Aluminum Tube Sealing Issues
AnC Tube Sealing Analysis
The plastic tube industry is continually developing new types of tubes, often multi-layer. These new tubes may solve various end user issues but create new sealing issues. Many of these new tubes cannot run on conventional sealing machines as they will create sealing issues on said conventional sealing machines. For example, low end sealing machines, such as Ultra-Sonic Sealing machines, often cannot seal these newer types of tubes. Larger higher throughput machines such as Norden, IWKA, Prosys, etc. require more precise adjustments to insure a good seal. These older, high production machines may not have the necessary precision in the adjustments to make and insure a good quality seal.
It is imperative that end user companies, who are using newer types of tubes, have the necessary equipment to evaluate the tube seal. For example the PTS-100 Tube Sealing Test Station is a good, cost effective instrument to evaluate the quality of the seal.
This article takes a standard Aluminum Tube and evaluates the seal by examining a cross section microscopic evaluation of the sealing area. The evaluation shows several issues that should be discussed.
Flaw in Sealing Area:
Several of the photos show a flaw in the sealing area. The flaw is similar to a fold in the multilayer tube. This is a good example of the newer, multi-layer tube manufacturing technology, causing difficulty in the actual sealing process. The reason for this flaw is due to excessive heat. Since this tube is a multilayer tube with an aluminum layer on the outside and plastic on the inside. If excessive heat is applied it will cause the aluminum and plastic to delaminate causing, what appears to be a fold in the outer surface. This type of defect could not happen with a single layer plastic tube.
The cross section shows how thin the seal actually is. This tube did pass the seal pressure test but is very close to being excessively thin, predictably causing future failures. In the last photo, the sealed wall thickness is only 0.005” (0.127mm). This is a little thicker than a standard piece of paper. It leaves the tube somewhat fragile and daily use may fail.
As new tubes (multi-layer) are introduced into the marketplace it increases demands on production equipment. Some older tube sealing machines will face greater difficulty in producing consistent reliable seals. Other production machines may have to be replaced with new Hot Air Sealing machines. The need for testing and evaluation equipment becomes more important as the tubes become more complex.
Laboratory test procedures:
The tube was sealed at the AnC production facility using an AnC TS-100 Sealing Machine and submitted for microscopic examination.
July 27, 2015:
Silver tube with no identifying markings with a blue cap, size approximate: 7” long by 1.5” in diameter.
Four as received photographs taken: overall view, end view and two side views of seal using a Nikon D90 SLR with a DX 18 – 55 mm lens.
Three sections of the heat seal was removed with a # 11 scalpel blade and mounted in a 1 inch diameter specimen mounts made of clear polyester casting resin. One section shows a surface defect in the seal on one side of the tube and the other section shows no defect.
July 28, 2015:
The mount was then ground and wet polished to 4000 grit paper.
The polished cross-sections were then examined and photographed using a AmScope SM-4TZ-144-SMT Trinocular Stereo microscope equipped with a 14 megapixel camera.
Figures 001 through 004 show the tube as received.
Figure 005 shows the seal area with deformation damage across the seal. It is unknown where or when this damage
was made on the tube .
Figure 006 shows the cross section through the damaged area of the seal.
Figure 007 shows a cross section away from the damaged area with different areas identified.
Figure 008 shows the cross section of the seal looking down the tube length.
Figure 009 shows the cross section with measurements at different points along the section.
Investigating Engineer: L. J. Havemann, Failure Analysis Engineer, Retired