How to solve the overflow of blow molding machine head?

Blow molding machine head overflow is a relatively common production failure. Today, let's talk about the treatment method of blow molding machine head overflow.

During the blow molding process, the occurrence of flash is extremely important to the extrusion operation. Any changes in the production process will cause the parison to be squeezed, pinch off at the top and bottom, blow molding a mold cavity item, and the pinch off at the top and bottom will also produce excess flash. Once the flash is generated, the efficiency of blow molding will be limited. For example, after molding, additional flash removal with special equipment may also damage the good finished product; because of the increased cooling time required for the thicker area of the flash, Therefore, the cycle time of molding production is also greatly extended. There are the following ways to solve this problem:

1. The flash cools slowly, and the flash occurs at the narrow point, which means that the thickness of the flash is usually twice the maximum thickness of the product. In this way, the flash cooling time is at least twice the total time required for the molding process. We can reduce the loss of cooling time by withdrawing the product before the flash is completely cooled, and withdrawing the product while the flash is still soft. But doing so will also cause some other problems: First, when the product is pulled out during the molding process, the flash is easy to roll up and stick to the product; second, the flash is too hot and it is difficult to trim it. The total loss in both cases can greatly increase the reject rate of the product.

The solution to this dilemma is to reduce the range difference between flash cooling time and product cooling time. Achieving this goal requires an understanding of the power of cooling and extrusion blow molding, as well as a method of translating the know-how into tool design and tool improvement. Cooling time is affected by the rate of heat removal from the mold, which in turn can be optimized by clever design of air, water, or cooling channel mold processing. The cooling medium commonly used is water.

The water flow pattern in the mold and the cooling rate related to the water flow pattern can be defined by the Reynolds number. Generally speaking, if the Reynolds number is less than or equal to 2100, the water flow in the pipeline will appear laminar flow, which is poor for the efficiency of heat removal; on the contrary, if the Reynolds number is greater than 2100, the water flow in the pipeline may appear turbulent, which Make the heat removal effect better. Obviously, when designing blow-molded cooling ducts, the first consideration is the design that results in the creation or improvement of turbulent patterns of water flow.

2. Remedial measures for overflow. First analyze several possible remedies to reduce the time loss caused by flash. For most blow molding, separate inserts are designed where the flash occurs, because the pinch off usually requires a dedicated metal insert, which is not only durable but also increases the rate of heat transfer. The designer's work when designing the plug-in or redesigning the existing plug-in is simplified, and the cooling efficiency can be greatly improved by designing the plug-in as a separate cooling area. Update practices, including cooling plug-ins, are usually reasonable and feasible.

The cross-section of the traditional blow-molded insert bond line is usually horizontal, the main reason for this is that it is simpler for the mold maker to manufacture and it is less investment to machine it in a straight form. However, the trapezoidal section can greatly increase the contact area between the mold and the flash, so the effect of heat removal will be better.

The cross-section of the trapezoidal insert can also increase the stability of the flash, making the heat tail more difficult to curl under thick heat. Combining the design of the insert as a separate cooling zone and the machining of the trapezoidal shape of the insert can reduce the cooling time by 4s. Additional trapezoidal cross-section grooves on the mold pinch off the insert, which improves cooling efficiency. For irregularly shaped parts, the entire bonding wire can be designed as a trapezoidal cross-section, and the bonding wire of the two halves can be compensated to ensure that the bonding wire touches together, which not only improves the stability of the flash, but also reduces the product failure rate.

The above content is the treatment method of blow molding machine head overflow.