Introduction

In designing and operating balancing machines, efforts already are made to minimize hazards arising from the use of the machines themselves. Rising demand for still greater safety in the working environment, however, requires additional protective measures, especially with respect to the rotor to be balanced. Potential hazards to the balancing machine operator or the surrounding workshop area can exist, e.g. by personnel coming into contact with machine components or the rotor, by rotor components or unbalance correction masses detaching and flying off or by the rotor lifting from the supports or disintegrating.

Special-purpose balancing machines, e.g. those used in the mass production automotive industry, normally incorporate all necessary protective measures because the workpiece, as well as the operating conditions of the machine, are known and can be taken into account by the machine manufacturer. For multipurpose balancing machines, however, where the workpieces to be balanced are generally unknown to the machine manufacturer, and are thus beyond his control, basic protective measures are limited to obvious hazards, e.g. from end-drive or belt-drive systems. However, the balancing machine manufacturer has to provide sufficient information for the user to assess possible hazards originating from a rotor when in the balancing machine, and from the intended use of the balancing machine. Together with this information, the user of the balancing machine has to state the possible hazards originating in his rotors in order to allow the balancing machine manufacturer to supply equivalent protective measures or the user has to provide adequate protective measures on his own.

When the rotors are not known in advance, e.g. in service and repair, a good estimation is needed. Table A.2 states typical values for different balancing machine sizes. But for each individual type of rotor to be balanced, the user of the balancing machine needs to check if the protective measures cover all hazards.

Most local regulations require certain minimum protective measures to be taken. Observance of such requirements in conjunction with the recommendations contained in this part of ISO 21940 will generally provide an adequate measure of protection to the balancing machine operator and surrounding workshop personnel. There may be applications, however, in which the recommended enclosures or other protective measures are so costly, or their use so time-consuming, that other protective precautions have to be considered, such as vacating the surrounding area for a sufficient distance, remote control of the balancing machine or work outside normal hours.

The consideration of accident probability can be important if a rotor needs to be balanced or spin-tested at or above its service speed, where major rotor failure cannot be excluded with as much certainty as during low-speed balancing.

On the other hand, a rotor being balanced at low speed may consist of an assembly of several components, such as a bladed turbine wheel. It is then important to consider whether an enclosure for low-speed balancing should withstand penetration of a turbine blade or whether it is sufficient to protect against unbalance correction masses that might fly off during balancing. If the probability of blade separation is practically non-existent, a light enclosure, which just protects against correction masses, may be sufficient.

Since this part of ISO 21940 deals with balancing machines and protective measures in general, no details of the risk can be stated for specific rotor types and balancing machines. Individual investigations, based on actual rotor parameters, will probably be required in each specific case. In this connection, risk analysis of possible accidents should include the characteristics of the balancing machine itself. For the extent of the ensuing damages, it may be of decisive importance to know how much unbalance can be endured by its supports and bearings due to partial rotor failure, e.g. rotor components becoming detached.

The significant hazards covered by this part of ISO 21940 are listed in Clause 4. The safety requirements and protective measures to prevent or minimize those hazards are identified in Clause 5, and procedures for verification of these requirements and protective measures are found in Clause 6.

BS ISO 21940-23:2012

Mechanical vibration. Rotor balancing - Enclosures and other protective measures for the measuring station of balancing machines

Current

Published:

30 Jun 2012