One of the most difficult applications to properly drain condensate involves calendar rolls. A typical corrugating machine with two single facers and a triple stack heater will have up to 18 rotating rolls to be drained to provide for a hot machine-typically 350 F on the calendar roll surface.

A wide variety of reputable manufacturers provide ROTARY JOINTS and condensate drainage equipment providing you with the opportunity to maintain uniform hot surfaces in your machine to provide a uniform bond and keep scrap levels low. Here are some tips to help you tie all the equipment offered into an efficient system.

As a cylinder turns the condensate which forms inside the roll is subject to centrifugal forces. As the RPM of the cylinder increases the condensate puddle which forms will begin to rotate from the 6 o’clock position and begin to walk up the inside cylinder surface. For clockwise rotation puddle will tend to move toward the 7-8-9 o’clock positions and for counter clock wise rotation toward the 5-4-3 o’clock positions.

To determine the position you need to know the roll RPM which can be either measured with a tachometer or calculated as follows-

1. Determine the calendar roll diameter in feet.

2. Calculate the roll diameter from Circumference = Diameter (feet) x 3.14.

3. As an example for a 30” roll, the circumference would be 7.85 feet (2.5 ft x 3.14).

4. For a 48” roll, the circumference would be 12.56 feet (4 ft x 3.14).

To calculate the roll RPM, divide the machine speed in feet per minute by the roll circumference. Use the highest machine speed for the worst case scenario in draining your rolls. As an example you operate your machine in a range of 400 to 650 feet per minute depending on weight and grade of liner board being run. Use the 650 FPM figure and calculate as follows-

1. For a 30” roll it would be 82.8 RPM (650 FPM divided by the circumference of 7.85 ft)

2. For a 48” roll it would be 51.8 RPM (650 FPM divided by the circumference of 12.56 ft)

The rule of thumb for the position of the condensate puddle is as follows:

• Up to 100 RPM the puddle would be at the 6 o’clock position

• Up to 150 RPM the puddle would be at the 7-9 o’clock positions for clockwise rotation and the 3-5 o’clock positions for counter clockwise rotation.

• Above 150 RPM the condensate is rimming around the entire inside surface of the calendar roll.

As with all rules of thumb they are designed to give you a gut feel as to what is in fact going on inside the roll. Many variables can come into the play but recognize the condensate puddle will move based on roll RPM.

ROTARY JOINTS are offered in many different styles and sizes. Consult with your corrugator machine manufacturer for suggestions, the rotary joint manufacturer or with us.

Here are some tips on joint installation that can save you a lot of problems.

• Make sure the rotary joint is properly supported and securely mounted depending on style.

• Make sure the FLEXIBLE HOSES supply steam and the drainage connections have a drape so as the joint is pressurized it can move radially away from the roll being drained. If your hoses are tied straight into the joint you in effect have hard piped the joint which will shorten the life of the joint and lead to premature wear and other problems.

• Hoses which are too long can kink and lead to drainage as well as failure problems.

• We suggest installation of isolation valves on both supply and return to you can quickly isolate a rotary joint in case of problems.

• Make sure the flexible hoses you select are rated for your steam pressures and temperatures. Resist the temptation to field repair leaking hoses and replace them. To our knowledge no rubber hoses are offered suitable for this service.

Placement and installation of the siphon pipe is part engineering and part trial and error. The end or tip of the siphon pipe should be placed as close as possible to the inside diameter of roll being drained. Ideally the gap should be 1/8 to ¼ inch to reduce the size of the condensate puddle which can impact heat transfer and increase machine drive HP requirements. Closer is generally better but be aware of the inside diameter not being concentric with the roll rotation and adjust to avoid siphon pipe contact with the roll inside diameter.

Siphons are typically either bent pipe or use a siphon elbow.

We tend to suggest siphon elbows be considered since the length of the lower siphon pipe can be determined and generally results in most consistent siphon gap inside the roll.

Another issue to consider is what to do with the machine steam system during periods when you are not running product. A typical corrugating machine will pull about 6,000 to 7,000 lb/hr of steam when operating. About 60-70% of the thermal energy is used to keep the machine hot so when the machine is idle about 3,600-5,000 lb/hr of energy is being used to maintain machine temperatures.

At first blush the solution would be to shut the steam off and pick up the savings but that can lead to major issues in getting back up to temperatures with the rotating rolls typically being the problem area. After trying many solutions, from simple to complex, we suggest you consider dropping boiler pressures back to a lower setting.

Assume you are operating two shifts five days a week. You might consider dropping back to say 50 psig steam pressure on the off shift and then shut down for the weekend. Corrugating machines tend to be unique so experiment and see what works best in your plant. Much will depend on your machine drainage and waste heat recovery systems. Contact us if you need suggestions on simple boiler set back options.

Volumes have been written on draining condensate from corrugator machines. Steam traps are typically still utilized in the majority of the installations and proper piping practices and steam selection can avoid a lot of problems.

The installations shown typically are suggested and work very well with one caveat. All steam traps will fail due the severe conditions under which they operate. Service life for traps will vary widely and depend on many factors such as hours of operations, pressure, condition of the steam and proper water treatment just to name a few.

Irrespective of STEAM TRAP TYPE and brand realize that all traps will fail-not if but when. The solution requires that you be vigilant and check traps on a regular basis for proper operation. Since the ability of the trap to operate properly is totally dependent on the health of the rotary joint treat them as a system. As you trouble shoot roll temperature issues a bad joint installation can cause trap problems and trap problems can lead to joint failures so always check both.

Since corrugator steam, condensate, and waste heat recovery systems come in many types and styles, establishing a base line when your steam systems are operating properly can save you a lot of trouble shooting time.

Examples of both a cascade and direct condensate return systems are shown in schematic format. Most likely you have a version of one of these systems in your plant. Schematic PDF

Cascade Return System Schematic

Direct Return System Schematic

Since either system can be complex and challenging to trouble shoot, having pressure gauges or transmitters installed on primary and secondary systems can be a life saver in locating and solving problems.

Consider installing them on-

• Primary steam headers

• Steam headers to single facers, triple stack heaters and double backer zones

• Condensate return headers

• Condensate return lines from single facers, triple stack heaters and double backer zones

• Boilers

• Boiler feedwater pump discharge lines

• Deaerator or feedwater heater

• Waste recovery systems

Always use good quality ½ to 1% accurate gauges. Install pressure gauge accessories such as pigtail siphons and shut off valves. For pressure gauges use a snubber on the siphon and liquid filled gauges to extend the gauge life. If you use pressure transmitters it is wise to install a mechanical gauge with the pressure transmitter to provide local readings and also verify the transmitter is operating properly.

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