used as high-grade voltage resistant materials. The chloride ion content in the epoxy resin needs to be controlled, and the free phenol content in the phenolic resin also needs to be measured. The alkali content of alkali free glass fiber is set at 0.5% or less according to the national standard. The product's purpose clearly states that the quality of raw materials must meet high requirements, and careful and strict control is necessary to ensure quality.

(5) The quality of adhesive tape has a significant impact on the selection of parameters such as pressure, temperature, and time during compression molding. The adhesive content and volatile matter are different among different factories. Setting a parameter scale, the appearance of the glass cloth after being glued on a vertical gluing machine will be brownish yellow. The adhesive content of the upper adhesive tape is measured to be between 30-42% and the volatile matter is between 0.8-1.5% (depending on the storage time and environment) by taking samples from the left, middle, and right sides of the fabric banner (to understand the uniformity of the glue tank). Sometimes, the flow rate is measured, such as flow rate of 10mm to 40mm (160 ℃ -5.0MPa-3min to 4min); Low molding pressure, slightly higher adhesive content, high molding pressure for compression molding, simple resin driving, low adhesive content.

(6) Cracking the shape problem: One of the I-shaped high-voltage switch insulation rods we encountered (length>1 meter, there are several standards), which was first-class in China at that time. Due to the cross-sectional shape of the rod being a fat and short I-shaped, its mechanical properties; The tensile strength is very high, but the four corners are prone to defects due to glue flow. The key is to cut (sort) and roll the pre impregnated tape at room temperature, perform cold pressing and pre molding, and then split along the edges of the mold to reduce the deformation resistance of the tape. This facilitates temperature rise, point pressing, glue flow, and continues until the entire mold cavity is filled with the tape during full pressure hot pressing; During the process of rolling the insulation tube, when the temperature of the upper roller reaches the point where the adhesive tape can be pulled out by hand, a filamentous shape can be pulled out. At this moment, the three rollers cooperate with the core rod to ensure even flow of adhesive between the layers of the tape, which is an important key point to ensure quality.

(7) Strict control: Throughout the entire production process, strict control is carried out. After demolding, the cut end face of the product must not have delamination defects. After immersing in insulation paint and drying, 100% of the products are tested for voltage resistance in the factory laboratory, and a certain proportion of the products are randomly selected to the Provincial Electric Power Laboratory for voltage resistance, dielectric loss factor, and other inspections. Samples have also been sent to Guilin Electric Science Institute for multiple type tests of high-voltage insulation rods, and high-level voltage resistant insulation rods (SW series, SN series) (including high-voltage resistant insulation tubes) have been supplied to several major high-voltage switch factories in China such as Xidian Company.

 

Reading source: BMC insulation products www.jmlicheng.com