New accumulator blow molders let you change colors quickly.

Quick head cleanout, easy-to-use controls, and economical design with lots of built-in flexibility and numerous standard options are claimed for the first line of accumulator-head industrial blow molding machines to be introduced by Graham Engineering Corp., York, Pa. (Initial details on these machines appeared in PT, April '95, p. 13.) The machines were designed with the aid of industry veterans Robert Slawska and Charles Magnani, both formerly of Sterling Extruder Corp., who also act as marketing consultants to Graham.

The machines are built to be cost-competitive in two ways. One is to hold down initial purchase price. The new models use parts common to Graham's wheel and shuttle machines wherever possible. Also, regenerative hydraulics allow use of smaller pumps and hoses, in addition to saving energy and speeding operation. Parison programming is accomplished with Vickers proportional valves instead of servos. This approach is less expensive, gives equally fast response, and is easier to maintain (less dirt-sensitive), says Slawska.

Second, the new machines are economical to use. Slawska emphasizes that the head design offers the quickest color changes of any accumulator machine on the market. "Color changes have always represented long production delays and a significant amount of wasted materials," he notes. "The new machines will compete on uptime." A complete clean-out and restart reportedly can be performed in one hour. (Graham offers to retrofit these heads on other brands of existing machines.)

The new machines are available with heads from 1 to 50 lb. Dual heads are offered for 3 to 20 lb, triple heads for 1, 3, and 6 lb. Standard clamp forces are 40-160 tons, with other sizes optional. Clamp sizes run from 36 x 26 in. to 72 x 60 in. Three tiebars are standard, four are optional. Graham's proprietary extruders come in 3-in. to 6.54-in. diam. with smooth or grooved bore. The standard head is said to run all forms of PE, as well as PP, ABS, PETG, and a wide range of engineering resins.

EASY-CLEAN HEAD DESIGN

Plunger and diverter on the heads can be hydraulically retracted to give full access for cleaning. Heads are said to be easy to assemble and disassemble, requiring few tools and having no complex parts to fit together. The plunger has no top surface where bleed-out plastic can accumulate and degrade. The plunger and programming-mandrel extension rod each has its O.D. coated with a hardened anti-seize material. An adjustable flow-diverter gap permits optimizing the melt "reknit" and concentricity of flow distribution. The design and close tolerances of the body, diverter, plunger, and program extension rod prevent side-to-side movement of the mandrel during parison formation.

QUICK-ACTING CLAMP

The roll-out damp is mounted on rails for easy access to the heads and molds. Full-length end frames and all-welded, unitized construction of end frames and base plate are said to minimize deflection. Small "kicker" cylinders provide fast opening. High-pressure clamping is also rapid, thanks to positive pressure on all cylinders, which is said to provide immediate lock-up tonnage. Besides eliminating clamping delay, positive-pressure hydraulic circuitry also prevents pump cavitation.

Parallel movement of platens is ensured by a rack-and-pinion yoke assembly. An electric motor and linear potentiometer permit pushbutton vertical adjustment of the clamp [+ or -]3 in. Simple two-point manual front-to-back horizontal clamp adjustment is standard. Powered adjustment is available as an option.

Graham also offers a robot part remover with pneumatic actuation, single- or dual-station water-cooled grippers, and optional hinged mounting to allow it to swing out of the way. Also optional is lateral position adjustment to permit recentering on the heads if necessitated by thermal expansion.

EASY-TO-USE CONTROLS

Graham uses the new Barber-Colman MACO 6500 system to control temperature, sequence, and parison programming (see PT, April '94, p. 23). This machine-mounted controller has a single power supply and an electroluminescent display whose high resolution allows condensing more information onto fewer screens than previous MACO 8000 CRT displays. The controller offers up to 24 temperature zones per chassis with manual or auto tuning, "standby" and "run" set-points, high/low and deviation alarms, and alarms for thermocouple break and heater burnout. Parison control provides four separate 100-point profiles per parison card, selectable interpolation methods, and closed- or open-loop control. SPC display is optional.

Graham has incorporated its own "value-added" software features into the MACO controls to make them even easier to use. All necessary information has been compressed into a maximum of nine screens (compared with up to 50 on the MACO 8000). Just five screens contain the most commonly used information - temperatures, parison profile, cycle monitor, clamp setup, and timers. In addition, Graham provides pressure-control feedback loops for programming backfill of each head independently. The latter feature makes it easy to synchronize multiple heads.