Rigid PVC Injection molding
Formulations, Blending, Compounding & Molding of PVC pipe fittings
Starting Point PVC Injection Molding Formulations for Pipe Fittings (Lower Cost >>>>>Higher Cost (Richer)
A B C
S-PVC (K-55) 100.0 100.0 100.0
K-175 Process Aid (R&H) 1.5 2.0 3.0
KM-611(or better) (R&H) 5.0 6.5 8.0
Stabilizer(TM-181DuPont) 1.5 2.0 2.5
CaCO3 (1micron) (Omya) 3.0 3.0 3.0
TiO2 Rutile 3.0 4.0 5.0
Lube system I
Ca stearate 1.5 1.5 1.5
165 Wax 0.5 0.5 0.5
AC 629A PE wax 0.2 0.2 0.2
OR Lube System II
Ca Stearate (R-1800) 0.8 0.8 0.8
Loxiol G-30 (Henkel) 1.0 1.0 1.0
Loxiol G-70 (Henkel) 0.3 0.3 0.3
HIGH INTENSITY MIXER BLEND CYCLE to prepare powder blend compound: ADDITION ADD MIX TO TEMPERATURE
1)-Room Temp. PVC Resin (alone*) 60 C/140 F
2. 60 C Stabilizer 85 C/185 F
3. 85 C Lubricants 100 C/212 F
( Stearates) ( Waxes)
4.100 C Non-Lubricating Powders 110 C/230 F
( Process Aids) ( Impact Modifiers) (Pigments) ( Fillers)
5. 110 C Drop to Cooling Mixer COOL TO 35 C/95 F * Preheating resin appears to cause some expansion of voids in the resin particles, enhancing their absorptive capability. NOTE: It may be desirable to go to 120 - 140 C drop temperature if the bulk density of the resin is lower. Also, stabilizer addition at 70-80 C may help if the resin is not as absorptive to liquids. The addition of lubricants (which melt and are absorbed) right after stabilizer addition would give these materials a greater chance for absorption before the end of the cycle.
PELLETIZING AND INJECTION MOLDING TIPS
It is best to PRE-Pelletize since most molding machines are not well equipped to handle powder blends (porosity, etc.) Pelletize at a 360-380deg.F(180-192deg.C) melt temperature in either a single screw, parallel or conical twin screw extruder.
INJECTION MOLDING TIPS (courtesy of Geon's Roger Stellar and Carl Toensing, Vinyl RETEC-96)1.- Keep melt no hotter than 385-400deg.F(195-205deg.C) will give a smooth, glossy melt. Use a needle pyrometer in an air shot to pre-check melt temp.
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2.- Shot weight= 50-80% of barrel capacity (capacity x?sp. gr.)
3.- Screw: 2.5:1- 2.8:1 compression ratio (maximum!)
4.- Barrel Heats????????? ?Rear????????Middle????????Front?????? ?Nozzle
75-150 Tons?????????? ?370deg.F??370deg.F???370deg.F???370deg.F
175-350 Tons????????? 340??????? ??350????????? ?350????????? ?360
350-500 Tons???????? ?340???????? ?345?????????? 345?????????? ?360
500-1000Tons???????? 340????????? 345?????????? 345????????? 360
5.-?Screw RPMs (To generate no more than a 10-15deg.F over-ride on material in each barrel zone.)
75-150 Tons?? ?55-80 RPM
175-350 Tons?? 55-80 RPM'
375-500 Tons?? 35-55 RPM
700-1000 Tons 25-35 RPM
6.- Back Pressure:?A 75-250 psi. range is typical. Screw RPM and backpressure settings will depend on screw compression ratio and design. The more severe the screw, the lower the RPM and backpressure settings need to be. Ideally, use backpressure and screw RPM to adjust screw recovery time to be slightly less than cooling cycle time while keeping a good melt temperature (385-400deg.F/ 195-205deg.C)
7.- Pressures: Suggested ranges for rigid PVC:
Injection= 800-1500 psi.
Packing=?400-800 psi.
Hold=?????300-600 psi
.8.- Injection Velocity:?Depends on nozzle and sprue bushing diameters, gate size, and wall thickness. A good starting point is: 0.75 in. to 1.0 in. per second(20-25 mm/sec.).
9.- Mold Temperatures: Inlet water temperature for most applications can be in the 70-90deg.F (22-32deg.C) range. Wall thicknesses greater than 0.150 in.(4 mm) can use cooler water (below 70deg.F), while thinner walls should use warmer water. Water to the core side of the mold should be 5-10deg. F cooler than the cavity side.\
10.-?Cooling Cycle Times: Time is obviously dependent on melt temperature, cooling water temperature, wall thickness and tool design. Suggested cooling cycles for various wall thicknesses:
Wall????????????????????????????? ?80deg. water????????????40 deg. water
0.150 in.--3.8mm????????????????? < 50 sec.?????????????????< 30 sec
0.180 in.-- 4.6mm???????????????? < 70 sec.????????????????< 55 sec.
0.250 in. -- 6.4mm??????????????? < 110 sec.??????????????< 75 sec.11.-
Shutting Down, Preventing Corrosion:
Use of a good purge is recommended in the barrel. Molds should be neutralized to prevent corrosion from off-gassing over time.
Owner at ML Photographer
11 个月Once the blender heats up, you are better off getting the stabilizer in immediately. It doesn't take much time to "pink" or "beige" the resin, and it happens very quickly. I have also found the the impact modifier can go in at the beginning and the blender should go to low speed for 2 minutes when the cal carbonate, TiO2, and process aid go in at the end.