Sewn fabric dunnage that fails can cost you time and money during packaging, shipping, kitting, and assembly. That’s why manufacturers, parts suppliers, rack fabricators, and logistics teams want rack bags where the seams won’t rip. Sometimes, however, seam failure happens when there’s no damage to the fabric dunnage itself. By understanding why this happens, you can make better design decisions.

The seams on parts bags can fail for many reasons, but there are four that relate to threads and stitching.

Thread type
Thread weight
Stitch count
Stitch type
 

Let’s take a look at each one.

THREAD TYPE

Using the wrong type of thread is a common mistake. That’s why it’s important to compare the rack bag environment to a thread’s material properties. If you’re designing sewn fabric dunnage that will be stored outdoors, remember that polyester thread offers greater weather resistance than cotton. Nylon thread is tough and durable, but will degrade when exposed to sunlight. Consider rack bag cleaning, too.

THREAD WEIGHT

Choosing the wrong thread weight can also cause seam failure. Thicker threads cost more, but they’re stronger. Thinner threads are lighter and less durable, but they cost less. Spools of thinner threads contain longer lengths, too. They’re easier to trim and may work well with a lighter-duty sewing machine, but using a lighter thread isn’t a bargain if your rack back design requires greater strength.  Tote bags can utilize thinner string, but that also depends on the size and weight of the automotive part being packed into the dunnage assembly.  

STITCH COUNT

Industrial sewing machines support a range of stitch counts. Because each stitch has an individual strength, increasing the number of stitches per inch increases the seam strength. In other words, a seam with 10 stitches per inch is stronger than a seam with 2 stitches per inch. More isn’t always better, however, and it’s possible to have too much of a good thing.

Stitching puts tiny holes into the base material. Because each stitch needs a hole for a knot, rack bags with more stiches have more holes. This can weaken the base fabric and allow sewn fabric dunnage to tear even when the seams remain intact. To avoid this problem, designers need a fabric dunnage supplier who can strike the right balance for stitch count.

STITCH TYPE

Lock stitches require a bobbin. With industrial sewing machines, these bobbins are large and time-consuming to change. Chain stitches offer an alternative, but it’s important to use lock stitches with sewn fabric dunnage. Otherwise, your rack bag’s seams can unravel. Lock stitching isn’t all you’ll need, however. When you use a lock stitch, use proper back-tacking to avoid having a single point failure.

CHOOSE SEWN FABRIC DUNNAGE FROM TPS

TPS supports rack bag design by selecting the right thread type and thread weight. We use the right stitch counts and stitch techniques in order to understand how to prevent problems like sagging pockets on work-in-process (WIP) bags, and can help you cut sewn fabric dunnage costs.  Whether your programs require sewn dunnage bags for totes, bulk boxes, or racks, we have the expertise to design and deliver the appropriate solution.