When looking for a supplier to manufacture zinc alloy perfume caps, it is essential to communicate and confirm certain issues with the supplier. How to ensure product quality during the die - casting process and how to address quality issues if they occur. Next, a veteran master with over 20 years of experience in the die-casting industry will tell you about what kinds of defects may occur during the die-casting process and the reasons behind them.

I. Porosity Defect

When a porosity defect occurs, you can observe some tiny bubbles or holes on the surface or inside of the cap. At this time, the surface of the cap is not smooth and appears less refined. Moreover, it may have insufficient strength during use and could deform or break.

Causes

1.Raw Material Treatment:

If the factory fails to pay attention to moisture - proofing when storing zinc alloy ingot raw materials and the raw materials have a high gas content, when the zinc alloy ingots are melted into liquid, these gases are easily trapped in the liquid, thus forming holes.

2.Die - Casting Process:

If the gating system is not designed reasonably, the molten metal liquid will generate vortices during flow, and air will be entrained, resulting in porosity; also, when the metal liquid is injected into the mold cavity at a too high speed, although there is air in the mold cavity originally, the injection of the metal liquid is too fast, and this air does not have enough time to escape. It is like quickly injecting water into a container, which will block the air and form bubbles. These bubbles are then encapsulated by the metal liquid, and porosity is thus produced.

3.Mold Factors:

The air in the mold cavity needs to be discharged through the vents in the mold. If the number of vents is insufficient, the depth is not enough, or they are blocked, the gas cannot be completely discharged, and porosity will occur.

II. Shrinkage Defect

This phenomenon exists not only in injection molding but also in die - casting. If the wall thickness of the product is too thick, the surface of the product will be concave or have holes, which will lead to dimensional deviations of the product. In such a case, it may affect the fit between the perfume cap and the bottle.

Causes

1.Metal Solidification Characteristics:

Similar to the principle of thermal expansion and contraction, when the metal liquid solidifies, its temperature decreases and its volume shrinks. If the wall thickness of the product is uneven, when the thin - walled part has already started to solidify and its volume shrinks, the surrounding liquid metal can flow in to supplement because the liquid metal can still flow. However, the thick - walled part solidifies slowly. During its solidification process, since the liquid metal of the entire casting has already started to solidify, there is not enough liquid metal that can flow to the thick - walled part to fill the voids caused by its volume shrinkage. This insufficient filling situation will lead to voids in the thick - walled part, and these voids will appear as shrinkage holes in the final casting.

2.Die - Casting Process Parameters:

The pressure of the die - casting machine is insufficient or the holding time is too short. The metal liquid cannot well fill the voids caused by shrinkage during solidification, and shrinkage defects will occur. It is like in the construction process, when the concrete solidifies and shrinks, it is necessary to add concrete in time to fill the voids and keep the building structure intact.

3.Mold Design:

If the mold cooling system is not designed reasonably, if the local cooling rate is too fast or too slow, it will also affect the solidification sequence and feeding effect of the metal liquid.

III. Flow Mark Defect

In simple terms, a flow mark is like a water - ripple - like or striped trace that can be seen on the surface of the perfume cap. When this defect occurs, the color and gloss of this part will be different from other areas. It mainly affects the appearance quality of the product, making the perfume cap look less refined and high - end.

Causes

1.Metal Liquid Flow State：

The zinc alloy perfume cap is formed by melting zinc alloy ingots into metal liquid and then pouring it into the mold cavity and cooling it. However, if during this process, the temperature of the metal liquid is uneven and the flow rate is unstable, flow marks will be formed. In other words, if the metal temperature is uneven, it is like some water in different places is hot and some is cold. The part with a higher temperature has better fluidity and a longer solidification time; the part with a lower temperature has poorer fluidity and a shorter solidification time. When the metal liquid enters the mold cavity, this difference in solidification time will lead to the formation of traces between the first solidified part and the later solidified part, that is, flow marks. For example, suppose a part of the metal liquid has a higher temperature and can still flow in the cavity for a while, while another part has a lower temperature and has already started to solidify. Then, during the subsequent flow process, the boundary between the flowing metal liquid and the already solidified part will have a water - ripple - like flow mark. If the flow rate of the metal liquid is unstable, it is like in a river, where the water flow speed is sometimes fast and sometimes slow, and the sediment (analogous to the metal liquid) will be deposited unevenly on the riverbed, forming a similar trace.

2.Mold Surface Condition：

If the surface of the mold cavity is rough, has oil stains, or the release agent is sprayed unevenly, it will also lead to flow marks.

3.Die - Casting Process Parameters

Excessive changes in injection speed and pressure and an unreasonable gating system will also cause flow mark defects. Injection speed and pressure are key parameters in the die - casting process. If the changes in injection speed and pressure are too large, the filling process of the metal liquid in the mold cavity will be unstable. For example, a sudden increase in speed will cause the metal liquid to impact, resulting in uneven distribution of the local metal liquid; a sudden increase in pressure will also change the flow state of the metal liquid. This unstable filling process will cause the metal liquid to form flow marks during solidification because the solidification time and state of the metal liquid in different positions are different under such unstable conditions. The gating system includes the gate, runner, etc. Its design purpose is to guide the metal liquid to enter the mold cavity smoothly. If the gating system is not reasonable, for example, the position of the gate is improper, the shape or size of the runner is inappropriate, it will cause turbulence or jetting when the metal liquid enters the cavity. Such a flow state will lead to the inability of the metal liquid to fill the cavity evenly, and flow marks will easily form after solidification. It is like pouring water into a container. If the pouring method (gating system) is incorrect, the water will flow chaotically in the container and leave traces.

IV. Cold Shut Defect

When this phenomenon occurs, you may need to consider changing the supplier. A cold shut is a gap or a zig - zag - like appearance formed on the surface of the perfume. Generally, it is a defect caused by the incomplete fusion of the metal liquid. The depth, width, or continuity of the gap is different. Such a cap is prone to leakage, which will affect the perfume sealing and the appearance of the product.

Causes

1.Metal Liquid Temperature：

During the die - casting process of zinc alloy liquid, temperature is a key factor. If the metal liquid temperature is too low, it is like a liquid becoming viscous in cold weather. In this case, the fluidity of the metal liquid becomes poor. When pouring into the mold, it cannot fill the mold cavity as smoothly as when the temperature is appropriate. When different parts of the metal liquid meet, it is difficult for them to fuse smoothly. It is like cold glue that is difficult to spread and bond evenly. This will lead to the formation of unfused gaps or zig - zag - like traces between the metal liquids, that is, cold shuts.

2.Mold Temperature:

The mold itself is a large iron block and has a cold surface. When in use, the mold temperature will rise. If at this time, the mold temperature is uneven, when the metal liquid contacts different positions of the mold wall, the cooling rate will be different. When the metal liquid contacts the mold wall with a lower temperature, it will quickly cool and solidify, while other parts of the metal liquid may still be in a liquid state. The already solidified part of the metal liquid will be like a barrier, hindering the flow and fusion of the subsequent liquid metal liquid. The subsequent metal liquid cannot combine well with the already solidified part, just like pouring liquid water onto a frozen lake, and the liquid water is difficult to fuse with the ice, thus forming a cold shut.

3.Die - Casting Process Parameters:

Injection speed and pouring time are important parameters in the die - casting process. If the injection speed is too slow, the speed of the metal liquid entering the mold cavity will be very slow. During this slow process, the metal liquid will continuously lose heat to the surrounding environment, resulting in a decrease in its own temperature. At the same time, if the pouring time is too long, the metal liquid will also have more exposure time to the external environment during the filling process, and more heat will be lost. When the temperature of the metal liquid decreases to a certain extent, its fluidity becomes poor, and it cannot fuse well in the mold cavity, and then a cold shut is produced. It is like slowly heating chocolate sauce with a small fire. Because the heating speed is too slow, it has already started to solidify before it is completely melted and cannot be mixed evenly.

V. Cracking Defect

Zinc alloy perfume caps may have hot cracks or cold cracks. Hot cracks usually occur at the end of the solidification of the casting, with irregular shapes, and are distributed in a net - like or straight - line shape on the surface or inside of the product; cold cracks are formed when the casting is cooled to a lower temperature, mostly in a straight - line shape, with different lengths and widths. Cracks will seriously reduce the strength and service life of the product and may even render the perfume cap completely unusable.

Causes

1.Metal Composition and Structure:

If the content of certain impurity elements in the zinc alloy is too high, it will increase the brittleness of the alloy. The coarse grain structure formed during the metal solidification process will also reduce the toughness of the material and easily cause cracks.

2.Die - Casting Stress:

During the die - casting process, mold opening and closing, solidification shrinkage of the metal liquid, etc. will generate internal stress. When the internal stress exceeds the strength limit of the material, cracks will occur.

3.Mold Design and Process:

If the draft angle of the mold is unreasonable and the ejection mechanism is not properly designed, it will lead to difficult demolding and generate excessive demolding stress, thus causing cracks. Die - casting process parameters, such as too fast a cooling rate, will also cause the material to generate large stress.

Whether it is zinc alloy or aluminum alloy, understanding these issues in the production of perfume caps by die - casting is of great help when looking for suppliers. We can investigate the mold - making ability of the supplier, the scale and site of the factory, the technical level of the personnel, etc., screen out high - quality die - casting suppliers, and then the project can be carried out better.