The cause and corrective action for usual defect
No.1 short shot
Definition:the phenomena that the melt resin cann`t fill all the corner of mold is conside short shot.
cause an corrective action:
I.The machine is not mathch with the product because that the cablitily of the plastical or the unit of shot is not enough
corrective action:
change more larger machime to keep up the largest unit of the machine more than 80% of the product's weight that include
the gating`weight.
II.The size of nozzle is too small and then result in the cold barden stopping melt resin flowing
corrective action:
change more larger nozzle
III.The design of the geat is faulty and then cause the melt resin to flow is difficult
Corrective action:
modify the git's size or it's position
IV.The resin cann't melt evenly and rusult in the injection pressure lowering too much.
Corrective action:
adminste the screw back pressure to make the resin melt evenly
V.The scoop for cold burden at the end of the geat is not adequacy because of it's deep or position,and result that the
cold burden to impede meld resin fill up the mold's impression.
corrective action:
enlarge the room of the scoop for cold burden or chage it's position.
VI:the mold is too cold and the melt resin flowing is difficult
Corrective action:
improve the mold's temperature to content with the need of product
No.2 FluSH
definition: the melt resin along the parting lines of mold or the interface of side core
Cause and corrective action:
I.the clamping fource is not enoagh and the melt resin flow out froming backlash
Corrective action:
increas clamping fource or change more langer machine
II.There is crevice for the nozzle is not completely touch the sprue Bush
Corrective action:
increase the fource of device for injecting.
III.The usland guid pins were weared and teared
Corrective action:
change guid pin that have been weared and teared.
V.There are miscellanous object on the parting lines of mold
Corrective action:
Clean the parting lines
VI.The projection of the product is too large or the temperature of the resin is too high.
Corrective action:
a:change more larger machine.
b:lower the temperature of resin
No3. Sink marks
Because of contraction of material after cooling ,the surface may have indentation mark tgpically at thick sections
cause and corrective action:
I.injecting pressare is not enough
We had betten improved injecting pressure when the product's shrinkage produce for the lower injecting pressure.
II.The short-time for hold pressure
If the time of hold pressure is not enough, The crinkling could not be make up in time and it is possible that the
melt resin back flow, at this time ,we should delay the hold-time
III.The injecting speed is too show
it will congealing quickly if the injecting speed is too slow
Iv.The unit of shot is not enocegh
in order to solove this problome we should added the unit of shot
V.The Temperature of mold or resin is too high, in this case the product`s cooled--speed is slow and when it shrinked
compeletely there will produce sink marks
VI.the size of git or lip is too small
The melt resin cann't be compressed completely because that the injecting pressure lose quickly for the small gatings
or lips ,so we should enlage the size of gatings or lips.
VII.the dabber is too thick
Usualy the dabber's thickness should be contraled in 50~80% of the wall ,and it should be more lighter at these position
that far away frow the lips, beside these, the dabble should be thicker and thicker from it's buttom in order to reduce
the diffrent crinble.
VIII.mold be cooled is not appropiatty
mold should be cooled completely and evenly to equal the shrinking
NO.4. Bubbles
definition:the moisture and the volatile matter that were hided in the melt resin be remnanted in the production when
injecting and found holes finaly,usualy, it caused by the moisture, volatile matter air and so on.
Corrective action:
I.dry the resin completely before molding.
II.lower the temperature of the end of the CYL. and improve the screw back pressure
III.lower the temperature of resin so that the resin cann't resolve
NO.5. Cracking
definition:The serious pull marks at the surfface of product is consided cracking
Cause:
I. drawing of patterns is difficult
II.the impression was filled too much
III.the temperature of the mold is too low
IV.the structure of produet is faultly.
Corrective action:
I.there should be enough gradient for drawing of patterns to avoid the fault of ejecting ,at the same thim we should checked
the size and position of ejector pin so that the fource of ejecting is equally
II.If the melt resin filled up mold is too much or the unit of injecting is too large it will increase the stress inside and result
in cracking when ejecting.In this condition, it will be more serious that all part of the mold transfigared and the ejecting
will be more difficult too.and usually the dabbles will crack.In order to reduce the extend of filled,we should reduce
the injecting pressure or the resin's temperature and mold's temperature.
NO.6. Stress marks
definition:A ltcallized white spots typically caused by pushing the materical near fracture point.It typically appears near
the ejector pin marks
stress marks is not cracking but is the prdecessor of cracking:It is caused by the serious stress inside and usually be found
on these prouduct that it's material is ABS, HIPS.
NO.7. Strain
The part surfaces that do not meet the surface specs in the drawing,typically a curved surface that is supposedly to be
flat
It was caused by usualy:
a.stress inside
b.temperature of mold or resin is not evenly
c.the faulty condition of injecting
d.the structure of product
The crrective action of it is depend on the structure of product. It is deffrent for deffrent reason
I.the thickness is not even or mold is not cooled proportionatly
It will strain because the diffrent cooling speed caused by the diffrent thinkness. So that the wall is more thicker or more
near by the lips, it will be cooled more effectively.
II.caused by the diffrent shrink
We usually adopt more lower temperature of mold or resin to reduce the hot-contraction and take high injecting pressure
or long hold-pressure's time to make up the hot-contraction.
NO.8. weld line
Two stream melt resin or more flow together and produce line be call weld line,It caused by following
I.the states of flowing because of the product`s struture
II.the capability of melt resin's flowing
III.the air,the volalile matter and release was draw into melt resin
The weld line was melt resin cann't weld completely because that the temperature of the front melt resin is lower
than other. It cann't inevitable that there appearace weld line around the product's windows and hopes.But when the
capability of resin's flowing is well, the weld line will become lighter or cann't be seen ,at the same time,the weld line
will become lighter too when raise up the resin or mold's temperature.
Change the number of lips or it's position ,the weld line's position will be changed . But we can set up a bath on the
weld line's end to changer the weld line`s position and then cut off it.
The weld line not only affect the appearance,but alose affect the strain.
corrective action:
I.raise up the temperature of resin or mold when it is too low
II.increase the injecting pressure when it is not enough
III.Increase the speed of injecting when it is too slow
IV.enlarge the size of lips or gating when it is too small
V.reduce the distance that from weld line to lips when the distance is too largre
VI.set up pin for releaseing when it's difficult to release
VII.change the number of lips or it's position when the lips are not proper
NO.9.Flow marks
definition:flow marks is the trace of the flowing melt resin and usually it radiate frow the center to around.The reason
of the flow marks takes from is that the original melt resin was cooled quickly and cann't mixed well with the
lasted resin
Corrective action:
I.improve the mold or resin's temperature
II.improve the injecting pressure
III.change the position of gating for cool-water
IV.enlage the size of lips or gatings
V.increase the unit of cushion
NO.10. Jetting marks
definition:jetting marks like a crawling snake after the melt resin inject in mold`s impression through the gate and congealing.
The jetting marks usually appearance on the product that their lips are their edge or have no scoop for cooling
materisl. And the reason of it as lik as the flow marks's
The corrective action to prevent the jetting marks was to improve resin's temperature or mold's and set up large
scoop for cooled material, changer the form of lips and enlarge the size of it`s or slow the injecting speed and so on.
NO.11.sliver steraks
definition:at the surfface or near by, these steraks look sliver and along the direction of flowing were called sliver steraks
cause :
I.there are moisture and volatilizing substance in resin
II.the resin stopping in the CYL. for long time
III.the resin resolved for the temperature raising abnormally
IV.the airways were stuffed and it's difficalt to release
V.there are oil or moisture on the surface of the mold
VI.diffrent resin mixed in it
VII.air in the cyl. and cann`t be released because that there are too much
VIII.resin resolved because of high temperature caused by high speed
Corrective action:
I.when the cablitily of the machine injecting or plasticing is not enough ,the resin at the front solidy quickly and then cause
to produce sliver steraks, At this time we should change more larger machine.
II.the resin stopping in the CYL. for long time,the air that risin resolved is too much and cann`t be releasd in time or
completely, so we should reduce the cycle-time as this time.
III.the circumstance of too-big injecting pressure and too-rapid iejecting velocity
If the thickness change rapidly ,flowing compressed resin expand be cause of fast pressure reduce,volatilizing and
analytical gas liquefy after touch on the mould,so we should reduce injecting pressure and relocity,make thickness
change equable
IV.The circumstance of air getting into screw
If the material barrel is cooled absolutely the temperature of barrel side is lower than heat rat,so the resin often scratch
screw,so we should reduce rotating velocity,increase screw back pressure,material is compressed then air can get off
from barrel side
V.When plastic contain water,rolatilizing substance,Strong absorption resin such as PMMA.ABS.AS...must be dried at first.
VI.When the temperature of mould is too low.
Under this circumstance plastic is solidfying rapidly,gas can't get off completely ,so mould temperature should increased
VII.When geat or gating is too small.
Because flow resistance increase,filling velocity decrease,resin solidize rapidly,It's neccessary to enlarge geat and gating.
VIII.When mould release diffcultly
If mould release diffcultly,increase vent is necessary.
VVI.When oil or water or release adhere to the sarface of impression.
When oil or water or release adnere to the surface of impression,Oil ,water or release will eraporate because of plastic heat
and liquidize whth resin solidizing,So we need cleaning mold,and Limit the use of release
NO.12.Burn Marks
Definition: Comman definitron of burn marks,mean the deformation of the surface of the product which is by over-heated,
and the blackness of acute part or gill,the front of the dabber.
Burn marks is caused by the air in mould,whill release slowly when the melt material get in,is compressed,its temperature
increase remarkablely ,There are two effective and prevent action Locating vent.Firstly, in the place of which air gather
easily or making use of the interval of eject pion and core pin,so remain air release rapidly.Secondly,lower the temperature,
reduce injecting pressure and velocity or enlarge the gate At last,Draw out air in the mould by facinating vacual bump,
vacunmizing the cavitig when forming
NO.13.Black Streaks
Definition :Black streaks mean the phenomena of black sereaks adhered on the product
Cause and corrective action:
I. cause:
When lubricant is lack,produced craping heat seariously and difficult releasing will cause burn
Comective action:
Add proper quantity of labricant,but if lubricant is more than 0.2%,on the contrary valatilizing substance of labricant
will help it burn easily,so black streaks produced:
II.cause:
The product is too small but machine is too large and then the resin resolved for long time stopping in the pipe
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