The 33-year-old plant operator at Coleman & Company's site in Meriden, Warwickshire, was hurt when his right arm was drawn in between the rollers and conveyor belt. The incident happened on 8 November 2012 at the company's premises.
The worker, from West Bromwich, suffered fractures along with wrist injuries and bruising. He later needed several skin grafts in hospital and has yet to return to work.
Solihull Magistrates' Court heard that without the swift reaction of colleagues, who ran to his aid to stop the machine, the injured worker could have lost his life.
Coleman & Company was prosecuted by the Health & Safety Executive (HSE) for two separate breaches of safety legislation.
The HSE found the incident could have been prevented had the company noticed that the machine's fixed guards had been either removed or lost, and had taken steps to replace them.
Coleman & Company Ltd of Shady Lane, Great Barr, Birmingham, pleaded guilty to breaching Section 2(1) of the Health and Safety at Work etc Act 1974 and section 11(1) of The Provision and Use of Work Equipment Regulations 1998 and was fined £3,500 and ordered to pay £1,114 in costs.
HSE inspector Karl Raw said after the hearing: "This was an avoidable incident involving a dangerous piece of equipment which is designed to crush concrete. As such, the consequences of a person coming into contact with moving parts of the machine can be severe.
"The worker involved was very fortunate not to have suffered even more serious injuries.
"Coleman & Company exposed workers to serious risk by failing to ensure that the workers were protected from dangerous moving parts of the machine by suitable guarding mechanisms. In addition, the company should have had a system of monitoring in place to identify if guards were missing, defective or inadequate."