Safety during the use of calenders in the rubber and plastics industries
Formerly SIM 03/2009/07
Summary
This guidance describes the safeguards that are required when using calenders in the rubber and plastics industries. The guidance for safeguarding older machines was previously contained in the RUBIAC publication Safeguarding of calenders in the rubber industry which has been withdrawn. RUBIAC have been replaced by the Tyre and Rubber Industry Safety Action Group (TRISAG) who have endorsed this guidance.
Introduction
A calender is a machine with two counter-rotating cylinders whose axes are often on the same vertical plane. The cylinders create a drawing-in and crushing hazard, termed a nip. They are normally smooth and can be heated or unheated. Material and/or rubber or plastic is passed under pressure through the cylinders to create either a rubber/plastic sheet of a required thickness, or apply a thin layer of rubber or plastic onto a cloth liner. Historically, calender injuries were quite high but guidance and improved safeguards have reduced the amount of incidents that now occur. However, there are still several reportable incidents a year caused by calenders.
Action
When inspectors visit rubber and plastics manufacturing processes and examine the operation of calenders they should consider the age of the calender and then note the relevant contents of the appendix when considering the calender operation. Consideration should be given to enforcement action if the safeguards detailed in the appendix have not been implemented.
Inspectors should provide copies of this guidance to calender users.
Background
The main nips on a typical calender are shown in Figure 1. Safeguards are therefore required to control this risk to the operator(s) when they approach the rolls, for example:
- during threading-up of materials;
- during malfunctions in the flow of materials or removal of trimmed waste;
- during setting/fault finding etc.
The safeguarding requirements for newer and older machines are set out in the appendix. This includes details of potential difficulties in using limited movement as one of the safeguards on older machines.
Figure 1 Typical calender showing main nips
For more information on calenders and other rubber issues see the relevant section of Introduction to rubber processing and safety issues on HSE's rubber website.
Inspectors should be aware that the Sector holds regular meetings with TRISAG and its Working Groups.
Appendix: Safety during the use of calenders
Newer machines
Information on safeguards and other guidance on newer calenders can be found in BS EN 1230111.
This section contains a summary of these safety requirements and other measure for controlling the hazards associated with the calender rolls. For full details of these and other requirements, dutyholders are advised to refer to the standard in full.
General
Mode selection switch
There should be a mode selector switch on the calender that includes control positions for the following actions:
- stopping;
- forward motion at slow speed;
- forward motion at production speed;
- reverse motion (if existing).
Start-up should only take place after an auditory warning signal sounds until the rollers start to rotate. The signal should have a minimum duration of 5 seconds. If it is necessary to remove or override certain guards or safety devices for start-up, ie in order to thread 'leaders' through the machine, then safety of the operator should be achieved by having the calender set in an appropriate control mode.
Where there is a reverse mode its operation should be by hold to run, with the reverse motion braked as soon as it is released. Selection of reverse mode should initiate a flashing luminous signal close to the new trapping zones created by the reverse movement. This should continue for as long as the mode switch is in the reverse motion position. The operator should have a clear view of new danger zones created by the reverse motion and to achieve this, visual aids such as mirrors or CCTV may be necessary.
Cleaning
The crushing hazard between calender rollers during cleaning operations should be prevented by designing the machine so that cleaning can take place:
- when the rollers are stationary;
- on the outrunning side of the rolls;
- on the in-running side of the rollers but outside of the danger zone.
If these can not be achieved then there should either be either automatic cleaning or additional safeguards fitted, as detailed in BS EN 12301.
Safeguard options
Prevent access to the trapping zone by safeguards fitted at the entrance to the trapping zone. This requires that there be a fixed guard fitted along the whole length of the rolls. Figure 2 shows typical safeguards for a calender.
Figure 2 Typical safeguards for a calender
Two options can be used for the guard:
Option A
- the gap between the guard and the surface of the roll does not exceed 6mm; and
- the gap between the guard and the tangent to the surface of the roll should not be less than 900.
Any gaps or openings in the guards should meet the requirements of BS EN 138572. If the guard needs to be removed for cleaning or setting operations then it should be designed as an interlock guard with guard locking that meets the requirements of BS EN 10883.
Option B
A feeding device positioned so that it acts as the fixed guard detailed in Option A. This should be associated with an interlock which allow the rolls to rotate only when the feeding device is in position.
Preventing access to the trapping zone by safeguards placed outside of the trapping zone
If safeguards can not be fitted to the entrance to the trapping zone for process reasons then access to the trapping zone can be prevented by using either an interlocked guard meeting BS EN 1088 or a trip device that will stop the rolls. This can be either a trip bar or a device such as a pressure sensing mat.
The trip bar should consist of a horizontal rigid bar that is actuated by a movement not exceeding 10mm. This should then trigger at least one position sensor that is actuated in the positive mode, with the control circuits manufactured from hardwired electro-mechanical components. The actuation of the bar should be by a force that does not exceed 200N with a response time that does not exceed 50 ms.
Actuation of the interlocked guard or trip bar should stop the calender rolls and cause either automatic separation of the rolls or allow separation to be achieved by means of a dedicated manual control. It must also be possible to reverse the calender rolls by a dedicated 'hold to run' control devise.
When the trip bar returns to its rest position it should not allow the calender to be restarted. There should also be a fixed guard that prevents access to the trapping zone from below the trip bar with a design that does not allow it to be used as a foothold.
Any access from the sides of the calender to the ends of the rolls on the in running side should be prevented by lateral fixed guards that take into account appropriate safety distances.
Performance of the safeguards once they have been actuated
Stopping the calender rolls
The opening of an interlocking guard or the actuation of a trip device, whether voluntary or involuntary, and by any part of the body, should bring the rolls to rest by braking within the specified stopping angle. The braking action should start as soon as the finger tips of the operator reach the danger zone and the rolls should all be at rest before the finger tips can reach the trapping zone. More information on stopping angles and calender roller speeds can be found in BS EN 12301.
Roll separation
After the opening of an interlocking guard or the actuation of a trip device has stopped the calender rolls, it should be possible to separate them. This can be either automatically or by a dedicated manual control. Separation should be achieved as quickly as possible, with the gap being as wide as possible and not less than 30mm. Roll separation should not cause any additional hazard ie unintentional closing should be prevented.
Rescue reverse movement
After the opening of an interlocking guard or the actuation of a trip device has stopped the calender rolls, in order to release any person trapped between the rolls or the rolls and material, it should also be possible to make a reverse movement of the rolls by the use of a dedicated hold to run device ie in addition to roll separation.
Older machines
Dutyholders should have compared the safeguards currently provided on older calenders with those detailed in the previous section and BS EN 12301 to determine if additional measures are required, ie by a risk assessment that considers factors such as:
- the current method of operation and existing methods of safeguarding - do the safeguards actually prevent access, are they adequate or is more required?
- whether it is practicable to fit further safeguarding measures;
- whether it is practicable to modify or change the method of operation;
- how severe any injury is likely to be;
- the possible effects on production.
The RUBIAC publication Safeguarding of calenders in the rubber industry applied to calenders that were in existence when it was published in 1998. Following publication it was identified that the advice regarding the provision and use of limited movement devices when threading-up calenders, contained in paragraph 49, was impractical to apply for most calenders that predated the publication. This was for technical reasons as limited movement devices caused damage to electrical motors and gear boxes of these machines.
Note: This information has been included because TRISAG have advised that there are still many pre-1998 calenders in use in the rubber industry. Identification of the age of the machine should be possible from the manufacturer's information supplied with the machine ie the ID plate.
The relevant paragraph 49 advice was that:
"If the calender rolls have to be in motion, a 'limited movement' control should be provided, capable of moving the smallest exposed roll a short pre-determined distance, say 25mm. Threading-up at normal production speeds or at 'crawl' is not safe, irrespective of the operators' level of experience. Even though a variable speed control may be available, its use as an aid in threading-up is not acceptable."
It was therefore agreed that limited movement devices need only be fitted where it was essential to remove or disturb the normal production guards for threading-up a calender For all other circumstances the guidance below should be applied to pre-1998 calenders to reduce the risk without a limited movement device being fitted:
- All the calender guards specified should be in position, correctly adjusted to the specified dimensions, in a sound state of repair and correct working order whenever a calender is to be threaded up.
- TRISAG members view is that a second person must always be in the vicinity of the machine during the whole of the threading operation so that they can stop the machine in an emergency.
- Except in the exceptional circumstances described below, threading up should be performed at a slow crawl speed of 12 linear feet per minute
(3.65 m per minute) or less. - The calender's normal operational speed control should be set to its lowest speed setting either before selecting slow crawl speed or to engage it. It is recommended that the selection of slow crawl speed is by means of a mode selector switch (ie a switch that allows either normal operation or slow crawl) that can be locked in the slow crawl position to avoid accidentally selecting normal operating speeds during threading-up. As a minimum requirement, if slow crawl speed is selected using the normal operating speed control, the slow crawl position should be permanently and clearly marked on it.
- In exceptional circumstances where, for technical reasons, a slow crawl speed of 12 linear feet per minute (3.65 m per minute) or less cannot be achieved, a higher speed is permissible for threading-up as long as it is the slowest speed at which the machine can be operated and it is achieved via a 'hold to run' control button.
- Where unprotected nips that are normally outrunning during production become in-running nips in reverse operation, the slow crawl speed should be achieved via 'hold to run' control buttons at the front and back of the calender The design should require both buttons to be depressed simultaneously unless guards are securely fixed in place that effectively prevent access to the nips.
References
- BS EN 12301:2000 Plastics and rubber machines - calenders - Safety requirements +A1:2008. Back to reference of footnote 1
- BS EN ISO 13857:2008 Safety of machinery. Safety distances to prevent hazard zones being reached by upper and lower limbs. Back to reference of footnote 2
- BS EN 1088:1995+A2:2008 Safety of machinery. Interlocking devices associated with guards. Principles for design and selection. Back to reference of footnote 3