There was no chuck guard fitted to the machine at Rotork UK's Huthwaite site the time of the incident on the 31 January 2014, Mansfield Magistrates' Court heard.
The 30-year-old worker was struck in the face and left with a fractured right eye socket, damaged teeth and bruising to the brain.
The injury was not life threatening, although he was unable to return to work for 10 months and is unable to carry out physical sports or drive at night.
HSE Inspector Robert Cox said: "Failing to identify appropriate guarding for machines can lead to serious accidents. There are well established standards which Rotork UK Ltd had failed to achieve."
Rotork UK Ltd was fined £15,000 and ordered to pay £1741.12 in costs and a victim surcharge of £120 after pleading guilty to breaching Regulation 11(1) of the Provision and Use of Work Equipment Regulations 1998 and Section 33(1)(c) and 33(2) of the Health and Safety at Work etc Act 1974.
