1. Common plastic materials:

(1) PMMA (Acrylic)

a. Shrinkage rate of 0.4%~0.7%. It is easy to burn in case of fire. The flame is close to smokeless. After the fire is extinguished, it will smoke. The flame is blue and yellow, giving off a sweet fruit flavor with a little smoke. It will still burn after the fire is removed. No need to use other materials for cleaning during shutdown.

b. After 24 hours at room temperature, absorb 0.3% of water. If necessary, bake at 75℃/2~4 hours. Dry with raw material beer for 2 hours, and bake for 3 hours in February to May when the sprue is added or the weather is humid.

c. Mold temperature should be 60℃, nozzle ≥5mm, melting temperature 210℃~270℃, if temperature is 260℃, material residence time should not exceed 8 minutes.

d. Temperature setting: rear: 150~210℃, middle: 170~230℃, middle: 180~250℃, front: 180~275℃, nozzle: 180~275℃, mold: 60~90℃.

e. Slow-speed injection can be used (to avoid high internal stress, multi-stage injection molding or progressive speed should be used, and the product thickness should be slow).

f. Screw speed matching cycle: the lower the back pressure, the better.

 

(2) ABS (often called super non-breaking glue)

a. The shrinkage rate is 0.4%~0.8%, adding 20% ​​GF glass fiber, and then 0.2%~0.4%.

b. The background color is ivory or white, the hot-melt viscosity decreases steadily as the temperature rises, and the melting point is 175°C.

c. When burning, it will produce a yellow flame with black smoke, giving off a strong alkali smell similar to rubber, and it is generally flammable and cannot be automatically extinguished.

d. Absorb water 0.2~0.35% within 24 hours at room temperature, if necessary, bake at 80℃/2~4 hours. Dry for 2 hours with the raw material beer, and bake for 4 hours from February to May when the sprue is added or the weather is humid. (Note: Must strictly abide by the first-in first-out management system of goods.)

e. The best mold temperature is 60℃, and the hot runner mold is not suitable for fireproof ABS.

f. Use slow glue back as much as possible, and the low temperature barrel has low back pressure.

g. Impact resistance: 220~260℃ is required, preferably 250℃.

Electroplating level: 250~275℃ is required, preferably 275℃.

Heat resistance grade: 240~280℃ is required, preferably 265~270℃.

Fire rating: 200~240℃ is required, preferably 220~225℃.

Transparent grade: 230~260℃ is required, 245℃ is better.

Glass fiber-containing grade: 230~270℃ is required, and the mold temperature is 60~95℃.

h. At 265℃, the barrel should not stay for more than 5~6 minutes, and at 280℃, it should not exceed 2~3 minutes.

i. The ABS material stays in the barrel for too long. Overheating of the barrel will cause no problem when the ABS product is ejected, but it may produce brown or tea streaks during the storage period. The difference in the residence time or the uncertainty of the cycle will cause the product to be stored. Discoloration occurred during the period.

j. Shooting speed: slow for fireproof grade (no decomposition), fast for heat resistant grade (reduce internal stress), to produce the best product, that is, with high gloss, high-speed multi-stage injection speed, and dry material , Melting glue and mold temperature should be high.

k. Screw speed: It is best to slow (matching cycle) and low back pressure.

l. The properties of ABS material can remain unchanged at 40~100℃, and the heat distortion temperature is 100℃.

 

(3) POM: often called Saigang

a. Material properties: Even at 50℃, its impact resistance remains good. POM-H has the largest impact strength, warpage strength, fatigue resistance and hardness. POM-K has better thermal stability. Alkali resistance and hot water resistance. The above two are crystals and have low water absorption. The shrinkage rate is 2%

b. POM is a highly crystalline material (approximately 80°C) with a high degree of shrinkage. The shrinkage of 0.1% will occur within 48 hours. The high mold temperature will increase the actual shrinkage of the shrinkage, but will reduce the shrinkage (precision products require Only use high mold temperature to produce stable products).

c. POM burns light blue, drips glue liquid, there is not much residual material and smoke, and emits a strong formaldehyde odor after flameout. The melting point of POM-H is 175℃, and the melting point of POM-K is 164℃.

d. POM baked 85℃/2~3 hours. POM-H/POM-K can be used at 215℃ (190~230℃), never exceed 240℃. Dry the raw material beer for 2 hours, and bake it for 3 hours when the sprue is added or the weather is humid from February to May.

e. If the equipment is good (no glue blocking point), POM-H can stay at 215°C for 35 minutes, and POM-K can stay at 205°C for 20 minutes without decomposition. Be careful to clean up. Put the waste into cold water. At the molding temperature, the melt cannot stay in the barrel for more than 20 minutes. POM-K can stay at 240°C for 7 minutes or 210°C for 20 minutes.

f. Temperature setting: rear: 165~210℃, middle: 162~200℃, middle: 170~210℃, front: 180~215 combustion, nozzle: 170~215℃, mold: 40~120℃.

g. Shooting speed: (filling speed) medium and fast, too slow will cause peeling, too fast will damage the gate.

h. Screw speed coordination cycle: the lower the back pressure, the better. The washing machine is best to be cleaned with polyolefin (POLYDEFIN), and the barrel cannot be shared with PVC or fireproof grade. Even if it is used, it must be thoroughly cleaned, otherwise it will explode.

 

(4) PC (often called bulletproof glue)

a. PC belongs to the polyester category, and the carbonated cheese combination is formed by the aromatic combination and burns slowly (the fire class is V1 or even V0).

b. Shrinkage: 0.006~0.008in (0.6%~0.8%), 30% glass fiber PC has 0.003~0.005in, PC/PBT blend has 0.008~0.01in.

c. Do not keep in contact with hot water above 60℃ for a long time. When PC burns, it will emit pyrolysis gas. The plastic will scorch and foam, but it will extinguish when it does not catch fire. It will extinguish when it is away from the fire source. Jet black, the temperature reaches 140 ℃ to start to soften, 220 ℃ melting, can absorb infrared spectrum.

d. Baking: 120℃/2~4 hours, PC/PBT blends are baked at 110℃, PC/ABS blends are baked at 110℃/1 hour, the mold temperature is 40~90℃, and the melting temperature is 250℃. Dry for 2 hours with the raw material beer, and bake for 4 hours when the sprue is added or the weather is wet from February to May.

e. The glue injection machine should be disassembled regularly to check its melting situation, because the end of the bubbles will be displayed on the surface of the product, and low-quality products may be produced (the appearance is still beautiful). The melting temperature of PC/ABS blends cannot exceed 280℃, the same is true for PC/PBT, and GFPC is between 305~330℃.

f. Temperature setting:

 

Unenhanced level:

After: 275~300℃, middle: 280~310℃, middle: 285~325℃,

Front: 285~315℃, nozzle: 280~310℃, mold: 80~120℃.

 

Enhanced level:

After: 300~315℃, middle: 305~320℃, middle: 310~345℃,

Front: 315~330℃, nozzle: 320~330℃, mold: 70~130℃.

g. Barrel residence time: at 320℃, it will degrade, produce carbon dioxide, turn yellow, and reduce mechanical properties. The processing temperature range should be avoided too long, and the residence time PC/PBT should be less than 7 minutes.

h. The faster the injection speed, the better, the slower the glue back speed, and the low back pressure (10BAR) helps prevent degradation caused by vaporization.

i. Do not use LDPE, POM, ABS, PA to wash the machine when it is shut down. These materials will contaminate PC and degrade it. HDPE, PS, PMMA should be used for cleaning.

j. Do not use a torch to clean the metal parts of the injection molding machine. It can be heated at 400℃ and then cleaned with a steel wire tool.

 

2. There are three main plastic flame retardant test grade standards:

(1) GB/T2408-2008 "Determination of the Burning Properties of Plastics Horizontal Method and Vertical Method"

(2) GB/T2406.2-2009 "Plastics Determination of Combustion Behavior by Oxygen Index Method"

(3) American standard UL94 flame retardant rating (UL94 flame retardant rating is a very important standard and has been widely adopted worldwide.)

Others include GB/T8924-2005 "Test Method for Fibre Reinforced Plastics Combustion Performance Oxygen Index Method", ASTM D2863, GB/T 5169.16, GB/T 5169.17, GB 4943.1 and so on.

Among them, 94-V is the vertical combustion test classification standard in UL94, which is mainly divided into three levels: V0, V1, and V2 (the vertical test in GB2408-2008 is also V0, V1, and V2). UL94 also has 5VA and 5VB. This grade is also the highest among plastic flame retardant grades.

Different levels require different technical indicators.

 

3. The significance of plastic burning performance test:

Combustion performance refers to some physical and chemical changes that occur when a material burns or encounters a fire. This performance is determined by the ignitability and flame propagation of the material surface, heat generation, smoke, carbonization, weight loss, and the generation of toxic products. measure.

(1) With the rapid development of the plastics industry, the variety of plastic products and the wide range of fields involved, plastic products have become a necessity in our daily lives, so in order to ensure safety, it is more advantageous to promote the production and use of plastic products. Combustion performance test is a necessary task;

(2) Plastic materials are flammable, and during the combustion process, smoke and gases harmful to the human body will be produced, which is very dangerous and threatens the safety of human life and property;

(3) The combustion performance test of plastic materials can help and guide us to conduct flame retardant research on materials and standardize the production of plastic products.

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