45 x 60 mm Aluminium Profile for Textile Machine Frames

01What excitation does a loom frame actually see?

Three sources, and they sit in different frequency bands. The first is the main shaft: a loom running at 600 picks per minute gives a 10 Hz fundamental. The second is the harmonic series above it, at 20, 30 and 40 Hz, which is where most of the energy above the fundamental actually lives. The third is the beat-up and the weft insertion, which are impacts rather than sinusoids and therefore put broadband energy into the frame, including at frequencies well above the running speed.

For a winder or a package conveyor the picture is simpler: one dominant frequency from the drive, plus a once-per-revolution component from any imbalance in the spindle or the package. Both are usually below 30 Hz.

02How do you estimate the natural frequency of a 45 x 60 span?

For a uniform beam with distributed mass and simple supports, the first bending mode is:

f1 = (pi / 2) x sqrt( EI / (m x L^4) )

where E is 69,000 N/mm2 for 6063-T5, I is the second moment of area about the bending axis in mm4, m is mass per unit length in kg/m, and L is the span in metres. The same number can be reached from the mid-span stiffness k = 48EI/L3 and the modal mass, which is 0.49 of the total mass for a simply supported beam; the two routes agree, and checking both is a good way to catch an arithmetic slip.

03Why does dynamic stiffness matter more than static stiffness?

Static stiffness tells you how far the frame moves under a steady load. Dynamic stiffness tells you how it responds to a load that changes direction ten times a second, and the two are related through damping and mass, not through the section alone. A frame can pass a deflection check at 1.8 m and still vibrate visibly, because the deflection check uses a load the frame never actually sees.

The transmissibility curve is the practical version of this. Below about 0.7 times the natural frequency the frame follows the machine almost rigidly. Between 0.7 and 1.4 times it amplifies. Above about 1.4 times it starts to isolate. That is why the target is either well below or well above the excitation, never in between, and why adding mass to a frame that is already resonant makes it worse rather than better.

04Where does micro-sliding destroy the joint?

At the faying surface inside the connection. An M10 bolt at 30 Nm develops roughly 17 to 20 kN of preload. With a friction coefficient of about 0.15 between two anodised aluminium faces, the slip resistance per interface is around 2.5 to 3 kN. Under a static load that is a large margin; under a reversing load it is a fatigue question, not a strength question.

The failure mode is fretting. Small relative movement, on the order of a few micrometres per cycle, breaks the anodic film, exposes bare aluminium, and generates oxide debris that is harder than the parent metal. The debris accumulates in the joint, the preload drops as the joint beds in, and the movement grows. The frame does not break; it loosens, and then it rattles at a frequency that has nothing to do with the machine’s running speed.

• Use a hardened washer under the head and under the nut; without one, the aluminium yields locally and the preload is lost in the first week.
• Re-torque after the first 100 hours, then at the first service interval. Bedding in accounts for most of the preload loss.
• Keep the joint dry and free of release agents. A lubricated joint has a lower friction coefficient and therefore lower slip resistance, which is the opposite of what people expect.
• Prefer a connector that engages both slot flanges over a single central bolt; the load path is shorter and the faying area larger.

05Should you isolate the foot or stiffen the frame?

Isolate the foot when the frame is already stiff enough and the problem is transmission into the floor or into a neighbouring machine. Stiffen the frame when the problem is relative movement inside the frame itself, which is what shows up as the yarn path moving rather than as noise.

The distinction is easy to make in the field: put a hand on the frame and on the floor. If the frame is quiet and the floor hums, isolate. If the frame itself is moving, isolation will not help, and in fact a soft foot mount lowers the system frequency and can make a marginal frame worse.

If you do isolate, size the pad so the mounted system frequency is at most 0.5 times the lowest excitation, and check the static deflection the pad introduces. A pad soft enough to isolate 10 Hz will deflect several millimetres under the machine weight, which changes the alignment of everything bolted to the frame.

0645 x 60 or 45 x 90 at 1.8 m?

At 1.8 m the 45 x 60 section sits at about 34 Hz and the 45 x 90 at about 44 Hz, on the estimates above. For a 600 rpm loom with harmonics to 40 Hz, neither is comfortably clear: 34 Hz is 13 percent from the 30 Hz harmonic, and 44 Hz is 10 percent from the 40 Hz harmonic. Going up a section moves the mode but does not automatically solve the problem, which is the part most selection tables leave out.

The three moves that actually work, in order of cost: shorten the span, add a mid support, or change the section. Shortening from 1.8 m to 1.5 m raises the frequency by 44 percent because it scales with 1/L2, taking 45 x 60 from 34 Hz to about 49 Hz. A mid support does the same thing in a different way. Changing to 45 x 90 raises it by about 29 percent, which is the least effective of the three per unit of cost.

Span

the clear distance between supports, not the cut length

Machine speed

picks per minute or drive frequency, so the harmonic band is known

Load on the span

cable, package, and any static equipment weight

Joint type

connector and bolt size, because the joint sets the real frequency

Foot condition

floor, existing pads, and whether the frame is tied to other machines

Section

45 x 60 mm four slot, 2.8 kg/m with 10.2 mm slots or 3.3 kg/m with 8 mm slots

Related sections and categories

The full 45 mm pitch range is under 45 Series Aluminium Profiles. For spans past 1.8 m the 45 x 90 mm six slot section at 4.10 kg/m is the next step up, and the bolted joint options are in joining plates.