Canadian Plastics

Central Drying: It’s All in the Details

The evaluation of three central drying and conveying systems for his custom molding plant all hinged on the engineering details of the individual components, says bala nagothu, president of tri-star p...

September 1, 2000   By Cindy Macdonald, associate editor



The evaluation of three central drying and conveying systems for his custom molding plant all hinged on the engineering details of the individual components, says bala nagothu, president of tri-star plastics.

Tri-Star has been growing rapidly in the past few years, and has now outgrown its 54,000 sq. ft. plant. The custom molder maintains a diversified customer base, and was recently certified to QS-9000 standard.

“We reached a point where manual loading was no longer feasible, so we had to decide whether to pursue individual loading and drying or central.

Considering our handling needs for multiple materials, factoring in the possibility for error, and the labor costs, we decided to go for a central system.”

A central system from Conair was installed last month at Tri-Star’s plant in Scarborough, Ont.

By centralizing the materials handling, Nagothu felt it would minimize the movement of material, and lower the possibility of material loss. As well, keeping the loaders and dryers away from the injection molding machines allows more room for robots, assembly, mold changes and operator functions.

“I initially looked at three suppliers,” says Nagothu. “Then I did background research using magazines and literature, and narrowed my selection to two suppliers that I would evaluate.”

“I got the impression that one company was answering my questions in a way they thought would make me happy. But with Conair, I was impressed that they took the time to educate me.

“It is critical to educate yourself about the details of the system — the construction of the heat boosters, the hopper design, handling of fines, etc. I have found that other people make a decision based on the impression of sophistication, then they have to solve small problems with their system and try to blame the suppliers. The key is to educate yourself before deciding.”

For example, Nagothu was worried about the different pellet sizes of regrind, virgin and masterbatch materials separating during the conveying. Conair suggested mounting blenders on the machine throat to alleviate this problem.

Another consideration was the hopper design. Conair’s drying hoppers are engineered to achieve mass flow, which means all the material at a given level in the hopper moves through at the same rate, instead of the material in the center funneling down more quickly.

“The most difficult aspect of system design is sizing the pumping system for the proper duty cycle,” explains Blair Stephen of Stephen Sales Group, Conair’s representative in Canada. “In this case, we separated the plant into two separate systems, one feeding ten machines, one handling eleven.” For flexibility, fantail manifolds near the drying banks allows the lines to be connected to different hoppers if needed.

The system uses one CD800 dryer and one CD400 dryer. Conair’s CD dryers are a carousel type that provides closed-loop desiccant regeneration for spike-free drying. Heat boosters for each hopper allow individual drying setpoints. As well, the dryers are equipped with a drying monitor which measures conditions inside the hopper.

Nagothu’s system also includes the SLC48 Sentral Loader Control from Conair. A high-speed industrial PC with a full-color touch-screen LCD control face drives the SLC48. A color-coded display gives operators an instant understanding of the status of each loader while additional screens give detailed information in plain language.

Planning ahead: When installed, the 21 drying hoppers will be mounted on individual stands so that the system can easily grow with Tri-Star as it moves to larger premises.


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