Resins are chemically synthesized or natural polymer compounds that come in a variety of types. Below are some common types of resins and their respective characteristics.
①Polyethylene
Characteristics:
(1) High shrinkage and easy deformation
(2) Requires long cooling time, and moldability is not so good.
(3) Mold shrinkage is highly dependent on mold temperature and is not stable.
(4) Need to be careful not to forcibly remove undercuts.
Molding and molding points:
(1) Design molds (gates, etc.) to accelerate material filling speed.
(2) Consider cooling method to make cooling speed uniform.
(3) Consider prevention of distortion and deformation
Shrinkage rate (x 1/1000): High density (20-50) Medium/low density (15-50)
②Polypropylene
Characteristics:
(1) Fairly good moldability
(2) Easy to mold, distort, and sink
(3) Hinge characteristics
Molding and molding points:
(1) Be careful about gate design for molded products with hinges.
(2) Preventive measures against sink marks and deformation are necessary.
Shrinkage rate (x1/1000): 10 to 25
③PVC
Characteristics: 1.
(1) Poor thermal stability and narrow molding temperature range
(2) Poor flow
(3) Poor appearance
(4) Corrodes molds
Key points for molding and molds
(1) Use runners and gates with low flow resistance.
(2) Mold surface treatment (plating) is necessary to prevent corrosion.
(3) Shrinkage rate (x 1/1000): Hard 1-5, Soft 10-50
④Polystyrene
Characteristics:
(1) Good flow, good moldability, and high molding efficiency
(2) Easy to crack
(3) Hard to produce burrs
Molding and molding points:
(1) Select an appropriate knockout mechanism, paying attention to cracks at the time of ejection.
(2) Make a draft angle of 1° or more to prevent cracks from forming in the molded product.
(3) Avoid undercuts in the mold.
Shrinkage rate (x 1/1000): 2 to 6
⑤Polycarbonate
Characteristics:
(1) High melting temperature, requiring high-pressure, high-temperature molding
2) Prone to cracking due to residual stress
(3) Easy to damage molds due to its hardness
(4) Hard to produce burrs
Key points for molding and molds:
(1) Pre-dry the material sufficiently.
(2) Runner and gate design with low flow resistance is necessary.
(3) Avoid inserting metal inserts as much as possible
(4) At least 2° of draft angle is required.
Shrinkage rate (x 1/1000): 5 to 7
⑥Polyamide
Characteristics
(1) Low melt viscosity and good flow characteristics
(2) Easy to produce burrs
(3) Shrinkage stability is poor
Molding and molding points:
(1) Precision molds are necessary to prevent burrs.
(2) Industrial parts require higher mold temperature and attention to crystallization
(3) Prevention of sink marks and improvement of dimensional stability
Shrinkage rate (×1/1000): Nylon 6: 6-14 Nylon 66: 8-15
⑦ABS Resin:
Characteristics:
(1) Flow is not good.
(2) Molded product characteristics are stable.
(3) Surface appearance of the gate area and welds are easily noticeable.
Molding and molding points:
(1) Select appropriate runners and gates for the flow.
(2) Appropriate gate position for weld
(3) Take a draft angle of 2° or more for high-pressure molding.
Shrinkage rate (x 1/1000): 3 to 8
⑧ Acrylic Resin
Characteristics
(1) Poor flow, filling defects, flow marks, and sink marks due to insufficient pressure can easily occur,
requiring high-pressure molding.
(2)High-pressure molding is required.
(3) Transparency is an issue in many optical applications.
Key points for molding and tooling:
(1) The draft should be as large as possible.
(2) Design of runners and gates for flow is important.
(3) Material temperature and mold temperature must be controlled carefully.
Shrinkage rate (x 1/1000): 2 to 25
⑨Polyacetal resin (POM)
Characteristics
(1) Poor flow and easy disassembly
(2) Flow marks occur at the gate.
(3) prone to sink marks and deformation
Molding and molding points:
(1) Runners and gates must be designed to improve flow and gate appearance.
(2) Control of molding conditions (especially cylinder and mold temperature) is necessary.
Shrinkage rate (x 1/1000): 20-25
Each of these resins has different properties and is suitable for different applications. When making a selection, it is important to match specific requirements such as material properties, durability, thermal properties, and chemical properties. Attention should also be paid to environmental impact and waste disposal.
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