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Glossary of Dip Molding

Terms

Air Trapping- A pocket on a dip mold mandrel or tool that will trap air during the dip process. This forms a hole in the coating and eliminates the need for a secondary operation of stamping the hole.

A.R.T.S. station- Automatic Rack Transfer System primarily designed to be used in conjunction with a rotary dip molding machine. The ARTS increases the number of operator positions for unloading and reloading racks without taking them offline. The system also allows positions for additional cooling and cleaning and priming metal parts for coating preparation or for automatically lubricating mandrels.

Blower- A high temperature air mover that increases turbulence and heat transfer to the mandrel or tool in the preheat oven. Blowers are also used in the cure oven to accelerate curing and decrease heat stratification (uneven heating).

Closable Dam-Some dip tank models employ a closable dam to completely stop the flow of plastisol over the weir during the actual dip cycle. This requires synchronization with the dip tank agitation and recirc pump cycle.

Dip Line- 1. The uppermost edge of the plastic coating that has been dipped. 2. An entire system or production line designed to convey raw material, prime or lube tools, preheat, dip, cure, cool, eject, and convey finished parts to a packaging area.

Drum Pump- A pneumatic pump that fits through a standard bung in a drum. Used to transfer plastisols from drums or totes to the dip molding tank reservoir.

Fill the Pipeline- This phrase refers to the process of initially starting a rotary or in line machine when “feeding” mandrels or tools to the machine. Depending on the cycle time and size of the machine, several cycles may be required after startup to actually completely preheat, dip, cure, cool and receive parts for stripping or unloading.

HMI-Human-Machine Interface. A graphic, numeric, or alphanumeric display that allows operator inputs by keypad, mouse, touch screen, keyboard or other device to setup and control the machine. The enhanced HMI for a dip molding machine is PC based control with custom screens for controls, diagnostics, production counting, secured (global) screen, temperature monitoring, and production setup. This HMI can also be accessed remotely from the factory to help with troubleshooting and upgrading features to the machine. Recipe storage (dip profiles, cycle times, cooling speeds and times, etc.) is also available on this type HMI. This HMI is usually networked into a LAN for other internal needs such as scheduling, production reporting, email, and SCADA (supervisory control and data acquisition) requirements. Historization can be achieved by storing process information onto the hard drive, CD, or other media for ISO or other agency tracking requirements. 

Interlock- An electrical or mechanical device that will not allow the machine to cycle if not in the correct position. i.e.- The turret on a rotary machine will not index unless the safety light curtain, cooling tank (if used), dip tank, oven doors, primer tank (if used), or safety gates are not in the correct position. An interlock screen on the HMI shows what interlocks are active.

Mandrel- usually a steel, aluminum or other alloy shape (extruded or machined) that will form the internal shape of a dip molded part. Multiple mandrels are normally mounted to a bar. The bar is then placed into a master rack or mounted directly on the arm of the machine.

Master Rack- a steel or aluminum frame with indentations or pins symmetrically placed in order to retain adapter bars. Master racks are usually designed for a specific dip molding machine and can be used with many similar bars of tooling.

Overhead Dip Station- This design is used with rotary and horseshoe style machines. It can be a 2 axis or three axis design. The 2 axis design removes preheated racks of tools or parts from the machine by using the vertical axis then laterally moves the parts to any of up to 4 dip tanks. Profile dipping is then accomplished by moving the rack of parts vertically, at different speeds, into a stationary dip tank. The 3 axis machine adds a lateral axis so that 2 or more pairs (4 or more tanks) of dip tanks, located side-by-side, can be accessed with diagonal motion. This cuts critical time lag getting preheated parts to the dip tank before they cool. Overhead dip stations are used when either multiple dips are required or when several colors or grades are being processed constantly (without the need to change dip tanks).

Pawl- The j-shaped gripper used on overhead dip stations to grab the rack of tools to be dip coated. These are usually pneumatically actuated in pairs.

P.I.D. Control- Proportional, Integral, Derivative control. A microprocessor based, algorithmic controller that analyses a particular analog input, compares it to a desired set point and creates an analog or digital output to modulate current (usually through a SSR or SCR) to an electric heater system. This can be a stand alone controller such as a Watlow 988 model control or can be part of a PLC control. 

Plastisol- Vinyl plastisols are dispersions of fine particle size polyvinyl chloride (PVC) resins in plasticizing liquids. In addition to the reins and plasticizers, heat and light stabilizers, color pigments, flame retardants, blowing agents, or many other additives can be included as determined by the intended product. Plastisols are liquid at room temperature. Depending on the compound, they can be pumped, sprayed, or cast. Once applied plastisols are fused with heat in relatively thick sections without concern for solvent or water blistering; they are commonly referred to as 100% solids material. As a plastisol is heater, fusion takes place and is converted into a tough, homogenous mass with excellent abrasion, aging, corrosion, and electrical resistance. These compounds can range in hardness from an 8 Durometer, Shore A, fishing lure plastisol, which is mostly plasticizers, to a 65 Durometer, Shore D, rotocasting plastisol which is mostly PVC resin.

PLC- Programmable Logic Controller. A microprocessor based controller programmed to create an analog or digital output based on the status of a particular input or group of inputs. The PLC controls the relays, contactors, solenoids, etc. that operate motors, blowers, valves etc. on the machine. Also used to create a digital output, based on P.I.D. parameters, to modulate a solid-state relay to control current to the electric heaters. An HMI is usually interfaced to the PLC in order for the machine operator to monitor the process and program certain machine and molding parameters.

Profile Dipping- Utilizes operator programmed speeds, positions and dwell times to change dip speeds at a given part of a tool or mandrel. Used for thick control and drip control. Can be used with traditional moving tank designs or with overhead dip systems. Requires the HMI option.

Recirculation Pump- Also called a recirc pump. Typically a pneumatic diaphragm pump used to remove plastisol from the dip tank reservoir and pump it into the dipping section of the tank. Most dip tank models control the liquid level by flowing the material over a fixed weir or dam.

Regenerative Brake- An electric brake used to slow or control the speed of a servomotor, AC motor or DC motor when control through an electronic controller.

Rotary Inverter- An attachment located at the dip station of a movable tank dip system that will rotate tooling or mandrels through the dip tank to eliminate air trapping, control drips, or form dip lines with radii.

Servo system- A closed-loop motion system using a current amplifier, servo controller, servomotor and a position feedback device such as an encoder to precisely control speed and position of a load. Dip systems use servos in conjunction with precision ball screws and synchronous belt drives to control dip length and wall thickness of a dip molded part. Profile dipping is accomplished by varying the speed of the servo based on a given or programmed position.

SSR- Solid-state relay. High current capacity relays used in modulating electric current to the heater elements.

Spring Set Brake- A motor brake that is designed to hold a load when power is removed. Power to the brake releases the load. These are used on oven door motors, cooling, and primer/lube lifts.

Strip Heater- An electric heater, usually mica insulated, used in most cure ovens. Air movement over these heaters transfer the heat from the strip heater to the plastic coating to be cured.

Tubular Heater- An electric heater with high surface temperatures usually used in the preheat section of the machine. Infrared radiation as well as air movement over these elements transfers heat to the tool or mandrel to be coated.

VFD- Variable frequency drive. Used to modulate AC motor speed by changing the frequency (and other variables) to the motor. Cooling lifts, agitators, and primer lifts typically employ VFD’s.

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