The “mismatch” that causes medical tube extrusion problems

有时，我听到了挤出机的消息，这些挤出机在无法获得所需的精度和质量水平。有人问这是否可能是一个问题科尔downstream equipment– like ourMedVac® cooling/sizing tanks– or how they are using them. Usually, however, their troubles relate to a mismatch between the materials they are extruding and the sizing/tooling approach that they’ve selected.

Before I explain further, let’s take a quick look at the sizing process.Vacuum sizing从热材料从挤出机中传递到真空水箱中的冷却水的点开始。在此界面上，挤出物通过尺寸工具，该工具管理管的受控尺寸。尺寸工具将外部压力（接触或非接触）与挤出物的自然收缩相结合，因为水冷却去除了热量。manbets下载尽管发生了外部真空尺寸，但管子的内部轮廓是通过管子内的轻微正压维持的，这是由空气在挤出过程中排出到管子剖面中的空气所产生的。

When you’ve got the right tooling working, optimizing the extrusion process is a straightforward, incremental process that uses the precision controls offered in theMedVac® tank和MedLine® puller/cutter和, if necessary, coordinates them with upstream extrusion process controls. But if you’ve got a tooling/material mismatch, that “dial in” the process is going to be a struggle, resulting in problems like:

• Slower-than-expected production rates, an inability to get line speed “right.”
• Inconsistencies in surface finish, including “chatter” marks
• 不可接受的尺寸可变性，导致不断需要“调整”设置。

好消息是，如果您要遇到这些问题，您会尽早看到它们，并且可以解决。坏消息是它们通常是由我谈论的那个不匹配引起的。考虑到您的材料，让我们回顾可用的尺寸选项：

• Contact sizing最适合较硬的材料，例如聚乙烯和聚丙烯。此过程涉及将一个或多个不锈钢尺寸磁盘放入工具中，然后将热挤出通过它们并进入冷却水中。通过与尺寸磁盘的倾斜边缘和水冷却引起的材料收缩的表面接触，可以通过表面接触来实现管道。manbets下载
• Non-contact sizing开发以处理柔软，粘材料，包括柔性PVC，聚氨酯和TPE。非接触式manbets下载工具取代了金属尺寸磁盘，其中像这样的粘性材料往往会捕捉或挂起，孔比挤出量稍大。冷却水被输送到该孔中，然后通过真空吸收到水箱中。水在管道周围形成薄液压层，其湍流和冷却作用有助于尺寸。
• Hybrid sizingis a third, much less common approach, which utilizes a specially built tool that combines elements of contact and non-contact sizing for materials and applications that don’t fit neatly with either approach. An example would be an extrusion involving a semi-rigid PVC that sticks to the sizing tooling, yet needs a higher vacuum level than non-contact sizing can provide. In this case, hybrid tooling would utilize a quench chamber to set a skin on the product that would then enable it to be sized using the contact sizing approach.

Determining the right amount of drawdown—the ratio between the extruded size/finished size of a tube—is an important factor when you’re using a contact sizing approach. The diameter you select for the contact sizing disk is especially important, since it plays a dual role: it must be small enough to properly size the tube (and prevent leakage from the vacuum tank), yet large enough to prevent excessive pulling force and an excessive degree of drawdown on the tube.

Providing the right amount of drawdown ensures dimensional stability while retaining the physical properties of the material that are essential to medical tube performance. Too much drawdown can result in longitudinal shrinkage and loss of essential physical properties due to stress on the molecular structure of the material.

MedVac flood-cooling/vacuum-sizing extrusion sizing tanks are part of Conair’s growing MedLine series ofcleanroom-ready production equipment. MedVac tanks give extruders a new level of control over all of the downstream factors involved in extrusion of high-quality, high-precision medical tubing. Conair MedLine equipment is pre-evaluated, pre-configured, pre-calibrated, fully-documented and ready for installation in your cleanroom.

If you’ve got questions—about extrusion applications or sizing/tooling problems—Conair has answers. Just send us a信息or give us a call.