Core pulling unit
Micron-accurate slide movements – low-maintenance, energy-efficient and cleanroom-capable without hydraulic oil.
The servo-electric core pulling unit SLY combines slide guidance, actuation, and assembly in one compact unit. Developed for highly precise slide tools and lift & strip moulds in medical technology, it enables µm-accurate positioning with reduced tool dimensions and minimal maintenance effort.
- Cleanroom-capable - oil-free operation for contamination-free processes
- Compact - external guidance outside the mould frame saves mould volume
- Smart - programmable motion profiles, reproducible without end stops
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Core-pull units move mould cores and slides - servo-electric instead of hydraulic
A core-pull unit is the drive unit that moves mould cores and slides in the injection mould: it pulls the core out of the solidified part before the mould opens and positions it precisely for the next cycle. Without core pull, undercuts, cross-holes and complex geometries cannot be demoulded.
Modern injection moulding applications place growing demands on surface quality, installation space and cleanliness. In medical technology in particular, even a minimal scratch determines whether a part is usable, while the available installation spaces are becoming tighter. Servo-electric core-pull units such as the SLY from Servomold resolve this conflict: oil-free, compact and with programmable motion profiles - reproducible without end stops.
For rotary demoulding tasks such as threaded cores, unscrewing units complete the range.
Advantages of servo-electric core-pull units over hydraulics
Oil-free
no contamination from hydraulic oil or leaks, cleanroom-capable
Compact
external guidance outside the mould frame saves mould volume
High forces
up to 12 kN with closed-loop, micron-accurate positioning
Fast
travel speed up to 600 mm/s with programmable ramps
Retrofit-capable
electrification of existing moulds without redesign
Low-maintenance
no hoses, seals or oil changes
Holding force: the core-pull unit must withstand the injection pressure
The most critical sizing question in core pull is not the movement but the holding. During the injection and holding pressure phases, the melt pressure acts on the projected core area and pushes the core back. The core-pull unit must absorb this force reliably over the entire cycle time - any compliance produces flash or dimensional deviations.
A hydraulic cylinder holds the core only by means of applied system pressure; if the pressure drops, the position is lost. The servo-electric SLY holds the position under closed-loop control via the servo motor and drive train and provides high forces for short periods - up to 12 kN. The required holding force results from melt pressure times projected core area and determines the unit size.
The Product Finder takes you from the core area to the matching unit size.
Servo-electric, hydraulic or pneumatic: the system comparison for core pull
Three drive types are available for core pull. These criteria show when the servo-electric drive is the technically robust alternative to hydraulics:
Drive medium: servo-electric is oil-free (electric power); hydraulic uses hydraulic oil with leakage and contamination risk; pneumatic uses compressed air.
Positioning: servo-electric is closed-loop controlled and micron-accurate with freely programmable intermediate positions; hydraulic and pneumatic work essentially only via end stops.
Holding force: servo-electric holds under closed-loop control, independent of applied pressure; hydraulic only with system pressure; pneumatic is usually insufficient for high injection pressures.
Force and speed: the SLY achieves up to 12 kN and 600 mm/s; pneumatics remain limited to small forces.
Energy: servo-electric draws power only during movement instead of a pump running continuously.
Cleanroom: servo-electric is suitable thanks to oil-free operation; hydraulics are critical; pneumatics only with oil-free air.
Maintenance: servo-electric has no hoses, seals or oil changes.
As soon as holding force, positioning accuracy or cleanroom requirements govern the process, servo-electric core pull is the robust alternative to hydraulics.
Sizing the core-pull unit: these parameters determine the unit size
Only a few parameters are decisive for selecting an SLY core-pull unit - the same ones previously used to size the hydraulic cylinder:
Force: up to 12 kN, depending on unit size.
Stroke: standard stroke lengths 75, 100 and 150 mm.
Speed: up to 600 mm/s - 150 mm in 0.5 s including acceleration and deceleration.
Moved mass: carriage weight max. 14 kg per unit.
Motion profile: freely programmable motion profiles with ramps, reproducible without end stops.
Installation situation: mounting position and available space outside the mould frame.
With these values, the Product Finder delivers the matching unit size.
Integration into the injection moulding machine: control via Servo MoldControl
Servo-electric core-pull units are operated via the Servo MoldControl controller. The injection moulding machine starts the movement via digital inputs and outputs; the controller regulates position, speed and force and reports the reached end position back.
Motion profiles are set up once and stored: the controller manages up to 100 programs, which are recalled reproducibly at mould changes and shorten setup times. Data runs via USB and Ethernet.
The SLY core-pull units in detail
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Significantly more compact form sizes by relocating the slide guides outside the mould frame.
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Unrivaled precision in assembly and positioning in all three axis directions.
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Servo-electric drive train with special ball screw spindle for clean and efficient operation
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Pre-stressed fine centering for µm-accurate positioning of the slide bodies.
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Maximum load capacity, stiffness, and accuracy thanks to low-maintenance linear guides with cage guidance.
Application areas for servo-electric core-pull units
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In medical technology, surface quality and cleanliness determine whether parts are usable – with transparent components, even a minimal scratch renders the part unusable. The SLY core-pull unit operates free of hydraulic oil and with a low-maintenance linear guide: no oil contamination and a significantly lower risk of wear-related scratches.
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FAQ – frequently asked questions about core-pull units
A core-pull unit moves mould cores or slides in an injection mould in order to demould undercuts and complex part geometries. It generates the force to release the solidified plastic from the core and positions the core precisely for the next cycle. Core-pull units are available in hydraulic, pneumatic and servo-electric versions.
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