Formowanie wtryskowe PVC: Kompletny przewodnik

PVC injection molding has emerged as one of the most versatile and cost-effective plastic molding options. As one of the most commonly used thermoplastics globally, polichlorek winylu (PVC) offers distinct advantages for manufacturers across industries.

However, effective PVC molding requires careful attention to processing parameters. Failing to adhere to recommendations can lead to part defects, equipment damage, and potential safety hazards.

Jako profesjonalista Producent form wtryskowych z tworzyw sztucznych, I am writing this comprehensive guide to cover everything you need to know about PVC injection molding, from material properties to processing equipment and parameters. By the end, you’ll have the knowledge to start molding quality PVC parts efficiently and safely.

Why Choose PVC for Injection Molding?

Before jumping into processing specifics, let’s look at what makes PVC a prime candidate for injection molding applications:

Efektywność kosztowa

PVC pellets are inexpensive and readily available. The material also allows high-volume production. These factors make PVC injection molding extremely cost-effective overall.

Odporność chemiczna

PVC offers good chemical resistance to acids, bases, salts, oils, and alcohols – making it suitable for chemical pipes, tanks, and other applications. However, PVC decomposes when exposed to strong oxidizing agents.

Stabilność wymiarowa

PVC parts maintain accuracy after molding. Low thermal expansion gives parts excellent dimensional stability for precision applications.

Toughness and Strength

PVC has high tensile and impact strength across a wide temperature range. Parts also have good abrasion and scratch resistance.

Flame Resistance

Rigid PVC grades are inherently flame-resistant and self-extinguishing. Therefore, PVC suits electrical applications without requiring additional fire retardant additives.

These well-rounded mechanical, chemical and thermal properties make PVC an exceptional choice for injection molding. Now, let’s look at the equipment involved.

PVC Injection Molding Equipment

Injection Molding Machine

Standard horizontal and vertical machines with reciprocating screws work well for PVC. Units should have proper temperature controllers and safety mechanisms.

Molds

Use hardened P20 steel or stainless steel (420 or 440 type) molds. The mold must have uniform cooling channels for quick heat dissipation. Good venting at the parting line is also crucial.

Screw

A general-purpose screw with a 2.5:1 compression ratio allows a wide PVC processing window. The screw should have an anti-corrosion coating at the tip and a ball-style check ring for consistent metering.

Dysza

Use open-flow nozzles to minimize holdup. Separate nozzle heaters help obtain the high nozzle temperatures needed for PVC without overheating the front barrel zone.

Barrel

Barrels with nitride surfaces offer maximum wear resistance and prevent material hang-up during recovery.

Temperature Controller

Reliable controllers that minimize temperature fluctuations are vital. Separate controllers for nozzle, barrel zones, and mold are preferred.

With suitable equipment in place, let’s examine PVC injection molding settings and procedures.

Optimized Processing Parameters

Pre-molding

• Store PVC resin properly to prevent pellet moisture absorption
• Dry pellets at 120°F-150°F for 1-2 hours if needed
• Clean mold thoroughly and apply mold release agent

Start-up

• Purge non-PVC materials from barrel
• Set barrel temperatures per resin supplier recommendations
• Use 345°F-375°F melt temperatures for most grades
• Check melt temperature directly with a pyrometer

Fill

• Injection speeds: Slow (thin parts) to moderate (thick parts)
• Injection pressure ~50-70% of maximum injection pressure

Pack

• Reduce injection pressure just as mold cavities fill
• Hold for 3-5 seconds at ~50-70% of injection pressure
• Minimize cushion (<0.25 inches)

Super

• Cooling time: 20-45 seconds
• Mold temperature: 50-120°F
• Cycle time primarily depends on part wall thickness

Wysuń

• Open mold only after adequate cooling
• Use proper draft angles and radii for easy part release

Closely following these processing guidelines minimizes defects like warpage, sink marks, and flash in the molded PVC parts.

Now that you know the fundamentals, let’s go over some key troubleshooting tips for PVC injection molding:

Troubleshooting Guide

Flashing

• Lower melt/mold temperatures
• Reduce injection speed/pressure
• Increase clamping force

Wypaczenie

• Increase mold temperature
• Zmniejsz prędkość wtrysku
• Optimize cooling time

Znaki zlewu

• Increase injection pressure
• Extend holding times
• Increase part wall thickness

Burn marks

• Lower barrel temperatures
• Reduce screw RPM
• Decrease back pressure

Delamination

• Increase mold and melt temperatures
• Lower injection speeds
• Check for partially blocked nozzle

While this covers the basics, every resin grade and part design needs customized parameter tuning. Documenting molding parameters is invaluable for repeatability.

Now you know everything involved in effective PVC injection molding – from suitable equipment and optimal settings to defect troubleshooting.

Armed with this processing knowledge, you can confidently specify PVC for your application, select proper machinery, and mold quality parts efficiently.

Remember to always adhere to safety protocols when handling PVC – including personal protective equipment. Also ensure proper ventilation during molding.

With meticulous care and attention to processing details, PVC injection molding will open limitless manufacturing possibilities at your facility!

Podsumowanie

Following optimized PVC injection molding procedures minimizes defects, improves part quality, and boosts productivity. Carefully control parameters like temperature, pressure and clamp force based on the resin grade and part design.