O que é marca de pia?
Amassados e marcas de afundamento são causados pelo encolhimento local causado pela vedação do portão ou falta de injeção de material.
A depressão ou microdepressão na superfície dos produtos moldados por injeção é um problema antigo no processo de moldagem por injeção. As amolgadelas são geralmente causadas pelo aumento da taxa de encolhimento dos produtos plásticos causado pelo aumento da espessura da parede. Eles podem aparecer perto do canto externo agudo ou da mudança repentina na espessura da parede, como a protuberância, a parte de trás do reforço ou do suporte, e às vezes em algumas partes incomuns. A causa raiz do amassado é a expansão térmica e a contração a frio do material, porque o coeficiente de expansão térmica do termoplástico é bastante alto. O grau de expansão e contração depende de muitos fatores, among which the plastic properties, the maximum and minimum temperature range and the cavity packing pressure are the most important factors, and the size and shape of the injection parts, the cooling rate and uniformity are also the influencing factors. Dents and shrinkage marks on plastic products are common molding defects. BENEFÍCIOS DO SISTEMA DE PROTÓTIPO PAPID:
Análise e eliminação de defeitos de marca de pia
1) Improper control of molding conditions
If the injection pressure is too low, the injection and holding time is too short, the injection rate is too slow, the material temperature and mold temperature are too high, the cooling of the plastic part is insufficient, the temperature during demoulding is too high, the temperature at the insert is too low or the material supply is insufficient, the surface of the plastic part will appear concave or orange peel like micro unevenness. Portanto, it is necessary to increase the injection pressure and injection speed, increase the compression density of the melt, extend the injection and holding time, compensate the melt shrinkage and increase the injection recoil. But the packing pressure should not be too high, otherwise it will cause convex mark.
1. If the depression and shrinkage mark occur near the gate, it can be solved by extending the holding time. The cooling time of the plastic part in the mold should be extended appropriately when the plastic part is concave at the wall thickness.
2. If the local shrinkage of the melt around the insert causes depression and shrinkage mark, which is mainly caused by the low temperature of the insert, we should try to increase the temperature of the insert.
3. If the nozzle hole of the injection molding machine is too small or the nozzle is partially blocked, the local loss of injection pressure will also cause depression and shrinkage mark. A respeito disso, the nozzle should be replaced or cleaned.
4. If the surface of plastic parts is depressed due to insufficient feeding, the feeding amount should be increased.
Além disso, the cooling of plastic parts in the mold must be sufficient. Por um lado, the melt temperature can be appropriately reduced by adjusting the barrel temperature; por outro lado, the setting of the mold cooling system can be changed to reduce the temperature of the cooling water, or the cooling of the concave parts can be properly strengthened on the premise of maintaining the uniform cooling of the mold surface and all parts as far as possible. Por outro lado, when the plastic part is demoulded under the condition of insufficient cooling, it is not only easy to produce shrinkage depression, but also local depression of the plastic part in the ejector due to hard demoulding.
2) Defeitos do molde
If the cross-section of runner and gate is too small, the mold filling resistance is too large, the gate setting is asymmetric, the mold filling speed is not balanced, the position of feed gate is not reasonable, and the mold exhaust affects the feeding, feeding and cooling, or the mold wear causes the pressure relief, it will lead to the surface depression and shrinkage mark of plastic parts. Portanto, the gate and gate cross-section should be appropriately expanded according to the specific situation The gate position should be set at the symmetrical position as far as possible, and the feeding gate should be set at the thick wall of the plastic part.
If the depression and shrinkage mark occur far away from the gate, it is generally due to the poor flow of molten material in a certain part of the mold structure, which hinders the pressure transmission. Portanto, the structure size of the gating system should be appropriately expanded, especially for the “bottleneck” which hinders the melt flow, the runner section must be increased, and it is better to extend the runner to the concave part.
For thick wall plastic parts, wing gate should be preferred. Desta maneira, for the plastic parts which are not suitable to set the gate directly on the plastic parts and are easy to produce residual deformation at the gate after molding, a wing body can be attached to the plastic parts, and then the gate can be set on the winglet. The gate on the winglet can use the reverse gate and the point gate, so as to transfer the concave defects of the plastic parts to the winglet, and then cut off the winglet after molding.
Além disso, it is necessary to frequently check whether there is wear relief or poor exhaust of the mold, and timely replace the consumable parts in the mold or improve the exhaust condition of the mold.
3) The raw material does not meet the molding requirements
1. If the shrinkage rate of molding raw materials is too high or the flow performance is too poor, and the lubricant in the raw materials is insufficient or the raw materials are wet, the surface of the plastic parts will produce depressions and shrinkage marks. Portanto, for plastic parts with high surface requirements, low shrinkage resin grade should be selected as far as possible.
2. If the underfill depression is caused by the poor flow of the molten material, an appropriate amount of lubricant can be added to the raw material to improve the fluidity of the molten material or increase the structural size of the gating system.
3. If the surface of plastic parts is depressed due to the moisture of raw materials, the raw materials should be pre dried.
4) Unreasonable shape and structure design of plastic parts
If the wall thickness of plastic parts varies greatly, the thick wall parts are prone to depression and shrinkage marks due to insufficient pressure. Portanto, when designing the shape and structure of plastic parts, the wall thickness should be as consistent as possible. For special cases, if the wall thickness of plastic parts is different, it can be solved by adjusting the structural parameters of the gating system.
Sobre JasonMould Industrial Company Limited
Jasonmould é um Fabricante de moldes da china de moldes de plástico- molde de injeção, moldes de fundição sob pressão, moldagem por sopro de plástico, moldagem rotacional, médico moldagem por injeção de plástico, dois tiros moldagem por injeção de plástico, inserir moldagem, sobremoldagem, moldagem por injeção de metal, moldagem por micro injeção, moldagem por injeção de pó, moldagem por injeção de cerâmica, moldagem por injeção de líquido, moldagem por injeção husky, molde doméstico, molde de fundição, ferramenta de molde, moldes personalizados, moldes da china, ferramentas de prototipagem rápida, ferramentas de prototipagem de plástico, ferramentas de punção, matriz e ferramentas para peças móveis / celulares, partes automotivas, aspirador de pó, ferramentas recarregáveis, telefones, copiadoras, computadores, alto-falantes multimídia, e muitos outros produtos eletrônicos e eletrodomésticos. E também um fabricante de produtos de plástico, fabricante de moldes China- peças de plástico, tanque de água de plástico, bolas de plástico, recipientes de plástico, fivela de plástico, âncora de plástico, cabide de plástico, colher de plástico, encaixe de tubo de plástico, tombo de plástico, talheres de plástico, copos de plastico, garrafas plásticas, bandeja de plastico, recipiente plástico de cosmético, caixa de plástico, recipiente de plástico para comida, cadeiras de plástico, tampas de plástico, tampa de plástico, tubos de plástico, canos de água de plástico, maçanetas de plástico, tubo de plástico, caixas utilitárias de plástico, prateleiras de plástico e assim por diante.
Contato:
Pessoa: James Yuan
Empresa: JasonMould Industrial Company Limited
Adicionar: LongGang Village,LongXi Town,BoLuo County,Cidade de HuiZhou,Província de Guangdong, China
Tel: 86-752-6682869
E-mail: [email protected]
Local: https://www.jasonmolding.com/custom-injection-molding/
