Carpet tufting creates a tough environment
for linear motion products. Processing synthetic fibers into carpet
backing using a high speed, reciprocating short stroke machining system,
a carpet manufacturer was experiencing unplanned downtime due to linear
bearing failure and massive profit loss due to thousands of yards in
scrapped end-product. Poor quality and damaged carpeting were sited as
the main reason the manufacturer lost up to 54,000 yards of carpet to
scrap. When PBC Linear came in to examine the application, they
discovered the root of the problem was the machine’s ball bushings
within push down foot assembly.
Each carpet tufting machine uses 36 ball bushing bearings and steel
shafting assembled into a pushdown foot system (4 bearings and 2 rods of
steel shafting per pushdown foot, an average of 9 pushdown feet per
machine). This system is utilized within the application to operate the
needle bar in quick, reciprocating up to 1600 cycles/minute short
strokes. The needle bar holds 4000 tufting needles that conduct the
crucial processing of the fibers. Precise and repeatable linear motion
is necessary for optimum manufacturing and the minimization of scrap.
The manufacturer also employs non-stain oil along the pushdown foot
assembly to ensure smooth linear motion and reduced friction.
The environment of the application is
typical for industrial machining. Dust, dirt, grease and carpet fiber
particles pose risk for contamination, but no adverse or caustic
chemicals are present. The carpet tufting machine is designed to run for
continuous, long cycles; therefore the performance is measured by the
life of the system and linear feet ran between replacement systems.
High speed reciprocating short stroke (.5’’-.625’’) created high impact
loads on the system; resulting wearing ball bushings and shafting. This
represented the bulk of the shutdown scenarios where maintenance and
product replacement were necessary. 1600 cycles/minute raised high
reverse inertia, prompting almost immediate wear of the ball bushings
and steel shafting. As operation continued, the ball bushings spall fine
metal particulate from the shafting, which accumulate within the
assembly, wear the seals, and allow lubricants to contaminate the
pushdown foot assembly and ball bushings. This mixed with metal
particulate created by the ball bushings and shafting to create “black
spots” on the finished carpeting. These black spots cannot be washed
out, resulting in scrap carpet.
The performance quality of the ball bushing
system also posed problems and created scores of scrap carpet. The
inaccurate tolerances (.005/.007’’) of the ball bushing system allowed
for rocking motion along the needle bar. This phenomenon, known as
needle wander/loss motion, results in loss of positioning and missed
tufts—leading to poor quality carpeting. This occurred almost
immediately after the initial installation, and grew more prevalent as
the system wore under use. Throughout operation, loss motion and
contaminated carpet resulted in 34,000-54,000 yards of scrap material
and lost profit.
To solve the
problem of wear and progressive wander/loss needle bar motion, PBC
Linear outfitted their Simplicity® self-lubricating bearing into the
specified pushdown foot assembly for the carpet tufting machine.
Simplicity’s close tolerance ID bearing (.6240’’-.6245’’) and close
running clearance (.0015’’-.0018’’) held the needle bar in tight
position for precise and repeatable operation. The bearing’s proprietary
FrelonGold® liner ran smoothly along steel shafting and eliminates wear
by evenly disbursing the load throughout the bearing; rather than the
small point of contact ball bushing products make with shafting.
Simplicity® bearings contain no rolling elements, thrive in heavy load
applications, and push contaminants such as dirt, carpet fiber
particulate and grease to the end of the stroke. In short, they were
designed to exceed expectations in applications like this.
Before PBC Linear’s Simplicity® pushdown foot system and undercarriage
were installed, the carpet tufting machines were in a state of constant
unplanned downtime due to high maintenance costs and upkeep. After the
Simplicity systems were installed in the carpet tufting systems, they
became the most productive machines in the plant! Linear footage between
maintenance rebuilds of the machine were increased from one million
linear feet to over three million. The carpet manufacturer was also
pleased to report a significant 95% reduction in scrapped product,
eliminating millions of dollars in scrap every year that was previously
thought of as “an acceptable loss.” Now, they have turned these losses
into pure profit!