1、 Analysis of the core causes of poor exhaust emissions
| Cause category |
Specific manifestations and mechanisms |
Typical data/phenomena |
| 1. Design defects in venting system |
-Insufficient depth of exhaust groove (<0.03mm)
- Small cross-sectional area of exhaust channel (<2mm ²)
- Long exhaust path (>50mm) |
When the cross-sectional area is less than 1mm ², the gas discharge velocity is less than 0.5m/s, resulting in a filling end gas pressure greater than 15MPa |
| 2. Limitations on mold structure |
-The fitting accuracy of the parting surface is too high (<0.01mm)
- the gap between the inserts is not utilized
- the flow channel of the multi cavity is unbalanced |
When the gap between the parting surfaces is 0.02-0.03mm, the natural exhaust efficiency can reach 70%;Fully enclosed structure exhaust efficiency<10% |
| 3. Influence of material properties |
-Rapid cooling of high viscosity materials (such as PC) melt front
- material volatile content>0.1%
- glass fiber orientation hinders exhaust |
The exhaust demand for PA66+30% fiberglass material has increased by 40%, requiring additional exhaust slots |
| 4. Process parameter mismatch |
-Injection speed greater than 90% leads to gas entrapment
- premature intervention of holding pressure
- melt temperature fluctuations greater than ± 5 ℃ |
When the injection speed is greater than 120mm/s, the probability of gas entrapment in the melt increases by 80%;The optimal pressure is triggered when filling 95% |
| 5. Insufficient maintenance of molds |
-Accumulation of carbides in the exhaust groove (thickness>0.01mm)
- contamination of the exhaust channel by the ejector pin lubricant |
A 0.01mm carbide layer can reduce exhaust efficiency by 50%;Clean up at least twice a month |
2、 Quantitative impact of adverse exhaust hazards
| Hazard type |
Changes in key parameters |
Quality defect performance |
Economic impact (based on 100000 cycles) |
| SHORT SHOT |
Filling rate<95% |
Short shot, missing contour |
The scrap rate increases by 8-12%, resulting in a loss of 30000 to 50000 yuan |
| Internal pores |
Porosity>0.5% |
Tensile strength decreases by more than 20% |
Mechanical performance failure leads to return, resulting in a loss of 100000 to 150000 yuan |
| Surface burnt |
Local temperature>material decomposition temperature+30 ℃ |
Carbonized black spots and VOC exceeding standards |
Appearance scrap rate of 5-8%, loss of RMB 20000 to 40000 |
| Flow mark/fusion mark |
Melt front temperature difference>15 ℃ |
Visible flow marks and weakened mechanical properties |
The cost of secondary processing has increased by ¥ 15000 to ¥ 30000 |
| Extended cycle |
Filling time increases by more than 0.5s |
Daily production decreases by 15-20% |
Annual production capacity loss of ¥ 500000 to ¥ 800000 |
3、 Systematic solutions and parameter standards
1. Optimization design of exhaust system
·
Multi stage exhaust structure:
·
| level |
position |
Groove depth (mm) |
Slot width (mm) |
function |
| Level 1 |
melt front |
0.02-0.03 |
3-5 |
Trace gas permeation and discharge |
| level 2 |
Main channel of parting surface |
0.05-0.08 |
6-8 |
Concentrated diversion |
| Level 3 |
Mold periphery |
0.15-0.2 |
10-15 |
Rapid pressure relief |
·
·
Vacuum assisted exhaust technology:
·
o Vacuum degree ≤ -0.09MPa (absolute pressure ≤ 10kPa)
o Response time<0.3s (triggered synchronously with injection action)
2. Improvement of mold structure
·
Gap utilization of inserts:
·
o Control the fit clearance of 0.02-0.03mm (H7/g6)
o Arrange exhaust holes with a diameter of 1-1.5mm and a spacing of 15-20mm
·
Composite structure of conformal cooling and exhaust:
·
o Open a micro exhaust groove (0.01mm deep) 0.5mm above the cooling water channel
o Adopting 3D printing of conformal airway (cross-sectional area ≥ 3mm ²)
3. Material and process control
·
Material pretreatment standards:
·
| Material type |
Drying temperature (℃) |
Drying time (h) |
Permitted volatile matter (%) |
| PC |
120±5 |
4-6 |
≤0.02 |
| ABS |
80±3 |
2-3 |
≤0.05 |
| POM |
90±2 |
3-4 |
≤0.03 |
·
4. Intelligent monitoring and maintenance
·
Online detection system:
·
| sensor type |
Monitored Parameters |
alarm threshold |
| Mold cavity pressure sensor |
Pressure fluctuation>± 5% |
>10% for 3 consecutive cycles |
| Infrared thermal imager |
Local temperature difference>20 ℃ |
Stop immediately when the temperature exceeds 30 ℃ |
| Gas concentration detector |
VOC＞50ppm |
>100ppm triggers alarm |
·
·
Preventive maintenance plan:
·
o Every 50000 cycles: Ultrasonic cleaning of exhaust tank+Three coordinate detection of deformation
o Quarterly: Vacuum system sealing test (leakage rate<0.5mL/min)
4、 Engineering verification case (PA6-GF30 mold for automotive intake manifold)
| Improvement measures |
Parameter changes |
Improvement effect |
| Increase vacuum exhaust (-0.09MPa) |
Residual gas content 0.08 → 0.02cm ³/g |
Internal porosity ranges from 7% to 0.3% |
| Optimize injection curve |
End speed from 90% to 50% |
Fusion mark strength increased by 40% |
| Adopting 3D printing for adaptive exhaust |
Exhaust efficiency from 55% to 92% |
Molding cycle from 38s to 32s (-15.8%) |
summarize
To eradicate poor exhaust, a "four in one" control system needs to be established:
1 Precision design: three-stage exhaust structure (groove depth 0.02-0.2mm)+vacuum assist (≤ -0.09MPa)
2 Material control: volatile matter<0.05%+additional exhaust for fiberglass materials
3 Intelligent process: Three stage injection speed control (end deceleration to 50%)+mold temperature fluctuation ＜ ± 3 ℃
4 Predictive maintenance: Ultrasonic cleaning every 50000 cycles+online pressure/temperature monitoring
For complex molds (such as multi cavity medical components):
· Using Moldflow software to predict the gas accumulation area at the front of the melt
· Pre install a Φ 0.5mm miniature exhaust pin at the gas trap location
· Using beryllium copper alloy with thermal conductivity greater than 200W/m · K to make inserts and accelerate local heat dissipation
This plan can reduce exhaust related defects by over 90%, increase production efficiency by 15% -25%, and reduce overall quality costs by 40% -60%.
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