Couplings absorb high torque loads

New model high speed veneer slicers from Merritt Plywood Machinery incorporate the latest servo drive technology with Zero-Max CD couplings.

New model high speed veneer slicers from Merritt Plywood Machinery produce up to 90 sheets per minute of high quality wood veneer in sheet sizes up to 4m long x 900mm wide x 0.5mm thick.

These systems are operated two to three shifts per 24 hour day with virtually no downtime for maintenance thanks largely to their robust design which incorporates the latest servo drive technology.

Merritt PMI of Lockport, New York designed its new MS-40 vertical veneer slicer with a patented vacuum flitch (wood log) loading mechanism which is fully integrated into the machine.

The design provides faster flitch loading and thinner backing boards resulting in higher veneer yield.

To achieve the 90 sheet per minute output, the servo drive turns at 2400rev/min with intermittent clockwise and anticlockwise cycle of 0.6s/5min.

The design challenges for the servo system - precision positioning and slicing, high reverse loads and continuous operation - require use of Zero-Max CD couplings which absorb the high torque loads and reciprocating motion.

"We evaluated different types of couplings for our MS-40 vertical veneer slicer and settled on the CD coupling because of its superior torque load handling features", reported Mark Lorenc, Design Engineer.

"With the rapid start/stop cycling of this system, motion control is really critical".

"The couplings absorb any backlash tendencies in the power train so there are no damaging forces imposed on the servomotor or other connected components in the system's drive train".

Three CD couplings are used in the power train of the system which has a T-shape configuration.

At the base of the T is the servomotor power source.

The output shaft of this servo motor connects to a Zero-Max CD coupling which connects to the input shaft of a right angle cone drive gear box which forms the top of the T-shaped drive system.

The two output shafts from the gearbox are connected to two additional CD couplings which connect to two lead screws.

These lead screws drive the reciprocating knife carriage which slices the sheets of wood veneer.

The goal for this drive train design is to keep motion under control with smooth, uninterrupted high speed operation.

That requires top notch engineering as well as the best off-the-shelf components which this system has.

There's ample power driving the system using a 40hp servomotor and a special low backlash worm drive with an output torque rating of 351Nm at 6 arc/min.

Lorenc said he and his engineers considered a variety of coupling alternatives for the drive train design.

They decided on the Zero-Max CD couplings because of their ability to handle high torque loads and dampen any backlash in the system from its reciprocating motion.

"We needed the most durable coupling we could find", reported Lorenc.

Acceleration is fast, and the change from clockwise to anticlockwise rotation can create problems for the system unless motion forces are controlled properly.

The torque loads imposed on the components are handled very well because of the CD coupling's unique torsional stiffness design.

The coupling has a patented open arm disc pack made of a rugged composite material which reacts to coupling forces with high torsional stiffness.

The coupling has the ability to lessen reaction loads in heavy duty applications like Merritt PMI's while absorbing and dampening shock and vibration.

The disc's composite material has a ply or fibre orientation to it, which gives it rigidity and also has damping effect on shock and noise.

Three CD couplings are used in the system.

Two Zero-Max 6A52QD models are used to connect the cross shaft and bevel gearbox.

With a 133mm diameter, these coupling sizes have continuous rated torque of 402Nm and torsional stiffness 168,656Nm/rad with a maximum of 5.65hp at 100rev/min.

One Zero-Max 6A76QD model coupling connects the servomotor and the cone drive gearbox.

It has a 197mm diameter with rated torque of 1763Nm and torsional stiffness of 609,303Nm/rad and a maximum of 24.75hp at 100rev/min.

Both couplings are the CD QD quick disconnect variety which means the hubs are machined to accept standard QD bushings and are easily assembled into the system.

No alignment tools are needed.

Lorenc and his engineers also preferred the CD couplings because they are designed to withstand harsh chemical and moisture environments with temperature extremes from -57 to +121C) so they handle the moisture rich environment in the Merritt PMI system without maintenance requirements or contamination problems.

(Conventional steel disc and elastomeric couplings often fail when operating in harsh environments).

In addition to hardwood veneer and plywood production systems, Zero-Max CD couplings have application in many different servomotor systems including packaging, machine tool, printing, paper converting and special machinery.

Back to top