NEWS
CONTACT US
Mobile Number: 18926501143
Mobile Number: 13689505165
101, Building 1, No. 8 Fangxing Road, Longdong Community, Baolong Street, Longgang District, Shenzhen
Analysis of the causes of secondary waste in injection molding of PFA plastic parts
Release time:
2016-12-16 15:56
Source:
Insufficient PFA plastic parts: mainly due to insufficient feeding, poor melting material filling flow, excessive inflation and poor exhaust, etc., the filling cavity is not satisfied due to excessive inflation and poor exhaust, and the shape of PFA plastic parts is incomplete or individual cavities are not filled when multiple cavities are used.
Cause analysis:
1. Improper injection quantity, insufficient feeding quantity, insufficient plasticizing capacity and insufficient surplus material
2.PFA GranulesDifferent or uneven pull
3.PFA particles in the hopper "bridge"
4. There is too much lubricant in the material, the gap between the screw or plunger and the barrel is large, and the molten material flows back too much.
5. Poor feed inlet balance when multi-cavity
6. The nozzle temperature is low, blocked or the aperture is too small, and the barrel temperature is low
7. The injection pressure is small, the injection time is short, the holding time is short, and the screw or plunger returns too early
8. The injection speed is too fast or too slow
9.PFA particles flow is too poor
10. Excessive flash overflows
11. Low mold temperature, fast cooling of PFA particles
12. The flow resistance of the mold gating system is large, the position of the feed port is improper, the cross section is small, the form is poor, and the process is long and tortuous
13. Poor exhaust, no cold material cavity or improper cold material cavity
14. Too much mold release agent, moisture in the cavity, etc.
15.PFA plastic wall is too thin, complex shape and large area
16.PFA particles contain more water and volatiles
17. There is a lot of inflation in the melting material.
Dimensional instability: mainly due to poor mold strength, poor precision, unstable injection machine work and unstable forming conditions, the dimensional changes of PFA plastic parts are unstable.
Cause analysis:
1. The machine electrical or hydraulic system is unstable
2. Forming conditions are not stable (temperature, pressure, time change), forming cycle is not consistent
3. Insufficient mold strength, bending and wear of the positioning rod
4. Poor mold accuracy, unstable movement of moving parts, inaccurate positioning
5. When the mold clamping is unstable, it is loose and tight, and it is easy to flash.
6. The gate is too small or uneven, and the multi-cavity feed port is poorly balanced
7.PFA particles are uneven or the dosage is uneven
8. Replacement of injection machine improper performance or uneven plasticizing
9.PFA plastic parts cooling time is too short, uneven cooling after demoulding
10. Inappropriate ratio of recycled materials to new materials
11. The shrinkage of PFA particles is unstable,
The crystallinity of the crystalline material is unstable
12.PFA plastic parts with poor rigidity and uneven wall thickness
13. Unstable post-treatment conditions of PFA plastic parts Bubbles: Residual gas in PFA plastic parts is caused by excessive inflation or poor exhaust in molten materials, and it is in small volume or in series of holes (note that it should be distinguished from vacuum bubbles).
Cause analysis:
1. The raw material contains water, solvent or volatile matter
2. The material temperature is high, the heating time is long, and the PFA particles are degraded.
3. Injection pressure is small
4. Plunger or screw back too early
5. Poor mold exhaust
6. Low mold temperature
7. The injection speed is too fast
8. There is moisture, grease, or improper release agent in the mold cavity
9.PFA plastic parts are not good, and the flow channel is not good. There are dead corners of gas storage (dents) or vacuum bubbles: due to poor pressure holding and feeding, PFA plastic parts have uneven cooling, uneven thickness and large shrinkage of PFA particles.
1. The flow channel and feed inlet are too small, or the quantity is not enough
2. The wall of PFA plastic part is too thick or uneven (collapse pit is easy to appear on the back of thick wall)
3. Improper location of the feed port is not conducive to feeding and feeding.
4. High material temperature, high mold temperature, short cooling time, easy to dent
5. Low mold temperature, easy to vacuum bubble
6. The injection pressure is small and the injection speed is slow
7. Injection and holding time is short
8. Insufficient feeding, insufficient feeding and insufficient surplus
9. Poor melt flow or excessive overflow
Excessive flash: due to poor mold clamping, excessive gap, PFA particles have too good fluidity, and excessive feeding causes PFA plastic parts to extrude excess flakes along the edge.
Cause analysis:
1. The parting surface is poorly closed, and the gap between the sliding parts of the cavity and the core part is too large.
2. Poor mold strength or rigidity
3. Poor mold parallelism
4. The mold is stressed in one direction or is not compressed during installation.
5. The injection pressure is too large, the clamping force is insufficient or the clamping mechanism is poor, and the injection machine template is not parallel
6. The projected area of PFA plastic parts exceeds the plastic area allowed by the injection machine
7.PFA particles have too much fluidity, high material temperature, high mold temperature and too fast injection speed
8. Excessive feeding amount
Poor welding: due to the low material temperature when the molten material is split and merged, the resin is not compatible with the compound and other reasons, the melting material is poorly welded when merged, resulting in obvious fine joint lines along the surface or inside of PFA plastic parts.
Cause analysis:
1. Low material temperature and low mold temperature
2. The injection speed is slow and the injection pressure is small
3. There are too many feed ports, improper positions, improper gating system forms, long process, large flow resistance, and rapid material temperature drop
4. Improper mold cooling system
5.PFA plastic parts have poor shape, too thin wall, too many inserts and uneven wall thickness, so that the materials meet at the thin wall
6. Low insert temperature
7.PFA particles have poor fluidity and fast cooling speed
8. There is water in the mold, lubricant, excessive inflation of molten material and excessive release agent
9. Poor mold exhaust
10. There are insoluble materials in the material, improper release agent and insoluble oil.
11. With aluminum foil and other thin sheet colorant
12. Poor fusion of fiber filler distribution
13. Cold material
Surface corrugation of PFA plastic parts: because the molten material does not flow neatly along the surface of the mold to fill the cavity but flows in a semi-solidified wave shape on the cavity surface or the molten material has stagnation.
Cause analysis:
1. Low material temperature, low mold temperature, low nozzle temperature
2. The injection pressure is small and the injection speed is slow
3. Improper cold material cavity with cold material
4. Poor fluidity of PFA particles
5. Improper mold cooling system
6. The gating system has a long process flow, a small cross-section, a small size of the feed port and its improper form and position, which makes the melt flow resistance and cooling fast.
7.PFA plastic thin wall, large area, complex shape
8. Insufficient feeding
9. The flow channel is tortuous and narrow, and the finish is poor
Poor demoulding: due to the strong filling effect, poor mold demoulding performance and other reasons, the PFA plastic parts are difficult to demoulding or PFA plastic parts are deformed or cracked after demoulding, or the residual direction of PFA plastic parts does not meet the design requirements.
Cause analysis:
1. Poor mold finish
2. The mold demoulding slope is not enough
3. The gap at the mold insert is too large and there is a flash.
4. Forming time is too short or too long
5. Mold core without air inlet
6. The mold temperature or fixed mold temperature is not appropriate
7. There are scars on the surface of the mold
8. Poor ejection mechanism
9. High injection pressure,
Long pressure holding time, high material temperature and mold temperature, too much feeding, long injection time, large feed inlet size
10. Improper release agent
11. Failure of material pulling rod
12. There is a clamp between the nozzle and the sprue sleeve, and the sprue sleeve sticks to the mold.
13. Cavity deformation, rebound large, so that PFA plastic parts fall in the cavity
14. Poor cooling system, cooling time is too long or too short
15. The movable core demoulding is not timely
16. Insufficient feeding
17.PFA granular brittle, easy to stick mold, shrinkage
18. The shape of PFA plastic parts is unfavorable for demoulding, the wall of PFA plastic parts is too thick, too thin or insufficient in strength, and stress concentration is easy.
Mica flake delamination peeling: due to the mixing of different materials or low mold temperature, the shearing effect of the molten material flowing along the mold surface is too large, causing the material to peel off in a thin layer and the physical properties to decrease.
Cause analysis:
1. Different PFA particles mixed
2. The same PFA particles are mixed at different levels
3. Unequal plasticization
4. Mix foreign matter
5. The material temperature is low, the mold temperature is low, the cold material well is small, the material fluidity is poor, and the material is cooled too fast.
6. Improper ratio of new and old materials
7. Silver phenomenon is serious
Gate sticking: due to mechanical resistance in the gate sleeve, insufficient cooling or failure of the pulling rod, the gate is stuck in the gate sleeve
1. Insufficient slope of runner, no release agent
2. Short cooling time, high nozzle and fixed mold temperature, large runner diameter
3. The pulling rod fails and there is no cold material hole.
4. The inner wall of the main runner is not smooth, with dents and scratches.
5. Poor strength of the connection between the runner and the main runner
6. The nozzle temperature is low, the nozzle is not in good agreement with the sprue sleeve, and the diameter of the sprue sleeve is smaller than that of the nozzle or there is material clamping.
Cold block and stiff block: due to cold material or poor plasticization and insufficient plasticization material, hard block PFA particles are sandwiched in PFA plastic parts.
Cause analysis:
1. The material temperature, mold temperature and nozzle temperature are low, and the injection speed is small.
2. Unevened plasticization
3. Insufficient plasticizing capacity of the injection machine, the capacity of the injection machine is close to the weight of PFA plastic parts, and the forming time is short
4. Mixed with impurities or different grades of material
5. The grain is uneven or too large
6. No main runner and cold material hole, or improper position of cold material hole
Poor transparency: due to the poor contact between the molten material and the surface of the mold, the surface of the PFA plastic part has small cavities that cause light radiation or PFA particles to decompose, there are foreign matter impurities, or the surface of the mold is not bright, resulting in poor or uneven transparency of the transparent PFA particles.
Cause analysis:
1. Low mold temperature, low material temperature and poor contact between melt and mold surface
2. The mold surface is not bright, oil and moisture
3. Too much or improper release agent
4. High material temperature or pouring system shear action, PFA particles decomposition
5.PFA particles contain high moisture, impurities, black stripes and silver
6. Poor plasticization
7. Poor cooling of crystalline materials, uneven or uneven wall thickness of PFA plastic parts
Silver wire markings: due to moisture or inflation in the material, excessive volatiles, excessive shearing action of the molten material, poor adhesion between the molten material and the mold surface, or rapid cooling or mixing of different materials or decomposition and deterioration, silvery white needle-like stripes or mica flaky markings (water marks) appear on the surface of PFA plastic parts along the material flow direction.
Cause analysis:
1.PFA particle temperature is too high, high mold temperature
2. The raw material contains high moisture and low volatile matter
3. Injection pressure is small
4. Inflation in the material, poor exhaust
5. The flow channel and feed inlet are small, and the shearing effect is large (especially when the mold temperature is low, the material temperature is low, the injection pressure is high, and the injection speed is fast)
6. There is moisture on the surface of the mold, lubricating oil (white marks on the surface of PFA plastic parts at this time) or excessive release agent, which is improperly selected.
7. The mold temperature is low, the injection pressure is small, the injection speed is slow to fill the melting material, the cooling is fast, and it is easy to form a thin layer of white or silvery white reflected light (often cold trace marks)
8. When the molten material flows from the thin wall to the thick wall, it expands, and the volatile matter vaporizes and liquefies into silver wire in contact with the surface of the mold.
9. Improper ingredients, mixed with different materials or insoluble materials (at this time, stratification and detachment are easy to occur)
Warping and deformation: internal stress caused by residual stress, shear stress, cooling stress and uneven shrinkage during forming; Poor demoulding, insufficient cooling, insufficient strength of PFA plastic parts, mold deformation and other reasons cause PFA plastic parts to have shape distortion, warping uneven or partial hole, uneven wall thickness and other phenomena.
Cause analysis:
1. The cooling time is not enough
2. High mold temperature
3.PFA plastic parts with improper shape, uneven wall thickness, insufficient strength, improper insert distribution and poor preheating
4. Low material temperature, small nozzle aperture and feed inlet, high injection pressure, low mold temperature, high shear stress when injection speed is high
5. The material temperature is high, the mold temperature is high, the filling effect of the inlet part is too high, the pressure holding feeding is too large, and the residual stress is large when the injection pressure is high (the internal stress of the plunger injection machine is greater)
6. Improper position of feed inlet, small size, low material temperature, low mold temperature, low injection pressure, fast injection speed, insufficient pressure keeping and shrinkage, poor shape of PFA plastic parts, uneven cooling, uneven distribution of fiber suspected seam filler, etc., resulting in obvious shrinkage directionality and uneven shrinkage
7. The mold temperature is uneven (the temperature of the fixed moving mold is uneven). The cooling unevenness is such as slow cooling of the wall thickness part, fast cooling of the thin wall part or fast cooling of the easily warped convex part of PFA plastic parts, and slow cooling of the easily concave bending part.
8.PFA particles plasticizing uneven, filling insufficient or excessive feeding
9. Short cooling time, uneven stress of PFA plastic parts during demoulding, improper cooling after demoulding, poor post-treatment and poor storage of PFA plastic parts
10. Poor mold strength, easy deformation, poor mold accuracy, unreliable positioning, and wear
11. The position of the feed inlet is improper, the material directly impacts the core or the force on both sides of the core is uneven.
Crack: due to excessive internal stress of PFA plastic parts, poor demoulding, uneven cooling, poor performance of PFA particles or poor design of PFA plastic parts and other defects (such as deformation), fine cracks occur on the surface of PFA plastic parts and near the feed inlet, or cracks occur or cracks do not occur under load and solvent.
Cause analysis:
1. Poor ejection during demoulding
2. The mold temperature is too low or uneven
3. The cooling time is too long or the cooling is too fast
4. The insert is not preheated or the preheating is not enough, or the cleaning is not clean.
5.PFA plastic parts have thin walls, small demoulding inclination, sharp corners and notches, and are prone to stress concentration.
6. Improper forming conditions and excessive stress (see warping deformation for details)
7. The size of the feed inlet is large and the form is improper, and the internal stress at the feed inlet is large.
8. Ununiform cooling after demoulding or after treatment
9.PFA granular brittle, mixed with foreign impurities
10. Improper release agent
11.AbsPFA particles or impact-resistant polystyrene PFA particles are prone to white fine lines at the ejector part of the ejector rod (generally disappear after hot baking)
12.PFA particle shrinkage direction is too large or filler uneven distribution
13.PFA plastic parts are warped and deformed, with poor welding
14.PFA plastic parts in poor storage and solvent contact
Black spots and black stripes: due to the decomposition of PFA particles or combustible volatiles in the material, air and the like are decomposed and burned under high temperature and high pressure, and the combustion substances are injected into the plastic cavity with the molten material, resulting in black spots and black stripes on the surface of PFA plastic parts, or charcoal burns along the surface of PFA plastic parts.
Cause analysis:
1.PFA particle decomposition (especially for heat sensitive PFA particles)
2.PFA particle debris is stuck into the gap between the plunger and the barrel
3. There are dead corners in the barrel, nozzle and mold for material storage decomposition
4. The cylinder is not clean
5. Poor mold exhaust or excessive clamping force
6. Inlet size is too small, improper position
7. There are flammable volatiles in PFA particles or on the cavity surface
8. Water-sensitive PFA granules are poorly dried and hydrolyzed to turn black
9. The material particles are uneven, the feeding amount is small, the temperature near the hopper side of the barrel is high, the rotating speed is high, the back pressure is small, and the material is inflated too much during plasticization.
10. Dyeing uneven dark material, pigment deterioration
Unevened color or discoloration: due to poor distribution of pigments or fillers, PFA particles or pigment discoloration on the surface of PFA plastic parts of uneven color.
Color unevenness with the phenomenon of different reasons are also different, near the feed inlet is mainly uneven pigment distribution, such as the whole part color unevenness is caused by poor thermal stability of PFA particles, welding parts color unevenness is related to the nature of the pigment.
Cause analysis:
1. Aluminum foil or flake pigment, shiny along the direction of material flow, non-directional distribution of pigment at feed inlet, welding part and multiple feed inlet, uneven color
2. With dry pigment, the pigment is only attached to the surface of the particles when the roller is stirred.
3. Pigment quality is not good
4. Plunger injection machine prone to uneven color
5. Unevenness of plasticization
6. The distribution of fiber seam filler is uneven, the accumulation is exposed or the resin in contact with the solvent is dissolved and lost, and the fiber seam is exposed.
7.PFA particles or pigment decomposition
8. The surface of the mold has moisture, oil or improper release agent, too much
9.PFA particles and pigments mixed with different materials
10. Low crystallinity or uneven wall thickness of PFA plastic parts, affecting transparency and causing uneven color
Brittleness of PFA plastic parts: due to poor PFA particles, obvious directionality, large internal stress and poor structure of PFA plastic parts, PFA plastic parts are brittle and easy to crack (especially in the direction of material flow).
Cause analysis:
1.PFA particles with poor performance or decomposition degradation or hydrolysis or poor pigment and deterioration
2. Forming temperature is too low
3. Poor welding, warping deformation
4.PFA particles wet or moisture content is too low (such as nylon 6)
5. Too much or insufficient feed of PFA particles
6. Mold temperature is too low
7.PFA plastic parts with poor design such as insufficient strength, acute angle and notch
8. The metal insert wrapping layer PFA particles are too thin, the insert preheating is not enough, and the cleaning is not clean.
9. There are impurities and insoluble materials in PFA particles
10. Poor plasticization or too large and uneven particles
11. Improper release agent, the mold is not clean
12. Shrinkage directional obvious, packing uneven distribution
13. Ununiform shrinkage, poor cooling and residual stress, etc., so that the internal stress is large.
14.PFA plastic parts in contact with solvent
15. The size, position and form of the feed inlet are not good, resulting in large internal stress, obvious direction, uneven distribution of filler, damage of fiber seam filler or setting of feed inlet at the bending force part of PFA plastic parts.
This article comes from:www.tflpfa.com
Popular Articles:Plasticizing process route of PFA particles